CN116474803B - CoMo composite material and preparation method and application thereof - Google Patents

Abstract

The invention relates to a CoMo composite material and a preparation method and application thereof, wherein the CoMo composite material comprises a Co-based metal center, a Mo-based metal center and a carrier, 10-20% of carbonyl sites are introduced on the surface of the CoMo composite material relative to a Co-based catalyst in the prior art while the balance between CO dissociative adsorption and CO non-dissociative adsorption on the surface of the catalyst is not damaged, after synthesis gas is converted into mixed alcohol, the conversion rate of the synthesis gas CO is 30-50%, the selectivity of the mixed alcohol is 33-48%, the mass ratio of ethanol in the mixed alcohol is 20-25%, the mass ratio of higher alcohol is 66-75%, the mass ratio of C5-C16 alcohol in the higher alcohol in the mixed alcohol is 55-60%, and the reaction condition is mild.

Description

A CoMo composite material and its preparation method and application

Technical Field

The present invention relates to the technical field of catalysts, and in particular to a CoMo composite material and a preparation method and application thereof.

Background Art

The preparation of ethanol and higher alcohols from coal, biomass, natural gas, etc. through synthesis gas conversion is a very important research topic in the prior art. Ethanol and higher alcohols are important raw materials and chemical intermediates in the field of chemistry and chemical industry, and are widely used in various fields. With the rapid development of my country's fine chemical industry, the annual average demand for higher alcohols in the domestic market is increasing. Therefore, it is of great significance to convert resources such as coal and biomass into ethanol and higher alcohols through synthesis gas.

For a long time, the synthesis gas to alcohol reaction has been subject to problems such as strong exothermic reaction and multiple and complex products. According to the reaction mechanism of synthesis gas conversion to prepare _C2+ alcohols, how to control the coordination between the dissociative adsorption of CO and the non-dissociative adsorption of CO to promote the synergy between the carbon chain growth active center and the carbonyl insertion active center catalysis, and how to coordinate the competition between the dissociative adsorption of CO, the non-dissociative adsorption of CO, and the _H2 adsorption active center are the key points of the research on the catalyst for the preparation of _C2+ alcohols from synthesis gas.

The conversion of syngas catalyzed by Co alone mainly produces hydrocarbon products due to the lack of non-dissociative adsorption in the catalyst, and the selectivity of alcohols in the products is very low. Since CO molecules undergo non-dissociative adsorption on the surfaces of Pd, Cu, _Co2C , _Mo2C , etc., the selectivity of alcohol products can be effectively improved by constructing a multi-active site catalyst system. However, the formation of higher alcohols requires close contact between the active sites, so how to construct a catalyst with multiple active sites that cooperate with each other, including CO dissociative adsorption, CO non-dissociative adsorption, and _H2 adsorption active centers, is a major difficulty in current research.

Hydrotalcite, also known as layered double hydroxides (LDHs), is a layered anion intercalation material, in which divalent metal ions and trivalent metal ions with similar radii are located on the layers, while anions are located between the layers to maintain electrical neutrality. LDHs have the characteristics of adjustable denaturation of layer elements, thermal instability (decomposable by high-temperature calcination), and exchangeable interlayer anions. In particular, the LDHs layers have a lattice positioning effect, and the metal atoms of the two valence states are isolated and stably exist. Therefore, it should be an effective way to obtain highly dispersed and highly stable catalysts through LDHs precursors containing active metals in the layers. Early studies have shown (d'Espinose, et al, J.Am.Chem.Soc.1995,117:11471) that when γ _{- A12O3} and some divalent metal cations (such as Ni2 ⁺ and Co2 ⁺ ) coexist in a slightly alkaline solution (7.0<pH<8.2), these cations will induce the dissolution of the surface _of γ- _A12O3 to produce Al3 ⁺ , which will then co-precipitate with Al3 ⁺ on the surface _of γ- _A12O3 to form hydrotalcite microcrystals. After that, a large number of studies have tried to synthesize the hydrotalcite precursor in situ on the support surface and then obtain the catalyst by high-temperature calcination. A series of effective preparation processes have been explored and a series of highly dispersed supported catalysts have been obtained.

CN 106000410 B discloses a stably dispersed CoMo composite material for preparing ethanol and higher alcohols from synthesis gas, belonging to the field of catalyst technology. The catalyst comprises a stably dispersed Co-based metal center and a carrier; the Co-based metal center is represented by Co-M, wherein M is Ga, Sn or In; the carrier is a composite oxide/γ-Al ₂ O ₃ carrier prepared by a hydrotalcite precursor method. Although the performance is stable when the reaction is 15 hours, the CO conversion rate can reach 43.5%, and the total alcohol selectivity can reach 59.0%, wherein about 92% of the alcohol products are ethanol and higher alcohols, but the catalyst structure stability time can only reach more than 100 hours, which still cannot meet the requirements of long-term operation required for industrial production.

CN 105903472 B discloses a uniformly distributed CoCu catalyst, which includes a CoCu metal center and a carrier; the CoCu metal center is represented as CoCu (enriched) or CoCu (enriched), wherein CoCu (enriched) indicates that the Cu center has a certain surface enrichment behavior, and CoCu (non-enriched) Cu center does not have a surface enrichment behavior; the carrier is a ZnAl composite oxide carrier prepared by a hydrotalcite precursor method. In the uniformly distributed CoCu catalyst obtained by the present invention, Cu and Co interact at the atomic level, and catalyze the conversion of synthesis gas under mild reaction conditions. The optimal catalytic performance that can be achieved is: CO conversion rate can reach 31.8%, total alcohol selectivity can reach 48.8%, wherein about 94.4% of the alcohol products are ethanol and higher alcohols, but only about 30.8% of the alcohol products are long-chain alcohols above C5, and the proportion of long-chain alcohols in industry is more important than that of short-chain alcohols, so the catalyst in this scheme still does not meet the current production catalysis requirements.

Based on the above situation, the prior art still has technical problems that need to be solved urgently, such as short catalyst life cycle, low selectivity in catalytic synthesis gas conversion to produce ethanol and higher alcohols, especially low selectivity for producing higher alcohols above C5, and high reaction temperature conditions.

Summary of the invention

In order to solve the above-mentioned technical problems, the carbonyl insertion sites on the surface of the CoMo composite material are increased without destroying the balance between CO dissociative adsorption and CO non-dissociative adsorption on the surface of the CoMo composite material. That is, the present invention provides a CoMo composite material, the CoMo composite material comprises a Co-based metal center, a Mo-based metal center and a carrier, the Co-based metal center is a Co _x1 Ga _x2 C _x3 particle, the Mo-based metal center is a Mo _y1 C _y2 particle, the CoMo composite material shows a 111 characteristic peak of the Co _x1 Ga _x2 C _x3 particle at a diffraction angle 2θ of 42.70±0.30°, and shows a 111 characteristic peak of the Mo _y1 C _y2 particle at a diffraction angle 2θ of 29.40±0.30°, the carrier is a composite oxide LDO@γ-Al ₂ O ₃ carrier, the composite oxide LDO is loaded on the surface of γ-Al ₂ O ₃ , and the specific surface area of the CoMo composite material is 170-250m ² /g, in the infrared adsorption diagram of CO adsorption saturation, the carbonyl adsorption sites account for 35-50% in the CoMo composite material.

Among them, in _{the Cox1Gax2Cx3} particles, the range of x1 is 2-4, the range of x2 is 0.5-2, _and the range of x is 0.5-1; in _{the Moy1Cy2} particles, the range of y1 is _1-3 , and the range of y2 is _0.5-2 ; and the composite oxides include ZnO, _Ga2O3 , and _Al2O3 .

Furthermore, the Co-based metal centers and the Mo-based metal centers are stably and evenly distributed on the surface or in the pores of the carrier, the interplanar spacing of the Co _x1 Ga _x2 C _x3 particles is 0.211±0.01 nm, and the interplanar spacing of the Mo _y1 C _y2 particles is 0.246±0.01 nm.

Furthermore, based on the overall mass percentage of the CoMo composite material, the loading amount of the Co element in the CoMo composite material is 1-2wt%, and the loading amount of the Mo element in the CoMo composite material is 0.1-1wt%.

Furthermore, the particle size of the CoMo composite material is in the range of 6-13 nm, the particle size of the Co _x1 Ga _x2 C _x3 particles is in the range of 9-13 nm, and the particle size of the Mo _y1 C _y2 particles is in the range of 6-10 nm.

Among them, based on the number of CoMo composite material particles, the number of CoMo composite material particles with a particle size range of 6-7nm (excluding 7nm) accounts for 1-2% of the CoMo composite material, the number of CoMo composite material particles with a particle size range of 7-8nm (excluding 8nm) accounts for 9-12% of the CoMo composite material, the number of CoMo composite material particles with a particle size range of 8-9nm (excluding 9nm) accounts for 31-41% of the CoMo composite material, the number of CoMo composite material particles with a particle size range of 9-10nm (excluding 10nm) accounts for 24-26% of the CoMo composite material, the number of CoMo composite material particles with a particle size range of 10-11nm (excluding 11nm) accounts for 11-12% of the CoMo composite material, the number of CoMo composite material particles with a particle size range of 11-12nm (excluding 12nm) accounts for 5-8% of the CoMo composite material, and the number of CoMo composite material particles with a particle size range of 12-13nm accounts for 1-3% of the CoMo composite material.

Furthermore, in the Co _x1 Ga _x2 C _x3 particles, x1 is 3, x2 is 1, and x3 is 0.5, and in the Mo _y1 C _y2 particles, y1 is 2, and y2 is 1, that is, the Co _x1 Ga _x2 C _x3 particles are Co ₃ Ga ₁ C _0.5 particles, the Mo _y1 C _y2 particles are Mo ₂ C ₁ particles, and the CoMo composite material is Mo ₂ C ₁ -Co ₃ Ga ₁ C _0.5 /ZnGaAl-LDO@γ-Al ₂ O ₃ .

The present invention also provides a method for preparing a CoMo composite material, comprising the following steps:

S1. Preparation of carbonate hydrotalcite precursor: using γ-Al ₂ O ₃ as Al source, in-situ growing CoZnGaAl-LDHs on the surface or in the pores of γ-Al ₂ O ₃ by urea method, to obtain CoZnGaAl-CO ₃ ^2- -LDHs@γ-Al ₂ O ₃ , i.e. carbonate hydrotalcite precursor;

S2, preparing a molybdate hydrotalcite precursor: using the carbonate hydrotalcite precursor obtained in S1 to prepare CoZnGaAl-MoO ₄ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., a molybdate hydrotalcite precursor;

S3. Preparation of CoMo composite material: placing the molybdate hydrotalcite precursor obtained in S2 in _H2 atmosphere and CO atmosphere successively for reduction and in-situ carbonization to obtain Mo _y1 C _y2 -Co _x1 Ga _x2 C _x3 /ZnGaAl-LDO@γ-Al ₂ O ₃ , namely the CoMo composite material.

Furthermore, the urea process in S1 comprises the following steps:

S1-1. Adding a mixed nitrate solution and urea to deionized water to form a mixed solution A, wherein the total concentration of metal ions in the mixed nitrate solution is in the range of 0.5-5 mol/L, and the mixed nitrate solution includes Co(NO ₃ ) ₃ ·6H ₂ O, Ga(NO ₃ ) ₃ ·xH ₂ O, and Zn(NO ₃ ) ₂ ·6H ₂ O.

Wherein, the range of x is ^3-9 , the concentration range of Co ³⁺ in the mixed nitrate solution is 0.5-0.8 mol/L, the concentration range of Ga ³⁺ in the mixed nitrate solution is 0.15-0.7 mol/L, the concentration range of Zn ²⁺ in the mixed nitrate solution is 0.5-1.2 mol/L, the concentration of urea is twice the total concentration of metal ions, and the volume ratio of deionized water to the mixed nitrate solution is (2.5-3.5):1;

S1-2, adding the dried γ-Al ₂ O ₃ into the mixed solution A prepared in S1-1 at a ratio of 0.4-0.6 g/mL, immersing for 2-5 hours, transferring them together into a high-pressure reactor, stirring for 0.5-2 hours under a N ₂ atmosphere, wherein the concentration of N ₂ in the N ₂ atmosphere is ≥99.9wt%, and after sufficient reaction and mixing, a mixed solution B is obtained, the mixed solution B is crystallized at 100-120°C for 12-24 hours, filtered, and the obtained solid is then washed with deionized water or ethanol by suction filtration until the pH of the filtrate is 6-8, and the washed solid is dried at 60-80°C for 12-24 hours to obtain CoZnGaAl-CO ₃ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., carbonate hydrotalcite precursor.

The reaction equations involved in the decomposition of urea include:

CO(NH ₂ ) ₂ +H ₂ O＝CO ₂ +2NH ₃

CO ₂ +H ₂ O＝CO ₃ ^2- +2H ⁺

NH ₃ +H ₂ O＝NH ₄ ⁺ +OH ^-

The purpose of using the high-pressure reactor is that carbon dioxide and ammonia will be generated during the decomposition of urea, so that the pressure in the high-pressure reactor rises to 4-5MPa. Under this pressure range, carbon dioxide dissolves in water to generate carbonate, and ammonia dissolves in water to provide an alkaline environment for preparing carbonate hydrotalcite precursors, that is, ammonia dissolves in water to generate hydroxide. At this time, the pH of the mixed solution is 10-13. The metal ions in the mixed nitrate solution combine with hydroxide to generate Co(OH) ₃ precipitation, Ga(OH) ₃ precipitation and Zn(OH) ₂ precipitation during the crystallization process, and are attached to the surface or pores _of γ- _Al2O3 in an in-situ growth manner. At the same time, the three cations of ^{Co3 +} , ^Ga3+ and Zn2 ⁺ will jointly induce the dissolution of the surface _of γ- _Al2O3 to generate Al3 ⁺ , and then the hydroxide and Al3 ⁺ will also generate Al(OH) ₂ on the surface or pores of γ- _Al2O3 . _3. Precipitation. All the precipitates generated above form lamellae of the carbonate hydrotalcite precursor. The carbonate is located between the lamellae to maintain the electrical neutrality of the carbonate hydrotalcite precursor.

Furthermore, the spacing between the layers of the carbonate hydrotalcite precursor is 0.759±0.03μm, the average particle size is 1.3-1.4μm, the carbonate is evenly distributed between the layers, and the carbonate hydrotalcite precursor shows characteristic peaks at diffraction angles 2θ of 11.63±0.30°, 23.35±0.30°, and 34.70±0.30°.

Furthermore, the roasting recovery method in S2 comprises the following steps:

S2-1, take the carbonate hydrotalcite precursor in S1 and place it in a reactor, and keep the reactor in a vacuum state, the vacuum degree is -0.1MPa to -0.075MPa, then introduce _N2 to restore the pressure in the reactor to normal pressure, that is, 0.01-0.01013MPa, and then adjust the _N2 flow rate to 30-60mL/min, then set the temperature program of the reactor to start heating, the heating rate is controlled to be 1-5℃/min, and after heating to 250-350℃, keep the temperature for 1-3h to obtain the intermediate CoZnGaAl-LDO@γ _{- Al2O3} ;

S2-2, placing the intermediate CoZnGaAl-LDO@γ-Al ₂ O ₃ prepared in step S2-1 into a molybdate solution, controlling the Co:Mo molar ratio to be (1-2):(1-5), stirring the mixture together under a N ₂ atmosphere for 12-24 h, wherein the concentration of N ₂ in the N ₂ atmosphere is ≥99.9wt%, filtering, and washing the obtained solid with deionized water or ethanol until the pH of the filtrate is 6-8. The washed solid is dried at 60-80°C for 12-24 h to obtain CoZnGaAl-MoO ₄ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., a molybdate hydrotalcite precursor, and completing the step of replacing carbonate with molybdate by a calcination reduction method.

The Co element, Zn element, Ga element and Al element in the molybdate hydrotalcite precursor all exist in the form of hydroxides.

Furthermore, the reactor in step S2-1 is a tubular furnace, and the carbonate hydrotalcite precursor is placed in a central constant temperature zone of the tubular furnace.

Furthermore, the calcination recovery method utilizes the adjustable characteristics of anions between the layers of hydrotalcite. The water in the carbonate hydrotalcite precursor is first evaporated at a calcination temperature of 250-350°C, and the carbonate between the layers of the carbonate hydrotalcite precursor is converted into _CO2 to cause the loss of anions between the layers. At the same time, under the protection of _N2 atmosphere, the concentration of _N2 in the _N2 atmosphere is ≥99.9wt%, and the intermediate CoZnGaAl-LDO@γ- _Al2O3 is placed in a molybdate solution, and the _molybdate enters between the layers to maintain the electrical neutrality between the molybdic acid and the hydrotalcite precursor.

Furthermore, the purpose of introducing _N2 is to prevent _CO2 from dissolving in water again to form carbonate during the roasting process.

Furthermore, the spacing between the layers of the molybdate hydrotalcite precursor is 0.904±0.03μm, the thickness of the layers is 0.05-0.2nm, the average particle size is 1.3-1.4μm, and the molybdate hydrotalcite precursor shows characteristic peaks at diffraction angles 2θ of 8.35±0.30°, 17.31±0.30°, and 28.90±0.30°, and its characteristic peaks are all moved forward relative to the characteristic peaks of the carbonate hydrotalcite precursor.

Furthermore, the reduction and in-situ carbonization in S3 specifically include the following steps:

S3-1, placing the molybdate hydrotalcite precursor prepared in S2 in a H ₂ atmosphere for reduction, heating the temperature to 600-700°C at a heating rate of 5-10°C/min and then keeping the temperature for 1-4h to obtain an intermediate CoGaMo/ZnGaAl-LDO@γ-Al ₂ O ₃ , wherein the concentration of H ₂ in the H ₂ atmosphere is ≥99.9wt%;

S3-2. After the system of the intermediate CoGaMo/ZnGaAl-LDO@γ-Al ₂ O ₃ obtained in S3-1 is cooled to 20-30°C, it is directly switched to a CO atmosphere. When all the H ₂ in the system is switched to CO, it is carbonized in situ, i.e., the temperature is increased to 280-290°C at a heating rate of 5-10°C/min and then kept warm for 1-3h to obtain Mo _y1 C _y2 -Co _x1 Ga _x2 C _x3 /ZnGaAl-LDO@γ-Al ₂ O ₃ , i.e., the CoMo composite material, wherein the concentration of CO in the CO atmosphere is ≥99.9wt%.

Furthermore, in step S3-1, the equipment used for hydrogen reduction and in-situ carbonization of the molybdate hydrotalcite precursor is a tubular furnace.

Further, in step S3-1, when the temperature rises to 100°C, Co(OH) ₃ , Ga(OH) ₃ , Zn(OH) ₂ , and Al(OH) ₃ in the molybdate hydrotalcite precursor will be dehydrated to generate Co ₂ O ₃ , Ga ₂ O ₃ , ZnO, and Al ₂ O ₃ ; when the temperature rises to 170°C, MoO ₄ ^2- in the molybdate hydrotalcite precursor will be decomposed to generate MoO ₃ ; when the temperature rises to 500-700°C, 40-95wt% of Co ₂ O ₃ , Ga ₂ O ₃ , and MoO ₃ in each of Co ₂ O ₃ , Ga ₂ O ₃ , and MoO ₃ will be reduced to CoGa alloy and Mo metal, i.e., a redox reaction will occur:

Co ²⁺ (Ga ³⁺ , Mo ⁴⁺ )H ₂ →Co ⁰ (Ga ⁰ , Mo ⁰ ),

Among them, since the reduction temperature does not reach the reduction temperature of ZnO and Al ₂ O ₃ , in this system, the Zn element and the Al element still exist in the form of ZnO and Al ₂ O ₃ .

Furthermore, in step S3-2, the purpose of in-situ carbonization in CO is to carbonize the CoGa alloy and Mo metal reduced in step S3-1 again to generate Co _x1 Ga _x2 C _x3 particles and Mo _y1 C _y2 particles, that is, to selectively carbonize the Co-Co sites on the surface of the CoGa alloy by redox reaction to convert them into C-Co-C, with a conversion rate of 10-20%, while increasing the carbonyl insertion sites on the catalyst surface without destroying the balance between CO dissociative adsorption and CO non-dissociative adsorption on the catalyst surface. From the infrared adsorption map of CO adsorption saturation, it can be obtained that the carbonyl adsorption sites account for 35-50% in the CoMo composite material.

Among them, Co _x1 Ga _x2 C _x3 particles have a strong ability to dissociate CO molecules and have good carbon chain growth ability. Mo _y1 C _y2 particles can catalyze the non-dissociative CO molecules and synergistically with Co _x1 Ga _x2 C _x3 particles to promote the production of ethanol and higher alcohols. The introduction of carbonyl insertion sites further increases the CO non-dissociative adsorption sites, further promoting the production of higher alcohols.

Furthermore, the CoMo composite material is Mo ₂ C ₁ -Co ₃ Ga ₁ C _0.5 /ZnGaAl-LDO@γ-Al ₂ O ₃ .

The present invention also provides an application of a CoMo composite material, wherein the CoMo composite material is used to convert synthesis gas into mixed alcohols, wherein the synthesis gas comprises CO and _H2 , wherein the volume fraction of CO in the synthesis gas is 30-70%, the volume fraction of _H2 in the synthesis gas is 30-70%, the mixed alcohol comprises ethanol and higher alcohols, the conversion rate of CO is 30-50%, and the selectivity of the mixed alcohols is 33-48%, wherein the mass proportion of ethanol in the mixed alcohols is 20-25%, the mass proportion of the higher alcohols is 66-75%, the higher alcohols comprise C3-C16 alcohols, and the mass proportion of C5-C16 alcohols in the higher alcohols is 55-60%.

Furthermore, based on the molar ratio of C element to the whole mixed alcohol, the molar fraction of C element in the mixed alcohol is 80-95%, the molar fraction of C element in the ethanol is 30-35%, and the molar fraction of C element in the higher alcohol is 50-60%.

Furthermore, the CoMo composite material is used to convert synthesis gas into mixed alcohols, comprising the following steps:

The CoMo composite material is loaded into a tubular reactor and kept in the same position as the thermocouple. Both ends of the tubular reactor are filled with quartz sand, and synthesis gas is introduced. The volume space velocity of the synthesis gas is 1500h ^-1 -8500h ^-1 . The temperature is then raised to a reaction temperature of 240 -300°C at a heating rate of 2-6°C/min, and the pressure of the tubular reactor is controlled at 2.5-3.5Mpa to carry out the reaction of converting the synthesis gas to prepare mixed alcohols. The reaction time is 24-48h.

Furthermore, the CoMo composite material has a stable structure for more than 200 hours when used to convert synthesis gas into mixed alcohols.

The beneficial effects of the present invention are:

1. The CoMo composite material of the present invention comprises _a Co-based metal center, a Mo-based metal center and a carrier, wherein the Co-based metal center is _{a Cox1Gax2Cx3 particle, and the Mo-based metal center is a Moy1Cy2 particle. The Cox1Gax2Cx3 particle has a strong ability to} dissociate CO molecules and has a good carbon chain growth ability. _{The Moy1Cy2 particle} can non-dissociate CO molecules and synergistically catalyze and promote the production of ethanol and higher alcohols with _{the Cox1Gax2Cx3} particles. The introduction of _carbonyl insertion sites further increases the CO non-dissociative adsorption sites, further promoting the production of higher alcohols.

2. The present invention selectively carbonizes the Co-Co site on the surface of the CoGa alloy by means of controllable surface carbonization to convert it into C-Co-C, and introduces a carbonyl insertion site on the surface of the CoMo composite material without destroying the balance between CO dissociative adsorption and CO non-dissociative adsorption on the catalyst surface. From the infrared adsorption diagram of CO adsorption saturation, it can be obtained that the carbonyl adsorption site accounts for 35-50% in the CoMo composite material. Compared with the catalyst introducing carbonyl sites in the prior art, 10-20% more carbonyl sites are introduced, and the structure of the Co-based catalyst in the prior art is changed, so that the conditions for catalytic conversion of synthesis gas are milder than those in the prior art, and the mass proportion of C5-C16 alcohol in the higher alcohol in the mixed alcohol is as high as 55-60% while ensuring a high CO conversion rate;

3. The present invention utilizes the adjustable interlayer anion property of hydrotalcite to first prepare a carbonate hydrotalcite precursor, then replace the carbonate with molybdate to prepare a molybdate hydrotalcite precursor, and finally reduce and in-situ carbonize it in _H2 atmosphere and CO atmosphere to obtain Mo _y1 C _y2 -Co _x1 Ga _x2 C _x3 /ZnGaAl-LDO@γ-Al ₂ O ₃ , i.e., the CoMo composite material. After the molybdate hydrotalcite precursor is reduced in hydrogen, it can be directly switched to CO for in-situ carbonization. The preparation method is simple and easy to operate.

4. The CoMo composite material prepared by the present invention has a CO conversion rate of 30-50% and a mixed alcohol selectivity of 33-48% after converting synthesis gas into mixed alcohols, wherein the mass proportion of ethanol in the mixed alcohols is 20-25%, and the mass proportion of higher alcohols is 66-75%, wherein the higher alcohols include C3-C16 alcohols, and the mass proportion of C5-C16 alcohols in the higher alcohols is as high as 55-60%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a scanning electron microscope image of a carbonate hydrotalcite precursor in Example 1 of the present invention;

FIG2 is an XRD graph of a carbonate hydrotalcite precursor and a molybdate hydrotalcite precursor in Example 1 of the present invention;

FIG3 is a scanning electron microscope image of the molybdate hydrotalcite precursor in Example 1 of the present invention;

FIG4 is an infrared adsorption diagram of CO adsorption saturation of the CoMo composite material in Example 1 of the present invention and the Co-based catalyst in Comparative Example 1;

FIG5 is an XRD graph of the CoMo composite material in Example 1 of the present invention;

FIG6 is a scanning electron microscope image of the CoMo composite material in Example 1 of the present invention;

FIG7 is a statistical diagram of the particle size distribution range of the CoMo composite material in Example 1 of the present invention;

FIG8 is a partially enlarged scanning electron microscope image of the CoMo composite material in FIG6;

FIG9 is an XRD graph of the carbonate hydrotalcite precursor in Comparative Example 1 of the present invention;

FIG. 10 is a scanning electron microscope image of the carbonate hydrotalcite precursor in Comparative Example 1 of the present invention.

DETAILED DESCRIPTION

The catalytic performance evaluation in the following examples and comparative examples of the present invention is carried out on a micro-tubular catalyst evaluation device, and the specifications of the reaction tube are d=10mm and l=600mm. The reaction device comprises three gas lines, which are respectively fed with _H2 , reaction gas and _N2 , wherein the reaction gas comprises Ar and synthesis gas, and the synthesis gas comprises _H2 and CO, and the volume composition ratio thereof is Ar: _H2 :CO=5:63.2:31.8, wherein Ar is an internal standard. Since the reaction is carried out under high temperature and high pressure, and the reaction gas is flammable, explosive and toxic, it is necessary to introduce inert _N2 for pressure holding treatment before each reaction to ensure that the device does not leak.

Example 1

The preparation method of the CoMo composite material in this embodiment comprises the following steps:

S1. Preparation of carbonate hydrotalcite precursor: Using γ-Al ₂ O ₃ as Al source, in-situ growth of CoZnGaAl-LDHs on the surface or in the pores of γ-Al ₂ O ₃ was performed by urea method to obtain CoZnGaAl-CO ₃ ^2- -LDHs@γ-Al ₂ O ₃ , i.e. carbonate hydrotalcite precursor:

Wherein, the urea method in S1 comprises the following steps:

S1-1. Adding a mixed nitrate solution and urea into deionized water to form a mixed solution A, wherein the total concentration of metal ions in the mixed nitrate solution is 3 mol/L, and the mixed nitrate solution includes Co(NO ₃ ) ₃ ·6H ₂ O, Ga(NO ₃ ) ₃ ·6H ₂ O (M=255.73), and Zn(NO ₃ ) ₂ ·6H ₂ O.

The concentration of Co ³⁺ in the mixed nitrate solution is 0.5 mol/L, the concentration of Ga ³⁺ in the mixed nitrate solution is 0.3 mol/L, and the concentration of Zn ²⁺ in the mixed nitrate solution is 0.7 mol/L. The concentration of urea is 6 mol/L, which is twice the total concentration of metal ions. The volume ratio of deionized water to the mixed nitrate solution is 2.5:1.

S1-2, adding the dried γ-Al ₂ O ₃ into the mixed solution A prepared in S1-1 at a ratio of 0.5 g/mL, immersing for 2 hours, transferring them together into a high-pressure reactor, stirring for 1 hour under N ₂ atmosphere, wherein the concentration of N ₂ in the N ₂ atmosphere is ≥99.9wt%, and after sufficient reaction and mixing, a mixed solution B is obtained, the mixed solution B is crystallized at 100°C for 12 hours, filtered, and the obtained solid is washed 3 times with deionized water, and then filtered once with ethanol until the pH of the filtrate is 7, and the washed solid is dried at 60°C for 12 hours to obtain CoZnGaAl-CO ₃ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., carbonate hydrotalcite precursor.

The reaction equations involved in the decomposition of urea include:

CO(NH ₂ ) ₂ +H ₂ O＝CO ₂ +2NH ₃

CO ₂ +H ₂ O＝CO ₃ ^2- +2H ⁺

NH ₃ +H ₂ O＝NH ₄ ⁺ +OH ^-

The purpose of using the high-pressure reactor is that carbon dioxide and ammonia will be generated during the decomposition of urea, so that the pressure in the high-pressure reactor rises to 4MPa. Under this pressure, carbon dioxide dissolves in water to generate carbonate, and ammonia dissolves in water to provide an alkaline environment for preparing carbonate hydrotalcite precursors, that is, ammonia dissolves in water to generate hydroxide. At this time, the pH of the mixed solution is 10. The metal ions in the mixed nitrate solution combine with hydroxide to generate Co(OH) ₃ precipitation, Ga(OH) ₃ precipitation and Zn(OH) ₂ precipitation during the crystallization process, and are attached to the surface or pores _of γ- _Al2O3 in an in-situ growth manner. At the same time, the three cations of Co3 ⁺ , Ga3 ⁺ and Zn2 ⁺ will jointly induce the dissolution of the surface _of γ- _Al2O3 to generate Al3 ⁺ , and then the hydroxide and Al3 ⁺ will also generate Al(OH) ₂ on the surface or pores of γ- _{Al2O3. 3.} Precipitation. All the precipitates generated above form lamellae of the carbonate hydrotalcite precursor. The carbonate is located between the lamellae to maintain the electrical neutrality of the carbonate hydrotalcite precursor.

As shown in FIG1 , the spacing between the layers of the carbonate hydrotalcite precursor (left side) is 0.759 μm, the average particle size (right side) is 1.3 μm, and the carbonate is evenly distributed between the layers. As shown in a in FIG2 , the carbonate hydrotalcite precursor shows characteristic peaks at diffraction angles 2θ of 11.63°, 23.35°, and 34.70°.

In FIG. 2 , c is the reference peak of the comparison card of hydrotalcite, and d is the reference peak of the comparison card of γ-Al ₂ O ₃ , which are used to compare the peak positions and play a comparison role.

S2. Preparation of molybdate hydrotalcite precursor: The carbonate hydrotalcite precursor obtained in S1 is subjected to a calcination reduction method to prepare CoZnGaAl-MoO ₄ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., molybdate hydrotalcite precursor:

The roasting recovery method in S2 comprises the following steps:

S2-1, take the carbonate hydrotalcite precursor in S1 and place it in the central constant temperature zone of a tubular furnace reactor, and keep the reactor in a vacuum state with a vacuum degree of -0.1 MPa, then introduce N ₂ to restore the pressure in the reactor to normal pressure, i.e. 0.01 MPa, and then adjust the N ₂ flow rate to 40 mL/min, then set the temperature rise program of the reactor to start heating, and control the heating rate to 5°C/min. After heating to 350°C, keep the temperature for 2 hours to obtain the intermediate CoZnGaAl-LDO@γ-Al ₂ O ₃ ;

S2-2, the intermediate CoZnGaAl-LDO@γ-Al ₂ O ₃ prepared in step S2-1 is placed in a molybdate solution, wherein the molybdate is Na ₂ MoO ₄ , and the Co:Mo molar ratio is controlled to be 1:4, and the mixture is stirred for 12 hours under a N ₂ atmosphere, wherein the concentration of N ₂ in the N ₂ atmosphere is ≥99.9wt%, and filtered. The obtained solid is washed 3 times with deionized water, and then filtered once with ethanol until the pH of the filtrate is 7. The washed solid is dried at 60°C for 12 hours to obtain CoZnGaAl-MoO ₄ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., a molybdate hydrotalcite precursor, and the step of replacing carbonate with molybdate by a calcination reduction method is completed.

The Co element, Zn element, Ga element and Al element in the molybdate hydrotalcite precursor all exist in the form of hydroxides.

The calcination recovery method utilizes the adjustable characteristics of anions between the layers of hydrotalcite. First, the water in the carbonate hydrotalcite precursor is evaporated at a calcination temperature of 350°C, and the carbonate between the layers of the carbonate hydrotalcite precursor is converted into _CO2 to cause the loss of anions between the layers. At the same time, under the protection of _N2 atmosphere, the concentration of _N2 in the _N2 atmosphere is ≥99.9wt%, and the intermediate CoZnGaAl-LDO@γ- _Al2O3 is placed in a molybdate solution, and the _molybdate enters between the layers to maintain the electrical neutrality between the molybdic acid and the hydrotalcite precursor.

The purpose of introducing _N2 is to prevent _CO2 from dissolving in water again to form carbonate during the roasting process.

As shown in FIG3 , the spacing between the layers of the molybdate hydrotalcite precursor (left side) is 0.904 μm, the average particle size (right side) is 1.4 μm, the thickness of the layer is 0.05 nm, and the thickness of the layer is calculated according to the Scherrer formula. As shown in FIG2 b, the molybdate hydrotalcite precursor shows characteristic peaks at diffraction angles 2θ of 8.35°, 17.31°, and 28.90°, and its characteristic peaks are all forward-shifted relative to the characteristic peaks of the carbonate hydrotalcite precursor (shown in FIG2 a).

In FIG. 2 , c is the reference peak of the comparison card of hydrotalcite, and d is the reference peak of the comparison card of γ-Al ₂ O ₃ , which are used to compare the peak positions and play a comparison role.

S3, preparing CoMo composite material: placing the molybdate hydrotalcite precursor obtained in S2 in _H2 atmosphere and CO atmosphere successively for reduction and in-situ carbonization to obtain Mo _y1 C _y2 -Co _x1 Ga _x2 C _x3 /ZnGaAl-LDO@γ-Al ₂ O ₃ , i.e. the CoMo composite material:

The reduction and in-situ carbonization in S3 specifically include the following steps:

S3-1, placing the molybdate hydrotalcite precursor prepared in S2 in a tube furnace for reduction in a H ₂ atmosphere, heating the temperature to 700°C at a heating rate of 5°C/min and then keeping the temperature for 2h to obtain an intermediate CoGaMo/ZnGaAl-LDO@γ-Al ₂ O ₃ , wherein the concentration of H ₂ in the H ₂ atmosphere is ≥99.9wt%, and the flow rate of hydrogen is 20ml/min;

S3-2. After the system of the intermediate CoGaMo/ZnGaAl-LDO@γ-Al ₂ O ₃ obtained in S3-1 is cooled to room temperature, it is directly switched to CO atmosphere, and the CO flow rate is adjusted to 20 ml/min for purging for 30 minutes. When all the H ₂ in the system is switched to CO, in-situ carbonization is carried out, that is, the temperature is increased to 280°C at a heating rate of 5°C/min and then kept warm for 2 hours. After naturally cooling to room temperature, it is switched to O ₂ /N ₂ with a volume fraction ratio of 1:99 for passivation for 2 hours, taken out and sealed for storage, to obtain Mo _y1 C _y2 -Co _x1 Ga _x2 C _x3 /ZnGaAl-LDO@γ-Al ₂ O ₃ with a Co:Mo molar ratio of 1:0.5, that is, the CoMo composite material, wherein the concentration of CO in the CO atmosphere is ≥99.9wt%.

In step S3-1, when the temperature rises to 100°C, Co(OH) ₃ , Ga(OH) ₃ , Zn(OH) ₂ , and Al(OH) ₃ in the molybdate hydrotalcite precursor will be dehydrated to generate Co ₂ O ₃ , Ga ₂ O ₃ , ZnO, and Al ₂ O _3. When the temperature rises to 170°C, MoO ₄ ^2- in the molybdate hydrotalcite precursor will decompose to generate MoO _3. When the temperature rises to 500-700°C, 55wt% of Co ₂ O ₃ , Ga ₂ O ₃ , and MoO ₃ in each of Co ₂ O ₃ , Ga ₂ O ₃ , and MoO ₃ will be reduced to CoGa alloy and Mo metal, that is, a redox reaction occurs:

Co ²⁺ (Ga ³⁺ , Mo ⁴⁺ )+H ₂ →Co ⁰ (Ga ⁰ , Mo ⁰ ),

Among them, since the reduction temperature does not reach the reduction temperature of ZnO and Al ₂ O ₃ , in this system, the Zn element and the Al element still exist in the form of ZnO and Al ₂ O ₃ .

In step S3-2, the purpose of in-situ carbonization in CO is to carbonize the CoGa alloy and Mo metal reduced _{in step S3-1 again to generate Cox1Gax2Cx3 particles and Moy1Cy2 particles , that} is, to selectively carbonize the Co-Co sites on the surface of the CoGa alloy by _redox reaction and convert them into C-Co-C with a conversion rate of 15%. The carbonyl insertion sites on the catalyst surface are increased without destroying the balance between CO dissociative adsorption and CO non-dissociative adsorption on the catalyst surface. From the infrared adsorption diagram of CO adsorption saturation (e in Figure 4), it can be obtained that the proportion of the carbonyl adsorption sites in the CoMo composite material is 35%, and the proportion is calculated as follows: 2017cm ^-1 , 2037cm ^-1 , and 2041cm ^-1 are adsorption peaks representing CO carbonyl insertion sites. The proportion of carbonyl adsorption sites can be calculated by calculating the proportion of these three adsorption peaks in all adsorption peaks.

Among them, Co _x1 Ga _x2 C _x3 particles have a strong ability to dissociate CO molecules and have good carbon chain growth ability. Mo _y1 C _y2 particles can catalyze the non-dissociative CO molecules and synergistically with Co _x1 Ga _x2 C _x3 particles to promote the production of ethanol and higher alcohols. The introduction of carbonyl insertion sites further increases the CO non-dissociative adsorption sites, further promoting the production of higher alcohols.

The CoMo composite material is Mo ₂ C ₁ -Co ₃ Ga ₁ C _0.5 /ZnGaAl-LDO@γ-Al ₂ O ₃ , and the CoMo composite material includes a Co-based metal center, a Mo-based metal center and a carrier, the Co-based metal center is a Co ₃ Ga ₁ C _0.5 particle, and the Mo-based metal center is a Mo ₂ C ₁ particle. As shown in FIG5 , the CoMo composite material shows a 111 characteristic peak of the Co ₃ Ga ₁ C _0.5 particle (A) at a diffraction angle 2θ of 42.70°, and shows a 111 characteristic peak of the Mo ₂ C ₁ particle (B) at a diffraction angle 2θ of 29.4°, wherein g is a comparison card comparison peak of the CoGa alloy phase, h is a comparison card comparison peak of the ZnAl-LDO@γ-Al ₂ O ₃ , and i is a comparison card comparison peak of the Co ₃ Ga ₁ C 0.5 particle. The contrast peak of the comparison card of the _0.5 particle serves as a comparison. By comparison, it can be proved that there is a corresponding phase in the CoMo composite material. The carrier is a composite oxide LDO@γ-Al ₂ O ₃ carrier, and the composite oxide LDO is loaded on the surface of γ-Al ₂ O _3. The specific surface area of the CoMo composite material is 170m ² /g. The interplanar spacing of the Co ₃ Ga ₁ C _0.5 particles is 0.211nm, and the interplanar spacing of the Mo ₂ C ₁ particles is 0.246nm. The particle size range of the CoMo composite material is 6-13nm, the particle size range of the Co ₃ Ga ₁ C _0.5 particles is 9-13nm, and the particle size range of the Mo ₂ C ₁ particles is 6-10nm.

As shown in Figure 6, it is a high-resolution electron microscope image of the CoMo composite material of this embodiment. From this figure, it can be seen that, based on the number of CoMo composite material particles, the number of CoMo composite material particles with a particle size range of 6-7nm (excluding 7nm) accounts for 2% of the CoMo composite material, the number of CoMo composite material particles with a particle size range of 7-8nm (excluding 8nm) accounts for 12% of the CoMo composite material, the number of CoMo composite material particles with a particle size range of 8-9nm (excluding 9nm) accounts for 41% of the CoMo composite material, the number of CoMo composite material particles with a particle size range of 9-10nm (excluding 10nm) accounts for 24% of the CoMo composite material, the number of CoMo composite material particles with a particle size range of 10-11nm (excluding 11nm) accounts for 12% of the CoMo composite material, the number of CoMo composite material particles with a particle size range of 11-12nm (excluding 12nm) accounts for 6% of the CoMo composite material, and the number of CoMo composite material particles with a particle size range of 12-13nm accounts for 3% of the CoMo composite material. The particle size distribution range statistics of the number of CoMo composite material particles are shown in Figure 7.

Among them, by partially enlarging FIG6 , Co ₃ Ga ₁ C _0.5 particles (C in FIG8 ) and Mo ₂ C ₁ particles (D in FIG8 ) can be clearly observed.

The CoMo composite material prepared in this example is used to convert synthesis gas into mixed alcohols. The synthesis gas includes CO and H ₂ , wherein the volume fraction of CO in the synthesis gas is 66.52%, the volume fraction of H ₂ in the synthesis gas is 33.48%, and the mixed alcohols include ethanol and higher alcohols.

The CoMo composite material is used to convert synthesis gas into mixed alcohols, comprising the following steps:

0.8 g of CoMo composite material was loaded into a tubular reactor and kept consistent with the position of the thermocouple. Both ends of the tubular reactor were filled with quartz sand, and synthesis gas was introduced. The volume space velocity of the synthesis gas was 2100 h ^-1 . After the temperature was raised to 260° C. at a heating rate of 5° C./min, the pressure of the tubular reactor was controlled at 3 MPa to carry out the reaction of converting the synthesis gas to prepare mixed alcohols. The reaction time was 24 h. The catalytic products were analyzed online and offline by gas chromatography. It was measured that the conversion rate of CO in the reaction under steady state was 40%, and the selectivity of mixed alcohols was 35%. Among them, the total mass proportion of ethanol and higher alcohols in the mixed alcohols was 90%, the mass proportion of ethanol was 20%, and the mass proportion of higher alcohols was 70%. The higher alcohols included C3-C16 alcohols, and the mass proportion of C5-C16 alcohols in the higher alcohols in the mixed alcohols was 55%.

Example 2

The preparation method of the CoMo composite material in this embodiment comprises the following steps:

S1. Preparation of carbonate hydrotalcite precursor: Using γ-Al ₂ O ₃ as Al source, in-situ growth of CoZnGaAl-LDHs on the surface or in the pores of γ-Al ₂ O ₃ was performed by urea method to obtain CoZnGaAl-CO ₃ ^2- -LDHs@γ-Al ₂ O ₃ , i.e. carbonate hydrotalcite precursor:

Wherein, the urea method in S1 comprises the following steps:

S1-1. Adding a mixed nitrate solution and urea into deionized water to form a mixed solution A, wherein the total concentration of metal ions in the mixed nitrate solution is 0.5 mol/L, and the mixed nitrate solution includes Co(NO ₃ ) ₃ ·6H ₂ O, Ga(NO ₃ ) ₃ ·6H ₂ O (M=255.73), and Zn(NO ₃ ) ₂ ·6H ₂ O.

The concentration of Co ³⁺ in the mixed nitrate solution is 0.5 mol/L, the concentration of Ga ³⁺ in the mixed nitrate solution is 0.3 mol/L, and the concentration of Zn ²⁺ in the mixed nitrate solution is 0.7 mol/L. The concentration of urea is twice the total concentration of metal ions, which is 1 mol/L. The volume ratio of deionized water to the mixed nitrate solution is 2.5:1.

S1-2, adding the dried γ-Al ₂ O ₃ into the mixed solution A prepared in S1-1 at a ratio of 0.5 g/mL, immersing for 2 hours, transferring them together into a high-pressure reactor, stirring for 1 hour under N ₂ atmosphere, wherein the concentration of N ₂ in the N ₂ atmosphere is ≥99.9wt%, and after sufficient reaction and mixing, a mixed solution B is obtained, the mixed solution B is crystallized at 120°C for 12 hours, filtered, and the obtained solid is washed 3 times with deionized water, and then filtered once with ethanol until the pH of the filtrate is 7, and the washed solid is dried at 60°C for 12 hours to obtain CoZnGaAl-CO ₃ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., carbonate hydrotalcite precursor.

The reaction equations involved in the decomposition of urea include:

CO(NH ₂ ) ₂ +H ₂ O＝CO ₂ +2NH ₃

CO ₂ +H ₂ O＝CO ₃ ^2- +2H ⁺

NH ₃ +H ₂ O＝NH ₄ ⁺ +OH ^-

The purpose of using the high-pressure reactor is that carbon dioxide and ammonia will be generated during the decomposition of urea, so that the pressure in the high-pressure reactor rises to 4MPa. Under this pressure range, carbon dioxide dissolves in water to generate carbonate, and ammonia dissolves in water to provide an alkaline environment for preparing carbonate hydrotalcite precursors, that is, ammonia dissolves in water to generate hydroxide. At this time, the pH of the mixed solution is 12. The metal ions in the mixed nitrate solution combine with hydroxide to generate Co(OH) ₃ precipitation, Ga(OH) ₃ precipitation and Zn(OH) ₂ precipitation during the crystallization process, and are attached to the surface or pores _of γ- _Al2O3 in an in-situ growth manner. At the same time, the three cations of Co3 ⁺ , Ga3 ⁺ and Zn2 ⁺ will jointly induce the dissolution of the surface _of γ- _Al2O3 to generate Al3 ⁺ , and then the hydroxide and Al3 ⁺ will also generate Al(OH) ₂ on the surface or pores of γ- _Al2O3 . _3. Precipitation. All the precipitates generated above form lamellae of the carbonate hydrotalcite precursor. The carbonate is located between the lamellae to maintain the electrical neutrality of the carbonate hydrotalcite precursor.

The distance between the layers of the carbonate hydrotalcite precursor is 0.759 μm, the average particle size is 1.3 μm, the carbonate is evenly distributed between the layers, and the carbonate hydrotalcite precursor shows characteristic peaks at diffraction angles 2θ of 11.63°, 23.35°, and 34.70°.

S2. Preparation of molybdate hydrotalcite precursor: The carbonate hydrotalcite precursor obtained in S1 is subjected to a calcination reduction method to prepare CoZnGaAl-MoO ₄ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., molybdate hydrotalcite precursor:

The roasting recovery method in S2 comprises the following steps:

S2-1, take the carbonate hydrotalcite precursor in S1 and place it in the central constant temperature zone of a tubular furnace reactor, and keep the reactor in a vacuum state with a vacuum degree of -0.1MPa, then introduce _N2 to restore the pressure in the reactor to normal pressure, i.e. 0.01MPa, and then adjust the _N2 flow rate to 40mL/min, then set the temperature rise program of the reactor to start heating, and control the heating rate to 1℃/min, and heat to 350℃ and keep it for 2h to obtain the intermediate CoZnGaAl-LDO@γ _{- Al2O3} ;

S2-2, the intermediate CoZnGaAl-LDO@γ-Al ₂ O ₃ prepared in step S2-1 is placed in a molybdate solution, wherein the molybdate is Na ₂ MoO ₄ , and the Co:Mo molar ratio is controlled to be 1:2, and the mixture is stirred together for 12 hours under a N ₂ atmosphere, wherein the concentration of N ₂ in the N ₂ atmosphere is ≥99.9wt%, and filtered. The obtained solid is then washed 3 times with deionized water, and then filtered once with ethanol until the pH of the filtrate is 7. The washed solid is dried at 60°C for 12 hours to obtain CoZnGaAl-MoO ₄ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., a molybdate hydrotalcite precursor, and the step of replacing carbonate with molybdate by a calcination reduction method is completed.

The Co element, Zn element, Ga element and Al element in the molybdate hydrotalcite precursor all exist in the form of hydroxides.

The calcination recovery method utilizes the adjustable characteristics of anions between the layers of hydrotalcite. First, the water in the carbonate hydrotalcite precursor is evaporated at a calcination temperature of 350°C, and the carbonate between the layers of the carbonate hydrotalcite precursor is converted into _CO2 to cause the loss of anions between the layers. At the same time, under the protection of _N2 atmosphere, the concentration of _N2 in the _N2 atmosphere is ≥99.9wt%, and the intermediate CoZnGaAl-LDO@γ- _Al2O3 is placed in a molybdate solution, and the _molybdate enters between the layers to maintain the electrical neutrality between the molybdic acid and the hydrotalcite precursor.

The purpose of introducing _N2 is to prevent _CO2 from dissolving in water again to form carbonate during the roasting process.

The spacing between the layers of the molybdate hydrotalcite precursor is 0.904 μm, the average particle size is 1.4 μm, the thickness of the layer is 0.05 nm, and the molybdate hydrotalcite precursor shows characteristic peaks at diffraction angles 2θ of 8.35°, 17.31°, and 28.90°, and its characteristic peaks are all moved forward relative to the characteristic peaks of the carbonate hydrotalcite precursor.

S3, preparing CoMo composite material: placing the molybdate hydrotalcite precursor obtained in S2 in _H2 atmosphere and CO atmosphere successively for reduction and in-situ carbonization to obtain Mo _y1 C _y2 -Co _x1 Ga _x2 C _x3 /ZnGaAl-LDO@γ-Al ₂ O ₃ , i.e. the CoMo composite material:

The reduction and in-situ carbonization in S3 specifically include the following steps:

S3-1. The molybdate hydrotalcite precursor prepared in S2 is placed in a tube furnace and first reduced in a H ₂ atmosphere, and the temperature is raised to 700°C at a heating rate of 5°C/min and then kept at this temperature for 2h to obtain an intermediate CoGaMo/ZnGaAl-LDO@γ-Al ₂ O ₃ , wherein the concentration of H ₂ in the H ₂ atmosphere is ≥99.9wt%, and the flow rate of hydrogen is 20ml/min;

S3-2. After the system of the intermediate CoGaMo/ZnGaAl-LDO@γ-Al ₂ O ₃ obtained in S3-1 is cooled to room temperature, it is directly switched to CO atmosphere, and the CO flow rate is adjusted to 20 ml/min for purging for 30 minutes. When all the H ₂ in the system is switched to CO, in-situ carbonization is carried out, that is, the temperature is increased to 280°C at a heating rate of 5°C/min and then kept warm for 2 hours. After naturally cooling to room temperature, it is switched to O ₂ /N ₂ with a volume fraction ratio of 1:99 for passivation for 2 hours, taken out and sealed for storage, to obtain Mo _y1 C _y2 -Co _x1 Ga _x2 C _x3 /ZnGaAl-LDO@γ-Al ₂ O ₃ with a Co:Mo molar ratio of 1:0.8, that is, the CoMo composite material, wherein the concentration of CO in the CO atmosphere is ≥99.9wt%.

In step S3-1, when the temperature rises to 100°C, Co(OH) ₃ , Ga(OH) ₃ , Zn(OH) ₂ , and Al(OH) ₃ in the molybdate hydrotalcite precursor will be dehydrated to generate Co ₂ O ₃ , Ga ₂ O ₃ , ZnO, and Al ₂ O _3. When the temperature rises to 170°C, MoO ₄ ^2- in the molybdate hydrotalcite precursor will decompose to generate MoO _3. When the temperature rises to 500-700°C, 50wt% of Co ₂ O ₃ , Ga ₂ O ₃ , and MoO ₃ in each of Co ₂ O ₃ , Ga ₂ O ₃ , and MoO ₃ will be reduced to CoGa alloy and Mo metal, that is, a redox reaction occurs:

Co ²⁺ (Ga ³⁺ , Mo ⁴⁺ )+H ₂ →Co ⁰ (Ga ⁰ , Mo ⁰ ),

Among them, since the reduction temperature does not reach the reduction temperature of ZnO and Al ₂ O ₃ , in this system, the Zn element and the Al element still exist in the form of ZnO and Al ₂ O ₃ .

In step S3-2, the purpose of in-situ carbonization in CO is to carbonize the CoGa alloy and Mo metal reduced in step S3-1 again to generate Co _x1 Ga _x2 C _x3 particles and Mo _y1 C _y2 particles, that is, to selectively carbonize the Co-Co site on the surface of the CoGa alloy by redox reaction and convert it into C-Co-C, with a conversion rate of 15%. The carbonyl insertion sites on the catalyst surface are increased without destroying the balance between CO dissociative adsorption and CO non-dissociative adsorption on the catalyst surface. From the infrared adsorption map of CO adsorption saturation, it can be obtained that the carbonyl adsorption sites account for 35% in the CoMo composite material.

Among them, Co _x1 Ga _x2 C _x3 particles have a strong ability to dissociate CO molecules and have good carbon chain growth ability. Mo _y1 C _y2 particles can catalyze the non-dissociative CO molecules and synergistically with Co _x1 Ga _x2 C _x3 particles to promote the production of ethanol and higher alcohols. The introduction of carbonyl insertion sites further increases the CO non-dissociative adsorption sites, further promoting the production of higher alcohols.

The CoMo composite material is Mo ₂ C ₁ -Co ₃ Ga ₁ C _0.5 /ZnGaAl-LDO@γ-Al ₂ O ₃ , and the CoMo composite material includes a Co-based metal center, a Mo-based metal center and a carrier, the Co-based metal center is a Co ₃ Ga ₁ C _0.5 particle, the Mo-based metal center is a Mo ₂ C ₁ particle, the CoMo composite material shows a 111 characteristic peak of the Co ₃ Ga ₁ C _0.5 particle at a diffraction angle 2θ of 42.70°, and shows a 111 characteristic peak of the Mo ₂ C ₁ particle at a diffraction angle 2θ of 29.4°, the carrier is a composite oxide LDO@γ-Al ₂ O ₃ carrier, the composite oxide LDO is loaded on the surface of γ-Al ₂ O ₃ , and the specific surface area of the CoMo composite material is 170 m ² /g. The interplanar spacing of the Co ₃ Ga ₁ C _0.5 particles is 0.211 nm, and the interplanar spacing of the Mo ₂ C ₁ particles is 0.246 nm. The particle size of the CoMo composite material is in the range of 6-13 nm, the particle size of the Co ₃ Ga ₁ C _0.5 particles is in the range of 9-13 nm, and the particle size of the Mo ₂ C ₁ particles is in the range of 6-10 nm.

Among them, based on the number of CoMo composite materials particles, the number of CoMo composite materials particles with a particle size range of 6-7nm (excluding 7nm) accounts for 2% of the CoMo composite materials, the number of CoMo composite materials particles with a particle size range of 7-8nm (excluding 8nm) accounts for 10% of the CoMo composite materials, the number of CoMo composite materials particles with a particle size range of 8-9nm (excluding 9nm) accounts for 39% of the CoMo composite materials, the number of CoMo composite materials particles with a particle size range of 9-10nm (excluding 10nm) accounts for 28% of the CoMo composite materials, the number of CoMo composite materials particles with a particle size range of 10-11nm (excluding 11nm) accounts for 12% of the CoMo composite materials, the number of CoMo composite materials particles with a particle size range of 11-12nm (excluding 12nm) accounts for 8% of the CoMo composite materials, and the number of CoMo composite materials particles with a particle size range of 12-13nm accounts for 1% of the CoMo composite materials.

The CoMo composite material prepared in this example is used to convert synthesis gas into mixed alcohols. The synthesis gas includes CO and H ₂ , wherein the volume fraction of CO in the synthesis gas is 66.52%, the volume fraction of H ₂ in the synthesis gas is 33.48%, and the mixed alcohols include ethanol and higher alcohols.

The CoMo composite material is used to convert synthesis gas into mixed alcohols, comprising the following steps:

0.8 g of CoMo composite material was loaded into a tubular reactor and kept consistent with the position of the thermocouple. Both ends of the tubular reactor were filled with quartz sand, and synthesis gas was introduced. The volume space velocity of the synthesis gas was 2400 h ^-1 . After the temperature was raised to 260° C. at a heating rate of 5° C./min, the pressure of the tubular reactor was controlled at 3 MPa to carry out the reaction of converting the synthesis gas to prepare mixed alcohols. The reaction time was 24 h. The catalytic products were analyzed online and offline by gas chromatography. It was measured that the conversion rate of CO in the reaction under steady state was 42.7%, and the selectivity of mixed alcohols was 33.4%. Among them, the mass proportion of ethanol and higher alcohols in the mixed alcohols was 88%, the mass proportion of ethanol was 22%, and the mass proportion of higher alcohols was 66%. The higher alcohols included C3-C16 alcohols, and the mass proportion of C5-C16 alcohols in the higher alcohols in the mixed alcohols was 57%.

Comparative Example 1

This comparative example is a common Co-based catalyst that does not contain Ga and Mo elements and is not in-situ carbonized, relative to Examples 1 and 2, and includes the following steps:

S1. Preparation of carbonate hydrotalcite precursor: Using γ-Al ₂ O ₃ as Al source, in-situ growth of CoZnAl-LDHs on the surface or in the pores of γ-Al ₂ O ₃ was performed by urea method to obtain CoZnAl-CO ₃ ^2- -LDHs@γ-Al ₂ O ₃ , i.e. carbonate hydrotalcite precursor:

Wherein, the urea method in S1 comprises the following steps:

S1-1. Adding a mixed nitrate solution and urea into deionized water to form a mixed solution A, wherein the total concentration of metal ions in the mixed nitrate solution is 0.5 mol/L, and the mixed nitrate solution includes Co(NO ₃ ) ₃ ·6H ₂ O and Zn(NO ₃ ) ₂ ·6H ₂ O.

The concentration of Co ³⁺ in the mixed nitrate solution is 0.5 mol/L, the concentration of Zn ²⁺ in the mixed nitrate solution is 0.7 mol/L, the concentration of urea is 1 mol/L, which is twice the total concentration of metal ions, and the volume ratio of deionized water to the mixed nitrate solution is 2.5:1;

S1-2, adding the dried γ-Al ₂ O ₃ into the mixed solution A prepared in S1-1 at a ratio of 0.5 g/mL, immersing for 2 hours, transferring them together into a high-pressure reactor, stirring for 1 hour under N ₂ atmosphere, wherein the concentration of N ₂ in the N ₂ atmosphere is ≥99.9wt%, and after sufficient reaction and mixing, a mixed solution B is obtained, the mixed solution B is crystallized at 120°C for 12 hours, filtered, and the obtained solid is then filtered and washed with deionized water for 3 times until the pH of the filtrate is 7, and the washed solid is dried at 60°C for 12 hours to obtain CoZnAl-CO ₃ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., carbonate hydrotalcite precursor.

As shown in FIG9 , the spacing between the layers of the carbonate hydrotalcite precursor (left side) is 0.759 μm, the average particle size (right side) is 1.3 μm, and the carbonate is evenly distributed between the layers. As shown in FIG10 j, the carbonate hydrotalcite precursor shows characteristic peaks at diffraction angles 2θ of 11.63°, 23.35°, and 34.70°. k is the comparison peak of the comparison card of hydrotalcite, and l is the comparison peak of the comparison card of γ-Al ₂ O ₃ , which are used to compare the peak positions and play a comparison role.

S2. Preparation of Co-based catalyst: The carbonate hydrotalcite precursor obtained in S1 is placed in a H ₂ atmosphere for reduction to obtain Co/ZnAl-LDO@γ-Al ₂ O ₃ , i.e., the Co-based catalyst:

The reduction in S2 specifically includes the following steps:

The carbonate hydrotalcite precursor prepared in S1 was placed in a tube furnace for reduction in a H ₂ atmosphere, heated to 700°C at a heating rate of 5°C/min and kept warm for 2h. After naturally cooling to room temperature, it was switched to O ₂ /N ₂ with a volume fraction ratio of 1:99 for passivation for 2h, taken out and sealed for storage, to obtain Co/ZnGaAl-LDO@γ-Al ₂ O ₃ , i.e., the Co-based catalyst.

From the infrared adsorption diagram of CO adsorption saturation (Fig. 4f), it can be seen that the carbonyl adsorption site accounts for 25% in the CoMo composite material.

The specific surface area of the Co-based catalyst is 189 m ² /g. The average particle size of the Co-based catalyst is 16 nm.

The Co-based catalyst prepared in this comparative example is used to convert synthesis gas into mixed alcohols. The synthesis gas includes CO and H ₂ , wherein the volume fraction of CO in the synthesis gas is 66.52%, the volume fraction of H ₂ in the synthesis gas is 33.48%, and the mixed alcohols include ethanol and higher alcohols.

The Co-based catalyst is used to convert synthesis gas into mixed alcohols, comprising the following steps:

0.5 g of Co-based catalyst was loaded into the tubular reactor and kept consistent with the position of the thermocouple. Both ends of the tubular reactor were filled with quartz sand, and synthesis gas was introduced. The volume space velocity of the synthesis gas was 2100 h ^-1 . After the temperature was raised to 260° C. at a heating rate of 5° C./min, the pressure of the tubular reactor was controlled at 3 MPa to carry out the reaction of converting the synthesis gas to prepare mixed alcohols. The reaction time was 24 h. The catalytic products were analyzed online and offline by gas chromatography. It was measured that the conversion rate of CO in the reaction under steady state was 29.9%, and the selectivity of mixed alcohols was 5.8%. Among them, the mass proportion of ethanol and higher alcohols in the mixed alcohols was 20.1%, the mass proportion of ethanol was 10.6%, and the mass proportion of higher alcohols was 9.5%. The higher alcohols included C3-C16 alcohols, and the mass proportion of C5-C16 alcohols in the higher alcohols in the mixed alcohols was 40.8%.

In summary, the Co-Co sites on the surface of the CoGa alloy are selectively carbonized by a controllable surface carbonization method to convert them into C-Co-C. The carbonyl insertion sites are introduced on the surface of the CoMo composite material without destroying the balance between the CO dissociative adsorption and the CO non-dissociative adsorption on the catalyst surface. From the infrared adsorption diagram of CO adsorption saturation, it can be obtained that the carbonyl adsorption sites account for 35-50% in the CoMo composite material. Compared with the catalysts introducing carbonyl sites (accounting for 25-30%) in the prior art, 10-20% more carbonyl sites are introduced, which changes the structure of the Co-based catalyst in the prior art and makes the conditions for catalytic conversion of synthesis gas milder than those in the prior art. While ensuring a high CO conversion rate, the mass proportion of C5-C16 alcohols in the higher alcohols in the mixed alcohols is as high as 55-60%, which better meets the demand for higher alcohols in industrial production.

It should be understood that the present invention is not limited to the contents and structures described above and shown in the drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims (10)

1. A CoMo composite material, characterized in that the CoMo composite material comprises a Co-based metal center, a Mo-based metal center and a carrier, the Co-based metal center is a Co _x1 Ga _x2 C _x3 particle, the Mo-based metal center is a Mo _y1 C _y2 particle, the CoMo composite material shows a 111 characteristic peak of the Co _x1 Ga _x2 C _x3 particle at a diffraction angle 2θ of 42.70±0.30°, and shows a 111 characteristic peak of the Mo _y1 C _y2 particle at a diffraction angle 2θ of 29.40±0.30°, the carrier is a composite oxide LDO@γ- Al ₂ O ₃ carrier, the composite oxide LDO is loaded on the surface of the γ- Al ₂ O ₃ carrier, the specific surface area of the CoMo composite material is 170-250 m ² /g, in the infrared adsorption diagram of CO adsorption saturation, the carbonyl adsorption site accounts for 35-50%, Among them, in the Co _x1 Ga _x2 C _x3 particles, the range of x1 is 2-4, the range of x2 is 0.5-2, and the range of x3 is 0.5-1; in the Mo _y1 C _y2 particles, the range of y1 is 1-3, and the range of y2 is 0.5-2; the composite oxide LDO includes ZnO, Ga ₂ O ₃ , and Al ₂ O ₃ . 2. The CoMo composite material according to claim 1 is characterized in that the Co-based metal centers and the Mo-based metal centers are stably and evenly distributed on the surface or in the pores of the carrier, the interplanar spacing of the Co _x1 Ga _x2 C _x3 particles is 0.211±0.01nm, and the interplanar spacing of the Mo _y1 C _y2 particles is 0.246±0.01nm. 3. The CoMo composite material according to claim 2, characterized in that, based on the overall mass percentage of the CoMo composite material, the loading amount of the Co element in the CoMo composite material is 1-2wt%, and the loading amount of the Mo element in the CoMo composite material is 0.1-1wt%. 4. The CoMo composite material according to claim 3, characterized in that the particle size range of the Co _x1 Ga _x2 C _x3 particles is 9-13 nm, and the particle size range of the Mo _y1 C _y2 particles is 6-10 nm. 5. The CoMo composite material according to claim 4, characterized in that in the Co _x1 Ga _x2 C _x3 particles, x1 is 3, x2 is 1, and x3 is 0.5, and in the Mo _y1 C _y2 particles, y1 is 2, and y2 is 1, that is, the Co _x1 Ga _x2 C _x3 particles are Co ₃ Ga ₁ C _0.5 particles, the Mo _y1 C _y2 particles are Mo ₂ C ₁ particles, and the CoMo composite material is Mo ₂ C ₁ - Co ₃ Ga ₁ C _0.5 /ZnGaAl-LDO@γ- Al ₂ O ₃ . 6. A method for preparing the CoMo composite material according to any one of claims 1 to 5, characterized in that it comprises the following steps: S1. Preparation of carbonate hydrotalcite precursor: using γ-Al ₂ O ₃ as Al source, in-situ growing CoZnGaAl-LDHs on the surface or in the pores of γ- Al ₂ O ₃ by urea method, to obtain CoZnGaAl-CO ₃ ^2- -LDHs@γ- Al ₂ O ₃ , i.e. carbonate hydrotalcite precursor; S2, preparing a molybdate hydrotalcite precursor: using the carbonate hydrotalcite precursor obtained in S1 to replace carbonate with molybdate by a calcination reduction method, to prepare CoZnGaAl-MoO ₄ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., a molybdate hydrotalcite precursor; S3. Preparation of CoMo composite material: placing the molybdate hydrotalcite precursor obtained in S2 in _H2 atmosphere and CO atmosphere successively for reduction and in-situ carbonization to obtain Mo _y1 C _y2 - Co _x1 Ga _x2 C _x3 /ZnGaAl-LDO@γ- Al ₂ O ₃ , i.e. the CoMo composite material. 7. The method for preparing the CoMo composite material according to claim 6, characterized in that the urea method in S1 comprises the following steps: S1-1. Adding a mixed nitrate solution and urea to deionized water to form a mixed solution A, wherein the total concentration of metal ions in the mixed nitrate solution is in the range of 1.15-5 mol/L, and the mixed nitrate solution includes Co(NO ₃ ) ₃ ·6H ₂ O, Ga(NO ₃ ) ₃ ·xH ₂ O, and Zn(NO ₃ ) ₂ ·6H ₂ O. Wherein, the range value of x is 3-9, the concentration range of Co ³⁺ in the mixed nitrate solution is 0.5-0.8 mol/L, the concentration range of Ga ³⁺ in the mixed nitrate solution is 0.15-0.7 mol/L, and the concentration range of Zn ²⁺ in the mixed nitrate solution is 0.5-1.2 mol/L, the concentration of urea is twice the total concentration of metal ions, and the volume ratio of deionized water to the mixed nitrate solution is (2.5-3.5):1; S1-2, adding the dried γ- Al ₂ O ₃ into the mixed solution A prepared in S1-1 at a ratio of 0.4-0.6 g/mL, immersing for 2-5 hours, transferring them together into a high-pressure reactor, stirring for 0.5-2 hours under a N ₂ atmosphere, wherein the concentration of N ₂ in the N ₂ atmosphere is ≥99.9wt%, and after sufficient reaction and mixing, a mixed solution B is obtained, the mixed solution B is crystallized at 100-120°C for 12-24 hours, filtered, and the obtained solid is then washed with deionized water or ethanol by suction filtration until the pH of the filtrate is 6-8, and the washed solid is dried at 60-80°C for 12-24 hours to obtain CoZnGaAl-CO ₃ ^2- -LDHs@γ- Al ₂ O ₃ , i.e., carbonate hydrotalcite precursor. The spacing between the layers of the carbonate hydrotalcite precursor is 0.759±0.03 μm, the average particle size is 1.3-1.4 μm, the carbonate is evenly distributed between the layers, and the carbonate hydrotalcite precursor shows characteristic peaks at diffraction angles 2θ of 11.63±0.30°, 23.35±0.30°, and 34.70±0.30°. 8. The method for preparing the CoMo composite material according to claim 7, characterized in that the calcination recovery method in S2 comprises the following steps: S2-1, take the carbonate hydrotalcite precursor in S1 and place it in a reactor, and keep the reactor in a vacuum state, the vacuum degree is -0.1MPa to -0.075MPa, then introduce _N2 to restore the pressure in the reactor to normal pressure, that is, 0.01-0.01013MPa, and then adjust the _N2 flow rate to 30-60 mL/min, then set the temperature program of the reactor to start heating, the heating rate is controlled to 1-5℃/min, and after heating to 250-350℃, keep warm for 1-3h to obtain the intermediate CoZnGaAl-LDO@γ _{-Al2O3 ,} S2-2, placing the intermediate CoZnGaAl-LDO@γ-Al ₂ O ₃ prepared in step S2-1 into a molybdate solution, controlling the Co:Mo molar ratio to be (1-2):(1-5), stirring the mixture together under a N ₂ atmosphere for 12-24 h, wherein the concentration of N ₂ in the N ₂ atmosphere is ≥99.9wt%, filtering, and washing the obtained solid with deionized water or ethanol until the pH value of the filtrate is 6-8, and drying the washed solid at 60-80°C for 12-24 h to obtain CoZnGaAl-MoO ₄ ^2- -LDHs@γ-Al ₂ O ₃ , i.e., a molybdate hydrotalcite precursor; The spacing between the layers of the molybdate hydrotalcite precursor is 0.904±0.03 μm, the thickness of the layers is 0.05-0.2 nm, the average particle size is 1.3-1.4 μm, and the molybdate hydrotalcite precursor shows characteristic peaks at diffraction angles 2θ of 8.35±0.30°, 17.31±0.30°, and 28.90±0.30°. 9. The method for preparing the CoMo composite material according to claim 8, characterized in that the reduction and in-situ carbonization in S3 specifically comprises the following steps: S3-1, placing the molybdate hydrotalcite precursor prepared in S2 in a H ₂ atmosphere for reduction, heating the temperature to 600-700°C at a heating rate of 5-10°C/min and then keeping the temperature for 1-4 h to obtain an intermediate CoGaMo/ZnGaAl-LDO@γ-Al ₂ O ₃ , wherein the concentration of H ₂ in the H ₂ atmosphere is ≥99.9wt%; S3-2. After the system of the intermediate CoGaMo/ZnGaAl-LDO@γ-Al ₂ O ₃ obtained in S3-1 is cooled to 20-30°C, it is directly switched to a CO atmosphere. When all the H ₂ in the system is switched to CO, it is carbonized in situ, i.e., the temperature is increased to 280-290°C at a heating rate of 5-10°C/min and then kept warm for 1-3 h to obtain Mo _y1 C _y2 - Co _x1 Ga _x2 C _x3 /ZnGaAl-LDO@γ-Al ₂ O ₃ , i.e., the CoMo composite material, wherein the concentration of CO in the CO atmosphere is ≥99.9wt%. 10. An application of the CoMo composite material according to any one of claims 1 to 5, characterized in that the CoMo composite material is used to convert synthesis gas into mixed alcohols, the synthesis gas comprises CO and _H2 , the volume fraction of CO in the synthesis gas is 30-70%, the volume fraction of _H2 in the synthesis gas is 30-70%, the mixed alcohol comprises ethanol and higher alcohols, the conversion rate of CO is 30-50%, and the selectivity of the mixed alcohol is 33-48%, wherein the mass proportion of ethanol in the mixed alcohol is 20-25%, the mass proportion of the higher alcohol is 66-75%, the higher alcohol comprises C3-C16 alcohol, and the mass proportion of C5-C16 alcohol in the higher alcohol is 55-60%.