TW201438817A - Catalyst for oxidizing ammonia and method for removing ammonia - Google Patents

Abstract

The disclosure provides a catalyst for oxidizing ammonia and a method for removing ammonia. The catalyst includes an oxide carrier, a first metal, and a second metal disposed on the oxide carrier. The oxide carrier includes CeO2, SiO2, Al2O3, or combinations thereof; the first metal includes copper, and the second metal includes silver, platinum, or palladium.

Description

Catalyst for oxidizing ammonia gas and method for removing ammonia gas from gas

The present invention relates to a catalyst, and a method of using the same, and more particularly to a catalyst for oxidizing ammonia gas and a method of using the catalyst.

The high-tech industry uses a large amount of ammonia (NH ₃ ) as a process (such as the MOVCD in the LED industry), while the unused ammonia is removed from the back-end pump into the exhaust gas treatment system. In the past, ammonia treatment was carried out by a manufacturer in a water-washing manner. However, this method produces an aqueous solution containing ammonia, which is biologically toxic, that is, secondary pollution occurs. As environmental regulations become more stringent, operators need to treat ammonia-containing aqueous solutions to very low concentrations (the concentration of ammonia nitrogen needs to be less than 20 mg/L) before they can be discharged. However, in order to reduce the concentration of ammonia nitrogen in the wastewater, the industry needs to provide additional sites and pay higher processing costs, and the treatment efficiency of ammonia gas wastewater is also limited.

In order to solve the above problems, the industry proposes to directly oxidize ammonia in the exhaust gas by means of a catalyst to convert ammonia into nitrogen (N ₂ ) and water (H ₂ 0), which has the advantages of large-scale treatment and no secondary pollution. . However, the catalyst used in the industry to oxidatively decompose ammonia in the exhaust gas still has the disadvantage that the nitrogen selectivity obtained at a low temperature is low. Based on the above, there is a need in the industry for a novel catalyst for oxidative decomposition of ammonia to overcome the problems of the prior art.

An embodiment of the invention provides a catalyst for oxidizing ammonia gas, comprising: an oxide support, wherein the oxide support comprises cerium oxide (CeO ₂ ), cerium oxide (SiO ₂ ), aluminum oxide ( Al ₂ O ₃ ), or a combination thereof; and a first metal and a second metal supported on the support, wherein the first metal is copper and the second metal is silver, platinum, or palladium .

According to another embodiment of the present invention, the present invention also provides a method for removing ammonia gas in a gas, comprising: placing the above-mentioned catalyst for oxidizing ammonia gas in an atmosphere at an operating temperature to make the atmosphere The ammonia gas is converted into nitrogen gas and water, wherein the operating temperature is equal to or greater than 280 ° C, and the method for removing ammonia in the gas has a removal rate of ammonia of more than 93%, and the nitrogen selectivity is greater than 90%.

The above and other objects, features, and advantages of the present invention will become more apparent and understood.

10‧‧‧catalyst for oxidizing ammonia

20‧‧‧Oxide support

21‧‧‧First metal

22‧‧‧Second metal

100‧‧‧System for removing ammonia from gases

110‧‧‧Reaction chamber

111‧‧‧ gas inlet end

112‧‧‧ gas outlet

120‧‧‧Fourier infrared spectroscopy (FT-IR) device

Fig. 1 is a schematic view showing a catalyst for oxidizing ammonia gas according to an embodiment of the present invention.

2 is a schematic view showing a system for removing ammonia gas from a gas according to an embodiment of the present invention.

Fig. 3 is a graph showing the ammonia removal rate and the nitrogen selectivity of the catalyst according to the embodiment of the present invention at different operating temperatures.

The following description will detail how the embodiments of the present invention are made and used. It will be appreciated that the various possible inventive concepts provided by these embodiments are implemented in a variety of specific ways. However, these specific embodiments are intended to illustrate and not to limit the invention.

The present invention provides a catalyst capable of oxidatively decomposing ammonia (NH ₃ ) into harmless nitrogen (N ₂ ) and water (H ₂ O) at a low temperature (less than or equal to 350 ° C), and the contact The method of treating ammonia gas. The catalyst has a removal rate of ammonia of more than 93%, and the nitrogen selectivity can be greater than 90%, improving the removal efficiency of the prior art at a low temperature (the reaction chamber temperature is less than or equal to 350 ° C) or generating a large amount of N ₂ O/NO. The disadvantage of _x (X is 1 or 2). Here, the term "nitrogen selectivity" refers to nitrogen obtained by oxidative decomposition of ammonia (NH ₃ ) with a catalyst, and the N atom thereof accounts for all nitrogen-containing products (for example, nitrogen (N ₂ ), nitrous oxide (including nitrogen). N atomic percentage of N ₂ O), nitric oxide (NO), nitrogen dioxide (NO ₂ ), and the like.

The catalyst for oxidizing ammonia gas according to the present invention comprises: an oxide support, wherein the oxide support comprises cerium oxide (CeO ₂ ), cerium oxide (SiO ₂ ), aluminum oxide, or And a first metal and a second metal are supported on the carrier, wherein the first metal is copper and the second metal is silver, platinum, or palladium. According to an embodiment of the invention, the weight ratio of the first metal to the second metal may be between 1:10 and 10:1, the total weight of the first metal and the second metal, and the oxide carrier. The weight ratio can be between 1:20 and 1:5.

Referring to FIG. 1, according to another embodiment of the present invention, the oxide carrier 20 for oxidizing ammonia gas may comprise an oxide or a mixed oxide having a high specific surface area (for example, cerium oxide ( CeO ₂ ), or a mixed oxide of cerium oxide and aluminum oxide (CeO ₂ -Al ₂ O ₃ ), and supporting a first metal 21 - a second metal 22 bimetal on the surface thereof (the first metal 21 is, for example Copper, the second metal 22 is, for example, silver, is used as a catalyst. Among them, cerium oxide (CeO ₂ ), or a mixed oxide of cerium oxide and aluminum oxide (CeO ₂ -Al ₂ O ₃ ), in addition to having a function as a structure promoter, cerium oxide (CeO ₂ ) further has a chemical accelerator Its function can greatly enhance the activity of copper-silver (Cu-Ag) at low temperature and nitrogen selectivity.

The preparation method of the above catalyst for oxidizing ammonia gas, according to another embodiment of the present invention, may comprise the following steps:

First use Ce(NO ₃ ) ₃ . 6H ₂ O and Al(NO ₃ ). 9H ₂ O was used as a precursor, and Ca(HCO ₃ ) _{2 was} used as a precipitant to synthesize a catalyst for oxidizing ammonia gas by a coprecipitation method. Next, copper (Cu) and silver (Ag) are supported on the surface of the mixed oxide of cerium oxide and aluminum oxide (CeO ₂ -Al ₂ O ₃ ) by an impregnation method or a deposition precipitation method.

The method for removing ammonia in a gas according to the present invention comprises: placing the above-mentioned catalyst for oxidizing ammonia gas in an atmosphere at an operating temperature, and converting the ammonia gas in the atmosphere into nitrogen gas and water, wherein The operating temperature is equal to or greater than 280 ° C (for example, 280-500 ° C, 280-450 ° C, or 280-310 ° C), and the method for removing ammonia in the gas can remove ammonia by more than 93%. And the nitrogen selectivity is also greater than 90%. In addition, according to other embodiments of the present invention, referring to FIG. 2, the present invention also provides a system 100 for removing ammonia in a gas, comprising: a reaction chamber 110 having a gas inlet end 111 and a gas The outlet end 112; the above-mentioned catalyst 10 for oxidizing ammonia gas is placed in the reaction chamber. In addition, in order to instantaneously measure whether the ammonia concentration of the treated gas reaches an emission standard, the system 100 for removing ammonia in the gas may further include a Fourier infrared light. A spectral (FT-IR) device 120 is coupled to the gas outlet end 112 of the reaction chamber 110.

In order to make the above and other objects, features, and advantages of the present invention more comprehensible, the specific embodiments and comparative examples of the present invention are used to illustrate the catalyst for oxidizing ammonia gas and removing gas in the present invention. A method of ammonia gas and a system for removing ammonia gas from a gas.

Preparation for oxidizing ammonia gas catalyst

Example 1

First, a mixed oxide of cerium oxide and aluminum oxide (CeO ₂ -Al ₂ O ₃ ) (the weight ratio of Ce:Al is 1:1) is synthesized by a coprecipitation method, wherein the cerium oxide and aluminum oxide (CeO) The mixed oxide of ₂ -Al ₂ O ₃ ) has a specific surface area of 102 m ² /g. Next, copper (Cu) and silver (Ag) are successively supported by the impregnation method on the mixed oxide of cerium oxide and aluminum oxide (CeO ₂ -Al ₂ O ₃ ) (hereinafter referred to as yttrium-aluminum oxide). The weight ratio of copper (Cu):silver (Ag):yttrium-aluminum oxide (CeO ₂ -Al ₂ O ₃ ) is 10:5:85. Next, the impregnated material was baked at 110 ° C for 5 hours, and then calcined at 500 ° C for 8 hours to obtain a catalyst (1).

Comparative Example 1

First, commercially available product γ-Al ₂ O ₃ (Merck, a specific surface area of 120-190 m ² /g) was used as an oxide support. The copper was supported on γ-Al ₂ O ₃ by an impregnation method, wherein the weight ratio of copper (Cu):γ-Al ₂ O ₃ was 10:90. Next, the impregnated material was baked at 110 ° C for 5 hours, and then calcined at 500 ° C for 8 hours to obtain a catalyst (2).

Comparative Example 2

First, commercially available product γ-Al ₂ O ₃ (Merck, a specific surface area of 120-190 m ² /g) was used as an oxide support. Next, platinum was supported on γ-Al ₂ O ₃ by an impregnation method, wherein the weight ratio of platinum (Pt):γ-Al ₂ O ₃ was 10:90. Next, the impregnated material was dried at 110 ° C for 5 hours and then calcined at 500 ° C for 8 hours to obtain a catalyst (3).

Example 2

The method of Example 1 was repeated except that the weight ratio of copper (Cu):silver (Ag):yttrium-aluminum oxide (CeO ₂ -Al ₂ O ₃ ) was 5:7.5:87.5, and a catalyst (4) was obtained.

Example 3

The method of Example 2 was repeated except that the weight ratio of Ce:Al of the cerium-aluminum oxide (CeO ₂ -Al ₂ O ₃ ) was 1:4, and the catalyst (5) was obtained.

Example 4

A bismuth-aluminum oxide (CeO ₂ -Al ₂ O ₃ ) was obtained by the method of Example 3 (the weight ratio of Ce:Al was 1:4), and copper (Cu) and platinum (Pt) were successively impregnated. Supported on the Ce-Al oxide, wherein the weight ratio of copper (Cu): platinum (Pt): lanthanum-aluminum oxide (CeO ₂ -Al ₂ O ₃ ) is 10:2:88. The catalyst (6) is obtained.

Example 5

The method of Example 3 was repeated except that the weight ratio of copper (Cu):silver (Ag):yttrium-aluminum oxide (CeO ₂ -Al ₂ O ₃ ) was 2.5:10:87.5, and a catalyst (7) was obtained.

Ammonia removal capacity and nitrogen selectivity measurement

Example 6

The above catalysts (1)-(7) were respectively packed in a quartz reaction tube (tube diameter: 4 mm), and then an atmosphere containing ammonia gas was passed (NH ₃ = 1%, O ₂ = 8%, N ₂ = 91%) (GHSV, gas hourly space velocity is 20000h ^-1 ) in a quartz reaction tube, the operating temperature is 310 ° C. At the outlet end of the reaction tube, the concentrations of NH ₃ , N ₂ O, NO, and NO ₂ were simultaneously monitored by a Fourier infrared spectroscopy (FT-IR) apparatus to convert the ammonia removal rate and the nitrogen selectivity.

The nitrogen selectivity is calculated as: [1-(2*C _out-N2O +C _out-NO +C _out-NO2 )/(C _In-NH3 -C _out-NH3 )]*100%

Wherein C _out-I represents the concentration of I species (eg, N ₂ O, NO, NO ₂ , and NH ₃ ) measured by the FTIR at the outlet end of the reaction tube, and C _In- NH ₃ is the NH ₃ concentration of the influent reaction tube.

The test results are shown in Table 1:

Example 7

The catalysts (5) to (7) were respectively packed in a quartz reaction tube (tube diameter: 4 mm), and then an atmosphere containing a high concentration of ammonia gas was passed (NH ₃ = 2.5%, O ₂ = 10%, H _{2 ).} =1%, N ₂ = 86.5%) (gas hourly space velocity (GHSV, gas hourly space velocity) is 20000 h ^-1 ) in a quartz reaction tube, and the operating temperature was 300 ° C. At the outlet end of the reaction tube, the concentrations of NH ₃ , N ₂ O, NO, and NO ₂ were simultaneously monitored by a Fourier infrared spectroscopy (FT-IR) apparatus to convert the ammonia removal rate and the nitrogen selectivity.

The test results are shown in Table 2:

It can be seen from Table 1 and Table 2 that the catalyst of the present invention, when operating temperature The ammonia removal rate can be greater than 99% at 300 ° C, and the nitrogen selectivity is much higher than the catalysts described in Comparative Examples 1 and 2 (with γ-Al ₂ O ₃ as the support and no bimetallic as the catalyst) In addition, since the catalyst of the present invention has a first metal (copper) and a second metal (silver, platinum, or palladium), in addition to being capable of oxidizing ammonia gas at a low temperature (acting by the second metal), A surface selective catalytic oxidation (SCR, selective catalysis oxidation) reaction (acting from the first metal). In addition, as can be seen from Table 2, the support used in the present invention (for example, cerium oxide, or a mixed oxide of cerium oxide and aluminum oxide) has a high oxygen storage function (provided by conversion of trivalent cerium and tetravalent cerium) Increasing or rapidly replenishing the amount of surface reactive oxygen, and the support used in the present invention has a synergy with the first metal and the second metal to improve surface selective catalytic oxidation (SCR) reactivity. It can maintain good ammonia removal rate and nitrogen selectivity in the presence of high concentrations of NH ₃ and H ₂ .

Example 8

The above catalyst (5) was packed in a quartz reaction tube (tube diameter: 4 cm), and then an atmosphere containing ammonia gas (NH ₃ = 2.5%, O ₂ = 10%, N ₂ = 87.5%) was introduced (gas hourly space) The velocity (GHSV, gas hourly space velocity) is 20000h ^-1 ) in the quartz reaction tube, and the concentration of NH ₃ , N ₂ O, NO and NO ₂ is simultaneously monitored by the Fourier infrared spectroscopy (FT-IR) device at the outlet end of the reaction tube. .

Then, under the above conditions, the ammonia removal rate and the nitrogen selectivity were measured at different operating temperatures (280 ° C, 300 ° C, 310 ° C, 320 ° C), and the test results are shown in Fig. 3.

It can be seen from Fig. 3 that the method for removing ammonia in the gas according to the present invention can convert ammonia gas into nitrogen gas and water at a low temperature (equal operating temperature is equal to or higher than 280 ° C), and the ammonia gas removal rate is 93%. Above, the nitrogen selectivity is greater than 90%.

While the invention has been described above in terms of several preferred embodiments, it is not intended to limit the scope of the present invention, and any one of ordinary skill in the art can make any changes without departing from the spirit and scope of the invention. And the scope of the present invention is defined by the scope of the appended claims.

10‧‧‧catalyst for oxidizing ammonia

20‧‧‧Oxide support

21‧‧‧First metal

22‧‧‧Second metal

Claims (9)

A catalyst for oxidizing ammonia gas, comprising: an oxide support, wherein the oxide support comprises cerium oxide (CeO ₂ ), cerium oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), Or a combination thereof; and a first metal and a second metal are supported on the carrier, wherein the first metal is copper and the second metal is silver, platinum, or palladium. The catalyst for oxidizing ammonia gas according to claim 1, wherein the weight ratio of the first metal to the second metal is 1:10 to 10:1. The catalyst for oxidizing ammonia gas according to claim 1, wherein the weight ratio of the total weight of the first metal and the second metal to the oxide support is 1:20 to 1:5. . The catalyst for oxidizing ammonia gas according to claim 1, wherein the oxide system is cerium oxide or a mixture of cerium oxide and aluminum oxide. The catalyst for oxidizing ammonia gas according to claim 4, wherein the mixture of cerium oxide and aluminum oxide has a weight ratio of cerium to aluminum of 1:10 to 1:1. The catalyst for oxidizing ammonia gas according to claim 1, wherein the second metal is silver. A method for removing ammonia gas in a gas, comprising: placing the catalyst for oxidizing ammonia gas according to claim 1 of the patent application in an atmosphere at an operating temperature, thereby converting ammonia gas in the atmosphere into Nitrogen and water. A method of removing ammonia from a gas as described in claim 7 wherein the operating temperature is equal to or greater than 280 °C. The method for removing ammonia in a gas as described in claim 7, wherein the method for removing ammonia in the gas has a removal rate of ammonia greater than 93% and a nitrogen selectivity greater than 90%.