DE10160359A1 - Catalyst used for cleaning gases (claimed) e.g. in the chemical and electronics industries, especially in the manufacture of ammonia and chips contains gold on a support - Google Patents

Abstract

Catalyst contains gold on a support. An Independent claim is also included for a process for the production of the catalyst comprising treating pyrogenically produced metal oxide, metalloid oxide and/or a mixed oxide using an aqueous gold salt solution adjusted to a pH of the isoelectric neutral point of the metal oxide, metalloid oxide and/or a mixed oxide, drying and calcining at 200-400 deg C in air, inert gas or forming gas. Preferred Features: The support is a pyrogenically produced metal oxide, metalloid oxide and/or a mixed oxide.

Description

The invention relates to a catalyst, a process its manufacture and its use.

In the chemical and electronic field, some high-purity gases can be used. In particular, may oxidizing and reducing gases, such as hydrogen, Carbon monoxide, hydrocarbons or oxygen, one Share of 5 ppb (ppb means parts per billion to the volume).

To purify nitrogen from the air fractional distillation is obtained, it is necessary remove the carbon monoxide it contains before it for example for the production of ammonia or for chip Manufacturing continues to be used.

It is known to remove carbon monoxide from nitrogen by bringing compressed air to temperatures from 120 to Heated 250 ° C and then passed over a catalyst. This turns carbon monoxide into carbon dioxide and so too Hydrogen contained in the air is oxidized to water.

The two products can then be adsorbed from the Air can be removed.

Palladium is usually used as the catalyst Alumina used. The carbon monoxide content can be reduced to a value of less than 10 ppb (see Brochure Fixed Bed Catalyst Degussa AG 09/98).

The known catalyst has the disadvantage that for the implementation of the oxidation reaction is relatively high Temperature must be set.

It is therefore the task of a catalyst develop that does not have these disadvantages.

The invention relates to a catalyst containing Gold on a support.

The gold can be either in elemental state or as an ion be applied to the carrier. The loading with gold can 0.1% by weight - 5.0% by weight.

Pyrogenically produced metal oxide and / or Metalloid oxide and / or mixed oxide, for example pyrogenic produced titanium dioxide can be used.

Pyrogenically produced metal oxides and / or metalloid oxides and / or mixed oxides and, for example, pyrogenic Titanium dioxide produced are known from Ullmann's Encyclopedia of Technical Chemistry Volume 21, page 464 (1982).

In a preferred embodiment of the invention, one can Use pyrogenic titanium dioxide as a carrier.

The carrier can be powdered or shaped. He can in Form of compacts and / or extrudates based on known Ways are made, used. Prefers extrudates are used.

In a preferred embodiment of the invention Extrudates of the pyrogenically produced titanium dioxide are used, which are known from US 5,120,701, and EP 0 452 619 A1 are known.

In a preferred embodiment of the invention, titanium dioxide compacts with the following physico-chemical characteristics:
Outside diameter: 0.7-25 mm
BET surface area
according to DIN 66 131: 1-50 m ² / g
Pore volume: 0.01-0.50 ml / g
Pore distribution: at least 90% of the pores in the range d _pores = 10-60 nm
Breaking strength: 10-150 N / compact
TiO ₂ phase: 20-100% rutile; Rest of Anate's whiteness
Berger:> 35
be used.

They can be made by making the pyrogen manufactured titanium dioxide in the presence of fully desalinated Water with a humidifier and / or if necessary a base and / or optionally a binder and / or optionally a deformation aid and / or possibly a pore former mixed, the mass obtained at pressures between 1 and 100 bar extruded into moldings, the moldings at Dries temperatures between 50 and 160 ° C and then in ambient air at temperatures from 200 to Calcined at 700 ° C for 1 to 5 hours.

The following substances can be used as humidifiers:
Alcohols, glycerin, diethylene glycol or polyethylene oxide

The following substances can optionally be used as bases in a mixture:
NH ₃ , urotropin, organic amines such as monoethanolamine

The following substances can be used as binders:
Cellulose derivatives, for example carboxymethyl cellulose, methyl hydroxyethyl cellulose (tylose) or unsubstituted cellulose, polyethylene, polypropylene, polyvinyl alcohol, polyacrylamide, polystyrene

The following substances can be used as deformation aids:
Lactic acid or other organic acids

The following substances can be used as pore formers:
Pulp (wood pulp) melamine, pentaerythite

The humidifier can - based on the Total mixture - contained in amounts of 5 to 50 wt .-% his.

The base can - based on the total mixture - in quantities from 0 to 20% by weight.

The binder can - in relation to the total mixture Amounts of 0.01 to 15 wt .-% may be included.

The deformation aid can - based on the Total mixture - contained in amounts of 0 to 10 wt .-% his.

The pore former can - based on the total mixture - in Amounts of 0 to 20 wt .-% may be included.

In one embodiment, the pyrogenically produced titanium dioxide can be treated with methylhydroxyethyl cellulose (tylose) and / or optionally CMC and / or optionally polyethylene oxide and / or optionally monoethanolamine and / or optionally NH ₃ and / or optionally lactic acid and / or optionally polyvinyl alcohol and / or optionally pulp and / or if necessary, mix melamine intensively in the presence of fully demineralized water, extrude the mass obtained at pressures between 1 and 100 bar into moldings, dry the moldings at temperatures between 50 and 160 ° C and then in ambient air at 200- Calcine temperatures of 700 ° C for 0.5-5 hours.

Another object of the invention is a process for the preparation of the catalyst, which is characterized in that pyrogenically produced metal oxide, metalloid oxide and / or mixed oxide by means of an aqueous gold salt solution which has a pH of the isoelectric neutral point of the metal oxide, metalloid oxide and / or mixed oxides is set, treated, dried and then calcined at a temperature of 200-400 ° C in air, inert gas or forming gas, consisting of 5% H ₂ and 95% N ₂ .

Forming gas not only serves to reduce Au ³⁺ ₂ O ₃ , but also helps with decomposition at higher temperatures, as the hydrogen in the forming gas (5% H ₂ /95% N ₂ ) binds the released oxygen as water.

HAuCl ₄ in water can be used as the gold salt solution. The concentration of the HAuCl ₄ solution in water can be 0.1 to 150 g / l, preferably 0.1 to 2.0 g / l. By drying and calcining, trivalent gold oxide is formed via the stage of gold hydroxide. This decomposes during the calcination with the formation of fine metallic gold particles.

The HAuCl ₄ is dissolved in water. AuCl ₃ + HCl is formed. This solution is acidic. From a pH = 3 upwards by adding a base such as NaOH, the steps HAuCl ₃ (OH) [pH = 3] → HAuCl ₂ (OH) ₂ → HAuCl (OH) ₃ → HAu (OH) ₄ [pH 10 to < 11] formed. The last connection then fails. According to the invention, all steps between pH = 3-9 / 10 are therefore possible. However, pH = 3-7 is advantageous, and especially 6-7 if TiO _{2 is used} as a carrier.

The setting near the isoelectric Neutral point can, for example, using sodium hydroxide solution or aqueous sodium carbonate solution or other known ones Buffer media are done. The pH can range from 3 to 7, preferably be 6-7. At a temperature of 60 A pH of 6 to 7 can be set up to 70 ° C.

When treating the carrier with the aqueous gold salt Solution, no gold is precipitated. Rather, the Chemical bond formation.

The neutral point is temperature dependent. However, one is increased temperature (> room temperature, <boiling temperature of the Reaction medium water) is advantageous since it is training the chemical bond carrier surface - gold salt particles favored or accelerated.

The temperature can range from room temperature to below the boiling point. A is preferred Temperature range of 60 to 80 ° C maintained.

The carrier can be loaded up to 80% by weight. In the When using titanium dioxide, the neutral point is pH 7 at a temperature of 70 ° C.

If necessary, the pH can be adjusted during loading be readjusted.

A second influence is the temperature. For example, for TiO ₂ pH = 7 at 70 ° C (or also pH = 7.5 at 40 ° C); for example, SiO ₂ pH = 4 can be set at 50 ° C. For example, with TiO ₂ with pH = 6 at 70 ° C, the entire production takes a little longer because the chemical reaction of the gold salt particles on the carrier surface is the rate-determining and at the same time critical step.

It is crucial that according to the invention very small and highly active particles are obtained by the manufacturing process. The loading of the TiO ₂ carrier, which is present as an extrudate, with gold can be 0.1 to 5.0% by weight.

The catalyst according to the invention has a purple-gray color when titanium dioxide is used as the carrier. It is stable in the air. The particle size of the active particles, which are located on the outer surface of the support, is 1-3 nm (see TEM according to FIGS. 3 and 4). Particles> 10 nm are inactive.

The catalyst of the invention can be used to purify Gases, especially for the removal of carbon monoxide and Hydrogen from the air can be used.

With the catalyst of the invention it is possible to Purification of compressed air, respectively oxygen-containing gases at significantly lower Temperatures in the range of 20 to 100 ° C, in Dependence on space velocity and concentration of the substances to be removed.

The cleaning means the removal of CO and H ₂ from air or oxygen-containing gases, H _{2 being converted} to H ₂ O and CO to CO ₂ .

The catalysts contained can be used several times with the same results can be used.

Examples

In the examples, the pyrogenically produced titanium dioxide P 25 is used as titanium dioxide, which is characterized by the following physico-chemical characteristics:

The BET surface is covered with nitrogen in accordance with DIN 66 131 certainly.

The pore volume is calculated from the sum of the micro, Meso- and macropores determined.

The breaking strength is determined by means of the Breaking strength tester from Erweka, type TBH 28, certainly.

The micro and mesopores are determined by recording an N ₂ isotherm and evaluating them according to BET, de Boer and Barret, Joyner, Halenda.

The macropores are determined by the Hg injection method. Example 1 8.0 kg titanium dioxide P 25: (100% TiO ₂ )
1.0 kg 2% tylose solution: (0.25% tylose)
100 g polyethylene oxide: (1.25% polyethylene oxide)
are kneaded in a kneading unit for 4-8 hours with the addition of deionized water. The plastic mass obtained in this way is extruded at pressures between 10-30 bar, dried at 70 ° C. and calcined for 4 hours after increasing the temperature gradually at 620 ° C. The moldings obtained in this way have the following physico-chemical characteristics: 1 outer diameter 1.5 mm 2 BET surface according to DIN 66 131 19 m ² / g 3 pore volume 0.32 ml / g 4 pore distribution 90% within 10-60 nm 5 breaking strength 55 N / extrudate 6 composition > 99% TiO ₂ 7 TiO ₂ phase 75% rutile, rest anatase

Example 2 manufacturing

1.7 g of a 30% HAuCl ₄ solution (7.5 × 10 ^-3 mol) are dissolved in 1500 ml of water (83.3 mol). The yellow-clear solution is heated to 70 ° C. (343 K) with stirring. 100 g of TiO ₂ extrudates according to Example 1 (1.25 mol) are now added. While checking the pH (for example by titration), a 0.2 N NaOH solution is now added quickly and the pH is adjusted to pH 7. After 2 h the pH remains constant. The excess water is decanted and discarded. An examination for possible residual amounts of gold, which is carried out using hydrazine, is negative.

The coated support is first dried in a drying cabinet at 80 ° C.-120 ° C. (105 ° C.) and then calcined at 250 ° C. under forming gas. The finished catalyst 0.5% Au / TiO ₂ has a violet-gray color and an average gold content of 305 ± 0.5 ng (nanograms per extrudate).

Example 3 manufacturing

100 g of TiO ₂ extrudates according to Example 1 (1.25 mol) are placed in 1.5 l of water (83.3 mol) and heated to 70 ° C (343 K). A pH of 7 is set using a Titrisol buffer solution. Now 1.67 g of a 30% gold chloride solution (1.5 mmol) are added. The pH is checked and kept at pH = 7. The end point of the complete uptake of gold by the carrier is confirmed, for example, by adding hydrazine to the water. There is no black precipitation. It is decanted off and proceed as in Example 1.

Example 4 application

In detail, the testing of the catalysts is carried out as follows:
20 ml of catalyst are placed in a tubular reactor made of stainless steel. Compressed air which has been humidified by means of a water saturator is passed through the reactor. The pressure is 6 bar abs. The flow is 7200 ml / min. The compressed air contains approx. 100-200 vppb CO and 200-1000 vppb H ₂ . The levels of carbon monoxide and hydrogen in the air can vary depending on the environment. For this reason, areas are given.

A temperature ramp of 180 ° C to room temperature is run within 20 hours. The temperature (temperature measurement in the catalyst bed) is determined at which a concentration> 5 vppb CO or H _{2 is} measured for the first time in the clean gas. The measurement is carried out using an RGA instrument from Trace Analytical. The gas concentrations are determined by means of IR spectroscopy.

evaluation

The data obtained (residual concentration CO and H ₂ , temperature, time) are shown as a graphic. The temperature and the concentration of unreacted carbon monoxide and hydrogen are logarithmically plotted against time. At the point of the breakthrough where CO and H ₂ can be detected for the first time, the associated temperature is read off as a measure of the activity of the catalyst.
(The assessment criterion for the catalyst activity is the temperature which is required in order to reach residual CO and H ₂ concentrations of ≤ 5 ppb)

With the catalyst according to the invention according to Example 2 the removal of carbon monoxide and hydrogen from air examined. The content of carbon monoxide and hydrogen is up to 1000 ppb.

The compressed air is passed over the catalyst at a temperature of 60 to 70 ° C. The hydrogen contained in the air is completely oxidized to water at this temperature, the carbon monoxide completely converted to CO ₂ .

H ₂ and CO can no longer be detected at an analytical detection limit of 5 ppb. The resulting products water and carbon dioxide can be removed from the air in a known manner. The results of this example are shown graphically in FIG. 2.

Example 5 State of the art Production of a palladium on alumina catalyst

300 g of γ (gamma) -Al ₂ O ₃ are placed in an impregnation drum. 7.5 g of a 20% by weight PdCl ₂ solution are added, which is diluted in 70 ml of water + 9 ml of NaOH solution (10% by weight). The aqueous solution is completely absorbed by the carrier. The catalyst is then dried at 110 ° C. and then washed with a basic solution. After drying again, the catalyst is reduced at 400 ° C in the forming gas stream.

The test or use of the catalyst obtained is carried out analogously to Example 4. No CO and H _{2 are} detected at temperatures 130 130 ° C.

The advantage of the catalyst according to the invention results from the comparison of FIGS. 1 and 2.

In the drawings Fig. 1, the Example 5 with a known catalyst (Pd on Al ₂ O ₃₎ and Fig. 2, the Application Example 4 with a catalyst according to the invention.

In the figures, the amounts of CO and H _{2 are} plotted against the time during which the reaction temperature is lowered and the limit temperature is subsequently determined. The limit temperature is the temperature at which CO and H ₂ can be detected in concentrations greater than 5 ppb.

It follows that when using the catalyst Reaction temperature in the range of the limit temperature or must be higher if the contents are lower than <5 ppb (= Volume ppb) in which fine gas is to be realized.

In the figures furthermore mean:
T _limit (CO) <24 ° C = the test was ended at 24 ° C because no CO could be detected at this point.

The levels of CO and H ₂ in the air can fluctuate, so a range from 100 to 500 and 500 to 1000 vppb is given.

GHSV means space velocity.

FIGS. 3 and 4 show scanning electron microscope (TEM) images of the catalyst according to the invention.

Fig. 3 shows the gold catalyst according to the invention at a magnification of 250,000 (* 2 for visual presentation), so 500,000.

Fig. 4 shows the gold catalyst according to the invention at a magnification of 750,000 (* 2 for visual presentation), thus 1.5m

The small, uniformly round gold particles on the TiO _{2 support} , with a size of 1-3 nm (10 ^-9 m), are clearly visible.

Claims (5)

1. Catalyst containing gold on a support. 2. Catalyst according to claim 1, characterized in that that the carrier is an oxidic carrier. 3. Catalyst according to claim 1 or 2, characterized characterized in that a pyrogenic carrier Metal oxide Metalloid oxide and / or mixed oxide used becomes. 4. Process for the preparation of the catalyst according to Claim 1, characterized in that pyrogenic manufactured metal oxide, metalloid oxide and / or Mixed oxide using an aqueous gold salt solution, the to a pH value of the isoelectric neutral point of the Metalloxides and / or Metalloidoxides and / or Mixed oxides is set, treated, dries and then at a temperature of 200-400 ° C in Air, inert gas or forming gas calcined. 5. Use of the catalyst according to claim 1 for Gas cleaning.