WO1991001175A1 - Low temperature oxidation process - Google Patents

Low temperature oxidation process Download PDF

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Publication number
WO1991001175A1
WO1991001175A1 PCT/GB1990/001146 GB9001146W WO9101175A1 WO 1991001175 A1 WO1991001175 A1 WO 1991001175A1 GB 9001146 W GB9001146 W GB 9001146W WO 9101175 A1 WO9101175 A1 WO 9101175A1
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catalyst
metal
oxide
oxidation
precious metal
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PCT/GB1990/001146
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French (fr)
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John Russell Richmond
Tale Abdu-Karim Dawood
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Uop Limited
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/864—Removing carbon monoxide or hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8643—Removing mixtures of carbon monoxide or hydrocarbons and nitrogen oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/64—Platinum group metals with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)

Definitions

  • This invention relates to the catalytic oxidation at low temperatures of certain molecules having molecular weights below 50.
  • compositions exist that are able to catalyze the oxidation of oxidizable materials at low temperatures.
  • US-A-4459270 discloses the removal of hydrogen from a gas containing both hydrogen and oxygen, at ambient temperature (e.g. 10 to 30°C) , using a catalyst comprising tin (IV) oxide and alumina as carrier, impregnated with both palladium and platinum.
  • US-A-4536375 discloses the oxidation of carbon monoxide using a catalyst comprising a precious metal (platinum, palladium, rhodium, iridium or ruthenium) supported on tin (IV) oxide, and promoted by one or more metals of Group lb, 3b, 7b or 8 of the Periodic Table (e.g. copper, nickel, manganese, silver or lanthanum).
  • a precious metal platinum, palladium, rhodium, iridium or ruthenium
  • tin (IV) oxide e.g. copper, nickel, manganese, silver or lanthanum
  • US-A-4639432 discloses another catalyst for oxidizing carbon monoxide comprising tin (IV) oxide, supported on which are: (i) palladium, (ii) at least one of platinum, ruthenium, rhodium and iridium, and (iii) at least one of copper, nickel, cobalt, iron, manganese, silver, lathanum, cerium, praseodymium and neodymium.
  • EP-A-0306944 provides a catalyst for low temperature oxidation, e.g. in a gas laser", which comprises platinum or palladium on an alumina or magnesia support, and optionally also comprising iron. Silica and tin compounds are absent.
  • EP-A-0306945 provides a similar catalyst in which the support is titania, and which optionally comprises rhenium oxide, iron oxide, ruthenium metal or oxide, copper metal or oxide, silver metal or oxide, sumarium oxide or europium oxide as promoter.
  • the support is titania, and which optionally comprises rhenium oxide, iron oxide, ruthenium metal or oxide, copper metal or oxide, silver metal or oxide, sumarium oxide or europium oxide as promoter.
  • Another related catalyst is disclosed in US-A-4808394 and comprises platinum and/or palladium and iron on an alumina support that has been impregnated with ammonium thiocyanate.
  • EP-A-330224 provides a catalyst obtained by impregnating a support with a platinum and/or palladium compound at a pH of at least 5. An iron compound may also be included.
  • GB- -2083944 discloses catalyst for oxidising carbon monoxide in a laser which comprises a platinum and/or palladium catalyst on a metallic substrate having an oxidized surface including alumina, the metal being steel containing aluminium, and optionally also chromium and yttrium.
  • the present invention provides a low temperature oxidation process in which an oxidizable material having a molecular weight below 50 is contacted at a temperature below 30°C with a catalyst which comprises one or more precious metals (e.g. platinum, palladium, ruthenium, rhodium, iridium, rhenium, and/or silver) supported on a reducible metal oxide selected from Fe 2 03, Ce 2 ⁇ 3, Zr0 2 »CuO, rare earth metal oxides, Mn0 2 , v 2 ⁇ 5 an ⁇ ⁇ Cr 2 ⁇ 3*
  • the catalyst defined above may be supported on an inert support, selected from silica, carbon, or silica- alumina. Suitable rare earth metal oxides include lanthanum, neodymium, and praseodymium.
  • the low temperature oxidation processes include in general the oxidation of oxidizable materials having molecular weights below 50, such as the oxidation of carbon monoxide, hydrogen, deuterium, tritium, nitrous oxide or nitric oxide.
  • Figure 1 shows the rate of oxidation of carbon monoxide over catalysts supported on carbon cloth
  • Figure 2 shows carbon monoxide oxidation over platinum/palladium catalysts supported on silica.
  • the composition of the catalyst can be varied within broad limits.
  • the amount of total precious metal can be from 0.5 to 60% by weight, more preferably 0.5 to 40% by weight, most preferably 10 to 40% by weight, based on reducible metal oxide.
  • the amount of catalytically-active material can be from 1 to 50% by weight, more preferably 2 to 25% by weight, most preferably 5 to 10% by weight, based on support.
  • the catalysts used according to the invention can be prepared by suitably adapting any convenient method known to those skilled in the art of catalyst manufacture.
  • the support in the embodiment employing an inert support, the support can be impregnated with solutions of decomposable compounds of the precious metal and of the metal forming the reducible oxide, the impregnated support can be dried, and then the decomposable compounds can be decomposed.
  • the reducible metal oxide can first be formed, and then impregnated with a solution of a compound of the precious metal.
  • the preferred anions of the decomposable salts will depend upon the metal, but chlorides should not in general be used. Palladium and platinum chlorides do not give successful catalysts.
  • the catalysts can be employed in various physical forms, for instance shaped articles (discs, rings, extrudates, or pellets), as monoliths, honeycombs, foams, or cloths.
  • the catalysts used according to the invention are particularly suitable for use at ambient or near ambient temperatures, for instance at a temperature from 10 to 30°C, preferably at about 20°C, or at temperatures below ambient, e.g. up to 20°C.
  • the catalysts can also be used when it is desirable to carry out oxidation at low temperatures e.g. at temperatures below 0°C, such as at -20°C.
  • Oxygen, air, or oxygen-enriched air can be employed where appropriate as the gas containing free oxygen in the process of the invention.
  • the oxidation catalysts used according to the invention will operate at ambient or sub-ambient temperatures to effect a variety of oxidation reactions such as the combination of carbon monoxide and oxygen in carbon dioxide gas lasers; in certain confined spaces where carbon monoxide may be generated, such as from the incomplete combustion of carbon-containing materials, for example in or near fires, in submarines, or other closed living quarters, or in ventilation systems.
  • all these catalysts may be used for the oxidation of hydrogen and its isotopes deuterium and tritium, where it is desired to convert the hydrogen isotope into water or deuterated or tritiated water.
  • Water and its heavier analogues are more readily removed from air or other gases than are hydrogen, deuterium or tritium, by means of drying materials such as silica gel, various molecular sieves and other desiccants.
  • the catalysts may also be used for the oxidation of low molecular weight hydrocarbons, having molecular weights below 50, such as ethylene.
  • the catalysts may be used inter alia for the following applications:
  • a carbon dioxide gas laser laser emission is initiated by an electrical discharge within a gas-tight envelope containing, typically, a mixture of carbon dioxide, nitrogen and helium in the proportions by volume of 3:2:2.5.
  • the electrical discharge in the gas also, unfortunately, causes some of the carbon dioxide to be dissociated into carbon monoxide and oxygen and, unless the dissociation products are removed, there is a loss of output from the laser due, for example, to arcing between the electrodes which are used to set up the electrical discharge in the gas.
  • transversely excited lasers that is, where the electrodes are so disposed as to cause excitation transverse of the laser axis
  • TEA transversely excited atmospheric pressure
  • Pt.Pd-(10% Cr 2 0 3 , 90% Fe 2 0 3 ) was prepared as follows:
  • 10% Cr 2 ⁇ 3 ⁇ 9()% Fe 2 ⁇ 3 Dase was prepared by precipitation with ammonia from mixed solutions of the nitrates in appropriate proportions, followed by drying, calcination at 400°C, and tableting into 1.5 x 13mm discs.
  • the base in tablet form was co- impregnated with a solution of tetraamine platinous hydroxide and tetraa ine palladium nitrate containing 8% Pt and 6% Pd. The excess solution was drained and the metal oxide base containing platinum and palladium was dried and calcined, at a temperature increasing from room temperature to 320°C. The catalyst was then reduced at room temperature in H 2 /N 2 .
  • Air containing 1,000 ppm of carbon monoxide was passed through a bed of catalyst in form of granules at a space velocity of 24,000 hr at room temperature and pressure.
  • the concentration of carbon monoxide in air was measured after the catalyst bed.
  • the results together with metal compositions in the catalyst are shown in Table 1.
  • These catalysts were made by combination of two precious metals (Pt and Pd) and reducible oxides Ce0 2 or Fe 2 ⁇ 3 on carbon cloth.
  • Carbon cloth with a BET surface area of 1200 m /g (2.6g) was impregnated with a metal nitrate solution containing the appropriate base metal salt.
  • the carbon cloth was dried in air at 40°C and the salt was decomposed at 200°C.
  • the cloth was impregnated with the solution of the salt, dried in air at 40°C and heated at 200 °C. After that the cloth was reduced in H 2 / 2 at ambient temperature.
  • the concentration of the metals solutions employed was as follows:
  • Air containing 1% of carbon monoxide and 3.5% of carbon dioxide saturated with water at 37°C was passed through a bed of catalyst containing 10 layers of carbon cloth catalyst 2 cm in diameter at space velocities of J2.600 ' h -1 and 37,000 h -1 .
  • the content of carbon monoxide after the catalyst bed was measured.
  • the results together with the metal composition are shown in Tables 2, 3 and 4, and Figure 1, which shows the results obtained at space velocity of 12,600 h _1 . It will be seen that in the absence of reducible metal oxide, a platinum-palladium catalyst supported on carbon cloth rapidly loses its effectiveness, whereas, in the presence of a reducible metal, its effectiveness improves with time.
  • the following series of catalysts was prepared by depositing the reducible oxide (Fe 2 ⁇ 3) on Si0 2 together with platinum and palladium metals.
  • the resulting calcined iron oxide containing Si0 2 was co- impregnated with tetraammine platinous hydroxide, and tetraammine palladium nitrate solution containing 2.28% Pt and 1.53% Pd. The excess solution was drained, and silica containing Pt, Pd and e 2 0 3 was dried and calcined as just described above. Then the catalyst was reduced in H 2 /N 2 at room temperature.
  • Air containing 1000 ppm of carbon monoxide was passed through a bed of catalyst in the form of 2-3 mm diameter spheres at a space velocity of 12,000 hr ⁇ at room temperature and atmospheric pressure. The concentration of carbon monoxide in air was measured after the catalyst bed.
  • Figure 2 shows the effect on catalyst activity for carbon monoxide oxidation at room temperature by adding Fe U3 to Si0 2 base containing Pt and Pd.
  • Catalyst was prepared by depositing two precious metals (using chlo ide-containing precious metal salts) on reducible metal oxide. Pt, Pd/(10% Cr 2 0 3 + 90% Fe 2 0 3 ). This catalyst prepared as in Example 1, but using chlo ide-containing precious metal salts.
  • the base (10% Cr 2 0 3 + 90% Fe 2 0 3 ) was prepared by precipitation from nitrate salts, followed by drying, calcination and tableting.
  • the base in disc form was co-impregnated with palladium (II) chloride (PdCl ) and hexachloroplatinu (IV) acid (H 2 PtCl 6 ), solution containing 5.6% Pd and 7.5% Pt.
  • the excess solution was drained, and the catalyst was dried and calcined, at a temperature increasing from room temperature to 320°C. The catalyst was then reduced at room temperature in H 2 /N 2 .
  • Catalyst composition 2% Pt 2% Pd/(10% cr 2 0 3 ; 90% Fe 2 0 3

Abstract

The oxidation of low molecular weight materials (e.g. carbon monoxide, hydrogen, hydrocarbons), can be carried out in a presence of a catalyst which comprises at least one precious metal (e.g. platinum, palladium, rhodium, ruthenium or iridium) supported on a reducible metal oxide selected from Fe2?O3?, Ce2?O3?, ZrO2?, CuO, rare earth metal oxides, MnO2?, V2?O5? and Cr2?O3?. Optionally the active catalyst (precious metal and reducible metal oxide) can be associated with an inert support, such as carbon cloth.

Description

LOW TEMPERATURE OXIDATION PROCESS
This invention relates to the catalytic oxidation at low temperatures of certain molecules having molecular weights below 50.
It is known that compositions exist that are able to catalyze the oxidation of oxidizable materials at low temperatures. For example, US-A-4459270 discloses the removal of hydrogen from a gas containing both hydrogen and oxygen, at ambient temperature (e.g. 10 to 30°C) , using a catalyst comprising tin (IV) oxide and alumina as carrier, impregnated with both palladium and platinum. US-A-4536375 discloses the oxidation of carbon monoxide using a catalyst comprising a precious metal (platinum, palladium, rhodium, iridium or ruthenium) supported on tin (IV) oxide, and promoted by one or more metals of Group lb, 3b, 7b or 8 of the Periodic Table (e.g. copper, nickel, manganese, silver or lanthanum). US-A-4639432 discloses another catalyst for oxidizing carbon monoxide comprising tin (IV) oxide, supported on which are: (i) palladium, (ii) at least one of platinum, ruthenium, rhodium and iridium, and (iii) at least one of copper, nickel, cobalt, iron, manganese, silver, lathanum, cerium, praseodymium and neodymium.
EP-A-0306944 provides a catalyst for low temperature oxidation, e.g. in a gas laser", which comprises platinum or palladium on an alumina or magnesia support, and optionally also comprising iron. Silica and tin compounds are absent.
EP-A-0306945 provides a similar catalyst in which the support is titania, and which optionally comprises rhenium oxide, iron oxide, ruthenium metal or oxide, copper metal or oxide, silver metal or oxide, sumarium oxide or europium oxide as promoter. Another related catalyst is disclosed in US-A-4808394 and comprises platinum and/or palladium and iron on an alumina support that has been impregnated with ammonium thiocyanate.
EP-A-330224 provides a catalyst obtained by impregnating a support with a platinum and/or palladium compound at a pH of at least 5. An iron compound may also be included.
GB- -2083944 discloses catalyst for oxidising carbon monoxide in a laser which comprises a platinum and/or palladium catalyst on a metallic substrate having an oxidized surface including alumina, the metal being steel containing aluminium, and optionally also chromium and yttrium.
A need still exists, however, for catalysts that will be effective for low temperature oxidation of a wide variety of oxidizable materials.
The present invention provides a low temperature oxidation process in which an oxidizable material having a molecular weight below 50 is contacted at a temperature below 30°C with a catalyst which comprises one or more precious metals (e.g. platinum, palladium, ruthenium, rhodium, iridium, rhenium, and/or silver) supported on a reducible metal oxide selected from Fe203, Ce2θ3, Zr02»CuO, rare earth metal oxides, Mn02, v2^5 an<^ Cr2^3* In an optional embodiment, the catalyst defined above may be supported on an inert support, selected from silica, carbon, or silica- alumina. Suitable rare earth metal oxides include lanthanum, neodymium, and praseodymium.
The low temperature oxidation processes include in general the oxidation of oxidizable materials having molecular weights below 50, such as the oxidation of carbon monoxide, hydrogen, deuterium, tritium, nitrous oxide or nitric oxide. The invention will be further illustrated below with reference to various examples and to accompanying Drawings in which:
Figure 1 shows the rate of oxidation of carbon monoxide over catalysts supported on carbon cloth; and
Figure 2 shows carbon monoxide oxidation over platinum/palladium catalysts supported on silica.
The composition of the catalyst can be varied within broad limits. For example, the amount of total precious metal can be from 0.5 to 60% by weight, more preferably 0.5 to 40% by weight, most preferably 10 to 40% by weight, based on reducible metal oxide.
When an inert support is employed, the amount of catalytically-active material (precious metal + reducible oxide) can be from 1 to 50% by weight, more preferably 2 to 25% by weight, most preferably 5 to 10% by weight, based on support.
The catalysts used according to the invention can be prepared by suitably adapting any convenient method known to those skilled in the art of catalyst manufacture. For example, in the embodiment employing an inert support, the support can be impregnated with solutions of decomposable compounds of the precious metal and of the metal forming the reducible oxide, the impregnated support can be dried, and then the decomposable compounds can be decomposed. When a support is not employed, the reducible metal oxide can first be formed, and then impregnated with a solution of a compound of the precious metal. The preferred anions of the decomposable salts will depend upon the metal, but chlorides should not in general be used. Palladium and platinum chlorides do not give successful catalysts.
The catalysts can be employed in various physical forms, for instance shaped articles (discs, rings, extrudates, or pellets), as monoliths, honeycombs, foams, or cloths.
The catalysts used according to the invention are particularly suitable for use at ambient or near ambient temperatures, for instance at a temperature from 10 to 30°C, preferably at about 20°C, or at temperatures below ambient, e.g. up to 20°C. The catalysts can also be used when it is desirable to carry out oxidation at low temperatures e.g. at temperatures below 0°C, such as at -20°C.
Oxygen, air, or oxygen-enriched air can be employed where appropriate as the gas containing free oxygen in the process of the invention.
The oxidation catalysts used according to the invention will operate at ambient or sub-ambient temperatures to effect a variety of oxidation reactions such as the combination of carbon monoxide and oxygen in carbon dioxide gas lasers; in certain confined spaces where carbon monoxide may be generated, such as from the incomplete combustion of carbon-containing materials, for example in or near fires, in submarines, or other closed living quarters, or in ventilation systems.
Similarly all these catalysts may be used for the oxidation of hydrogen and its isotopes deuterium and tritium, where it is desired to convert the hydrogen isotope into water or deuterated or tritiated water. Water and its heavier analogues are more readily removed from air or other gases than are hydrogen, deuterium or tritium, by means of drying materials such as silica gel, various molecular sieves and other desiccants. The catalysts may also be used for the oxidation of low molecular weight hydrocarbons, having molecular weights below 50, such as ethylene.
The catalysts may be used inter alia for the following applications:
1. Breathable gases
2. Laser applications
3. Gas purification
4. Emission control
In a carbon dioxide gas laser, laser emission is initiated by an electrical discharge within a gas-tight envelope containing, typically, a mixture of carbon dioxide, nitrogen and helium in the proportions by volume of 3:2:2.5. The electrical discharge in the gas also, unfortunately, causes some of the carbon dioxide to be dissociated into carbon monoxide and oxygen and, unless the dissociation products are removed, there is a loss of output from the laser due, for example, to arcing between the electrodes which are used to set up the electrical discharge in the gas. In transversely excited lasers (that is, where the electrodes are so disposed as to cause excitation transverse of the laser axis) including TEA (transversely excited atmospheric pressure) lasers, the dissociation products carbon monoxide and oxygen, tend to cause the electrical discharge to split up into localised arcs, again with a very significant loss of output. In both cases, this degradation of the discharge can ultimately lead to the failure of the device unless steps are taken to remove the dissociation products which are the cause of the degradation.
In the so-called "flowing gas" type of laser, these dissociation products are swept bodily away and replaced by fresh carbon d ioxide , but in sealed carbon dioxide laser s , s teps mus t be taken either to prevent the dissociation of the carbon dioxide in the f irst place , or else to ef fect the recombination of the carbon monoxide and oxygen , vi rtually as or very shortly after they are produced , i f such lasers are to operate at o r close to peak efficiency. The catalysts used according to the invention can be used for combination of the carbon monoxide and hydrogen, reforming cabon dioxide.
The following Examples illustrate the preparation and use of catalysts in processes according to the invention.
Example 1
A series of catalysts was prepared by depositing two precious metals on reducible metal oxide. Pt.Pd-(10% Cr203, 90% Fe203) was prepared as follows:
10% Cr2θ3 ~ 9()% Fe2^3 Dase was prepared by precipitation with ammonia from mixed solutions of the nitrates in appropriate proportions, followed by drying, calcination at 400°C, and tableting into 1.5 x 13mm discs. The base in tablet form was co- impregnated with a solution of tetraamine platinous hydroxide and tetraa ine palladium nitrate containing 8% Pt and 6% Pd. The excess solution was drained and the metal oxide base containing platinum and palladium was dried and calcined, at a temperature increasing from room temperature to 320°C. The catalyst was then reduced at room temperature in H2/N2.
Test Conditions
Air containing 1,000 ppm of carbon monoxide was passed through a bed of catalyst in form of granules at a space velocity of 24,000 hr at room temperature and pressure. The concentration of carbon monoxide in air was measured after the catalyst bed. The results together with metal compositions in the catalyst are shown in Table 1.
All the catalysts in this table were prepared as just described above, except that Pt.Ru/10% Cr2θ3.90% Fe 2°3 was prepared by depositing Ru metal first from ruthenium nitrosyl nitrate solution containing 5.5% of Ru and then Pt metal.
Table 1
(Metals Composition)
Catalyst Conversion After t(min) Pt Pd Ru
1.0
Figure imgf000009_0001
Example 2
These catalysts were made by combination of two precious metals (Pt and Pd) and reducible oxides Ce02 or Fe2θ3 on carbon cloth. Carbon cloth with a BET surface area of 1200 m /g (2.6g) was impregnated with a metal nitrate solution containing the appropriate base metal salt. The carbon cloth was dried in air at 40°C and the salt was decomposed at 200°C. Then the cloth was impregnated with the solution of the salt, dried in air at 40°C and heated at 200 °C. After that the cloth was reduced in H2/ 2 at ambient temperature.
The concentration of the metals solutions employed was as follows:
(a) 4.77g. of Ce (N03) 3.6H20 made up to 40 ml with deionized water,
(b) 11.13g. of Fe(N03) 2.9H20 made up to 40 ml with deionized water,
(c) 2.15g. of [Pd(NH3)4] (N03)2 containing 35.65% Pd and 2.40g of [Pt(NH3)4] (0H)2 containing 16% Pt made up to 40 ml. with deionized water.
Test
Air containing 1% of carbon monoxide and 3.5% of carbon dioxide saturated with water at 37°C was passed through a bed of catalyst containing 10 layers of carbon cloth catalyst 2 cm in diameter at space velocities of J2.600 ' h-1 and 37,000 h-1. The content of carbon monoxide after the catalyst bed was measured. The results together with the metal composition are shown in Tables 2, 3 and 4, and Figure 1, which shows the results obtained at space velocity of 12,600 h_1. It will be seen that in the absence of reducible metal oxide, a platinum-palladium catalyst supported on carbon cloth rapidly loses its effectiveness, whereas, in the presence of a reducible metal, its effectiveness improves with time.
Table 2
Catalyst Pt.Pd Fe203/carbon cloth maintaining 3.6% Pt, 6.8% Pd, 8.1% Fe.
CO (ppm) t/min
Figure imgf000011_0001
Table _4
Catalyst Pt.Pd/carbon cloth containing 7.88% Pd, 4.3% Pt. At GHSV 12600 h_1 CO (ppm) t/min
10,000 0
65 1
2,000 5
Example 3
The following series of catalysts was prepared by depositing the reducible oxide (Fe2θ3) on Si02 together with platinum and palladium metals.
(A) Pt. Pd/Si02 (for comparison.)
8.5g of Si02 (ex.Shell) 2-3mm diameter spheres were co- impregnated with a solution of tetraammine platinous hydroxide [PtfN^)4] (OH)2, and tetraammine palladium nitrate [Pd(NH3)4(N03)2 containing 1.53% Pd and 2.28%. The excess solution was drained, and silica containing platinum and palladium was dried and calcined, the temperature being raised from room temperature to 320°C. The catalyst was then reduced in H2/N2 at room temperature.
(B) Pt.Pd Fe203/Si0?
12g. of Si02 based 2-3mm diameter spheres were impregnated with ferric nitrate solution Fe(NO3) 3.9H20 containing 9.2% Fe. The excess solution was drained, and Si02 containing iron oxide was dried and calcined, the temperature being raised from room temperature to 320°C.
The resulting calcined iron oxide containing Si02 was co- impregnated with tetraammine platinous hydroxide, and tetraammine palladium nitrate solution containing 2.28% Pt and 1.53% Pd. The excess solution was drained, and silica containing Pt, Pd and e203 was dried and calcined as just described above. Then the catalyst was reduced in H2/N2 at room temperature.
Test Condition
Air containing 1000 ppm of carbon monoxide was passed through a bed of catalyst in the form of 2-3 mm diameter spheres at a space velocity of 12,000 hr~ at room temperature and atmospheric pressure. The concentration of carbon monoxide in air was measured after the catalyst bed.
Figure 2 shows the effect on catalyst activity for carbon monoxide oxidation at room temperature by adding Fe U3 to Si02 base containing Pt and Pd.
Metal compositions
%Pt %Pd %Fe
Pt.Pd/Si02 2.0 1.5
Pt.Pd. Fe203/Si02 2.0 1.5 10.0
In the absence of Fe2U3, the initial catalyst activity was steadily lost, whereas when the catalyst contained Fe2θ3, its activity was maintained over an extended period.
Example 4 (for comparison)
Catalyst was prepared by depositing two precious metals (using chlo ide-containing precious metal salts) on reducible metal oxide. Pt, Pd/(10% Cr203 + 90% Fe203). This catalyst prepared as in Example 1, but using chlo ide-containing precious metal salts.
The base (10% Cr203 + 90% Fe203) was prepared by precipitation from nitrate salts, followed by drying, calcination and tableting. The base in disc form was co-impregnated with palladium (II) chloride (PdCl ) and hexachloroplatinu (IV) acid (H2PtCl6), solution containing 5.6% Pd and 7.5% Pt. The excess solution was drained, and the catalyst was dried and calcined, at a temperature increasing from room temperature to 320°C. The catalyst was then reduced at room temperature in H2/N2.
Catalyst composition : 2% Pt 2% Pd/(10% cr203 ; 90% Fe203
Test Conditions: There were the same as described in Example 1
The results are shown below in Table 5 together with the results of the catalyst prepred from non-chloride precious metals salts.
Table 5
CO Conversion (%)*
Time/min Cat (A) Cat (B)
0 0 0 3 78.7 99.0 10 56.9 99.1 20 40.6 99.1 25 99.1 30 29.7 (A) Catalyst prepared from chloride-containing precious metal salts.
(B) Catalyst prepared from non-chloride precious metal salts.
The results in Table 5 for CO oxidation on Pt Pd/10% r203 ; 90% e203 catalyst shows that the catalyst prepared from chloride-containing precious metal salts shows poor activity and stability by comparison with the same catalyst made from non- chloride precious metal salts, which shows good activity and stability under same testing conditions.

Claims

1. A process for the oxidation of an oxidizable material having a molecular weight below 50 by contacting said material with a gas containing free oxygen in the presence of a catalyst, characterized in that said contact is carried out at a temperature of up to 30°C and the catalyst comprises at least one precious metal supported on at least one reducible metal oxide selected from Fe203, Ce203, Zr02, CuO, rare earth metal oxides, Mn02, V20^ and Cr203-
2. A process according to Claim 1 wherein the oxidizable material is carbon monoxide, hydrogen, deuterium, tritium, nitrous oxide or nitric oxide.
3. A process according to Claim 1 or 2 wherein the catalyst is used for the oxidation of carbon monoxide in a carbon dioxide laser.
4. A process according to any one of Claims 1 to 3 characterised in that the precious metal is selected from platinum, palladium, ruthhenium, rhodium, iridium, rhenium or silver.
5. A process according to any one of Claims 1 to 4 characterised in that the amount of precious metal is from 0.5 to 60% by weight, based on reducible metal oxide.
6. A process according to any one of Claims 1 to 5 characterised in that the precious metal and reducible metal are associated with an inert support selected from silica, silica- alumina, and carbon.
7. A process according to Claim 6 characterised in that the total amount of precious metal and reducible metal oxide is from 1 to 50% by weight based on inert support.
PCT/GB1990/001146 1989-07-25 1990-07-25 Low temperature oxidation process WO1991001175A1 (en)

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WO2002001655A2 (en) * 2000-06-28 2002-01-03 The Gillette Company Hydrogen recombination catalyst
US6492298B1 (en) 1999-03-29 2002-12-10 Kabushiki Kaisha Toyota Chuo Kenkyusho Ordinary-temperature purifying catalyst
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US6500576B1 (en) 2000-06-28 2002-12-31 The Gillette Company Hydrogen recombination catalyst
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GB2234450A (en) 1991-02-06
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ZA905859B (en) 1992-01-29

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