DD297340A5 - LOW TEMPERATURE OXIDATIONSKATALYSALTOREN - Google Patents

Abstract

The oxidation of low molecular weight materials (eg, carbon monoxide, hydrogen, hydrocarbons) may be carried out in the presence of a catalyst comprising at least one noble metal (eg, platinum, palladium, rhodium, ruthenium, or iridium) on a reducible metal oxide as a carrier material selected among Fe2O3, Ce2O3 ZrO2, CuO, rare earth oxides, MnO2, V2O5 and Cr2O3. This catalyst can also be treated with an inert carrier material, such. Carbon fabric. {Method; Oxidation; Catalyst; precious metals; Metal oxide Traeger}

Description

For this 2 pages drawings

Field of application of the invention

The invention relates to the catalytic oxidation of certain molecules having molecular weights below 50 at low temperatures.

Characteristic of the known technical solutions

As is known, there are compositions which can catalyze the oxidation of oxidizable substances 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, stannic oxide and alumina as a carrier impregnated with both palladium and platinum. US-A-4536375 discloses the oxidation of carbon monoxide using a catalyst containing a noble metal (platinum, palladium, rhodium, iridium or ruthenium) supported on stannic oxide as carrier material, the reaction being controlled by one or more metals of the metals Group 1 b, 3 b, 7 b or 8 of the Periodic Table (eg, copper, nickel, manganese, silver or lanthanum) is promoted. US-A-4 639 432 discloses another catalyst for the oxidation of carbon monoxide comprising stannic oxide as a support material and the following supported catalysts: (i) palladium, (ii) at least one of platinum, ruthenium, rhodium and Iridium; and (iii) at least one of copper, nickel, cobalt, iron, manganese, silver, lanthanum, zer, praseodymium and neodymium.

EP-A-0306944 provides a catalyst for low-temp oxidation, e.g. Example, in a glass laser comprising platinum or palladium on an alumina or magnesia support material and optionally also iron. Silica and tin compounds error

EP-A-0306945 offers a similar catalyst with supported titanium (IV) oxide optionally containing rhenium oxide, iron oxide, metallic ruthenium or rehydrium oxide, metallic copper or copper oxide, metallic silver or silver oxide, samarium oxide or europium oxide as promoter.

Another related catalyst is disclosed in US-A-4808394 and contains platinum and / or palladium and iron on an alumina support material impregnated with ammonium thiocyanate.

EP-A-0330224 offers a catalyst obtained by impregnating a support material with a platinum and / or palladium compound at a pH of at least 5. An iron compound may also be included

GB-A-2083944 discloses a catalyst for the oxidation of carbon monoxide in a laser comprising a platinum and / or palladium catalyst on an oxidized alumina-containing metallic support, the metal being steel, the aluminum and optionally chromium and yttrium contains.

Object of the invention

The aim of the invention is an improved catalytic oxidation process for oxidizable substances with a molecular weight below 50.

-2- 297 340 Explanation of the essence of the invention

The object of the invention is such a process with catalysts which are effective in the low-temperature oxidation of a variety of oxidizable substances. This object is achieved by bringing the oxidizable substance having a molecular weight below 50 at a temperature below 30 ⁰ C with a gas containing free oxygen in the presence of a catalyst in contact, which is a noble metal or more precious metals (eg. Platinum, palladium, ruthenium, rhodium, iridium, rhenium and / or silver) on a reducible metal oxide as support material, which comprises Fe ₂ O ₃ , Ce ₂ O ₃ , ZrO ₂ , CuO, selenium oxides, MnO ₂ , V ₂ Oe and Cr ₂ O _{3 is} selected. Optionally, an inert carrier material selected from silica, carbon or silica-alumina may also be used for the catalyst defined above. Suitable rare earth metal oxides include lanthanum, neodymium and praseodymium. The cryogenic oxidation processes generally involve the oxidation of oxidizable materials having molecular weights below 50, such as the oxidation of carbon monoxide, hydrogen, deuterium, tritium, nitrogen (I) oxide or nitrogen dioxide.

The invention will be explained in more detail below with reference to various Ausführungsbe, games and accompanying drawings. Show here

Fig. 1: the oxidation rate of carbon monoxide over catalysts on carbon fabric as support material and Fig. 2: the oxidation of carbon monoxide over platinum / palladium catalysts on silica as support material.

The composition clei catalyst can be varied within wide limits. For example, the total amount of noble metal may be between 0.5 and 60% by weight, preferably between 2 and 25% by weight, and most preferably between 5 and 10% by weight, based on the support material.

The catalysts used in this invention can be prepared by appropriate adaptation to any suitable method known to those skilled in the art of catalyst preparation. For example, in the inert carrier embodiment, the carrier material can be impregnated with solutions of decomposable compounds of the noble metals and the metal forming the reducible oxide, the impregnated carrier dried, and then the decomposable compounds decomposed. If no carrier is used, first the reducible metal oxide can be formed and then impregnated with a solution of a compound of the noble metal. Which anions of the decomposable salts are preferably used depends on the metal, but generally no chlorides should be used. Palladium and platinum chlorides do not provide successful catalysts.

The catalysts can be used in various physical forms, for example as moldings (discs, rings, extrudates or pellets), as monoliths, honeycombs, foams or fabrics.

The catalysts used in the invention are particularly suitable for use at or near the ambient temperature, for. Example, at a temperature of 10 up to 30 "C, preferably at about 20 ° C, or at temperatures below ambient temperature, eg., Up to 2O ⁰ C. The catalysts can also be used when carrying out the oxidation at low Temperatures is desirable, for example, at temperatures below ^{0 0} C, about -20 ° C.

Oxygen, air or oxygen-enriched air may optionally be used in the process of the invention as the gas containing free oxygen.

The oxidation catalysts used in the invention operate at ambient temperatures or below and cause a variety of oxidation reactions, such as. As the compound of carbon monoxide and oxygen in carbon dioxide gas lasers, in certain closed spaces where carbon monoxide may arise, such. B. incomplete combustion of carbonaceous materials, for example, at or near fires, in submarines or other closed lounges or in lifts technical facilities.

Similarly, all of these catalysts can be used for the oxidation of hydrogen and its isotopes deuterium and tritium, if the conversion of the hydrogen isotope into water or heavy or excess water is desired. Water and its heavier analogue are easier to remove from air or other gases than hydrogen, deuterium, or tritium with desiccants such as silica gel, various molecular sieves, and other siccatives.

The catalysts may also be used for the oxidation of hydrocarbons having low molecular weights below 50, such as. B.

of ethylene.

The catalysts can be used, inter alia, for the following applications:

1. breathable gases

2. Laser applications

3. Gas cleaning

4. Emission limitation

In a carbon dioxide gas laser, the laser emission is triggered by an electrical discharge within a gas tight envelope, which typically contains a 3: 2: 2.5 by volume mixture of carbon dioxide, nitrogen and helium. Unfortunately, the electrical gas discharge also causes the dissociation of some carbon dioxide into carbon monoxide and oxygen, and if the dissociation products are not removed, the output of the laser is reduced, for example, by arcing between the electrodes, which serve to generate the electrical discharge in the gas. In cross-excited lasers (ie, where the electrodes are arranged to cause transverse laser excitation) including TEA lasers (cross-excited normal pressure lasers), the dissociation products usually cause carbon monoxide and oxygen to split the electrical discharge into localized arcs, which in turn causes a very significant loss of output power. In either case, this degeneration of the discharge may eventually lead to equipment failure if no steps are taken to remove the dissociation products that cause degeneration.

In the so-called "gas flow" laser type, these dissociation products are expelled as a whole and replaced by fresh carbon dioxide, but in closed carbon dioxide lasers steps must be taken to either prevent the dissociation of the carbon dioxide or the recombination of carbon monoxide and oxygen practically during or shortly after When such lasers are to be used with the highest efficiency or in the vicinity thereof, the catalysts used according to the invention can be used to combine carbon monoxide and hydrogen, carbon dioxide again being formed.

In the following examples, the preparation and use of catalysts in eriindungsgemäßen methods are explained in more detail.

Exemplary embodiments

example 1

A series of catalysts was prepared by depositing two precious metals on reducible metal oxide.

Pt.Pd (10% Cr ₂ O ₃ , 90% Fe ₂ O ₃ ) was prepared as follows:

The substrate of 10% Cr ₂ O ₃ - 90% Fe ₂ O ₃ was prepared by precipitation with ammonia from mixed solutions of the nitrates with appropriate mixing ratios, followed by drying, roasting at 400 ° C and tableting into slices of 1.5 χ 13 mm , The tablet tablet was mix-impregnated with a solution of tetrammineplatinum (II) hydroxide and tetramminepalladium nitrate containing 8% Pt and 6% Pd. The excess solution was drained and the platinum and palladium-containing metal oxide pad was dried and roasted at a temperature increasing from room temperature to 320 ° C. The catalyst was then reduced in H ₂ / N ₂ at room temperature.

test conditions

Air containing 1000 ppm carbon monoxide was passed through a granular catalyst bed at room temperature and atmospheric pressure at a space velocity of 24,000 h-1. The concentration of carbon monoxide in air was measured after passing through the catalyst bed. The results and the metal compositions in the catalyst are shown in Table 1.

All of the catalysts in this table were prepared as just described, except for Pt.Ru/10% Cr ₂ O ₃ + 90% Fe ₂ O ₃ which was prepared by first adding Ru metal Ru from ruthenium nitrosyl nitrate solution containing 5.5% Ru Was deposited, followed by the deposition of metallic Pt.

Table 1 implementation to (Metal composition) Pd Ru catalyst % t / min • Pt 2.5 _ 99.1 25 2.0 Pt.Pd / 10% Cr ₂ O ₃ - 1.0 + 90% Fe ₂ O ₃ 96.2 25 2.5 Pt.Ru/10% Cr ₂ O ₃ 2.0 - + 90% Fe ₂ O ₃ 90.6 25 1.5 1.3 - Pt.Pd / CeO ₂ 87.5 15 2.7 1.5 - Pt.Pd / CuO + Cr ₂ O ₃ 30.0 5 2.0 Pt.Pd / ZrO ₂

Example 2

These catalysts were prepared by combining two precious metals (R and Pd) and the reducible oxides CeO ₂ and Fe ₂ O ₃ on carbon fabric.

Carbon cloth having a BET specific surface area of 120μmVg (2.6g) was impregnated with a metal nitrate solution containing the appropriate backbone metal salt. The carbon cloth was dried in air at 40 ° C and the salt was decomposed at 200 ⁰ C. Then, the fabric was impregnated with the salt solution, dried in air at 40 ⁰ C and erliitzt to 200 ° C. Thereafter, the tissue was reduced in H ₂ / N ₂ at ambient temperature.

The concentration of the metal solutions used was as follows:

(a) 4.77 g of Ce (NO ₃ J ₃ .6H ₂ O, made up to 40 ml with deionized water,

(b) 11.13g Fe (NO ₃ I ₂ - 9H ₂ O, made up to 40ml with deionized water,

(c) 2.15 g of [Pd (NH ₃ J ₄ ] (NO ₃ ) ₂ having a Pd-Go content of 35.65% and 2.40 g of [Pt (NH ₃ J ₄ ] (OH) ₂ having a Pt content of 16%, filled up to 40ml with deionized water.

exam

Air with a carbon monoxide content of 1% and a carbon dioxide content of 3.5%, which was saturated at 37 ⁰ C with water was conducted at space velocities of 1260Oh ^-1 and 37000h ^"1 through a catalyst bed of 10 layers of carbon fabric catalyst of 2cm diameter After passing through the catalyst bed, the carbon monoxide content was measured The results and the metal composition are shown in Tables 2, 3 and 4 and in Figure 1, where Figure 1 shows the results obtained at a space velocity of 12,600 hours were. It can be seen that in the absence of the reducible metal oxide, a platinum-palladium catalyst on carbon fabric as support rapidly loses its effectiveness while its effectiveness in the presence of a reducible metal oxide improves over time.

-4- 297 Table 2 Catalyst PtPd FejOV carbon fabric with 3.6% R; 6.8% P; 8.1% Fe

CO (ppm) t (min) At 12 600 h " ¹ gas space velocity 10000 0.0 60 60 1 10 5 8th 10 At 37 000 h ~ 'gas space velocity 15 11 15 15 15 20

Table 3

Catalyst PtPd Ce0 ₂ / carbon fabric with 4.9% R; 7.6% Pd; 5.9% Ce

CO (ppm) t (min)

At 12 600h " ¹ gas space velocity 10000 0.0

At 37 000 h " ¹ gas space velocity

40 1 7.5 6 5.5 10 5.0 11 5.0 15 5.0 20 5.0 25

Table 4

Catalyst R.Pd / carbon fabric with 7.88% Pd; 4.3% R

CO (ppm). t (min)

At 12600 h " ¹ gas space velocity

10000 0.0 65 1 2000 5

Example 3

The following series of catalysts was prepared by depositing the reducible oxide (Fe ₂ O ₃ ) on SiO ₂ together with metallic platinum and palladium.

(A) Pt.Pd / SIOj (for comparison)

8.5 g SiO 2 spheres of 2-3 mm diameter (the outer shell) were treated with a solution of tetrammineplatinum (II) hydroxide [R (NH ₃ ) ₂ ] (OH) ₂ and tetramminepalladium nitrate [Pd (NH ₃ I ₄ ] (NO _{3) 2} mixture is impregnated with a content of 1.5% Pd and 2.28% Pt. the excess solution was drained and the platinum- and palladium-containing silica was dried and toasted, during which the temperature from room temperature increased to 320 ° C The catalyst was then reduced in H ₂ / N ₂ at room temperature.

(B) PtPdFe ₂ CVSIO ₂

12g SiO ₂ -based balls 2-3mm in diameter were impregnated with Fe (NO ₃ J ₃ .9 H ₂ O) Fe Fe ₂ content (9.2% Fe) and the excess solution was drained off and the SiO ₂ -containing SiO ₂ -based iron oxide was dried and toasted, during which the temperature from room temperature up to 32O ⁰ C increased.

The resulting SiO ₂ -contained calcined iron oxide was mix-impregnated with tetramminepatinate (II) hydroxide and tetrammine palladium nitrate solution containing 2.28 pt and 1.53% Pd. The excess solution was drained off and the R, Pd or Fe ₂ O ₃ -containing silica was dried and roasted as described above. Then the catalyst was reduced in H ₂ / N ₂ at room temperature.

test conditions

Air with a carbon monoxide content of 10OOppm was conducted at room temperature and atmospheric pressure with a space velocity of 12000h ^"1 through a catalyst bed in the form of 2-3mm sized spheres. The concentration of carbon monoxide in the air was measured after the passage through the catalyst bed.

Figure 2 shows the effect of adding Fe ₂ O ₃ to the Pt uni! Pd-containing SiO ₂ base on the catalyst activity for the carbon monoxide oxidation at room temperature.

metal compositions % Pt % Pd % Fe 2.0 2.0 1.5 1.5 10.0 Pt.Pd / SiOj Pt.Pd.Fe ₂ O ₃ / SiO ₂

In the absence of Fe ₂ O ₃ , there was a steady decrease in catalyst activity from the initial value, while the activity of the Fe ₂ O ₃ -containing catalyst was maintained over a longer period of time.

Example 4 (for comparison) The catalyst was formed by deposition of two precious metals (using chloride-containing noble metal salts)

made reducible metal oxide.

Pt.Pd / (10% Cr ₂ O ₃ + 90% Fe ₂ O ₃ ). This catalyst was as in Example 1, but using chloride-containing Produced precious metal salts. The backing (10% Cr ₂ O ₃ + 90% Fe ₂ O ₃ ) was prepared by precipitation from nitrate salts and then dried, roasted and

tableted. The disc-shaped pad was mix-impregnated with palladium dD chloride (PdCl ₂ ) and hexachloroplatinic acid (H ₂ PtCl ₆ ), the solution containing 5.6% Pd and 7.5% Pt. The excess solution was drained and the

Catalyst was dried and toasted, during which the temperature from room temperature up to 32O ⁰ C increased. The Catalyst was then reduced in H ₂ / N ₂ at room temperature. Catalyst composition: 2% Pt, 2% Pd / (10% Cr ₂ O ₃ , 90% Fe ₂ O ₃ ) test conditions The conditions were the same as described in Example 1. The results are shown in Table 5 below, along with the results of the catalyst which did not

chloride-containing noble metal salts was prepared.

Table 5

CO conversion (%) ^# Cat. (B) Time (min) Cat. (A) 0 0 0 99.0 3 78.7 99.1 10 56.9 99.1 20 40.6 99.1 25 - - 30 29.7

(A) Catalyst prepared from chloride-containing noble metal salts

(B) Catalyst prepared from non-chloride noble metal salts

The results of the CO oxidation on the Pt.Pd / 10% Cr ₂ O ₃ catalyst shown in Table 5; 90% Fe ₂ O ₃ shows that the catalyst prepared from chloride-containing noble metal salts has poor stability and activity compared to the same catalyst prepared from non-chloride noble metal salts and exhibits good activity and stability under the same test conditions.

Claims (7)

1. A process for the oxidation of an oxidizable substance having a molecular weight below 50 by contact of the material with a gas containing free oxygen, in the presence of a catalyst, characterized in that the contact takes place at a temperature up to 30 ⁰ C and the catalyst at least contains a noble metal on at least one reducible metal oxide as a support material which is selected from Fe ₂ O ₃ , Ce ₂ O ₃ , ZrO ₂ , CuO, the oxides of the Seita in earth metals, MnO ₂ , V ₂ O ₆ and Cr ₂ O ₃ . 2. The method according to claim 1, characterized in that the oxidizable substance is carbon monoxide, hydrogen, deuterium, tritium, nitrogen dioxide or nitrogen (II) -o-id. 3. The method according to claim 1 or 2, characterized in that the catalyst for the oxidation of carbon monoxide is used in a carbon dioxide laser. 4. The method according to any one of claims 1 to 3, characterized in that the precious metal is selected from platinum, palladium, ruthenium, rhodium, iridium, rhenium or silver. 5. The method according to any one of claims 1 to 4, characterized in that the noble metal in an amount between 0.5 and 60 wt .-%, based on the reducible metal oxide, is used. 6. The method according to any one of claims 1 to 5, characterized in that the noble metal and the reducible metal oxide are bonded to an inert support material which is selected from silica, silica-alumina and carbon. 7. The method according to claim 6, characterized in that the total amount of the noble metal and the reducible metal oxide is between 1 and 50 wt .-%, based on the inert carrier material.