DE10132441A1 - Mixed oxide catalysts and their use for catalytic combustion - Google Patents

Abstract

The invention relates to mixed oxide catalysts comprised of aluminum oxide and zirconium oxide and of a metal of group VIII, and to a method for the production thereof. Catalysts of this type are suited for catalytically combusting hydrocarbons and CO with air or oxygen.

Description

The invention relates to mixed oxide catalysts made of aluminum and zirconium oxide and an element from group VIII or the elements Mn, Y, V, Pb, Ce and Process for their preparation. Such catalysts are suitable for catalytic Combustion of hydrocarbons and CO with air or oxygen.

Possible areas of application are catalytic combustion for exhaust gas cleaning in Power plants and industrial plants, the catalytic combustion of fuels (Natural gas, petroleum) for energy generation in power plants at high Temperatures, the cleaning of kitchen air in ovens and over hobs, odor removal from indoor air and use as sensors from burning substances such as methane, hydrocarbons or CO. In particular in the latter examples, low operating temperatures, high temperature and long-term stability as well as poison resistance.

In the past, a wide variety of catalysts for these applications have already been tested and patented. In all cases, the combustion of methane requires temperatures above 450 ° C. B. a temperature-stable substrate on which there is a mixed oxide impregnated with Pd made of Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ and a rare earth oxide (JP 09262472); Oxides of the form AB _1-x C _x O ₃ (where A = rare earth metals or alkali metals, B = Mn, Co, or Cr; C = Nb or Ta, 0.1 <x <1) (JP 08012334); a ZSM 5 loaded with In (JP 06262039); a mordanite-type zeolite supported with Co, Mg, Rh, Pd and Pt (JP 5115751); a mixed oxide of MgO, copper oxides and metals of the Pt group (JP 03238048); a catalyst containing both Pd and Al-Mn mixed oxide (JP 01139911, JP 08020054); a temperature-stable carrier which is coated with Al-Si mixed oxides and contains Pd and / or PdO as active component (JP 63175638, JP 08008992); a combined system of 1. a Pd-Pt-Ni oxide as an active component and 2. Pt or Pt-Pd as an active component on a monolithic aluminum oxide support (JP 63080849, JP 05045295). Furthermore, various perovskites are described, on the one hand of the type A _1-x A1 _x M _1-y M1 _y O ₃ (meaning: A = rare earth element; A1 = Ag, Au; M = M1 = transition metal; x, y = 0 -0.9) (JP 61011149, JP 05043416) and secondly of the type La _1-x Ce _x CoO ₃ (x = 0-0.2). Patent BO 096A000063 describes catalysts of the type A ₂ B ₃ O _{6 ± d} , where A is an alkaline earth metal, an alkali metal, a lanthanoid or a solid solution thereof, B is a transition metal, an element of group III or a solid solution of them is. The value for d is between 0 and 1. With these catalysts, the combustion of methane is possible from a temperature of 450 ° C. Sales of more than 50% in the low-temperature combustion of methane are only observed with Mn, Fe or Co-stabilized ZrO ₂ at temperatures above 450 ° C (VS Choudhary, BS Uphade, SG Pataskar, A. Keshavaraja, Angew. Chem. 108 (1996) 2538). 50% methane combustion was already observed with Pd / Al ₂ O ₃ catalysts at 300 ° C (D. ROth, P. Gélin, M. Primet, E. Tena, Appl. Catal. A, General 203 (2000) 37 ). With Ce-stabilized Pd / Al ₂ O ₃ catalysts, methane combustion still requires temperatures above 350 ° C (G. Groppi, C. Cristiani, L. Lietti, C. Ramella, M. Valentini, P. Forzatti, Catalysis Today, 50 (1999) 399). Similar temperatures are also required for catalytic low-temperature methane combustion with Pd / SnO ₂ catalysts (K. Sekizawa, H. Widjaja, S. Maeda, Y. Ozawa, K. Eguchi, Appl. Catal. A, General 200 (2000) 211). Baerns and co-workers recently reported that to date there have been no catalysts that catalytically burn hydrocarbons at temperatures below 150 ° C (U. Rodemerck, D. Wolf, OV Buyeskaya, P. Claus, S. Senkan, M. Baerns, Chem. Eng. J. 82 (2001) 3).

We have now surprisingly found that catalysts that Mixed oxides of 60 to 90 mol% aluminum oxide and 10 to 40 mol% zirconium oxide and a maximum of 10 mol% of one or more metals selected from the Group VIII elements and elements Mn, Y, V, Pb, Ce, contain the catalytic combustion of CO, methane and other hydrocarbons Catalyze temperatures between room temperature and 250 ° C.

• a) einen oxidischen Träger, bestehend aus einem Aluminium/Zirkonium- Mischoxid, der beispielsweise poröse, inerte, feste, widerstandsfähige, amorphe oder kristalline Struktur aufweisen kann, und
• b) ein oder mehrere Elemente, ausgewählt aus der VIII. Gruppe und den Elementen Mn, Y, V, Pb, Ce.

A catalyst according to the invention thus comprises

• a) an oxidic carrier consisting of an aluminum / zirconium mixed oxide, which can have, for example, porous, inert, solid, resistant, amorphous or crystalline structure, and
• b) one or more elements selected from the VIII. Group and the elements Mn, Y, V, Pb, Ce.

Group VIII metals include Pt, Pd, Rh, Ir, Ru, and Au. On inventive catalyst is, for. B. a Pt-containing Al-Zr mixed oxide, containing 1 to 3 mol% Pt, 15 to 30 mol% Zr oxide and 70 to 85 mol% Al oxide, which enables catalytic combustion from 60 ° C.

For high temperature applications, the elements Fe, Mn, Y, V, and Pb as suitable.

• 1. durch Imprägnieren des Mischoxids mit einem oder mehreren Elementen entsprechend der Aufzählung unter (b);
• 2. über eine Sol-Gel-Methode, bei der aus einer organischen Lösung von Metallsalzen von Metallen entsprechend der Aufzählung unter (b) mit Aluminium- und Zirkonverbindungen unter Zusatz von Wasser und eines Reaktionsbeschleunigers ein Gel gebildet wird, das anschließend kalziniert wird. Als Aluminium- und Zirkonverbindungen eignen sich vor allem die Alkoxide, Carboxylate, Acetylacetonate und Dioalte, vorzugsweise die n- und iso-propoxide und -butoxide. Die Kalzinierung erfolgt beispielweise über ein Temperaturprogramm:
  
  
  kalziniert wird.

The catalysts of the invention can be prepared using different methods:

• 1. by impregnating the mixed oxide with one or more elements in accordance with the list under (b);
• 2. Using a sol-gel method in which a gel is formed from an organic solution of metal salts of metals according to the list under (b) with aluminum and zirconium compounds with the addition of water and a reaction accelerator, which is then calcined. Particularly suitable as aluminum and zirconium compounds are the alkoxides, carboxylates, acetylacetonates and dioalts, preferably the n- and iso-propoxides and butoxide. The calcination is carried out, for example, using a temperature program:
  
  
  is calcined.

Component (s) are listed under (b) expediently in a total concentration of 0.1-10 mol percent.

example 1 Preparation of a Pt-containing catalyst Pt ₃ Zr ₂₀ Al ₇₇ O _158.5

80 mg of platinum (II) chloride (0.3 mmol) were dissolved in 50 ml (0.65 mol) of isopropanol, then 3.7 ml (30 mmol) of 4-hydroxy-4-methyl-2-pentanone, 0, 62 ml (2.2 mmol) of zirconium n-propoxide, 1.98 ml (7.2 mmol) of aluminum sec-butoxide, and 0.18 ml (10 mmol) of dist. Water and 21.6 µl (0.6 mmol) concentrated hydrochloric acid were added. The solution obtained was stirred until it gelled, and the gel obtained then on the temperature ramp:


calcined.

A catalyst with the approximate composition Pt ₃ Zr ₂₀ Al ₇₇ O _158.5 was thus obtained.

The platinum content of the catalyst according to the invention is about 3 mol percent, the surface is 146 m ² / g. The material has a mesoporous structure, the most common are pores of 4.62 nm in size, 88% of the pores are between 2 and 8 nm in size. TEM images show that the platinum is present in predominantly 5-50 nm large, crystalline domains. In EDX analyzes of these domains, aluminum is found in addition to Pt, but no zirconium. The matrix of zirconium and aluminum is largely amorphous, platinum can be found everywhere in these EDX analyzes, which indicates atomic distribution. The zirconium to aluminum ratio shows a good agreement with the theoretical value.

Example 2 Oxidation of methane

100 mg of the Pt catalyst described above, which had previously been ground in a ball mill for 15 minutes, were introduced into a gas phase reactor and a mixture of methane and synthetic air was passed through. The following parameters were used: 40 ml / min methane and 26 ml / min synthetic air. The following table shows the CO ₂ content of the product gas flow and the O ₂ conversions (as an indicator for the methane conversions) at the different temperatures.

Example 3 Use of a Pt ₆ Zr ₂₀ Al ₇₃ O _149.5 catalyst

100 mg of a Pt catalyst according to the invention of the approximate composition Pt ₆ Zr ₂₀ Al ₇₃ O _149.5 (synthesis analogous to the Pt catalyst described above), which had previously been ground in a ball mill for 15 minutes, were introduced into a gas phase reactor and mixed made of methane and synthetic air. The following parameters were used: 40 ml / min methane and 26 ml / min synthetic air. The following table shows the CO ₂ content of the product gas flow and the O ₂ conversions at the different temperatures.

Example 4 Oxidation of butane

100 mg of the Pt catalyst from Example 1, which had previously been ground in a ball mill for 15 minutes, were introduced into a gas phase reactor and a mixture of butane and synthetic air was passed through. The following parameters were used: 1 ml / min butane and 99 ml / min synthetic air. The table below shows the CO ₂ content of the product gas flow and the butane conversions at the different temperatures.

Example 5 Oxidation of carbon monoxide

Analogously to Example 4, a mixture of CO and air (1: 100, 100 ml / min) was passed over the catalyst (100 mg) at different temperatures. The composition of the product gas was continuously analyzed with sensors (O ₂ , CO, CO ₂ ). Quantitative conversion was achieved at temperatures above 150 ° C.

Example 6

100 mg of the catalyst doped with 6 mol% M (preparation analogous to Example 1) were introduced into a gas phase reactor and a mixture of methane and synthetic air was passed through (40 ml / min methane, 26 ml / min synthetic air) at a temperature of 800 ° C burned. While sales initially fell slightly, they remained constant over 24 hours. The following sales resulted:

Claims (11)

1. Catalysts, the mixed oxides of 60 to 90 mol% of aluminum oxide and 10 to 35 mol% of zirconium oxide and a maximum of 10 mol% of at least one Metal selected from group VIII and the metals Mn, V, Y, Pb, Ce included. 2. Catalysts according to claim 1, which one or more of the metals Pt, Pd, Rh, Ir, Ru, or Au included 3. Catalysts according to claim 2, containing 1 to 3 mol% Pt, 15 to 30 Mol% zirconium oxide and 70-85 mol% aluminum oxide. 4. A process for the preparation of a catalyst according to claims 1 to 3, a mixed oxide consisting of 60 to 90 mol% of aluminum oxide and 10 to 35 mol% of zirconium oxide, with up to 10 mol% of one or more Elements of group VIII or the metals Mn, V, Y, Pb, Ce impregnated becomes. 5. The method according to claim 4, wherein as elements of group VIII Pt, Pd, Rh, Ir, Ru, or Au can be used. 6. A process for the preparation of catalysts according to claims 1 to 3, being from an organic solution of metal salts of metals, selected from group VIII and the metals Mn, V, Y, Pb, Ce, with Aluminum and zirconium compounds with the addition of water and one Reaction accelerator a gel is formed, which is then calcined becomes 7. The method according to claim 6, wherein as an organic solvent Isopropanol is used. 8. The method according to claims 6 to 7, wherein as aluminum and Zirconium compounds n- or iso-propoxides or butoxides, alkoxides, Carboxylates, acetylacetonates or dioalts can be used. 9. The method according to claims 6 to 8, wherein as a reaction accelerator an acid or base is used. 10. Use of catalysts according to claims 1 to 3 for Combustion of organic air pollution and carbon monoxide at temperatures from room temperature to 250 ° C. 11. Use of catalysts according to claims 1-3 for catalytic Combustion of fuels at temperatures from 700 to 1300 ° C for Electricity.