DE1129771B - Process for the production of a catalyst for the oxidative cleaning of engine exhaust gases - Google Patents

Description

Process for the preparation of a catalyst for the oxidizing Purification of engine exhaust gases It is known that those in the exhaust gases of internal combustion engines contained toxic or malodorous substances, e.g. B. Hydrocarbons and their Oxidation products, nitrogen oxides, carbon oxides and the like, by catalytic oxidation can largely be eliminated and that in this way the harmful effects the exhaust gases can be greatly reduced. Lately one is using for this purpose Catalysts containing platinum and palladium, the support material of which is mostly made from Aluminum oxide or mixtures thereof with aluminum silicates. The cleaning effect Such catalytic converters when used in the exhaust pipes of vehicles come from practical needs are very close. Even after the previously required The high noble metal contents of these catalysts maintained at about O, lQ / o could be, their introduction in the automotive series production is so far at the low mechanical strength of the catalyst particles failed.

Instead of granular catalysts, they are not catalytic either effective support framework with a superficially deposited on this framework Catalyst substance used wordell. The catalyst framework consists for example made of porcelain rods anchored between plates and on their surface an aluminum oxide precious metal catalyst with a platinum and / or palladium content from 1 to 2 percent by weight is applied in a very thin layer. This catalyst bodies are sensitive to mechanical stress, but have higher Temperatures a good dimensional stability. They are used to some extent for cleaning of the exhaust gases from diesel engines and the exhaust gases from Otto engines, if the the latter run on unleaded fuel. Measured by their lifespan, they are so expensive that serial installation in motor vehicles has not yet been possible could enforce.

The numerous attempts to develop suitable catalysts have shown that in addition to the catalytic Qualities such as low light-off temperature, high reaction speed, unspecific Oxidation effect, insensitivity to impurities contained in the exhaust gas of dust, soot7, oil and lead oxide, the mechanical properties, abrasion resistance and dimensional stability at high temperatures for the operating costs of the exhaust gas purification are of great importance.

The invention is a method for producing a Catalyst for the oxidizing Cleaning of engine exhaust, which is an aluminum silicate or aluminum silicate-aluminum oxide mixture and 0.06 to 0.12 percent by weight palladium and / or contains platinum and is arranged as a grain layer in the exhaust pipe of the engine is.

The inventive method is characterized in that the Catalyst before its use an annealing treatment at temperatures that at least are equal to the temperatures later prevailing in operation, preferably at 900 is subjected to 10000 C.

The production of such catalysts takes place according to known methods, for example by the fact that the carrier material is granulated, e.g. B. by extrusion or pelletizing, then drying and calcining and that the molded Carrier material is impregnated with a salt solution of the activating metal. The impregnated catalyst is thermally aftertreated in a manner known per se.

According to the invention, however, temperatures are used that are at least are the same as the temperature that will later prevail in operation, but advantageously higher lie. During the catalytic afterburning of engine exhaust gases on the catalytic converter Temperatures of up to 8500 C have been measured in a catalyst bed. The post-treatment temperature is therefore expediently set to 900 to 10,000 ° C.

The catalyst is expediently in particle sizes of 2 to 8 mm, preferably 4 to 6 mm, applied and as a layer of 20 to 80 mm, preferably 30 to 60 mm, switched into the flow path of the engine exhaust gases, advantageously such that the Exhaust the catalyst from top to bottom flows through. The amount of catalyst is dimensioned so that 10 to 80 parts of the volume of exhaust gas (normal conditions) per second 1 space part catalyst (bulk volume) is omitted.

The only prerequisite for the good effectiveness of the catalyst is that the raw exhaust gas with a temperature of at least 2500 C, but at most from 800 to 8500 C, enters the catalyst and that for the oxidation of the untreated Exhaust gas existing combustible components enough oxygen is available. This oxygen content is in the exhaust gases of diesel engines and two-stroke gasoline engines usually present.

In exhaust gases from four-stroke gasoline engines or in other exhaust gases with insufficient Oxygen content is also means of combustion air in a manner known per se sucked into a venturi connected in the exhaust pipe in front of the catalyst layer.

The catalyst used according to the invention is insensitive to.die Contaminants contained in the exhaust gases of the vehicle engines. He can have a Driving distances of up to 50,000 km can be used without any loss of effectiveness. This corresponds to a driving time of around 600 to 1000 hours. He will neither through the given mechanical stresses due to the influence of high temperatures, which can reach about 9000 C in the catalyst layer, changed disadvantageously. The cleaning effect of the catalyst according to the invention is even after 1000 operating hours still so high that the exhaust gases from two-stroke and four-stroke engines treated with it, Regardless of whether they are diesel engines or Otto engines, they are practically free of carbon oxide and smell are.

Example 1 To purify the engine exhaust gases of a motor vehicle, 3.5 kg of an extruded catalyst with a grain size of 6 mm, the bulk volume of which was 3.71, was placed in the exhaust pipe as a layer 40 mm thick. The catalyst, which was annealed at 9500 C for several hours, consisted of: about 50 percent by weight of the silo, about 40 percent by weight of Al2 O3, about 8 percent by weight of Fe2O, about 0.08 percent by weight of Pt whose speed in the full load range was 3,500 rpm. Commercially available leaded gasoline was used as fuel. The catalyst was still fully active after 1000 operating hours. The engine exhaust gases were cleaned to such an extent that the bad smell characteristic of two-stroke engines was no longer perceptible at a short distance behind the vehicle. The exhaust gas analysis gave the following picture: Salary salary Exhaust component before entering after leaving the catalyst of the catalyst Hydrocarbons 8 g / Nm3 1 glNmS Aldehydes. . 0.2 g / Nm3 0.02 g / NmS Nitrogen oxides. . . 0.3 g / Nms 0.05 g / NmS Carbon monoxide. . . 3.5 volume 0.001 volume percent percent The exhaust gases contained the oxygen required for the catalytic oxidation, so that it was not necessary to add fresh air to the exhaust gases before the catalytic treatment. About 85e / o of the oxygen content was consumed during the catalytic oxidation.

Example 2 A catalyst with the composition 45 percent by weight Si O2 47 percent by weight Al2 O3 6 percent by weight Fe2. O3 0.07 percent by weight Pt Remaining impurities that had been pretreated at 6000 C were used to clean the engine exhaust gases of a motor vehicle used. The cleaning performance was good as long as the temperatures 6000 C not exceeded in the catalytic converter. However, some catalyst dust was formed, because this catalyst was not hard enough to meet the mechanical requirements resist.

In a further experiment the same catalyst was used under operating conditions used, the temperatures in the catalyst of 9000 C resulted. This resulted severe shrinkage of the catalyst. There was a decrease in volume observed between 10 and 20 per cent. This could create cavities in the catalytic converter housing train through which the exhaust gases could escape untreated. The loose ones shrunken catalyst particles were subjected to severe mechanical wear Exposed to vibrations and friction, so that the mechanical strength of the Catalyst was overwhelmed and a strong abrasion was caused.

A catalyst with the same composition was before his Used for the purpose of engine exhaust gas cleaning pre-annealed at 9500 C. This catalyst was still about as active as the, despite the high pretreatment temperature previously described. But it was much harder and later held all mechanical ones and thermal requirements in the catalytic converter housing. The catalyst shrank no longer noticeable even at continuous operating temperatures of 9000 C, so that after 1000 operating hours the catalyst was still tightly packed in the housing and there was abrasion could hardly be determined.

Claims (2)

PATENY CLAIMS: 1. Process for the manufacture of a catalyst for the oxidative cleaning of exhaust gases from internal combustion engines, which is an aluminum silicate or aluminum silicate-aluminum oxide mixture and 0.06 to 0.12 percent by weight palladium and / or contains platinum and is arranged as a grain layer in the exhaust pipe of the engine is, characterized in that the catalyst is subjected to an annealing treatment before it is used at temperatures that are at least equal to those that will later prevail in operation Temperatures are, preferably at 900 to 10000 C, is subjected. 2. The method according to claim 1, characterized in that a carrier mass with 40 ° / e Al2O3, 50% SiO2 and 8% Fe2O3, which are dried and calcined in a known manner and with 0.08% platinum is impregnated, which is subjected to annealing treatment. Documents considered. German Patent No. 660 870; French patent specification no. 1 153 546.