DE1291339B - Process for cleaning engine exhaust gases by afterburning in the presence of catalysts - Google Patents

Description

It is already known to use catalytic converters for the afterburning of engine exhaust gases ■ from activated metal oxides, such as active aluminum, beryllium, magnesium, zirconium, thorium oxide, or Mixtures of these oxides, e.g. B. aluminum beryllium oxide, and with active metals such as platinum, Silver, copper, nickel or combinations such as copper-chromium, are impregnated. It is also known Use vanadium oxide alone or with additives on active clay. More well-known Proposals concern the use of metal wires or metal strips on their surface Platinum is applied, or pieces of ceramic material covered with a thin, platinum-containing Layer of active aluminum oxide are coated. They were also recommended as catalysts y-iron oxide in a mixture with porous substances, mixtures of copper oxide - aluminum oxide, manganese, Copper, cobalt, silver oxide on activated alumina, cobalt oxide, nickel oxide, manganese oxide, titanium oxide, Iron oxides and cobalt lithium oxide on aluminum oxide. Improved stability of the catalysts against poisoning by the lead compounds contained in the engine exhaust gas should be achieved by that lead compounds are added to the catalysts during manufacture.

It has now been found that engine exhaust gases can be obtained by afterburning in the presence of catalysts, the platinum metals in a total amount of 0.01 to 0.4 percent by weight on a carrier Contain aluminum oxide, can, if you use a catalyst according to the invention, its Alumina support before loading with the platinum metals to temperatures of over 600 to 1500 ° C has been heated.

These catalysts are characterized by particularly high activity at low temperatures, improved Service life and a lower sensitivity to what may be present in the exhaust gas Lead compounds.

Active aluminum, beryllium, magnesium, zirconium, thorium oxide or mixtures thereof, such as aluminum-beryllium-oxide, aluminum-thorium oxide, are suitable as supports for the catalysts. Before applying the active components, they must be heated to temperatures above 600 ^° C., preferably above 700 ^° C., e.g. B. 800 to 1200 ⁰ C, are heated. Even higher temperatures, e.g. B.

those between 1200 and 1500 ^° C. are advantageous in many cases. During the thermal pretreatment of the supports, water vapor can be present or absent. In the presence of steam, a shorter heating time will generally be sufficient to achieve the same effect.

Among the various modifications of the active alumina (. Eg γ, η- or jial ₂ O ₃₎ is known to when heated to temperatures from 600 to 1200 ⁰ C by X-ray detectable conversions while reducing the inner surface and change the pore structure Experienced. Intermediate stages of this transformation are referred to as <5 alumina, and the end product of the transformation is the α-form.

Particularly suitable active components are the platinum metals, e.g. B. platinum, palladium or iridium on its own or in mixtures. The platinum metals are used in amounts of 0.01 to 0.4 percent by weight, in particular 0.03 to 0.1 percent by weight applied to the carrier.

When installing the catalytic converter in a suitably constructed container, it must be ensured that that the catalyst particles are not swirled by the pulsating flow of the exhaust gases. The exhaust gases should therefore be passed in such a way through the catalyst, for. B. from top to below, that the catalyst layer remains at rest. Otherwise there will be catalyst losses due to abrasion a.

The catalytic converters are ideally suited for the afterburning of exhaust gases from gasoline engines and Diesel engines.

example

Alumina hydrate (about 40% boehmite and 60% bayerite) was kneaded with the addition of water and nitric acid to form a viscous mass which was shaped by extrusion and cutting into cylindrical particles 4 mm in diameter and 5 to 10 mm in length. After drying at 100 ⁰ C, the moldings were then heated first at 600 ⁰ C (Sample A), a further part (sample B) to 800 to 850 ° C and a third portion (Sample C) at 1200 ⁰ C in the air .

The individual samples showed the following physical data:

Heating time
and temperature Radiographic
composition BET
surface Middle
Pore radius Total-
pore volume 3 hours, 600 ^° C
3 hours, 600 ^° C
4 hours, 800 to 850 ^° C
3 hours, 600 ^° C
4 hours, 1200 ⁰ C JVj-Al ₂ O ₃ .
} <5-Al ₂ O ₃
} U-Al ₂ O ₃ 273.5 m7g
88.3 m ² / g
2.35 m ² / g 18.5 Ä
52.1 Ä
3360 Ä 0.25 cm ³ / g
0.23 cm ³ / g
0.378 cm ³ / g

The samples were examined as follows: A single-cylinder four-stroke mm »r (type: BASF- (ifc'j'i rihi - test engine) with a displacement of" ¹ Z -: -; * Aurde at full load iienremüc einc iremüc : - :; gten equals »^ -; -.; ^ -« - · - <. 2.5 k "" performance, unc inte '' ■ • 'si -'? -: -.--- · -. - chjc ·.! -. "inrbenzn · - with 0.034 Voiü-Tiprnzer- H <^> = - m; -> betrsäOen. The whole \ öga> became ne; s: --u J (X. ¹ C through a 15 cm hone layer of .e *> - c <;% -! ί Carrier A and Carrier C from top to bottom the carrier the following amounts of lead:

carrier

(I carrier A ...
Ϊ Carrier C ..

Share of total

, Lead content amount of lead des

j ⁿⁱ > ^{ch I () 0} laps j _{ve (} . _needed gasoline

33.18 g
23.34 g

66.4 ""
46.7%

Under the same conditions, more lead is deposited on the carrier A made of γ, Jj-Al ₂ O ₃ than on the carrier C made of H-Al ₂ O ₃ . With carrier B made of <5-Al ₂ O ₃ , practically the same values as with carrier C were obtained.

Catalysts were prepared from supports A, B and C by applying 0.05 percent by weight. These catalysts were tested under the same conditions with a load of about 12,000 volumes of exhaust gas per volume of catalyst and hour for afterburning the exhaust gas mixed with additional air on the above engine. The gas composition before (v) and after (n) the catalyst after 100, 200 and 250 Operating hours are given in Tables I and II below. The inlet temperature of the gas was 450 ^° C.

CO V η Tabel II platinum V η C. V H η C. V O ₂ η 4.0 0 Carrier C with 9.05% (Volume percentage) 2.8 0 6.7 2.1 7.2 13.3 Loading 4.2 0 2.7 0 6.3 2.0 6.0 12.6 instinctual 3.9 0 H ₂ 2.5 0 6.5 1.9 7.0 11.9 5 hours 100 200 ¹⁰ 250

As the analytical values show, there is a noticeable decrease in the catalyst from carrier A Determine activity, but not in the case of the catalyst from carrier C. With the catalyst off Carrier B practically the same values as with the catalyst from carrier C were obtained.

Table I.

CO V η Carrier A with 0.05% platinum V η C. V > 2 η CO ₂ V η Be 4.1 0 (Volume percentage) 1.9 0 6.4 2.2 7.4 13.4 instinctual
hours 4.2 0.2 l 2.8 0.3 6.3 2.3 7.5 13.0 3.9 0.8 2.4 0.4 6.0 2.0 7.4 12.0 100 200 250

Claims (2)

Patent claims: 1. Process for cleaning engine exhaust gases by afterburning in the presence of catalysts, the platinum metals in a total amount of 0.01 to 0.4 percent by weight on a carrier Contain from aluminum oxide, characterized in that a catalyst is used, the aluminum oxide carrier before the Loading with the platinum metals has been heated to temperatures of over 600 to 1500 ° C. 2. The method according to claim 1, characterized in that the carrier used is δ- or α-alumina or mixtures of these alumina.