DE1184328B - Oxidation catalysts and processes for their preparation - Google Patents

Description

Oxidation Catalysts and Processes for Their Preparation The Invention relates to new oxidation catalysts for the combustion of impurities in gas streams and methods of making them. The new catalysts of the invention are especially in exhaust systems of internal combustion engines to prevent or reduce the release of carbon monoxide and other unburned or partially burned Products used in the atmosphere. This can create smoke-like fog ("smog" 3 forming substances from the exhaust gases of internal combustion engines practically completely removed.

The combustion of fuels in a vehicle engine, e.g. B. a normal gasoline or diesel engine is known to be relatively incomplete.

A considerable part of the fuel is in unburned or partially oxidized state released into the atmosphere as exhaust gas and leads especially in urban areas for air pollution. The exhaust gases from internal combustion engines contain a mixture of toxic substances such as carbon monoxide and other undesirable substances oxidizable compounds such as saturated and unsaturated hydrocarbons, oxygen-containing organic compounds, such as aldehydes and organic acids, which are due to the The above-mentioned relatively incomplete combustion of the fuels is present.

"Cold start exhaust gases" are used in the description to refer to the exhaust gases denotes which are formed during the operation of internal combustion engines when these at low temperatures of 250 to 350 ° C. Such gases contain proportionally large amounts of unburned or partially burned fuel up to Make up 50 per cent of the fuel supplied to the engine.

Under "idle exhaust gases" are to be understood such exhaust gases, which are formed in internal combustion engines during negative acceleration or when idling will. These gases also contain significant amounts of unburned or partial burned fuel. The quantities are in the same order of magnitude as for the cold start exhaust gases.

The amount of unburned or partially burned oxidizable Compounds in exhaust gases vary considerably. Such gases are contained in the generally 2 to 3 percent by volume of carbon monoxide and 0.1 to 0.3% of a mixture saturated and unsaturated hydrocarbons and oxygenated organic ones Compounds such as aldehydes and organic acids. The amount of these substances in exhaust gases depends on the internal combustion engine and the conditions under which it is operated, away.

Since internal combustion engines, such as gasoline engines, normally use an air mixture that is rich in petrol run, for example, during normal driving conditions of a motor vehicle about 1 to 4Q / 0 of the fuel fed to the engine as unburned or partial Burned material in the form of the above mixture: -Discharge in the exhaust gases. This amount increases to about 2 to 8 ° / o when the engine is idling, and kauri when the engine is idling Cold start or negative acceleration up to 50 ° / 0.

It is already known to clean or remove the above Exhaust gases to use certain oxidation catalysts. Such catalysts were usually placed in the exhaust pipe of internal combustion engines and combined with a mixture of air and the exhaust gases of the engines, un-i to oxidize the undesirable components of the exhaust gases catalytically and thus to remove. Certain special oxidation catalysts have also been proposed to be used in specially designed W. puff pots in such a way that air with the Exhaust gases are mixed immediately before these gases come into contact with the catalyst will. The air serves as a source of oxygen for catalytic oxidation. One of those a typical catalytic muffler is described in U.S. Patent 2,909,415. Because of the difficulty of having a sufficiently active oxidation catalyst available to face the sharp fluctuations in temperature and concentration at oxidizable substances, as they are usually found in the above-mentioned exhaust gases are working, but have so far found such oxidation catalysts and / or or mufflers containing such catalysts are not worth mentioning Use. There are also known combustion chambers, the inner wall of which is partially a firmly adhering, highly refractory ceramic layer with oxidation catalyst properties having, this layer containing a mixture of certain rare earth metals.

The oxidation catalysts discussed above work at Temperatures below 450 ° C not or not effective. Such catalysts are generally ineffective in catalytic oxidation if they are aerated Cold start exhaust gases at temperatures of 250 to 350 ° C during start conditions be brought together. The addition of air to the exhaust gases, although necessary is to provide oxygen for the catalytic oxidation of the exhaust gases usually also sets the temperature of the exhaust gases below 450 ° C down.

The purpose of the invention is to find new oxidation catalysts and processes to provide for their production, the disadvantages identified above counter effectively.

The invention provides new oxidation catalysts available, those by a content of activated porous metal oxide of metals of the group 11, III, IVa and VIa of the Periodic Table are marked on its Surface a mixture of a predominant amount of copper oxide and a smaller amount Amount of a rare earth metal oxide or a mixture of rare earth oxides Has earth metals.

The present invention also provides catalysts of the types described Type available in which the active porous metal oxide is certain below has defined physical properties that make it practically complete Oxidation and removal of toxic and smog-forming gases and vapors in the exhaust gases of internal combustion engines.

The present invention is based in part on the finding that a Catalyst, which is an active porous metal oxide of metals of group 11, III, IVa and VIa of the Periodic Table, which has a preferably uniform mixture of a predominant amount of copper oxide and an oxide of one or more of the rare earth metals, preferably one Oxide of one or more rare earth metals, which lead to higher valence levels than the trivalent stage are oxidizable, contains an extremely active oxidation catalyst represents.

The active porous metal oxides of metals of group II, III, IVa and VIa of the Periodic Table are metal oxides that are difficult to melt and are one have a certain crystal structure and a defined X-ray diffraction diagram before activation exhibit. During activation, usually by heating to elevated temperatures occurs, such a metal oxide loses its crystallinity to a considerable extent and shows an X-ray diffraction diagram, albeit less clearly defined than the corresponding catalytically inactive porous metal oxide.

Particularly useful catalytically active, porous metal oxides for present invention are porous aluminum oxide, thorium oxide, chromium oxide, magnesium oxide, Zirconium oxide and beryllium oxide. Of these active porous metal oxides, aluminum oxide, Thorium oxide and zirconium oxide preferred.

Aluminum oxide is particularly preferred.

According to the invention it was found that when bringing a Mixing of air and exhaust gases from internal combustion engines with the new catalytic converter of the invention at temperatures in the range of 250 to 950 ° C practically all unwanted oxidizable constituents are catalytically oxidized to carbon dioxide and water and thereby the exhaust gases are cleaned.

It is known that the aforementioned porous metal oxides exist in a special form or have to be manufactured in order to be catalytic to be active. So are z. B. from aluminum several crystalline forms known, z. B. the so-called -, y-, X and A-aluminum oxide. In general, y-aluminum oxide can be used by heating precipitated aluminum hydroxide or by decomposing an aluminum salt, for example aluminum nitrate, at temperatures between about 425 and 540 ° C. It is also known that when γ-aluminum oxide is heated to over 1150 ° C this Form little by little into A-alumina, x-alumina and finally into the trigonal crystalline or α-aluminum oxide passes over, which catalytically without further processing is inactive. However, such a-aluminum oxide can be made catalytically active, for example by treatment with ammonium nitrate and nitric acid and then Calcination. However, it has been found in the present invention that any of the above named catalytically active, porous aluminum oxides or other activated, refractory porous metal oxides can be used for the purposes of the invention.

Although you can use any porous aluminum oxide with the above Use properties for the catalysts of the invention, but it has been found that a commercially available catalytic A-alumina is preferably used.

As a constituent or part of the catalysts of the invention Active porous metal oxides found particularly useful are by pore volume from about 0.2 to about 0.4 ml / g and an average pore diameter of 70 to 90 A marked. The measurement of pore size, including pore volume and pore diameter on various porous materials is detailed by C. L. Drake and H. L. Ritter in the journal "Industrial and Engineering Chemistry", Analytical Edition, Vol. 17, pp. 782 to 791 (1945). The methods specified there were essentially used to determine the average pore diameter and other pore measurements of the catalytically active, porous metal oxides that are present in the Catalysts of the invention were used. The preferred catalytic active, porous metal oxides are further characterized by a specific Surface of 50 to 150 m2 / g, preferably 80 to 120 m3 / g, measured according to the Method by Brunauer, E m e t and T e 11 e r, sAdvances in Colloid Science «, Vol. I, pp. 1-36 (1932), New York, Interscience Publishers.

One of the activated porous metal oxides which is used in a preferred embodiment of the catalysts according to the invention is a catalytically active A-aluminum oxide, which is produced by calcination at temperatures between 400 and 900 ° C., preferably 450 to 550 ° C., of ou-aluminum oxide trihydrate . During the calcination, numerous large pores form due to the loss of water and the simultaneous recrystallization of aluminum oxide, and a porous, catalytically active A-aluminum oxide is usually obtained, which has the following characteristic X-ray diffraction diagram d-values (filtered Cu-K radiation) and having relative intensities. 10 means the strongest diffraction. d-values Relative intensity 2, 4 4 2, 27 2 2, 11 3 1, 98 2 1, 53 1, 39 10 The porous A-aluminum oxide produced in the manner described is characterized by a pore volume of 0.25 to 0.35 ml / g, a specific surface area of 90 to 100 m2 / g and an average pore diameter of 70 to 90 Å.

As noted above, the new catalysts are used to manufacture the new catalysts the invention a mixture of copper oxide and certain oxides of the rare earth metals, preferably those of the cerium group, e.g. B. cerium, praseodymium, neodymium or samarium Europium, or a mixture of copper oxide and mixtures of these rare earth metal oxides, applied to the surfaces of any of the activated porous metal oxides.

The mixtures of copper oxide and rare earth metal oxides can on the surface including the surfaces within the pores of any the aforementioned activated porous metal oxides in various ways applied or incorporated. For example, you can have an active porous Metal oxide with a dispersion of copper oxide and one or more of the rare ones Earth metal oxides in a volatile organic solvent such as methanol, ethanol or acetone. The solvent is then left out of the porous metal oxide evaporate. The active porous metal oxides can also be separated in any order with a dispersion of copper oxide in a volatile organic solvent and with a dispersion of one or more of the rare earth metal oxides in one volatile liquid to be treated. However, this offers separate treatment no benefits, and a single treatment with a mixture of copper oxide and one or more of the rare earth oxides containing dispersions preferred.

Another and preferred procedure for applying the mixture of copper oxide and one or more of the rare earth metal oxides on the surface of the porous metal oxide consists in that the porous metal oxide with mixtures from Copper salts and one or more rare earth metal salts. The mentioned Salts are formed when heated to a temperature above the melting point of the salts converted into copper oxide and rare earth metal oxides.

Another and particularly preferred procedure is that Treating or bringing together the porous metal oxide, preferably active Aluminum oxide, expediently in granulated or granular form with an aqueous one Solution containing a water-soluble, thermally decomposable copper salt, preferably Copper acetate or copper nitrate, and a water-soluble, thermally decomposable one contains rare earth metal salt, preferably praseodymium acetate or praseodymium nitrate. In some cases it may be desirable to repeat the treatment several times, for example one, two or three times. The mixture obtained is then used Evaporation of the water and for the conversion of the copper salts and the rare earth metal salts heated to a correspondingly high temperature. The working temperature for implementation this conversion is preferably between about 250 and 950 ° C. One receives on this way a granulated or granular catalyst, which is an active porous Metal oxide with an even mixture of copper oxide and a rare earth metal oxide contains on its surface.

It is possible to prepare the catalysts of the invention use any thermally decomposable copper and rare earth metal salt, e.g. B. the Formates, acetates and nitrates, but the nitrates are particularly preferred.

The proportion of copper oxide in the mixture of copper oxide and one or more of the rare earth metal oxides on the active porous metal oxide fluctuate to some extent. In general, the proportion is 10 to 20 parts by weight Copper in the form of copper oxide on the surface of 100 parts by weight of the active porous metal oxide.

The copper oxide is usually in the form of copper (In-oxide, however, it can also be in the form of a mixture of cupric and cuprooxides.

The proportion of rare earth metal oxides in the mixture of copper oxide and one or more of the aforementioned rare earth metal oxides usually about 05 to 0.4 parts by weight of rare earth metal in the form of its oxide per 100 parts of the active porous metal oxide. The rare earth metal oxides, which the preferred constituents of the catalyst of the invention exist usually in one or more oxide forms. For example, praseodymium, terbium, Neodymium, cerium and dysprosium in general are trivalent oxides, which lead to higher valence levels are oxidizable.

For example, praseodymium oxides can have a valence of 3, 4 or 5, and it can exist in three oxide forms, e.g. B. Prsosn PrOs and Pr6Oll.

The praseodymium is usually present as a trivalent metal oxide.

Those according to the invention prepared in the manner described above Catalysts can act as oxidation or dehydrogenation catalysts in a number can be used by methods e.g. B. for cracking and refining in the Oil industry, as well as for the oxidation of oxidizable, toxic and smog-forming substances in the exhaust gases of internal combustion engines.

The inventive catalysts described above can z. B. as powder, coarse or fine granules, extruded pieces, discs, tablets, Cookies and the like can be produced. The catalysts can be in these forms by coarse grinding, fine grinding, extrusion or tableting of the finished Catalysts can be obtained in a manner known per se. In some cases it can the active porous metal oxide prior to incorporation of oxides of copper and one or more of the rare earth metals in its surface in the desired physical Form can be made.

The particular physical form or shape of the oxidation catalysts of the invention generally depends on the environment in which the catalyst should be used, as well as the respective use. Should the catalyst z. B. be brought together with the exhaust gases of internal combustion engines, so is a catalyst in the form of cookies, tablets or granules is advantageous. the the latter form is particularly preferred.

The size and shape of the catalyst chips, granules or tablets can fluctuate to some extent.

In a preferred embodiment of the invention, granular catalysts are used of irregularly shaped granules with an average width of 1.6 up to 0.8 mm and an average length of 2.4 to 5.6 mm, especially for Use in mufflers is desirable, through which exhaust gases are released into the atmosphere be dismissed.

The activated porous metal oxides are in granular form through Breaking large masses of inactive or non-activated porous metal oxides and seven of the broken material through a number of seven prior to activation of the porous metal oxide.

The amount of copper nitrate and praseodymium nitrate in the for impregnation of the porous A-alumina solution used may to some extent, depending on vary in the amount of solution one wishes to use. However, it was called found particularly favorable, a solution with a content of 50 to 75, especially from 65 to 75 percent by weight copper nitrate and from 0.2 to 3.0, especially from 0.6 to Use 1.2 weight percent praseodymium nitrate. It was also considered expedient found to use this solution in such an amount that it was removed from the porous alumina is completely absorbed.

In other words, the preferred amount of the solution depends to some extent Extent depends on the pore volume of the aluminum oxide. In one embodiment in which the porous aluminum oxide has a pore volume between 0.3 and 0.4 ml / g found it appropriate to add 100 parts by weight of the porous A-aluminum oxide with 30 to 40 parts by weight of the above solution.

The product obtained in this way is a moist mass, at which one cannot detect any liquid.

In general, it is desirable to remove the absorbed water by evaporation, preferably to be removed by heating to a temperature of 70 to 90 ° C.

The dried product can then, as described above, to 300 to 900 ° C until the copper nitrate and praseodymium nitrate are in the appropriate Has converted oxide. These oxides are evenly mixed on the surface of the granular, porous A-aluminum oxide ceramic melted. The oxidation catalyst is active over a wide temperature range discussed below, and can be used for the catalytic oxidation and cleaning of exhaust gases from internal combustion engines be used.

In general, it was found that 1 part by volume of the catalysts of the Invention about 10,000 to 40,000 standard parts by volume of exhaust gas per hour for 150 Oxidized up to 300 hours of operation. In other words, you can use the catalysts of the invention between 85 and 100 0/0 that in the exhaust gases of internal combustion engines, z. B. automotive engines, containing hydrocarbons and oxygenated organic substances, such as aldehydes and ketones, and more than 90 duo of those available Carbon monoxide during about 9,000 to 18,000 kilometers of driving and in some cases oxidize even more catalytically.

The following examples illustrate the invention.

Unless otherwise stated, parts and percentages relate to on weight.

Example 1 75 parts of an aqueous solution containing 60% copper nitrate and 0.25% contains praseodymium nitrate, 100 parts by weight of granular, porous A-aluminum oxide an average width of 2.38 mm and an average Length of 5.56 mm mixed. The l-aluminum oxide used has a pore volume of 0.3 ml / g, a specific surface area of 100 m '/ g and an average Pore diameter of about 85 A. The mixture is heated to 75 ° C. This soaks a solution completely porous alumina. Once the mixture is dry, it is heated to 500 ° C for 6 hours. The copper nitrate and the praseodymium nitrate are transformed into the corresponding oxides, which on the surfaces, including adhere to the pore surfaces of the aluminum oxide as a firmly adhering layer. The on The catalyst produced in this way consists of an A-aluminum oxide with practically the same pore volume, pore diameter and specific surface area as that untreated A-aluminum oxide, but it has a uniform surface on its surface Mixture of 15 parts of copper in the form of copper oxide and 0.08 parts of praseodymium in the form of praseodymium oxide.

Example 2 The procedure of Example 1 is repeated, however 100 parts of A-aluminum oxide with 75 parts of an aqueous 60 "/ copper nitrate and 0.5 0/0 solution containing praseodymium nitrate mixed. The catalyst obtained is similar to that of example 1, but contains a uniform mixture of 15 Parts of copper as copper oxide and 0.15 parts of praseodymium as praseodymium oxide to 100 Parts of the granular, porous A-aluminum oxide.

Example 3 The procedure of Example 1 is repeated, however 100 parts of a finely divided porous γ-aluminum oxide with a pore volume of 0.2 ml / g, a specific surface area of 70 m '/ g and an average Pore diameter of 75 Å used in place of the porous x-aluminum oxide.

The finely divided catalyst, which is a mixture of 15 parts by weight Copper in the form of copper oxide and 0.8 parts by weight of praseodymium in the form of praseodymium oxide on the surface of the γ-aluminum oxide, is pressed into round cookies with a diameter of 9.52 mm.

Example 4 The procedure of Example 3 is repeated, however 100 parts of the finely divided porous γ-aluminum oxide with 80 parts of a 75 ° / 0 copper nitrate and 0, 9 0/0 neodymium nitrate containing solution mixed. Of the Catalyst prepared in this way contains 100 parts of γ-aluminum oxide the surface of the aluminum oxide is a uniform mixture of 20 parts by weight Copper as copper oxide and 0.3 parts by weight of neodymium as neodymium oxide.

Example 5 The procedure of Example 4 is repeated, however 100 parts of a finely divided porous, activated thorium oxide with a Pore volume of 0.2 ml / g and a specific surface area of 60 mz / g with the Solution of Example 4 mixed.

The catalyst prepared in this way contains 100 parts each of thorium oxide a uniform mixture of 20 parts of copper as copper oxide and 0.3 parts of neodymium as neodymium oxide on the surface of the thorium oxide.

Example 6 A cylindrical tube 45.72 cm long with a diameter of 5.08 cm is installed in the exhaust line in such a way that it is 0.057 m3 / min receives the exhaust gases described below from a four-cylinder gasoline engine, which is operated at a speed of 1800 rpm. At this speed the exhaust gas contains gaseous organic substances, including hydrocarbons and oxygen-containing organic compounds in an amount from 0.15 to 0.4 Percentage by volume, and between 2 and 3 ° / o carbon monoxide.

The proportion of organic substances in the exhaust gas flow is determined using a Liston-Becker ultrared analyzer, model 15, which sensitizes with n-hexane is. The carbon monoxide content of the exhaust gas stream is analyzed according to O r s a t.

The upstream 22.86 cm long part of the pipe is with wrapped around a 22.86 cm electrical resistance heater. This can the temperature of the gases within the temperature range of 250 to 950 ° C adjustable, just before these gases come into contact with the catalyst bed come. The catalyst bed is in the downstream 22.86 cm long part of the pipe arranged. The upstream portion of the tube also contains one Air inlet, in which one can pump in controlled amounts of air in order to create a flow of exhaust gas with an air content of 4 to 34 percent by volume. The air-exhaust gas mixture is then heated by the heating element controlled by a thermostat. The downstream 22.8 cm long portion of the tube contains 0.351 of the catalyst bed. A continuous measurement of an exhaust gas mixture containing 20% air by volume shows that the amount of gaseous substances present is of the order of 0.1 to 0.3 percent by volume and the amount of carbon monoxide present between 1 and is 2 percent by volume during operation of the four cylinder engine.

The gases are sequential according to the methods listed above measured.

The catalyst of Example 1 is converted into that described above Pipe brought in, connected to the exhaust pipe and 0.35 l of the above The catalyst is continuously kept with the mixture of air and exhaust gases a temperature between 270 and 300bC of the four-cylinder engine), until the catalyst is drowned out.

As soon as significant amounts of gaseous organic substances, e.g. B. 0.05 volume percent, and carbon monoxide, e.g. B. 0.5 volume percent, in the exhaust gas occur, which is brought into contact with the catalyst, the experiment is terminated.

The four-cylinder wM engine ran on normal unleaded petrol. The gas stream brought together with the catalyst bed is continuously increased organic substances such as hydrocarbons and organic substances containing oxygen according to the ultrarbtspektralanäjytischea method described above and on carbon monoxide measured with the aid of the device according to O r s a t.

The one made from a mixture of exhaust gases and 20 percent air by volume existing gas flow will be with the catalyst bed for 150 hours or accordingly 9000 kilometers before the catalytic converter is exhausted. The exhaust gases then contain 0.05% by volume of gaseous organic substances and 0.5% by volume Carbon monoxide.

During the 150 hours of operation, the catalytic converter removes it from the exhaust gases practically all carbon monoxide and more than 85% of the above organic Fabrics.

The exhaust gas is 1n0 times the volume every hour of the catalytic converter during the entire 150 hours of operation.

Example 7 The procedure of Example 6 is repeated, however the catalyst of Example 2, which contains twice as much praseodymium oxide as the catalyst of Example 1, in the pipe to form the catalyst bed in the exhaust line brought in.

The engine is operated for 250 hours corresponding to 15,000 kilometers driven, before the catalyst no longer has a sufficient amount of carbon monoxide and the said gaseous organic substances are removed from the exhaust gases.

Example 8 The catalyst of Example 1 is used on a six-cylinder Chevrolet motor vehicle, Built in 1955, road tested. The catalyst is here in a common muffler introduced. During this experiment the catalyst removed 88, the gaseous organic matter and 98% of the carbon monoxide from the exhaust gases of the chevrblet engine.

Similar catalysts as the catalysts of Example 1 and 2, which, however, contain kv rare earth metal oxide, remove a few) 'than 50' '/ (, of hydrocarbons and coblen monoxide from the exhaust gas of the above mentioned four-cylinder engine.

These catalysts are generally exhausted after 25 hours of operation and after that they can no longer contain significant amounts of organic substances and carbon monoxide Remove from the exhaust gas stream.

When testing the in Examples 3, 4 and. 5 produced catalysts in the manner described in Example 6, these catalysts removed over 95% of organic substances, e.g. hydrocarbons and oxygen-containing organic substances Compounds, and more than 99% of the carbon monoxide from the exhaust gases during one Operating time of over 100 hours of the internal combustion engines.

Claims (1)

Claims: 1. Oxidation catalyst, g e k e n n n z e i c h -n e t d u r c h a content of catalytically active, porous metal oxide of metals of group II, III, IVa and VIa of the periodic table, which is on its surface a mixture of about 10 to 20 parts by weight of copper in the form of copper oxide and about 0.05 to 0.4 parts by weight of a rare earth metal in the form of oxide has per 100 parts by weight of the porous metal oxide. "2. Catalyst according to claim 1, characterized in that the porous metal oxide is aluminum oxide and that the rare earth metal is oxidizable to valence levels above 3. 3. Catalyst according to claim 2, characterized in that the optionally grained Aluminum oxide has a pore volume of about 0.2 to about 0.4 ml / g and a specific Has a surface of about 50 to 150 m2 / g and has a uniform surface on its surface Mixture of about 10 to 20% copper oxide, calculated as Cu, and about 0.05 to 0.4 per cent. Praseodymium oxide or neodymium oxide, calculated as metal, carries. 4. Catalyst according to claim 3, characterized in that the aluminum oxide has an average pore diameter of 790 Å. 5. Process for the preparation of an optionally granular catalyst according to claims 1 to 4, characterized in that the catalytically active, porous metal oxide in a manner known per se with an aqueous solution of a copper salt a thermally decomposable acid and 0.2 to 3.0 percent by weight of an acid decomposable rare earth metal salt from the cerium group impregnated until the solution has practically penetrated the pores of the porous metal oxide, whereupon the obtained Mixture dries and then heated to a temperature of about 400 to 900 ° C. Documents considered: German Auslegeschrift No. 1 141 982.