MXPA97000913A - Fighter of the contamination of the - Google Patents

Abstract

The present invention relates to a combination of an internal combustion engine and an exhaust apparatus connected to said machine wherein the exhaust apparatus comprises a CO oxidation catalyst for converting CO and / or hydrogen to an exhaust gas that leaves the machine as CO2 and / or H2O by reaction with oxygen, and a hydrocarbon oxidation catalyst to convert the hydrocarbon in the exhaust gas that leaves the machine, such as CO2 and water by reaction with oxygen, when putting in contact the exhaust gas of the machine comprising CO, hydrogen and hydrocarbon with the CO oxidation catalyst and simultaneously or subsequently contacting the exhaust gas with the hydrocarbon oxidation catalyst, in which the CO oxidation catalyst is of ignition temperature for CO and / or hydrogen lower than the ambient temperature, under the operating conditions of the exhaust of the internal combustion machine, and n where control means are provided to control the machine in such a way that when starting the machine at room temperature the exhaust gas produced by the machine optionally, supplemented by secondary sources of oxygen, CO and / or hydrogen and on contacting with the oxidation catalyst of CO and / or hydrogen contains sufficient oxygen and sufficient CO in such a way that an exothermic reaction of the oxygen with the CO and / or the hydrogen in the oxidation catalyst generates sufficient heat to raise a temperature of the oxidation catalyst of CO from ambient temperature at least up to the ignition temperature of the hydrocarbon oxidation catalyst

Description

AIR POLLUTION COMPETITOR This invention ST refers to an engine having an exhaust apparatus connected thereto, and to a method for converting CO and hydrocarbon in the exhaust gas of an engine to C02 and water, in order to combat air pollution. The motor can be a stationary motor, but it is especially a > . motor vehicle. The engine can be endowed with energy through oil (gasoline), diesel, natural gas or other hydrocarbon or oxygenated fuel. The invention will be described with particular reference to engines with petroleum fuels, but it is not considered to be limited thereto. The main pollutants in the exhaust gas of an oil engine are monoxide. .- carbon (CO), hydrocarbons and nitrogen oxides. The amount of these pollutants that is emitted in the exhaust gas into the air is generally reduced by means of catalysts in the engine exhaust system. The CO is converted to C02 by a CO oxidation catalyst. The hydrocarbon is converted to C02 and water by a hydrocarbon oxidation catalyst. The nitrogen oxides are converted to nitrogen by a nitrogen oxides reduction catalyst. A so-called three-way catalyst converts CO, hydrocarbon and nitrogen oxides in this way. The three-way catalysts are composed of a mixture of catalytically active materials, one being active for the conversion of CO and hydrocarbons * and one for the conversion of nitrogen oxides. The three-way catalysts are generally based on rhodium mixed with platinum and / or palladium. As the regulations that govern the amount of pollutants that can be emitted from petroleum engines become stricter, attention has been focused on the start-up phase from the ambient temperature. For the present purposes, the ambient temperature can be defined as 25 ° C. Hydrocarbon emissions are higher in this phase because the hydrocarbon oxidation catalyst has not been heated to its operating temperature. The "ignition" temperature is the temperature at which 50% of the pollutant is converted. When starting a motor at room temperature, the time it takes for the hydrocarbon oxidation catalyst to heat up to its ignition temperature is significant, and in that time a significant amount of hydrocarbon is emitted into the air. The present invention is designed to reduce the time, and hence reduce the amount of hydrocarbon emitted. The invention provides an engine that has an exhaust device connected thereto, the exhaust system of which contains a CO oxidation catalyst to convert the CO into the exhaust gas leaving the engine to C02, by reaction with oxygen, and a '' hydrocarbon oxidation catalyst to convert the hydrocarbon in the exhaust gas leaving the engine to C02 and water, by reaction with oxygen, by contacting the exhaust gas containing the CO and the hydrocarbon with the catalyst of oxidation of CO, and simultaneously or subsequently with the hydrocarbon oxidation catalyst, wherein the CO oxidation catalyst is of ,,: * ignition for CO and / or hydrogen below room temperature, under operating conditions, and the engine and exhaust system are adapted so that when the engine is started at room temperature, the exhaust gas it comes into contact with the CO oxidation catalyst, contains enough oxygen and sufficient CO and / or hydrogen so that the exothermic reaction of the oxygen with the CO and / or the hydrogen generates enough heat to raise the temperature of the oxidation catalyst of CO from ambient temperature at least up to the ignition temperature of the hydrocarbon oxidation catalyst, so that the hydrocarbon oxidation catalyst is at a temperature of at least the ignition temperature of the oxidation catalyst. The invention also provides a method for converting CO and hydrocarbon in the exhaust gas of an engine to C02 and water, in order to combat air pollution, by contacting the exhaust gas with a CO oxidation catalyst and simultaneously or subsequently with a hydrocarbon oxidation catalyst, wherein the CO oxidation catalyst is of ignition for CO and / or hydrogen below room temperature, under operating conditions, and • - - the method is conducted so that when starting the engine at room temperature, the exhaust gas that comes into contact with the CO oxidation catalyst contains enough oxygen and sufficient CO and / or hydrogen, the exothermic reaction of oxygen with CO and hydrogen generates enough heat to raise the temperature of the CO oxidation catalyst from room temperature at least up to the ignition temperature of the hydrocarbon oxidation catalyst, so that the hydrocarbon oxidation catalyst is at a temperature of at least the ignition temperature of the hydrocarbon oxidation catalyst. In the present invention, the exothermic reaction of oxygen with CO and / or hydrogen generates sufficient heat to raise the temperature of the CO oxidation catalyst from room temperature to at least the ignition temperature of the hydrocarbon oxidation catalyst. This contrasts with the past, in which the heat of the engine transported by the exhaust gas, sometimes supplemented by electrical heating of the catalyst or gas, has been necessary to raise the temperature to the ignition temperature of the hydrocarbon oxidation catalyst. Thus, in a typical system, the engine heat could raise the temperature of a CO oxidation catalyst to its ignition temperature (eg, the ignition temperature for CO), and the subsequent exothermic reaction could then raise the temperature further until a combination of the exothermic reaction and the engine heat could raise the temperature (often by an additional approximately 100 ° C) to the ignition temperature of the hydrocarbon oxidation catalyst. As the engines have been developed, their manufacturers have adapted them so that the exhaust gas that leaves the engine contains less CO. Less CO is thus emitted into the air or less CO has to be converted by the CO oxidation catalyst. To facilitate engine handling, the air-fuel ratio used when starting the engine is generally rich, for example, there is an excess of fuel above the stoichiometric ratio (1: 14.65) required for fuel combustion. In this way, there has been insufficient oxygen or insufficient CO at the start of the engine to raise the temperature to the ignition temperature of the hydrocarbon oxidation catalyst; it has required extra heat, usually comprising engine heat, to do this. The amount of hydrogen in the exhaust gas that exits the engines in the past has been extremely small. It has been found that similar considerations apply for CO; the exothermic reaction of oxygen and hydrogen to produce water through a CO oxidation catalyst, whose ignition temperature for hydrogen is lower than the ambient temperature under operating conditions that rapidly raise the temperature to the ignition temperature of the oxidation catalyst of hydrocarbon, if enough oxygen and hydrogen is present. In the present invention, when the engine is started at room temperature, the CO oxidation catalyst, due to its ignition temperature which is lower than room temperature, can immediately begin its exothermic reaction. Because there is sufficient oxygen and sufficient CO and / or hydrogen, the exothermic reaction itself provides sufficient heat to heat the exhaust gas from room temperature to at least the ignition temperature of the hydrocarbon oxidation catalyst. The heat of the engine is a bonus. Accordingly, the hydrocarbon oxidation catalyst reaches its ignition temperature rapidly appreciably. It can be verified if the exothermic reaction present generates enough heat to raise the temperature of the CO oxidation catalyst, from the ambient temperature to at least the ignition temperature of the hydrocarbon oxidation catalyst, or if the heat from any place is also necessary to do this, by putting the gas from the exhaust gas composition but at room temperature, in contact with the CO oxidation catalyst and observing whether its temperature rises to the ignition temperature of the hydrocarbon oxidation catalyst. Alternatively, it can be tested by moving the CO oxidation catalyst and the hydrocarbon oxidation catalyst away from the engine; Although the heat of the engine has been partially lost by this, by means of the exhaust gas, the present system will still work. Of course, the present system could also work if all the heat of the engine initially carried by the exhaust gas had been lost by the exhaust gas. In addition to the reduced ignition time and hence the reduced hydrocarbon emissions, the present invention provides other advantages. Because the engine heat is not necessary for the hydrocarbon oxidation catalyst to reach its ignition temperature, it does not need to be close to the engine; Because the ignition temperature of the CO oxidation catalyst is below room temperature, it does not need to be near the engine. Consequently, either or both catalysts can be placed away from the motor. This means that the catalyst can suffer less thermal degradation, and does not need to be accommodated in restricted space near the engine, but can be accommodated under the floor of a vehicle. An additional advantage flowing from the ability to position the CO oxidation catalyst or the hydrogen oxidation catalyst away from the engine is that in such a position the catalyst is less affected by the heat carried in the exhaust gas. from the engine, and hence from a temperature measurement device, usually a thermocouple, in the nearest catalyst indicates the degree to which oxidation of CO or hydrocarbon is occurring, because the device is less influenced by this engine heat. Such a device can be used as an on-board diagnostic means, so that the operation of the catalyst can be measured and verified periodically. Accordingly, in a particular embodiment, a temperature measuring device 0 measures the temperature of the CO oxidation catalyst or the hydrocarbon oxidation catalyst, and this device is linked to and controls a screen indicating the operation of the catalyst in its reaction, as determined by the temperature 5 measured by the temperature measuring device.

The present invention makes it possible for ignition of the hydrocarbon to be remarkably achieved quickly, and this means that bypass systems and their associated valves in the past can be avoided in arrangements to accelerate ignition. In a preferred embodiment, the present escape apparatus does not contain a bypass system; in a preferred embodiment, the apparatus does not contain valves. An additional advantage is that since the hydrocarbon oxidation catalyst reaches its operating temperature more rapidly, the heat from the exhaust gas after the catalyst can be used to heat the interior of a vehicle, for example by means of a heat exchanger, so that the interior heats up more quickly than when it relies only on conventional media, using heat from the radiator. Accordingly, in a preferred embodiment, the exhaust apparatus also contains means for using the heat from the exhaust gas after it makes contact with the hydrocarbon oxidation catalyst, in order to heat the interior of a vehicle. In the present invention, there is more oxygen and more CO and / or hydrogen when starting the engine, than that which was described or suggested in the past with a CO oxidation catalyst, whose ignition temperature for CO and / or hydrogen is below room temperature under operating conditions. In addition to the oxygen in the exhaust gas leaving the engine, the present invention preferably employs a secondary source of oxygen. Oxygen is conveniently air. The secondary source can be an air pump. To provide more hydrogen than any in the exhaust gas leaving the engine, a secondary source of hydrogen may be employed. This can be for example a reformer for converting the fuel such as hydrocarbon, for example methane, or alcohol, for example methanol or ethanol, to hydrogen, for example by partial combustion. The source can be, for example, a '"'" "so-called" hot zone "reactor, in such a reactor a fuel such as hydrocarbon or methanol is injected with oxygen into a mass of the catalyst, so that a front part of the reaction gas is formed around the point of injection, to form hydrogen by partial combustion To provide more CO than any in the exhaust gas leaving the engine, and optionally to provide more oxygen too, a partial combustion burner can be used, more CO and / or hydrogen than any is normally present in the exhaust gas leaving the engine, it can be provided by adapting the electronic engine management system This can be done for example by the proper arrangement of the memory and / or control circuitry over the "chip" (microlasca) engine management The ~ "composition of the exhaust gas can be changed by the engine management system if desired after the ig tion of the hydrocarbon oxidation catalyst, for example to reduce the amount of CO and the exhaust gas leaving the engine. This can be done by adjusting a time interval. Alternatively, a feedback mechanism can be employed from a - '- temperature measuring device, which measures the temperature of the exhaust gas, for example in the hydrocarbon oxidation catalyst. An advantage of the present invention, however, is that no temperature feedback mechanism is necessary. Preferably, the CO aspect is used more than the hydrogen aspect. Accordingly, preferably the CO oxidation catalyst is at the ignition temperature for the CO lower than the ambient temperature under operating conditions, and the engine and the exhaust apparatus are adapted so that when the engine is started at room temperature, The exhaust gas that comes into contact with the CO oxidation catalyst contains sufficient oxygen and sufficient CO, so that the exothermic reaction of oxygen with CO generates sufficient heat to raise the temperature of the CO oxidation catalyst from room temperature to at least the ignition temperature of the hydrocarbon oxidation catalyst, so that the oxidation catalyst of hydrocarbon is at a temperature of at least the ignition temperature of the hydrocarbon oxidation catalyst. The amount of CO necessary in the exhaust gas which makes contact with the CO oxidation catalyst depends on the rise in temperature required by the exothermic reaction to reach the ignition temperature of the hydrocarbon oxidation catalyst. In general, the higher the temperature, the greater the amount of CO needed. In general, the exhaust gas that makes contact with the CO oxidation catalyst when the engine is started at room temperature contains more than 0.5% by volume, preferably more than 2%, especially more than 4%, of CO; usually it contains less than 10% CO by volume. The provision of more CO in the exhaust gas that makes contact with the CO oxidation catalyst is contrary to the direction in which the engine manufacturers have been developing the engines, as mentioned above. Usually, the exhaust gas contacting the CO oxidation catalyst contains sufficient oxygen, so that substantially all of the CO and / or hydrogen in the gas is reacted by the CO oxidation catalyst. Otherwise the CO and / or hydrogen is emitted into the air, or alternative means have to be employed to treat any excess, for example an additional downstream catalyst. In a strategy to start the engine at room temperature, the air-fuel ratio of the combustion mixture in the engine is little or almost stoichiometric, for example above 14.5. In an alternative, such a strategy is employed, the air-fuel ratio being rich, for example below 14.65, and a secondary source of oxygen, to provide oxygen to the exhaust gas which contacts the CO oxidation catalyst at start the engine at room temperature. The CO oxidation catalyst is also advantageously the hydrocarbon oxidation catalyst, in which case the exhaust gas makes contact with them simultaneously. This can be done by using a material that is catalytically active for the oxidation of CO and hydrocarbon. Alternatively, this can be done by employing a mixture of a material which is catalytically active for the oxidation of CO with a different material, which is catalytically active for hydrocarbon oxidation. The hydrocarbon oxidation catalyst can be contacted subsequent to contact with the CO oxidation catalyst; this can be achieved by having the hydrocarbon oxidation catalyst downstream of the CO oxidation catalyst, for example by having the CO oxidation catalyst on the front of a honeycomb monolith and the hydrocarbon oxidation catalyst on the hydrocarbon oxidation catalyst. the back of the monoli to. The exothermic reaction of the oxygen with the CO and / or the hydrogen heats the CO oxidation catalyst to at least the ignition temperature of the hydrocarbon oxidation catalyst. When the CO oxidation catalyst is the hydrocarbon oxidation catalyst, the latter is then automatically at a temperature of at least the ignition temperature of the hydrocarbon oxidation catalyst. When the CO oxidation catalyst is not the hydrocarbon oxidation catalyst, so that the exhaust gas makes contact with the hydrocarbon oxidation catalyst after making contact with the CO oxidation catalyst, then the heat from the catalyst Oxidation of CO is used to heat the hydrocarbon oxidation catalyst, usually by the exhaust gas carrying heat from the CO oxidation catalyst to the hydrocarbon oxidation catalyst. The CO oxidation catalyst is an ignition temperature for CO and / or hydrogen below room temperature, under operating conditions, in an engine exhaust system. This is beneficial for the environment, due to characteristics such as high temperatures, physical shocks, high gas flow and inhibitors in the exhaust gas. Some CO oxidation catalysts may be of ignition temperature for CO and / or hydrogen lower than room temperature, when they are in a more tolerant environment, but not in the present situation. In the present invention, the exhaust gas which is contacted with the CO oxidation catalyst may contain, for example, 1-20% by volume of water. It may contain, for example, 1-20% by volume of CO2. It may contain, for example, 100-2000 ppm of NO. It may contain, for example, 100-10000 ppm hydrocarbon. It may contain, for example, 0.2 to 20 ppm of SO .. In this specification, ppm means parts per million in volume. Preferably, the CO oxidation catalyst is of positive order kinetics with respect to the CO in its oxidation reaction. This contrasts with the typical catalysts for exhaust systems, which are of the negative order or zero order. For a catalyst with negative order kinetics with respect to CO, increasing the CO concentration could decrease the rate or rate of CO oxidation at temperatures below the ignition temperature. For a catalyst with zero order kinetics with respect to CO, the increase in CO concentration could leave the oxidation rate of CO at temperatures below the ignition temperature unchanged. The consequence of negative-order or zero-order kinetics is that the additional CO could not cause a larger exotherm on the CO oxidation catalyst until after the catalyst is ignited, so that at temperatures below the ignition temperature, the higher CO levels could not cause an increase in the reaction rate or in the heat generated. However, for a catalyst with positive order kinetics with respect to CO, an increase in the concentration of CO could lead to an increase in the reaction rate, and thus to the generation of heat. Hence, such a catalyst is advantageous in the present invention, where there is sufficient CO and / or hydrogen, for example by increasing its amounts by operating the motor, so that the exotherm generates enough heat to raise the temperature from the temperature environment to the ignition temperature of the hydrocarbon oxidation catalyst. Suitable materials for use as the present CO oxidation catalyst or the hydrocarbon oxidation catalyst, can be selected from the known catalysts, although a CO oxidation catalyst which is ignited below room temperature under the conditions of operation, has not been used commercially in the past to treat engine exhaust gas, as far as we know. It can be ascertained by tests if any given CO oxidation catalyst satisfies the present ignition characteristic. In a preferred embodiment, the CO oxidation catalyst comprises a catalyst (hereinafter referred to as the high interaction catalyst) which is of ignition temperature for CO and / or hydrogen below room temperature, under operating conditions, and which is composed of metal oxide particles between which noble metal particles are uniformly incorporated, the catalyst having such a high interaction between the noble metal particles and the metal oxide particles which, without hydrogen pretreatment, shows the formation of empty anionic spaces on the surface of the metal oxide at a temperature lower than that of the corresponding catalyst, without reduction pre-treatment with hydrogen, containing the same amount of the metal oxide particles and the noble metal particles, and prepared by the impregnation of the metal oxide particles with the pr noble metal ecursor, and calcining it to convert the precursor to the noble metal particles. The high interaction catalyst has an extremely high degree of interaction between the noble metal particles and the metal oxide particles. This degree of interaction can be achieved by the coprecipitation of the noble metal particles and the metal oxide particles. Catalysts of this degree of interaction are described, for example, in a European patent specification No. 602865A, the content of which is incorporated by reference herein. The metal oxide preferably comprises one or more of CeO, ZrO ^, TiO ,, and SnO :, especially CeO. The high interaction catalyst usually contains 0.1 to 30% by weight of the noble metal particles, based on the total weight of the noble metal particles and metal oxide particles. Alternatively, other catalysts having a high degree of interaction between the noble metal and an intermixed metal oxide can be employed. The CO oxidation catalyst preferably comprises (eg consists of or includes) one or both of platinum and palladium, and hence the noble metal in the high interaction catalyst preferably comprises one or both of platinum and palladium. It will be appreciated, however, that platinum and / or palladium are not in an environment as was commonly used to treat engine exhaust gas, but in an environment in which their CO ignition temperature under operating conditions is ?? below room temperature. In order to also treat nitrogen oxides in the exhaust gas of engines, the exhaust apparatus usually also contains a catalyst for reducing the nitrogen oxides in the exhaust gas, to nitrogen. The catalytically active material for this usually comprises rhodium. Conveniently, a three-way catalyst is used, which treats the CO, the hydrocarbon and the nitrogen oxides. Advantageously, the present CO oxidation catalyst is a three-way catalyst. In a preferred embodiment, the exhaust apparatus contains at least one (usually one or two) separate three-way catalyst to convert the CO in the exhaust gas to CO by reaction with oxygen, hydrocarbon in the exhaust gas to CO, and water by reaction with oxygen, and nitrogen oxides in the exhaust gas to nitrogen. In this way, the present CO oxidation catalyst and the hydrocarbon oxidation catalyst can be used when starting the engine, the catalyst or separated three-way catalysts can be used as the main catalyst. Any of the catalysts described above in relation to the present invention can be formulated in the usual manner. Usually, the catalyst comprises catalytically active material on a support, which is generally a refractory metal oxide, for example alumina. In the case of the high interaction catalyst, the noble metal is already mixed with the metal oxide, so that a separate support can not be necessary. The support should preferably be of a high surface area, for example greater than 20 pr / g. The catalytically active material, optionally on a support, is preferably carried on a carrier, for example when being carried on a meter but preferably when being carried in the channels of a monolith in the form of a honeycomb through which the exhaust gas flows. The monolith can be metal or ceramic. By sale, any of the catalysts and their carriers are of low thermal mass. The present method, and the engine and the exhaust apparatus, are usually such that the volume ratio of the CO oxidation catalyst and any carrier thereof (eg, a honeycomb monolith) to the displacement of the engine is less than 3. , preferably less than 1, especially less than _ * 0.1. This is a measure of the physical size of the catalyst and carrier needed, for example in a can or in a box in the exhaust system. The exhaust apparatus also preferably contains a hydrocarbon trap, which traps the hydrocarbon in the exhaust gas at lower temperatures, and releases it at higher temperatures to bring it into contact with the hydrocarbon oxidation catalyst, preferably to put it in contact with the hydrocarbon oxidation catalyst. Also contact with the CO oxidation catalyst. In this way, the hydrocarbon can be stored while the exothermic reaction on the CO oxidation catalyst heats the hydrocarbon oxidation catalyst, and then the hydrocarbon released when the hydrocarbon oxidation catalyst can better treat the hydrocarbon. The hydrocarbon trap is preferably upstream of the hydrocarbon oxidation catalyst, and preferably upstream of the CO oxidation catalyst. Alternatively, the hydrocarbon trap and the catalyst can be mixed, or the trap can be a layer above or below a catalyst layer. The materials for the hydrocarbon trap are known per se. Usually, the hydrocarbon trap comprises a zeolite. An appropriate zeolite is a zeolite subjected to ion exchange, such as Co / ZSM-5 or Pt / ZSM-5, but other materials, including impregnated zeolites and non-metallized zeolites, can be used. The preferred materials for the hydrocarbon trap are those that have a trapping effect also on nitrogen oxides (particularly NOT), so that they are also trapped at lower temperatures, and released at higher temperatures. The hydrocarbon trap can comprise the material known as silicalite, as a hydrocarbon trap material, at a good cost. It is desirable that when the engine is started at room temperature, the CO oxidation catalyst is not placed at sufficient concentrations of hydrocarbon and / or nitrogen oxides (particularly NO) so that the oxidation of CO is inhibited, and hence that the ignition is delayed. The hydrocarbon trap described above and the CO oxidation catalyst can thus be accommodated to achieve this. In some cases in the past, it has been proposed to add fuel to the exhaust gas, upstream of an initial catalyst in order to improve the purification of the exhaust gas during the cold engine starting periods. In the present invention, it is much preferred that the fuel is not added to the exhaust gas. It has been found that it may be advantageous to sweep the gas, usually air, preferably heated air, over the CO oxidation catalyst. '' before starting the engine, to reduce the amount of gas that has been adsorbed on the catalyst.

Such adsorbed gas can be H; 0 (water vapor), CO ?, NO or hydrocarbon. Hence, in a preferred embodiment, the exhaust apparatus also contains the means for thereby sweeping the gas over the catalyst. After such pretreatment, the catalyst may have increased catalytic activity for the conversion of CO when the engine is started at room temperature. The catalyst is preferably in the state resulting from this sweep, whether this has been achieved in this way or otherwise. The exhaust apparatus preferably contains the means for drying, or keeping dry, the CO oxidation catalyst before it is brought into contact with the exhaust gas, preferably before starting the engine. The hydrocarbon oxidation catalyst and, if employed, the hydrocarbon trap, are preferably likewise pre-dried or kept dry. The means for keeping the CO oxidation catalyst dry may, for example, be a device for preventing back-diffusion of the air from the outside to the exhaust pipe; The device can be a total shut-off valve or a desiccant water trap. The pre-drying can be performed by sweeping the gas described above. The means for sweeping the gas or pre-drying may for example comprise a pump for providing a gas stream, usually air, on the catalyst, preferably after the engine has been turned off. The air is preferably hot air, for example air at 350-500 ° C.

Advantageously, the residual heat of the engine, for example that transferred to the exhaust apparatus, is used so that the air used is heated. The exhaust apparatus also preferably contains a water trap for trapping the water when the engine is started at room temperature, before the water can come into contact with the CO oxidation catalyst. The presence of water can adversely affect the operation of the CO oxidation catalyst, and particularly the hydrocarbon trap. The water trap is preferably upstream of the CO oxidation catalyst, and preferably upstream of the hydrocarbon trap, if it is employed. Alternatively, the water trap may be mixed with the CO oxidation catalyst and / or the hydrocarbon trap, or a layered arrangement may also be employed. The water trap preferably comprises a molecular sieve for trapping water, such as zeolite 5A, although zeolite 3A, 4A or 13X can be used. Most zeolites adsorb water in preference to hydrocarbon adsorption, but zeolites of smaller pore size are generally preferred. The water trap and the hydrocarbon trap can also comprise the same material. In a preferred embodiment, the water trap is dried by the means for drying, described above. In this embodiment, the drying medium may incorporate a secondary water trap to dry the gas, usually air, from a gas pump in order to dry the main water trap. The secondary water trap can be dried or regenerated during engine operation, by using waste heat, for example from the engine, for example with a relatively low gas flow from the pump. In the past, CO oxidation catalyst has been placed in the so-called close coupled position near the engine, generally 20-30 cm from the outlet of an engine pipe, as measured by the gas flow length . This is because the engine heat has been necessary to ignite the catalyst. In the present invention, such engine heat is not necessary. Consequently, due to its oxidation activity at below ambient temperature, the present CO oxidation catalyst can be placed anywhere in the exhaust system rather than having to be placed in the close-coupled position. This is a great advantage. This means that the catalyst does not need to be in the very restricted space for the engine in a vehicle; rather, the catalyst can be under the floor of the vehicle. The catalyst can be at least 50 cm, for example at least 1 meter, but usually less than 10 meters, generally less than 4 meters, as measured by the length of the gas flow, from the gas outlet exhaust from the engine, for example from the outlet of an engine pipe. Because this can be far from the heat generated by the engine, the catalyst does not need to be so thermally durable. Preferably, the maximum temperature to which the current catalyst in the invention is subjected is less than 950 ° C, preferably less than 850 ° C, especially less than 700 ° C, particularly less than 500 ° C. The diverting or bypass apparatus may be present around the present apparatus, so that it does not meet the exhaust gas throughout the operation of the engine after the ignition of the hydrocarbon oxidation catalyst, but any valves that Operating such an appliance may be subject to lower temperatures as it is farther from the engine. When secondary air injection is used upstream of the CO oxidation catalyst, as is preferred, similarly it does not need to be in the engine space, but may be further away. An additional benefit of the CO oxidation catalyst when it is far away is that possible problems can be avoided that it interferes with the operation of a separate three-way main catalyst. Of course, in a particularly interesting embodiment of the present invention, the present CO oxidation catalyst is downstream of a three-way catalyst. Similarly, other devices whose position depends on the CO oxidation catalyst, such as the hydrocarbon oxidation catalyst, a hydrocarbon trap, a water trap, a means for sweeping the gas or a means for drying the oxidation catalyst. of CO as described above, may be away from the engine and therefore subject to lower temperatures. Lower temperatures can make it possible for the water trap to trap water for a longer time, and the hydrocarbon trap traps hydrocarbon for a longer time. The CO oxidation catalyst does not depend essentially on the heat in the exhaust gas leaving the engine when starting the engine at room temperature, in order to reach the ignition temperature of the hydrocarbon oxidation catalyst. Consequently, this initial heat can be used for other purposes, for example to heat the interior of a vehicle, usually by means of a heat exchanger to transfer the heat from the exhaust gas to the air that passes inside. Consequently, in a preferred embodiment, the exhaust apparatus also contains the means for using the heat from the exhaust gas, before it comes into contact with the CO oxidation catalyst, in order to heat the interior of a vehicle. In this way, the interior of a vehicle can be heated more quickly than when it relies only on conventional means, which use heat from the radiator. Alternatively, or in addition, the initial heat can be used to heat the engine oil more quickly, leading to more efficient engine operation. Taking the heat from the exhaust gas, before it comes into contact with the CO oxidation catalyst, can also be advantageous thereby reducing the maximum temperature at which the catalyst is exposed. However, the initial heat in the exhaust gas can be used to help raise the temperature of the CO oxidation catalyst, or the CO oxidation catalyst to the ignition temperature of the hydrocarbon oxidation catalyst, thus using this heat initial for other purposes, which must be balanced by the need to achieve ignition of the hydrocarbon at the desired time. The ignition temperature for the CO and / or hydrogen of the present CO oxidation catalyst, it is below the ambient temperature. This is much lower than the ignition temperature of current commercial CO oxidation catalysts in engine exhaust, which is usually about 150 ° C or higher. A system analogous to that of the present invention, but employing a CO oxidation catalyst whose ignition temperature is below that of current commercial catalysts, but above that of the present catalyst, could have some of the advantages of the present invention, but not all, since some heat, such as engine heat, may be necessary to raise the temperature of the catalyst to its ignition temperature.

The present invention can be applied to engines in general, whose exhaust gas contains CO and hydrocarbon. This is applicable to impoverish (reduce the proportion of fuel in the mixture of air and fuel) in combustion engines, for example diesel engines. Preferably, the engine is an oil (gasoline) engine. The engine is preferably that of a vehicle. The present method, and the engine and the exhaust system, are remarkably effective in converting the hydrocarbon in the cold start period. Usually, these decrease the total amount of hydrocarbon emitted from the exhaust in the first 50 seconds after starting the engine at room temperature, by a factor of at least 2, preferably by a factor of at least 5, compared to the amount emitted by the engine without the present exhaust system. Usually, the total amount of the hydrocarbon emitted in the first 100 seconds after starting the engine at room temperature is less than 0.4 g, preferably less than 0.1 g, especially less than 0.04 g. The invention is illustrated by the following drawings, in which: Figure 1 is a schematic diagram of a preferred engine and exhaust apparatus, according to the invention; Figure 2 is a graph of the temperature of the exhaust gas against time in a test; Figure 3 is a graph of the conversion of the three pollutants against time in the test, using a commercially available catalyst; Figure 4 is a graph of the corresponding conversion using a catalyst which can be used according to the present invention; Figure 5 is a graph of the corresponding conversion using the same catalyst but not drying; Figure 6 is a graph of the corresponding conversion using a lower amount of CO in the feed; Figure 7 is a graph of the reaction order of CO for oxidation of CO, on the commercially available catalyst; Figure 8 is a corresponding graph for the present catalyst; Figure 9 is a graph of the CO in grams versus time in a United States Federal test for the commercially available catalyst; Figure 10 is a corresponding graph of the hydrocarbon against time; Figure 11 is a plot of the CO in grams against the time for the same catalyst after drying, in the same test but with a higher amount of CO and 02 in the feed gas; Figure 12 is a corresponding graph of the hydrocarbon against time; Figure 13 is a plot of the CO in grams against the time for the present catalyst after drying in the same Federal test, except for an additional air source; Figure 14 is a corresponding graph of the hydrocarbon against time; Figure 15 is a plot of the CO in grams against time, for the same catalyst in the same test, but with a larger amount of CO and 02 in the feed gas; Figure 16 is a corresponding graph of the hydrocarbon against time; Figure 17 is a graph of CO in grams versus time, for the present catalyst placed away from the engine; Figure 18 is a corresponding graph of the hydrocarbon against time; Figure 19 is a plot of the CO in grams against time, for the present catalyst, which has a hydrocarbon trap upstream and a water trap upstream thereof; Figure 20 is a corresponding graph of hydrocarbon against time; Figure 21 is a graph of the exhaust gas and the temperature of the catalyst against time, for the commercially available catalyst; Figure 22 is a graph of the exhaust gas and the temperature of the catalyst against time, for the present catalyst; Figure 23 is a graph of% conversion of CO against time, for a different catalyst used in accordance with the present invention; and Figure 24 is a corresponding graph of% hydrocarbon (HC) conversion versus time. Figures 2-24 are more fully described in the following Examples. With reference to Figure 1, the exhaust gas from an engine is passed to the exhaust apparatus containing a water trap (for example a molecular sieve), a hydrocarbon trap (marked HC trap in the diagram) and a Oxidation catalyst of CO / combined hydrocarbon oxidation catalyst, of the ignition temperature for CO below 25 ° C. The water trap, the hydrocarbon trap and the catalyst are dried before each engine start, by means of an air pump that takes in ambient air and passes it through a second molecular sieve water trap (for example r ~. zeolite 5A) which is heated by the residual heat 0 of the engine, and which continues to operate after the engine has been turned off. The secondary molecular sieve is dried during the normal operation of the engine, by the combination of the residual heat of the engine and an air flow from the air pump, and after the engine is shut off, the secondary molecular sieve and the pump provide dry air hot to dry the water trap, the hydrocarbon trap and the catalyst. In this arrangement, at least one additional catalyst, which may be for example a three-way catalyst, may be incorporated within the exhaust apparatus, upstream or downstream of the oxidation catalyst of CO / hydrocarbon oxidation catalyst, combined . The invention is illustrated by the following Examples.

EXAMPLE 1 AND COMPARATIVE EXAMPLE 1 Two automobile exhaust catalysts are each coated on a honeycomb-shaped monolith, cordierite (a "partition") that has 400 cells for every 6.45 cm2 (400 cells per square inch). The volume of the catalyst and the monolith was 0.7 liter. The catalysts were tested in a mixture of depleted, synthetic gas of composition: NO 500 ppm C3H ^ 400 ppm C7H9 (toluene) 100 ppm CO, 15% HrO 10% O 3% CO 4% (reduced to 0.5% at time = 200 seconds in the run) Ar the rest One of the catalysts, here referred to as the present catalyst, consists of Pd, Pt and CeO;, and contains 4% by weight of Pd and 2% by weight of Pt, and was prepared by coprecipitation as described in European specification No. 602865A. The other catalyst, used for comparison, is a commercially available low ignition catalyst, called JM154 from Johnson Matthey PLC, and consists of Pd and Pt on a support of Al203-Ce02-Zr02, and contains 8% by weight of Pd and 2% by weight of Pt. An ignition experiment is conducted as follows: At the beginning of the experiment, the catalyst is covered by a flow of argon and the temperature at the inlet of the catalyst is maintained at 30 ° C. At the time = 65 seconds in the test, the synthetic exhaust gas mixture is introduced to the reactor at a gas hourly space velocity of 30,000. The temperature of the exhaust gas at the inlet is gradually raised as shown in Figure 2. After reaching approximately 350 ° C, the reactor is maintained at that temperature for approximately 5 minutes, after which the exhaust gases are removed of the feed and the reactor is cooled in a dry air flow. After the catalyst reaches 30 ° C, the feed gas is changed back to argon and the experiment is repeated in a second run. Figures 3 and 4 show the ignition results on the two catalyst formulations in the second run. Figure 3 (Comparative Example 1), which gives the results for the commercial catalyst, shows that the CO and the hydrocarbons are ignited (a conversion figure of 0.5) as a group at approximately 190-200 seconds in the run. Figure 4 (Example 1) that gives the results for the present catalyst under identical conditions, shows that it ignites almost instantaneously, converting all the CO and almost all the hydrocarbon, almost immediately after they have been introduced to the reactor. This illustrates that the present catalyst, when used with the present ignition strategy, produces remarkably rapid ignition.

EXAMPLE 2 AND COMPARATIVE EXAMPLE 2 Figures 5 and 6 show the results of two ignition tests on the present catalyst, carried out in the manner described in Example 1, except as noted. Figure 5 (Example 2) shows the results of the first run using the fresh catalyst. Figure 6 (Comparative Example 2) shows the results of a third run, carried out immediately after the second run, but again after cooling the catalyst in dry air. In this run, all reactor conditions remained the same, except that the CO feed level was adjusted to 0.5% throughout the entire run. A comparison of Figures 4 and 5 shows the benefits of running the runs on a catalyst that has been "pre-dried". The initial starting condition of the catalyst is clearly important, as shown in Figure 5 (fresh catalyst) ignition at approximately 90-110 seconds in the first run, whereas when the catalyst has been "dried" in an air flow before of the second run, the ignition occurs almost instantaneously. The same improvement in ignition performance has been observed, when the catalyst has been heated to 200 ° C under nitrogen, and then cooled before starting an experiment. The comparison of Figures 4 and 6 shows the advantages of increased CO levels in the feed at start-up. In Figure 6, where a much lower amount of CO has been used at start-up (an insufficient amount for the exothermic reaction itself to generate enough heat to raise the catalyst temperature to the ignition temperature of the hydrocarbon), ignition of CO is significantly retarded in relation to to that of Figure 4. More importantly than the ignition of the delayed CO is the effect that it has on the ignition of the hydrocarbon, which now occurs approximately at 170-200 seconds in the test. This shows that the almost instantaneous ignition mechanism of the hydrocarbon, shown in Figure 4, depends on the high level of CO and the almost instantaneous CO conversion.; the high temperature generated in the catalyst due to the high speed of the exothermic CO oxidation reaction leads to temperatures that exceed the ignition temperature of the hydrocarbon.

EXAMPLE 3 AND COMPARATIVE EXAMPLE 3 The effect of the CO feed level on the oxidation reaction rate of CO was examined under impoverished conditions (5% O O, 1-4% CO) for the comparative catalysts (Comparative example 3) and present (Example 3 ) described in Example 1, and Comparative Example 1, although the catalysts were used in powder form (not coated on a monolith). The results are summarized in the Table and in Figures 7 and 8. As can be seen from Figure 7, the comparative catalyst shows CO kinetics of negative order for the oxidation of CO, which means that by increasing the amount of CO in the feed, is conducted at a reduced rate of oxidation of CO at feed levels of 1-4%. However, as shown in Figure 8, the present catalyst shows the kinetics of positive, inverse order. The reaction order for these two catalysts has been estimated, and as shown in the Table, is positive for the present catalyst and slightly negative for the comparative catalyst. This is an important consideration for a catalyst to react with high levels of CO in an exhaust stream.

TABLE Catalyst Comparative CO Reaction Order -0.3 Present 0.5 EXAMPLE 4 AND COMPARATIVE EXAMPLES 4-6 The ignition performance tests for the comparative catalysts (Comparative Examples 4 and 5) and the catalysts present (Example 4 and Comparative Example 6) described in Example 1 and Comparative Example 1, were carried out in a Ford Contour 2-liter car , of petroleum fuel. The volume of the catalyst and the monolith was 0.7 liters. The coating load (catalytically active material plus support) was 0.18 g per cmJ (3 g per cubic inch). The catalysts have been tested in a test of the United States Federal Test Procedure (FTP) in the frontal position under the floor. Figures 9 and 10 show the operation of the comparative catalyst during test 1, in which the standard start strategy was used. The normal configuration of this car is rich boot. Figure 9 shows the CO levels of the feed gas (precatalyst) and the exhaust pipe (post-catalyst) in terms of g / s. As can be seen from this graph, CO ignition occurs approximately 40 seconds after the test. Figure 10 shows the results for hydrocarbon, with the ignition again occurring approximately 40 seconds after the test. Figures 11 and 12 show the same catalyst in a second test, in which the amount of CO in the feed gas has been significantly increased (the level of 02 was also increased, in order to maintain the same stoichiometry as in the test whose results are shown in Figures 9 and 10). Between test 1 and test 2, anhydrous nitrogen gas was blown over the catalyst in order to "dry" the catalyst. As can be seen from Figures 11 and 12, there is virtually no observed advantage due to the higher CO levels at the inlet, and the drying of the catalyst. The ignition times for each of these pollutants remain almost unchanged. Figs. 13 and 14 show the depleted ignition operation (Comparative Example 6) of the present catalyst using normal engine starting, except that an additional source of air has been coupled in order to ensure the conditions of depletion on the catalyst at startup. This experiment is the fourth in a series, so that the catalyst has already undergone the "drying" treatment described above. These Figures show an improvement in emissions compared to the results for the comparative catalyst shown in Figures 9-12, thus indicating the advantages of the present catalyst under these starting conditions. Figures 15 and 16 show the operation (Example 4) of this catalyst in the FTP test, where additional CO and 0 have been injected over the catalyst, as described above. Here, a remarkable advantage in the ignition of CO and hydrocarbon, is observed as a result of the highest levels.

EXAMPLES 5 AND 6 The ignition performance tests of the present catalyst as described in Example 4, with and without a combination of a water trap and a hydrocarbon trap, have been performed in a Ford Contour automobile. Startup was used in the depleted state with increased CO, as described at the end of Example 4. Figures 17 and 18 show the results (Example 5) of test 1, in which the frontal position below the floor is occupied by a monolith bare, and the rear position below the floor is occupied by the present catalyst. The excellent performance of the present catalyst is again shown (this is the second run in a series, and thus it is following the drying procedure described in Example 4). It is evident from Figure 18, however, that in the first 10 seconds of the test the hydrocarbon is not converted. This is because the catalyst has not yet been heated sufficiently to convert the hydrocarbons in the first 10-15 seconds. Figures 19 and 20 show the results (Example 6) of test 2, in which the frontal position below the floor now contains a mid-size partition covered with zeolite 5A (a desiccant material) followed by a medium-sized partition covered with ZSM5 (a hydrocarbon trap) . The rear position below the floor again contains the present catalyst. The excellent performance for CO oxidation is again shown in Figure 19. Figure 20 shows that the hydrocarbon trap effectively reduces hydrocarbon emissions in the first 10-15 seconds of the experiment.

EXAMPLE 7 AND COMPARATIVE EXAMPLE 7 The temperature of the catalyst (in Comparative Example 7) was measured during test 2 of Comparative Example 5, in which the comparative catalyst occupies the frontal position under the floor, and additional CO has been added to the exhaust feed. These results are shown in Figure 21. It is clear that the "medium bed" temperature of the catalyst remains below the catalyst inlet temperature (measured at a point just in front of the frontal position under the floor) to everything length of the first 35 seconds. The relevant temperatures have also been measured (in Example 7) during test 1 of Example 5, in which the present catalyst has been used in the rear position under the floor, and a blank wall occupies the frontal position below the floor. floor. These results are shown in Figure 22. The inlet temperature, which is still measured at the entrance to the frontal position under the floor, is virtually identical to that shown in Figure 21. The trace for the frontal position under the floor , which is now non-catalytic, appears similar to the first 35 seconds of the average bed temperature of the comparative catalyst (before ignition occurs on the septum in Figure 21). However, the temperature of the rear partition below the floor (the present catalyst) increases very rapidly, reaching 200 ° C in the first 15 seconds of operation. It is important to note that this rapid heating of the catalyst occurs not due to the specific heat coming from the engine, but due to the heat of reaction coming from the combustion of CO, hydrogen and hydrocarbon, on the catalysts. The rapid temperature rise of the present catalyst shown in Figure 22 illustrates a further advantage of the present invention, since a thermocouple placed within the catalyst can simply be used as a diagnostic means for the operation of the catalyst.

EXAMPLE 8 A catalyst was prepared according to the following recipe: tetraamine-plat inohydrocarbonate (TPtHC) was dissolved in citric acid, and added to a solution of Pd (N0.). This solution was then mixed with a solid mixed oxide of ceria-zirconia, which was 70% Ce02 and 30% Zr02 by weight. This suspension was heated gently to remove the excess liquid, dried overnight, and then calcined at 500 ° C for two hours. The resulting catalyst was 4% Pd and 2% Pt by mass. This catalyst was then coated on monolithic substrates at a load of 0.18 g / cm3 (3 g / cubic inch), and loaded into the two under-floor positions of a Ford Contour car. The FTP tests were run with the increased CO and air feed at start-up, as discussed in Examples 4 and 5. Figures 23 and 24 show the conversion of CO and hydrocarbon as a function of start-up time, for two consecutive runs. It can be observed from Figure 23, that the conversion of CO is above 90% practically immediately, and remains high throughout the first 250 seconds of the test. Figure 24 shows that the hydrocarbon conversion remains high throughout the crucial start phase of the test. The prominent behavior of low temperature ignition has been achieved.

Claims (21)

1. An engine that has an exhaust or exhaust device connected to it, whose exhaust contains a CO oxidation catalyst to convert the CO to the exhaust gas leaving the engine, to CO? by reaction with oxygen, and a hydrocarbon oxidation catalyst to convert the hydrocarbon in the exhaust gas leaving the engine, to C02 and water by reaction with oxygen, by contacting the exhaust gas containing the CO and the hydrocarbon with the CO oxidation catalyst, and simultaneously or subsequently with the hydrocarbon oxidation catalyst, wherein the CO oxidation catalyst is of ignition temperature for CO and / or hydrogen below room temperature, under the operating conditions, and the engine and exhaust system are adapted so that when the engine is started at room temperature the exhaust gas which comes into contact with the CO oxidation catalyst, contains sufficient oxygen and sufficient CO and / or hydrogen so that the exothermic reaction of oxygen with CO and / or hydrogen generates enough heat to raise the temperature of the CO oxidation catalyst from the temp ambient temperature at least up to the ignition temperature of the hydrocarbon oxidation catalyst, so that the hydrocarbon oxidation catalyst is at a temperature of at least the ignition temperature of the hydrocarbon oxidation catalyst. , __ ..

2. An engine according to claim 1, wherein the exhaust gas which is contacted with the CO oxidation catalyst, contains sufficient oxygen so that substantially all of the CO and / or hydrogen in the gas is reacted by means of the CO oxidation catalyst.

3. An engine according to claim 1 or 2, wherein the CO oxidation catalyst is also the hydrocarbon oxidation catalyst.

4. An engine according to any of claims 1 to 3, wherein the CO oxidation catalyst is of positive order kinetics with respect to the CO in its oxidation reaction.

5. An engine according to any of the preceding claims, wherein the CO oxidation catalyst comprises a catalyst which is of ignition temperature for the CO and / or the hydrocarbon, below the ambient temperature under the operating conditions, and which is composed of metal oxide particles, among which noble metal particles are uniformly incorporated, the catalyst having such a high interaction between the noble metal particles and the metal oxide particles so that, with the pretreatment of oxygen reduction , this shows the formation of anionic voids on the surface of the metal oxide at a lower temperature than that shown by the corresponding catalyst, without reduction pre-treatment with hydrogen, which contains the same amount of metal oxide particles and metal particles noble, and prepared by impregnating the oxide particles with the noble metal precursor, and calcined to convert the precursor to the noble metal particles.

6. An engine according to claim 5, wherein the metal oxide comprises one or more of CeO ?, ZrO, Ti02 and SnO? .

7. An engine according to any of the preceding claims, wherein the CO oxidation catalyst comprises one or both of platinum and palladium.

8. An engine according to any of the preceding claims, wherein the exhaust apparatus also contains a catalyst for reducing nitrogen oxides to nitrogen, in the exhaust gas.

9. An engine according to any of the preceding claims, wherein the exhaust apparatus also contains a hydrocarbon trap, which traps hydrocarbon in the exhaust gas at lower temperatures, and releases it at higher temperatures, to bring it into contact with the exhaust gas. CO oxidation catalyst.

10. An engine according to claim 9, wherein the hydrocarbon trap comprises a zeolite.

11. An engine according to any of the preceding claims, wherein the exhaust apparatus also contains the means for sweeping the gas through the CO oxidation catalyst, before starting the engine, to reduce the amount of gas that has been adsorbed. on the catalyst. and __

12. An engine according to claim 11, wherein the means for sweeping the gas is a means for sweeping hot air.

13. An engine according to any of the preceding claims, wherein the exhaust apparatus contains the means for drying, or keeping dry, the CO oxidation catalyst before it comes into contact with the exhaust gas.

14. On an engine according to claim 13, wherein the means for drying the catalyst comprises a pump, for providing a gas stream over the catalyst after the engine has been turned off.

15. An engine according to any of the preceding claims, wherein the exhaust apparatus also contains a water trap for catching water when the engine is started at room temperature, before the water can come into contact with the CO oxidation catalyst. .

16. An engine according to any of the preceding claims, wherein the exhaust apparatus also contains at least one three-way, separate catalyst to convert the CO in the exhaust gas to C02, by reaction with oxygen, the hydrocarbon in the exhaust gas to C02 and water by the reaction with oxygen, and the nitrogen oxides in the exhaust gas, to nitrogen.

17. An engine according to any of the preceding claims, which is that of a vehicle.

18. An engine according to claim 17, wherein the exhaust apparatus also contains the means for using the heat from the exhaust gas, before it is brought into contact with the CO oxidation catalyst, in order to heat the interior of the vehicle.

19. An engine according to claim 17 or 18, wherein the exhaust apparatus also contains the means for utilizing the heat from the exhaust gas, after it is contacted with the hydrocarbon oxidation catalyst, for the purpose of of heating the interior of the vehicle.

20. An engine according to any one of the preceding claims, wherein a temperature measuring device measures the temperature of the CO oxidation catalyst or the hydrogen oxidation catalyst, and this device is linked to and controls a screen indicating operation of the catalyst in its reaction, as determined by the temperature measured by the temperature measuring device.

21. A method to convert CO and hydrocarbon in the exhaust gas of an engine, to C02 and water, in order to combat air pollution, by contacting the exhaust gas with a simultaneous CO oxidation catalyst or subsequently with a hydrocarbon oxidation catalyst, wherein the CO oxidation catalyst is of ignition temperature for CO and / or hydrogen below room temperature, under operating conditions, and the method is conducted so that the start the engine at room temperature, the exhaust gas comes into contact with the CO oxidation catalyst, contains enough oxygen and enough CO and / or hydrogen, so that the exothermic reaction of oxygen with CO and / or hydrogen generates sufficient heat to raise the temperature of the CO oxidation catalyst from room temperature to at least the ignition temperature of the hydrocarbon oxidation catalyst, so that the The hydrocarbon oxidation scaler is at a temperature of at least the ignition temperature of the hydrocarbon oxidation catalyst.