摘要:
A process for preparing a catalyst which has a catalytically active coating of high surface area finely divided materials and catalytically active components on an inert carrier structure. A powder mixture of the finely divided materials used is impregnated with a solution of precursor compounds of the catalytically active components. By suitable combination of the finely divided materials and the precursor compounds and appropriate management of the impregnation process, a highly dispersed deposition and adsorption of the catalytically active components is ensured on the finely divided materials. Then ai aqueous coating dispersion is produced using the impregnated powder mixture and the carrier structure is coated therewith. The coating is then dried and calcined.
摘要:
A catalyst for purifying the exhaust gases of diesel engines, which catalyst contains at least one zeolite and, additionally, at least one of the support oxides aluminum oxide, silicon dioxide, titanium dioxide and aluminum silicate and at least one of the noble metals platinum, palladium, rhodium and iridium. In this catalyst the atoms of the noble metals have a mean oxidation number of less than +2.5, on average more than 3 metal ligands and less than 3 oxygen ligands and are present on the zeolites and support oxides in the form of crystallites having a mean particle size of from 1 to 6 nm.
摘要:
A process for checking the operability of an exhaust gas purification catalyst for diesel engines, which has a light-off temperature and a degree of conversion rCO for carbon monoxide (CO), by direct measurement of the carbon monoxide concentration in combination with a temperature measurement. To evaluate the remaining catalytic activity of the catalyst the difference &Dgr;T between the current catalyst exit temperature TE of the exhaust gas and the light-off temperature TCO,50%,fresh of the fresh catalyst for carbon monoxide stored as a function of the speed and load &Dgr;T=TE−TCO,50%,fresh is determined and the degree of conversion rCO for carbon monoxide is ascertained.
摘要:
An oxidation catalyst for internal combustion engines which contains platinum on a finely divided support material and containing lead as a promoter. The catalytic activity of the oxidation catalyst can be increased greatly by promoting the catalyst with lead at a molar ratio of lead to platinum of 2:1. The light-off temperatures of the promoted catalyst are well below the corresponding temperatures for a conventional, lead-free catalyst.
摘要:
The present invention relates to a catalyst for the purification of exhaust gases from an internal combustion engine, which comprises a catalytically active coating on an inert ceramic or metal honeycomb body, said coating comprising at least one platinum group metal selected from the group consisting of platinum, palladium, rhodium and iridium on a fine, oxidic support material. As an oxidic support material, the catalyst comprises a low-porosity material on the basis of silicon dioxide that comprises aggregates of essentially spherical primary particles having an average particle diameter of between 7 and 60 nm.
摘要:
The present invention relates to a catalyst for the purification of exhaust gases from an internal combustion engine, which comprises a catalytically active coating on an inert ceramic or metal honeycomb body, said coating comprising at least one platinum group metal selected from the group consisting of platinum, palladium, rhodium and iridium on a fine, oxidic support material. As an oxidic support material, the catalyst comprises a low-porosity material on the basis of silicon dioxide that comprises aggregates of essentially spherical primary particles having an average particle diameter of between 7 and 60 nm.
摘要:
A catalyst for purifying exhaust gases of a diesel engine. The catalyst contains two functional layers superimposed on an inert supporting body, whereby the first layer, which is situated directly on the supporting body, has a nitrogen oxide storage function and the second layer, which is in direct contact with the exhaust gas, has a catalytic function. The second functional layer additionally has a hydrocarbon-storage function and its catalytic function is provided by catalytically active noble metals of the platinum group which are deposited in highly dispersed form on finely divided, acidic carrier materials. Nitrogen oxides in the oxygen-rich exhaust gas of a diesel engine can be converted with optimal utilization of the reductive constituents contained in the exhaust gas. For this purpose, no reducing agents going beyond the reductive components (carbon monoxide and hydrocarbons) which are contained as a consequence of incomplete combustion need to be added to the exhaust gas. Nevertheless, rates of conversion in respect of the nitrogen oxides are obtained, averaged over practical driving cycles, which lie distinctly above the rates of conversion of conventional reduction catalysts.
摘要:
A method for removing nitrogen oxides and particulate matter from the lean exhaust gas of a combustion engine that also contains low concentrations of sulfur oxides. The exhaust gas stream is passed over a nitrogen oxide storage catalyst and a particulate filter, where nitrogen oxides and sulfur oxides are adsorbed by the storage catalyst under lean exhaust gas conditions and the particulate matter is deposited on the particulate filter. The storage catalyst is in a first cycle is periodically denitrated by enriching the exhaust gas regeneration of the particulate filter. Desulfurization of the nitrogen oxide storage catalyst is carried out in a second cycle by raising the temperature of the lean exhaust gas to a value at which the particulate matter combustion on the particulate filter is initiated and then the storage catalyst can be desulfurized by enriching the exhaust gas.
摘要:
The invention relates to a method for desulfating a nitrogen oxide storage catalyst that contains stored nitrogen oxides and sulfur oxides and that forms part of an exhaust gas purification system of a lean-burn engine. The method provides that, to initiate desulfation, the temperature of the catalyst is increased to the point where thermal desorption of the nitrogen oxides stored in the catalyst sets in, and the onset of thermal desorption of the nitrogen oxides is used as the signal to enrich the air/fuel mixture to perform the desulfation.
摘要:
The present invention provides a process for regenerating the catalytic activity of catalysts that have oxidizing functions. A catalyst that is located in the exhaust gas line of a diesel engine that preferably contains a catalytically active coating on a honeycomb carrier that does not have a filter function and that has at least one oxidizing function is regenerated. As a result of time-restricted increases in the exhaust gas temperature upstream of the catalyst to a value greater than 450° C., the combustion of soot particles and hydrocarbons deposited on the catalyst is initiated, and thus, the catalytic activity of the catalyst is at least partly regenerated.