Mesoporous oxide molecular sieves for absorbing nitrogen oxides in oxidizing engine exhaust gas

A method for treating exhaust gas containing carbon monoxide, hydrocarbons, and nitrogen oxides generated by a lean-burn internal combustion engine, the method comprising the step of:

• bringing said exhaust gas from said lean-burn engine in contact with a catalyst comprising an aluminum oxide material molecular sieve including at least 0.1 wt % precious metal selected from the group consisting of platinum, palladium, rhodium, and a mixture of any of them, said aluminum oxide material sieve being the reaction product by sol-gel techniques of components comprising:
• a. neutral surfactant;
• b. alkoxides of (I) aluminum, (II) at least one of:
• i) alkali metals and ii) alkaline earth metals, and optionally, (III), a lanthanide metal;
• c. water;
• and
• d. alcohol;
• wherein said components are mixed to form an aluminum oxide material gel which is subsequently washed with a liquid in which the surfactant is soluble and in which the oxide is substantially insoluble to recover the aluminum oxide material which includes interconnected pores of mesoporous dimensions;
• wherein under lean-burn conditions, where said exhaust gas contains more oxygen than is required for oxidizing components to be oxidized in the exhaust gas, nitrogen oxides are absorbed on said catalyst material and when the oxygen concentration in said gas is lowered the absorbed nitrogen oxides are desorbed and reduced over said precious metal.