Catalyst and process for treating exhaust gases from internal-combustion engines

Claim 2

Catalyst for the treatment of the exhaust gases from internal combustion engines, characterised in that it comprises: a support based on a refractory oxide and an active phase consisting of cerium, iron, at least one metal chosen from amongst platinum and palladium and at least one metal chosen from amongst iridium and rhodium, the content of platinum and/or palladium being between 0.04 and 0.5% by weight, relative to the support, the content of iridium and/or rhodium being between 0.002 and 0.1 % by weight, relative to the support, the ratio of the weight of platinum and/or palladium to the weight of iridium and/or rhodium being between 4 and 40 and preferably between 7 and 20, the content of iron being between 0.1 and 3.5% by weight, relative to the support, and the content of cerium being between 0.3 and 7% by weight, relative to the support.

Claim 3

Catalyst according to Claim 1, characterised in that the support based on a refractory oxide is chosen from amongst silica, alumina, aluminosilicates and mixed oxides comprising alumina together with silica, with zirconium oxide, with cerium oxide and/or with titanium oxide.

Claim 4

Catalyst according to Claim 2, characterised in that the support based on a refractory oxide is a support based on alumina which has a specific surface area of between 25 and 250 m 2 /g, a total pore volume of between 0.5 and 2 cm 3 /g, and a macroporosity such that the volume of the pores of diameter greater than 1,000 A is between 0.05 and 0.6 cm 3 /g.

Claim 5

Catalyst according to Claim 3, characterised in that the support based on alumina has a specific surface area of between 70 and 150 m 2 /g, a total pore volume of between 0.8 and 1.7 cm 3 /g, and a macroporosity such that the volume of the pores of diameter greater than 1,000 A is between 0.2 and 0.5 cm3/g.

Claim 6

Catalyst according to Claim 3, characterised in that the support based on alumina has been produced by autoclaving agglomerates of active alumina in a neutral or acid medium, and drying and calcining the product.

Claim 7

Catalyst according to Claim 3, characterised in that the support based on alumina has been produced by proceeding in accordance with the following steps: A. An ultrafine boehmite sol or a pseudoboehmite sol, the boehmite sol being free of amorphous alumina and the concentration by weight of the sol, expressed as AI 2 O 3 , being between 10 and 25%, is mixed, at a pH below 7.5 and preferably of between 4 and 7, with a proportion of between 30 and 95% by weight (relative to the total solids) of spheroidal alumina particles which are essentially in the form of at least one phase taken from the group comprising the gamma, delta and theta phases, these particles having a microporous volume of between 0.4 and 1 cm 3 /g and preferably_of between 0.7 and 1 cm 3 /g, and a specific surface area of between 100 and 350 m 2 /g, and the diameter of the particles being between 1 and 50 microns and preferably being such that at least 50% of the spheroidal particles have a diameter Ø centred around a mean value 0̸ M such that 0̸ = 0̸ M ± 20%0̸ M . B. Drops of the mixture are brought to a spheroidal shape and gelled, preferably in accordance with the so-called oil-drop technique. C. The gelled beads are isolated, dried and calcined at a temperature of between 550 and 1,100°C.

Claim 8

Catalyst according to any one of Claims 3 to 6, characterised in that the support based on alumina has been treated with a pore-forming agent taken from the group comprising the pore-forming agents based on cellulose, naphthalene, natural gums and synthetic polymers.

Claim 9

Catalyst according to any one of Claims 3 to 6, characterised in that the support based on alumina has been heat-stabilized by introducing into it an alkaline earth metal, silica and/or a trivalent rare earth.

Claim 10

Catalyst according to Claim 1, characterised in that the content of platinum and/or palladium is between 0.05 and 0.15%, the content of iridium and/or rhodium is between 0.005 and 0.02%, the content of iron is between 0.5 and 2% and the content of cerium is between 0.3 and 4.4%.

Claim 11

Catalyst according to Claim 1 or 9, characterised in that active phase consists of cerium, iron, rhodium, platinum and/or palladium.

Claim 12

Catalyst according to any one of the preceding claims, characterised in that the active phase furthermore contains at least one metal chosen from amongst copper, nickel, manganese, tin, germanium, uranium and rhenium.

Claim 13

Process for the treatment of the exhaust gases from internal combustion engines, which, in particular, makes it possible to eliminate the greater part of the carbon monoxide, of the uncombusted hydrocarbons and of the nitrogen oxides present in these gases, characterised in that the catalyst according to any one of Claims 1 to 11 is used.