Abrasion-resistant carrier catalyst

A process for producing a carrier catalyst comprising a porous inorganic carrier material impregnated with a metal component selected from the group consisting of palladium, rhodium, a combination of palladium and rhodium, and a combination of palladium and a metal of the copper group, wherein the carrier material comprises "theta" and "kappa" aluminum oxide and 0 to 10 wt-% of "alpha" aluminum oxide and is free of "gamma" and "delta" aluminum oxide, and wherein the porous carrier has a pore diameter distribution with a single maximum (monomodal pore distribution) in the range from 70 to 150 nm or with two maxima (bimodal pore distribution) in the range from 10 to 150 nm, and a median pore diameter between 30 and 50 nm;

• said process comprising the steps of
• mixing amorphous (chi) aluminum oxide with aluminum oxide hydrate excluding beta-monohydrate at a weight ratio of 33.69:20.50 to 44.21:7.17 and added water to obtain a carrier mixture;
• forming the carrier mixture to a desired shape;
• calcining the carrier mixture for 4.5 to 6.5 hours at a temperature between 1,045.degree. and 1,055.degree. C.;
• impregnating the carrier mixture with the metal component;
• and
• calcining the impregnated carrier mixture to produce said carrier catalyst.

A continuous process for treating water containing at least one substance selected from the group consisting of nitrite and nitrate in order to decrease at least one of the oxygen content, the nitrite content and the nitrate content thereof, with selective formation of nitrogen, said process comprising the steps of

• introducing hydrogen gas into the water;
• contacting the hydrogen-containing water with an effective amount of a carrier catalyst comprising a porous inorganic carrier material impregnated with a metal component selected from the group consisting of palladium, rhodium, a combination of palladium and rhodium, and a combination of palladium and a metal of the copper group, wherein the carrier material comprises "theta" and "kappa" aluminum oxide and 0 to 10 wt-% of "alpha" aluminum oxide and is free of "gamma" and "delta" aluminum oxide, and wherein the porous carrier has a pore diameter distribution with a single maximum (monomodal pore distribution) in the range from 70 to 150 nm or with two maxima (bimodal pore distribution) in the range from 10 to 150 nm, and a median pore diameter between 30 and 50 nm;
• and
• maintaining the pH of the water at not more than pH 8.