Hydrogen-water deuterium exchange over nickel-chromia supported on alumina: II. Catalytic activities and effectiveness factors

Abstract

The activities of nickel and nickel-chromia on alumina catalysts for hydrogen-water deuterium exchange were measured with 5.5 mm diameter spheres in a fully mixed, fixed bed reactor and with powder of the same catalysts in a packed bed, flow reactor. The promoting effect of chromia on the alumina supported nickel was not as large as it was for coprecipitated nickel-chromia catalysts. There was evidence that the alumina support was, itself, acting as a promotor. The activity was not affected by the nature of the anions in the impregnating solution used to prepare the catalyst, except for nickelous sulfate which gave much lower rates. Powdered catalysts had a higher activity than large particles unless the nickel was in only the outer layers of the spheres. When the nickel was uniformly distributed throughout the spheres, the effectiveness factors could be calculated satisfactorily from the model of Wakao and Smith [ Ind. Eng. Chem. Fundam. 3, 123 (1964)]. This model was less satisfactory when the catalyst structure was altered by multiple impregnations followed by calcining. When the water pressure was much less than the hydrogen pressure, low effectiveness factors resulted largely from the slow diffusion of water in and out of the pores.