Gerhard P. Nowack

Nickel arsenide for selective hydrogenation of diolefins

Abstract Precipitated nickel arsenate on alumina after reduction in hydrogen at 420 °C to nickel arsenide, nominally Ni 3 As 2+x , is a very active and selective catalyst for hydrogenation of diolefins to the corresponding olefin, provided some catalyst modifier is present. Kinetic data obtained by following the hydrogenation of 1,5-cyclooctadiene, using carbon monoxide as a catalyst modifier, indicate the reaction proceeds by a series of reversible isomerization steps to the 1,3-conjugated diene which is hydrogenated to the corresponding olefin. Integrated rate equations which correlate the conversion-flow rate data show the reaction rates to be fractional order in both hydrogen and diene concentrations with isomerization and hydrogenation steps inhibited by carbon monoxide. It appears that carbon monoxide competes with dienes for sites and is more tightly held than the monoene. In effect, the adsorption of carbon monoxide excludes the monoene from further reaction on nickel arsenide.