Hydrogenation of para-chloronitrobenzene over supported ruthenium-based catalysts

Abstract

The catalytic hydrogenation of para-chloronitrobenzene to para-chloroaniline has been investigated over a series of ruthenium catalysts of widely varying dispersions and on supported bimetallics RuM ( M = Sn, Pb, Ge ). The kinetics follow a Langmuir-Hinshelwood mechanism with competitive adsorption of hydrogen and chloronitrobenzene at low or intermediate concentrations of substrate and a zero order at high concentrations. At saturation of the metal surface for the organic substrate, the dipolar interactions in the adsorbed phase then left free some sites for the adsorption of hydrogen. The rate of reaction expressed per surface metal atom is larger on poorly dispersed ruthenium catalysts, and increases upon alloying by tin, lead or germanium. These variations can be accounted for assuming that catalytic activity is larger on the dense planes of the ruthenium particles.