THE ELECTROCATALYTIC HYDROGENATION OF GLUCOSE .1. KINETICS OF HYDROGEN EVOLUTION AND GLUCOSE HYDROGENATION ON RANEY-NICKEL POWDER

The kinetics of H-2 evolution and glucose reduction to sorbitol was investigated using a batch slurry reactor containing Raney nickel powder catalyst. In the presence and absence of glucose, hydrogen evolution proceeds via a Volmer-Heyrovsky mechanism, with both steps simultaneously rate controlling at low overpotentials and the Volmer reaction rate limiting at high cathodic overvoltages. A kinetic model for the electrocatalytic hydrogenation of glucose with simultaneous H-2 generation was developed and tested. The model contains rate equations for the individual Volmer, Heyrovsky, and glucose hydrogenation steps, a Langmuir adsorption isotherm for glucose, an equation describing the shift in open-circuit potential due to glucose adsorption on the nickel catalyst, and steady-state atomic hydrogen and charge balance relationships. The theory accurately predicted potentiostatic polarization data and glucose hydrogenation rates. The results indicate that the mechanism for sorbitol formation with electrogenerated atomic hydrogen on Raney nickel is the same as that for the high temperature and pressure chemical catalytic hydrogenation process.