HYDROGENATION OF 3-METHYL-BUTENAL ON PT(110) - COMPARISON WITH PT(111)

The gas-phase hydrogenation of 3-methyl-butenal or prenal, was studied , at temperature equal to 353 K, on the (110) plane of platinum and co mpared to previous results obtained on Pt(111). The selectivity was fo und to be very structure sensitive. This has been ascribed to steric f actors which determine when the unsaturated bond is on a substituted c arbon atom. The combination of the use of well characterized surfaces as catalysts, and of the determination of the kinetics of the reaction led us to propose a Langmuir-Hinshelwood type mechanism. The nature o f the reaction intermediates, di-sigma or tetra-sigma activated adsorb ed species, depends upon the reactant pressure and upon the geometry o f the surface. This catalytic study on model surfaces is of particular interest in understanding the selectivity of real catalysts whose ato mic arrangement is possibly defined and controlled.