HYDROGENATION OF PROPYNE OVER PALLADIUM CATALYSTS

The hydrogenation of propyne on a range of supported palladium catalysts has been investigated. The catalysts all showed 100% selectivity to propene. A non-steady-state regime was observed when the catalysts were brought on line. During this period there was significant carbon laydown resulting in a surface Pd:C ratio of 1:3 with two of the catalysts tested. Once this level of laydown was reached, steady-state operation was achieved. In the steady state the amount of carbon laydown was reduced and activity was reproducible; the orders of reaction for propyne and dihydrogen were obtained. The order with respect to dihydrogen varied between 1.3 for the Pd/zirconia to 0.6 for the Pd/silica, while the order for propyne varied between 0.0 and 0.4. Analysis of the surface species by infrared spectroscopy revealed the presence of a horizontal and vertically bonded propyne, a di-sigma adsorbed propene and propylidyne. A mechanism for the reaction system has been postulated.