Pd/TiO2 catalysts were modified by exposure to triphenylphosphine to assess the impact of the presence of the ligand on the selective removal of acetylene from ethylene rich feeds. The ligand modified metal created a catalyst which showed significantly improved selectivity as a result of a decrease in the extent of over-hydrogenation of ethylene to ethane. The physical presence of the ligand modifier is thought to create sites which permit adsorption of acetylene but hinder access of ethylene to metal sites. In addition, the rate of acetylene hydrogenation appeared to be enhanced in the presence of the modifier consistent with a promotional effect. A potential contribution to enhanced selectivity due to suppression of sub-surface hydrogen formation/diffusion cannot be discounted.
We thank SABIC for funding a studentship (F. M. M.) and permission to publish this work and Dr. A. M. Ward (SABIC) and Dr R. P. K. Wells (University of Aberdeen) for useful discussions and contributions. We are also grateful to Prof. C.Hardacre and Ms. L. Mantarosie, Queen's University Belfast for performing preliminary high pressure testing on these catalysts. We also thank MKS Instruments for the loan of the Cirrus QMS instrument.