A comparative study of Pd supported on MCM-41 and SiO2 in the liquid phase hydrogenation of phenyl alkyl acetylenes mixtures

Competitive hydrogenation reactions between phenyl alkyl acetylenes over Pd/MCM-41 and Pd/SiO2 catalysts have been studied. The catalysts were prepared by impregnation MCM-41 and SiO2 with Pd(acac)2 precursor, with metal content close to 1 wt.%. All the supports were characterised by nitrogen adsorption-desorption isotherms at 77 K, XRD, TGA measurements. The catalysts were characterized by H, and CO chemisorption, XPS and TEM measurements. Three competitive reaction systems I-phenyl-i-pentyne/1-phenyl-1-propyne, Iphenyl-1-pentyne/1-phenyl-l-butyne, 1-phenyl-1-butyne/1-phenyl-1-propyne have been examined. The results show that the competitive reaction results in an increase of the hydrogenation rate for phenyl alkyl acetylene with minor alkyl chain size in all studied systems. However, the 1-phenyl-1-pentyne/1-phenyl-1-propyne couple revealed a rate enhancement for 1-phenyl-1-propyne, but 1-pheny-1-pentyne single activity is higher than 1-phenyl- 1 -pentyne mixture, being the hydrogenation of 1 -phenyl- 1 -propyne more favoured. Kinetic analysis of the reactions revealed that often the hydrogenation of the phenyl alkyl acetylenes is a zero order in a competitive environment. 1 -Phenyl-1 -propyne was very sensitive to the presence of the second phenyl alkyl acetylene. Competitive hydrogenation also increases the selectivity to the respective alkenes as can be expected from the competition for active sites. (c) 2005 Elsevier B.V.. All rights reserved.