Acetylene hydrogenation on sol-derived Pd/SiO2

Pd/SiO2 (1.08 wt.%) catalyst has been synthesised via sot-derived route using poly(diallyldimethylammonium chloride) (PDDA) polycation as ionic stabiliser. The immobilised sot (monomer/Pd2+ = 1.25) fixed at pH = 8.5 onto Aerosil 200 contains Pd particles of 3.1 nm number-mean diameter. The catalyst prepared was subjected to various treatments and the obtained samples were characterised by transmission electron microscopy (TEM), CO and O-2 chemisorption, and temperature programmed oxidation (TPO) and temperature programmed desorption (TPD). The immobilised sot showed good thermal stability but oxidation of PDDA to get "polymer free" sample causes sintering of Pd particles. Initial activities and product selectivities for hydrogenation of acetylene in propene were recorded. The immobilised sample even in "as prepared state" possesses hydrogenation activity. Treatments at different temperatures in H-2 or Ar enhance the catalytic activity suggesting an increase in space around the metal particle. The PDDA modified sample exhibits better competition selectivity than the "polymer free" sample pointing to surface structure variations caused by geometric/steric effects. (C) 2003 Elsevier B.V. All rights reserved.