Evaluation of deactivation mechanisms of Pd-catalyzed hydrogenation of 4-isobutylacetophenone

Pd catalysts were investigated for the hydrogenation of 4-isobutylacetophenone (4-IBAP) and for Pd/SiO2 an improved (compared with the non-patented literature) yield of nearly 80% of the desired product 1-(4-isobutylphenyl)ethanol (4-IBPE) was obtained. However, severe catalyst deactivation was observed. The spent catalyst was characterized using a wide variety of thermal (TGA, TPO-MS), microscopic (TEM), and spectroscopic (DRIFT, LEIS) characterization techniques. Pd leaching did not occur. Oligomerization of 4-IBAP by condensation reactions due to the acidity imparted by the presence of isolated silanol groups on SiO2 is proposed as one of the causes of catalyst deactivation. Pd crystallite growth and strong chemisorption of the H2O liberated by 4-IBPE hydrogenolysis also contributed to the loss of catalytic activity. The conclusions are supported by the high stability of Pd black in catalyzing the reaction.