Effect of Additives on the Reactivity of Palladium Surfaces for the Chemisorption and Hydrogenation of Carbon Monoxide: A Surface Science and Catalytic Study

摘要

This research studied the role of surface additives on the catalytic activity and chemisorptive properties of Pd single crystals and foils. Effects of Na, K, Si, P, S, and Cl on the bonding of CO and H and on the cyclotrimerization of acetylene on the (111), (100) and (110) faces of Pd were investigated in addition to role of TiO sub 2 and SiO sub 2 overlayers deposited on Pd foils in the CO hydrogenation reaction. On Pd, only in the presence of oxide overlayers, are methane or methanol formed from CO and H sub 2 . The maximum rate of methane formation is attained on Pd foil where 30% of the surface is covered with titania. Methanol formation can be achieved only if the TiO/sub x//Pd surface is pretreated in 50 psi of oxygen at 550 sup 0 C prior to the reaction. The additives (Na, K, Si, P, S, Cl) affect the bonding of CO and hydrogen and the cyclotrimerization of acetylene to benzene by structural and electronic interactions. In general, the electron donating additives increase the desorption temperature of CO and increase the rate of acetylene cyclotrimerization and the electron withdrawing additives decrease the desorption temperature of CO and decrease the rate of benzene formation from acetylene. (ERA citation 12:047990)