Chemical Modification of Chemisorptive and Catalytic Properties of Nickel

Several reactions representing important categories of catalytic systems have been studied on chemically modified single crystal surfaces. These reactions are methanation of CO and CO:. hydrogenolysis of ethane. hydrogenation of ethylene. and q&propane ring-opening and hydrogenolysis. Poisoning of the above reactions by ordered. suhmonolayer coverages of sulfur shou large nonlinear effects for sulfur coverages versus reactivity attenuation. These data together with related chemisorption results are reviewed with emphasis on the author’s own work. These studies suggest that the dominant effect in poisoning by sulfur is an electronic one and extends over distances larger than the atomic radius. Related studies have addressed the role of potasstum promoters in nickel catalysts for methanation. Potassium decreases the rate of methane formation and increases the rate of higher hydrocarbons relative to the clean nickel surface. Similar results have been reported for supported nickel catalysts suggesttng that support effects play a small role in catalytic promotion by potassium.