PALLADIUM-ENHANCED REDUCIBILITY OF NICKEL IN NAY

The presence of palladium has been found to strongly enhance the reducibility of nickel in NaY. Pretreatment conditions have a pronounced effect on the temperature-programmed reduction (t.p.r.) profiles of monometallic and bimetallic palladium/nickel catalysts. At high pH, Ni is hydrolyzed in supercages; at low pH, Ni2+ ions migrate to smaller cages. Reduced Pd particles in the supercages, in close contact with NiO clusters, enhance their reducibility; the protons formed during Pd reduction, however, redisperse them to form Ni2+ ions, thus decreasing their reducibility. Two mechanisms are thought to contribute to the Pd-enhanced reduction of Ni2+ ions. One involves the formation of NiPd ion pairs in the small cages; the other requires migration of Ni2+ ions out of small cages to interact with reduced Pd particles in supercages. © 1990.