The effect of a nickel promoter on the reducibility of a commercial Cu/ZnO/Al2O3 catalyst for CO oxidation

CO oxidation was studied for a commercial Cu/ZiiO/Al(2)O(3) catalyst with and without a nickel promoter. The addition of a small amount of nickel can effectively enhance the activity of the Cu/ZnO/Al(2)O(3) catalysts. A strong interaction between Ni(2+) ions and Al(2)O(3) is the main factor causing an increase in the catalytic activity of Cu/ZnO/Al(2)O(3). Owing to the formation of CuAl(2)O(4), complete reduction of the Cu/ZnO/Al(2)O(3) catalyst is difficult, even if pretreated by reduction at 573 K for 5 h. As Ni(2+) ions complex with Al(2)O(3) in the copper catalyst and form NiAl(2)O(4), they weaken the interaction between Cu(2+) and Al(2)O(3), leading to enrichment of the catalyst surface in Cu(2+) ions. This Ni addition could induce the aggregation of Cu atoms on the surface into larger Cu particles, possibly leading to a lower Cu surface area or easy reduction to Cu(0) by H(2). (C) 2007 Elsevier B.V. All rights reserved.