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/ZnO/Al2O3 catalyst with and without a nickel promoter. The addition of a small amount of nickel can effectively enhance the activity of the Cu/ZnO/Al2O3 catalysts. A strong interaction between Ni2+ ions and Al2O3 is the main factor causing an increase in the catalytic activity of Cu/ZnO/Al2O3. Owing to the formation of CuAl2O4, complete reduction of the Cu/ZnO/Al2O3 catalyst is difficult, even if pretreated by reduction at 573 K for 5 h. As Ni2+ ions complex with Al2O3 in the copper catalyst and form NiAl2O4, they weaken the interaction between Cu2+ and Al2O3, leading to enrichment of the catalyst surface in Cu2+ 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 Cu0 by H2.