Catalytic oxidation of CO on Sodium-treated NiO/Al 2O 3 solid

Abstract

The influence of Na-pretreatment of γ-Al 2O 3 on the catalytic oxidation of CO over NiO/Al 2O 3 was investigated. The effect of such treatment on the concentration of the catalytically active phase (NiO) in the uppermost surface layers of the catalyst was also studied by the X-ray photoelectron spectroscopic investigation of various solids. The results revealed that the addition of Na 2O (0.45 wt%) decreased the catalytic activity (reaction rate constant per unit surface area) of the pretreated solid. However, the activity was found to increase monotonically by increasing the amount of sodium added in the range 1.35–6 wt%. The sodium-pretreatment of γ-Al 2O 3 resulted in a decrease in the concentration of Ni on the catalyst surface to an extent proportional to the amount of Na2O present. These findings have been attributed to blocking of some sites of Al2O3 surface by Na+ ions thus decreasing the amount of Ni 2+ ions retained on its surface. The observed increase in catalytic activity of sodium-treated solid (containing more than 0.45 wt%) might be due to dissolution of some Na + ions in the NiO lattice which lowered its Fermi-level, leading to an increase in the degree of p-type semiconducting character of the doped NiO catalyst.