Water–Gas Shift Activity over Ni/Al2O3 Composites

The water–gas shift (WGS) performance of 10%Ni/Al2O3, 20%Ni/Al2O3 and 10%Ni/CaO-Al2O3 catalysts was studied to reduce CO concentration and produce extra hydrogen. Ni was added onto the Al2O3 support by an impregnation method. The physicochemical properties of nickel catalysts that influence their catalytic activity were examined. The most influential factors in increasing the CO conversion for the water–gas shift reaction are Ni dispersion and surface acidity. Ni metal sites were identified as the active sites for CO adsorption. The main effect of nickel metal was reducing the adsorbed CO amount by reducing the active site concentration. The 10%Ni/Al2O3 catalyst was more active for the WGS reaction than other catalysts. This catalyst presents a high CO conversion rate (75% CO conversion at 800 °C), which is due to its high Ni dispersion at the surface (6.74%) and surface acidity, thereby favoring CO adsorption. A high Ni dispersion for more surface-active sites is exposed to a CO reactant. In addition, favored CO adsorption is related to the acidity on the catalyst surface because CO reactant in the WGS reaction is a weak base. The total acidity can be evaluated by integrating the NH3-Temperature-Programmed Desorption curves. Therefore, an enhancement of surface acidity is identified as the favored CO adsorption.