Study of NiO/Al2O3 and NiO/Zn-Al2O3 catalysts for water gas shift reaction

Abstract

Nickel-based catalysts are of great importance for the generation of hydrogen from natural gas. Within this process, the conditions in which commercial NiO/Al2O3 is converted to Ni0/Al2O3 catalyst should be further investigated. A widely used technique to identify Ni2+ reduction conditions and the different compounds or types of particles in which this element is present is temperature-programmed reduction. In this work, the type of nickel oxide particles occurring on Al2O3 and ZnO-Al2O3-based supports were studied by different techniques, such as energy-dispersive X-ray spectroscopy, FTIR, the BET method, X-ray diffraction (XRD), and Temperature Programmed Reduction (TPR). All materials were evaluated in the water gas shift reaction (WGS), and the influence of their characteristics on the catalytic activity was assessed. Solids were prepared at different temperatures and Ni/Zn molar ratios. The results showed the presence of NiO in all materials, as well as the presence of ZnO, NiAl2O4, and ZnAl2O4 in materials prepared at higher temperatures. In all the materials calcined at the lowest temperature, the formation of NiO particles that fail to interact with the supports was prioritized. As the calcination temperature increased, NiO aggregates were formed, which, to a greater degree, interacted with the supports, whereby nickel aluminate was detected in all materials prepared at 750 °C. Zinc increased the selectivity but decreased specific surface area and activity through the WGS reaction. The solid labeled AZ15-500 showed higher activity and selectivity, reaching values of 100% for the water gas shift reaction.