Steam reforming of toluene as a biomass tar model compound over CeO2 promoted Ni/CaO–Al2O3 catalytic systems

Abstract

Steam reforming of toluene as a biomass tar model compound was performed over Ni supported CaO–Al2O3 (Ca–Al) and CeO2 promoted CaO–Al2O3 (Ca–Al–Ce) catalysts to explore promotional effect of CeO2 on Ca–Al support. Among all the catalysts tested, Ni/Ca–Al–Ce(0.2) catalyst gave superior catalytic performance over other catalysts. The basic strength of catalytic supports measured by CO2 TPD and Hammett indicator methods indicates Ca–Al–Ce(0.2) support has higher surface basicity and base strength compared to Ca–Al and other Ca–Al–Ce(x) supports. Furthermore, CO pulse chemisorption results showed that Ni/Ca–Al–Ce(0.2) catalyst has a higher amount of surface metallic nickel compared to other Ni/Ca–Al–Ce catalysts. TPR analysis reveals that the redox property of CeO2 can enhance the reducibility of supported nickel species, which is further confirmed using XPS analysis, where addition of CeO2 enhanced the interaction of Ni species with Ce by reducing the interaction of Ni species with the Al support, resulting in the formation of Ni° rich surface. However, formation of bulk NiO species was also observed for the catalyst having higher amount of CeO2. TGA analysis on spent catalysts reveals that all CeO2-containing catalysts generally result in lower carbon formation rates as compared to Ni/Ca–Al catalyst.