Steam reforming of toluene as a biomass tar model compound over CeO_2 promoted Ni/CaO-Al_2O_3 catalytic systems

摘要

Steam reforming of toluene as a biomass tar model compound was performed over Ni supported CaO-Al_2O_3 (Ca-Al) and CeO_2 promoted CaO-Al_2O_3 (Ca-Al-Ce) catalysts to explore promotional effect of CeO_2 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 CO_2 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 CeO_2 can enhance the reducibility of supported nickel species, which is further confirmed using XPS analysis, where addition of CeO_2 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 CeO_2. TGA analysis on spent catalysts reveals that all CeO_2-containing catalysts generally result in lower carbon formation rates as compared to Ni/Ca -Al catalyst.