Sol–gel synthesis of Ni/Al2O3 catalysts for toluene reforming: Support modification with alkali, alkaline earth or rare-earth dopant (Ca, K, Mg or Ce)

Abstract

In this study, the influence of alkali, alkaline earth or rare-earth dopant (i.e. Ca, K, Mg or Ce) addition in 10 wt% Ni/γ-Al2O3 catalyst were studied on the material physicochemical properties and catalytic activity. Twelve doped Ni/γ-Al2O3 catalysts were synthesized by sol–gel process in aqueous medium. One Ni/γ-Al2O3 catalyst without dopant was also synthesized as reference material. The addition of 1.5 wt% of alkali (i.e. Ca, K or Mg) did not influence the acido-basicity properties of the catalysts due to low interactions with the support. All samples doped with 1.5 wt% of oxide (i.e. Ca, K, Mg or Ce) presented a decrease of benzene selectivity up to 73% and a decrease of the amount of carbon deposit up to 40%. These results were attributed to a higher degradation of the intermediate compounds of toluene and the carbonaceous compounds because of a higher amount of H2O and CO2 molecules adsorbed on these oxides. Among the different compositions of Ni/γ-Al2O3 catalysts doped with two different types of oxides (i.e. K+Ca) showed the most interesting performances with an increase of 20% in conversion and a decrease of 10% in carbon deposition. Therefore, it showed that low-cost elements (as Ca and K) can be added in small amount to increase the catalytic properties without the need of the expensive ceria element.