Sustainable Ni/Ca 1−xSr xTiO 3 catalyst prepared in situ for the partial oxidation of methane to synthesis gas

Abstract

A series of mixed metal oxides of the compositions Ca 1− x Sr x Ti 1− y Ni y O ( x = 0–1.0, y = 0–1.0) were prepared by the citrate method, and was tested for the oxidation of CH 4 to synthesis gas. Analytical results clearly showed the presence of Ca 1− x Sr x Ti 1− y Ni y O perovskite structure, where Sr substituted all the Ca sites while Ni substituted the Ti sites in the range of y < 0.1. Among the catalysts tested, the compositions of x = y = 0.2 showed the highest activity. Either Ni species in the Ca 0.8Sr 0.2Ti 1− y Ni y O perovskite structure or NiO originally separated from the perovskite structure during the preparation was in situ reduced to Ni metal during the CH 4 oxidation. The Ni metal thus formed showed high activity for synthesis gas production, where Ca 0.8Sr 0.2TiO 3 perovskite has an important role as a carrier of the Ni catalyst. Three catalysts of the composition Ca 0.8Sr 0.2Ti 1.0Ni 0.2O were then prepared by citrate, impregnation and mixing methods. The highest activity was obtained with the citrate, followed by the impregnation of Ni on Ca 0.8Sr 0.2TiO 3 perovskite. The catalyst prepared by the mixing method afforded no perovskite, resulting in low activity. The amount of coke formation over the Ni catalysts after the reaction for 150 h was as follows: citrate < impregnation ⪡ Ni γ-Al 2O 3 as the comparison. Ca 0.8Sr 0.2TiO 3 perovskite was effective as the carrier of the Ni catalyst for the partial oxidation of CH 4 to synthesis gas. Ni/Ca 0.8Sr 0.2TiO 3 prepared by the citrate method is the most sustainable against coke formation during the reaction. It is likely that the citrate method gave high Ni dispersion over the perovskite as well as strong metal-support interaction between Ni and the perovskite, resulting in both high activity and high sustainability against coke formation.