Partial oxidation of propane over Ru promoted Ni/Mg(Al)O catalysts: Self-activation and prominent effect of reduction–oxidation treatment of the catalyst Original Research Article

Ru (0.1–0.5 wt%) loaded Ni/Mg(Al)O catalysts have been prepared by adopting the “memory effect,” i.e., the reconstitution of Mg(Ni)–Al hydrotalcite from the Mg(Ni, Al)O periclase after the heat-treatment, and their catalytic activities have been tested in the partial oxidation of propane. The Ru–Ni0.5/Mg2.5(Al)O catalysts were prepared by dipping Mg2.5(Al,Ni0.5)O periclase derived from Mg2.5(Ni0.5)–Al hydrotalcite in an aqueous solution of Ru(III) nitrate. The reconstitution of hydrotalcite took place by the “memory effect” and was simultaneously accompanied by Ru incorporation in the hydrotalcite layer, leading to the formation of the active Ni–Ru bimetal loaded catalyst after the calcination followed by the reduction. Upon O2 purging at 700 °C during the propane partial oxidation at 600 °C, the Ru–Ni0.5/Mg2.5(Al)O catalyst showed no deactivation, while the Ni0.5/Mg2.5(Al)O catalyst was totally deactivated by the Ni oxidation. Moreover, the Ru–Ni0.5/Mg2.5(Al)O catalysts were self-activated under the reaction conditions without reduction pre-treatment with H2. The activity of the Ru–Ni0.5/Mg2.5(Al)O catalysts was enhanced with increasing the Ru loading after the reduction–oxidation pretreatment. After the treatment, two types of Ni reduction peak were observed in the TPR of the catalysts: the 1st peak observed around 550 °C was weakened, whereas the 2nd peak observed around 750 °C was enhanced, with increasing the Ru loading. The 1st is assigned to non-active Ni2+ ions having square-pyramidal coordination in the outermost layer of the Mg(Al)O structure, while the 2nd is probably of active Ni–Ru bimetallic species composed of finely dispersed Ni metal particles combined with Ru.