The Role of Ni Species Distribution on the Effect of Ce as a Promoter in C2-ODH Reaction

Abstract

The aim of work was to analyse and discuss the effect of cerium on the catalytic behaviour of different types of nickel species in the oxidative dehydrogenation of ethane. Ni–Al and Ni–Ce–Al catalysts were prepared from cerium nitrate and nickel nitrate or nickel acetate as a precursor. As-prepared materials were characterized by using of XRD, DR UV–Vis spectroscopy and H2-TPR. It was found that the addition of cerium affects both the reducibility of nickel species and the population of nickel species. Firstly, the addition of cerium led to the significant decrease of the reduction peak at 755–785 °C to about 40 °C due to the Ni–Ce interaction at both Ni–Ce–Al–NO3 and Ni–Ce–Al–ac catalysts. Secondly, the addition of cerium affected the relative population of nickel species in tetrahedral and octahedral coordination, which population originated from used nickel precursor. The presence of cerium in Ni–Ce–Al–NO3 catalysts led to the decrease in the relative population of Ni(T d ) species, while the crystal size of NiO in Ni–Ce–Al–ac catalysts decreased with increasing Ce/Ni ratio. The highest ethylene productivity was achieved on catalysts with Ce/Ni molar ratio 0.13. Catalysts exhibited an ethylene productivity up to 1.0 gC2=·g cat −1 ·h−1 with a selectivity of 82 % (Ni–Ce–Al–NO3) and 1.3 gC2=·g cat −1 ·h−1 with a selectivity of 75 % (Ni–Ce–Al–ac).