Influence of Zn and Fe promoters on Ni-Bi/γ-Al2O3 catalyst for oxidative dehydrogenation of n-butane to butadiene

This study investigated the effects of Zn and Fe metal oxide species as promoters on NiO-Bi2O3/γ-Al2O3 in the oxidative dehydrogenation (ODH) of n-butane to produce butadiene. Ni-Bi-O, Ni-Zn-Bi-O, Ni-Fe-Bi-O, and Ni-Zn-Fe-Bi-O catalysts supported on γ-Al2O3 were synthesized, characterized, and evaluated in a packed bed flow reactor at different temperatures and O2/n-butane molar ratios. Substituting 50 wt.% of Ni with one or both promoters were found to enhance both the butadiene selectivity. Among the synthesized catalysts, Ni-Zn-Fe-Bi-O/γ-Al2O3 (10 wt.% Ni-5 wt.% Zn-5 wt.% Fe-30 wt.% Bi) showed the highest butadiene selectivity of 49.0% with 18.6% n-butane conversion at 450 °C and a molar feed ratio of O2/n-butane = 2.0. This enhanced performance was attributed to the synergetic effects of Ni, which simultaneously improved the first-step dehydrogenation selectivity via a promotion with Zn and the second-step dehydrogenation selectivity by the incorporation of Fe. Moreover, Zn allowed the surface reduction to occur at lower temperatures, while Fe balanced the densities of strong basic sites with weak and moderate acid sites (0.183 mmol CO2/g-cat and 0.188 mmol NH3/g-cat, respectively). The aforementioned results were confirmed with CO2/NH3 temperature-programmed desorption and H2 temperature-programmed reduction experiments. Under this reaction condition, the catalyst maintains good stability over 15 h of time-on-stream.