Promotional Effect of Ni on a CrO_x Catalyst Supported on Silica in the Oxidative Dehydrogenation of Propane with CO₂

Abstract

As CrO_x catalysts supported on the SBA-15 support (Cr/Si) are highly active, they represent potentially promising catalysts for the oxidative dehydrogenation of propane with CO₂ (ODHP). However, reduction of the active sites (Cr³⁺) during the reaction is known to lead to severe deactivation. The findings reported herein indicate that after the addition of 0.5 wt % Ni to 10 wt % Cr/Si (0.5 Ni-Cr/Si), the catalytic activity was stable and the selectivity was high. Reduced CrO_x was easily regenerated by the addition of Ni, as evidenced by a three-step H₂-temperature programmed reduction analysis. In addition, ex situ XPS results revealed that Cr³⁺ was maintained only in the Ni-promoted catalyst whereas Cr³⁺ was easily reduced to Cr²⁺ in the non-promoted catalyst during the reaction. The role of the Ni added to the catalyst elucidates that Ni induces the dissociation of CO₂ to CO and activated O (O*_ads). Then, the generated O*_ads regenerates the reduced CrO_x. Consequently, the Ni-promoted Cr/Si catalyst enhances the catalytic stability of propylene in the ODHP reaction.