Research progress of CO oxidative dehydrogenation of propane to propylene over Cr-free metal catalysts.

CO-assisted oxidative dehydrogenation of propane (CO-ODHP) is an attractive strategy to offset the demand gap of propylene due to its potentiality of reducing CO emissions, especially under the demands of peaking CO emissions and carbon neutrality. The introduction of CO as a soft oxidant into the reaction not only averts the over-oxidation of products, but also maintains the high oxidation state of the redox-active sites. Furthermore, the presence of CO increases the conversion of propane by coupling the dehydrogenation of propane (DHP) with the reverse water gas reaction (RWGS) and inhibits the coking formation to prolong the lifetime of catalysts via the reverse Boudouard reaction. An effective catalyst should selectively activate the C-H bond but suppress the C-C cleavage. However, to prepare such a catalyst remains challenging. Chromium-based catalysts are always applied in industrial application of DHP; however, their toxic properties are harmful to the environment. In this aspect, exploring environment-friendly and sustainable catalytic systems with Cr-free is an important issue. In this review, we outline the development of the CO-ODHP especially in the last ten years, including the structural information, catalytic performances, and mechanisms of chromium-free metal-based catalyst systems, and the role of CO in the reaction. We also present perspectives for future progress in the CO-ODHP.