CO 2 -assisted oxidative dehydrogenation of propane (CO 2 -ODHP) is an attractive strategy to offset the demand gap of propylene due to its potentiality of reducing CO 2 emissions, especially under the demands of peaking CO 2 emissions and carbon neutrality. The introduction of CO 2 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 2 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 2 -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 2 in the reaction. We also present perspectives for future progress in the CO 2 -ODHP.

The Fe-doped silicalite-1 zeolite as a matrix was employed to implant GaN nanocrystallites via a combined wet impregnation with in situ nitridation method. Direct spectroscopic evidences under a vacuum unraveled that the incorporation of the isolated framework Fe atoms could cause the generation of more interior silanols and especially hydrogen-bonded groups of silanol nests, where the solvated Ga3+ ions and urea in an N2 atmosphere at high temperatures were transformed into the highly dispersed GaN nanocrystallites that were embedded simultaneously in defects of the Fe-silicalite-1 matrix with the binding structure of Si–O–GaN. Moreover, the particle size distribution of GaN can be tuned from the nanoscale (14.6 ± 3.5 nm) to sub-nanoscale (2.7 ± 0.4 nm) by regulating the molar ratio of Si/Fe. Combining the results of the temperature-programmed surface reaction (TPSR) with the measurements of temperature-programmed desorption and mass spectra (TPD-MS) using the probe molecules of C3H8 and CO2, it was proposed that isolated framework Fe species were active sites for the catalytic conversion of CO2, while the nanostructured GaN was responsible for the adsorption and activation of C3H8. Catalytic results and kinetics show that the CO2-assisted oxidative dehydrogenation of propane (CO2-ODHP) over GaN/Fe-silicalite-1 proceeds by following a two-step coupling process (direct dehydrogenation of propane (DDP) + reverse water gas shift (RWGS)) and also is a structure-sensitive reaction characterized by the dependence of GaN particle size on the specific catalytic activity and apparent activation energy of converting C3H8 and CO2. Without the occurrence of GaN sintering, the slight loss of catalytic activity caused by coke deposition was confirmed by linearly correlating the normalized amount of coke with the deactivation rate.