Insight into forced hydrogen re-arrangement and altered reaction pathways in a protocol for CO2 catalytic processing of oleic acid into C8–C15 alkanes

Abstract

A new vision of using carbon dioxide (CO₂) catalytic processing of oleic acid into C₈–C₁₅ alkanes over a nano-nickel/zeolite catalyst is reported in this paper. The inherent and essential reasons which make this achievable are clearly resolved by using totally new catalytic reaction pathways of oleic acid transformation in a CO₂ atmosphere. The yield of C₈–C₁₅ ingredients reaches 73.10 mol% in a CO₂ atmosphere, which is much higher than the 49.67 mol% yield obtained in a hydrogen (H₂) atmosphere. In the absence of an external H₂ source, products which are similar to aviation fuel are generated where aromatization of propene (C₃H₆) oxidative dehydrogenation (ODH) involving CO₂ and propane (C₃H₈) and hydrogen transfer reactions are found to account for hydrogen liberation in oleic acid and achieve its re-arrangement in the final alkane products. The reaction pathway in the CO₂ atmosphere is significantly different from that in the H₂ atmosphere, as shown by the presence of 8-heptadecene, γ-stearolactone, and 3-heptadecene as reaction intermediates, as well as a CO formation pathway. Because of the highly dispersed Ni metal center on the zeolite support, H₂ spillover is observed in the H₂ atmosphere, which inhibits the production of short-chain alkanes and reveals the inherent disadvantage of using H₂. The CO₂ processing of oleic acid described in this paper will significantly contribute to future CO₂ utilization chemistry and provide an economical and promising approach for the production of sustainable alkane products which are similar to aviation fuel.