Selective Light Hydrocarbon Production from CO<sub>2</sub> Hydrogenation over Na/ZnFe<sub>2</sub>O<sub>4</sub> and CHA-Zeolite Hybrid Catalysts
Eun Cheol, Kwang Hyun Kim, Ju Hyeong Lee, Ju Hyeong Lee, Sejin Jang, Hyo Eun Kim, Jin Ho Lee, Jin Ho Lee, Eun Hyup Kim, Haneul Kim, Ja Hun Kwak, Jae Sung Lee, Jae Sung Lee
Abstract
Carbon dioxide hydrogenation to value-added fuels and chemicals has been studied widely as a means to recycle the most-troublesome greenhouse gas. The reaction produces hundreds of different chemicals, and therefore, selectivity control toward specific desired products is of paramount importance. In this study, a hybrid catalyst system consisting of Na/ZnFe 2 O 4 (ZFO) and a CHA-zeolite (SSZ-13 or SAPO-34) is developed to maximize C 2 –C 4 light hydrocarbon production. Utilizing the compact 3.8 Å pore size of CHA-zeolites, the Na/ZnFe 2 O 4 catalyst-produced long-chain hydrocarbons are efficiently shortened to C 2 –C 4 hydrocarbons with over 55% selectivity in the hybrid systems. Notably, ZFO + SAPO-34 shows a preference for light olefins, while ZFO + SSZ-13 uniquely enhances selectivity for C 3 products. The difference is attributed to the much stronger acid sites present in SSZ-13 than in SAPO-34, which promote hydrogenation of olefins and the ethylene-to-propane conversion reaction in particular. Further modification of SSZ-13 with steam treatment leads to the dealumination of its framework and an enhanced activity of the ethylene-to-propane reaction, yielding 32.8% of C 3 -selectivity. Accordingly, a hybrid catalytic system combining a CO 2 Fischer–Tropsch catalyst with a CHA-zeolite is a promising route to produce light hydrocarbons from CO 2 hydrogenation more selectively than single catalysts. This work also demonstrates that acidity control could be a powerful tool to manipulate the reaction pathway that occurs on zeolite catalysts.