Role of zirconium in direct CO2 hydrogenation to lower olefins on oxide/zeolite bifunctional catalysts.

Direct production of lower olefins (C 2 = −C 4 = : ethylene, propylene and butylene), basic carbon-based building blocks, from carbon dioxide (CO 2 ) hydrogenation is highly attractive, although the selectivity towards olefins has been too low. Here we present a series of bifunctional catalysts contained indium-zirconium composite oxides with different In:Zr atomic ratios and SAPO-34 zeolite, which can achieve a selectivity for C 2 = –C 4 = as high as 65–80% and that for C 2 –C 4 of 96% with only about 2.5% methane among the hydrocarbon products at CO 2 conversion of 15–27%. The selectivity of CO via the reverse water gas shift reaction is lower than 70%. The product distribution is completely different from that obtained via CO 2 -based Fischer-Tropsch synthesis and deviates greatly from the classical Anderson-Schulz-Flory distribution. The zirconium component plays a critical role in determining the physicochemical properties and catalytic performance of bifunctional catalysts. Catalyst characterization and density functional theory calculations demonstrate that the incorporation of a certain amount of zirconium can create more oxygen vacancy sites, stabilize the intermediates in CO 2 hydrogenation and prevent the sintering of the active nanoparticles, thus leading to significantly enhanced catalytic activity, selectivity of hydrocarbons and stability for direct CO 2 hydrogenation to lower olefins at the relatively high reaction temperature of 380 °C. [ABSTRACT FROM AUTHOR]