Co-Promoted In<sub>2</sub>O<sub>3</sub>/ZrO<sub>2</sub> Integrated with Ultrathin Nanosheet HZSM-5 as Efficient Catalysts for CO<sub>2</sub> Hydrogenation to Gasoline
Wenhui Li, Jiaxing Zhang, Xiao Jiang, Minchen Mu, Anfeng Zhang, Chunshan Song, Xinwen Guo
Abstract
Carbon dioxide (CO2) hydrogenation to gasoline through the methanol-mediate route using the metal oxide/ZSM-5 tandem catalyst has attracted considerable attention to reduce the pernicious effect of CO2 on global climate change and to reduce our dependence on fossil fuels. The C5+ molecules are preferred to pass through the straight channels of ZSM-5 zeolite, where side reactions may occur on the acid sites and the catalyst is deactivated due to pore blockage. Thus, the thickness of ZSM-5 along the straight channel, namely the b-axis direction, is crucial to manipulating the product distribution and catalyst lifetime. Here, HZSM-5 nanosheets with different thicknesses (2 nm to 2 μm) along the b-axis were synthesized controllably and composited with In2O3/ZrO2 as tandem catalysts for CO2 hydrogenation to gasoline. In2O3–ZrO2/HZSM-5 with a thickness of 20 nm shows the highest selectivity toward C5+ hydrocarbons under isoconversional conditions and no deactivation after 150 h of reaction with less carbon deposition compared with the 2 μm one. Comparative activity tests and characterization results demonstrate that an appropriate length of straight channels can benefit the production of C5+ hydrocarbons through the polymerization of short-chain molecules while preventing the cracking of long-chain hydrocarbons on acid sites. Adding an appropriate loading of Co into tandem catalysts with optimal composition gives rise to further enhancement in CO2 conversion by 10%, and a slight increase in C5+ selectivity. This can be attributed to the Co-induced hydrogen spillover from metallic Co to support ZrO2, facilitating the formation of the key intermediate and its subsequent hydrogenation steps. This study provides insights into designing effective and anti-carbon deposition tandem catalysts for CO2-to-gasoline by manipulating the channel length–resident time–acidity relationship and the promoter effect.