Selective Transformation of CO 2 and H 2 into Lower Olefins over In 2 O 3 -ZnZrO x /SAPO-34 Bifunctional Catalysts.

Because lower olefins (C-2(=)-C-4(=)) are important bulk petrochemicals, their direct production from CO2 hydrogenation is highly attractive. However, the selectivity towards C-2(=)-C-4(=) by the modified Fischer-Tropsch synthesis is restricted to 56.7 % with high undesired methane selectivity. Here, a series of bifunctional catalysts containing In2O3-ZnZrOx oxides and various SAPO-34 zeolites with different crystal sizes (0.4-1.5 mu m) and pore structures was developed for the production of lower olefins by CO2 hydrogenation. The C-2(=)-C-4(=) selectivity reached as high as 85 % among all hydrocarbons with very low CH4 selectivity of only 1 % at a CO2 conversion of 17 %. This demonstrated that the small crystal size, hierarchical pore structure, and appropriate amount of Bronsted acid sites of SAPO-34 endowed the bifunctional catalysts with high C-2(=)-C-4(=) selectivity. This work shows an efficient way for developing bifunctional catalysts for direct CO2 hydrogenation to lower olefins.