Direct synthesis of iso-olefins from carbon dioxide hydrogenation via tandem catalysis

The direct production of iso-olefins using carbon dioxide and hydrogen is a promising alternative to traditional petrochemical routes, but it has not been fully achieved due to the lack of suitable catalysts and processes for the conversion. Herein, we report a tandem process for the direct synthesis of C 4 -C 7 iso-olefins from carbon dioxide and hydrogen. The process proceeds by hydrogenation of carbon dioxide to C 4 -C 7 n-olefins over a potassium-doped ferroferric oxide and subsequent selective isomerization to C 4 -C 7 iso-olefins over a silica-alumina xerogel. A high C 4 -C 7 iso-olefin selectivity of 35.2% with 37.8% CO 2 conversion is obtained. Experiments reveal that the presence of high-density weak Lewis acid sites and the absence of Brønsted acid sites in the silica-aluminum xerogel can inhibit the cracking and hydrogenation of olefin intermediates during isomerization reaction under a hydrogen-rich atmosphere, resulting in the selective formation of C 4 -C 7 iso-olefins with a 6.9 iso-/n-olefin ratio.