Syngas to Olefins over a CrMnGa/SAPO-34 Bifunctional Catalyst: Effect of Cr and Cr/Mn Ratio

Metal oxide in a bifunctional catalyst plays crucial roles in catalytic activity for syngas conversion to olefin (STO). Here, ternary co-precipitated CrMnGa oxides with various Cr/Mn ratios were prepared and combined with SAPO-34 for an STO reaction. By adjusting the Cr:Mn:Ga atomic ratio to 3:2:1, a high CO conversion (43.5%) with light olefin selectivity (87.0%, CO2 free) is achieved under the reaction conditions of 400 °C, 3.0 MPa, and 3000 mL·h–1·g–1. The increase in the Cr/Mn ratio facilitated the CrMnGa catalyst reduction and enhanced surface oxygen vacancies contents and H2 dissociation ability. The mechanism reveals that *CH3O species act as the reaction intermediate for the reaction of CO with the surface OH group and the subsequent hydrogenation. More importantly, the introduction of Cr enhanced the CO activation ability at high temperatures and thus provided a well temperature match for intermediate generation over CrMnGa oxide and further transformation into light olefin over SAPO-34. This study provides a strategy for rational design of highly active metal oxides, which could be used to combine with other zeolites for syngas conversion to high value-added chemicals.