Bifunctional catalyst MoS_x@H-Beta for highly selective conversion of CO₂ to C_2-6 hydrocarbons

We report here a bifunctional catalyst MoSx@H-Beta for highly selective conversion of CO2 to C2-6 hydrocarbons. The catalyst is prepared using a two-step solid reaction method. Firstly, MoOx@H-Beta, with MoOx+ clusters at the exchangeable site of the zeolite, is obtained by sublimating and reacting MoO3 with zeolitic H+ sites during heating. Then, MoOx@H-Beta is converted into MoSx@H-Beta through a vulcanization reaction, by heating the mixture of MoOx@H-Beta and sulphur powder in flowing 5 vol% H-2/N-2. During the vulcanization of molybdenum oxide clusters, the zeolitic H+ sites are recovered. Two types of active sites, i.e., molybdenum sulfide clusters and the zeolitic H+ sites, are intimately encapsulated in channels of the MoSx@H-Beta catalyst. Over the catalyst, more than 75% of selectivity to C2-6 hydrocarbons in organic products at similar to 13% of CO2 conversion is obtained under the optimal reaction conditions of 300 degrees C, 4 MPa, CO2/H-2 = 1/3, and 1600 mL g(-1) h(-1). The characterization results indicate that CO2 is firstly hydrogenated into intermediate CH3OH over the MoSx sites, which is subsequently converted into C2-6 hydrocarbons over the adjacent Br & oslash;nsted acid sites in channels of H-Beta zeolite. The MoSx clusters are highly dispersed and occupied in channels of H-Beta zeolite, exhibiting an excellent stability during 200 h on stream. The cooperative mechanism between molybdenum sulfide clusters and Br & oslash;nsted acid sites of H-Beta zeolite constitutes the nature of a bifunctional catalyst, demonstrated by theoretical calculations, well accounting for its high catalytic performance.