A novel alkylation process of benzene with CO2 and H2 over bifunctional ZnxCeyZrzO/Z5 catalyst

Abstract

The synergy between the two active sites in Zn 3 Ce 1 Zr 3 O that the active hydrogen atoms provided by ZnO species hydrogenated the adsorbed CO 2 at adjacent oxygen vacancy of cerium zirconium solid solution effectively improved the CO 2 hydrogenation selectivity. While the HZSM-5 zeolite with moderate acidity was beneficial to the rapidly alkylation of methoxy intermediate with benzene. Coupling Zn x Ce y Zr z O with HZSM-5 could contribute to the well kinetic matching between CO 2 activation and alkylation, thus affording an effective bifunctional catalyst Zn x Ce y Zr z O/Z5 for highly selective conversion of benzene with CO 2 and H 2 into toluene and xylene. • In situ alkylation process of benzene with CO 2 and H 2 to produce TX is proposed. • The synergy in Zn x Ce y Zr z O promoted the CO 2 hydrogenation kinetics. • Zn x Ce y Zr z O/Z5 contribute to the well matching of CO 2 activation and alkylation. • The mechanism of the alkylation of benzene with CO 2 and H 2 is proposed. Alkylation of benzene using CO 2 and H 2 to toluene and xylene (TX) can not only give value-added chemical products but also alleviate the greenhouse effect. The key to achieving this goal is to develop a highly efficient catalyst. Herein, a class of bifunctional catalysts containing series of Zn x Ce y Zr z O metal oxide and HZSM-5 was prepared and studied for the catalytic properties. Higher CO 2 conversion and alkylation utilization were achieved using the Zn x Ce y O coupling with HZSM-5 compared to its counterpart ZnO and CeO 2 , revealing synergy between the ZnO and CeO 2 . More strikingly, the Zn x Ce y Zr z O, synthesized by insertion of Zirconia (Zr) atoms into CeO 2 , can not only improve the concentration of oxygen vacancy but also facilitate CO 2 adsorption. After coupling with HZSM-5, the alkylation utilization of CO 2 was significantly improved and the unwanted CO selectivity was obviously reduced by hindering the RWGS reaction. The optimal bifunctional catalyst Zn 3 Ce 1 Zr 3 O/Z5 showed alkylation utilization of 24%, unwanted CO selectivity of only 64% and the TX selectivity as high as 82%. In situ DRIFTS results confirmed that the methanol generated on the Zn x Ce y Zr z O metal oxide via the formate-methoxy intermediates mechanism was rapidly alkylated on HZSM-5 with benzene to produce TX.