Abstract:
In this study, the Co-WO
x catalyst was successfully prepared by directly introducing Co
2+ dopant in a dynamic solvothermal synthesis process, and the obtained Co-WO
x was used for the catalytic epoxidation of 1-hexene. The structures of WO
x before and after the doping were analyzed by XRD, SEM, TEM, Raman, XPS as well as
in-situ NH
3-FTIR. The results show that the doping of Co
2+ has not obvious effect on the crystal phase and main growth direction of WO
x, but can effectively reduce the content of Brönsted acid (B acid) site on the surface of WO
x catalyst and increase the content of oxygen vacancy at the same time. In the epoxidation reaction, the obtained Co-WO
x catalyst (Co/W = 0.1) can increase the selectivity of 1,2-epoxyhexane from 26.9% of pure WO
x to 55.7% with a 5.3% decrease in 1-hexene conversion. The improvement of Co-WO
x performance is mainly attributed to two aspects: (1) the reduction of B acid site on the surface of WO
x inhibits the ring opening hydrolysis of 1,2-epoxyhexane; (2) The increase of oxygen vacancies on the surface of WO
x promotes the activation of H
2O
2, ensuring that the conversion rate of 1-hexene does not decrease significantly, and an increase in the utilization of oxidant H
2O
2 by 13.5%. Combined with the characterization results and reaction data, the epoxidation mechanism of 1-hexene with W−O−OH as active intermediate is proposed.