(Zn)MgAl Hydrotalcite-Based Composite Oxide Nanostructures for Propane Dehydrogenation

Different amounts of Zn contained MgAl-layered double hydrotalcites topologically transformed into mixed oxide (xZn-O) nanomaterials through calcination at a high temperature. The degree of polymerization and reducibility of ZnOx species have been systematically investigated, as they are closely linked to the activity of propane dehydrogenation (PDH). For the xZn-O (x < 25%) catalysts, highly dispersed Zn species dominate owning to the strong lattice confinement effect of MgAlxOy supports. These catalysts exhibit a high turnover frequency (TOF) value, 93% propylene selectivity, and a slow increase in C3H8 conversion due to their strong resistance to over reduction. With an increase in Zn content, surface-supported ZnO nanoparticles and bulk ZnO crystal species emerge. Based on the results of characterization and calculation, as the degree of polymerization of the ZnOx species increases, they become more easily reduced, and the activation energy for C3H6 formation decreases, suggesting that the coordinatively unsaturated ZnOx species nearby oxygen vacancies are the active sites for PDH. However, these also lead to a decrease in C3H6 selectivity and an increase in coke selectivity (deactivation constant). Therefore, the appropriate degree of polymerization and reducibility of ZnOx species is critical for achieving efficient catalytic PDH.