Tuning the Reactivity of Zn Sites in HZSM-5 Zeolite for Light Alkane Activation

Bifunctional metal-modified zeolites have been widely employed for various catalytic transformations such as dehydroaromatization (DHA), dehydrogenation, hydrocracking, and hydroisomerization, and their catalytic activity mainly relies on the structure of the metal sites inside the pores of the zeolites. Here, we show that the reactivity of Zn sites (in HZSM-5) for light alkane activation/DHA can be enhanced by treating Zn-exchanged HZSM-5 with an oxalic acid (OA) solution under hydrothermal or solvothermal conditions to form Zn oxalate@HZSM-5 as an intermediate to the active Zn sites. Specifically, the activity of the OA-treated Zn-ZSM-5 catalyst in propane DHA was enhanced by about 460% in contrast to the same sample without treatment. We suggest that the reactivity of Zn sites for light alkane activation was enhanced because of the formation of polymeric Zn oxalate segments, which tuned the coordination structure of the Zn sites upon H2-assisted activation.