Silicalite-1 zeolite acidification by zinc modification and its catalytic properties for isobutane conversion

Abstract

A series of Zn-modified Silicalite-1 (S-1) zeolites (Zn_x/S-1) were prepared by the wetness-impregnation method and applied in the catalytic conversion of isobutane. The structure and location of Zn species in Zn_x/S-1 were investigated using UV-Vis and N₂ physical adsorption. The acidity and origin of the acid sites in Zn_x/S-1 were studied by NH₃-temperature programmed desorption and Fourier-transform infrared analysis. The catalytic performance of Zn_x/S-1 for isobutane conversion was investigated in a fixed-bed microreactor. In the experiments, the acidity of S-1 zeolite was dramatically increased by modification with Zn, with both Lewis and Brønsted sites identified in Zn_x/S-1. The relationship between Brønsted acid sites and Zn–OH groups on ZnO clusters of Zn_x/S-1 was also revealed for the first time. Furthermore, Zn_x/S-1 catalysts exhibited excellent catalytic performances in both isobutane dehydrogenation and butene isomerization reactions. A high selectivity of total butene products ranging from 84.6 to 97.2 was achieved on the catalysts with different Zn loadings. Moreover, the linear correlation between isobutane conversion and the acid amount (determined by NH₃-TPD) confirmed that the weak-to-medium acid sites in Zn_x/S-1 should play a key role in isobutane conversion.