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 (Znx/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 Znx/S-1 were investigated using UV-Vis and N2 physical adsorption. The acidity and origin of the acid sites in Znx/S-1 were studied by NH3-temperature programmed desorption and Fourier-transform infrared analysis. The catalytic performance of Znx/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 Znx/S-1. The relationship between Brønsted acid sites and Zn–OH groups on ZnO clusters of Znx/S-1 was also revealed for the first time. Furthermore, Znx/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 Znx/S-1 should play a key role in isobutane conversion.