Influence of the acid sites density in the acetone transformation over bifunctional Pt/H[Ga]ZSM5 catalysts

Abstract

The purpose of this work is to elucidate the effect of acid sites density on the catalytic behaviour of a series of bifunctional catalysts prepared by supporting platinum (about 1.00 wt.%) on MFI-type gallosilicates (H[Ga]/ZSM5 with Si/Ga atomic ratio = 16, 46 and 145). The XPS characterization studies of the bifunctional catalysts allowed to detect the presence of framework as well as extraframework gallium species for the catalyst with highest density of acid sites (Si/Ga = 16), while only framework Ga species could be detected for catalysts with lower acid site density. It was also verified in all the bifunctional catalysts the presence of three types of metal sites: Pt (0), Pt–O ads and PtO species. The results obtained in the synthesis of MIBK from acetone with the different bifunctional solids, indicate that as the density of the acid sites increases, the solids start to behave solely as acid catalysts. This phenomenon is probably related to the presence of extraframework gallium species in the catalyst with higher surface acidity, capable to interact with the platinum species and thus provoking the passivation of the metallic phase, while in the solids with lower surface acidity it seems to exist a better balance between the acidic–metallic functionalities.