Characterization of bifunctional Pt/H[Ga]ZSM5 and Pt/H[Al]ZSM5 catalysts

Two supports (gallosilicate and aluminosilicate MFI) as well as the corresponding Pt/MFI bifunctional catalysts were characterized by X-ray photoelectron spectroscopy (XPS) to determine the chemical species on their surfaces. The presence of extra-structural gallium was observed in Pt/H[Ga]ZSM5, which could be found most probably as Ga2O3; the presence of Pt0, Pt-Oads, and PtO in Pt/H[Ga]ZSM5 and Pt/H[Al]ZSM5 was also observed. It was evidenced an increase in surface gallium concentration as the content of platinum increases in the Pt/H[Ga]ZSM5 solids. The bifunctional catalysts were catalytically tested under standard conditions by the acetone transformation reaction. The results of the catalytic test confirms that the 1.00 wt.% Pt/H-[Al]ZSM5 catalyst shows an initial global activity four times higher than the 1.00 wt.% Pt/H-[Ga]ZSM5 one, and additionally a selectivity to the desired product (methyl isobutyl ketone, MIBK), three times higher. The activity and selectivity results observed for the Pt/H-[Ga]ZSM5 solids are remarkably similar to those found for the pure H[Ga]ZSM5 support. These results clearly show that the platinum metallic centers on the Pt/H[Ga]ZSM5 catalysts are not active for the hydrogenation reactions of the olefinic and/or carbonylic double bonds, probably due to passivation caused by the gallium species on the surface of the bifunctional catalysts, as proposed in the scheme.