Preparation and characterization of bifunctional catalysts of the Pd, Pt/H[Ga]MFI types

An MFI type galosilicate was synthesized and characterized employing XRD, N₂ adsorption at -196 °C, chemical analysis by ICP-AES, and XPS. This material was used in the preparation of Pd/H[Ga]ZSM5 and Pt/H[Ga]ZSM5 bifunctional catalysts, calcined under dry air for 6 h at 500 and 300 °C, respectively, and then reduced "in situ" under H₂ flow for 6 h at 500 °C. The bifunctional catalysts were also characterized by XRD, N₂ physisorption, TEM, chemical analysis, and XPS. The support possesses an MFI structure with excellent crystallinity, as shown by XRD. Bulk chemical analysis shows a (Si/Ga)_ICP-AES atomic ratio of 16. The absence of Ga₂O₃ is suggested by both XRD and XPS (at surface level). The atomic ratio at the surface, (Si/Ga)_XPS, is the same as that found by ICP-AES, suggesting that Ga is distributed homogeneously. XRD and N₂ physisorption results of the bifunctional catalysts suggest that metal incorporation does not affect sensibly the structure of the support. Dispersion of Pd and Pt in either catalyst was estimated from TEM analysis, indicating in both cases values of the order of 80%. The atomic ratios (Si/Ga)_XPS at the surface were 16 for Pd/Galosilicate, and 4 for Pt/Galosilicate, suggesting that Pt promotes migration of Ga towards the external surface of the solid, a phenomenon that is not observed for the Pd/H[Ga]ZSM5 catalyst. Degaliation promoted by Pt could be explained assuming that Pt and Ga could form stable chemical species, as might be indicated by XPS results. The transformation of acetone to MIBK was employed as catalytic test. These results indicate very different behaviors for either bifunctional catalyst.