Acetone transformation over Pt/H[Al]ZSM5 and Pt/H[Ga]ZSM5 catalysts: Evidences of a Pt–Ga interaction

Abstract

Acetone transformation into methyl–isobutyl ketone (MIBK) under hydrogen atmosphere, using bifunctional catalysts of the platinum supported over medium-pore zeolites (MFI)-type, was studied. This methodology offers a number of advantages; however, since it implies working at low hydrogen pressure ( P H 2 ) with respect to the acetone pressure ( P Ac), a rapid catalyst deactivation is observed. Therefore, to minimize deactivation of bifunctional catalysts, a solid with less strong acidic sites has been considered as a platinum support. In this sense, the use of an MFI-type gallosilicate has been deemed convenient to compare the results with those obtained over a catalyst of the platinum/aluminosilicate MFI-type. The H[Al]ZSM5 and H[Ga]ZSM5 solids were synthesized and evaluated by means of DRX, nitrogen adsorption at −196 °C, TPD–NH 3 and chemical analysis, and later used as a support for the metallic phase. Platinum of 0.50 wt.% was introduced by means of the exchange–impregnation method and the Pt(NH 3) 4Cl 2 salt was used as a platinum precursor. The solids were calcinated under dry air flow at 300 °C for 6 h and then reduced under dry hydrogen atmosphere at 500 °C also for 6 h. The bifunctional catalysts obtained, 0.50Pt/H[Ga]ZSM5 (Si/Ga=42) and 0.50Pt/H[Al]ZSM5 (Si/Al=40), were evaluated by means of chemical analysis, nitrogen adsorption, transmission electronic microscopy (TEM), electronic paramagnetic resonance (EPR), and the model reactions of toluene-hydrogenation and n-heptane hydrocracking under the conditions established in previous works. Acetone transformation was run in a dynamic reactor at 160 °C, atmospheric pressure, P Ac/ P H 2 =3 and variable WHSV. The results obtained with the model reactions and the acetone transformation shows that metallic centers in the Pt-gallosilicate catalysts exhibit a much lower hydro-dehydrogenating activity than that of the metallic centers in the Pt-aluminosilicate catalyst; this, together with the EPR results, seems to indicate that a strong interaction between platinum and a species of structural or extra-structural gallium (EFGS) of the support used has occurred over the Pt/H[Ga]ZSM5 catalyst.