Microwave-assisted polyol synthesis of Pt/H-ZSM5 catalysts

Abstract

Three H-ZSM5 solids with Si/Al atomic ratios of 22, 71 and 96 were synthesized and characterized by X-ray diffraction (XRD), ICP-AES chemical analysis and nitrogen physisorption at −196 °C. These were employed as supports in the synthesis of Pt/H-ZSM5 catalysts with platinum contents around 1 wt.%, by means of the microwave-assisted polyol method: platinum salt solutions in ethylene glycol were irradiated at powers of 184 and 461 W for time periods of 30 and 60 s in order to obtain Pt nanoparticles suspensions which were mixed with the supports and ultrasonically irradiated for 30 min to obtain the catalysts. This methodology allowed the synthesis of the catalysts efficiently and in relatively short times. Characterization of the catalysts by XRD showed that the ultrasonic irradiation did not affect the support structure. X-ray photoelectron spectroscopy revealed the presence of Pt(0) species on the solids surfaces. Temperature-programmed reduction studies suggested an effect of the time and power of microwave irradiation on the reducibility of the catalysts, i.e., at the shorter times and lower irradiation powers, the reducibility of the platinum species decreases. Catalytic testing through the hydrogenation of toluene indicated that there is an effect of time and power of microwave irradiation on the initial hydrogenation activity of the Pt/H-ZSM5 catalysts. The catalyst prepared from suspensions irradiated at 461 W for 60 s showed the highest activity, which seems to be related to the lower particle size and better dispersion of Pt.