Thermal Stabilities of MCM-41-Modified Pd/Al2O3 for Ethanol Adsorption and Oxidation

The thermal stabilities of palladium (Pd) catalysts supported on MCM-41-modified Pd/Al2O3 calcination at 1000 degrees C were investigated for the adsorption and catalytic combustion of ethanol. MCM-41 (0, 30, 50, 70, and 100 wt %)-modified Al2O3 materials were prepared by the in situ coprecipitation method. The catalysts were characterized by N-2 adsorption-desorption, X-ray diffraction, and scanning electron microscopy-energy dispersive spectrometry. It was found that MCM-41 less than 50 wt % was conductive to the increase in specific surface area and pore volume of the catalysts even after 1000 degrees C calcination which had a positive relationship with the adsorption performance of ethanol. Pd/Al2O3, prepared in this study, presented a sheet-like morphology which could attach on the surface of MCM-41. Meanwhile, the introduction of MCM-41 into Al2O3 could hinder the phase transition of gamma-Al2O3 to delta-Al2O3 and prevent the collapse of the pore structure in MCM-41, thus avoiding the aggregation of Pd particles effectively at 1000 degrees C. Cat-50% (50 wt % MCM-41 into Pd/Al2O3) showed the best ethanol adsorption performance with the longest breakthrough time and highest adsorption capacity at 40, 60, and 80 degrees C because of its good textual properties, while Cat-70% presented the highest activity with higher CO2 yield at 200 degrees C, reaching 90% ethanol conversion at 220 degrees C, owing to its good dispersion of Pd particles. In addition, the introduction of MCM-41 could inhibit the production of acetaldehyde to some extent. The long-term stability test demonstrated that MCM-41-modified Pd/Al2O3 had good stability for catalytic oxidation of ethanol for the stable conversion for 500 h at 300 degrees C and gas hourly space velocity of 10,000 h(-1).