Structure-Activity Relationships of Au/Al2O3 Catalyst for the Selective Oxidative Esterification of 1,3-Propanediol and Methanol

1.5 wt. % Au/Al2O3 catalysts were prepared using the deposition-precipitation or colloid-deposition method and calcined at different temperatures for the selective oxidative esterification reaction of 1,3-propanediol and methanol to form methyl 3-hydroxypropionate (3-HPM). The catalysts were characterized by nitrogen adsorption, transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy, X-ray photoelectron spectra (XPS), CO2 temperature-programmed desorption (CO2-TPD) and NH3 temperature-programmed desorption (NH3-TPD). The effect of the calcination temperature of the catalyst prepared by the deposition-precipitation method on the catalytic performance for the selective oxidative esterification of 1,3-propanediol was studied. The results showed that the conversion of 1,3-propanediol and the selectivity of 3-HPM increased at first and then decreased with the increase of the calcination temperature of catalyst. The highest conversion of 1,3-propanediol and selectivity of 3-HPM at the optimal calcination temperature of 350 degrees C were 92.0% and 88.5%, respectively. Considering the effects of preparation method and calcination temperature, it could be concluded that the metallic Au nanoparticles with appropriate particle size in coordination with the suitable amount of weak and middle acid and base sites, were favorable to the oxidative esterification of 1,3-propanediol and methanol to 3-HPM. Moreover, we found that the 1.5 wt. % Au/Al2O3 catalyst could be effectively recovered without obvious decline of the catalytic properties.