Solvent-free efficient oxidation of benzyl alcohol on nano-Pd/Al2O3: Effect of palladium source and pH value

PA-Na-x and PA-H-1 catalysts were prepared by a cation-assisted polyol method using different Pd sources (Na2PdCl4 or H2PdCl4) and pH values (x = 1, 2, 3 or 5), and applied to solvent-free oxidation of benzyl alcohol (BzOH). As confirmed by multiple analytical characterizations, the base number, Pd0 content and abundance of oxygen vacancies for PA-Na-x prepared were higher than those on PA-H-1, and their synergistic effect made PA-Na-x possess the higher BzOH conversion and benzaldehyde selectivity. The contents of Pd0 and oxygen vacancies on PA-Na-x showed an inverted volcano trend with the increase of the pH value. PA-Na-x also followed the inverted volcano order for the catalytic activity, where PA-Na-1 prepared from Na2PdCl4 at pH 1 exhibited the best catalytic efficiency with a turnover frequency of 29.5 s−1 and 94.8% selectivity of benzaldehyde, and excellent stability. This study provided an efficient method of preparing nano-Pd catalysts. [Display omitted] •Pd/Al2O3 was prepared by a cation-assisted reduction method of polyol at 50 °C.•Pd source and pH can tune Pd0 content, abundance of oxygen vacancies, and base number.•There is a strong metal-support interaction in PA-Na-x prepared form Na2PdCl4.•PA-Na-1 exhibits a turnover number of 29.5 s-1 with a selectivity of 94.8%.