Steric Effect on the Catalytic Performance of the Selective Oxidation of Alcohols Over Novel Crystalline Mo-V-O Oxide

The Mo-V-O crystalline oxide with novel pore structure and consisting uniform six- and seven-member rings on the a-b plane is investigated for the selective oxidation of alcohols of different steric hindrance in liquid phase. The research target is to correlate catalytic activity with the pore structure of the crystal. Specially, substituted pyridines are employed as probe molecules to study poison effect which is closely related to the steric hindrance. As a result, the oxidation of benzyl alcohol, 1-hexanol and cyclohexanol produces aldehydes or ketones as main products. The oxidation of substrates with methyl groups on the carbon next to alcohol group mainly affords dehydrated products as olefins. The catalytic results with adding substituted pyridines in the oxidation of benzyl alcohol, 1-hexanol and 2-hexanol suggest that the active sites are located around the pore area, and are reachable by pyridine, not by substituted pyridines, such as 2-methylpyridine, 2-ethylpyridine and 2, 6-dimethylpyridine. Competitive adsorption on active sites between pyridine and benzyl alcohol remarkably decreases catalytic activity, which 2, 6-dimethylpyridine affects slightly. We have discussed that the adsorption-activation model of substrate is greatly dependent on its steric hindrance.