Catalysts and catalytic reactions

Catalysts for oxidation reactions can be roughly divided into three categories: metals and metal ions, transition metal oxides and polyoxometalates (heteropolyacid compounds), and redox molecular sieves.

Metals and metal ions

Precious metal catalysts are usually loaded on activated carbon and widely used for the oxidative dehydrogenation of alcohols and diols and carbohydrate oxidation reactions. The main disadvantage of precious metal catalysts is trade deactivation, which limits their industrial application to a certain extent. Transition metal ion loading on ion exchange resins can be used for oxygen catalyzed transfer reactions, such as the selective oxidation of various unsaturated alcohols catalyzed by Cr (3) and Ce impregnated in Nafion (polytrifluorosulfonic acid resin) using TBHP (tert butanol peroxide) or sodium bromate as oxygen acceptors.

Loading metal ions onto ion exchange resin can prolong the lifespan of the catalyst. Cr/NAFK is used to catalyze the oxidation of 1-phenylethanol, and the recovered catalyst can be reused after the reaction. Although the yield of acetophenone is slightly reduced, there is no significant loss of Cr. Using a 60% hydrogen peroxide solution as the oxidant, polystyrene sulfonic acid ion exchange resin exchanged with Pd (2) is used to catalyze the oxidation of 2-methylnaphthalene. The yield of dimethyl1,4-naphthoquinone (vitamin K) reaches 55% -60%, which is higher than traditional organic synthesis reactions using stoichiometric oxidants.

MoO2 (2) and VO are bonded onto ion exchange resin as solid catalysts, and hydrogen peroxide is used as an oxidant to catalyze the epoxidation of olefins. The Mo containing catalyst showed only a 7% decrease in activity after five cycles of use, while the V containing catalyst showed no significant change in activity after seven cycles of use. At present, various resins with chelating groups have been developed as carriers for Mo and V catalysts for the epoxidation of olefins.