Catalytic oxidation of low-carbon polyols to primary carboxylic acids: Advances on catalyst design and mechanistic studies

Catalytic oxidation of low-carbon polyols to primary carboxylic acids is regarded as an important technology for sustainable traditional oxidation processes in industry. Despite decades of research and several breakthroughs in catalyst design, the precise reaction mechanism underlying the formation of specific carboxylic acids remains elusive. In this review, the oxidation of low-carbon polyols to primary carboxylic acids over metallic catalysts is systematically summarized with a focus on surface reaction mechanisms and catalyst design strategies. Essentially, the activation of C-H bond and the competitive adsorption/desorption of oxygen-containing intermediates serve as critical issues in determining the reaction mechanism. Insights into the reaction mechanism, the structure-performance relationships of oxophilic metal-based catalysts in various low-carbon polyol oxidation reactions lay the groundwork for rational catalyst design and manufacturing: (I) well-dispersed acidic sites can enhance the electronic density of oxophilic metals, thereby improving the H abstraction efficiency, while an adequate number of weak basic sites on the surface is beneficial for the adsorption of oxygen-containing intermediates; (II) the downshifted d-band center of oxophilic metal sites results in greater catalytic efficiency for C-H bond activation. This review aims to provide a comprehensive understanding of oxidation mechanisms and guide the rational design of efficient catalysts.