Heterogeneous Catalysts for Toluene Oxidation

The selective activation of C(sp3)-H bonds in toluene to produce high value-added oxygenated chemicals represents a pivotal challenge and opportunity for both fundamental researches and industrial applications. Since the C(sp3)-H bonds are both thermodynamically robust and kinetically inert, conventional catalytic techniques for the activation process require the use of toxic, aggressive, and costly reagents under rather harsh conditions. By virtue of high stability and ease separation of catalysts, heterogeneous catalysis, especially heterogeneous photocatalysis, has emerged as promising candidates for the activation of C-H bonds under mild conditions. In the current review, we summarize the development of heterogeneous thermocatalysts, photocatalysts, and electrocatalysts, as well as their catalyst modification strategies and reaction mechanisms for toluene oxidation. We examine and analyze these catalytic systems based on conversion and selectivity, recyclability, reaction scale, substrate scope, reaction conditions (e.g., temperature, pressure, and oxidants), and so on. Finally, we provide our perspectives on challenges and opportunities toward the future research for the high-performance heterogeneous catalytic systems for toluene oxidation.