Heterolytic H2 Activation in Heterogeneous Hydrogenation/Hydroprocessing Catalysis

Abstract

In heterogeneous catalysis, heterolytic H2 activation for (selective) hydrogenation and hydroprocessing reactions involves the dissociation of adsorbed H2 molecules into proton (Hδ+) and hydride (Hδ−) on the catalyst surface. This approach offers several advantages, including high selectivity for polar bond (s), a low energy barrier for H2 dissociation, a high capacity for reaction-favorable H2 adsorption, and reduced catalyst poisoning. This requires the construction of frustrated Lewis pairs on the catalyst surface, satisfying specific criteria, such as having an abundant quantity of Lewis pairs with steric hindrance and maintaining a certain distance of 3–5 Å between the pairs. This review highlights intrinsic catalyst properties for heterolytic H2 activation based on state-of-the-art reports. The main components necessary for this activation include supports with strong basic sites and/or oxygen vacancies, and/or metals of single atom. For this purpose, designed catalytic materials aim to strengthen the Lewis acidity and basicity, improve the polarization of Lewis pairs, enrich oxygen vacancies, maximize the interfacial area between metal species and Lewis base, and enhance metal–support interaction. Therefore, heterogeneous catalysts retaining such heterolytic H2 activation characteristics will be significantly effective in various hydrogenation and hydroprocessing reactions.