Metal-Loaded Hollow Carbon Nanostructures as Nanoreactors: Microenvironment Effects and Prospects for Biomass Hydrogenation Applications

Over the past decade, metal-loaded hollow carbon nanostructures have been hailed as man-made nanoreactors (MHC nanoreactors) for extensive applications in dealing with energy and environmental issues due to their tailorable structure and electronic properties. Unlike conventional reports of hollow nanostructures with regard to synthetic methodologies or structural properties, a distinctive viewpoint on the microenvironment effects of MHC nanoreactors, i.e., metal–support interaction effect, reactant enrichment effect, molecular sieving effect, spatial compartmentation effect, and metal stabilization effect, is highlighted herein from this perspective. Furthermore, to emphasize the great potential of MHC nanoreactors in constructing a sustainable energy system to achieve a greener modern lifestyle, a review of the applications of MHC nanoreactors in the hydrogenation of typical biomass-derived molecules is presented. Additionally, prospects for broader biomass valorization applications of MHC nanoreactors, i.e., in situ hydrogen source-assisted hydrogenation, hydrogenation-involved cascade-type reactions, hydrogenation product distribution modulation, stability prolongation and recyclability enhancement, are forecasted. Toward the end of this paper, some feasible suggestions are further proposed for the enhancement of the catalytic reactivity, selectivity, stability, and sustainability of MHC nanoreactors in biomass hydrogenation, with a sincere expectation to contribute to the development of a highly efficient biomass refining system.