Targeted engineering of metal@hollow carbon spheres as nanoreactors for biomass hydrodeoxygenation

Metal@hollow carbon spheres as nanoreactors (MHCSs) are receiving extensive attention in biomass hydrodeoxygenation (HDO) due to well-defined active site, confined void space, modifiable surface, and tunable mass transfer rate. All their exciting properties heavily depend on the controllable and ingenious design of the MHCSs with desired physical and chemical microenvironment. In this paper, different synthesis strategies, based on template approaches and encapsulation technologies, for the construction of oriented MHCSs have been comprehensively reviewed. Additionally, a distinctive viewpoint on structure-activity correlation of MHCSs is presented in terms of achieving perfect adjustment of geometric categories such as cavity size, pore structure, shell thickness, multi-shell structure. Furthermore, the functionalization chemical microenvironment of MHCSs is discussed, including heteroatomic doping engineering, surface functionalization and defect engineering. The potential prospects of novel multifunctional MHCSs for broader biomass valorization are proposed, providing guidance for the rational design of advanced catalysts for a highly efficient biomass refining system.