Zeolite confinement-catalyzed cleavage of C–O/C–C bonds in biomass

Abstract

The rise of sustainable bio-based fuels and chemicals has emerged as an attractive and viable solution to reduce fossil fuel use, which is essential for green and sustainable development. Metal@zeolites have been well developed for the effective cleavage of C–O/C–C bonds in biomass due to their controlled synthesis and unique structural properties, but there is still no review on the current status and future development trends in this field. In this review, synthetic strategies for encapsulating the metal within the zeolite are first summarized: from host–guest to ligand-stabilized direct hydrothermal synthesis to the progressive development of multistep synthesis methods, including solvent-free synthesis, metal-containing-seed-directed synthesis, cationic polymer-assisted synthesis and template-guiding synthesis etc., which reduce the use of solvents and organics to facilitate further large-scale production and enable more controlled construction of fine structures, such as metal size and metal encapsulation positions, to exhibit superior catalytic performance. Furthermore, the enhanced stability, selectivity and activity exhibited by metal@zeolite in biomass hydrodeoxygenation (HDO) due to unique confinement effects are described in detail through four aspects: metal size effect, zeolite encapsulation effect, and shape-selective and synergy effects. Notably, the unique distribution of metal and acidic sites in metal@zeolite shows high efficiency in the cascade reaction of biomass upgrading by reducing the diffusion limitation of intermediates and regulating the sequence of each reaction step. Finally, the current challenges and perspectives in the construction and upgrading of catalytic biomass by metal@zeolites are presented, which is expected to pave the way for the rational design of metal@zeolites to more effectively facilitate biomass upgrading.