Layered double hydroxides-based metal nanocatalysts: Confinement engineering, microenvironment effect and applications in catalytic conversion of biomass

Rational design and targeted synthesis of efficient supported metal nanocatalysts for catalytic transformation of renewable biomass into value-added chemicals and fuels has attracted increasing attentions in heterogeneous catalysis. Precisely tailoring the surface microenvironment of supported metal nanocatalysts including geometric coordination environment and electronic state of metal active sites, especially for highly dispersed single atoms (SAs), nanoclusters (NCs) and nanoparticles (NPs), plays significant roles in improving catalytic performance for biomass conversion. Owing to the atomic-level uniform distribution of constituent metal species, flexible chemical compositions, unique confinement effect and topological transformation property, layered double hydroxides (LDHs) as a family of 2D layered nanomaterials, are believed to be ideal structure platforms to acquire highly dispersed supported metal nanocatalysts with well-designed surface microenvironments. Herein, classic synthesis approaches of LDHs precursors and typical confinement synthesis strategies of highly dispersed LDHs-based metal nanocatalysts (e.g. SAs, NCs, NPs) with specific surface microenvironments are systematically discussed. Particular emphasis is placed on specific microenvironment effects of LDHs-based metal nanocatalysts and their advanced applications for reductive, oxidative and reforming upgrading of various biomass-derived molecules with aim to reveal structure–property relationship and catalytic reaction mechanism. Finally, challenges and perspectives are illustrated to provide further guidance for developing high-performance LDHs-based metal nanocatalysts for efficient and sustainable biomass transformation.