Layered Double Hydroxide-Based Catalysts: Recent Advances in Preparation, Structure, and Applications

Layered double hydroxides (LDHs) are a class of functional anionic clays, which consist of positively charged host layers (brucite-like M(OH)(6) octahedra) and interlayer anions. By virtue of their unique combination of structural features (including the tunability of both host layers and interlayer guest anion, exfoliation property, structure topological transformation, confinement effect), LDHs have many potential applications in heterogeneous catalysis-as catalysts themselves, catalyst supports, or catalyst precursors. In addition, the properties of LDH-based catalysts can be tailored for specific purposes by facile modulation of their surface/interface defect structure (e.g., oxygen vacancy defects or metal defects), controlling the concentration/strength of surface acid/base sites, tuning the geometric/electronic structure of active sites, or by taking advantage of the confinement effect intrinsic to 2D materials. In addition, by utilizing the topological structural transformation of LDH precursors, supported metal catalysts can be obtained (as single metals, bimetallic alloys or heterostructures, and intermetallic compounds) with tunable particle size/morphology and intriguing electronic properties. The main focus of this review is on recent advances in structure design, preparation, and catalytic applications of LDH-based heterogeneous catalysts. In addition, future challenges and development strategies are discussed from the viewpoints of modulation of intrinsic active sites and establishment of scalable fabrication processes.