A Structure‐Preserving, Dimensionality‐Increasing Strategy for the Stepwise Synthesis of Microporous α‐MoO ₃ with a Broad (100) Surface

Metal oxides with diverse structures and dimensionalities are typically synthesized via solid-state or hydrothermal reactions. However, it is quite difficult to retain the structures of the starting materials when 0D metal salts or molecular clusters are used as precursors because higher-dimensional structures form by structural reorganization through isomerization and decomposition/condensation reactions. In this study, we demonstrated a structure-preserving, dimensionality-increasing strategy for the synthesis of 2D α-MoO₃ from 0D [Mo₂O₅(H₂O)₆]²⁺ species via a 1D [Mo₂O₆{(CH₃)₂NCHO}]_n intermediate while maintaining the structures of the precursors. By simple temperature-controlled calcination, metastable crystals of α-MoO₃ in which the (100) plane was the broad face were successfully synthesized, differing from conventional α-MoO₃ in which the (010) plane is the broad face. In addition, the prepared metastable crystals possessed large surface areas, unusual micropores, and surface-exposed coordinatively unsaturated Mo sites, allowing them to serve as high-performance acid catalysts. This synthesis strategy is expected to facilitate the synthesis of metastable structures and the design of defects and surface structures at the atomic level.