Self-Assembling of a Mo–Al Composite toward Efficient Catalysts for RWGS Reaction: Overcoming the Trade-off between Ultrasmall Size and High Loading

Molybdenum carbides have received attention for the reverse water gas shift (RWGS) reaction. Normally, MoCx-based catalysts are synthesized via a high-temperature carbonization of 1100 K, leading to the agglomeration of the active phase. In order to minimize the atomic motion leading to single growth, insertion of heteroatoms has been attempted with the usage of components in the catalyst substrate. The current work applied the self-assembling strategy to prepare a Mo–O–Al composite instead of traditional impregnation before carburization. The dynamic structure evolution and detailed coordination environment of the active phase are investigated by in situ X-ray diffraction, quasi in situ X-ray photoelectron spectroscopy, in situ transmission electron microscopy, and temperature-programmed surface reaction techniques. Our findings reveal that Al doping enables carburization at a lower temperature (200 °C) via the topotactic pathway, yielding α-MoCx (fcc); even at a loading as high as 40 wt %, the catalyst maintains an ultrasmall particle size (1 nm). The optimized catalyst exhibits a RWGS reaction rate of 52.1 μmolCO2·gMo–1·s–1 at 400 °C, representing a 2.5-fold enhancement over bulk β-Mo2C. This work provides a possible solution for maintaining high dispersion at high metal loading for catalyst preparation, specially requiring a high temperature during either synthesis or reaction.