Transition metal modified Al2O3 mesoporous nanospheres for catalysis of organic reactions

The performance of metal oxide-based catalysts are usually determined by their characteristics such as material composition, morphology, and surface/interface properties. Therefore, rational design of metal oxide-based catalysts with special surface/interface characteristics and porous microstructure still needs further research. In this work, a facile two-step solvothermal-annealing method is developed for the synthesis of transition metal (TM) modified Al2O3 (TM-Al2O3, TM = Cu, Fe, Ni, Co) nanospheres. The influences of different ratios of solvents (e.g., water and glycerol) on the morphology and particle size of the nanocatalysts are explored. Benefitting from the nano-spherical morphology and unique mesoporous structure, the representative catalyst (i.e., Cu-Al2O3) exhibits favorable catalytic performance in 4-nitrophenol reduction and benzyl alcohol oxidization reactions. The turnover frequency of Cu-Al2O3 is high up to 35.9 min-1 for the reduction of 4-nitrophenol, which is higher than that of its counterparts (i.e., Fe-Al2O3, Ni-Al2O3, and Ni-Al2O3) and many recently reported Al2O3-based catalysts. Moreover, the pH of the reaction system is regulated to enhance the catalytic efficiency in selective oxidization of benzyl alcohol by an additive addition strategy. These results suggest that the nano-spherical and mesoporous morphology is indeed effective for the activity enhancement of TM-Al2O3 catalysts. The same catalyst designing concept and performance regulation strategy may be extended to other TM-modified metal oxide systems, making it possible to tune the catalytic behavior for various chemical reactions.