Preparation of Mo-Embedded Mesoporous Carbon Microspheres for Friedel–Crafts Alkylation

Herein we report the preparation of Mo-embedded mesoporous carbon microspheres (Mo@C) in which molybdenum trioxide (α-MoO3) phase as high as 42% can be included. The precursor solid synthesized from a hydrothermal route consists of highly dispersed molybdenum dioxide (MoO2) crystals with the size of 3–6 nm. Carbonization of this solid precursor strengthens the sphere structure and generates micro- and mesopores within the resultant biphasic nanocomposite. Upon the carbonization, some of the MoO2 nanocrystals are further reduced to Mo2C. The oxidation states of encapsulated molybdenum can be tuned to Mo6+ (i.e., α-MoO3) by calcination in air at 300 °C without causing loss of carbonaceous matrixes. With this treatment, more mesopores are generated and specific surface area of sample is increased to 371 m2/g. Interestingly, the surface of these nanocomposites is amphiphilic due to copresence of hydrophilic and hydrophobic groups, which favors the particle dispersion. The α-MoO3 embedded mesoporous carbon microspheres show high catalytic activity toward benzylation of toluene; a 100% conversion of benzyl alcohol can be reached just within 1 h of reaction at 110 °C. On the contrary, the MoO2/Mo2C embedded carbon microspheres are inactive, confirming that the high oxidation state Mo6+ accounts for active sites in this Friedel–Crafts alkylation reaction.