Preparation of Mo-embedded mesoporous carbon microspheres for friedel-crafts alkylation

Abstract

Herein we report the preparation of Mo-embedded mesoporous carbon microspheres (Mo@C) in which molybdenum trioxide (α-MoO 3) phase as high as 42% can be included. The precursor solid synthesized from a hydrothermal route consists of highly dispersed molybdenum dioxide (MoO 2) 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 MoO 2 nanocrystals are further reduced to Mo 2C. The oxidation states of encapsulated molybdenum can be tuned to Mo 6+ (i.e., α-MoO 3) 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 m 2/g. Interestingly, the surface of these nanocomposites is amphiphilic due to copresence of hydrophilic and hydrophobic groups, which favors the particle dispersion. The α-MoO 3 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 MoO 2/Mo 2C embedded carbon microspheres are inactive, confirming that the high oxidation state Mo 6+ accounts for active sites in this Friedel-Crafts alkylation reaction. © 2012 American Chemical Society.