Mechanism of W(CO)6 sonolysis in diphenylmethane

The present work analyses the mechanism of W2C/C nanocomposite formation during sonolysis of W(CO)6 in diphenylmethane (DPhM) solutions. Carbon supported WCx nanoparticles attract much interest as an alternative fuel cell electrocatalysts. Sonolysis of neat DPhM under the effect of 20 kHz power ultrasound in argon at 80 °C yields a sonopolymer as a solid product and acetylene, hydrogen, methane, diacetylene and benzene as gaseous products. Diacetylene is formed due to the secondary sonochemical dimerisation of acetylene obtained at the primary stage of DPhM sonolysis. FTIR and μ-Raman studies show that the sonopolymer consists of a mixture of some polymeric partially oxidized aromatic species, and disordered carbon. Sonolysis of W(CO)6 in diphenylmethane solutions follows the first order kinetics. This process yields monodispersed 2–3 nm X-ray amorphous WCx nanoparticles embedded in amorphous sonopolymer. The annealing of air sensitive as-prepared solids in an inert atmosphere at 600 °C causes formation of stable W2C/C nanocomposite with W2C average particle size in the range of 4–7 nm and hexagonal carbon fine particles with the average size of 30–40 nm. Kinetic study revealed that tungsten carbide is formed inside the cavitation bubble due to the reaction of tungsten nanoparticles originated from primary sonolysis of W(CO)6 with acetylene produced as a result of diphenylmethane sonochemical degradation.

► Sonolysis of W(CO)6 in diphenylmethane yields W2C/C nanocomposite.
► Sonolysis of neat diphenylmethane gives a solid carbonaceous product.
► Also sonolysis of diphenylmethane produces H2, C2H2, C4H2, C6H6 and CH4 in the gas phase.
► C4H2 is formed due to the secondary sonochemical dimerisation of C2H2.
► W2C is formed inside the cavitation bubble by the reaction of W nanoparticles with C2H2.