Catalytic activity and stability of carbon supported V oxides and carbides synthesized via pyrolysis of MIL-47 (V)

Substantial leaching of active V species often limits the reusability of V-based soild catalysts in liquid phase oxidation reactions and therefore requires the development of more stable, novel materials. This paper first reports the synthesis of active vanadium (V) oxide and carbide species dispersed on a carbon support via the pyrolysis of MIL-47 (V), a V-based metal-organic framework (MOF) template. The phase transition of V species present in this MOF template was achieved by varying the pyrolysis temperatures ranging from 600 to 1100 degrees C to synthesize a series of carbon catalysts with different surface and bulk phases of V. Notably, the pyrolysis of MIL-47 (V) provided carbon supports with high surface areas (similar to 350 m(2) g(-1)), high mesoporosities (V-MESO/V-PORE similar to 0.88), high V quantities (35-70 wt.%), and small (similar to 18 nm) V crystallites dispersed on the surface. These desired properties were not observed when V was supported on activated carbon (V/AC) via conventional impregnation. The V/AC catalyst showed lower mesoporosity (similar to 0.63), lower V quantity (similar to 25 wt.%), and larger V crystallites (similar to 27 nm) compared to the catalyst produced from MIL-47 (V) pyrolysis under identical conditions. Of additional note, the pyrolysis of MIL-47 (V) could yield an isolated bulk phase of V carbide at low pyrolysis temperatures (i.e., >900 degrees C). This phase was not attainable when V/AC was synthesized via pyrolysis even at higher temperatures (i.e., 1100 degrees C). The catalytic performance of the resulting V on carbon catalysts was evaluated in a liquid-phase oxidation reaction of dibenzothiophene. The V carbide catalysts exhibited good activities and enhanced stabilities, as evidenced by lower amounts of V species leached (<20%) during recycle runs compared to the conventional V/AC catalyst (V leaching similar to 6%). This study marks a signifcant improvement in the synthesis of supported V catalysts with reduced leaching in liquid-phase oxidation reactions compared to materials synthesized via conventional impregnation techniques. (C) 2016 Elsevier B.V. All rights reserved.