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

• Pyrolysis of MIL-47 (V) generated V on carbon with enhanced mesoporosity, larger V loading, and smaller V crystallites compared to analogues synthesized via impregnation.
• Pyrolysis of MIL-47 (V) produced V carbide at a lower pyrolysis temperature compared to an impregnation technique.
• V carbide catalysts displayed significantly reduced V leaching compared to V oxide catalysts during the oxidation of dibenzothiophene.
• Pyrolyzed MIL-47 (V) provided enhanced catalytic stability compared to analogues synthesized via impregnation in the oxidation of dibenzothiophene.

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 °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 (∼ 350 m2 g−1), high mesoporosities (VMESO/VPORE ∼0.88), high V quantities (35–70 wt.%), and small (∼ 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 (∼0.63), lower V quantity (∼25 wt.%), and larger V crystallites (∼ 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 °C). This phase was not attainable when V/AC was synthesized via pyrolysis even at higher temperatures (i.e., 1100 °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 ∼56%). 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.

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