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

Abstract

Substantial leaching of active V species often limits the reusability of V-based soild catalysts in liquidphase 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 m 2 g-1), high mesoporosities (V MESO /V PORE~ 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 liquidphase 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.

Metal organic frameworks as precursors for the manufacture of advanced catalytic materials

“…Kim et al worked on the synthesis of active vanadium oxide and carbide species dispersed on a carbon support from a V-based MOF template and evaluated its catalytic performance in the liquid-phase oxidation of dibenzothiophene (DBT) with tert-butyl hydroperoxide (TBHP). 186 The activated MIL-47(V) was carbonized under Ar with a ramp rate of 10 1C min À1 at temperatures ranging from 600 1C to 1100 1C for 6 h. After cooling to 25 1C under Ar, the resulting catalyst was passivated under 1% of O 2 in He for 1.5 h prior to exposure to ambient atmosphere. Notably, the pyrolysis of MIL-47(V) provided carbon supports with high surface areas (B300-400 m 2 g À1 ), high mesoporosity (V meso /V pore B 0.9), high V loadings (35-70 wt%), and small (B18 nm) V crystallites dispersed on the surface.…”

Metal‐Organic Framework‐Based Catalysts for Oxidative Desulfurization

“…These mesoporous materials showed enhanced catalytic activity in the oxidation of DBT (using TBHP as oxidant) when compared with the pyrolyzed microporous MIL‐125(Ti). Controlled pyrolysis of MIL‐47(V) was also investigated by the same group, generating vanadium on carbon with enhanced mesoporosity, higher metal loading, and smaller V crystallites compared to analogues synthesized via impregnation (Figure ) . The MOF derived V materials showed different composition depending on the pyrolysis temperature, ranging from different V oxides to V carbide.…”

Highly Selective Oxidation of Ethyl Lactate to Ethyl Pyruvate Catalyzed by Mesoporous Vanadia–Titania

“…In addition, these catalysts are also prone to leaching. 20 On the basis of our earlier experience with doped mixed oxides for the oxidative dehydrogenation of propane, 21 we hypothesized that doping vanadium ions into the mesoporous TiO 2 lattice would solve these problems. Titania–vanadia hybrids have been made using various methods, including hydrothermal, 22 , 23 sol–gel, 24 electrochemical, 25 spray pyrolysis, 26 and coprecipitation.…”