Direct oxidation of methanol to high value oxygenated chemicals on V2O5/TiO2 based catalysts is a green alternative to the commercial methods. But the V–Ti based catalysts are challenged by the relatively low reactivity. Herein, we demonstrated a facile and practicable strategy to directly fabricate hollow structure VOx/TiO2 nanofibers (VTO-HNF) through the coelectrospinning and calcination method. The effects of V/Ti ratio on the structure, the surface chemistry and methanol oxidation performance were investigated in detail. VTO-HNFs with appropriate V/Ti ratio have hierarchical structure, large surface area, uniform nanoparticles, narrowed grain sizes, and high dispersions of vanadium. Moreover, both the oxidation properties and the acidities of the catalyst were enhanced due to the high content of surface V4+. The VTO-HNF catalysts featured excellent activities and reliable stability for the selective oxidation of methanol to methyl formate (MF) and dimethoxymethane (DMM). The MF yield reached 90% at 150 °C, which is comparable with the noble metal based catalysts. In situ NAP-XPS investigations suggested that the variable valence of vanadium was involved in the oxidation of methanol.
The direct oxidation of toluene by O 2 to benzaldehyde with high efficiency is a bright route for the green production of benzaldehyde but still a significant challenge. In this study, we develop a ligand modification strategy by bonding organophosphonic acid (OPA) to VTiO x /γ-Al 2 O 3 to restructure its interface microenvironment for enhancement of toluene oxidation to benzaldehyde. The as-prepared catalyst exhibits excellent selectivity over 99 % under mild conditions. Results of comprehensive characterizations and calculations reveal that the OPA bonding in bidentate with the V 6-coordinated species causes noticeable phase reconstruction between VO x and TiO 2 , thereby generating nearby new reactive oxygen species, which is responsible for the conversion of toluene to benzaldehyde at temperatures as low as ∼50 °C, much lower than that over VO x /TiO 2 (>130°C). The interface microdomain around the bonding site of OPA helps to significantly weaken the methyl C H bond of toluene molecule in reaction manifested as the significant decrease in apparent activation energy. Hence, the current work reveals a novel mechanism of the typical catalyst VO x /TiO 2 under OPA bonding, which is useful to solve the classic difficult reaction of toluene to benzaldehyde by O 2 oxidation.
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