The controlled oxidation states of the H4PMo11VO40 catalyst induced by plasma for the selective oxidation of methacrolein

Abstract

In this paper, low-temperature dielectric-blocked discharge plasma (DBD) was employed for the first time to treat silica-doped H₄PMo₁₁VO₄₀ (HPAV) catalysts (DBD(Ar/x)-MF-Catal) and apply them in the catalytic methacrolein (MAL) selective oxidation to produce methacrylic acid (MAA). This work investigates in detail the controllable regulation of the concentration of oxidation states on silica-doped HPAV catalysts by adjusting the DBD discharge with controlled changes in voltage, current, treatment time, and treatment medium. It reports the intrinsic correlation between oxidation states and MAL oxidation performance. The research results indicated that the catalytic performance was related to the presence of oxygen vacancies and oxygen species (VO²⁺), and are the main reason for the selective oxidation of MAL to MAA. Besides, the generation of oxygen vacancies and VO²⁺ altered localized electrons, which resulted in the easier activation of O₂. Theoretical calculations of DFT also proved the formation mechanism of oxygen vacancies and VO²⁺ and electron properties on high-performance polymers, which elucidated the intrinsic influence of catalyst components. The DBD(Ar/10)-MF-Catal catalysts with suitable VO²⁺ and oxygen vacancy concentrations exhibited the highest catalytic performance with 90 % MAL conversion and 70 % MAA selectivity and showed good stability (500 h).