Selective Methacrolein Oxidation Catalyzed with Heteropoly Compounds: Effect of the Oxidation State Modulated with Hydrogen Pretreatment

ABSTRACT: The chemical state of catalysts is a vital factor affecting their catalytic performance. Herein, a method for controllable modification of the chemical state was proposed for the heteropoly catalyst in the methacrolein oxidation reaction to methacrylic acid by means of hydrogen pretreatment. The inherent relationship between the chemical state and the catalytic performance of the Keggin catalyst was systematically investigated. The changes in structure and element valence induced by hydrogen pretreatment were characterized with various methods, including XRD, FTIR, UV, Raman, SEM, O2-TPD, XPS, and ESR spectra. The pretreatment conditions were optimized on a fixed-bed tubular reactor, and the favored chemical state of the catalyst was obtained. This report provides an effective approach to activating the Keggin catalyst for oxidation reactions.