Effect of pH Value on the Properties of Molybdenum-Based Multiphasic Oxide Catalysts in Selective Oxidation of Isobutene to Methacrolein

The effect of different pH values on Mo-Bi-Fe-Co-Mn multiphasic oxide catalysts prepared via co-precipitation methods was studied.In addition,selective oxidation of isobutylene to methacrolein(MAL) reaction was evaluated.The structures and crystal phases of the catalysts were characterized by X-ray diffraction(XRD),Fourier transform infrared(FTIR) spectroscopy,X-ray photoelectron spectroscopy(XPS),N2 adsorption-desorption,and temperature-programmed reduction of H2(H2-TPR).The characterization results showed that the structures and properties depended on the pH during preparation.The amount of the special crystalline phase MX on the catalysts increased with increasing pH value during the preparation process.When the precipitation pH value was 7,the crystalline phase MX reached maximum levels on the corresponding sample.The conversion of isobutene and selectivity for methacrolein were 99.9% and 95.6%,respectively.When increasing the precipitation pH,the MX content decreased,and the conversion of isobutene and selectivity for methacrolein decreased.The results revealed that synergistic effects or cooperation between multiphasic oxides and the special phase MX might be important for improving catalytic performance.