The study of structure-property relationships of heteropolyacids regulated by cesium sources in selective oxidation with methacrolein

The selective oxidation of methacrolein (MAL) to methacrylic acid (MAA) is a crucial step in the C4 process for producing methyl methacrylate (MMA). While Cs-modified polyoxometalates (POMs) are known to enhance the catalytic activity in this reaction, wherein the influence of different cesium sources on their performance remains unexplored. This work systematically investigates the effect of varying cesium sources on the performance of (NH₄⁺)_XCu_0.2CsH_2.8-XPMo₁₁VO₄₀ (BPAV) series catalysts. Characterization results show that the introduction of CsOH facilitates the formation of spherical microstructures in the catalyst, significantly increasing its specific surface area (13.74 m²/g) and medium acid amounts (1.46 mmol/g). XPS analysis further confirms that CsOH enhances the interaction between cesium ions and polyoxometalate anions, promoting the electron transfer from Cs ions to POM anions and the formation of abundant V⁴⁺ species (V⁴⁺/V⁵⁺ = 2.23) for enhanced redox capability. The BPAV catalyst with CsOH/POM molar ratio of 1 achieves the optimal performance, exhibiting 85.5 % MAL conversion and 90.5 % MAA selectivity. Furthermore, the BPAV catalyst with CsOH source also demonstrated excellent catalytic performance in the selective oxidation of propionaldehyde and isobutyraldehyde, with product selectivity surpassing 90 % in both reactions. These findings offer new insights and perspectives for the design of high-efficiency aldehyde oxidation catalysts.