Catalytic performance of V-MCM-41 nanocomposites in liquid phase limonene oxidation: Vanadium leaching mitigation

Chemical stability and catalytic performance of MCM-41 materials functionalized with vanadium by template ion exchange (TIE) were studied. Solids with different vanadium loadings were synthesized and characterized by a multi-technique approach. Their textural and chemical properties were analyzed by low and high angle XRD, N-2 adsorption-desorption, SEM, UV-vis DR, XPS, FTIR-Py and ICP-OES. All solids exhibited a highly ordered mesoporous structure, characteristic of MCM-41 materials. Their specific areas, pore diameters and pore volumes were found to be suitable for application as catalysts in liquid phase oxidation reactions. From different tests of limonene oxidation with H2O2, it was found that isolated cations (V delta+) are more likely to be the active sites for this reaction. Additionally, results show that high vanadium content actually lowers catalytic performance and favors sub-product formation by secondary reactions. Recycling tests were performed using the lowest vanadium content sample, finding that considerable leaching of active species took place after two reactions cycles. Wet impregnation with titanium was tested as a strategy for vanadium leaching mitigation. Solids with different titanium loadings were synthesized and evaluated. One of the bimetallic materials was selected according to its enhanced catalytic activity which accounts for an interesting synergistic effect between vanadium and titanium. This solid also displayed a superior chemical stability, since the absence of leaching was successfully proven in successive reaction cycles.