Effect of tungsten loading on zirconia impregnated MCM-41 and its catalytic activity on transesterification reaction

WO3/ZrO2 weight % (WO3/ZrO2 = wt% = 4/22, 8/22, 15/22, 15/30 and 15/40) was impregnated on Si-MCM-41. The crystalinity, textural property, surface feature and surface acidity of the materials were characterized by XRD, N2-physisorption isotherm (BET), NH3-TPD, Laser-Raman and XRF. The XRD and BET results revealed that the materials were hexagonally ordered mesoporous (pore size = 2.58–3.07 nm) materials. High angle XRD showed the presence of tetragonal ZrO2 (crystallite size L = 14.88 nm) and monoclinic ZrO2. The catalytically active t-ZrO2 was stabilized by increasing wt% of WO3. Raman spectra confirmed the presences of crystalline WO3 along with t-ZrO2 and m-ZrO2 which was not detected by high angle XRD. WO3 restrict the phase transfer from metastable t-ZrO2 to thermodynamically favoured m-ZrO2. NH3-TPD results indicated the presence of weak acid sites and it increased with an increase in tungsten loading on mesoporous materials. There was no appreciable increase in acid sites by increasing ZrO2. The catalytic activity was studied on transesterification of diethyl oxalate diester with various alcohols in liquid phase system under autogeneous pressure. When the t-ZrO2 phase increases the selectivity of diester also increases. However the optimum metal oxide loading on Si-MCM-41 was with 15 % WO3/22 % ZrO2/Si-MCM-41. Hence the materials can be a convenient and suitable acid catalyst for transesterification.