TY - JOUR T1 - Vanadium dispersion and catalytic activity of Pd/VOx/SBA-15 catalysts in the Wacker oxidation of ethylene JF - Microporous and Mesoporous Materials Y1 - 2015 A1 - Barthos, Róbert A1 - Hegyessy, András A1 - Klébert, Szilvia A1 - Valyon, József KW - H2-TPR KW - Pd/V catalysts KW - SBA-15 KW - UV–Vis KW - Wacker oxidation AB - Transmission electron microscopy (TEM), X-ray diffractometry (XRD), in situ diffuse reflectance ultra violet – visible (UV–Vis) spectroscopy, and temperature-programmed reduction by hydrogen (H2-TPR) were used to identify the vanadia forms in vanadium-containing SBA-15 preparations (VOx/SBA-15). Wacker type supported Pd/VOx/SBA-15 catalysts were obtained by introducing Pd into VOx/SBA-15 samples using conventional impregnation method. The activity of the catalysts was tested in the gas phase partial oxidation of ethylene by O2 in the presence of H2O (Wacker oxidation). VOx/SBA-15 sample was obtained by micelle-templated synthesis using vanadium-containing synthesis gel. The vanadium became incorporated in the silica structure from the gel in near to atomic dispersion. This catalyst was quite active in ethylene oxidation to CO2 but had low Wacker activity. Isolated, polymeric and bulk vanadia species were identified in the VOx/SBA-15 prepared by wet impregnation/calcination method. The specific surface area of the sample was found to be smaller than that of the neat SBA-15 support because some pores were blocked by vanadia agglomerates. The corresponding Pd/VOx/SBA-15 catalyst showed high selectivity for acetaldehyde formation but the activity was relatively low due to low accessible active surface. A third VOx/SBA-15 sample was obtained by applying directed surface reaction between silanol groups of dehydrated SBA-15 and anhydrous solution of vanadyl acetylacetonate. Large number of accessible Pd/VOx sites were present in the corresponding Pd/VOx/SBA-15 catalyst. Latter catalyst induced ethylene oxidation to acetaldehyde with high yield at temperatures ≤160 °C and with good yield to acetic acid at temperatures ≥160 °C. VL - 207 SN - 1387-1811 UR - http://www.sciencedirect.com/science/article/pii/S1387181115000050 JO - Microporous and Mesoporous Materials ER -