Impact of silica structure of copper and iron-containing SBA-15 and SBA-16 materials on toluene oxidation

Copper and iron modified SBA-15 and SBA-16 materials were prepared by incipient wetness impregnation technique and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 physisorption, temperature-programmed reduction (TPR-TGA), UV-Vis diffuse reflectance and Mössbauer spectroscopy. Formation of finely dispersed copper and iron-oxide species was observed on both supports, whereas copper ferrite could be evidenced only on SBA-15. It was found that the structural and surface properties of the mesoporous supports determine the type of formed metal oxides, their dispersion, reducibility and the catalytic activity in total oxidation of toluene. On SBA-16 support penetration of metal salt into the bimodal channel system is hindered therefore separate copper- and iron-oxide phases are formed on the outer surface of catalysts. The catalytic activity and stability are lower due to the easier agglomeration of particles. On SBA-15 support finely dispersed metal-oxides can be found in the mesoporous channels. Their interaction is favored to form bimetallic phases enhancing the catalytic activity and stability in total oxidation of toluene

Vanadium dispersion and catalytic activity of Pd/VOx/SBA-15 catalysts in the Wacker oxidation of ethylene

Transmission electron microscopy (TEM), X-ray diffractometry (XRD), in situ diffuse reflectance ultra violet e visible (UVeVis) 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 0C and with good yield to acetic acid at temperatures >~160 0C

Transformation of ethylbenzene-m-xylene feed over MCM-22 zeolites with different acidities

Transformation of ethylbenzene (EB, 22 wt%)-m-xylene (78 wt%) mixture was carried out over zeolite MCM-22 catalysts with different acidities. The modification of the number and strength of the acid sites was attained by: (i) dealumination by steaming and successive acid treatment and (ii) isomorphous substitution of framework Al for boron ([Al,B]MCM-22). The effect of platinum introduction was also investigated. The strong decrease in the Brønsted acidity, concomitant to the dealumination procedure, appears unfavorable since it leads to a drastic diminish of the degree of EB conversion, not compensated by satisfactory level of m-xylene isomerization. [Al,B]MCM-22 is a modification with much better performance, most probably because it contains both strong, Al-connected acid sites but in lower amount than in the parent sample, and weaker boron-generated sites and practically no any Lewis sites. Parent zeolite [Al]MCM-22 as well as B-substitution possess promising properties for ethylbenzene–m-xylene mixture transformation catalyst with adequate degree of EB conversion and extent of p-xylene approach to equilibrium as well as low xylene loss

Recyclable solid-phase biocatalyst with improved stability by sol–gel entrapment of β-d-galactosidase

Abstract β-d-Galactosidase from Kluyveromyces lactis was for the first time immobilized by entrapment in hybrid organic-inorganic sol–gel materials with microporous structure, obtained from alkoxy silanes and alkyl substituted alkoxy silanes, in different combinations. The immobilization matrix was tailored by fine tuning of several parameters, such as: nature of alkyl group of silane precursors, molar ratio of silane precursors, nature of additives, protein concentration. Unlike other enzymes, β-d-galactosidase showed the best catalytic activity at low alkyl group content in the sol–gel matrix, at a molar ratio of 7:1 between the tetraalkoxysilane alkyl-trialkoxysilane precursor. The immobilized enzyme demonstrated enhanced storage, pH and thermal stability compared to the soluble enzyme. The composite sol–gel materials were characterized by transmission electron microscopy, scanning electron microscopy, fluorescence confocal microscopy, and porosity measurement. The biocatalyst was successfully reused in five reaction cycles, maintaining more than 60% of the initial activity