Partial Oxidation of Methanol Over Highly Dispersed Vanadia Supported on Silica SBA-15

Abstract

The partial oxidation of methanol to formaldehyde (FA) was studied over highly dispersed vanadia supported on mesoporous silica SBA-15 (VO x /SBA-15). VO x /SBA-15 catalysts were prepared by a novel grafting/ion-exchange method and characterized using UV-VIS-and Raman spectroscopy. The resulting surface vanadium oxide species (0-2.3 V/nm 2 ), grafted on the inner pores of the SBA-15 silica matrix, consist of tetrahedrally coordinated monomeric and polymeric vanadia. The VO x /SBA-15 catalysts are active and highly selective for the production of FA between 300 and 400°C. Comparison of the reactivity results with literature data reveals that a better catalytic performance can be obtained over vanadia supported on mesoporous silica in comparison with conventional silica samples with the same vanadium loading. Raman characterization of the catalyst after reaction at high conversion indicates that dispersed vanadia partly agglomerates into vanadia crystallites during methanol oxidation.

Redox Properties of Vanadium Ions in SBA-15-Supported Vanadium Oxide: An FTIR Spectroscopic Study

“…Silica SBA-15 was synthesized according to published procedures. 35 Details of the catalyst preparation are described elsewhere. 33 Functionalization of SBA-15 was achieved by stirring 2.5 g of SBA-15 in 100 mL of toluene at 338 K. 42 To this suspension was added 6.5 g of 3-aminopropyltrimethoxysilane (APTMS) with stirring.…”

“…33,34 SBA-15 is a promising new support material as (i) it possesses a well-defined structure based on the presence of uniform hexagonally arrayed channels and a narrow pore size distribution, 35 (ii) its large internal surface area (>800 m 2 /g) allows for the dispersion of a high number of catalytically active sites, 33 and (iii) its thick framework walls (3.1-6.4 nm) provide considerable hydrothermal stability, which exceeds those of the thinner-walled MCM-41 materials. Only recently, we have demonstrated the excellent performance of this catalyst system in methanol oxidation to formaldehyde and in propane oxidation to acrylic acid.…”

The mechanism for the controlled synthesis of highly dispersed vanadia supported on silica SBA-15

“…Furthermore, it opens the possibility to study catalysis on well-defined, spatially separated transition metal centers. Despite its great potential use for catalytic applications, there have been only few reports on the preparation and application of SBA-15 supported vanadium oxide catalysts [4][5][6][7][8][9].…”

“…Vanadium oxides supported on silica exhibit high activity and selectivity for a number of model oxidation reactions, such as the partial oxidation of methane [10,11], methanol oxidation to formaldehyde [8,[12][13][14], and the oxidative dehydrogenation of ethane to ethylene [15]. To understand the correlation between structural and catalytic properties of dispersed vanadia, various techniques including infrared [16-18a,18b], Raman [19][20][21][22][23], UV-visible [16,17,20,24,25], solid-state 51 V NMR [21], and X-ray absorption spectroscopy [18,26] have been used.…”

“…Here, we focus on the synthesis of a VO x / SBA-15 catalyst with a loading of 2.7 wt% V. This vanadium loading was chosen because it is well below loadings, at which formation of V 2 O 5 crystals was observed (9 wt% V) [33]. Recently, this material was shown to exhibit an excellent catalytic performance in methanol partial oxidation to formaldehyde and propane partial oxidation to acrylic acid [8,9].…”