Toluene oxidation on chromium- and copper-modified SiO2 and SBA-15

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

“…In all samples reduction of finely dispersed separate copper oxide phase can be observed with the appearance of an intensive peak at 523 K. This reduction temperature is lower than that of bulk commercial CuO between 523 and 623 K, and it is probably due to the smaller crystallite size. During the impregnation procedure a part of copper can react with the silanol groups of the support and these copper silicate species can be reduced to metallic state at higher temperatures, up to 673-773 K [10]. Therefore in copper-containing samples a second reduction peak can be observed at 673-773 K. The latter one is more pronounced and shifted to higher temperature for 9Cu/SBA-16 sample.…”

“…ferrite phase, which is in good accordance with the appearance of a CuFe alloy upon reduction evidenced by Mössbauer spectroscopy. The simultaneous presence of Cu 2+ /Fe 3+ pairs in the catalysts leads to higher catalytic activity for all bicomponent samples due to the easier oxygen release, according to Mars-van Krevelen mechanism [10,39]. …”

“…These changes are indicating that in the presence of iron higher amount of CuO phase is formed because the interaction of copper with the silica wall is hindered. According to our former investigations [10], copper on mesoporous silica materials can be reduced to metallic state up to 670 K, however, on iron containing catalysts total reduction cannot be achieved up to 873 K. This can be explained by the stabilization of a part of Fe 3+ species in the silica matrix by the reaction with silanol groups [36]. These kinds of Fe 3+ can be reduced up to 873 K only to Fe 2+ state and their total reduction to metallic state proceeds only over 1073 K. Consequently, on iron containing samples the higher temperature peaks (623-673 K) can be associated with the reduction of iron containing phases in different forms, such as small Fe 2 O 3 nanoclusters, copper ferrite, and ionic iron species connected to silica wall.…”

“…A wide variety of metal ions (Fe, Ti, V, Cr, Cu, Mn etc.) has been introduced into the silica matrix to obtain materials with tunable catalytic properties [4][5][6][7][8][9][10][11][12][13][14][15]. The high surface area and pore volume of the mesoporous supports allow high loadings of the active phase, and their large pore size makes the diffusion of the reactants easier, allowing enhanced availability of the catalytically active sites [16].…”

The effects of alkali metal on structure of manganese oxide supported on SBA-15 for application in the toluene catalytic oxidation

“…As we all know, the mesopore-silica with uniform hexagonal pores and regular pore channels exhibits unique structure properties, and promotes metal oxides to be well dispersed on the support and enhances the diffusion of reactant [15,16]. Recently more attention has been focused on the application of mesoporous silica for toluene oxidation [16][17][18][19].…”