Characterization of vanadium/silica and copper/silica aerogel catalysts

Abstract

Vanadiumjsilica and copper/silica aerogels have been prepared using the sol-gel method followed by C02 exchange and supercritical extraction. Structural properties of samples supercritically dried, oxidized and used in reactions studies conducted with a feed representing the average composition of automobile exhaust from a lean burn engine were investigated using laser Raman spectroscopy and temperature-programmed reduction. No evidence of crystalline V2O5 was found for the vanadium/silica aerogel, freshly extracted, oxidized or following exposure to reaction conditions using these techniques. However, resuIts obtained for the copper/silica sample indicate that changes in the structure of the copper species had occurred as the sample was oxidized and exposed to reaction conditions. Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

Performance of Metal-Catalyzed Hydrodebromination of Dibromomethane Analyzed by Descriptors Derived from Statistical Learning

“…The structural information gained from the utilization of XRD was corroborated by Raman spectroscopy (Figure b). All catalysts displayed low-frequency bands centered at 490 and 603 cm –1 , which are characteristic of the SiO 2 support. , In addition, the Raman spectrum of Ir/SiO 2 evidenced bands at 548 and 716 cm –1 , which could be ascribed to a minor IrO 2 phase, , and the spectrum of Cu/SiO 2 displayed a band at 972 cm –1 , suggesting that a Cu x SiO y phase is likely present in the respective supported Ir and Cu catalysts. , The presence of Cu x SiO y could explain the reduction peak at ca . 500 K observed in H 2 -TPR (Figure S6).…”

“…57,58 In addition, the Raman spectrum of Ir/SiO 2 evidenced bands at 548 and 716 cm −1 , which could be ascribed to a minor IrO 2 phase, 59,60 and the spectrum of Cu/SiO 2 displayed a band at 972 cm −1 , suggesting that a Cu x SiO y phase is likely present in the respective supported Ir and Cu catalysts. 61,62 The presence of Cu x SiO y could explain the reduction peak at ca. 500 K observed in H 2 -TPR (Figure S6).…”

Synthesis of highly thermostable copper-nickel nanoparticles confined in the channels of ordered mesoporous SBA-15 silica

“…The shape and the maximum of the primary peak is attributed to weakly dispersed CuO while the second peak is due to the hardly reducible copper species such as copper silicate or even copper oxide confined in the micropores of SBA-15. [62][63][64] According to the literature, the reduction temperature of CuO depends on the particle size and dispersion, lower reduction temperatures being associated to higher dispersion. [65][66][67] Therefore, the maximum at 344 C is explained by a weak dispersion of the CuO particles supported on SBA-15.…”

Epoxide-assisted alumina aerogels by rapid supercritical extraction

“…7 Copper and vanadium supported on silica aerogels have demonstrated reductive activity for the conversion of NO to N 2 and H 2 O. 8 Copper-silica aerogels have also been used for the reduction of NO in the presence of hydrocarbons, 8 a reaction of interest to the automotive industry because it doesn't use NH 3 as the reductant. Mixed silica and alumina aerogels have been used for the oligomerization of propene to polypropylene 9 , and mixed titania-silica aerogels supporting rhodium have been used in the hydrogenation of benzene 10 .…”