Vanadia–silica and vanadia–cesium–silica catalysts for oxidation of SO₂

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• 作者：Pâ ; rvulescu ; Vasile I. ; Paun ; Cristina ; Pâ ; rvulescu ; Viorica ; Alifanti ; Mihai ; et. al.
• 关键词：Mesoporous V₂O₅&ndash ; SiO₂ catalysts promoted with Cs ; In situ Raman ; EPR ; XRD characterization
• 刊名：Journal of Catalysis
• 出版年：2004
• 期刊代码：97_00219517
• 类别：ce
• 出版时间：July 1, 2004
• 卷：225
• 期：1
• 页码：24-36
• 文件大小：443 K

摘要

Mesoporous vanadia–silica catalysts have been prepared by three different sol–gel procedures using tetraethylorthosilicate (TEOS), vanadyl acetylacetonate (VAA), or VOCl₃ and in some cases quaternary ammonium salts ((CH₃)₃C₁₄H₂₉N⁺Br⁻ or (C₁₀H₂₁)₄N⁺Br⁻) as surfactants. According to procedure A, TEOS and VAA were concomitantly hydrolyzed, in procedure B TEOS was prehydrolized and vanadium precursor was added to the silica sol, and in procedure C both TEOS and vanadium precursors were separately prehydrolized. The sol–gel procedures were controlled by checking the effect of the hydrolysis pH, refluxing time, surfactant, and conditions of gellifications (slow evaporation at room temperature or autoclavization). The samples were dried under vacuum, first at room temperature, then at 373 K, and finally calcined at 773 K. ICP-AES analysis indicated for all samples a vanadium content of around 6.5 wt%. The samples were impregnated with Cs₂SO₄ resulting in a Cs:V ratio of 3:1 and then dried and calcined under the same conditions. The catalysts were characterized using several methods: sorption isotherms of N₂ at 77 K, XRD, and XPS. The results of the characterization indicated that during calcination of the V/Cs catalysts vanadia is dissolved in a sulfate containing molten salt. The activity of these catalysts for the oxidation of SO₂ was tested in a gas containing 2%SO₂, 19%O₂, 79%N₂ in the temperature range 523–823 K. Similar experiments with gases containing 10%H₂O in the feed or with wet catalysts were also performed. The activation of the catalysts and the catalytic behavior were monitored by in situ Raman and EPR spectroscopy. These characterization techniques indicated that the active molten phase contains vanadium oxosulfato complexes similar to the V₂O₅–M₂S₂O₇ (M=alkali metal)-based industrial catalyst, where kieselghur is used as carrier material. The high dispersion of vanadium in the studied catalysts results in an increased catalytic activity for the oxidation of SO₂ contained in feed gases with low SO₂ content.