Zirconia-supported heteropoly acids: Characterization and catalytic behavior in liquid-phase veratrole benzoylation
Zirconia-supported heteropoly acids: Characterization and catalytic behavior in liquid-phase veratrole benzoylation
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DOI：
10.1016/j.jcat.2005.09.016
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发表时间：
2005-12-10
影响因子：
7.3
通讯作者：
Halligudi, SB
中科院分区：
文献类型：
--
作者：
Devassy, BM;Halligudi, SB
以氧化锆负载的硅钨酸(STA)为催化剂，研究了藜芦醇与苯甲酸酐(BA)的液相苯甲酰化合成3，4-二甲氧基二苯甲酮的反应。制备了不同负载量(5~25wt%)和不同焙烧温度(600~850℃)的催化剂。用X射线衍射仪、拉曼光谱、差热分析、X射线光电子能谱、NH3-TPD、红外光谱、吡啶吸附和Durv-Vis光谱对催化剂进行了表征。X射线衍射仪结果表明，STA的存在延缓了氧化锆的晶化，稳定了四方相中的氧化锆。用拉曼光谱表征了最佳负载量(15%)的催化剂，结果表明，在750℃时，催化剂上的主要钨物种是以氧化锆固定的单氧钨酸盐。催化剂表现出Bronsted和Lewis两种酸性，且在750℃焙烧的氧化锆(15SZ-750)上，15%的STA具有最高的Bronsted酸性和总酸性。催化剂的活性依赖于STA的覆盖度，最高的活性对应于硅钨酸盐在氧化锆上的单分子膜。此外，比较了15SZ-750与氧化锆负载的磷钨酸(15%，750℃焙烧，15PZ-750)和二氧化硅负载的硅钨酸(15%，300℃焙烧，15SS-300)的催化活性，结果表明，二氧化硅负载的硅钨酸和磷钨酸是高效稳定的固体酸催化剂，而二氧化硅负载的硅钨酸则被浸出到反应介质中，催化反应均匀。在反应温度为120℃、藜芦醇与BA的摩尔比为5的条件下，活性最高的催化剂15SZ-750的BA转化率为99%，失活催化剂可通过焙烧再生，活性不会有明显的损失。(C)2005 Elsevier Inc.保留所有权利。
The liquid-phase benzoylation of veratrole with benzoic anhydride (BA) to 3,4-dimethoxy benzophenone was investigated using zirconia-supported silicotungstic acid (STA) as a catalyst. Catalysts with different STA loadings (5-25 wt%) and calcination temperatures (600-850 degrees C) were prepared by suspending zirconium oxyhydroxide in methanol solution of STA followed by drying and calcination. These catalysts were characterized by XRD, Raman spectroscopy, DTA, XPS, NH3-TPD, FFIR pyridine adsorption, and DRUV-vis spectroscopy. XRD results indicated that the presence of STA retarded the crystallization of zirconia and stabilized ZrO2 in tetragonal phase. Characterization of the catalyst with optimum STA loading (15%) by Raman spectroscopy showed the presence of zirconia-anchored mono-oxotungstate as the major tungsten species up to 750 degrees C. The catalysts showed both Bronsted and Lewis acidity, and 15% STA on zirconia calcined at 750 degrees C (15 SZ-750) had the highest Bronsted acidity and total acidity. The catalytic activity was found to depend on STA coverage, and the highest activity corresponded to the monolayer of silicotungstate on zirconia. Further, a comparison of the catalytic activity of 15 SZ-750 with zirconia-supported phosphotungstic acid (15%, calcined at 750 degrees C, 15 PZ-750) and silica-supported silicotungstic acid (15%, calcined at 300 degrees C, 15 SS-300) showed that silicotungstic acid and phosphotungstic acid supported on zirconia acted as efficient and stable solid acid catalysts, whereas silicotungstic acid supported on silica was leached into the reaction medium and catalyzed the reaction homogeneously. Under the reaction conditions of 120 degrees C and a veratrole-to-BA molar ratio of 5, the most active catalyst, 15 SZ-750, showed 99% BA conversion, and the deactivated catalyst could be regenerated by calcination without appreciable loss in activity. (c) 2005 Elsevier Inc. All rights reserved.