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XAFS Study of Silica-supported Chromium-based Catalyst
Zhang Huiab1,2, Kou Yuanb2
1.Key Laboratory for Science and Technology of Controllable Chemical Reaction of Education Ministry, Beijing University of Chemical Technology , Beijing 100029;2.College of Chemistry and Molecular Engineering, Peking University, Beijing 100871)
Abstract:
Silica-supported sodium-modified chromium catalyst Na-7.5%Cr/SiO2is found to be active for simultaneous activation of methane and carbon dioxide to aromatics(SAMCA). The best result shows the methane conversion of 4.0% and the selectivity of 48.7% to aromatics (benzene+toluene). X-ray absorption Cr K-edge fine structure analyses (XANES and EXAFS) and XPS are employed to study the surface structure of the catalyst. Both Cr6+and Cr3+are present on the surface, while the prosperous of Cr6+on the surface is observed. The results demonstrate that the dual-center(mixed oxidation state)/mixed site-symmetric structure—Td-Cr(VI)/Oh-Cr(III) is the catalytic active sites of Na-7.5%Cr/SiO2in SAMCA. A possible catalyst model of double-sites activation mechanism in SAMCA has been tentatively proposed.
Key words:  XANES, EXAFS, Silica-supported Cr catalyst, Dual-center/mixed site-symmetries, Double-sites activation
FundProject:
二氧化硅担载铬基催化剂的XAFS研究
张慧1, 寇元2
1.北京化工大学可控化学反应科学与技术基础教育部重点实验室,北京,1100029 北京大学化学与分子工程学院,北京,100871;2.北京大学化学与分子工程学院,北京,100871
摘要:
考察了二氧化硅担载铬基催化剂Na-7.5%Cr/SiO2在甲烷-二氧化碳共活化制芳烃(SAMCA)新反应中的催化活性, 最佳结果为甲烷转化率4.0%,芳烃选择性48.7%.用扩展X射线吸收精细结构(EXAFS)和X射线吸收近边结构(XANES), 以及X光电子能谱(XPS)等方法研究了SAMCA反应催化剂Na-7.5%Cr/SiO2的结构.结果表明, 催化剂表面主要存在Cr(VI)和 Cr(III)两种物种, 六价铬相对在表面富集,催化剂呈明显的无定形特征.结合其SAMCA反应活性结果, 认为催化剂中单金
关键词:  EXAFS  XANES  铬基催化剂  双中心混合位置对称性  双位活化
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