文献类型：期刊文献

英文题名：Catalysis mechanism of Pd(II)@PVA membrane catalyst studied from the aspect of molecular level micro-defects by positron annihilation spectroscopy

作者：Xu, Mengdie[1];Zhao, Jing[1];Luo, Chao[1,2];Liu, Qi[1];Zeng, Minfeng[1];Qi, Chenze[1];Xia, Rui[3];Cao, Xingzhong[3];Wang, Baoyi[3]

机构：[1]Shaoxing Univ, Coll Chem & Chem Engn, Zhejiang Key Lab Alternat Technol Fine Chem Proc, Shaoxing 312000, Peoples R China;[2]Shaoxing Univ, Dept Med & Hlth, Yuanpei Coll, Shaoxing 312000, Peoples R China;[3]Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China

年份：2019

卷号：156

起止页码：128

外文期刊名：RADIATION PHYSICS AND CHEMISTRY

收录：SCI-EXPANDED(收录号：WOS:000460717500017)、、EI(收录号：20184706111835)、Scopus(收录号：2-s2.0-85056635598)、WOS

基金：The authors acknowledge the financial support from the National Natural Science Foundation of China, China (Grant number: No. 11475114, 11875193, 11575117), and Zhejiang Province Fundamental Public Welfare Research Project, China (Grant number: No. LGG18E030004).

语种：英文

外文关键词：Positron annihilation; Micro-defects; Catalysis mechanism; Polyvinyl alcohol; Heck reactions

外文摘要：In this study, an insightful understanding of the correlations of the molecular level micro-defects structure and catalytic performance of palladium species supported on polyvinyl alcohol (Pd(II)@PVA) membrane heterogeneous catalyst have been studied with positronium probe and other structural characterization methods. The micro-defects size both in crystalline region (D-c) and amorphous region (D-a) of PVA matrix increases gradually with the Pd species loading and membrane catalyst recycle times. As a result of a synergism of micro-defects enlargement caused by solvents swelling and highly thermal motions of macromolecular segments at high temperature, a number of instantaneously connected micro-defects channel rather than a single micro-defect in the real reaction state might provide enough open spaces for the coupling reactions. This catalysis mechanism from the aspect of molecular level micro-defects structure is powerfully supported by comparing the catalytic performances of a common Pd(II)@PVA membrane catalyst and a PVA layer sealed Pd(II)@PVA membrane catalyst applied in Heck reactions. As the recycle times increases, the compactness and regularity of PVA molecular chain segments stacking decreases obviously, which promotes the Pd leaching and causes gradually decrease in catalytic efficiency of the recycled Pd(IH@PVA membrane catalyst. The mechanical properties, morphology, crystalline behavior, and swelling properties of the Pd(II)@PVA membrane catalysts are also characterized and explained in view of the changes of molecular level micro-defects structure.