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Insightful understanding of the correlations of the microstructure and catalytic performances of Pd@chitosan membrane catalysts studied by positron annihilation spectroscopy
RSC Advances ( IF 3.9 ) Pub Date : 2018-01-17 00:00:00 , DOI: 10.1039/c7ra12407d Qi Liu 1 , Mengdie Xu 1 , Jing Zhao 1 , Yudong Wang 1 , Chenze Qi 1 , Minfeng Zeng 1 , Rui Xia 2 , Xingzhong Cao 2 , Baoyi Wang 2
RSC Advances ( IF 3.9 ) Pub Date : 2018-01-17 00:00:00 , DOI: 10.1039/c7ra12407d Qi Liu 1 , Mengdie Xu 1 , Jing Zhao 1 , Yudong Wang 1 , Chenze Qi 1 , Minfeng Zeng 1 , Rui Xia 2 , Xingzhong Cao 2 , Baoyi Wang 2
Affiliation
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In this study, the catalytic performances of palladium supported on chitosan (Pd@CS) membrane heterogeneous catalysts have been studied from the aspects of free volume by positron annihilation lifetime spectroscopy (PALS). The results showed that the variation in free volume hole size of the Pd@CS membrane catalyst was closely associated with microstructure evolutions, such as increase of Pd content, valence transition of Pd by reduction treatment, solvent swelling, physical aging during catalyst recycling, and so on. The PALS results showed that both the mean free volume hole size of the Pd0@CS membrane in the dry or swollen state (analyzed by the LT program) and its distribution (analyzed by the MELT program) are smaller than the molecule size of the reactants and products in the catalysis reaction. However, the results showed that the Pd0@CS membrane catalyst has excellent catalytic activity for the Heck coupling reaction of all the reactants with different molecule size. It was revealed that the molecule transport channels of the Pd0@CS membrane catalyst in the reaction at high temperature was through a number of instantaneously connected free volume holes rather than a single free volume hole. This hypothesis was powerfully supported by the catalytic activity assessment results of the CS layer sealed Pd0@CS membrane catalyst. Meanwhile, it was confirmed that the leaching of Pd0 nanoparticles of the reused Pd0@CS membrane catalyst during the recycling process was also through such instantaneously connected free volume holes.
中文翻译：
通过正电子湮没光谱研究 Pd@壳聚糖膜催化剂的微观结构和催化性能的相关性的深刻理解
本研究通过正电子湮没寿命光谱（PALS）从自由体积方面研究了壳聚糖负载钯（Pd@CS）膜非均相催化剂的催化性能。结果表明，Pd@CS膜催化剂自由体积孔径的变化与微观结构演变密切相关，如Pd含量的增加、还原处理引起的Pd价转变、溶剂溶胀、催化剂回收过程中的物理老化以及很快。PALS 结果表明，Pd 0的平均自由体积孔尺寸@CS 膜在干燥或膨胀状态下（由 LT 程序分析）及其分布（由 MELT 程序分析）小于催化反应中反应物和产物的分子大小。然而，结果表明，Pd 0 @CS膜催化剂对所有不同分子大小的反应物的Heck偶联反应都具有优异的催化活性。结果表明，Pd 0 @CS膜催化剂在高温反应中的分子传输通道是通过多个瞬时连接的自由体积孔而不是单个自由体积孔。CS层密封Pd 0的催化活性评估结果有力地支持了这一假设@CS 膜催化剂。同时证实，再利用的Pd 0 @CS膜催化剂在回收过程中Pd 0纳米颗粒的浸出也是通过这种瞬时连接的自由体积孔。
更新日期：2018-01-17
中文翻译：
通过正电子湮没光谱研究 Pd@壳聚糖膜催化剂的微观结构和催化性能的相关性的深刻理解
本研究通过正电子湮没寿命光谱（PALS）从自由体积方面研究了壳聚糖负载钯（Pd@CS）膜非均相催化剂的催化性能。结果表明，Pd@CS膜催化剂自由体积孔径的变化与微观结构演变密切相关，如Pd含量的增加、还原处理引起的Pd价转变、溶剂溶胀、催化剂回收过程中的物理老化以及很快。PALS 结果表明，Pd 0的平均自由体积孔尺寸@CS 膜在干燥或膨胀状态下（由 LT 程序分析）及其分布（由 MELT 程序分析）小于催化反应中反应物和产物的分子大小。然而，结果表明，Pd 0 @CS膜催化剂对所有不同分子大小的反应物的Heck偶联反应都具有优异的催化活性。结果表明，Pd 0 @CS膜催化剂在高温反应中的分子传输通道是通过多个瞬时连接的自由体积孔而不是单个自由体积孔。CS层密封Pd 0的催化活性评估结果有力地支持了这一假设@CS 膜催化剂。同时证实，再利用的Pd 0 @CS膜催化剂在回收过程中Pd 0纳米颗粒的浸出也是通过这种瞬时连接的自由体积孔。
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