tailieunhanh - Báo cáo hóa học: " Supported quantum clusters of silver as enhanced catalysts for reduction"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Supported quantum clusters of silver as enhanced catalysts for reduction | Leelavathi et al. Nanoscale Research Letters 2011 6 123 http content 6 1 123 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Supported quantum clusters of silver as enhanced catalysts for reduction Annamalai Leelavathi Thumu Udaya Bhaskara Rao Thalappil Pradeep Abstract Quantum clusters QCs of silver such as Ag7 H2MSA 7 Ag8 H2MSA 8 H2MSA mercaptosuccinic acid were synthesized by the interfacial etching of Ag nanoparticle precursors and were loaded on metal oxide supports to prepare active catalysts. The supported clusters were characterized using high resolution transmission electron microscopy scanning electron microscopy X-ray photoelectron spectroscopy and laser desorption ionization mass spectrometry. We used the conversion of nitro group to amino group as a model reaction to study the catalytic reduction activity of the QCs. Various aromatic nitro compounds namely 3-nitrophenol 3-np 4-nitrophenol 4-np 3-nitroaniline 3-na and 4-nitroaniline 4-na were used as substrates. Products were confirmed using UV-visible spectroscopy and electrospray ionization mass spectrometry. The supported QCs remained active and were reused several times after separation. The rate constant suggested that the reaction followed pseudo-first-order kinetics. The turn-over frequency was s-1 per cluster for the reduction of 4-np at 35 C. Among the substrates investigated the kinetics followed the order SiO2 TiO2 Fe2O3 Al2O3. Introduction Monolayer-protected quantum clusters QCs composed of a few atoms show unique properties due to their novel atomic and electronic structure. Their discrete electronic states produce well-defined luminescence in clusters such as Au25 Au23 Au22 Au8 etc. 1-7 . They have attracted the attention of various fields such as sensors biolabels live cell-targeted imaging 4 single molecule electroluminescence 8 opto-electronics 9 and catalysis 10 . In the case of Au25 single crystal X-ray analysis has shown .