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Supported quantum clusters of silver as enhanced catalysts for reduction.

Leelavathi A, Bhaskara Rao TU, Pradeep T - Nanoscale Res Lett (2011)

Bottom Line: We used the conversion of nitro group to amino group as a model reaction to study the catalytic reduction activity of the QCs.The turn-over frequency was 1.87 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.

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Affiliation: DST Unit of Nanoscience (DST UNS), Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India. pradeep@iitm.ac.in.

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 1.87 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.

No MeSH data available.


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Negative ion LDI mass spectrum of Ag7,8 loaded on alumina. One of the features is expanded in the inset, along with the theoretical pattern.
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Figure 3: Negative ion LDI mass spectrum of Ag7,8 loaded on alumina. One of the features is expanded in the inset, along with the theoretical pattern.

Mentions: Further confirmation of the presence of Ag QCs in the supported material was available from LDI-MS as shown in Figure 3. It gives characteristic features of AgnSm-. Laser irradiation at 337 nm cleaves AgS-C, bond and AgnSm clusters alone are observed in the gas phase. The intact chemical composition of the QC was not observed, as typical of the spectra of thiolated clusters [34,38]. AgnSm- species observed in the gas phase are dissociation products as well as gas phase reaction products. Intact clusters, along with the monolayers, are seen only in MALDI-MS and ESI-MS of the free clusters [34]. One of the interesting aspects of silver is its isotope distribution, which helps us to unambiguously assign the ions. To illustrate this, the experimental isotope pattern of one cluster fragment is compared with its theoretical pattern in the inset of Figure 3. It may be noted that the clusters do not fragment upon adsorption on the alumina surface, as properties of the clusters such as luminescence are retained on the oxide surface.


Supported quantum clusters of silver as enhanced catalysts for reduction.

Leelavathi A, Bhaskara Rao TU, Pradeep T - Nanoscale Res Lett (2011)

Negative ion LDI mass spectrum of Ag7,8 loaded on alumina. One of the features is expanded in the inset, along with the theoretical pattern.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211169&req=5

Figure 3: Negative ion LDI mass spectrum of Ag7,8 loaded on alumina. One of the features is expanded in the inset, along with the theoretical pattern.
Mentions: Further confirmation of the presence of Ag QCs in the supported material was available from LDI-MS as shown in Figure 3. It gives characteristic features of AgnSm-. Laser irradiation at 337 nm cleaves AgS-C, bond and AgnSm clusters alone are observed in the gas phase. The intact chemical composition of the QC was not observed, as typical of the spectra of thiolated clusters [34,38]. AgnSm- species observed in the gas phase are dissociation products as well as gas phase reaction products. Intact clusters, along with the monolayers, are seen only in MALDI-MS and ESI-MS of the free clusters [34]. One of the interesting aspects of silver is its isotope distribution, which helps us to unambiguously assign the ions. To illustrate this, the experimental isotope pattern of one cluster fragment is compared with its theoretical pattern in the inset of Figure 3. It may be noted that the clusters do not fragment upon adsorption on the alumina surface, as properties of the clusters such as luminescence are retained on the oxide surface.

Bottom Line: We used the conversion of nitro group to amino group as a model reaction to study the catalytic reduction activity of the QCs.The turn-over frequency was 1.87 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: DST Unit of Nanoscience (DST UNS), Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India. pradeep@iitm.ac.in.

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 1.87 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.

No MeSH data available.


Related in: MedlinePlus