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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.

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.


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XPS spectra of supported quantum clusters. XPS expanded spectra in the Ag 3d (a), C 1s (b), S 2p (c), and Al 2p (d) regions of Al2O3@Ag7,8 QCs before (black), after 1st (red) and 3rd cycles (green) of catalysis.
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Figure 6: XPS spectra of supported quantum clusters. XPS expanded spectra in the Ag 3d (a), C 1s (b), S 2p (c), and Al 2p (d) regions of Al2O3@Ag7,8 QCs before (black), after 1st (red) and 3rd cycles (green) of catalysis.

Mentions: XPS investigation of the catalyst was carried out before and after the reaction. Survey spectra of Al2O3@Ag7,8 before and after the reaction are shown in Additional file 7, Figure S6, and the expanded regions are shown in Figure 6. Spectral shift due to charging was corrected with respect to C 1s at 285.0 eV. Expanded spectra in the Ag 3d region show binding energies of 367.9 and 374.0 eV due to Ag 3d5/2 and Ag 3d3/2, respectively of Ag (0). S 2p shows a peak at 161.7 eV, Al 2p shows a peak at 74.6 eV, and O 1s appears at 530.8 eV. All the data correspond to the fresh catalyst. The O 1s position indicates hydroxyl groups at the surface, as expected. The C 1s region shows two peaks at 285.0 and 288.3 eV, corresponding to the CH/CH2 and -COO- groups. After three cycles, Ag 3d shows peaks at 367.9 and 374.1 eV; corresponding to Ag (0). Al 2p, O 1s, and S 2p did not change significantly. The C 1s region shows a reduction in the peak intensity of the -COO- feature. Reduction in the intensities of sulfur and carbon is noticed. This indicated a slight desorption of the MSA monolayer.


Supported quantum clusters of silver as enhanced catalysts for reduction.

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

XPS spectra of supported quantum clusters. XPS expanded spectra in the Ag 3d (a), C 1s (b), S 2p (c), and Al 2p (d) regions of Al2O3@Ag7,8 QCs before (black), after 1st (red) and 3rd cycles (green) of catalysis.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: XPS spectra of supported quantum clusters. XPS expanded spectra in the Ag 3d (a), C 1s (b), S 2p (c), and Al 2p (d) regions of Al2O3@Ag7,8 QCs before (black), after 1st (red) and 3rd cycles (green) of catalysis.
Mentions: XPS investigation of the catalyst was carried out before and after the reaction. Survey spectra of Al2O3@Ag7,8 before and after the reaction are shown in Additional file 7, Figure S6, and the expanded regions are shown in Figure 6. Spectral shift due to charging was corrected with respect to C 1s at 285.0 eV. Expanded spectra in the Ag 3d region show binding energies of 367.9 and 374.0 eV due to Ag 3d5/2 and Ag 3d3/2, respectively of Ag (0). S 2p shows a peak at 161.7 eV, Al 2p shows a peak at 74.6 eV, and O 1s appears at 530.8 eV. All the data correspond to the fresh catalyst. The O 1s position indicates hydroxyl groups at the surface, as expected. The C 1s region shows two peaks at 285.0 and 288.3 eV, corresponding to the CH/CH2 and -COO- groups. After three cycles, Ag 3d shows peaks at 367.9 and 374.1 eV; corresponding to Ag (0). Al 2p, O 1s, and S 2p did not change significantly. The C 1s region shows a reduction in the peak intensity of the -COO- feature. Reduction in the intensities of sulfur and carbon is noticed. This indicated a slight desorption of the MSA monolayer.

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