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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.

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UV-vis spectra of the reduction of 4-np as a function of time with NaBH4 in the presence of supported QCs at 15°C (a), 25°C (b), and 35°C (c). Spectrum of 4-ap is given for comparison. Decrease in the concentration of 4-np and corresponding increase in the concentration of 4-ap are marked.
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Figure 4: UV-vis spectra of the reduction of 4-np as a function of time with NaBH4 in the presence of supported QCs at 15°C (a), 25°C (b), and 35°C (c). Spectrum of 4-ap is given for comparison. Decrease in the concentration of 4-np and corresponding increase in the concentration of 4-ap are marked.

Mentions: Aqueous solution of 4-np shows characteristic absorption maximum at 317 nm due to the n → π* transition (Figure 4) [40,41]. Upon addition of freshly prepared ice-cold aqueous NaBH4 solution, the peak position of 4-np red shifted to 400 nm. This indicates the formation of 4-nitrophenolate ion in alkaline solution. The color of the solution deepened (from pale yellow to deep yellow). Without the addition of clusters, reduction was not observed as seen from the retention of the color. Even for several days, the peak at 400 nm due to 4-nitrophenolate ion remained unaltered.


Supported quantum clusters of silver as enhanced catalysts for reduction.

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

UV-vis spectra of the reduction of 4-np as a function of time with NaBH4 in the presence of supported QCs at 15°C (a), 25°C (b), and 35°C (c). Spectrum of 4-ap is given for comparison. Decrease in the concentration of 4-np and corresponding increase in the concentration of 4-ap are marked.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: UV-vis spectra of the reduction of 4-np as a function of time with NaBH4 in the presence of supported QCs at 15°C (a), 25°C (b), and 35°C (c). Spectrum of 4-ap is given for comparison. Decrease in the concentration of 4-np and corresponding increase in the concentration of 4-ap are marked.
Mentions: Aqueous solution of 4-np shows characteristic absorption maximum at 317 nm due to the n → π* transition (Figure 4) [40,41]. Upon addition of freshly prepared ice-cold aqueous NaBH4 solution, the peak position of 4-np red shifted to 400 nm. This indicates the formation of 4-nitrophenolate ion in alkaline solution. The color of the solution deepened (from pale yellow to deep yellow). Without the addition of clusters, reduction was not observed as seen from the retention of the color. Even for several days, the peak at 400 nm due to 4-nitrophenolate ion remained unaltered.

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