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928681 
Journal Article 
Sol–gel-entrapped nano silver catalysts-correlation between active silver species and catalytic behavior 
Pârvulescu, VI; Cojocaru, B; Pârvulescu, V; Richards, R; Li, Z; Cadigan, C; Granger, P; Miquel, P; Hardacre, C 
2010 
Yes 
Journal of Catalysis
ISSN: 0021-9517
EISSN: 1090-2694 
272 
1 
92-100 
WOS:000279090500011 
Silver colloids prepared by reducing AgNO(3) in aqueous solution with sodium citrate were embedded in alumina following two different preparation procedures resulting in samples containing 3 and 5 wt.% silver. Characterization of these materials using TEM. XPS, XAES, CP/MAS NMR, XRD, and adsorption-desorption isotherms of nitrogen showed that embedding the pre-prepared silver colloids into the alumina via the sol-gel procedure preserved the particle size of silver. However, as XAES demonstrates, the catalysts prepared in a sol-gel with a lower amount of water led to embedded colloids with a higher population of Ag(+) species. The catalytic behaviors of the resultant catalysts were well correlated with the concentration of these species. Thus, the active silver species of the catalysts containing more Ag(+) species selectively converts NO to N(2). However, subsequent thermal aging leads to an enhancement of the conversion of NO parallel to slight alteration of the selectivity with the appearance of low amounts of N(2)O despite an increase of Ag(+) species. Accordingly, an optimal surface Ag(0)/Ag(+) ratio is probably needed, independently of the size of silver particles. It was found that this optimal ratio strongly depends on the operating conditions during the synthesis route. (C) 2010 Elsevier Inc. All rights reserved. 
Silver colloids; Sol-gel synthesis; NO reduction with hydrogen and CO