Short CommunicationUltrasmall silver nanoparticles supported on silica and their catalytic performancesfor carbon monoxide oxidationLongbao Yua,?, Yayu Shia, Zhen Zhaob,?, Hengbo Yina, Yuechang Weib, Jian Liub, Wenbing Kanga,Tingshun Jianga, Aili WangaaSchool of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, ChinabState Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, Chinaa b s t r a c ta r t i c l ei n f oArticle history:Received 25 August 2010Received in revised form 16 November 2010Accepted 8 December 2010Available online 17 December 2010Keywords:CO oxidationAg nanoparticle catalystSize effectSchiff baseTheultrasmallAgnanoparticlessupportedonsilicawerepreparedbyanovelandfacilemethod,whichwasbasedontheintroductionofthefunctionalmonomersalicylaldimineSchiffbaseintoaSiO2matrix.Theultrasmallsilica-supported Ag nanoparticles were characterized by means of XRD, TEM, UV–Vis, XPS and BET, and tested for COoxidation.ItwasfoundthatthecatalyticoxidationofCOovertheultrasmallAgnanoparticlecatalystswasastrongsize dependent reaction and the Ag particle size in a range of 3–5 nm was favorable for CO oxidation.© 2010 Elsevier B.V. All rights reserved.1. IntroductionMetal nanoparticles are particularly attractive catalysts for manyindustrially important reactions owing to their possessing a largersurface-to-volume ratio and a higher concentration of partiallycoordinated surface sites than the corresponding bulk materials. Fortheir applications in heterogeneous catalysis, metal nanoparticlesare usually immobilized on the supports such as SiO2, Al2O3 andzeolitesbythefollowingmethods:(a)impregnation,(b)ionexchange,(c) precipitation and(d) sol–gelmethods [1–4]. A great dealof studiesdiscloses that the methods and preparation parameters have a greatinfluence on the size, size distribution, shape and crystallographicstructure of nanoparticles, and subsequently on the catalytic per-formance [5–8]. So the development of the methodologies for pre-paring the supported metal nanoparticles is strongly needed.The catalytic oxidation of CO has been extensively studied for itswide applications in closed-cycle CO2lasers, fuel cells and environmen-tal pollution control devices [9–11]. A number of metal nanoparticlecatalysts (e.g. Au/TiO2, Ag/SiO2and Pt/Al2O3) have been demonstratedto be very effective in CO oxidation [12–14]. Haruta et al. found that thesmall Au nanoparticles supported on titania were highly active for COcatalyticoxidationandtheiractivitiesincreasedwiththedecreaseoftheaverage Au particle size [15]. Goodman et al. reported that Aunanoparticles of about 3.5 nm had the highest activity for CO catalyticoxidation in a series of Au/TiO2model catalysts [16]. There were alsosome studies on the size effect of Ag nanoparticles in CO catalyticoxidation: Bao et al. reported that the SiO2-supported Ag particles of 6–8 nm had relatively high activity for CO catalytic oxidation [13].Recently, Bao et al. found that the mesostructured silica-supported Agnanoparticles with a uniform size of around 3–5 nm had a very highactivity for CO catalytic oxidation, giving 100% CO conversion at roomtemperature [17]. Very recently, Qu et al. also reported that the silica-supported Ag nanoparticles with a mean particle size of 4.5–5.5 nmwere favorable for the low-temperature CO oxidation [18]. In previousliterature, the SiO2-supported Ag nanoparticle catalysts were usuallyprepared by traditional impregnation or incipient wetness impregna-tion process, in which the size-controlling of Ag particles was achallenge [3,11,19]. Especially, it was difficult to get the ultrasmall Agnanoparticles with a narrow size distribution, based on the reportedresults.Thislimitationofthesynthesismethodsimpededthestudiesonthe Ag particle size effect in CO catalytic oxidation.Herein, we have developed a new method for the preparation ofthe SiO2-supported Ag nanoparticles by introducing the salicylaldi-mine Schiff base into a SiO2matrix. The remarkable improvement inthe Ag particle size-controlling by this method allowed us to directlyprobe the size effect of Ag particles in CO catalytic oxidation.2. Experimental2.1. Catalyst preparationTypically, for catalyst a, 6 g of poly (ethylene glycol) (PEG) wasdissolved in 240 g of deionized H2O, and a mixture of 0.3 g of theCatalysis Communications 12 (2011) 616–620? Corresponding authors.E-mail addresses: longbaoyu@ujs.edu.cn (L. Yu), zhenzhao@cup.edu.cn (Z. Zhao).1566-7367/$ – see front matter © 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.catcom.2010.12.012Contents lists available at ScienceDirectCatalysis Communicationsjournal homepage: www.elsevier.com/locate/catcom
