RESEARCH PAPER Palladium nanoparticles on silica-rich substrates by spontaneous reduction at room temperature Rau ´ l Pina-Zapardiel • Isabel Montero • Antonio Esteban-Cubillo • Jose ´ S. Moya • Wayne D. Kaplan • Thangadurai Paramasivam • Carlos Pecharroma ´n Received: 28 January 2011 / Accepted: 9 July 2011 / Published online: 23 July 2011 Ó Springer Science+Business Media B.V. 2011 Abstract Metallic palladium nanoparticles ( \ 5 nm) have been spontaneously obtained from an acid solution of palladium chloride salt on silica-rich substrates (sepiolite, microfibrous silica, fumed silica, and milled silica glass) without any additional reduc- tion treatment. Variable proportions of metallic palla- dium were straightforwardly obtained, depending on the nature of the substrate. The presence of a large amount of silanol groups acting as nucleation centers, seem to be a requisite to obtain small Pd nanoparticles. Additionally, an absorbance maximum associated to a surface plasmon resonance corresponding to the spherical particles of metallic palladium has been identified at a wavelength of 238 nm. The large specific surface of the employed substrates with the palladium nanoparticles suggest that these materials could be used for gas catalysis. Keywords Palladium  Sepiolite  Nanoparticles  Spontaneous reduction  Catalysts Introduction It is well supported in the literature that, palladium has a strong catalytic activity for hydrogenation (Sangeetha et al. 2009; Pham-Huu et al. 2000; Demir et al. 2004; Niu et al. 2001), oxidation (Cordi and Falconer 1996; Hoflund et al. 2003; Shim et al. 2008), combustion (Demoulin et al. 2006), and hydrogenolysis (Urbano and Marinas 2001; Scott et al. 1997; Bernas et al. 2008) reactions in gaseous and liquid phases (Janiak 2008; Karpinski et al. 1996; Juszczyk et al. 1998). Various methods have been described for the synthesis of Pd nanoparticles to increase the catalytic activity, including hydrothermal processes (Park et al. 2005), sol–gel (Guo and Tao 2007), and electrochemical methods (Ebrahimi et al. 1999) or chemical vapor deposition (Veprek 1999). In any case, metallic palladium nanoparticles are usually obtained after a thermal reduction treatment from palladium oxide or oxyhydroxide precursor. As a consequence of the low energy required in the reduction process (182 kJ/mol) (Ho et al. 1996), and as it corresponds to a noble metal, weak reducing agents such as ethanol, ethylene glycol, and ascorbic acid (Okumura et al. 2005) are usually employed to reduce Pd precursors (Desforges et al. 2005; Back et al. 2006). Palladium nanoparticles are commonly deposited on a matrix for improving the sensitivity of some R. Pina-Zapardiel  I. Montero  J. S. Moya  C. Pecharroma ´n (&) Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain e-mail: cpg@icmm.csic.es A. Esteban-Cubillo TOLSA S.A. R&D Department, Ctra Vallecas-Mejorada del Campo, 28031 Madrid, Spain W. D. Kaplan  T. Paramasivam Department of Materials Engineering, Technion-Israel Institute of Technology, 32000 Haifa, Israel 123 J Nanopart Res (2011) 13:5239–5249 DOI 10.1007/s11051-011-0508-7