Synthesis of Nanorods with Ni Cores and Porous Silica Coatings N. Shukla • J. B. Miller • E. Coletta • A. D. Ondeck • V. Pushkarev • A. J. Gellman Received: 11 August 2010 / Accepted: 1 December 2010 / Published online: 5 January 2011 Ó Springer Science+Business Media, LLC 2010 Abstract Nanorods with a Ni core and a silica coating have been prepared using a one-step synthesis and char- acterized using a variety of methods. Nitrogen adsorption isotherms have been used to characterize the pore size and the internal surface area of the silica shells grown on the Ni nanorods. Spectroscopic characterization of CO adsorbed on the Ni nanoparticle cores has been used to verify that the pore structure of the silica shells allows CO to access the Ni core; this property is critical to the use of core–shell structures as industrial catalysts. To demonstrate their resistance to physical and chemical degradation, the properties of the silica-coated Ni nanoparticles have been measured both before and after treatment at high temper- ature (623 - 1073 K) and exposure to a reducing atmo- sphere (hydrogen gas). Annealing at high temperatures reduces, but does not eliminate, the porosity of the silica shells. Keywords Nanoparticulate catalyst Á Silica coatings Á Ni nanoparticles 1 Introduction Over the past decade there has been widespread interest in wet chemical synthesis of nanoparticles and their applica- tions in various fields. One area in which nanoparticles can play an important role is heterogeneous catalysis. There have been many reports of nanoparticle synthesis for applications in catalysis, but two major challenges must be addressed before such synthetically produced nanopartic- ulate catalysts can be used commercially to their full potential [1–3]. The first is the development of simple, cost-effective synthetic routes that yield nanoparticles with uniform shape and size and expose a uniform set of crystal planes selected to provide high catalytic activity and selectivity. The second challenge is the development of strategies to make the particles resistant to sintering in the extreme chemical and thermal environments that charac- terize many important catalytic processes. Sintering destroys the shapes of the nanoparticles and causes changes in particle size distribution, typically increasing the mean particle size. Sintering and adsorbate induced changes in particle shape undermine some of the potential advantages that chemically synthesized nanoparticulate catalysts have over conventional particulate metal catalysts. There are many strategies to avoid the sintering of nanoparticulate catalysts; the method explored in this work has been to coat the nanoparticles with protective silica coatings of con- trolled thicknesses. It is challenging to control the thickness of the silica coating; however, it is equally important that the silica coating be porous so that reactant molecules have access to the nanoparticle core during catalysis. Such silica shells can provide contaminant resistance [4–6], while also serving to reduce sintering and thus, improved thermal stability [7–12]. The pores of the silica shells can be tai- lored in size and chemical properties such that reactant N. Shukla Á J. B. Miller Á A. J. Gellman US DOE—National Energy and Technology Laboratory, 626 Cochrans Mill Rd., Pittsburgh, PA 15236-0940, USA N. Shukla (&) Institute for Complex Engineered Systems, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA, USA e-mail: nisha@andrew.cmu.edu J. B. Miller Á E. Coletta Á A. D. Ondeck Á V. Pushkarev Á A. J. Gellman Department of Chemical Engineering, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213, USA 123 Catal Lett (2011) 141:491–497 DOI 10.1007/s10562-010-0531-9