FORDE ET AL . VOL. 8 ’ NO. 1 ’ 957 –969 ’ 2014 www.acsnano.org 957 December 16, 2013 C 2013 American Chemical Society High Activity Redox Catalysts Synthesized by Chemical Vapor Impregnation Michael M. Forde, †,§ Lokesh Kesavan, † Mohd Izham bin Saiman, † Qian He, ‡ Nikolaos Dimitratos, † Jose Antonio Lopez-Sanchez, † Robert L. Jenkins, † Stuart H. Taylor, † Christopher J. Kiely, ‡ and Graham J. Hutchings †, * † Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Main Building Park Place, Cardiff, CF10 3AT, United Kingdom, and and ‡ Department of Materials Science and Engineering, Lehigh University, 5 East Packer Avenue, Bethlehem, Pennsylvania 18015-3195, United States. § Present address: Department of Chemistry, University of the West Indies, St. Augustine Campus, Trinidad and Tobago. T he application of nanoparticulate ma- terials as heterogeneous catalysts is an attractive proposition when high selectivity to desired products needs to be coupled with high productivity and robust catalyst stability. 1 The high surface area-to- volume ratio of metal nanoparticles, which directly results from their very small particle size, can improve catalytic activity. 2,3 Re- cently, there have been many reports of highly active catalysts prepared by a number of liquid phase routes, e.g. sol-immobilization and electrochemical deposition, chosen specifically to afford supported metal nano- particles with controlled size, composition, and dispersion. 4À7 Although these prepara- tive routes are well established, it is often difficult in practice to control the physical dimensions and composition of supported metal nanoparticles. 8 For example, using sol- immobilization techniques, colloids containing nanoparticles with tunable size can generally be prepared for a wide number of metals and then deposited onto various supports. However, there are many parameters which influence the mean size of colloidal nano- particles, (e.g., varying the nature and con- centration of stabilizer ligand, reaction volume, nature and concentration of the reducing agent, synthesis temperature/ pressure/pH, solvent identity). This in- creases the complexity of applying a gen- eral protocol in the preparation of new materials in a systematic manner. Addition- ally, undesirable growth of the colloidal particles can occur, especially with aging in solution, or more commonly when the material is heat treated after deposition onto the support leading to inhomogene- ities in the final material. 2 Furthermore, adsorption of the preformed colloidal nano- particles onto a support surface may also cause the nanoparticle to restructure upon deposition and during subsequent heat * Address correspondence to: hutch@cardiff.ac.uk. Received for review November 5, 2013 and accepted December 16, 2013. Published online 10.1021/nn405757q ABSTRACT The use of precious metals in heterogeneous catalysis relies on the preparation of small nanoparticles that are stable under reaction conditions. To date, most conventional routes used to prepare noble metal nanoparticles have drawbacks related to surface contamination, particle agglomeration, and reproducibility restraints. We have prepared titania-supported palladium (Pd) and platinum (Pt) catalysts using a simpli fied vapor deposition technique termed chemical vapor impregnation (CVI) that can be performed in any standard chemical laboratory. These materials, composed of nanoparticles typically below 3 nm in size, show remarkable activity under mild conditions for oxidation and hydrogenation reactions of industrial importance. We demonstrate the preparation of bimetallic PdÀPt homogeneous alloy nanoparticles by this new CVI method, which show synergistic effects in toluene oxidation. The versatility of our CVI methodology to be able to tailor the composition and morphology of supported nanoparticles in an easily accessible and scalable manner is further demonstrated by the synthesis of Pd shell ÀAu core nanoparticles using CVI deposition of Pd onto preformed Au nanoparticles supported on titania (prepared by sol immobilization) in addition to the presence of monometallic Au and Pd nanoparticles. KEYWORDS: catalysis . bimetallic nanoparticle . nanoalloy . gold . palladium . platinum . coreÀshell structures . hydrogenation . oxidation ARTICLE