Catalysis Today 235 (2014) 58–71 Contents lists available at ScienceDirect Catalysis Today j o ur na l ho me page: www.elsevier.com/locate/cattod Heterogeneous catalyst preparation in ionic liquids: Titania supported gold nanoparticles Camella Oumahi a,b , Jean Lombard a,b , Sandra Casale a,b , Christophe Calers a,b , Laurent Delannoy a,b , Catherine Louis a,b , Xavier Carrier a,b,∗ a Sorbonne Universités, UPMC Univ Paris 06, UMR CNRS 7197, Laboratoire de Réactivité de Surface, F-75005 Paris, France b CNRS, UMR 7197, Laboratoire de Réactivité de Surface F-75005 Paris, France a r t i c l e i n f o Article history: Received 26 December 2013 Received in revised form 12 March 2014 Accepted 16 March 2014 Available online 3 April 2014 Keywords: Ionic liquids Gold nanoparticles Catalysts preparation UV–vis XPS Selective hydrogenation a b s t r a c t This work reports the use of ionic liquids (ILs) as solvent for the synthesis of Au/TiO 2 heterogeneous catalysts. It is shown that the versatility of the physico-chemical properties of ILs makes them inter- esting solvents for a broad control of supported metal nanoparticles (NPs) size and for a fine-tuning of metal–support interaction. Synthesis and deposition of Au NPs on TiO 2 are carried out through a col- loidal route in imidazolium-based ILs (1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF 6 ) and trifluoromethanesulfonate (BMIMOTf)) and in a Deep Eutectic Solvent (DES, choline chloride and urea). The stabilization of the dispersed NPs and their deposition on an oxide carrier is investigated in pure ILs and in the presence of extra stabilizing agents (1-methylimidazole or polyvinylpyrrolidone). In the absence of TiO 2 , the NPs stability varies with the composition of the IL (BMIMOTf > BMIMPF 6 > DES) and is critically depending on the addition of an extra stabilizing agent (SA). Conversely, when gold NPs are synthesized in the presence of TiO 2 in imidazolium ILs, the addition of a SA is no longer required since the oxide support acts as a stabilizer for the gold colloids and prevents aggregation of NPs. A detailed XPS investigation of the surface composition of the TiO 2 -supported gold catalysts shows that the cationic part of the imidazolium ILs on the one hand and urea in DES on the other hand are co-adsorbed with gold NPs upon deposition on TiO 2 , probably decorating and stabilizing the Au NPs. The fate of the anionic part of the ILs (PF 6 - , OTf - and Cl - ) is highly depending on the type of IL. Limited surface adsorption is reported for triflate (BMIMOTf) and chloride anions (DES), the latter being fully removed upon calcination, while PF 6 - (BMIMPF 6 ) remains adsorbed on the surface during Au NPs deposition and leads to PO x - and F - surface species upon calcination. The surface composition controls the intrinsic catalytic activity (TOF) in the selective hydrogenation of butadiene. It is shown that the surface doping of supported Au NPs with P and F anionic deposits (synthesized in BMIMPF 6 ) has a promoting effect for the intrinsic catalytic activity. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Ionic liquids (ILs) are a new class of promising solvents with unique properties such as high thermal and chemical stability, very low vapor pressure and a good ability to dissolve a wide variety of organic and inorganic compounds [1,2]. These characteristics make them attractive for practical applications in various fields of research such as energy storage for example since ionic liquids are interesting candidates for substituting conventional electrolytes in ∗ Corresponding author at: CNRS, UMR 7197, Laboratoire de Réactivité de Surface, F-75005 Paris, France. Tel.: +33 1 44 27 36 25; fax: +33 1 44 27 60 33. E-mail addresses: xavier.carrier@upmc.fr, camella.oumahi@hotmail.fr (X. Carrier). electrochemical energy devices [3]. In the field of catalysis, ionic liq- uids are intensively studied for homogeneous reactions in biphasic processes [4–7] or for supported ionic liquid phase systems (SILP) in order to immobilize molecular homogeneous catalyst on a support [8]. Conversely, the use of ionic liquids as solvent for synthesiz- ing heterogeneous catalyst is seldom reported [9–11]. However, the versatility of their physico-chemical properties makes them interesting solvents for a wide control and modulation of the spe- ciation and solubility of metal precursors and for a fine-tuning of metal–support interactions as compared to water, a solvent with exceptional but limited properties. Ionic liquids are most commonly composed of an organic cation such as dialkylimidazolium, alkylammonium, alkylpyridinium and of an inorganic anion such as tetrafluoroborate, hexafluorophos- phate or halide. ILs are characterized by a high degree of self http://dx.doi.org/10.1016/j.cattod.2014.03.029 0920-5861/© 2014 Elsevier B.V. All rights reserved.