Short Communication On the impact of Cu dispersion on CO 2 photoreduction over Cu/TiO 2 Dong Liu a , Yolanda Fernández a, b , Oluwafunmilola Ola a , Sarah Mackintosh a , Mercedes Maroto-Valer a, ⁎, Christopher M.A. Parlett c , Adam F. Lee c, ⁎, Jeffrey C.S. Wu d, ⁎ a Center for Innovation in Carbon Capture and Storage (CICCS), Faculty of Engineering, University of Nottingham, UK b Instituto Nacional del Carbón, CSIC, Apartado 73, 33080, Oviedo, Spain c Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK d Department of Chemical Engineering, National Taiwan University, Taipei, 10617, Taiwan abstract article info Article history: Received 14 November 2011 Received in revised form 9 March 2012 Accepted 16 March 2012 Available online 27 March 2012 Keywords: Photocatalysis Titania CO 2 Copper Methane A family of Cu/TiO 2 catalysts was prepared using a refined sol–gel method, and tested in the photocatalytic re- duction of CO 2 by H 2 O to CH 4 using a stirred batch, annular reactor. The resulting photoactivity was benchmarked against pure TiO 2 nanoparticles (synthesised by an identical sol–gel route). CO 2 photoreduction exhibited a strong volcano dependence on Cu loading, reflecting the transition from 2-dimensional CuOx nanostructures to 3-dimensional crystallites, with optimum CH 4 production observed for 0.03 wt.% Cu/TiO 2 . © 2012 Elsevier B.V. All rights reserved. 1. Introduction The natural environment is well-versed in maintaining an equilibri- um between carbon dioxide (CO 2 ) fixed through photosynthesis, and that released into the atmosphere via normal biochemical processes. However, this natural equilibrium has been strongly perturbed over the past few centuries through increased CO 2 emissions arising from fos- sil fuel combustion. The consequent dramatic rise in atmospheric CO 2 concentrations is well documented as the major contributor to ongoing climate change [1]. The most promising strategies proposed to slow, and eventually reverse, these rising CO 2 emissions are a switchover to re- newable energy sources, or implementing carbon capture and storage technologies (CCS) [2] alongside conventional chemical processes. Direct CO 2 utilisation as a chemical feedstock (notably for methane or methanol production) remains poorly exploited by current industrial processes, hence there exists great potential for new clean technologies for large- scale CO 2 fixation [3]. CO 2 photoreduction is one such promising method for ameliorat- ing atmospheric CO 2 levels, while simultaneously providing energy- rich or chemically useful products such as CO, methane (CH 4 ), methanol (CH 3 OH), formaldehyde (HCHO) or formic acid (HCOOH). A major chal- lenge to such chemistry remains the development of efficient photocata- lysts for direct CO 2 photoreduction offering high quantum yields, activity and selectivity. TiO 2 is widely used in photocatalysis due to it's low cost and toxicity, thermal stability and photo-response under UV irradiation, and thus may be viewed as a potential candidate for CO 2 . However, the highest CO 2 photoreduction rate achieved using unpromoted TiO 2 is only 25 μmol.g cat −1 .hr −1 [4,5], and consequently too low for industrial commercialisation. Methods to modify the titania band gap, such as N-doping, or the addition of metal or oxide promoters to promote sepa- ration of photo-excited charge carriers and increase their lifetime for re- action with adsorbates, have both shown promise as routes to improve CO 2 photoreduction activity [6–8]. However, to date, there has been little effort to optimise promoter loadings or understand their impact upon TiO 2 catalysed CO 2 photoreduction. Here we systematically explore the influence of Cu promotion via incorporation during sol–gel synthesis, upon photocatalytic CH 4 production from CO 2 , and demonstrate that the resulting Cu 2 O dispersion plays a critical role in regulating the photo- catalytic performance of Cu/TiO 2 , wherein highly-dispersed (likely 2- dimensional islands) Cu 2 O nanostructures maximise the CH 4 yield. 2. Experimental 2.1. Catalyst preparation Pure and copper loaded TiO 2 were prepared by a modified sol–gel method adapted from Wu et al. [9] employing titanium (IV) n-butoxide (Ti(OC 4 H 9 ) 4 , Acros Organics, 99%) and copper (II) chloride (CuCl 2 .2H 2 O, Certified AR, 99%) precursors. To provide the stoichiometric amount of water for hydrolysis of the titanium precursor, 0.02 mol of Ti(OC 4 H 9 ) 4 was mixed with 0.08 mol of n-butanol (C 4 H 9 OH, Certified AR, 99.5%) and 0.08 mol of acetic acid (CH 3 COOH, Acros Organics, Glacial 99.8%). Catalysis Communications 25 (2012) 78–82 ⁎ Corresponding authors. Tel.: + 44 29208 74778; fax: + 44 29208 74030. E-mail address: leeaf@cardiff.ac.uk (A.F. Lee). 1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2012.03.025 Contents lists available at SciVerse ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom