Mesoporous TiO 2 /SBA-15, and Cu/TiO 2 /SBA-15 Composite Photocatalysts for Photoreduction of CO 2 to Methanol
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Mesoporous TiO2/SBA-15, and Cu/TiO2/SBA-15 Composite Photocatalysts for Photoreduction of CO2 to Methanol Hsien-Chang Yang Æ Hsin-Yu Lin Æ Yu-Shiang Chien Æ Jeffrey Chi-Sheng Wu Æ Hsin-Hsien Wu
Received: 18 May 2009 / Accepted: 13 June 2009 / Published online: 8 July 2009 Ó Springer Science+Business Media, LLC 2009
Abstract A series of mesoporous TiO2/SBA-15, Cu/TiO2 and Cu/TiO2/SBA-15 composite photocatalysts were prepared by sol–gel synthesis for photoreduction of CO2 with H2O to methanol. It was found that optimum amount of titanium loading of TiO2/SBA-15 was 45 wt% which exhibited higher photoreduction activity than pure TiO2. An addition of copper on TiO2 or TiO2/SBA-15 catalyst as cocatalyst was found to enhance the catalytic activity because copper serves as an electron trapper and prohibits the recombination of hole and electron. Keywords Titanium dioxide Mesoporous silica SBA-15 Carbon dioxide Photoreduction
1 Introduction To overcome environmental problems related to greenhouse gas emissions and to fulfill the energy needs of future generations, research efforts are underway to
Electronic supplementary material The online version of this article (doi:10.1007/s10562-009-0076-y) contains supplementary material, which is available to authorized users. H.-C. Yang H.-H. Wu Energy and Environment Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan H.-Y. Lin (&) Y.-S. Chien Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan e-mail: [email protected] J. C.-S. Wu Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
develop sustainable and renewable energy sources. Since photocatalystic water splitting using a TiO2 photoelectrode was first demonstrated by Fujishima and Honda in 1972 [1], the development of effective photocatalyst for splitting of water into hydrogen and oxygen has been studied extensively. Besides water splitting, photoreduction of CO2 with H2O to fuel such as methanol and methane [2] is particularly interesting, since CO2 is the most abundant greenhouse gas and is the one of the cheapest carboncontaining raw materials. Transforming one mol of CO2 into methanol requires 228 kJ which is an uphill reaction and is energetically unfavorable from the thermodynamic perspective. To be an effective photocatalyst for CO2 photoreduction with H2O, band edge of conduction band should be more negative than the reduction potential of CO2 and has a more positive valence band level than the oxidation potential of H2O. The direct monoelectronic electrochemical reduction potential of CO2 is about -2 V, hence it is believed that the photoreduction of CO2 with H2O occurs via a complex mechanism involving multielectron (one to six electrons) transfer processes [3, 4]. A number of semiconductor photocatalysts such as TiO2, SrTiO3, CaFe2O4, SiC, ZnS, CdS [5] and Ti-containing mesoporous silica [2] are reported to be active for methanol synthesis by photoreduction of CO2 with H2O under UV irradiati
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