Abstract
We investigated the photocatalytic behavior of gold nanoparticles supported on CeO2–TiO2 nanostructured matrixes in the CO preferential oxidation in H2-rich stream (photo-CO-PROX), by modifying the electronic band structure of ceria through addition of titania and making it more suitable for interacting with free electrons excited in gold nanoparticles through surface plasmon resonance. CeO2 samples with different TiO2 concentrations (0–20 wt %) were prepared through a slow coprecipitation method in alkaline conditions. The synthetic route is surfactant-free and environmentally friendly. Au nanoparticles (<1.0 wt % loading) were deposited on the surface of the CeO2–TiO2 oxides by deposition–precipitation. A benchmarking sample was also considered, prepared by standard fast coprecipitation, to assess how a peculiar morphology can affect the photocatalytic behavior. The samples appeared organized in a hierarchical needle-like structure, with different morphologies depending on the Ti content and preparation method, with homogeneously distributed Au nanoparticles decorating the Ce–Ti mixed oxides. The morphology influences the preferential photooxidation of CO to CO2 in excess of H2 under simulated solar light irradiation at room temperature and atmospheric pressure. The Au/CeO2–TiO2 systems exhibit much higher activity compared to a benchmark sample with a non-organized structure. The most efficient sample exhibited CO conversions of 52.9 and 80.2%, and CO2 selectivities equal to 95.3 and 59.4%, in the dark and under simulated sunlight, respectively. A clear morphology–functionality correlation was found in our systematic analysis, with CO conversion maximized for a TiO2 content equal to 15 wt %. The outcomes of this study are significant advancements toward the development of an effective strategy for exploitation of hydrogen as a viable clean fuel in stationary, automotive, and portable power generators.
Highlights
Over past decades, the environmental issues related to the use of non-renewable energy sources, the massive emission of greenhouse gases and the exponential growth of world energy consumption, have been fostering the research on renewable and environmentally friendly energy sources
The theoretical band gap of CeO2 is about 6.0 eV between the states of O 2p and Ce 5d;13 the experimental band gap is only around 3.2 eV, a value approaching that of other two semiconductors largely employed in photocatalysis, TiO2 and ZnO.[14]
A first weight loss occurs, about 5−10 wt %, up to 200 °C, attributed to the decomposition and carriers is the most common mechanism exploited in surface plasmon resonance (SPR)- degradation of organic moieties derived from the synthesis mediated catalysis, local heat generation and near-field (mainly titania precursor, titanium(IV) isopropoxide (TTIP))
Summary
The environmental issues related to the use of non-renewable energy sources, the massive emission of greenhouse gases and the exponential growth of world energy consumption, have been fostering the research on renewable and environmentally friendly energy sources. Non-stoichiometric CeO2−x compounds can be formed by reduction of Ce(IV) to Ce(III) with oxygen release and the concomitant formation of oxygen vacancies within the crystal structure, leading to a high oxygen mobility without suffering variations from its lattice, even after considerable loss of oxygen.[11] Thanks to this redox capability, known as oxygen storage capacity (OSC), cerium oxides are considered excellent oxygen buffers and are very active in oxidation reactions.[12] The theoretical band gap of CeO2 is about 6.0 eV between the states of O 2p and Ce 5d;13 the experimental band gap is only around 3.2 eV, a value approaching that of other two semiconductors largely employed in photocatalysis, TiO2 and ZnO.[14] Most probably this is due to the O 2p → Ce 4f transition, even though the origin of this reduced band gap is still controversial.[15]. Present efficient absorption in the visible light region through localized surface plasmon resonance (LSPR)[29] and, supported
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