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Issue 5, 2009
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The role of acidic sites and the catalytic reaction pathways on the Rh/ZrO2 catalysts for ethanol steam reforming

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Abstract

Rh catalysts supported on ZrO2-based oxides were studied for ethanol steam reforming (SR) reaction. Pure ZrO2 as the support resulted in higher H2 production yield compared to the ZrO2 oxide decorated with CeO2, Al2O3, La2O3 or Li2O at the reaction temperature of 300 °C. Above 450 °C, all the catalysts exhibited similar catalytic activity. However, at low reaction temperatures (below 400 °C), a significant enhancement in the catalytic activity, selectivity and stability was achieved by replacing the ZrO2 support prepared by a precipitation method (ZrO2–CP) with that prepared by a hydrothermal method (ZrO2–HT). A deactivation was observed during the EtOH SR reaction at 300 °C on the two catalysts of Rh/ZrO2–CP and Rh/ZrO2–HT. NH3TPD experiments confirmed that the ZrO2–HT support had two types of acidic sites while the ZrO2–CP support had only one type of weak acidic sites. DRIFTS studies showed that the absorption of EtOH molecules was strong on the Rh/ZrO2–HT catalyst and a number of C2 oxygenates were accumulated on the catalyst surface. Meanwhile, the EtOH absorption on the Rh/ZrO2–CP catalyst was weak and the accumulation of CO, carbonate and CHx was observed. It is concluded that the relatively strong Lewis acidic sites in the Rh/ZrO2–HT catalyst is responsible for the strong absorption of EtOH molecules, and the subsequent C–H breakage step (formation of acetaldehyde or called as dehydrogenation reaction) is a fast reaction on it; on the Rh/ZrO2–CP catalyst, the EtOH adsorption was weak and the C–C breakage was the dominating reaction which led to the accumulation of surface CO, CHx and CO2 species. Therefore, it is believed that, in order to promote the absorption of EtOH molecules and to reduce the formation of metastable carbonaceous species (C2 oxygenates) during the reaction, the catalyst should be enhanced both with Lewis acidity and with C–C bond breakage function. Also, it was found that the Rh particle size and distribution, as well as the surface area of the catalyst, were not important factors in determining the catalytic performance.

Graphical abstract: The role of acidic sites and the catalytic reaction pathways on the Rh/ZrO2 catalysts for ethanol steam reforming

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Publication details

The article was received on 04 Aug 2008, accepted on 18 Sep 2008 and first published on 05 Nov 2008


Article type: Paper
DOI: 10.1039/B813446D
Citation: Phys. Chem. Chem. Phys., 2009,11, 872-880
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    The role of acidic sites and the catalytic reaction pathways on the Rh/ZrO2 catalysts for ethanol steam reforming

    Z. Zhong, H. Ang, C. Choong, L. Chen, L. Huang and J. Lin, Phys. Chem. Chem. Phys., 2009, 11, 872
    DOI: 10.1039/B813446D

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