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

Ziyi Zhong*, Hanwee Ang, Catherine Choong, Luwei Chen, Lin Huang, Jianyi Lin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

39 Scopus citations

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 ZrO 2 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 (ZrO 2-HT). A deactivation was observed during the EtOH SR reaction at 300°C on the two catalysts of Rh/ZrO2-CP and Rh/ZrO 2-HT. NH3-TPD experiments confirmed that the ZrO 2-HT support had two types of acidic sites while the ZrO 2-CP support had only one type of weak acidic sites. DRIFTS studies showed that the absorption of EtOH molecules was strong on the Rh/ZrO 2-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 (C 2 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.

Original languageEnglish
Pages (from-to)872-880
Number of pages9
JournalPhysical Chemistry Chemical Physics
Volume11
Issue number5
DOIs
StatePublished - 2009
Externally publishedYes

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