Elsevier

Catalysis Today

Volume 146, Issues 1–2, 15 August 2009, Pages 76-81
Catalysis Today

Study on the steam reforming of ethanol over cobalt oxides

https://doi.org/10.1016/j.cattod.2008.12.010Get rights and content

Abstract

A high valence cobalt oxide, CoOx, was prepared from a cobalt nitrate aqueous solution through precipitation with sodium hydroxide and oxidation by hydrogen peroxide. Furthermore, pure nanocrystalline cobaltic oxide (Co3O4) particles were obtained from the CoOx by calcination at 300, 500 and 700 °C (labeled as C300, C500 and C700, respectively). All samples were characterized by X-ray diffraction (XRD), Raman spectroscopy and temperature-programmed reduction (TPR). Their catalytic activities toward steam reforming of ethanol (SRE) were tested in a fixed-bed reactor. The results showed that the phase components were transferred upon the treatment temperature, i.e., the CoOx exhibited mainly CoO(OH), C300, C500 and the C700 exhibited Co3O4. The as-prepared CoOx catalyst under low temperature possessed high activity. The best yield of hydrogen (YH2) approached the theoretical value around 375 °C. Under H2O/EtOH molar ratio of 13 and 22,000 h−1 gas hourly space velocity (GHSV) for the as-prepared CoOx catalyst, the YH2 arrived 5.72 and only minor CO (<2%) and CH4 (<0.8%) were detected.

Introduction

The current shortage of global energy and stringent emission regulations has stimulated interest in renewable energies. Fuel cells have been investigated as possible devices for direct conversion of the chemical energy of fuels (H2 and O2) into electrical energy that is able to provide clean and highly efficient electric power for both mobile and stationary applications [1]. The use of hydrogen as an energy carrier can support sustainable economic growth as well as reduce pollution and greenhouse gas emissions. From the environmental point of view the use of ethanol is preferred because renewable ethanol obtained from biomass offers high hydrogen content, non-toxicity, safe storage and easy handling [2], [3], [4]. The production of hydrogen from steam reforming of ethanol (SRE) could favor the use of hydrogen as an alternative fuel, addressing the difficulties of on-board hydrogen storage and distribution. Moreover, a high yield of hydrogen can be obtained from the SRE reaction [5], [6], [7], [8]:C2H5OH + 3H2O  6H2 + 2CO2

Our previous study discussed the supported and unsupported cobalt oxide in the oxidation of carbon monoxide [9], [10], [11]. In addition, the cobalt-based catalysts were considered as effective in steam reforming of ethanol [5], [6], [12], [13], [14], [15]. In order to understand the role of active cobalt phases on SRE reaction, this study used X-ray diffraction (XRD), temperature programmed reduction (TPR) and Raman spectroscopy to characterize the cobalt oxides. Steam reforming of ethanol was performed using a water/ethanol to evaluate the capabilities of these materials to produce H2 from a renewable and environmentally friendly fuel source. This study aimed to develop a highly efficient and more stable catalyst for the SRE using lower temperatures to generate H2 with high selectivity and low CO in the outlet gas, which could facilitate relatively easier down-steam CO clean-up of PEMFC applications.

Section snippets

Catalyst preparation

The as-prepared cobalt oxide (assigned as CoOx) with a high valence state of cobalt was synthesized by the precipitation–oxidation method in an aqueous solution. The precipitation process was carried out at 50 °C, with 50 ml of 0.6 M Co(NO3)2·H2O solution added drop by drop to 100 ml of 3.2 M NaOH solution; 100 ml of H2O2 (50 wt%) was then introduced dropwise under constant stirring. The precipitate was then filtered, washed with deionized water, and dried in an oven at 110 °C for 24 h. The dried CoOx

Characterization of cobalt oxides

Fig. 1 shows the XRD profiles of cobalt oxides, which indicates that the as-prepared CoOx [Fig. 1(a)] pattern matches the JCPDS 14-0673 file that identifies cobalt oxyhydroxide, CoO(OH), with a hexagonal structure (particle size around 10 nm) coupled with Co3O4. By increasing the calcined temperature, increasingly sharper peaks appear, whose positions and relative intensities are indicative of pure Co3O4 for C300, C500 and C700 samples [Fig. 1(b)–(d)]. Their mean particle size increase with the

Conclusion

An excellent ethanol reforming catalysts was developed in this study. The as-prepared CoOx catalyst under low temperature possessed high activity. The best YH2 approached the theoretical value around 375 °C. Under an EtOH/H2O molar ratio of 1/13 and 22,000 h−1 GHSV for the as-prepared CoOx catalyst, the YH2 arrived 5.72 and only minor CO (<2%) and CH4 (<0.8%) were detected.

Acknowledgement

We are pleased to acknowledge the financial support for this study by the National Science Council of the Republic of China under contract number NSC 96-2113-M-606-001-MY3.

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