Ceria–zirconia stabilised tungsten oxides for the production of hydrogen by the methane–water redox cycle

• Published in: International journal of hydrogen energy 2010-09, Vol.35 (17), p.8953-8961
• Main Authors: Sim, Andrew, Cant, Noel W., Trimm, David L.
• Format: Article
• Language: English
• Subjects: Alternative fuels. Production and utilization; Applied sciences; C (programming language); Carbon monoxide; Ceria–zirconia; Energy; Exact sciences and technology; Fuels; Hydrogen; Hydrogen production; Methane; Oxides; Redox cycle; Reduction by methane; Reoxidation by water; Tungsten; Tungsten oxide; Tungsten oxides; Zirconium dioxide
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2010.06.062

The generation of essentially pure hydrogen through a redox cycle using methane and then water has been investigated for a series of tungsten oxides stabilised by ceria–zirconia. The calcined starting materials were largely monoclinic WO 3 with CeO 2 and ZrO 2 undetectable by XRD. Samples containing 80% and especially 69% WO 3 showed additional XRD lines due to a phase of unknown composition. Temperature programmed reduction to 750 °C in methane converted samples containing WO 3 alone to WC together with small amounts of tungsten metal and a WC 1− x phase. Reoxidation in water at the same temperature then produced CO and H 2 in corresponding amounts. Under the same conditions the 69% WO 3 sample was reduced only as far as WO 2 and reoxidation yielded H 2 largely free of CO. The reoxidation product was not WO 3 but consisted of various non-stoichiometric oxides with composition WO 2+x ( x = 0.72, 0.83, etc). The reduction–reoxidation cycle could be repeated many times without loss of hydrogen production efficiency.