Cu-Cr, Cu-Mn, and Cu-Fe Spinel-Oxide-Type Catalysts for Reforming of Oxygenated Hydrocarbons Pussana Hirunsit and Kajornsak Faungnawakij* National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency, Thailand Science Park, Patumthani 12120, Thailand * S Supporting Information ABSTRACT: Effective hydrogen production is achieved via steam reforming of the oxygenated hydrocarbons, including methanol and dimethyl ether, over Cu-based spinel-oxide catalysts. CuFe 2 O 4 , CuMn 2 O 4 , and CuCr 2 O 4 were well- crystallized in spinel structures and were provided with low specific surface areas below 2 m 2 g -1 . Upon reduction, the spinels possessed Cu + -rich surfaces when compared with a commercial Cu/ZnO/Al 2 O 3 , which resulted in better catalytic performance in methanol steam reforming (MSR). The composite catalysts of the Cu spinel and γ-Al 2 O 3 were promising for dimethyl ether steam reforming (DMESR) in terms of activity, selectivity, and stability. The descending order of the DMESR activity over the composite catalysts was as follows: CuFe 2 O 4 -γ-Al 2 O 3 > CuMn 2 O 4 -γ-Al 2 O 3 > CuCr 2 O 4 -γ-Al 2 O 3 , which was in line with the MSR activity over Cu-spinel catalysts. This revealed that the MSR activity strongly contributed to the high DMESR activity using the composite Cu-spinel catalysts and γ-Al 2 O 3 . The theoretical calculations demonstrated that the observed MSR reactivity trend follows the reactivity of the MSR rate-limiting step of methoxy dehydrogenation. The required active sites are shown to be both Cu and metal oxide in the facilitation of methoxy dehydrogenation. 1. INTRODUCTION Hydrogen has been widely considered to be an alternative clean energy carrier and the research and development of hydrogen production systems is of significant current interest for hydrogen storage and fuel cell applications. The attractive premise of fuel cells is that they are essentially clean energy conversion devices, initially consuming both hydrogen and oxygen and in return providing a source of electricity with only environmentally benign water as a chemical product. Addition- ally, there are multiapplication devices in that they have the potential to be utilized in a broad variety of settings, including residential, commercial, and vehicular. Given the upside potential and keen interest in fuel cells, and hence the need for the necessary ingredient of hydrogen, we now consider known technologies that can be used to produce hydrogen, such as catalytic reforming and photocatalysis for water splitting. 1-3 Spinel-oxide-type catalysts have played a crucial role in various catalytic applications, such as the removal of gaseous pollutants, 1 steam/dry reforming, 4-7 and water-gas shift reactions. 8 Cu-based spinels have been proposed as reforming catalysts for hydrogen generation from hydrocarbon fuels. 9 Steam reforming is a promising method to produce hydrogen from various fuels for fuel-cell applications because it provides a high-quality reformate. Oxygenated hydrocarbon fuels such as methanol (MeOH), ethanol, and dimethyl ether (DME) are of interest for the reforming process. DME is currently recognized as a promising H 2 source because it is a biomass-derived fuel that possesses high hydrogen-to-carbon ratio. Moreover, DME is preferable to MeOH because of its nontoxicity, and it can be catalytically reformed at lower temperatures than methane and ethanol. 6,9,10 In addition, the well-developed infrastructure used for liquefied petroleum gas (LPG) can be adapted to DME because of their similar physical properties. An excellent review of DME from the standpoint of availability, economics, and environmental cleanliness has been clearly published. 11 Dimethyl ether steam reforming (DMESR) comprises two sequential reactions: DME hydrolysis to MeOH, followed by methanol steam reforming (MSR) to hydrogen and carbon dioxide. 12-14 In general, DME hydrolysis proceeds over solid- acid catalysts, while MSR occurs over Cu- and Pd-based catalysts. 15-19 A mixture of solid-acid and metal-based catalysts is generally required for DMESR. Autothermal reforming conditions could be applied over these catalysts under appropriate reaction conditions to improve the energy efficiency of the reforming system. 14,20 Development of DMESR catalysts has been implemented to improve their performance to meet practical requirements. The types of solid- acid catalysts and metal catalysts, catalyst preparation conditions, and reforming conditions significantly contribute to the catalytic performance and behaviors. As for solid-acid catalysts, alumina exhibited excellent stability under DMESR conditions. 21 As for metal catalysts, the Cu-based spinel oxides were reported to be highly active compared with the Received: August 2, 2013 Revised: October 15, 2013 Published: October 15, 2013 Article pubs.acs.org/JPCC © 2013 American Chemical Society 23757 dx.doi.org/10.1021/jp407717c | J. Phys. Chem. C 2013, 117, 23757-23765