Efficient and stable Ni–Ce glycerol reforming catalysts: Chemical imaging using X-ray electron and scanning transmission microscopy

Abstract

Nickel–ceria composite catalysts prepared by a microemulsion method showed outstanding catalytic behavior in hydrogen production by glycerol steam reforming. Contrarily to usual Ni-based catalysts, the system allows long-term stability and nearly absence of by-products, particularly methane and carbon monoxide. With the help of scanning transmission electron microscopy and energy dispersive X-ray spectroscopy we confirmed the key role played by an intimate intermixing of Ni and Ceria components at reaction conditions. In addition, chemical imaging maps as well as more conventional techniques, such as Temperature Programmed Oxidation (TPO) and X-ray Photoelectron Spectroscopy (XPS) were used to identify the carbon containing (including coke) species nature and to establishing their chemical relevance. Combination of these techniques points out that the optimum interphase contact, reached for a specific 20:80 molar Ni:Ce formulation, allows; (i) to keep the Ni particle size controlled with absence of significant formation of coke and thus without deleterious effects on the long-term stability of the catalysts; and (ii) to eliminate undesirable side reactions such as methanation.