Catalysts Development and Mechanistic Study of Ethanol Steam Reforming for Low Temperature H2 Production

Abstract

Hydrogen is anticipated as the renewable fuel for the next generation. It is a clean energy carrier (or a clean fuel) for the generation of electricity without producing any pollutants through fuel cell systems. Ethanol steam reforming (ESR) is a promising technology to produce H2 for small scale on site or on board applications. However, challenges remain for the development of the catalysts, such as stability, coking and the selectivity to H2. Fundamental understanding on the reaction network is still inadequate. In this thesis, two of the most extensively studied catalysts, Al2O3-supported Ni and Rh, are intensively investigated for low temperature ESR. Ca and Fe are respectively added to the Ni and Rh catalysts to improve their catalytic performance, with significantly enhanced H2 yield and catalysts stability. Various characterization techniques such as X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and tapered element oscillating microbalance (TEOM) are employed to study the effect of the promoters (Ca and Fe) and the reaction mechanisms. The deactivation mechanism in the Ni/Al2O3 system is found to be closely related to Ni particle size, catalyst electronic properties, and the steam gasification ability of Ca-modified Al2O3 support. In the Rh-Fe catalyst formulation, the promotion of Rh with Fe is achieved at molecular level. The close proximity of the Rh and Fe sites facilitates the transfer of the adsorbed reaction by-product, CO, from Rh to coordinately unsaturated iron oxides. The subsequent water?gas shift reaction results in a high H2 yield, extremely low CO selectivity, and a pronouncedly long Rh life span at T = 673 K.