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Understanding Sulfur Poisoning and Carbon Deposition on Rh-Ni/Al2O3 Catalysts during Steam Reforming of Logistic Fuels

Satish Lakhapatri and Martin A. Abraham. Chemical and Environmental Engineering, University of Toledo, 2801 W. Bancroft, 3048 Nitschke Hall, Toledo, OH 43606

Towards attaining sustainable development, it is imperative to use the existing energy reserves efficiently with practically no environmental issues. In view of the same, it looks fitting to use fuel cells for both stationary and mobile applications in future. While the efficiency in a typical internal combustion engine rarely exceeds 20%, fuel cell normally operates around 40%-60%. One of the options being suggested is to use hybrid system consisting of a conventional internal combustion engine (ICE) for propulsion and a fuel cell powered auxiliary power unit (APU). On-board production overcomes the problems associated with transportation and delivery of hydrogen. In the present study, hydrogen is produced by steam reforming of logistic fuels present on-board. Deactivation of the catalyst due to both, sulfur poisoning and carbon deposition, is a major hurdle in such a process. The present work was undertaken to understand sulfur poisoning and carbon deposition in deactivation during steam reforming of logistic fuels on a Rh-Ni catalyst supported on γ-alumina. The study was extended to Rh-Pd-Ni catalyst supported on γ-alumina.

Steam reforming of logistic fuel was conducted at 800oC at atmospheric pressure using n-hexadecane as the surrogate for logistics fuel and thiophene as the source of sulfur. Close examination of the fresh catalyst using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) revealed the presence of two kinds of active metal particles; one containing Ni and the other containing predominantly Rh. Temperature programmed reduction (TPR) and X-ray diffraction (XRD) confirmed the formation of aluminates of both nickel and rhodium due to high calcinations temperatures. It was observed that sulfur preferentially adsorbs on the surface of nickel particles while protecting rhodium, which remains active for steam reforming. There was no bulk nickel sulfide formation and only surface adsorption was seen. Also, whiskers of carbon were seen in catalysts containing no or very low rhodium content while presence of high rhodium prevented the formation of the same.