(33f) Understanding Sulfur Poisoning in Steam Reforming of N-Hexadecane: Catalyst Characterization Studies

Steam reforming of logistics fuel, such as jet fuel and diesel is an effective means of hydrogen production for fuel cells. One of the main problems in reforming logistics fuels is simultaneous deactivation due to coking and presence of sulfur. Sulfur content can vary ranging from few ppm in diesel to over thousand ppm in jet fuel. In order to improve the sulfur resistance of metal supported catalysts, we must know how sulfur chemisorbs on the metal sites. Understanding the mechanism of sulfur interaction would help us get insights into deactivation and thereby help in designing a better catalyst for improved performance. In the present work, diesel steam reforming was carried out using n-hexadecane as a surrogate to study effect of sulfur and coking on deactivation.

Steam reforming of n-hexadecane was conducted at 800 deg C, 1 atm and S/C ratio of 3 with different Rh-Ni catalysts supported on γ-alumina. Thiophene was used as the source of organic sulfur at 1000 wppm. In general, the presence of sulfur increased the coking on the support but had negligible effect on the metal coke. Presence of Rh in small quantities tends to increase sulfur resistance but when present in higher amounts gave lower hydrogen yields. Lower yields, at higher Rh content, was explained based on sulfur adsorption capacities. Also, carbon morphology of spent catalysts was studied using Scanning electron microscopy. Varying degrees of both filamentous and encapsulating carbon were observed in spent catalysts. Various other factors such as nickel particle sintering, phase transformation, degree of reduction and support acidity were discussed to explain deactivation. Techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, Transmission electron microscopy, Temperature programmed oxidation, reduction and ammonia desorption were employed in the present study.