Effect of hydrogen sulfide on the catalytic activity of Ni-YSZ cermets

• Published in: Journal of molecular catalysis. A, Chemical Chemical, 2008-03, Vol.282 (1), p.9-21
• Main Authors: Kuhn, John N., Lakshminarayanan, Nandita, Ozkan, Umit S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Carbon deposition; Catalysis; Catalyst deactivation; Chemistry; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; General and physical chemistry; Ni-YSZ; SOFC; Sulfur; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2007.11.032

The effect of H 2S upon the activity and stability of Ni-YSZ (yttria-stabilized zirconia) cermets was examined for model anode chamber reactions. Reactions with H 2O (water-gas shift reaction, steam reforming) were more strongly affected by sulfur compared to CO or CH 4 oxidation reactions. For reactions involving CH 4, hydrocarbon decomposition was the dominant reaction pathway at higher temperatures; however, this reaction path was inhibited by sulfur exposure. ▪ Ability to operate solid oxide fuel cells (SOFCs) on fuels containing carbon and sulfur with a minimal amount of deactivation is an important technical hurdle. For this reason, the influence of H 2S upon the activity and stability of Ni-YSZ (yttria-stabilized zirconia) cermets was examined for model anode chamber reactions. Reactions with H 2O (water-gas shift reaction, steam reforming) were more strongly affected by sulfur compared to CO or CH 4 oxidation reactions. For reactions involving CH 4, hydrocarbon decomposition was the dominant reaction pathway at higher temperatures; however, this reaction path was inhibited by sulfur exposure. Changes in the steam reforming activity of sulfur-treated samples with increasing temperature or with high-temperature H 2 treatment suggested sulfur migration to more active sites or surface restructuring. Such changes in active sites appear to be accelerated in the presence of H 2O. Direct poisoning of YSZ was eliminated since activity differences for the water-gas shift reaction, CH 4–H 2O reforming, and partial CH 4 oxidation were negligible with and without H 2S exposure. Reaction results were complemented by X-ray diffraction (XRD), laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with CO as a probe molecule.