title: Why does the Conductivity of a Nickel Catalyst Increase during Sulfidation? An Exemplary Study Using an In Operando Sensor Device.
abstract: In order to study the sulfidation of a catalyst fixed bed, an in operando single pellet sensor was designed. A catalyst pellet from the fixed bed was electrically contacted and its electrical response was correlated with the catalyst behavior. For the sulfidation tests, a nickel catalyst was used and was sulfidized with H₂S. This catalyst had a very low conductivity in the reduced state. During sulfidation, the conductivity of the catalyst increased by decades. A reaction from nickel to nickel sulfide occurred. This conductivity increase by decades during sulfidation had not been expected since both nickel and nickel sulfides behave metallic. Only by assuming a percolation phenomenon that originates from a volume increase of the nickel contacts when reacting to nickel sulfides, this effect can be explained. This assumption was supported by sulfidation tests with differently nickel loaded catalysts and it was quantitatively estimated by a general effective media theory. The single pellet sensor device for in operando investigation of sulfidation can be considered as a valuable tool to get further insights into catalysts under reaction conditions.
authors.affiliation: Department of Functional Materials, Zentrum für Energietechnik (ZET), University of Bayreuth, 95440 Bayreuth, Germany. functional.materials@uni-bayreuth.de.|Department of Chemical Engineering, Zentrum für Energietechnik (ZET), University of Bayreuth, 95440 Bayreuth, Germany. functional.materials@uni-bayreuth.de.
authors.forename: Peter
authors.initials: P
authors.lastname: Fremerey
authors.affiliation: Department of Chemical Engineering, Zentrum für Energietechnik (ZET), University of Bayreuth, 95440 Bayreuth, Germany. Andreas.Jess@uni-bayreuth.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Jess
authors.affiliation: Department of Functional Materials, Zentrum für Energietechnik (ZET), University of Bayreuth, 95440 Bayreuth, Germany. functional.materials@Uni-Bayreuth.de.
authors.forename: Ralf
authors.initials: R
authors.lastname: Moos
keywords: fixed bed catalyst; in operando; nickel to nickel sulfide transformation; percolation; sulfur poisoning