Electrospun copper oxide nanofibers for H 2 S dosimetry

Abstract. This study reports on a sensor concept to measure in situ sulfur poisoning (sulfidation) of refinery catalysts, in this case, of commercial silica pellets loaded with highly dispersed nickel. Catalyst pellets were poisoned in diluted H 2 S between 100 and 400 • C and the sulfidation of the catalyst was observed. During this process, nickel sulfides are formed on the catalyst according to X-ray diffraction spectra and energy dispersive X-ray spectroscopy data. The sulfidation kinetics was quantitatively described by a shrinking core model. Representative catalyst pellets were electrically contacted, and their impedance was recorded in situ during sulfidation. At the beginning, the particles are highly insulating and behave capacitively. Their conductivity increases by decades during sulfidation. At high temperatures, an almost constant slope in the double-logarithmic representation vs. time can be found. At low temperatures, the conductivity remains constantly low for a long time but changes then rapidly by decades, which is also indicated by the phase that drops from capacitive to ohmic behavior. Since nickel sulfides exhibit a lower conductivity than nickel, the conductivity increase by decades during sulfidation can only be explained by electrically conducting percolation paths that form during sulfidation. They originate from the increased volume of sulfides compared to the pure nickel metal.

Section: Impedance Measurement Resultssupporting

confidence: 89%

Is it possible to detect in situ the sulfur loading of a fixed bed catalysts with a sensor?

Fremerey

Jess

Moos

2015

“…In the literature, this change in the accumulationlevel is detected mainly optically (Tanaka et al, 1999;Sasaki et al, 2001;Maruo, 2007) or gravimetrically (Matsuguchi et al, 2005). Recently impedimetric approaches have emerged (Varghese et al, 2001;Mattoli et al, 2007;Helwig et al, 2008;Geupel et al, 2010;Hennemann et al, 2012a;Groß et al, 2012c). Regeneration has to be initiated if saturation effects limit the sorption rate of the sensitive layer or if the sensing characteristic is deteriorated.…”

Section: Direct Amount and Indirect Concentration Detectionmentioning

confidence: 99%

Overview on conductometric solid-state gas dosimeters

Marr

Groß²,

Moos

2014

Abstract. The aim of this article is to introduce the operation principles of conductometric solid-state dosimeter-type gas sensors, which have found increased attention in the past few years, and to give a literature overview on promising materials for this purpose. Contrary to common gas sensors, gas dosimeters are suitable for directly detecting the dose (also called amount or cumulated or integrated exposure of analyte gases) rather than the actual analyte concentration. Therefore, gas dosimeters are especially suited for low level applications with the main interest on mean values. The applied materials are able to change their electrical properties by selective accumulation of analyte molecules in the sensitive layer. The accumulating or dosimeter-type sensing principle is a promising method for reliable, fast, and long-term detection of low analyte levels. In contrast to common gas sensors, few devices relying on the accumulation principle are described in the literature. Most of the dosimeter-type devices are optical, mass sensitive (quartz microbalance/QMB, surface acoustic wave/SAW), or field-effect transistors. The prevalent focus of this article is, however, on solid-state gas dosimeters that allow a direct readout by measuring the conductance or the impedance, which are both based on materials that change (selectively in ideal materials) their conductivity or dielectric properties with gas loading. This overview also includes different operation modes for the accumulative sensing principle and its unique features.

“…It offers high reactivity to hydrogen sulfide (H 2 S), but stays nearly unaffected by minor amounts of methane, nitrogen oxides or hydrogen at operating temperature (ca. 160 • C; Choi et al, 2013;Hennemann et al, 2012a). As shown by Choi et al, the conductance changes 2 orders of magnitude under 1000 ppm H 2 exposure.…”

Section: Introductionmentioning

confidence: 88%

“…Additionally, the continuous reaction of copper oxides with H 2 S accumulates increasing amounts of sulfur. This offers the possibility to detect the absolute amount of H 2 S over a defined period of time and estimate the averaged concentration (Hennemann et al, 2012a;Marr et al, 2014;Ramgir et al, 2010).…”

Section: Copper Oxide As H S Sensormentioning

confidence: 99%

H<sub>2</sub>S dosimeter with controllable percolation threshold based on semi-conducting copper oxide thin films

Seitz

Beck

Hennemann

et al. 2017

Self Cite

Abstract.Copper oxides, such as CuO and Cu 2 O, are promising materials for H 2 S detection because of the reversible reaction with H 2 S to copper sulfides (CuS, Cu 2 S). Along with the phase change, the electrical conductance increases by several orders of magnitude. On CuO x films the H 2 S reaction causes the formation of statistically distributed Cu x S islands. Continuous exposition to H 2 S leads to island growth and eventually to the formation of an electrical highly conductive path traversing the entire system: the so-called percolation path. The associated CuO x / Cu x S conversion ratio is referred to as the percolation threshold. This pronounced threshold causes a gas concentration dependent switch-like behaviour of the film conductance. However, to utilize this effect for the preparation of CuO-based H 2 S sensors, a profound understanding of the operational and morphological parameters influencing the CuS path evolution is needed.Thus, this article is focused on basic features of H 2 S detection by copper oxide films and the influence of structural parameters on the percolation threshold and switching behaviour. In particular, two important factors, namely the stoichiometry of copper oxides (CuO, Cu 2 O and Cu 4 O 3 ) and surface morphology, are investigated in detail. CuO x thin films were synthesized by a radio frequency magnetron sputtering process which allows modification of these parameters. It could be shown that, for instance, the impact on the switching behaviour is dominated by morphology rather than stoichiometry of copper oxide.