Tim Delrieux, Shweta Sharma, Florian Maurer, Joachim Czechowsky, Camelia Nicoleta Borca, Dmitry Karpov, Camilo Cárdenas, Patrick Lott, Maria Casapu, Thomas L. Sheppard* and Jan-Dierk Grunwaldt*,
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引用次数: 0
Abstract
Understanding the deactivation induced by sulfur poisoning is crucial for designing more efficient palladium-based monolithic catalysts for methane oxidation. This study employs advanced characterization techniques, including X-ray absorption spectroscopy (XAS), X-ray fluorescence (XRF), spatially resolved activity measurements (SpaciPro), and synchrotron X-ray tomography, to investigate the effects of sulfur poisoning and regeneration from the atomic to the reactor scale. This includes structural changes, i.e., oxidation state and chemical speciation in axial direction of a catalyst bed/coated monolithic channel as well as in the coated catalyst layer. Integral activity and spatially resolved kinetic measurements revealed that sulfur significantly reduces the catalytic activity for methane oxidation, in particular, from the beginning of the channel/catalyst bed. Gradients in sulfur concentration were observed along the axial direction of the coated channel of the monolithic honeycomb catalysts by XRF, supported by XAS. At the meso scale, X-ray holotomography provided three-dimensional (3D) maps (∼400 μm diameter) uncovering some heterogeneous sulfur distribution within the catalyst layer due to different porosity/material structure. The sulfur gradients correlate with the catalytic activity as a function of the axial position of the reactor as uncovered by SpaciPro. Complementary XAS analysis at the S K-, Pd K-, and L3-edges uncovered details on the chemical structure changes (i.e., changes in Pd and S oxidation states) during poisoning and regeneration leading to loss of catalytic activity. They show that it is challenging to fully regenerate the Pd catalyst and its activity by a mild reductive treatment, particularly after prolonged sulfur exposure, as sulfur predominantly remains in its oxidation state +6. The insights obtained allow for quantifying sulfur-induced deactivation in technical catalysts as a function of composition and the location in the reactor. The insights may be used to develop and assess more stable catalysts in the future.
期刊介绍：
ACS Catalysis is an esteemed journal that publishes original research in the fields of heterogeneous catalysis, molecular catalysis, and biocatalysis. It offers broad coverage across diverse areas such as life sciences, organometallics and synthesis, photochemistry and electrochemistry, drug discovery and synthesis, materials science, environmental protection, polymer discovery and synthesis, and energy and fuels.
The scope of the journal is to showcase innovative work in various aspects of catalysis. This includes new reactions and novel synthetic approaches utilizing known catalysts, the discovery or modification of new catalysts, elucidation of catalytic mechanisms through cutting-edge investigations, practical enhancements of existing processes, as well as conceptual advances in the field. Contributions to ACS Catalysis can encompass both experimental and theoretical research focused on catalytic molecules, macromolecules, and materials that exhibit catalytic turnover.
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