Elucidating the role of earth alkaline doping in perovskite-based methane dry reforming catalysts

Parastoo Delir Kheyrollahi Nezhad; Maged F Bekheet; Nicolas Bonmassar; Albert Gili; Franz Kamutzki; Aleksander Gurlo; Andrew Doran; Sabine Schwarz; Johannes Bernardi; Sebastian Praetz; Aligholi Niaei; Ali Farzi; Simon Penner

doi:10.1039/d1cy02044g

Elucidating the role of earth alkaline doping in perovskite-based methane dry reforming catalysts

Catal Sci Technol. 2022 Jan 6;12(4):1229-1244. doi: 10.1039/d1cy02044g. eCollection 2022 Feb 21.

Affiliations

¹ Reactor & Catalyst Research Lab, Department of Chemical Engineering, Faculty of Chemical and Petroleum Engineering, University of Tabriz Tabriz Iran.
² Fachgebiet Keramische Werkstoffe/Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin Hardenbergstr. 40 10623 Berlin Germany.
³ Department of Physical Chemistry, University of Innsbruck Innrain 52c A-6020 Innsbruck Austria simon.penner@uibk.ac.at +4351250758199 +4351250758003.
⁴ Institut für Chemie, Technische Universität Berlin Sekretariat TC 8, Straße des 17. Juni 124 10623 Berlin Germany.
⁵ Advanced Light Source, Lawrence Berkeley National Laboratory Berkeley California 94720 USA.
⁶ University Service Center for Transmission Electron Microscopy, TU Wien Wiedner Hauptstrasse 8-10 A-1040 Vienna Austria.
⁷ Institute of Optics and Atomic Physics, Technische Universität Berlin Hardenbergstraße 36 10623 Berlin Germany.

Abstract

To elucidate the role of earth alkaline doping in perovskite-based dry reforming of methane (DRM) catalysts, we embarked on a comparative and exemplary study of a Ni-based Sm perovskite with and without Sr doping. While the Sr-doped material appears as a structure-pure Sm_1.5Sr_0.5NiO₄ Ruddlesden Popper structure, the undoped material is a NiO/monoclinic Sm₂O₃ composite. Hydrogen pre-reduction or direct activation in the DRM mixture in all cases yields either active Ni/Sm₂O₃ or Ni/Sm₂O₃/SrCO₃ materials, with albeit different short-term stability and deactivation behavior. The much smaller Ni particle size after hydrogen reduction of Sm_1.5Sr_0.5NiO₄, and of generally all undoped materials stabilizes the short and long-term DRM activity. Carbon dioxide reactivity manifests itself in the direct formation of SrCO₃ in the case of Sm_1.5Sr_0.5NiO₄, which is dominant at high temperatures. For Sm_1.5Sr_0.5NiO₄, the CO : H₂ ratio exceeds 1 at these temperatures, which is attributed to faster direct carbon dioxide conversion to SrCO₃ without catalytic DRM reactivity. As no Sm₂O₂CO₃ surface or bulk phase as a result of carbon dioxide activation was observed for any material - in contrast to La₂O₂CO₃ - we suggest that oxy-carbonate formation plays only a minor role for DRM reactivity. Rather, we identify surface graphitic carbon as the potentially reactive intermediate. Graphitic carbon has already been shown as a crucial reaction intermediate in metal-oxide DRM catalysts and appears both for Sm_1.5Sr_0.5NiO₄ and NiO/monoclinic Sm₂O₃ after reaction as crystalline structure. It is significantly more pronounced for the latter due to the higher amount of oxygen-deficient monoclinic Sm₂O₃ facilitating carbon dioxide activation. Despite the often reported beneficial role of earth alkaline dopants in DRM catalysis, we show that the situation is more complex. In our studies, the detrimental role of earth alkaline doping manifests itself in the exclusive formation of the sole stable carbonated species and a general destabilization of the Ni/monoclinic Sm₂O₃ interface by favoring Ni particle sintering.