Methane Catalytic Combustion under Lean Conditions over Pristine and Ir-Loaded La1-xSrxMnO3 Perovskites: Efficiency, Hysteresis, and Time-on-Stream and Thermal Aging Stabilities

Catherine Drosou; Ersi Nikolaraki; Theodora Georgakopoulou; Sotiris Fanourgiakis; Vassilios T Zaspalis; Ioannis V Yentekakis

doi:10.3390/nano13152271

Methane Catalytic Combustion under Lean Conditions over Pristine and Ir-Loaded La_1-xSr_xMnO₃ Perovskites: Efficiency, Hysteresis, and Time-on-Stream and Thermal Aging Stabilities

Nanomaterials (Basel). 2023 Aug 7;13(15):2271. doi: 10.3390/nano13152271.

Authors

Catherine Drosou¹, Ersi Nikolaraki¹, Theodora Georgakopoulou¹, Sotiris Fanourgiakis¹, Vassilios T Zaspalis^{2

3}, Ioannis V Yentekakis^{1

4}

Affiliations

¹ Laboratory of Physical Chemistry and Chemical Processes, School of Chemical and Environmental Engineering, Technical University of Crete, 731 00 Chania, Crete, Greece.
² Department of Chemical Engineering, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece.
³ Chemical Process and Energy Resources Institute, Center for Research and Technology Hellas (CPERI/CERTH), 570 01 Thermi, Thessaloniki, Greece.
⁴ Institute of GeoEnergy, Foundation for Research and Technology-Hellas (FORTH/IG), 731 00 Chania, Greece.

Abstract

The increasing use of natural gas as an efficient, reliable, affordable, and cleaner energy source, compared with other fossil fuels, has brought the catalytic CH₄ complete oxidation reaction into the spotlight as a simple and economic way to control the amount of unconverted methane escaping into the atmosphere. CH₄ emissions are a major contributor to the 'greenhouse effect', and therefore, they need to be effectively reduced. Catalytic CH₄ oxidation is a promising method that can be used for this purpose. Detailed studies of the activity, oxidative thermal aging, and the time-on-stream (TOS) stability of pristine La_1-xSr_xMnO₃ perovskites (LS_XM; X = % substitution of La with Sr = 0, 30, 50 and 70%) and iridium-loaded Ir/La_1-xSr_xMnO₃ (Ir/LS_XM) perovskite catalysts were conducted in a temperature range of 400-970 °C to achieve complete methane oxidation under excess oxygen (lean) conditions. The effect of X on the properties of the perovskites, and thus, their catalytic performance during heating/cooling cycles, was studied using samples that were subjected to various pretreatment conditions in order to gain an in-depth understanding of the structure-activity/stability correlations. Large (up to ca. 300 °C in terms of T₅₀) inverted volcano-type differences in catalytic activity were found as a function of X, with the most active catalysts being those where X = 0%, and the least active were those where X = 50%. Inverse hysteresis phenomena (steady-state rate multiplicities) were revealed in heating/cooling cycles under reaction conditions, the occurrence of which was found to depend strongly on the employed catalyst pre-treatment (pre-reduction or pre-oxidation), while their shape and the loop amplitude were found to depend on X and the presence of Ir. All findings were consistently interpreted, which involved a two-term mechanistic model that utilized the synergy of Eley-Rideal and Mars-van Krevelen kinetics.

Keywords: LSM perovskites; catalytic methane oxidation; hysteresis phenomena; iridium; lean conditions; thermal aging stability.

Grants and funding

T7DKI-00356/The European Union and Greek national funds under the call "Greece-China Call for Proposals for Joint RT&D Projects