Toward Environmentally Benign Catalyst Composition: Effect of Fe Substitution on Crystal Structure and Redox Behavior in Lanthanum Cobaltite Catalysts for CO Oxidation

The Journal of Physical Chemistry C, vol. 128, pp. 3281–3294

Abstract

The substitution of transition metals in perovskite catalysts has a significant impact on their catalytic performance. In this study, we explore the effect of iron (Fe) substitution on the crystal structure and redox behavior of lanthanum cobaltite (LaCoO 3 ) catalysts for CO oxidation. Addressing concerns related to the toxicity, cost, and environmental impact of cobalt-based perovskite, LaCoO 3, our research aims to contribute to the development of environmentally more benign solid catalysts. Fe-substituted lanthanum cobaltite catalysts, denoted as LaCo 1– x Fe x O 3 with ( x = 0.00, 0.25, 0.50, 0.70, and 1.00), were synthesized using a sol–gel combustion method. The crystal structures and phase compositions were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Characterization results revealed that Fe substitution leads to compositionally induced structural changes in the catalysts, enhancing their reducibility and potentially impacting their catalytic activity in CO oxidation. Temperature-programmed reduction was conducted to evaluate the redox behavior and demonstrate that the Fe strongly enhances the reducibility of Co 3+ to Co 2+ while inhibiting further reduction to Co 0 species. The combined results of H 2 -TPR, X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller method (BET) surface area analyses indicate that an appropriate level of Fe substitution in LaCoO 3 increases the concentration of oxygen vacancies and increases the surface area, thereby enhancing the catalytic performance in CO oxidation. Although the 25% Fe-doped LaCoO 3 exhibits a larger surface area with a higher concentration of oxygen vacancies, the Fe-free catalyst (LaCoO 3 ) demonstrates the highest catalytic activity at high temperatures. This may be attributed to the formation of carbonate species on the surface of the highly Fe-doped catalyst, which can act as poisoning species rather than reaction intermediates. The findings highlight the importance of transition metal doping in tailoring catalytic properties and optimizing the performance of perovskite-based catalysts for sustainable and efficient CO oxidation processes.

Authors 10

1. Ahed Abouserie corresponding Aachen Center for Automotive Catalytic Systems Aachen Institute of Inorganic Chemistry

   RWTH Aachen University

   Affiliation as printed

   Center for Automotive Catalytic Systems Aachen, RWTH Aachen University, 52062 Aachen, Germany

   Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen, Germany

2. Daniel Röhrens Aachen Center for Automotive Catalytic Systems Aachen Institute of Inorganic Chemistry

   RWTH Aachen University

   Affiliation as printed

   Center for Automotive Catalytic Systems Aachen, RWTH Aachen University, 52062 Aachen, Germany

   Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen, Germany

3. Dario Formenti Aachen Institute of Inorganic Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen, Germany

4. Xiaochao Wu Aachen Center for Automotive Catalytic Systems Aachen Institute of Inorganic Chemistry

   RWTH Aachen University

   Affiliation as printed

   Center for Automotive Catalytic Systems Aachen, RWTH Aachen University, 52062 Aachen, Germany

   Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen, Germany

5. Lena Patterer Aachen Materials Chemistry

   RWTH Aachen University

   Affiliation as printed

   Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany

6. Felix Ott Aachen Center for Automotive Catalytic Systems Aachen Chair of Heterogeneous Catalysis and Chemical Technology

   RWTH Aachen University

   Affiliation as printed

   Center for Automotive Catalytic Systems Aachen, RWTH Aachen University, 52062 Aachen, Germany

   Chair of Heterogeneous Catalysis and Chemical Technology, RWTH Aachen University, Worringerweg 2, 52074 Aachen, Germany

7. Gianluca Dalfollo Aachen Institute of Inorganic Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen, Germany

8. Jochen M. Schneider Aachen Materials Chemistry

   RWTH Aachen University

   Affiliation as printed

   Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany

9. Regina Palkovits Aachen Center for Automotive Catalytic Systems Aachen Chair of Heterogeneous Catalysis and Chemical Technology

   RWTH Aachen University

   Affiliation as printed

   Center for Automotive Catalytic Systems Aachen, RWTH Aachen University, 52062 Aachen, Germany

   Chair of Heterogeneous Catalysis and Chemical Technology, RWTH Aachen University, Worringerweg 2, 52074 Aachen, Germany

10. Ulrich Simon Aachen Center for Automotive Catalytic Systems Aachen Institute of Inorganic Chemistry

    RWTH Aachen University

    Affiliation as printed

    Center for Automotive Catalytic Systems Aachen, RWTH Aachen University, 52062 Aachen, Germany

    Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074 Aachen, Germany