Synthesis And Characterization Of Layered Oxides And Their Application As Passive Nox Adsorbers

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The diversity and synthetic tunability of nonstoichiometric mixed metal oxides make them excellent candidates for passive NOx adsorption (PNA). They are typically synthesized via sol-gel methods, which can produce an extensive compositional variety of layered oxides. Although it offers limited levers for controlling the oxide surface, sol-gel provides opportunities to maximize the surface area by optimizing a variety of synthetic parameters to reduce calcination temperature. As extensive characterization is needed to interpret the catalytic performance of these complex non-stochiometric mixed metal oxides, various bulk (X-ray powder diffraction and iodometric titrations) and surface (X-ray photoelectron spectroscopy and Brunauer–Emmett–Teller theory) characterization techniques are discussed. First, the B-site of R-P oxides La0.5Sr1.5BO4+δ (B = Mn, Fe, Co, Ni) was varied, and La0.5Sr1.5NiO4+δ was found to perform the best with a surface NOx density of 38.1 μmol NO/m2, followed by La0.5Sr1.5CoO4+δ, La0.5Sr1.5MnO4+δ and La0.5Sr1.5FeO4+δ. Then, the A-site of R-P oxides La2-xSrxNiO4 (x = 0 – 1.5) was varied, and SND improved as Sr was introduced in the oxide, with La0.5Sr1.5NiO4 exhibiting the best performance. Density Functional Theory (DFT) indicated lattice O as the primary binding site. The Sr = 0 oxide was determined to be the most hyperstoichiometric in oxygen, with δ decreasing as Sr content increased. The best performing oxide (La0.5Sr1.5NiO4) possessed the largest number of oxygen vacancies. While these studies show promising trends in tuning the PNA properties of R-P oxide via compositional modulation, further studies are required to better understand the exact mechanism by which NO binds these oxides as a function of their composition.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.