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Access Type

WSU Access

Date of Award

January 2020

Degree Type


Degree Name



Chemical Engineering and Materials Science

First Advisor

Eranda Nikolla


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.

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