Date of Completion

1-31-2020

Embargo Period

1-29-2021

Keywords

Monolithic catalysts, Nanoarrays, Titanium dioxide, Titanates, Heterogeneous catalysts, Mass Transfer, Automotive emission control

Major Advisor

Pu-Xian Gao

Associate Advisor

Steven L. Suib

Associate Advisor

Brian Willis

Associate Advisor

Seok-Woo Lee

Associate Advisor

Avinash Dongare & Jie He

Field of Study

Materials Science and Engineering

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

Monolithic catalysts, also known as structured catalysts, account for an important category of catalysts which are widely used in the fields of automotive emission control, chemical processes, and energy industries. Despite the success of the state-of-the-art washcoated monolithic catalysts in different fields, challenges and bottlenecks have emerged with the increasingly stringent regulations and requirements for high-performance catalysts. To meet these challenges, a new class of structured catalysts, the so-called nanoarray-based monolithic catalyst configuration, was invented and demonstrated a decade ago. Since then, strategies are being developed in order to achieve the industrial-level manufacturing and further improvement of the nanoarray-based monolithic catalysts. In this dissertation, a novel microwave-assisted hydrothermal method is developed for the scalable synthesis of uniform layered protonated titanates (LPTs) nanoarrays, a precursor of TiO2, on various two dimensional (2D) and three dimensional (3D) monolithic substrates at low temperatures but with high production rates. The conventional solvothermal method was also optimized for the synthesis of rutile TiO2 nanoarrays by considering the solvent effects on the heterogeneous growth. Taking advantages of the high cation exchange capacity of the LPT nanomaterials, platinum (Pt) based diesel oxidation catalysts (DOC) and Cu-Ce-Mn oxide-based selective catalytic reduction (SCR) catalysts were prepared via an ion-exchange assisted loading method. Spectroscopy analysis evidenced the intercalation of Pt2+ cations into the interlayers of the titanate frameworks through the ion-exchange procedure, which alters the chemical and electronic structures of the catalysts, and improves the hydrothermal stability of the catalysts. The co-doping of different transition metal elements onto the LPT nanoarrays results in the synergistic effects between different elements towards the selective reduction of NO. Particularly, the addition of Cu promotes the low-temperature activity by increasing the reducibility of the Mn-based NH3-SCR catalysts, and Ce can increase the high-temperature N2-selectivity by altering the surface adsorption properties of the Mn-based catalysts. Finally, the mass transport properties of the metal oxide nanoarray-based monolithic catalysts were studied and compared with the state-of-the-art washcoated counterparts by experimental measurements and theoretical modeling. The results indicated that the nanoarray-based catalysts showed lower internal mass transfer resistance compared with the washcoated catalysts, which provides a new path towards designing high-performance nanoarray-based monolithic catalysts with low internal diffusion limitations.

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