자료유형  

 학위논문

Control Number  

0017163024

International Standard Book Number  

9798384015963

Dewey Decimal Classification Number  

660

Main Entry-Personal Name  

Ramos-Yataco, Jordy.

Publication, Distribution, etc. (Imprint  

[S.l.] : Northwestern University., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

242 p.

General Note  

Source: Dissertations Abstracts International, Volume: 86-02, Section: B.

General Note  

Advisor: Notestein, Justin M.

Dissertation Note  

Thesis (Ph.D.)--Northwestern University, 2024.

Summary, Etc.  

요약Natural gas is the source of building blocks for many of the day-to-day products of modern society, and its availability has increased due to new extraction technologies. Methane is the main component of natural gas, but its direct transformation to higher-value chemicals has not reached industrial application. As a result, the copious amounts of methane only have relatively low-value uses as a source of synthesis gas or as a heating source. Extensive research in the last three decades on heterogeneous catalysis has proposed several catalytic systems to directly transform methane to higher hydrocarbons under high-temperature conditions. This thesis evaluates the impact of structure on the catalytic activity of benchmark catalysis for oxidative coupling of methane (OCM) and methane dehydroaromatization (MDA). Additionally, after these insights were recognized, novel approaches to increase the catalyst's performance, and especially stability, were explored.Through extensive catalytic evaluation of a set of OCM catalyst formulations, different alkali metals (A) in catalysts with the overall formulation of A2WO4-MnOx/SiO2 or A2WO4-LaMnOx/SiO2 are demonstrated to be active and stable in transforming methane to light olefins. In analyzing product distributions over this wide variety of materials studied, it was observed that propylene and ethylene partial pressures are always found in constant proportions with respect to each other, independent of catalyst formulation. This observation leds to the evaluation of the effect of C2H4 cofeeding to promote the formation of C3+ higher olefins on the benchmark Na2WO4-MnOx/SiO2 catalyst. Under specific reaction conditions, this does increase C3+ selectivity, but at the expense of also promoting increased COx formation.MDA studies were first carried out on Mo/H-ZSM-5, the benchmark material for this reaction. Coke formation on external surfaces is a major deactivation route, and the effect of passivating external crystal surfaces was evaluated under MDA conditions. External surfaces were modified using atomic layer deposition (ALD), which enabled deposition on external surfaces without impacting bulk textural properties. In the case of SiO2, the overcoat has a positive impact on integrated yields of aromatics, while an Al2O3 overcoat reduces the formation of aromatics over the lifetime of the catalyst. This modification also impacts the nature of the coke formed on the spent catalysts. Under a deliberately harsh isothermal-oxidative regeneration process, these performance differences are not maintained. Characterization of the modified Mo/H-ZSM-5 shows that the MoOx pre-catalyst centers - formed after synthesis or each regeneration step - progressively redistribute, leading to permanent deactivation. This redistribution is impacted by SiO2 and Al2O3 overcoats, but it cannot be prevented entirely.The benchmark catalyst for MDA is Mo/H-ZSM-5, and a vast variety of approaches have been explored, generally with the goal of increasing aromatics yields. However, the deactivation behavior with time on stream has been much less studied, even though this places the largest limit on yields, overall catalyst lifetime, and process economics. As such, multiple variables related to Mo/H-ZSM-5 synthesis were evaluated with respect to the deactivation behavior of the catalyst. Synthesis variables included are Mo loading, Mo loading method, and Si/Al2 ratio of H-ZSM-5. Additionally, catalysts were also studied over multiple cycles of oxidative regeneration. Many materials showed differences in performance, but in analyzing the collected catalytic results, all materials had overlapping curves of CH4 conversion vs product selectivity (deactivation profile). This behavior provides evidence of a non-selective deactivation of Mo/H-ZSM-5, where the active sites are present on all materials and deactivate with no special preference. Additionally, catalytic results from the last three decades of academic research on MDA were collected and re-interpreted. This analysis showed remarkable similarity of the deactivation profiles of all materials, independent of most materials' synthesis or treatment strategies. Several other synthesis or reaction engineering strategies are clearly seen to be detrimental in this analysis, but the analysis also highlights a small number of useful strategies to pursue in MDA research, including some less-explored metals that modify catalyst deactivation profiles showed higher selectivity at a given conversion.After considering Mo/H-ZSM-5 and its many modified variants, one hypothesis that emerges is that the Bronsted acid sites in these materials principally serve as anchoring sites that facilitate high dispersion of the MoOx precatalyst. A consequence of oxidative regeneration (coke combustion) is the loss of Bronsted acid sites under hydrothermal conditions, which in turn leads to aggregation of MoOx or AlMoOx domains that are catalytically inactive for the formation of aromatics. Considering this, non-zeolitic, mixed oxide supports with Bronsted acid sites were explored. While not as selective, these supports potentially offer more hydrothermal stability and provide a greater diversity of anchoring sites for the MoOx precatalyst centers.

Subject Added Entry-Topical Term  

Chemical engineering.

Subject Added Entry-Topical Term  

Physical chemistry.

Subject Added Entry-Topical Term  

Analytical chemistry.

Index Term-Uncontrolled  

Atomic layer deposition

Index Term-Uncontrolled  

Methane dehydroaromatization (MDA)

Index Term-Uncontrolled  

Non-selective deactivation

Index Term-Uncontrolled  

Catalysts

Index Term-Uncontrolled  

Hydrocarbons

Added Entry-Corporate Name  

Northwestern University Chemical and Biological Engineering

Host Item Entry  

Dissertations Abstracts International. 86-02B.

Electronic Location and Access  

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Control Number  

joongbu:657100