Date of Award
Doctor of Philosophy (PhD)
Biomedical and Chemical Engineering
Biomass;Heterogeneous Catalysis;Hydrothermal Gasification;Reaction Engineering;Sewage Sludge Treatment;Spectroscopy
Chemical Engineering | Engineering
Mechanistic study of methylketone oxidative scission over supported vanadium oxides Biomass is increasingly recognized as a sustainable alternative to petroleum for the production of commodities and chemicals. The oxidation of carbonyl groups to carboxylates and selective C-C scission are promising strategies for enhancing reactivity and selectivity during the processing of platform chemicals. Oxidative cleavage of methyl ketones, significant for both reactions, has been well-studied under homogeneous catalysis. However, the mechanisms driving heterogeneous catalysis, often preferred for vapor-phase molecule upgrading, remain unclear in aerobic atmospheres over solid catalysts. To resolve the mechanism, the oxidative scission of 3-methyl 2-butanone (3M2B) over a vanadium oxide catalyst supported by gamma alumina is investigated through detailed kinetic and spectroscopic analyses. Oxidative cleavage of 3M2B on both reducible vanadium oxide and non-reducible γ-Al2O3 are observed. in situ Fourier-Transform Infrared (FTIR) and Diffuse Reflectance Ultraviolet-Visible spectroscopy shed light on the formation of surface species and the changes occurring in metal oxides. As a result, mechanisms for oxidative cleavage facilitated solely by gaseous dioxygen and lattice oxygen, integrating elements from both Eley-Rideal and Mars-van Krevelen reaction pathways are proposed, which are applicable to solid acidic metal oxides. Further diagnostic experiments involving the blocking of acid sites through pyridine and 2,6-ditert-butylpyridine cofeeding are conducted on both steady-state reactors and in situ FTIR. The active acid sites as predominantly Brønsted acid sites and Lewis acid sites originating from vanadium cations are identified. Moreover, ammonia cofeeding reveal distinct oxygen sources for the production of ketone or aldehyde and carboxylic acid: gaseous dioxygen and lattice oxygen, respectively. Building on these findings, we propose a reaction mechanism for the oxidative scission of 3M2B over supported vanadium oxides. Hydrothermal Gasification Reaction of Model Organic Compounds in Water on Ni/SiO2 for harvesting renewable energy from wastewater In an effort to improve energy efficiency in wastewater treatment processes, this paper proposes a method of hydrothermal gasification of products derived from the hydrothermal liquefaction of activated sewage sludge for renewable energy harvesting. The focus of this study is hydrothermal gasification, which has the potential to convert the majority of carbon from hydrothermal liquefaction products into renewable natural gas for power generation. To test the feasibility of this proposed method, hydrothermal gasification of model organic compounds is investigated. The equilibrium of reactions involving various organic compound feedstocks under different temperatures and pressures is calculated theoretically. Thermodynamic optimization determines that low temperature and high pressure are ideal operating conditions for testing the reaction on Ni/SiO2 catalysts. At 500°C and 10 bar, the residence times of different reactants on the catalyst are manipulated to investigate the contact time required for reaching equilibrium and the effectiveness of the Ni/SiO2 catalyst. Similarly, a mixture of multiple organics is used as a feedstock to test the robustness of the reaction and catalyst in handling complex feedstocks. Catalyst deactivation is investigated under various conditions, including high temperature and pressure, hydrothermal conditions, and reaction conditions. The deactivation mechanism of the catalyst is found to be coke deposition and metal sintering. Lastly, the impact of water concentrations on the hydrothermal gasification reaction is studied, revealing that water is beneficial to the kinetics while not affecting the thermodynamics of the reaction within a certain range.
Liu, Bowei, "Heterogeneous Reactions on Supported Metal Catalysts Targeting Sustainable Carbon and Energy Production" (2023). Dissertations - ALL. 1738.
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