Date of Award
Doctor of Philosophy (PhD)
Biomedical and Chemical Engineering
Chemical Engineering | Engineering
Ketone hydrogenation:A model system of carbonyl (ketone) hydrogenation, acetone hydrogenation over supported Pt catalysts in the gas-phase fixed bed reactor was investigated to understand both the mechanism and rate controlling steps in a fundamental level. The experiments and outcomes include the detailed macro- and micro-kinetic analysis of hydrogenation of acetone. The apparent reaction orders of hydrogen and acetone, apparent activation energies, and observed kinetic isotope effects over a large range of temperatures and concentrations (compound partial pressures) are reported in this document. Generally speaking, the ketone hydrogenation over metal surfaces in vapor phase comply with the mechanism that hydrogen atoms add sequentially to the adsorbed ketone to form corresponding alcohols, namely Horiuti-Polanyi mechanism. For acetone hydrogenation, it is also concluded that the two sequential surface reactions, respectively involving the formation of isopropoxy and surface isopropanol, each exert partial surface reaction rate control the overall rate of hydrogenation under most experimental reaction conditions. A comprehensive degree of rate control analysis are performed with a set of intrinsic kinetic parameters (e.g., elementary reaction barriers) and surface coverages of intermediate species under experimental conditions. In the meanwhile, from the microkinetic modeling, the optimized group of elementary kinetic parameters are generated out for rate prediction of acetone hydrogenation under various range of reaction conditions in the vapor phase, e.g., partial pressures, temperature. Additionally, the results of isotope effect experiments by switching between hydrogen and deuterium at different reaction temperatures demonstrate a quite minor apparent kinetic isotope effects; however, the hydrogen addition steps are reconciled as the rate determine steps during microkinetic modeling, where the experimental data fits best to the scenario by assuming atomic hydrogen and other surface species do not adsorb and desorb at the same metal sites. Finally, the apparent kinetic isotope findings are considered systematically as the overall influence of elementary kinetic isotope effect and equilibrium isotope effect.
As a much-deployed noble metal catalysts on carbonyl hydrogenation, platinum and ruthenium are well compared under the similar level of reaction microkinetics with and without solvation effect, which includes the apparent reaction orders, apparent reaction barriers and kinetic isotope effect, optimized kinetic and thermodynamic parameters, and rate controlling scenarios. Both of Langmuir isotherm adsorption and Temkin isotherm adsorption (lateral interaction) are counted respectively for the comparison of ketone hydrogenation over Pt and Ru catalysts. In the solvent system, various solvents (alkane, water, ether and alcohol) are tested and analyzed with their contributions to the hydrogenation kinetics under a range of solvent partial pressures and reaction temperatures with lateral interaction model applied.
Alcohol and ketone aminations:A large set of secondary alcohol and ketone aminations, which represents another type of carbonyl reduction process, is studied to achieve the optimal ruthenium-based catalyst efficiency in both vapor and aqueous reactors. In the vapor phase approach, isopropanol amination is regarded as model reaction for secondary alcohol system, where ammonia and hydrogen partial pressures, reactor contact time and temperature are comprehensively tuned to understand the trends of the related amination environment. As a systematic catalyst evaluation, a list of other secondary alcohols is tested under the optimal reaction condition to benchmark the best catalyst performance, e.g., reactant conversion, production selectivity and product yield. To fulfill the target of producing 3-amino tetrahydrofuran, the THF based alcohol aminations are examined separately to explore the trends, which is different from normal secondary alcohols. In the aqueous phase method, 2-octanol amination in solvents are tested at various temperatures to identify the optimal reaction condition.
After probing the macroscopic scale of catalyst impact on alcohol and ketone amination, the kinetics and reaction mechanism studies are carried out from the packed bed reactor in gas phase, where isopropanol is chosen as the represented molecule. The kinetic investigation part includes the apparent reactant orders, e.g., isopropanol, ammonia and hydrogen, reaction activation energies. The reaction mechanism result reveals that the secondary alcohol amination follows the sequential steps on alcohol dehydrogenation to ketone and ketone amination (carbonyl reduction) to amine product, where the rates of each step are compared as well. Besides, the kinetics of alcohol amination within solvent effect is measured at multiple space velocities and thermodynamic ratios to determine the relative amination rate within different types of solvents.
Gao, Xin, "Rational Design of Supported Metal Catalysts for Carbonyl Reduction During Biomass Upgrading" (2021). Dissertations - ALL. 1485.
Available for download on Friday, November 01, 2024