Kinetic and spectroscopic studies on solutions of two iridium(I) complexes—trans-chlorocarbonylbis(triphenylphosphine)iridium(I), Ir(CO)Cl(PPh3)2, and μ-dichlorotetrakis (cyclooctene)-di-iridium(I) , [IrCl(C8H,14)2]2—are described, especially for reactions involving activa-tion of molecular H2, molecular O2, and olefins. The studies also illustrate the importance of solvent effects. The catalytic activity of Ir(CO)Cl(PPh3)2 for hydrogenation of maleic acid has been surveyed using a range of solvents—pyridine, dimethylsulfoxide (DMSO), dimethylacetamide (DMA), dimethylformamide (DMF), acetone, sulfolane, acetonitrile, nitromethane and formamide. Where activity is observed, the mechanism appears to involve activation of hydrogen by a square-planar four-coordinate Ir(I) olefin complex. The DMA, DMF and DMSO solvent systems, which are very similar in terms of coordinating ability and dielectric constant, do show catalytic activity and this results from the dissociation of a phosphine molecule from the iridium at some stage to form the required four-coordinate catalyst 1: [series of chemical reactions] The sulfolane system is more active than the DMA, DMF and DMSO systems, but shows much more complicated kinetics. The hydrogenation appears to proceed in part via the phosphine dissociation path outlined in the above scheme, but the major pathway involves a cationic inters mediate Ir (CO) (PPh3)2 (olefin)+, 2, formed via chloride dissociation from the five-coordinate olefin complex. Diethylmaleate is hydrogenated in sulfolane, however, primarily via the phosphine dissociation path. Solvents that are too strongly coordinating (pyridine) or too weakly coordinating (nitromethane) lead to catalytically inactive systems. The catalytic homogeneous hydrogenation of hexene-1, cyclooctene using DMA solutions of [IrCl(C8H14)2]2 involves a monomeric species. The strongly coordinating solvent or the added olefin are thought to cleave the chloride bridge in [IrCl^gH^^J^* The hydrogenation mechanism can be outlined as [series of chemical reactions] where Ir is a complex already containing coordinated olefin. Selective hydrogenation of cyclooctene in a mixture of cyclooctene and hexene-1, the catalytic isomerization of hexene-2 and the catalytic hydrogenolysis of molecular 02 to water, all using [IrCl(C8H 14)2]2 complex in DMA are described and discussed. Molecular 0 is activated by DMA solutions of [IrCl2(C8H14)2]2 containing excess chloride; the major species believed to be present in solution is [IrCl2(C8H14)2]2⁻ . The solution initially absorbs one 02 per iridium. Product characterization proved to be difficult but the solutions catalytically oxidize cumene likely via a hydroperoxide free radical intermediate and the data are discussed in terms of the following equilibria: [series of chemical reactions] During some preliminary studies to investigate possible activation of CO under mild conditions using Ir complexes in aqueous solutions, the iridium(III) dicarbonyl [Ph4As]⁺ [Ir(C0)2C14]⁻•2H20, and a new cluster carbonyl tentatively formulated [Ir(CO)2]n, were synthesized. / Science, Faculty of / Chemistry, Department of / Graduate

The catalytic conversion of cyclohexanol to cyclohexanone using a combination of rhodium trichloride trihydrate and ferric chloride in the presence of molecular oxygen was investigated. No conversion to cyclohexanone occurred in the absence of rhodium trichloride trihydrate, but some degree of conversion was found in the absence of ferric chloride. The optimum conditions for catalytic oxidation were produced by using a combination of rhodium trichloride trihydrate and ferric chloride, and under these conditions the rate of conversion to the ketone declined steadily, until the mixture contained approximately U0% cyclohexanone. For a fixed amount of cyclohexanol and rhodium trichloride trihydrate it was found that there was an optimum amount of ferric chloride necessary to produce the maximum yield in the shortest possible time. Addition of ferric chloride in excess of this optimum amount tended to suppress the rate of conversion to the ketone. This can probably be explained by the additional production of water and cyclohexene (see below). Using a cyclohexanol/ferric chloride ratio in the optimum range at a given temperature, increasing the rhodium trichloride trihydrate concentration beyond a certain level did not significantly increase the final yield, or the reaction rate. The oxidation reaction occurred under acidic conditions, this acidity being the result of interaction between ferric chloride and cyclohexanol (and cyclohexanone) , The acidity of a typical system was found to decline rapidly as the reaction progressed. Cyclohexene was produced in a side reaction, together with water. This is presumably the result of cyclohexanol undergoing an elimination reaction under acidic conditions. Using the optimum cyclohexanol/ferric chloride ratio at 100deg, the the cyclohexene content remained at less than 10%, during the course of the reaction. Introduction of cyclohexene in amounts in excess of 20 % greatly suppressed the conversion to cyclohexanone, presumably due to strong complexation of the olefin with a rhodium species. water was produced during the catalytic oxidation in amounts greater than could be accounted for by production of cyclohexene. This additional water content of the reaction mixture in a closed system was in good agreement with that predicted on the basis of the equation: [ ] The presence of water in the reaction mixture tended to suppress the oxidation of cyclohexanol to cyclohexanone. Using the optimum ratio of components, very little conversion to the ketone occurred in the presence of oxygen, at temperatures below 50deg. Increasing the temperature from 100deg to 150deg increased the rate of oxidation but had little effect on the final yield of cyclohexanone. , Oxygen was found to be necessary for catalytic oxidation to occur. The measured oxygen absorption for a reaction mixture containing an optimum ratio of components, was found to be in good agreement with that predicted by the above equation. Using an optimum ratio of components in the presence of oxygen, the conversion to cyclohexanone was limited to approximately 40%. This limit was probably due to an interaction between cyclohexanone and some active rhodium species essential for catalytic activity. / Science, Faculty of / Chemistry, Department of / Graduate

The Fischer-Tropsch synthesis (FTS) process, better known for its ability to produce synthetic fuel via the hydrogenation of CO, has shown potential to produce valuable chemicals when ammonia is added to the feed. In this work certain aspects of the pathway to the formation of N-containing compounds that form when NH₃ is added during FTS, using mostly iron based catalysts is investigated. In addition, the effect this has on the FTS reaction itself is evaluated. To achieve this goal, both theoretical and experimental techniques are used in this study. The CO adsorption and dissociation reactions are assumed to be important elementary reactions for many proposed FTS pathways. In the theoretical part of this thesis, spin-polarized periodic density functional theory (DFT) calculations are employed to study aspects of the initial stage of the pathway on a model Fe(100) surface. Considering the formation of N-containing hydro- carbons, one would assume that NH₃ initially adsorbs and dissociates on the catalyst surface, which could take place in the presence of CO. The surface chemistry of these adsorbates is well studied both experimentally and theoretically, but their co-existence has not yet been evaluated on model Fe surfaces. Initially a platform is generated by calculating the individual potential energy surfaces (PES) for the decomposition of CO and NH₃ on Fe(100) at a coverage of ϴ = 0.25 ML. These calculations provided the basis for comparing the adsorption and dissoci- ation profiles of CO and NH₃ on the Fe(100) surface via the use of the same computational methodology, and importantly making use of the same exchange correlation functional (RPBE) for both adsorbates. Furthermore, it was desired to evaluate the kinetics and thermodynamics of the NH₃ decomposition on the Fe(100) surface at relevant temperatures and pressures (by combining the DFT results with statistical thermodynamics) to better understand the role of NHₓ surface species involved in the pathway to the formation of the N-containing compounds on a model catalyst surface. The DFT results that are reported for the individual decomposi- tion PES for CO and NH₃ were generally found to be in close agreement with what has been reported in previous DFT studies and deduced experimentally for the relevant adsorption and decomposition pathways. The resulting Gibbs free energies for the PES suggests that NH₂ may be kinetically trapped on the Fe(100) surface at a coverage of ϴ = 0.25 ML and the reaction conditions (T = 523 K and p*NH₃ = 0.2 bar) where NH₃ is co-fed with synthesis gas during FTS. The individual adsorptions of CO and NHₓ (with x = 3, 2, 1, 0) were compared to their coadsorbed states, by calculating the heat of mixing (ΔEmix) and the activation barriers (Eₐ) for CO dissociation in the presence and absence of the NHₓ surface species on the Fe(100) sur- face. Similar to the individual adsorption of NH₃, the 0 K regime inherent to DFT calculations is bridged by calculating the Gibbs free energy of mixing for CO + NH₃ on Fe(100) at higher temperatures. Both repulsive and attractive interaction energies were calculated for the various coadsorbed states (CO + NHₓ on Fe(100)) and similarly some configurations resulted in an energetically favored or unfavored heat of mixing. The activation barrier for CO dissociation was lowered when coadsorbed with NH₃ and NH₂, and raised when coadsorbed with NH and N. With all the coadsorbed structures the CO dissociation reaction became more endothermic. Previous experimental studies have shown a concomitant reduction in oxygenate selectivity with an increase in the selectivity for N-containing compounds, when NH₃ is added during FTS. It is well-known that oxygenates undergo secondary reactions when using iron-based catalysts in FTS. In addition, the catalyst used in aforementioned studies (precipitated Fe/K) are active for the amination reactions of oxygenates. It is therefore hypothesized that some oxygenates pro- duced via the primary FTS pathway are converted to N-containing compounds via a secondary reaction. The experimental part of this thesis is therefore aimed at testing this hypothesis. A base case study included a comparison between a Fe-catalyzed slurry phase FTS reaction and a FTS reaction with all parameters remaining unchanged, except for the addition of 1 vol % NH₃ to the syngas (CO + H₂) feed. The activity (CO and H₂ conversion) data collected did not reveal any appreciable loss in the rate of the FTS reaction when 1 vol % NH₃ was added and steady state was reached (, that is after 48 hours time on stream (TOS)). A slower carburization period was however observed when comparing the CO conversion during the first 24 hours TOS, and further supported by the slow increase in CO₂ selectivity during the same period. The use of two-dimensional gas chromatography (GC × GC-TOF/FID) allowed for the discovery of a formation of a range of secondary and tertiary amines, not reported in previous studies. The expected loss in oxygenate selectivity was observed and further probed by co-feeding 1-octanol with the feed (CO + 2H₂ + 1 vol % NH₃) via a saturator. These results clearly indicated a significant loss in oxygenate formation as a result of secondary conversion to N-containing compounds. Questions regarding the stability of aliphatic nitriles prompted the co-feeding of nonanitrile under similar conditions. The results obtained after co-feeding nonanitrile, sug- gests that nonanitrile is readily converted to secondary and tertiary amines and that the ratios of aliphatic alcohols and nitriles are close to equilibrium. The use of CO₂ as carbon source, the investigation of the product spectrum at higher space velocities and the use of Rh-based catalysts, when NH₃ is added during FTS were included in shorter studies. The combination of these results, adds to the knowledge pool for the case where NH₃ is present in the FTS regime, as a poison or reactant. Additional information regarding the path to the formation of N-containing compounds was obtained via the detailed analysis of the product spectra with two-dimensional gas chromatography and the subsequent co-feeding reactions. The results ob- tained via co-feeding reactions, can be used to devise strategies to increase the selectivity of the desired N-containing compounds.

The preferential oxidation of CO (CO-PROX) has been identified as one route of further reducing the trace amounts of CO (approx. 0.5 - 1 vol%) in the H2-rich reformate gas after the high- and low-temperature water-gas shift reactions. CO-PROX makes use of air to preferentially oxidise CO to CO₂, reducing the CO content to below 10 ppm while minimising the loss of H₂ to H₂O. In this study, a Co₃O₄/γ-Al₂O₃ model catalyst was investigated as a cheaper alternative to the widely used noble metal-based ones. The CO oxidation reaction in the absence of hydrogen has been reported to be crystallite size-dependent when using Co₃O₄ as the catalyst. However, studies looking at the effect of crystallite size during the CO-PROX reaction are very few. Metal-support interactions also play a significant role on the catalyst's performance. Strong metal-support interactions (SMSI) in Co₃O₄/Al2o₃ catalysts give rise to irreducible cobalt aluminate-like species. Under CO oxidation and CO-PROX reaction conditions, such strong interactions in a similar catalyst can have a negative effect on the performance of Co₃O₄ but can keep its chemical phase intact i.e., help prevent the reduction of the Co₃O₄ phase. The catalysts used to investigate these two effects (i.e., crystallite size and metal-support interactions) were synthesised using the reverse micelle technique from which nanoparticles with a narrow size distribution were obtained. Certain properties of the microemulsions prepared were altered to obtain five catalysts with varying Co₃O₄ crystallite sizes averaging between 3.0 and 15.0 nm. Four other catalysts with different metal-support interactions were also synthesised by altering the method for contacting the support with the cobalt precursor. The crystallite size of Co₃O₄ in these four catalysts was kept in the 3.0 - 5.0 nm size range.

Polymer electrolyte fuel cells have shown great potential in providing clean energy with no emissions. The kinetics of the cathode reaction, i.e. the oxygen reduction reaction (ORR) are sluggish necessitating high loadings of the catalyst metal, i.e. platinum. Platinum is a limited resource and expensive. Its price has been one of the major drawbacks in wide scale commercialisation of fuel cells. In an effort to improve the activity of the catalyst and therefore reduce Pt loadings on the catalyst, Pt can be alloyed with transition metal elements (e.g. Ni, Co and Fe) to form bimetallic catalysts. Alloying has been known to improve the activity and stability of a catalyst for the ORR. The enhanced activity of the alloys originates from the modified electronic structures of the Pt in these alloy catalysts which reduces the adsorption of spectator species therefore increasing the number of active sites for the ORR (Wang et al., 2012 (2)). The aim of this study was to gain a better understanding of the influence of Pt alloy particle size and active surface morphology on the ORR activity. The Pt alloy that was investigated was Pt₃Co/C. The surface morphology was modified by varying the Pt/Pt₃Co loading on a carbon support. The catalysts were prepared using thermally induced chemical deposition. The support used was Vulcan-XC-72R. The effects of varying the metal loadings on the ORR was investigated. The loadings that were investigated were 20, 40, 60 and 80 wt. % Pt and Pt₃Co. The alloy catalysts were subjected to annealing at 900 °C and acid leaching. The catalysts were analysed using electrochemical characterisation techniques such as cyclic voltammetry, CO stripping voltammetry, rotating disk electrode and rotating ring disk electrode. Physical characterisation of the catalysts was also implemented. The techniques used were x-ray diffraction, thermogravimetric analysis and transmission electron microscopy. The Pt particles on the carbon support were found not to agglomerate significantly despite the loading being increased. This trend was also observed for the Pt₃Co/C catalysts even after heat treatment and leaching. The lack of agglomeration was credited to a new reactor system developed in this work. The particle growth increased from low loadings to high loadings for both the Pt/C and Pt₃Co/C catalysts. Particle growth was more significant for the Pt₃Co/C catalysts at high loadings. At lower loadings (20 and 40 wt. %) the particle sizes between the Pt/C and Pt₃Co/C catalysts were comparable despite the Pt₃Co/C catalysts undergoing annealing and leaching. The mass specific activity of the Pt/C catalysts was not improved by alloying with the exception of the 20 wt. % catalyst which saw an enhancement factor of 1.66. The surface specific activity of the Pt/C catalysts was improved significantly with factors of 2.40 and 3.11 being recorded for the 20 and 80 wt. % Pt₃Co/C catalysts respectively. The enhancement factors of the intermediate loadings (40 and 60 wt. %) were lower and fairly similar at 1.30 and 1.35 respectively.

Thesis advisor: Jeffery A. Byers / Thesis advisor: Chia-Kuang Tsung / Host-guest chemistry provides a unique platform for catalysis by combining the specificity of homogeneous catalysts with the stability and recyclability of heterogeneous catalysts. Metal-Organic Frameworks (MOFs), such as UiO-66 are ideal hosts for host-guest catalysis. The vast porous network UiO-66 forms is chemically and thermally stable and the individual cages that make up the crystals can be modified by simple organic syntheses. The method developed in our group provides a mild, synthetically simple route for non-covalent organometallic guest encapsulation that decouples host synthesis from guest encapsulation. In this study, the so-called aperture opening encapsulation method is tested using an unstable class of iron-based carbon dioxide hydrogenation catalysts. The study results in launching an extensive investigation into the driving force behind aperture opening encapsulation with the goal of increasing guest loadings. Various methods to achieve this goal are explored including synthesizing novel UiO-66 linkers and taking advantage of factors such as columbic force. In conclusion, the information gained from a bigger picture examination of aperture opening encapsulation directly leads to guest loadings high enough to utilize useful characterization techniques. Accordingly, a standard protocol for characterization of iron catalysts encapsulated in UiO-66 is developed. / Thesis (MS) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Matthias M. Waegele / The properties of electrified interfaces, such as surface structure of metal catalyst, local pH, coverage of surface-adsorbed intermediates, interfacial electric field, and water structure, influence the activity and selectivity of electrocatalytic reactions. Because these interfacial properties often influence each other and undergo changes with applied potential, it is very challenging to identify the key characteristics of the interface that directly modulate electrocatalytic reactions. In this thesis, we demonstrate in-situ probing of electrochemical interfacial properties by employing surface-enhanced infrared (IR) absorption spectroscopy (SEIRAS) in conjunction with surface-adsorbed CO (COads) as a molecular probe of the Cu/aqueous electrolyte interface. This interface shows potential for the reduction of CO2 and CO to a wide variety of hydrocarbons. The CO and CO2 reduction reactions (CO/CO2RR) feature COads as an intermediate; therefore, this interface is conveniently probed by COads. In the first part if this thesis, we focus on investigating the dynamics of the surface morphology of the electrode during electrocatalysis. We found that the surface morphology of polycrystalline Cu undergoes reconstructions during CO/CO2RR. We determined that these reconstructions can be induced by COads and the local pH. As a result of the surface reconstructions, new specific surface sites form that can effect catalytic activity. For example, we detected an electrochemically inert COads population that appears as a result of reconstruction processes. Further, to form a rigorous connection between the product formation and the atomic-level surface morphology of rough polycrystalline Cu electrodes, we combined SEIRAS with differential electrochemical mass-spectrometry (DEMS). We established the potential-dependence of the line shape of the C≡O stretch band as an indicator of the atomic-level surface morphology. The last part of the thesis focuses on the determination of properties of the electrochemical double layer. Specifically, we elucidated the effects of cation identity on the electrochemical double layer. By evaluating the C≡O stretch frequency in the presence of alkali metal cations (Li+, K+, and Cs+), we determined that the promotion of the CO reduction reaction is associated with a cation-dependent interfacial field. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Proton exchange membrane fuel cell (PEMFC) has been reported as clean and efficient energy technology from conversion of H₂. However, one of the main challenges remains the storage and transport of hydrogen. The promising alternative is to produce H₂ on site by a reformer using a H₂-dense liquid as a fuel, a technology known as fuel processing. Methanol is an attractive source of H₂ compared to other fuels as it presents several advantages, i.e. it is obtained sulphur-free, has a high H to C ratio and therefore produces a H₂-rich reformate, can be reformed at low temperatures (200 - 300°C) and is a liquid at ambient conditions so that it can be easily handled. Typically, Cu-based catalysts are used for steam reforming of methanol due to their high activity (i.e. H₂ production) and high selectivity towards CO₂. As CO poisons anodic catalyst of PEMFC, high selectivity towards CO₂ is crucial so as to eliminate or at least minimize CO removal load downstream a fuel processor. However, Cubased catalysts are thermally unstable and suffer deactivation due to sintering at high temperatures (> 250°C). Moreover, Cu-based catalysts are pyrophoric and therefore difficult to handle. Recent studies show that PdZn catalysts are very promising as they exhibit comparable activity and selectivity to Cu-based ones. Furthermore, PdZn catalysts are thermally stable in the typically methanol steam reforming temperature range (200 - 300°C). Most literature attributes high CO₂ selectivity of PdZn catalysts to formation of PdZn alloy. It is generally agreed that PdZn alloy is formed when PdZn catalysts are reduced in H₂ at high temperatures (> 250°C). In this work, a Pd/ZnO catalyst aimed at 2.5 wt% Pd was successfully prepared via incipient wetness impregnation and the duplicate preparation of the catalyst was successful. Both impregnation catalysts were confirmed by ICP-OES to contain similar weight Pd loadings i.e. 2.8 and 2.7 wt%, respectively. The actual Pd loading (ICP-OES) was slightly higher than the target loading (2.5 wt%) due to Pd content of Pd salt underestimated during catalyst preparation. Furthermore, crystallite size distribution, i.e. PdO crystallites on ZnO support, was similar (i.e. 6.7 ± 2.4 nm and 6.3 ± 1.9 nm) for both impregnation catalysts.

The preferential oxidation (PROX) reaction is an effective process for the removal of trace amounts of carbon monoxide from a reformate stream. Tricobalt tetraoxide (Co₃O₄) is the candidate for CO-PROX in a H₂ rich gas and could be an alternative to the rare and expensive PGMs. This study investigates the effect of different Co₃O₄ morphologies in the preferential oxidation of carbon monoxide in H₂ rich gas. Reports have shown morphology dependency in CO oxidation in the absence of hydrogen, no study has investigated the morphology dependency in H₂ rich atmospheres. Different morphologies of nanocubes, nanosheets and nanobelts were prepared using hydrothermal mn and precipitation. Conventional spherical nanoparticles from our group were included to compare the activity of conventional nanoparticles with nanoparticles of different morphology. The model catalysts were supported on silica spheres which were also prepared. The CO-PROX experiments were conducted in the in situ UCT-developed magnetometer and PXRD capillary cell instruments by induced reduction at temperatures between 50 and 450°C. Catalyst tests showed two distinct temperature regions with maximum activity. In the range of 150 – 175ᵒC, activity decreased from nanoparticles > amine nanosheets > nanobelts. However, the surface area specific rate of CO₂ formation displayed an inverse trend. In the region of 225 – 250ᵒC, nanocubes > NaOH nanosheet > HCl nanocubes showed maximum activity. The surface area specific rate was the same for amine nanocubes and NaOH nanosheets. None of the model catalysts retained their morphology after the temperature was ramped from 50ᵒC to 450ᵒC, and back to 50ᵒC. The catalysts were partially reduced to metallic Coo (other phase being CoO). Figure 1: In situ PXRD analysis and kinetics of CH4, CO and CO₂ showing the behaviour of Co₃O₄/SiO₂ (amine nanocubes) under CO-PROX conditions

Supported nano-catalyst technologies are key for increasing the catalyst utilisation and achieving economically feasible platinum metal loadings in hydrogen polymer electrolyte fuel cells (PEFCs). High surface area carbons are commonly utilised as support materials for platinum due to low cost, large surface areas and high conductivity. However, PEFCs using this technology undergo oxidation of carbon supports, significantly reducing the lifetime of the fuel cell. In this work, silicon carbide and boron carbide are investigated as alternative catalyst support materials to carbon, for the oxygen reduction reaction for low temperature fuel cells. Electrochemical testing, accelerated degradation studies as well as advanced characterisation techniques were used to clarify the structure-property relationships between catalyst morphology, metal-support interaction, ORR activity and surface adsorption onto the Pt nanoparticles. Extended X-ray Absorption Fine Structure (EXAFS) analysis gave insights into the shape of the clustered nanoparticles while X-ray Photoelectron Spectroscopy (XPS) and in-situ X-ray Absorption Near-Edge Spectroscopy (XANES) analysis provided information into how the metal-support interaction influences surface adsorption of intermediate species. Electronic metal-support interactions between platinum and the carbide supports were observed which influenced the electrochemical characteristics of the catalyst, in some cases increasing the oxygen reduction reaction activity, hydrogen oxidation reaction activity and Pt stability on the surface of the support.