Reported herein is a brief summary of the history, properties, and applications of amine-boranes. The past methods devised for their preparation are described and the routes used to produce the compounds used in the work presented here are detailed. Building on prior synthetic approaches to amine-boranes, a new carbon dioxide mediated synthesis is presented. Proceeding through a monoacyloxyborane intermediate, the borane complexes of ammonia, primary, secondary, tertiary, and heteroaromatic amine are provided in 53-99% yields. Utilizing the amine-boranes obtained from the methods described, two divergent methods for direct amidation are introduced. The first uses amine-boranes as dual-purpose reagents, where the carboxylic acid is first activated by the borane moiety to form a triacyloxyborane-amine complex. This allows the delivery of the coordinated amine to form the amide products. A series of primary, secondary, and tertiary amides were prepared in 55-99% yields using this protocol, which displays a broad functional group tolerance. Extended from this dual-purpose methodology, a catalytic amidation is described. Utilizing ammonia-borane as a substoichiometric (10%) catalyst, a series of secondary and tertiary amide are prepared directly from carboxylic acids and amines in 59-99% yields, including amines containing typically borane reactive functionalities including alcohols, thiols, and alkenes. Amine-boranes are additionally used in two borylation methodologies. By reaction with <i>n</i>-butyl lithium, the amine-boranes are converted to the corresponding lithium aminoborohydrides, which upon reaction with a terminal alkyne provides the alkynyl borane-amine complexes in 65-98% yields. This process is compatible with both alkenes and internal alkynes, as well as a range of aprotic functionalities. A new strategy for aminoborane synthesis is also described and applied to the borylation of haloarenes. Activation of a series of amine-boranes with iodine produces the iodinated amine-borane, which undergoes dehydrohalogenation with an appropriate base to produce either monomeric or dimeric aminoboranes. Several aminoboranes were synthesized exclusively as the monomeric species, which due to their greater reactivity, were used directly in the synthesis of a series of aryl boronates in 65-99% yields.

<div>Thermochemical processing using fast-pyrolysis technology has been used to upgrade feedstocks like biomass and natural gas and more recently studied for plastic recycling. This work aims to improve the selectivity to desired products from a pyrolysis process through better catalysts and reactor design.</div><div>Fast-pyrolysis of biomass to fuels is considered a promising technology due to the higher yields to liquid fuel products. However, the process suffers from low carbon efficiency to hydrocarbon products due to carbon losses to biochar, accounting for 25-40 wt.% of the product stream depending on the biomass type. Using a combination of inorganic free-model compounds, biomass pretreatments and mass spectrometric analyses coupled with lab-scale reactor experiments, the char contribution from the lignocellulosic components (cellulose, hemicellulose, and lignin) and mineral content was investigated. The lignocellulosic components were found to follow the order: Lignin > Hemicellulose > Cellulose. Addition of inorganic salts (K, Na and Ca) to cellobiose, a model compound for cellulose, was found to catalyze additional dehydration reactions on primary pyrolysis products (e.g., levoglucosan) to yield secondary products (e.g., 5-HMF), and produce more char. This knowledge of char formation contributors can enable optimization of the bio-refining process sequencing using process system engineering tools and thus achieve higher carbon efficiency for biomass conversion.</div><div>While biomass has been viewed as a future energy source, there is a need for a transition fuel with the lowest possible greenhouse gas (GHG) footprint. Shale gas, consisting primarily of methane, is a potential candidate due to its large availability and high hydrogen to carbon ratio. Recently, single-atom catalysts have been studied as stable and non-coking catalysts for the non-oxidative coupling of methane (NOCM) to higher hydrocarbons (like ethylene). However, lack of post reaction catalyst characterization and rigorous kinetic testing have raised questions on the stability of these materials. This work combines homogenous (Chemkin simulations, gas phase kinetics) and heterogeneous reaction kinetic studies (reaction orders, steady state kinetics), coupled with microscopy (Scanning and Transmission Electron Microscopy (SEM, TEM)) and surface characterization tools (BET, TGA, Raman spectroscopy, CO-IR spectroscopy) to understand the role of the solid materials during NOCM. Post reaction catalyst characterization using transmission electron microscopy (TEM) analysis on the spent samples (CH4 treated at 975 deg C for 3 hours) reveals that the materials containing Pt single atoms (SA) and Pt nanoparticles (NP) are found to sinter to particles approximately 5-7 nm in size. Ethylene hydrogenation experiments, a kinetic probe for surface Pt, shows initial ethane formation rates that are four orders of magnitude lower on the isolated Pt+2 sites, found on Pt SAs, when compared to the rates obtained if all the surface Pt were assumed to be metallic. These results suggest that single atoms are not the active sites. However, under same reaction conditions (50 mL min-1 CH4 flow and 975 deg C), the ethylene formation rates (in mol h-1) on the solid materials are 2-7 times higher than the empty tube rates, indicating that the surface plays a role during NOCM. Addition of incremental amounts of the solid material increases methane conversion, extrapolating to the bare tube conversion at zero loading. This indicates that the solid materials improve the NOCM performance.</div><div>Experiments with pure methane feeds indicate that the solid materials are found to deactivate due to coking on the surface, evidenced by the coke buildup observed using thermogravimetric analysis (TGA) and the initial time-on-stream kinetic results showing rapid methane deactivation. Raman spectroscopy on the spent catalysts indicate at the development of a similar graphite-like surface intermediate under steady state conditions on all the materials. When compared under the same reaction conditions (975 deg C, 60 mL min-1 Pure CH4 with 10% UHP N2 feed, space velocity = 39.6 L h-1 gcat-1), these coked surfaces show a linear dependence for the ethylene formation rate (in mol h-1 gcat-1) with the spent surface area of the material (in m2 gcat-1). This observation is irrespective of the type of the material studied (alpha Al2O3, Davisil SiO2, 1 wt.% Pt/CeO2, Graphene, Graphite, etc.). In conclusion, these results prove that the spent surface area is critical for NOCM.</div><div>Similar experimental setup was used to study the dehydrogenation of methane, ethane, and propane mixture in the gas phase. Initial experiments at 1 bar pressure and reaction temperatures ranging from 650-850 deg C revealed that ethylene and hydrogen are the main gas phase products, with methane acting as a diluting agent under these reaction conditions. These results could enable direct processing of the shale gas without the use of a conventional ethane/propane separation step. These results were further studied by the system engineers using ANSYS ChemkinPro. For practical applications, these experiments were suggested to be performed at much higher operating pressures (~30 bar) and low residence time (~0.2 s), with a quick quenching step added after the reactor to prevent change in the exit stream compositions. A new reaction system was built to experimentally validate these recommendations.</div>

<p>The strong metal support interaction (SMSI) is among the best-known classes of metal-oxide interfacial interactions in heterogeneous catalysis, which is defined by the coverage of surface oxide on metal nanoparticles, forming a metal-oxide interface. However, there is limited insight in the atomic scale understanding of the structure of the SMSI oxide. In this work, surface science techniques including scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS) and low energy electron diffraction (LEED) were employed to investigate interfacial interactions in multiple catalytic systems, including ZnO-Pd, ZnO-Pt, and MoOx-Pt. To utilize the capabilities of the surface science techniques and to mimic a catalytic metal nanoparticle in SMSI state, ultrathin oxide films were prepared on metal single crystals as inverse model catalysts.</p> <p>The structural and chemical transformations of ultrathin zinc (hydroxy)oxide films on Pd(111) were studied under varying gas phase conditions (UHV, 5×10−7 mbar of O2 and D2/O2 mixture). Under oxidative conditions, zinc oxide forms partially hydroxylated bilayer islands on Pd(111). Sequential treatments of the submonolayer ZnOxHy films in D2/O2 mixture (1:4) at 550 K evoked structural transformations from bilayer to monolayer and to a PdZn near-surface alloy, in accompany with the reduction of Zn, demonstrating that zinc oxide as a non-reducible oxide, can spread on metal surface and show an SMSI-like behavior in the presence of hydrogen. A mixed canonical – grand canonical phase diagram revealed that the monolayer intermediate structure is a metastable structure formed during the kinetic transformation, and the near-surface alloys are stable under the D2/O2 conditions. Grand canonical phase diagram predicted that under real SMSI conditions zinc oxide films on Pd nanoparticles would be stabilized by hydroxylation with stoichiometries such as ZnOH and Zn2O3H3. Based on the experimental and theoretical observations, we propose that the mechanism of metal nanoparticle encapsulation involves both surface (hydroxy)oxide formation as well as alloy formation, depending on the environmental conditions.</p> <p>Hydroxylation plays a more important role in the ZnO/Pt(111) system. Different from Pd(111), zinc oxide tends to form monolayer graphite-like ZnO films on Pt(111) under oxidative conditions at submonolayer coverages. This structure is extremely susceptible to hydroxylation at room temperature, leading to spontaneous formation of honeycomb-like Zn6O5H5 films in hydrogen. The interaction of the two distinct structures with Pt were investigated by XPS, STM, and HREELS with CO, C2H4, and NO as probe molecules. Zn exhibits a partially reduced oxidation state in Zn6O5H5 and donates negative charge to surface Pt in the confined rings, leading to a switch from linear CO adsorption to bridged CO adsorption in accompany with a 50 cm-1 shift of ν(CO) towards lower frequencies. C2H4 readily forms ethylidyne (*CCH3) species at room temperature once adsorbed on Pt(111), while the formation of ethylidyne is weakened on the Zn6O5H5/Pt(111) surface. In summary, this study demonstrated a unique metal-hydroxide interaction, which serves as a novel approach for the modification of metal catalysts.</p> <p>The partial coverage of metal surfaces by oxides could be utilized to passivate specific sites of catalysts, improving the activity and stability. Herein, we studied the structure of surface Mo oxides on Pt(111) and Pt(544) using STM, XPS, and HREELS. At 0.08 ML coverage, Mo oxide tends to form 1~2 nm clusters and the majority of Mo is in +5 oxidation state. The Mo oxide clusters tend to aggregate near the monoatomic Pt steps, showing a higher local density compared to the wide terraces. Therefore, our results provide experimental evidence for the site-selective growth of Mo oxides at step sites, which could prevent the leaching of active component in catalysts under real reaction conditions.</p> <p>Overall, through atomic-level characterization of inverse model catalysts, we provided insights into the nature of metal-oxide interactions in multiple systems. The surface oxide films influence the property of metal surfaces in various ways, including migration, alloy formation, electronic perturbation, geometric confinement, and site-selective blocking. These findings emphasize the necessity of understanding the real structure of catalytic surfaces under different reaction conditions and shed light on rational design of oxide supported metal nanoparticle catalysts.</p>

<p dir="ltr">Since its inception, the field of heterogeneous catalysis has evolved to address the needs of the ever-growing human population. Necessity, after all, fosters innovation. Today, the world faces numerous challenges related to anthropogenic climate change, and that has necessitated, among other things, a search for new catalysts that can enable renewable energy conversion and storage, sustainable food and chemicals production, and a reduction in carbon emissions. This search has led to the emergence of many promising classes of materials, each having a unique set of catalytic properties. Among such candidate materials, high-entropy alloys (HEAs) have very recently shown the potential to be a new catalyst design paradigm. HEAs are multimetallic, disordered alloys containing more than four elements and, as a result, possess a higher configurational entropy, which gives them considerable stability. They have many conceivable benefits over conventional bimetallic alloy catalysts—greater site heterogeneity, larger design space, and higher stability, among others­. Consequently, there is a need to explore their application in a wide range of thermal and electrocatalytic reaction systems so that their potential can be realized.</p><p dir="ltr">In the past few decades, first principles-based approaches involving Density Functional Theory (DFT) calculations have proven to be effective in probing catalytic mechanisms at the atomic scale. Fundamental insights from first principles studies have also led to a detailed understanding of reactivity and stability trends for bimetallic alloy catalysts. However, the express application of first principles approaches to study HEA catalysts remains a challenge, due to the large computational cost incurred in performing DFT calculations for disordered alloys, which can be represented by millions of different configurations. A combination of first principles approaches and computationally efficient machine learning (ML) approaches can, however, potentially overcome this limitation.</p><p dir="ltr">In this thesis, combined workflows involving first principles and machine learning-based approaches are developed. To map catalyst structure to properties graph convolutional network (GCN) models are developed and trained on DFT-predicted target properties such as formation energies, surface energies, and adsorption energies. Further, the Monte Carlo dropout method is integrated into GCN models to provide uncertainty quantification, and these models are in turn used in active learning workflows that involve iterative model retraining to both improve model predictions and optimize the target property value. Dimensionality reduction methods, such as principal components analysis (PCA) and Diffusion Maps (DMaps), are used to glean physicochemical insights from the parameterization of the GCN.</p><p dir="ltr">These workflows are applied to the analysis of binary, ternary, and quaternary alloy catalysts, and a series of fundamental insights regarding their stability are elucidated. In particular, the origin and stability of “Pt skins” that form on Pt-based bimetallic alloys such as Pt₃Ni in the context of the oxygen reduction reaction (ORR) are investigated using a rigorous surface thermodynamic framework. The active learning workflow enables the study of Pt skin formation on stepped facets of Pt₃Ni (with a complex, low-symmetry geometry), and this analysis reveals a hitherto undiscovered relationship between surface coordination and surface segregation. In another study, an active learning workflow is used to identify the most stable bulk composition in the Pd-Pt-Sn ternary alloy system using a combination of exhaustively sampled binary alloy data and prudently sampled ternary alloy data. Lastly, a new GCN model architecture, called SlabGCN, is introduced to predict the sulfur poisoning characteristics of quaternary alloy catalysts, and to find an optimal sulfur tolerant composition.</p><p dir="ltr">On another front, the electrocatalytic activity of quinary HEAs towards the ORR is investigated by performing DFT calculations on HEA structures generated using the High-Entropy Alloy Toolbox (HEAT), an in-house code developed for the high-throughput generation and analysis of disordered alloy structures with stability constraints (such as Pt skin formation). DFT-predicted adsorption energies of key ORR intermediates are further deconvoluted into ligand, strain, and surface relaxation effects, and the influence of the number of Pt skins on these effects is expounded. A Sabatier volcano analysis is performed to calculate the ORR activities of selected HEA compositions, and correspondence between theoretical predictions and experimental results is established, to pave the way for rational design of HEA catalysts for oxygen reduction.</p><p dir="ltr">In summary, this thesis examines stability and reactivity trends of a multitude of alloy catalysts, from conventional bimetallic alloys to high-entropy alloys, using a combination of first principles approaches (involving Density Functional Theory calculations) and machine learning approaches comprising graph convolutional network models.</p>

<p dir="ltr">Vegetable oils are a fundamental part of human civilization. Beyond their nutritional value and functional implementation in food applications, their triglyceride structure facilitates their implementation as industrial inputs. Furthermore, applications such as metal gear fluids and gear oil represent a valuable market due to their environmental impact and widespread application. Soybean oil is one of the most produced oilseeds in the U.S., and recently, novel oil varieties such as high oleic soybean oil (HOSBO) tackle drawbacks in the use of vegetable oil such as the heterogeneous fatty acid composition by increasing the concentration of oleic acid. This dissertation evaluates the successful implementation of HOSBO and SBO as lubricant and gear oils through epoxy ring opening reactions for synthesizing polyols and estolides. Epoxidation of double bonds in unsaturated fatty acids creates reaction sites for the branching of fatty acids in estolides or hydroxylated moieties in the case of polyols. The difference in fatty acid composition is shown in terms of thermomechanical characteristics. HOSBO polyols and estolides are solid to semi-solid greases with high viscosities and SAE grades as gear oils from 85W up. In contrast, SBO-derived oils have lower viscosities and a larger viscosity index.</p><p dir="ltr">The second part of this research focuses on the kinetics of the hydroxylation defined by distinctive fatty acid compositions. The sites of reaction in the double bonds can be, in part, sterically hindered by the glycerol backbone. Thus, this chapter focuses on the influence of the reaction rates given the fatty acid composition of the oil. Consumption of epoxide groups in HOSBO and SBO was modeled under pseudo-first-order kinetics. The results highlight the benefit of using HOSBO with reaction rates at least 30% faster than SBO. Furthermore, the progress of the reaction was monitored by FTIR, which highlighted the formation of ether groups corresponding to the addition of 1-propanol branches. However, further optimization steps must focus on the controlled removal of water in order to prevent the esterification of the oil and the resulting increase of free fatty <a href="" target="_blank">acids</a><a href="#_msocom_1" target="_blank">[EAS1]</a> .</p><p dir="ltr"><a href="#_msoanchor_1" target="_blank">[EAS1]</a>Seems to end abruptly</p><p><br></p>

<div><div><div><p>Pincer ligands are a cornerstone of modern transition metal catalysis. An increasing interest in bimetallic catalysis motivated us to develop binucleating variants of these mononucleating ligands. Expanded variants of the PDI and PyBOX ligands were targeted, leading to the development of the Naphthyridine Diimine (“NDI”) and Naphthyridine Bisoxazoline (“NapBOX”) ligands, respectively. Metalation of NDI with appropriate metal precursors yielded Fe2, Co2 and Ni2 complexes which exhibited unique stoichiometric and catalytic reactivity. Metalation of the NapBOX ligand with nickel carboxylate salts yielded Ni2 complexes which were capable of catalyzing an asymmetric intermolecular [4+1] cycloaddition reaction between 1,1-dichloroalkene-derived vinylidenes and 1,3-dienes. Each of these processes were studied experimentally and computationally in order to understand the fundamental reactivity of organic substrates across metal-metal bonds.</p></div></div></div>

<p>Various organic reactions, including important synthetic reactions involving C–C, C–N, and C–O bond formation as well as reactions of biomolecules, are known to be accelerated when the reagents are present in confined volumes such as sprayed or levitated microdroplets or thin films. This phenomenon of reaction acceleration and the key role of interfaces played in it are of intrinsic interest and potentially of practical value as a simple, rapid method of performing small-scale synthesis. This dissertation has three focusing subtopics in the field of reaction acceleration: (1) application of reaction acceleration in levitated droplets and mass spectrometry to accelerate the reaction-analysis workflow of forced degradation of pharmaceuticals at small scale; (2) fundamental understanding of mechanisms of accelerated reactions at air/solution interfaces; (3) discovery the use of glass particles as a `green' heterogeneous catalysts in solutions and systematical study of solid(glass)/solution interfacial reaction acceleration as a superbase for synthesis and degradation using high-throughput screening.</p><p><br></p><p>Reaction acceleration in confined volumes could enhance analytical methods in industrial chemistry. Forced degradation is critical to probe the stabilities and chemical reactivities of therapeutics. Typically performed in bulk followed by LC-MS analysis, this traditional workflow of reaction/analysis sequence usually requires several days to form and measure desirable amount of degradants. I developed a new method to study chemical degradation in a shorter time frame in order to speed up both drug discovery and the drug development process. Using the Leidenfrost effect, I was able to study, over the course of seconds, degradation in levitated microdroplets over a metal dice. This two-minute reaction/analysis workflow allows major degradation pathways of both small molecules and therapeutic peptides to be studied. The reactions studied include deamidation, disulfide bond cleavage, ether cleavage, dehydration, hydrolysis, and oxidation. The method uses microdroplets as nano-reactors and only require a minimal amount of therapeutics per stress condition and the desirable amount of degradant can be readily generated in seconds by adjusting the droplet levitation time, which is highly advantageous both in the discovery and development phase. Built on my research, microdroplets can potentially be applied in therapeutics discovery and development to rapidly screen stability of therapeutics and to screen the effects of excipients in enhancing formulation stabilities.</p><p><br></p><p>My research also advanced the fundamental understanding of reaction acceleration by disentangles the factors controlling reaction rates in microdroplet reactions using constant-volume levitated droplets and Katritzky transamination as a model. The large surface-to-volume ratios of these systems results in a major contribution from reactions at the air/solution interface where reaction rates are increased. Systems with higher surface-active reactants are subject to greater acceleration, particularly at lower concentrations and higher surface-to-volume ratios. These results highlight the key role that air/solution air/solution interfaces play in Katritzky reaction acceleration. They are also consistent with the view that reaction increased rate constant is at least in part due to limited solvation of reagents at the interface.</p><p><br></p><p><br></p><p>While reaction acceleration at air/solution interfaces has been well known in microdroplets, reaction acceleration at solid/solution interfaces appears to be a new phenomenon. The Katritzky reaction in bulk solution at room temperature is accelerated significantly by the surface of a glass container compared to a plastic container. Remarkably, the reaction rate is increased by more than two orders of magnitude upon the addition of glass particles with the rate increasing linearly with increasing amounts of glass. A similar phenomenon is observed when glass particles are added to levitated droplets, where large acceleration factors are seen. Evidence shows that glass acts as a ‘green’ heterogeneous catalyst: it participates as a base in the deprotonation step and is recovered unchanged from the reaction mixture. </p><p><br></p><p>Subsequent to this study, we have systematically explored the solid/solution interfacial acceleration phenomena using our latest generation of a high-throughput screening system which is capable of screening thousands of organic reactions in a single day. Using desorption electrospray ionization mass spectrometry (DESI-MS) for automated analysis, we have found that glass promotes not only organic reactions without organic catalysts but also reactions of biomolecules without enzymes. Such reactions include Knoevenagel condensation, imine formation, elimination of hydrogen halide, ester hydrolysis and/or transesterification of acetylcholine and phospholipids, as well as oxidation of glutathione. Glass has been used as a general `green' and powerful heterogeneous catalyst.</p>

<p dir="ltr">Zeolites are microporous crystalline aluminosilicates that are widely used as catalysts for upgrading hydrocarbons and oxygenates to higher value chemicals and fuels. The substitution of tetrahedral Si⁴⁺ with Al³⁺ in a charge-neutral silica framework ([SiO_4/2]) generates anionic centers ([AlO_4/2]^-), which charge-compensate Brønsted acid protons (H⁺) that serve as active sites for catalysis. Brønsted acid sites in aluminosilicates of diverse topologies have similar acid strength, but can be located within varying intracrystalline (or internal) microporous environments (0.4‒2 nm diameter) or at extracrystalline (or external) surfaces and mesoporous environments (>2 nm diameter); yet, catalytic diversity exists, <i>even</i> for a fixed zeolite framework topology, because micropores impose constraints on molecular access to and from intracrystalline active sites and provide van der Waals contacts that influence the stabilities of reactive intermediates and transition states. Tailoring the material properties of a given zeolite framework for targeted catalytic applications requires strategies to design both the bulk crystallite properties (e.g., morphology, active site density) that influence intracrystalline diffusion and the secondary environments that surround active sites and influence intrinsic kinetics, and further necessitates molecular-level insights to elucidate the influences of bulk and active site properties on catalysis. In this work, we provide synthetic and post-synthetic strategies to respectively tune active site environments within varying micropore voids and at external surfaces of zeolites, and develop gas-phase toluene methylation and liquid-phase mesitylene benzylation as probe reactions to quantify the catalytic consequences of active site environments on aromatic alkylation catalysis.</p><p dir="ltr">The MFI framework (orthorhombic phase) consists of 12 crystallographic distinct tetrahedral-sites and 26 unique framework oxygen atoms located around channels (~0.55 nm diameter) or channel intersections (~0.70 nm diameter). The synthesis of MFI zeolites using the conventional tetra-<i>n</i>-propylammonium (TPA⁺) organic structure directing agent (OSDA) is known to place framework Al and their attendant H⁺ sites within the larger intersection environments, because electrostatic interactions are favorable between such locations of [AlO_4/2]^- and the quaternary N⁺ center in TPA⁺ that becomes positioned rigidly within channel intersections during crystallization. The methylation of toluene by dimethyl ether (DME; 403 K) on MFI-TPA zeolites of fixed active site densities (~2 Al per unit cell) result in <i>ortho</i>-xylene (<i>o</i>-X; ~65%) as the major product over <i>para</i>-xylene (<i>p</i>-X; ~27%) and <i>meta</i>-xylene (<i>m</i>-X; ~8%). In contrast, toluene methylation on MFI zeolites (~2 Al per unit cell) synthesized using non-conventional OSDAs, such as ethylenediamine (EDA) or 1,4-diazabicyclo[2.2.2]octane (DABCO), predominantly forms <i>p</i>-X (~75%) over <i>o</i>-X (~23%) and <i>m</i>-X (~2%). Within the subsets of MFI-TPA and MFI-EDA/DABCO zeolites, measured xylene formation rates and isomer selectivities are independent of crystallite sizes (0.1‒13 µm), toluene conversions (0.02‒2.0%) and external H⁺ content (up to 9% external H⁺ per total Al), indicating negligible effects of diffusion-enhanced secondary xylene isomerization reactions at intracrystalline or extracrystalline domains. The invariance of xylene isomer selectivity with reactant pressures (0.2‒9 kPa toluene, 25‒66 kPa DME) or methylating agent (1‒4 kPa methanol) indicate that differences in reactivity of toluene to form each xylene isomer reflects differences in the stabilities of their respective kinetically relevant transition states that share the same reactive intermediate. Measured xylene isomer formation rate constants and rate constant ratios, obtained from mechanism-derived rate expressions and interpreted using transition state theory formalisms, are used alongside density functional theory (DFT) calculations to reveal that intersection void environments (~0.70 nm diameter) similarly stabilize all three xylene transition states over unconfined surfaces (>2 nm diameter) without altering the established aromatic substitution patterns, while channel void environments (~0.55 nm diameter) preferentially destabilize bulkier <i>o</i>-X and <i>m</i>-X transition states thereby resulting in high intrinsic <i>p</i>-X selectivity. DFT calculations reveal that the ability of protonated DABCO complexes to reorient within MFI intersections and participate in additional hydrogen-bonding interactions with anionic Al centers during synthesis, facilitates the placement of Al in smaller channel environments that are less favored by TPA⁺. These molecular-level details, enabled by combining synthesis, characterization, kinetics and DFT, establish a mechanistic link between OSDA structure, active site placement and transition state stability, and provide active site design strategies orthogonal to crystallite design approaches that rely on complex reaction-diffusion phenomena.</p><p dir="ltr">For various reactions including toluene methylation at higher reaction temperatures (573‒773 K) and toluene conversions (>10%), extracrystalline H⁺ sites in MFI zeolites are reported to influence reactivity, selectivity, and deactivation behavior during catalysis in undesired ways. Post-synthetic chemical treatments to passivate external H⁺ sites on MFI zeolites result in unintended (but not always undesirable) changes to bulk structural properties and Al and H⁺ contents. The number of extracrystalline H⁺ sites is difficult to quantify using conventional spectroscopic or titrimetric methods, especially when present in dilute amounts on samples whose surfaces have been passivated. The systematic treatment of MFI zeolites (2.4, 5.7 and 7.1 Al per unit cell) using ammonium hexafluorosilicate (AHFS) at varying treatment duration times, AHFS concentrations and number of successive treatments resulted in MFI zeolites that retain their bulk structural properties and total Al and H⁺ contents, except for one parent MFI sample containing a significant amount of non-framework Al species. The benzylation of mesitylene by dibenzyl ether (363 K) occurs exclusively at external H⁺ sites because the bulky 1,3,5-trimethyl-2-benzylbenzene product is sterically prevented from forming at intracrystalline H⁺ sites. The intrinsic zero-order rate constant (per external H⁺) for mesitylene benzylation is extracted from rate measurements (per total Al) on a suite of untreated MFI samples with known amounts of external H⁺ sites (1‒15% external H⁺ per total Al) quantified using bulky 2,6-di-<i>tert</i>-butylpyridine base titrants. Measured zero-order rate constants on AHFS-treated MFI zeolites are used to quantify the extent to which AHFS treatments passivate external H⁺ sites, revealing efficacies that depend on the specific treatment conditions and the parent sample used. The developed kinetic methods demonstrate the utility of catalytic probes, when compared to stoichiometric probes based on spectroscopic or titration methods, in amplifying and quantifying dilute concentrations of external H⁺ sites on zeolites. The methods enable comparisons of the efficacy of various post-synthetic passivation strategies and permit rigorous assessments of the influence of external H⁺ during acid catalysis.</p><p dir="ltr">Overall, this work provides (post-)synthetic strategies to tune active site environments within intracrystalline micropores or at extracrystalline surfaces and develops quantitative kinetic probes that enable a molecular-level understanding of catalytic consequences of active site environments on aromatic alkylation reactions. Taken together, the methodology and findings of this study have broader implications in zeolite catalyst design for selectively upgrading traditional fossil feedstocks (crude oil and shale gas) and emerging feedstocks (biomass and waste plastics).</p>

<p dir="ltr">Insights from research into the natural photosynthetic processes are applied to inform the rational design of inorganic catalysts. The study of these synthetic systems – artificial photosynthesis – will lead towards the development of a device able to absorb light, convert and store the energy in the form of chemical bonds. The water-splitting reaction, a bottleneck of the photosynthetic process, is a key barrier to overcome in this endeavor. Thus, the focused study of water-oxidation catalysts able to facilitate this difficult reaction is performed, in order to develop a green-energy solution in the form of an artificial photosynthesis system.</p>

<p dir="ltr">Directed hydrogenation, in which product geometric selectivity is dictated by the binding of an ancillary directing group on the substrate to the catalyst, is typically achieved by homogeneous Rh and Ir complexes. No heterogeneous catalyst has been able to achieve equivalently high directivity due to a lack of control over substrate binding orientation at the catalyst surface. In this work, we demonstrate through structure-activity studies that careful control of surface ensemble geometry in bimetallic nanoparticle catalysts can confer hydroxyl-directed selectivity in heterogeneous double bond hydrogenation. We postulate that the oxophilic alloy component binds hydroxyl groups to pre-orient the molecule on the surface, while proximal noble metal atoms impart facially selective addition of hydride to the olefin. We found that controlling the degree of surface alloying between oxophilic and noble metal component as well as alloy component identity is critical to maximizing reaction selectivity and starting material conversion. Our optimized catalysts exhibit good functional group tolerance on a variety of cyclohexenol and cyclopentenol scaffolds, with Pd-Cu and Pt-Ni systems being developed for the diastereoselective hydrogenation of tri- and more challenging tetra-substituted olefins, respectively. The applicability of this method is then demonstrated in a four-step synthesis of a fine fragrance compound, (1<i>R</i>,2<i>S</i>)-(+)-<i>cis</i>-methyldihydrojasmonate (Paradisone®), with high yield and enantiopurity.</p>