<div>Biomass-derived fuels have long been considered as a possible replacement for traditional liquid fuels derived from petroleum. However, biomass as a feedstock requires significant refinement prior to application as a liquid fuel. The H2Bioil process has previously been proposed in which biomass is pyrolyzed and the resulting vapors are passed over a catalyst bed for upgrading to hydrocarbon products in a hydrogen environment [1]. A PtMo catalyst has been developed for the complete hydrodeoxygenation (HDO) of biomass pyrolysis vapors to hydrocarbons [2]. However, the product hydrocarbons contain a large fraction of molecules smaller than C4 which would not be suitable as liquid fuels. In fast hydropyrolysis of poplar followed by hydrodeoxygenation over a PtMo/MWCNT catalyst at 25 bar H2 and 300oC, only 32.1% of carbon is captured in C4 – C8 products; 21.7% of carbon is captured in C1 – C3 hydrocarbons [2]. Here, approaches are examined to increase selectivity of H2Bioil to desired products. Aldol condensation catalysts could be used prior to the HDO catalyst in order to increase the carbon number of products. These products would then be hydrodeoxygenated to hydrocarbons of greater average carbon number than with an HDO catalyst alone. Application of a 2% Cu/TiO2 catalyst to a classic aldehyde model compound, butanal, shows high selectivity towards aldol condensation products at low H2 pressures. In more complex systems which more closely resemble biomass pyrolysis vapors, this catalyst also shows significant yields to aldol condensation products, but substantial carbon losses presumed to be due to coke formation are observed. Both glycolaldehyde, a significant product of biomass pyrolysis, and cellulose, a component polymer of biomass, have been pyrolyzed and passed through aldol condensation followed by hydrodeoxygenation in a pulsed fixed-bed microreactor. Glycolaldehyde aldol condensation resulted in the formation of products in the C2-C¬9 range, while the major aldol condensation products observed from cellulose were C7 and C8 products. Carbon losses in glycolaldehyde aldol condensation were reduced under operation at increased hydrogen partial pressures, supporting the hypothesis that increasing selectivity to hydrogenation products can reduce coke formation from primary aldol condensation products. </div><div>The use of feeds which have undergone genetic modification and/or pretreatment by other catalytic processes may also lead to improvements in overall product selectivity. The influence of genetic modifications to poplar lignin on the pyrolysis plus HDO process are investigated, and it is found that these materials have no effect on the final product distribution. The product distribution from a poplar sample which has had lignin catalytically removed is also examined, with the conclusion that the product distribution strongly resembles that of cellulose, however the lignin-removed sample shows high selectivity towards char which is not seen from cellulose. </div><div><br></div>

<div>As shale gas exploitation has been developed, production of shale gas in the US has rapidly increased during the last decade. This has motivated the development of techniques to covert shale gas components (mainly C₁ to C₃) to liquid fuels by catalytic conversion. The main goal of the dissertation is to study the geometric and electronic structures of the metal catalysts, which are crucial for understanding the structure-property relationship.</div><div><br></div><div><div>The fi?rst project studies bimetallic Pt-Bi catalyst for non-oxidative coupling of methane. In a recent publication published in ACS catalysis, Pt-Bi/ZSM-5 catalyst</div><div>has been shown to stably convert methane into C2 for 8 hours under non-oxidative conditions. In this thesis, structure of the Pt-Bi/ZSM-5 was shown with HAADF</div><div>imaging, synchrotron XAS and XRD. A new surface cubic Pt₃Bi phase on Pt nanoparticles with Pt-Bi bond distance of 2.80 A was formed. Formation of noble metal intermetallic alloys such as Pt₃M may be the clue for non-oxidative conversion of methane.</div></div><div><br></div><div><div>The second and third project highlight strong metal-support interaction catalysts for propane dehydrogenation. Chemisorption showed partial coverage of the SMSI oxides</div><div>on the surface of the nanoparticles. In situ X-ray absorption near edge (XANES), resonant inelastic X-ray scattering (RIXS), X-ray photoelectron spectroscopy (XPS)</div><div>have shown that little electronic effect on the metal nanoparticles. The catalyst activity per mol of metal decreased due to the partial coverage of the SMSI oxides on the surface of the catalysts. The catalysts, however, had higher selectivity due to smaller ensembles inhibiting hydrogenolysis.</div></div><div><br></div><div><div>In the fourth project Pt-P catalyst was investigated to understand the promoting effect of P.Pt-P catalysts had much higher selectivity for propane dehydrogenation</div><div>(>95%). These give two types of catalysts, a PtP₂-rich surface on Pt core and full PtP₂ ordered structure, which were con?rmed by scanning transmission electron microscopy (STEM), and in situ methods of EXAFS, synchrotron XRD, XPS, and Resonant Inelastic X-ray Spectroscopy (RIXS). The PtP₂ structure has isolated Pt</div><div>atoms separated by P₂atoms. In addition XANES, XPS and RIXS indicate a strong electronic modi?cation in the energy of the valence orbitals.</div></div><div><br></div><div><div>It can be concluded from the Pt-Bi catalyst that intermetallic alloys might be selective for NOCM. Therefore, promoters with higher reduction temperature, such as Mn and Cr, should be used to have stable catalysts at high temperature. Moreover, both Pt-Bi and Pt/CeO₂suggest that selective catalysts for propane dehydrogenation and NOCM may have some correlation. Further studies would be conducted to understand the correlation between the two reactions.</div></div>

<p></p><p>Biomass and shale gas have been proposed as alternate sources of liquid hydrocarbon fuels. Traditional petroleum refining, however, is not capable of directly converting either the highly oxygenated molecular structure of lignocellulosic biomass or the low molecular weight alkanes of shale gas into liquid fuels. In this work, we investigate two processes to generate fuels by upgrading low molecular weight species present in biomass pyrolysis vapors and in shale gas via carbon-carbon coupling reactions of low molecular weight species present in biomass pyrolysis vapors and shale gas. </p> <p>In the first process, fast pyrolysis and hydrodeoxygenation are used to convert woody biomass into hydrocarbons. However, 22% of the carbon in this process forms C₁-C₃ species which are unsuitable for use as liquid fuels. Aldol condensation has been proposed as a means of leveraging carbonyl groups present in the pyrolysis product distribution prior to hydrodeoxygenation in order to couple low molecular weight species such as glycolaldehyde to transform the C₁-C₃ fraction into C₄₊ species. We demonstrate that aldol condensation of fast pyrolysis vapors results in a large (10%) reduction in carbon yield to C₆ species and only a small (5%) reduction in carbon yield to C₁-C₃ species to form C₇₊ products, suggesting that higher molecular weight species undergo significant reaction over the aldol condensation catalyst. We demonstrate a pathway by which levoglucosan can be converted into levoglucosenone, which then forms C₇₊ species through self-aldol condensation and condensation with light oxygenates. </p> <p>In the second process, light olefins in shale gas, consisting primarily of ethane and propane, are dehydrogenated and oligomerized into higher molecular weight species. Ni cation sites exchanged onto microporous materials catalyze ethene oligomerization to butenes and heavier oligomers, but also undergo rapid deactivation. The use of mesoporous supports has been reported in the literature to alleviate deactivation in regimes of high ethene pressures and low temperatures that cause capillary condensation of ethene within mesoporous voids. Here, we reproduce prior literature findings on mesoporous Ni-MCM-41 and report that, in sharp contrast, reaction conditions that nominally correspond to ethene capillary condensation in microporous Ni-Beta or Ni-FAU zeolites do not mitigate deactivation, likely because confinement within microporous voids restricts the formation of condensed phases of ethene <a>that are effective at solvating and desorbing heavier intermediates that are precursors to deactivation</a>. Deactivation rates are found to transition from a first-order to a second-order dependence on Ni site density in Ni-FAU zeolites with increasing ethene pressure, suggesting a transition in the dominant deactivation mechanism involving a single Ni site to one involving two Ni sites, reminiscent of the effects of increasing H₂ pressure on changing the kinetic order of deactivation in our prior work on Ni-Beta zeolites.</p><br><p></p>

<p> Propylene oxide (PO), is a key intermediate in the production of value-added products, such as polyurethanes and propylene glycol. Current industrially practiced methods of propylene epoxidation, including hydrochlorination, epoxidation by organic peroxides, and the Hydrogen Peroxide to Propylene Oxide (HPPO) process either produce PO unselectively, necessitating energy intensive separation processes, produce environmentally damaging byproducts, or require several sequential reaction vessels. A potential solution for these issues exists in the form of a single-step, highly selective gas phase reaction to produce PO. Industrial adoption of a process utilizing this technology has not occurred due to the failure of state-of-the-art Au/TS-1 catalysts, consisting of gold supported on titanium MFI, to meet economic targets for hydrogen use efficiency, selectivity to PO, and PO rate-permass, improvement on all of which has been hindered by a lack of understanding of how Au-TS-1 catalysts fundamentally operate. Therefore, the goal of this work has been to understand the active site requirements and reaction kinetics with the aim of lowering barriers to commercialization of this more environmentally benign process. Once we had developed a general understanding of product inhibition, we applied this knowledge to the kinetics of propylene epoxidation over Au/TS-1 catalysts. We measured gas phase kinetics in a continuous stirred tank reactor (CSTR) free from temperature and concentration gradients. Apparent reaction orders measured at 473 K for H2, O2, and propylene for a series of Au-DP/TS-1 with varied Au and Ti contents were consistent with those reported previously. Co-feeding propylene oxide enabled measurement of the apparent reaction order in propylene oxide and the determination that relevant pressures of propylene oxide reversibly inhibit propylene epoxidation over Au-DP/TS-1, while co-feeding carbon dioxide and water had no effect on the propylene epoxidation rate. The measured reaction orders for propylene epoxidation, after corrected to account for propylene oxide inhibition, are consistent with a ‘simultaneous’ mechanism requiring two distinct, but adjacent, types of sites. H2 oxidation rates are not inhibited by propylene oxide, implying that the sites required for hydrogen oxidation are distinct from those required for propylene epoxidation. 26 We then shifted focus to elucidate structural details of gold active sites and their interaction with Ti active sites. To determine whether the roles of extracrystalline and intracrystalline gold nanoparticles supported on titanosilicate-1 on direct propylene epoxidation are intrinsically different, the kinetics of direct propylene epoxidation were measured in a gas-phase continuous stirred tank reactor (CSTR) over PVP-coated gold nanoparticles (Au-PVP/TS-1) deposited on TS-1 supports. The PVP-coated gold nanoparticles were too large to fit into the micropores of TS-1, even after ligands were removed in situ by a series of pretreatments, as confirmed by both TEM and TGA-DSC. The activation energy and reaction orders for H2, O2, propylene, propylene oxide, carbon dioxide, and water for propylene epoxidation measured on Au-PVP/TS-1 catalysts were consistent with those reported for Au/TS-1 prepared via deposition-precipitation (Au-DP/TS-1). However, while the reaction orders for hydrogen oxidation on Au-PVP/TS-1 were similar to those measured on AuDP/TS-1, a decrease in activation energy from approximately 30 kJ mol−1 for Au-DP/TS-1 to 4-5 kJ mol−1 for Au-PVP/TS-1 suggests there is a change in mechanism, rate-limiting step, and/or active site for hydrogen oxidation. Additionally, an active site model was developed which determines the number of Ti within an interaction range of the perimeter of extracrystalline Au nanoparticles (i.e., the number of Au-Ti active site pairs). Turnover frequencies estimated for this active site model for a dataset containing both Au-DP/TS-1 and Au-PVP/TS-1 were ∼20x higher than any previous report ( 80 s−1 vs. 1-5 s−1 at 473 K) for catalytic oxidation on noble metals, suggesting that the simultaneous mechanism occurring over proximal Au-Ti sites alone is incapable of explaining the observed rate of propylene epoxidation and that short-range migration of hydrogen peroxide is necessary to account for the catalytic rate. The agreement of reaction orders, activation energy, and active site model for propylene epoxidation on both Au-DP/TS-1 and Au-PVP/TS-1 suggests a common mechanism for propylene epoxidation on both catalysts containing small intraporous gold clusters and catalysts with exclusively larger extracrystalline nanoparticles. Rates of hydrogen oxidation were found to vary proportionally to the amount of surface gold atoms. This is also consistent with the hypothesis that the observed decrease in hydrogen efficiency and PO site-time-yield per gold mass with increasing gold loading are driven primarily by the gold dispersion in Au/TS-1 catalysts. </p>

<p>Producing bio-based commodity chemicals, such as polymers and fuels, is of significant interest as petroleum reserves continue to decline. A major roadblock to bio-based production is high processing costs. These costs are associated with the need for highly-specialized catalysts to produce bio-based commodity chemicals from agricultural products and wastes. This prevents bioprocessing facilities from fully taking advantage of commodities of scale, where purchasing materials in greater quantities reduces the material cost. Discovering catalysts capable of being used in multiple production pathways could reduce the per unit processing of a biorefinery. <br> Recent works have shown that maleic acid can be used for multiple conversion reactions of plant material to valuable products: xylose to furfural, glucose to hydroxymethylfurfural (HMF), and the pretreatment of lignocellulosic material for second generation biofuel production. This work evaluates the use of maleic acid as a catalyst for producing HMF from corn starch, with a specific focus on reducing operating costs. Additionally, the use of maleic acid as a liquefaction catalyst for producing corn stover slurries is tested. </p> <p>To evaluate HMF production from starch, a combined computational and experimental approach is used. Through modelling and experimental validation, molar HMF yields of ~30% are reached by incorporating dilute dimethylsulfoxide and acetonitrile into the reaction mixture. However, HMF yield was limited by low stability in the reaction media. The addition of activated carbon to the reactor overcomes challenges with second order side reactions, resulting in HMF selling prices that are competitive with similar petroleum-derived chemicals. The key technical roadblocks to commercialization of HMF production are identified as solvent recycling and HMF separation efficiency in a sensitivity analysis. During liquefaction of corn stover, maleic acid was found to reduce the yield stress required to begin slurry flow through a pipe. However, a reduction in the free water content of the reactor through binding of water in the matrix of biomass limited liquefaction, resulting in solids concentrations not financially feasible at scale. To overcome this, maleic acid treatment was performed at solids contents of 25%, followed by a water removal step and enzymatic liquefaction at 30% solids. Yield stress was reduced from >6000 Pa for untreated samples to ~50 Pa for samples treated with maleic acid and enzymes sequentially. Such treatment reduces the challenges associated with feeding solid biomass into a pretreatment reactor. Additionally, reduced slurry yield stress results in lower capital costs, since smaller pumps can be used in the production facility. </p> This work provides a step forward in transitioning away from a petroleum-based economy to a bio-based economy without significant disruptions in product pricing and availability.

<p>In recent decades, alternatives to traditional coal and fossil fuels were utilized to reduce carbon emissions. Among these alternatives, natural gas is a cleaner fuel and is abundant globally. Shale gas, a form of natural gas that also contains light alkanes (C2-C4), is presently being employed to produce olefins, which can be upgraded to higher molecular weight hydrocarbons. This thesis describes efforts to develop new catalytic materials and characterizations for the conversion of shale gas to fuels.</p> <p>In the first half, silica supported Pt-Cr alloys containing varying compositions of Pt and Pt₃Cr were used for propane dehydrogenation at 550°C. Although a change in selective performance was observed on catalysts with varying promoter compositions, the average nano-particle structures determined by <i>in situ</i>, synchrotron x-ray absorption spectroscopy (XAS) and x-ray diffraction (XRD) were identical. Further, this work presents a method for the characterization of the catalytic surface by these methods to understand its relationship with olefin selectivity. From this, we can gain an atomically precise control of new alloys compositions with tunable surface structures.</p> <p>Once formed by dehydrogenation, the intermediate olefins are converted to fuel-range hydrocarbons. In the second half, previously unknown single site, main group Zn²⁺ and Ga³⁺ catalysts are shown to be effective for oligomerization and the resulting products follow a Schutlz Flory distribution. Mechanistic studies suggest these catalysts form metal hydride and metal alkyl reaction intermediates and are active for olefin insertion and b-H elimination elementary steps, typical for the homogeneous, Cossee-Arlman oligomerization mechanism. Evidence of metal hydride and metal alkyl species were observed by XAS, Fourier transform infrared spectroscopy (FTIR), and H₂/D₂ isotope exchange. Understanding the reaction intermediates and elementary steps is critical for identifying novel oligomerization catalysts with tunable product selectivity for targeted applications. </p> <p> Through controlled synthesis and atomic level <i>in situ </i>characterizations, new catalysts compositions can be developed with high control over the resulting performance. An atomically precise control of the catalyst structure and understanding how it evolves under reaction conditions can help shed light on the fundamental principles required for rational catalyst design. </p>

<div><div><div><p>Lewis acid zeolites contain framework metal heteroatoms that catalyze sugar iso- merization reactions at different turnover rates depending on the local coordination around metal centers and the polarity of their confining secondary environments. Post-synthetic modification routes that react metal precursors with framework va- cancy defects in dealuminated Beta zeolites (Sn-Beta-PS-OH) are developed as an alternative synthetic strategy to the hydrothermal crystallization of Sn-Beta zeolites (Sn-Beta-HT-F). Post-synthetic routes provide the ability to systematically tailor the structural features of active and defect sites in Sn-zeolites, especially in composition ranges inaccessible to materials crystallized by hydrothermal routes (Si/Sn < 100; > 2 wt.% Sn), yet often result in incomplete or unselective Sn grafting within framework vacancy defects and form extraframework metal oxide domains and residual defect sites. The development of robust post-synthetic routes to prepare Sn-zeolites with intended active and defect structures has been limited by the dearth of characteri- zation techniques to unambiguously detect and quantify such structures present in stannosilicate materials, and of mechanistic links between such structures and the turnover rates of catalytic reactions.</p><p><br></p><p>The presence of framework Sn centers that can expand its coordination shell from four- to six-coordinate structures, and small extraframework tin oxide domains that cannot, were unambiguously detected from diffuse reflectance UV-Visible spectra of stannosilicate materials measured after dehydration treatments (523 K, 0.5 h) to discern ligand-to-metal charge transfer bands for tetrahedrally-coordinated Sn heteroatoms (< 220 nm, > 4.1 eV) and those for tin oxide domains (> 230 nm, < 4.1 eV). Liquid-phase grafting of stannic chloride in dichloromethane reflux (333 K) enables preparing Sn-Beta zeolites with higher framework Sn content (Si/Sn = 30– 144; 1.4–6.1 wt.% Sn) than grafting performed in isopropanol reflux (423 K, Si/Sn > 120; 1.6 wt.% Sn). This reflects competitive adsorption of isopropanol solvents with stannic chloride at framework vacancy defects during grafting procedures, consistent with infrared spectroscopy (IR) and temperature-programmed desorption (TPD) of dealuminated Beta samples after saturation with isopropanol at reflux temperatures (423 K), and not any limitations inherent to the structure of vacancy defects within dealuminated zeolite supports that would prevent reaction with metal precursors as often proposed.</p><p><br></p></div></div></div><div><div><div><p>This insight enabled preparing Sn-Beta zeolites with varying densities of residual defects, via dichloromethane-assisted grafting of stannic chloride to different extents, into dealuminated Beta supports of different initial Al content (Si/Al = 19–180) and mineralizing agent used for hydrothermal crystallization of the parent Al-Beta sam- ple (e.g., fluoride or hydroxide). Preparation of low-defect Sn-Beta zeolites using post-synthetic routes (Sn-Beta-PS-F) first required the synthesis of parent Al-Beta zeolites in fluoride media to minimize residual siloxy defects (OSi−) formed during crystallization, and dilute Al content (Si/Al > 100, < 0.6 Al (unit cell)−1), to min- imize the density of intrapore silanol groups formed after dealumination and high temperature oxidative treatment. The methanol packing density within microporous voids of Sn-Beta zeolites was assessed from relative volumetric uptakes at the point of micropore filling from single-component methanol (293 K) and nitrogen (77 K) adsorption isotherms, and decreased systematically among samples with increasing density of silanol groups. The total density of silanol groups within micropores and at external crystallite surface in Sn-Beta zeolites was quantified by H/D isotopic ex- change during temperature-programmed surface reactions (500–873 K), and within microporous voids from IR spectra measured after saturation of microporous binding sites with CD3CN (2275 cm−1, 303 K). In situ IR spectra collected at low methanol pressures (P/P0 < 0.2, 303 K) provide further evidence that methanol molecules ar- range in localized clusters within Sn-Beta-PS-F, but form extended hydrogen-bonded networks within Sn-Beta-PS-OH.</p><p><br></p></div></div></div><div><div><div><p>Glucose-fructose isomerization rate constants (373 K) were used to probe the lo- cal coordination of Sn heteroatoms and the polarity of the secondary environment as influenced by silanol defects within microporous cavities. Ex situ pyridine titration of Sn-Beta-HT-F samples suppressed isomerization rates (per total Sn, 373 K) after only a subset of Sn sites were poisoned, which correspond to the number of open Sn sites quantified ex situ via CD3CN IR (303 K), providing further evidence that open Sn sites are dominant active sites for glucose isomerization. First-order isomerization rate constants (373 K) decrease with increasing Sn content when normalized by total Sn density, and are invariant when normalized by the number of open Sn sites, be- cause open Sn sites are grafted preferentially within Sn-Beta-PS-OH (Si/Sn = 30–144; 1.4–6.1 wt.% Sn) at low Sn densities. Isomerization rate constants (per open Sn, 373 K), however, are lower by ∼4x and ∼15x on Sn-Beta-PS-F (Si/Sn = 284; 0.7 wt.% Sn) and Sn-Beta-PS-OH, respectively, than on Sn-Beta-HT-F. Open Sn sites catalyze aqueous-phase glucose isomerization at higher turnover rates (373 K) when their mi- croporous surroundings contain silanol defects present in low (hydrophobic) densities than high (hydrophilic) densities, which are characteristic of Sn-Beta-HT-F and Sn- Beta-PS-OH samples, respectively. This reflects reorganization of extended water networks, which are stabilized in high-defect, hydrophilic micropore environments, at kinetically relevant 1,2-hydride shift transition states that incurs entropic penal- ties that lower turnover rates. This thesis highlights the development of synthesis- structure-function relationships to guide the preparation of catalytic materials with intended active and defect site structures within confining reaction environments, the development of characterization techniques for the identification and quantification of such structures, and the influence of such structures on turnover rates of liquid-phase sugar isomerization.</p></div></div></div>

Brønsted and Lewis acid sites located within microporous solids catalyze a variety of chemical transformations of oxygenates and hydrocarbons. Such reactions occur in condensed phases in envisioned biomass and shale gas upgrading routes, motivating deeper fundamental understanding of the reactivity-determining interactions among active sites, reactants, and solvents. The crystalline structures of zeolites, which consist of SiO₄ tetrahedra with isomorphously-substituted M⁴⁺ (e.g., Sn⁴⁺, Ti⁴⁺) as Lewis acid sites, or Al³⁺ with charge-compensating extraframework H⁺ as Brønsted acid sites, provide a reasonably well-defined platform to study these interactions within confining voids of molecular dimension. In this work, gas-phase probe reactions that afford independent control of solvent coverages are developed and used to interpret measured rate data in terms of rate and equilibrium constants for elementary steps, which reflect the structure and stability of kinetically relevant transition states and reactive intermediates. The foundational role of quantitative kinetic information enables building molecular insights into the mechanistic and active site requirements of catalytic reactions, when combined with complementary tools including synthetic approaches to prepare active sites and surrounding environments of diverse and intended structure, quantitative methods to characterize and titrate active sites and functional groups in confining environments, and theoretical modeling of putative active site structures and plausible reaction coordinates.<br><div><br></div><div>Bimolecular ethanol dehydration to diethyl ether was developed as a gas-phase catalytic probe reaction for Lewis acid zeolites. A detailed mechanistic understanding of the identities of reactive intermediates and transition states on Sn-Beta zeolites was constructed by combining experimental kinetic measurements with density functional theory treatments. Microkinetic modeling demonstrated that Sn active site configurations undergo equilibrated interconversion during catalysis (404 K, 0.5–35 kPa C₂H₅OH, 0.1–50 kPa H₂O) from hydrolyzed-open configurations ((HO)-Sn-(OSi≡)₃---HO-Si) to predominantly closed configurations (Sn-(OSi≡)₄), and identified the most abundant productive (ethanol-ethanol dimer) and inhibitory (ethanol-water dimer) reactive intermediates and kinetically relevant transition state (S_N2 at closed sites). Mechanism-based interpretations of bimolecular ethanol dehydration turnover rates (per Lewis acidic Sn, quantified by CD₃CN IR) enabled measuring chemically significant differences between samples synthesized to contain high or low densities of residual Si-OH defects (quantified by CD₃CN IR) within microporous environments that confine Sn active sites. Hydrogen-bonding interactions with Si-OH groups located in the vicinity of Sn active sites in high-defect Sn-Beta zeolites stabilize both reactive and inhibitory intermediates, leading to differences in reactivity within polar and non-polar micropores that reflect solely the different coverages of intermediates at active sites. The ability of confining microporous voids to discriminate among reactive intermediates and transition states on the basis of polarity thus provides a strategy to mitigate inhibition by water and to influence turnover rates by designing secondary environments of different polarity via synthetic and post-synthetic techniques. </div><div><br></div><div>Despite the expectation from theory that Sn active sites adopt the same closed configurations after high-temperature (823 K) oxidation treatments, distinct Sn sites can be experimentally identified and quantified by the ν(C≡N) infrared peaks of coordinated CD₃CN molecules, and a subset of these sites are correlated with first-order rate constants of aqueous-phase glucose-fructose isomerization (373 K). In contrast, <i>in situ</i> titration of active sites by pyridine during gas-phase ethanol dehydration catalysis (404 K) on a suite of Sn-zeolites of different topology (Beta, MFI, BEC) quantified the dominant active site to correspond to a different subset of Sn sites than those dominant in glucose-fructose isomerization. An extensive series of synthetic and post-synthetic routes to prepare Sn-zeolites containing Sn sites hosted within diverse local coordination environments identified a subset of Sn sites located in defective environments such as grain boundaries, which are more pronounced in Beta crystallites comprised of intergrowths of two polymorphs than in zeolite frameworks with un-faulted crystal structures. Sn sites in such environments adopt defect-open configurations ((HO)-Sn-(OSi≡)₃) with proximal Si-OH groups that do not permit condensation to closed configurations, which resolves debated spectroscopic assignments to hydrolyzed-open site configurations. Defect-open Sn sites are dominant in glucose-fructose isomerization because their proximal Si-OH groups stabilize kinetically relevant hydride shift transition states, while closed framework Sn sites are dominant in alcohol dehydration because they stabilize S_N2 transition states via Sn site opening in the kinetically relevant step and re-closing as part of the catalytic cycle. The structural diversity of real zeolite materials, whose defects distinguish them from idealized crystal structures and allows hosting Lewis acid sites with distinct local configurations, endows them with the ability to effectively catalyze a broad range of oxygenate reactions.</div><div><br></div><div>During aqueous-phase catalysis, high extra-crystalline water chemical potentials lead to intra-pore stabilization of H₂O molecules, clusters, and extended hydrogen-bonded networks that interact with adsorbed intermediates and transition states at Lewis acid sites. Glucose-fructose isomerization turnover rates (373 K, per defect-open Sn, quantified by CD₃CN IR) are higher when Sn sites are confined within low-defect, non-polar zeolite frameworks that effectively prevent extended water networks from forming; however, increasing exposure to hot (373 K) liquid water generates Si-OH groups via hydrolysis of siloxane bridges and leads to lower turnover rates commensurate with those of high-defect, polar frameworks. Detailed kinetic, spectroscopic, and theoretical studies of polar and non-polar titanosilicate zeolite analogs indicate that extended water networks entropically destabilize glucose-fructose isomerization transition states relative to their bound precursors, rather than influence the competitive adsorption of water and glucose at active sites. Infrared spectra support the stabilization of extended hydrogen-bonded water networks by Si-OH defects located within Si- and Ti-Beta zeolites, consistent with ab initio molecular dynamics simulations that predict formation of distinct thermodynamically stable clustered and extended water phases within Beta zeolites depending on the external water chemical potential and the nature of their chemical functionality (closed vs. hydrolyzed-open Lewis acid site, or silanol nest defect). The structure of water confined within microporous solids is determined by the type and density of intracrystalline polar binding sites, leading to higher reactivity in aqueous media when hydrogen-bonded networks are excluded from hydrophobic micropores.</div><div><br></div><div>Aluminosilicate zeolites adsorb water to form (H₃O⁺)(H₂O)_n clusters that mediate liquid-phase Brønsted acid catalysis, but their relative contributions to the solvation of reactive intermediates and transition states remain unclear. Bimolecular ethanol dehydration turnover rates (per H⁺, quantified by NH₃ temperature-programmed desorption and <i>in situ</i> titrations with 2,6-di-<i>tert</i>-butylpyridine) and transmission infrared spectra measured on Brønsted acid zeolites under conditions approaching intrapore H₂O condensation (373 K, 0.02–75 kPa H₂O) reveal the formation of clustered, solvated (C₂H₅OH)(H⁺)(H₂O)_n intermediates, which are stabilized to greater extents than bimolecular dehydration transition states by extended hydrogen-bonded water networks. Turnover rates deviate sharply below those predicted by kinetic regimes in the absence of extended condensed water networks because non-ideal thermodynamic formalisms are required to account for the different solvation of transition states and MARI. The condensation of liquid-like phases within micropores that stabilize reaction intermediates and transition states to different extents is a general phenomenon for Brønsted acid-catalyzed alcohol dehydration within zeolites of different topology (CHA, AEI, TON, FAU), which governs the initial formation and structure of clustered hydronium-reactant and water-protonated transition state complexes. Systematic control of liquid-phase structures within confined spaces by gas-phase measurements around the point of intrapore condensation enables more detailed mechanistic and structural insights than those afforded by either kinetic measurements in the liquid phase, or structural characterizations of aqueous systems in the absence of reactants.</div>

<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>