Zeolites serve as essential catalytic platforms for many industrial processes, including emerging ethanol-to-olefins (ETO) upgrading technologies. Although metal-loaded (Cu, Zn, Y) dealuminated beta (deAlBeta) zeolite powders are promising catalysts for direct ETO conversion with high selectivity to butene-rich C3+ olefins necessary for production of sustainable aviation fuels (SAF), development of these materials as shaped technical bodies through the incorporation of binders is required for scale-up and commercial viability. Here, we report the ethanol upgrading performance of Cu-Zn-Y/deAlBeta extruded catalysts formulated with either alumina or kaolin clay binders. Both extrudates exhibit high ethanol dehydration reactivity which competes with the initial ethanol dehydrogenation step in the direct ETO reaction network. Consequently, elevated selectivity to dehydration side products (ethylene, diethyl ether) at ∼100% ethanol conversion is observed on Cu-Zn-Y/deAlBeta extrudates compared to the powder catalyst, which inhibits production of desired C3+ olefins. Utilizing microscopy and spectroscopic characterizations, we attribute this to Al migration from binder to zeolite particles within the extrudates, thus re-aluminating the zeolite and generating Brønsted acid sites active for dehydration reactions. This work elucidates the effects of binder incorporation on ETO product distributions and emphasizes that binder selection must be carefully considered during design of extruded zeolite catalysts.

Copper and rare earth element-containing dealuminated Beta zeolites (CuREE/deAlBeta) are promising catalysts for the conversion of ethanol to C3+ olefins en route to sustainable aviation fuel. Product selectivities over CuREE/deAlBeta depend on the identity of the REE. Here, a suite of La/deAlBeta catalysts of varied La loading are prepared, and their reactivities, selectivities, and apparent C-C coupling kinetics in the cascade reaction between ethanol and acetaldehyde are reported. Ex situ and in situ titrations to quantify Lewis acidic La sites quantify distinct numbers of sites, suggesting a distribution of site types. Across a series of REE/deAlBeta catalysts (REE = Y, La, Lu, Yb, Gd), the selectivity to secondary products correlates with the pyridine heats of adsorption at REE Lewis acid sites. The turnover frequency (per Lewis acid site) for C-C coupling was similar across the series of REE/deAlBeta catalysts. Y/deAlBeta and La/deAlBeta, which have the most disparate secondary product selectivities, had similar kinetics for C-C coupling. These findings demonstrate the complexity of quantifying active sites in REE/deAlBeta zeolites, and the sensitivity of the selectivity, but not the reactivity for C-C coupling, to the identity of the REE atom in REE/deAlBeta zeolites.

Glycerol is a sustainable carbon source that can serve as a feedstock for functionalized molecules with desirable properties for a range of applications. Previous work has established the oxidation of glycerol-derived diether secondary alcohols (e.g., 1,3-dimethoxy-propan-2-ol) to symmetric glycerol-derived diether ketones (e.g., 1,3-dimethoxy-propan-2-one) via Swern oxidation and aqueous-phase oxidative dehydrogenation. Here, we report the acetalization of symmetric ketones with 1,2-propanediol to produce acetals, which are useful as green solvents and fuel additives. Metallosilicate catalysts (M = Zr, Hf, and Ga) were synthesized via a fast and simple one-pot method such that metal atoms were incorporated into a porous silica matrix (M-xerogels) as dispersed Lewis acid sites. The Lewis and Br & oslash;nsted acid site densities of these materials were quantified at multiple M loadings via pyridine chemisorption and transmission infrared spectroscopy. Per Lewis acid site time yields (STYs) for acetalization of 1,2-propanediol with 3-pentanone, used as a model acetalization reaction, were highest for Ga-xerogel and lowest for Hf-xerogel. Apparent activation energies for this model reaction are reported over representative Zr-, Hf-, and Ga-xerogels, and apparent reaction orders are reported over Ga-xerogels. The impact of solvent identity, equilibrium limitations, and water concentration on STY over the Ga-xerogel are reported and demonstrate that in addition to the thermodynamic impacts of water on acetalization, water also inhibits the kinetics of acetalization. Acetalization of 1,3-dimethoxy-propan-2-one with 1,2-propanediol is reported over Ga-xerogel (tert-butanol solvent, T = 313-343 K, autogenous pressure), resulting in the formation of 2,2-bis(methoxymethyl)-4-methyl-1,3-dioxolane. The reusabilities of the catalysts are reported, demonstrating deleterious effects of intermediate washing with acetone and similar impacts of either intermediate washing with tert-butanol or intermediate calcination prior to reuse. These findings provide insight toward the formation of functionalized (and tunable) glycerol-derived acetals over amorphous solid Lewis acid catalysts.

Direct conversion of bioethanol to C3+ olefins is a promising pathway for sustainable aviation fuel (SAF) production, but catalyst deactivation limits long-term operation. The stability and deactivation mechanisms of multifunctional Cu–Y/Beta zeolite catalysts were investigated for ethanol-to-olefins conversion over 300 h time-on-stream in the presence of H2. Catalytic testing reveals progressive losses in ethanol conversion and C3+ olefin selectivity accompanied by increased acetaldehyde formation. The catalyst testing studies correlate with a suite of characterizations of fresh, spent, and regenerated catalysts to identify the deactivation factors. The loss of Y Lewis acid sites is the primary deactivation element. Reversible acid site deactivation is caused by coke deposition, which blocks Y-derived Lewis acid sites responsible for aldol condensation, MPV reduction, and alcohol dehydration. Minor irreversible deactivation is observed and possibly results from hydrothermal dehydroxylation of Y–silanol interactions. This causes permanent loss of Lewis acidity without zeolite framework degradation or Y aggregation. Cu sites undergo limited agglomeration into small nanoparticles but contribute insignificantly to catalyst deactivation under the investigated time frame. Oxidative regeneration removes coke and redistributes Cu sites, leading to full recovery of the initial catalytic performance though the Y Lewis acid sites are unable to fully recover. These findings establish Lewis acid site degradation as the primary deactivation mechanism impacting long-term catalyst stability.

The catalytic dehydrogenation of ammonia borane (AB) to H2 in solution is an appealing route for H2 release since the reaction can release three equivalents of H2 at moderate reaction temperatures. The role the solvent plays in the reaction kinetics, and the solvent properties that contribute to catalytic activity are examined in this work on supported ruthenium nanoparticles. Supported ruthenium nanoparticles were dispersed on γ-Al2O3 using incipient wetness impregnation and characterized using X-ray diffraction, inductive coupled plasma optical emission spectroscopy, infrared spectroscopy, and transmission electron microscopy. Reaction kinetics were measured in a well-characterized semi-batch reactor with constant inert headspace flow. The measured H2 release rates were highest in water, followed by methanol solvent producing the second highest H2 release rate. 1-propanol, 2- propanol, and 1-butanol solvent resulted in substantially lower rates of H2 release whereas rates in aprotic solvents were near background levels. Post-reaction 11B NMR spectra from reaction in protic solvents revealed the presence of dehydrogenated boron species, indicating that the dehydrogenation of the BH3 portion of AB and the deprotonation of the solvent were likely steps in AB dehydrogenation, consistent with observation of HD in the effluent of AB reactions in deuterated solvents. Derived rate constants from regressions of rate data to a Langmuir Hinshelwood mechanism in the zero-order and first-order kinetic regimes correlated with the deprotonation enthalpy of the solvent and kinetic diameter. Trends with solvent deprotonation enthalpy were contradictory to measured reaction rates and the rate-determining step. However, trends with kinetic diameter were found to more accurately describe differences in measured rates. Apparent pre-exponential factors were inversely correlated with both entropy loss for adsorption and solvent kinetic diameter, suggesting either that transition state formation is less entropically favorable for large solvents, or that large solvents occupy more surface sites than smaller solvents, reducing the number of available sites for reaction. This study demonstrates that the solvent identity affects the release of H2 from AB by influencing the AB adsorption equilibrium, that subsequent release of H2 from AB is faster in small protic solvents, and that methanol and water are the most effective solvents for AB solvolysis.

Depolymerization is a key pathway in the transition to polymer circularity. By breaking down polymers into their original (or new) building blocks to create new products, the polymer "cycle" can be closed. However, polyvinyl chloride (PVC), a ubiquitous thermoplastic, has been largely absent from research in depolymerization, although it has some unique advantages compared to other commodity vinyl polymers. Here, we present methods for depolymerizing PVC via ozonolysis, a well-established and practiced method for the oxidative cleavage of alkenes. By intentionally introducing sequences of conjugated C═C bonds to produce dehydrochlorinated PVC (DHPVC), the sites are introduced into the polymer backbone that are readily cleaved by ozone (O3). Subsequently, an oxidative workup with conc. H2O2 results in terminal carboxylic acids. These methods resulted in molecular weight reductions on the order of 5-8 (i.e., ∼12%-20% of the initial value), depending on the source PVC used. A key achievement was the generation of a liquid/waxy "ultra-low-molecular-weight" PVC product, which has been previously unreported. Our methods successfully minimize waste while creating new and potentially valuable products. The depolymerization products formed from PVC could serve as plasticizers or feedstocks for additional chemical transformations.

Inclusion of boron in growth mixtures for aluminosilicate Beta zeolites has been used previously as a strategy to vary zeolite crystallite sizes, yet prior reports describe limited compositional regimes of silicon-to-aluminum and silicon-to-boron molar ratios in which the Beta topology will crystallize. This study demonstrates that manipulation of growth mixture compositions can enable crystallization of Beta zeolites across a broader range of silicon-to-aluminum and silicon-to-boron molar ratios in boron-and aluminum-containing Beta zeolites (B-AlBeta) than previously reported. B-Al-Beta samples are characterized by X-ray diffraction, solid-state 11B magic angle spinning nuclear magnetic resonance (MAS NMR), nitrogen physisorption, elemental analysis, scanning electron microscopy, and ammonia temperature programmed desorption (TPD). Silicon-to-aluminum molar ratios in the crystallized B-Al-Beta solids were directly proportional to those present in growth mixtures, reflecting more equal extents of Si and Al incorporation than is typical when aluminosilicate Beta is synthesized in hydroxide media. Beta crystallite sizes were found to increase with increasing B content at constant Si/Al ratio. Ammonia TPD protocols developed previously to selectively quantify protons at Al-O-Si linkages, but not at B-OSi linkages, in B-Al-MFI zeolites were demonstrated here to also do so for B-Al-Beta zeolites. These synthesis and characterization protocols enable synthesis of Beta zeolites with constant silicon-to-aluminum ratios but varied crystallite sizes, achieved via variation in the silicon-to-boron molar ratio, and selective quantification of the Br & oslash;nsted acid sites associated with Al centers in the framework.

Solid-acid-catalyzed etherification of glycerol with ethanol produces glycerol-derived ethers that are promising as chemical building blocks and low-volatility solvents for CO2 capture and biomass fractionation. Because water is formed as a coproduct, catalysts with lower void polarity may improve performance by reducing the impact of intraporous water. Here, we examined how zeolite framework topology and void polarity influence glycerol etherification. To do so, we synthesized H-Beta zeolites with varied Si/Al in hydroxide (H-Beta-OH) or fluoride (H-Beta-F) media and combined water adsorption, concentration–time measurements, reuse tests, initial-rate measurements, water inhibition experiments, and kinetic analysis under kinetic control. Lower integrated ν(OH) region area and water uptake indicated fewer intraporous silanol defects and lower void polarity in the fluoride-synthesized samples, consistent with reduced void polarity. Concentration-time profiles showed that monoethyl ethers were the primary products, whereas higher ethers formed sequentially at longer turnover numbers. Experiments starting from 1,3-diethoxypropan-2-ol confirmed a reversible reaction network, and the same first-order model captured trends for reactions initiated from either glycerol or this di-ether. Reusability tests showed partial deactivation, but most activity was recovered after calcination, and H-Beta-F retained a higher rate after reuse than H-Beta-OH. Initial-rate measurements and transport analysis confirmed intrinsic kinetic control. Across H-form zeolites, H-Beta showed the highest turnover frequency, followed by H-MFI, H-FAU, and H-MOR. Within the H-Beta series, turnover frequencies were largely insensitive to acid-site density but increased with decreasing water uptake. Water inhibition experiments showed rate suppression in the order H-Beta-OH-13 > H-Beta-F-20 > H-Beta-F-96, linking lower void polarity to weaker water inhibition. Comparative kinetic analysis showed similar glycerol reaction orders but larger first-order apparent rate constants and lower activation energies for H-Beta-F than for H-Beta-OH. Apparent entropies of activation were less favorable for more hydrophobic samples, indicating that rate enhancements arose primarily from enthalpic rather than entropic effects. These results identify void polarity as a design parameter for zeolite-catalyzed glycerol etherification.

The oxidation of propane was investigated over iron phthalocyanine (FePC) catalysts, which share structural motifs with heme enzymes as well as iron nitrogen-doped carbon (Fe-N-C) materials. Propylene formation occurs via a cascade pathway including hydroxylation and dehydration, with negligible combustion. Fe-N-C shows a higher gravimetric rate of propylene formation, while FeCl16PC@FAU is more stable, suggesting that Fe centers in Fe-N-C evolve during reaction in agreement with operando XAS results. Apparent reaction orders were less than unity with respect to both C3H8 and N2O over Fe-N-C, FeCl16PC/FAU, and FeCl16PC@FAU, while apparent water reaction orders were negative over Fe-N-C and FeCl16PC/FAU. These apparent reaction orders are consistent with an Eley-Rideal reaction mechanism. Apparent activation energies were similar over Fe-N-C, FeCl16PC/FAU, and FeCl16PC@FAU (similar to 110 kJ mol(-1)) and were consistent with DFT-calculated free energy barriers. Similar trends in predicted coverages of most abundant surface intermediate (MASI) species and degree of rate control with increasing partial pressure of propane are observed between FeCl16PC/FAU and Fe-N-C. At low propane partial pressures (<1 kPa) the predicted MASI is adsorbed oxygen and the rate determining step is C-H activation, while at higher propane partial pressures (>3 kPa) the MASI is adsorbed propanol and the rate-determining step is propanol desorption. However, this model suggests that N2O decomposition, C-H activation, and propanol desorption are all kinetically relevant elementary steps over both Fe-N-C and FeCl16PC/FAU. These findings validate FePC as a representative model of Fe-N-C for propane oxidation, and provide valuable kinetic insights for future alkane oxidation studies over Fe and other M-N-4 materials.

Rare-earth element (REE) incorporation into dealuminated zeolites has been shown to catalyze a variety of selective oxygenate transformations, including ethanol to olefins, yet the structure and function of REE-incorporated Lewis acid zeotypes remain unclear. In this study, we proposed five yttrium acid site configurations and evaluated each against experimental physicochemical characterization techniques including X-ray absorption spectroscopy and pyridine Fourier transformed infrared spectroscopy (FTIR). Our analysis identified three fundamental site motifs, defect-open, dehydrated defect-open, and geminal hydroxyl, stabilized by adjacent silanol defects and hydroxyl groups that agreed with spectroscopic characterization. By comparing ethanol dehydration kinetics, we identified that interconvertible defect-open and dehydrated defect-open sites are kinetically relevant for catalytic turnovers. The three yttrium open site structural motifs from Y/deAlBeta were extended to 14 other REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) to explore trends in Lewis acid strength, assessed via pyridine adsorption energies and supported by experimentally measured pyridine FTIR. A linear correlation between Lewis acid strength and highest occupied molecular orbital + lowest unoccupied molecular orbital energies was established, offering a predictive framework for understanding structure-function relationships in REEs incorporated into dealuminated Beta zeotypes. These findings provide molecular-level insight into REE incorporation and its role in tuning Lewis acid strength for the selective catalytic transformation of biomass-derived oxygenates into chemicals and liquid fuels.

Increasing data availability is paramount to efforts to validate computational models of heterogeneous catalysts. In the course of experimental heterogeneous catalysis research, one large dataset that is often underreported are reaction rates collected over long times on stream during experiments designed to measure apparent kinetic parameters (e.g., apparent activation energies and apparent reaction orders). These data can allow comparisons of deactivation rates across classes of catalysts, which could be useful to largescale models of catalyst restructuring or carbon deposition. Beyond gradual decreases (or increases) in rates or selectivities with time on stream, these data can also include unique transients immediately following step changes from one operating condition to the next. These transients can go unreported entirely and could reveal information about reaction mechanisms that could validate (or invalidate) kinetic models of a given chemistry. In this contribution, we report examples of long time-on-stream data from three distinct classes of reactions: cascade reaction of ethanol and acetaldehyde over Lewis acidic zeolites, oxidative coupling of methanol and dimethylamine over Au-based bimetallic catalysts, and methane oxychlorination over supported palladium catalysts. We discuss possible origins for the various types of transients encountered in the course of collection of apparent kinetic parameters in these chemistries, with all of these data made available in tabulated format. Lastly, we provide an example for the data reduction from an example data set to parameters and figures that would typically be reported in a manuscript regarding reaction kinetics, as a demonstration of what information can go unreported during typical data processing.

Ruthenium catalysts are promising for the catalytic release of H2 from ammonia borane (AB). The reaction kinetics and the role of the support in the release of H2 from AB in methanol solvent were studied using a series of Ru nanoparticle catalysts on various supports (SiO2, carbon, gamma-Al2O3, and TiO2). Catalysts were synthesized using incipient wetness impregnation and solution deposition (SD) methods and characterized using N2 physisorption, X-ray diffraction, inductively coupled plasma-optical emission spectroscopy, CO diffuse reflectance infrared Fourier transform spectroscopy, and transmission electron microscopy. The reaction kinetics were examined by measuring initial rates using a semi-batch reactor with a constant flow through the headspace analyzed by online mass spectrometry. The Ru/TiO2-SD and Ru/C catalysts had the highest measured initial rates compared to the Ru/SiO2 and Ru/Al2O3. Measured apparent activation energies were relatively similar between all catalysts. Regression of initial rates as a function of AB concentration was done for two different rate equations derived from two different proposed mechanisms for AB methanolysis. Both mechanisms were able to sufficiently describe trends in H2 formation rate versus concentration at low AB concentrations. However, determination of which of the two proposed mechanisms best captures the trends in the data trends was inconclusive due to the lack of a statistically significant difference between degree-of-fit of the two models. Stability tests showed that Ru/C was less prone to deactivation over repeated use compared to Ru supported on the oxides. This study presents a comprehensive examination of the kinetics of AB methanolysis on different supported Ru catalysts; analysis of reaction mechanisms on all catalysts revealed similar apparent first order rate constants from either proposed kinetic models. This study demonstrates that while the support has relatively little influence on the measured reaction rates, carbon may be a preferred support given the decreased deactivation observed relative to the other supports tested.

Oxidation of cyclohexane with tert-butyl hydroperoxide (TBHP) is a common probe reaction for molecular complexes, though the kinetics of this reaction are seldom reported. Here, we synthesize metal-nitrogen-doped carbons (M-N-Cs) and a series of zeolite-encapsulated metal phthalocyanine (MPC) catalysts and compare their reactivity in cyclohexane oxidation with TBHP. These materials all have primary binding sites that include square planar metals bound to four nitrogen atoms (M-N4 sites). We measure the apparent activation energy for this reaction, and compare the reactivity of M-N-C and MPC catalysts with varied metal central atoms (M = Fe, Mn, Co, Cu, Cr, Ni), of which Fe-containing catalysts are the most reactive. Fe-N-C catalysts are more stable with reuse than FePC catalysts. Apparent reaction orders are less than one for both reactants, suggesting a surface mediated reaction. Cyclohexanol and cyclohexanone form in parallel at short reaction times, while cyclohexanol further reacts to cyclohexanone at longer reaction times. DFT calculations show that the reaction may follow a radical-mediated Eley-Rideal mechanism that is primarily mediated via tert-butoxy radicals formed at the metal site. Microkinetic modeling of the proposed mechanism reproduces experimental trends in product rates and selectivity of the main reaction products without requiring any parameter estimation. This study demonstrates that M-N-C and MPC catalysts perform cyclohexane oxidation with TBHP with similar per metal-atom initial rates. These results will enable judicious use of cyclohexane oxidation with TBHP as a probe reaction to compare reactivity of catalysts with M-N4 active sites.

PdAu/SiO2 catalysts were synthesized by strong electrostatic adsorption (SEA) and characterized by TEM, DRIFTS, XRD, XAS, and O-2-TPD. The use of group 1 alkali salt solutions to control pH during SEA syntheses led to uptake of alkali metals observed reductions in the densities of terminal silanol groups of the SiO2 support. In the absence of alkali metals, PdAu/SiO2 catalyzes oxidative C-N bond formation between methanol and dimethylamine (DMA), yielding dimethylformamide (DMF) with similar to 95 % carbon selectivity (CO2 similar to 5 %) at temperatures below 413 K. When Na, K, and Cs were present on the catalyst, methyl formate (MF) and tetramethylurea (TMU) were observed as additional products (combined similar to 30 % carbon selectivity) while only TMU was detected for the Li-promoted catalyst. Total coupling product rate increased for promoted samples in the order Li < Na < Cs < K, and the apparent kinetics over the Cs-promoted catalyst were distinct from those over the alkali-free catalyst as the apparent reaction order with respect to DMA decreased and the apparent activation energy increased. This work demonstrates the sensitivity of oxidative coupling reactions to alkali metal promoters and the opportunity to achieve alkali promotion of metal catalysts during SEA synthesis.

Understanding the dynamic evolution of Cu species under varying environmental conditions is critical for addressing challenges related to the activity and the stability of copper-based catalysts in thermo-, photo-, and electrocatalysis. However, metal–metal interactions between dual single atoms and their effects on Cu evolution after exposure to different environmental molecules remain underexplored. Herein, we synthesized bimetallic Cu-Y/Beta catalysts with dual single-atom Cu and Y sites and monometallic Cu-Beta catalysts with isolated Cu sites in dealuminated Beta zeolites. By varying Cu and Y compositions, diatomic interactions were studied under H 2 and ethanol atmospheres. With 6 wt% Y loading, approximately 0.4 wt% of Cu species in Cu-Y/Beta remained partially oxidized as Cu(I) after reduction in pure H 2 at 350 °C, in contrast to the full transition to metallic Cu observed in Cu-Beta. Combining X-ray absorption spectroscopy with kinetic studies revealed that metallic Cu became the predominant species after reduction with H 2 as Cu loading increased from 0.4 to 1.7 wt%, quadrupling the initial ethanol dehydrogenation rate and demonstrating the dominant role of Cu(0) sites. Scanning transmission electron microscopy and density functional theory simulations indicated spatial proximity between dual single-atom Cu and Y sites and elucidated Cu speciation controlled by diatomic interactions.

Aerobic oxidative dehydrogenation (ODH) of secondary alcohols is catalyzed by both platinum and platinum-bismuth catalysts in water. Symmetric 1,3-diether-2-alcohols are high-value glycerol-derived products and ODH of these alcohols to form analogous ketones over heterogeneous catalysts has not been reported previously. Reported herein are initial turnover frequencies (TOFs, per surface Pt), apparent activation energies, and apparent reaction orders for the ODH of several glycerol-derived oxygenates over Pt and PtBi particles supported on silica. Initial ODH rates were obtained from batch reactions (313-353 K, 0.01-2 M substrate). Apparent reaction orders were consistent with a rate-determining step involving alcohol alpha C-H bond activation over adjacent surface sites. Apparent activation energies measured in the first order kinetic regime over Pt and PtBi catalysts were similar for a range of substrates. Similar aliphatic alcohols (e.g., 2-butanol, 3-pentanol, and 4-heptanol) were not measurably converted under these conditions. Computational analysis of solvation energy, solvated binding free energy, and the binding structure collectively suggest that the experimentally observed reactivity of 1,3-dimethoxypropan-2-ol and 1,3-diethoxypropan-2-ol results from their relatively weak binding to the surface, whereas the lack of reactivity for 3-pentanol and 4-heptanol may result from them binding too strongly to the surface. These findings suggest secondary alcohol ODH occurs via a similar mechanism over Pt and PtBi particles and that the presence of ether linkages increases the rate of ODH in water.

Selective dimethylformamide formation occurs over PdAu; reactivity and selectivity are sensitive to Pd : Au ratio. Reaction kinetics suggest a crowded surface and that beneficial effects of surface hydroxyls are induced by co-feeding water.

Heterogeneous catalysis is driven by the interaction of reactant molecules and the catalyst surface. The locus of this interaction as well as the surrounding ensemble of atoms is referred to as the catalyst active site. Active site characterization attempts to distinguish active catalytic sites from inactive surface sites, to elucidate the structural and chemical nature of active sites, and to quantify active site concentration. Numerous techniques have been demonstrated to provide compositional and structural information about the active sites within a catalyst. However, each technique has its own limitations and experimental pitfalls that can lead to data misinterpretation or irreproducible results. This work aims to provide an overview of the types of data that can be collected, to outline common experimental challenges and how to avoid them, and to assemble relevant references for the most used active site characterization techniques. More broadly, we aim to outline best practices for researchers to collect, interpret, and report active site characterization data in a way that provides the most benefit to the broader catalysis community. Increasing the rigor and reproducibility of active site characterization offers a strategy to better link properties with catalytic performance and to enable the community to develop consensus concerning these relationships.

In this work, yttrium containing dealuminated Beta zeolites (Y/deAlBeta) were synthesized and characterized by various spectroscopic techniques to improve understanding of ethanol upgrading over these materials. Characterization results indicate yttrium atoms partially condense with framework silanol nests formed during dealumination of parent Al-Beta supports. Active sites for conversion of ethanol and acetaldehyde to butadiene were quantified on a series of Y/deAlBeta catalysts (0.1–10 vawt% yttrium) via ex situ chemisorption and transmission Fourier transformed infrared (FTIR) spectroscopy measurements by first measuring the integrated molar extinction coefficient (IMEC) for pyridine bound to Lewis acidic yttrium sites. In situ titrations with pyridine demonstrate that the number of sites quantified by ex situ chemisorption IR is quantitatively similar to the number of sites that catalyze butadiene formation, which varies (from 0.05 to 0.35) across the series of catalysts. In situ pyridine titrations impact butadiene site time yields (STY), but not crotonaldehyde STY, indicating that a distribution of yttrium sites is present, and that discrete yttrium site types participate in distinct steps in the pathway from ethanol to butadiene. Apparent kinetic parameters including activation energies and reaction orders were measured, these suggest differences in reactant (or reactant-derived intermediate) surface coverages result in higher STYs (per mol Y or per Lewis acidic Y site) for samples with low Y loadings relative to those with higher Y loadings. Isotopic labeling experiments evince the existence of other kinetically relevant steps in addition to the crotonaldehyde transformation to crotyl alcohol. Together, these findings provide further guidance into the heterogeneities in site structures in yttrium-containing zeolites and their relevance for the various steps in the pathway from ethanol to C4 products useful for production of sustainable aviation fuel and renewable butadiene.

Single-site copper-based catalysts have shown remarkable activity and selectivity for a variety of reactions. However, deactivation by sintering in high-temperature reducing environments remains a challenge and often limits their use due to irreversible structural changes to the catalyst. Here, we report zeolite-based copper catalysts in which copper oxide agglomerates formed after reaction can be repeatedly redispersed back to single sites using an oxidative treatment in air at 550 degrees C. Under different environments, single-site copper in Cu-Zn-Y/deAlBeta undergoes dynamic changes in structure and oxidation state that can be tuned to promote the formation of key active sites while minimizing deactivation through Cu sintering. For example, single-site Cu2+ reduces to Cu1+ after catalyst pretreatment (270 degrees C, 101 kPa H-2) and further to Cu-0 nanoparticles under reaction conditions (270-350 degrees C, 7 kPa EtOH, 94 kPa H-2) or accelerated aging (400-450 degrees C, 101 kPa H-2). After regeneration at 550 degrees C in air, agglomerated CuO was dispersed back to single sites in the presence and absence of Zn and Y, which was verified by imaging, in situ spectroscopy, and catalytic rate measurements. Ab initio molecular dynamics simulations show that solvation of CuO monomers by water facilitates their transport through the zeolite pore, and condensation of the CuO monomer with a fully protonated silanol nest entraps copper and reforms the single-site structure. The capability of silanol nests to trap and stabilize copper single sites under oxidizing conditions could extend the use of single-site copper catalysts to a wider variety of reactions and allows for a simple regeneration strategy for copper single-site catalysts.