Design Of Improved Catalysts Research Articles

Electrodeposited Manganese Dioxides and Their Composites as Electrocatalysts for Energy Conversion Reactions.

Enhancing the efficiencies of electrochemical reactions for converting renewable energy into clean chemical fuels as well as generating clean energy is critical to achieving carbon neutrality. However, this enhancement can be achieved using materials that are not constrained by resource limitations and those that can be converted into devices in a scalable manner, preferably for industrial applications. This review explores the applications of electrochemically deposited manganese dioxides (MnO2) and their composites as electrochemical catalysts for oxygen evolution (OER) and hydrogen evolution reactions for converting renewable energy into chemical fuels. It also explores their applications as electrochemical catalysts for oxygen reduction reaction (ORR) and bifunctional OER/ORR for the efficient operation of fuel cells and metal-air batteries, respectively. Manganese is the second most abundant transition metal in the Earth's crust, and electrodeposition represents a binder-free and scalable technique for fabricating devices (electrodes). To propose an improved catalyst design, the studies on the electrodeposition mechanism of MnO2as well as the fabrication techniques for MnO2-based nanocomposites accumulated in the development of electrodes for supercapacitors are also included in this review.

Elucidating Fundamental Structure-Function Relationships for Iridium Oxide Catalysts in PEM Water Electrolyzers

Proton exchange membrane water electrolysis (PEMWE) will contribute substantially towards decarbonization efforts and is expected to make up 40% of the green hydrogen market.1 A primary barrier for PEMWE scale-up is the detrimentally high usage of iridium for the oxygen evolution reaction catalyst. To achieve large-scale PEMWE deployment, loading reductions from 2-3 mgIr cm-2 to 0.10 mgIr cm-2 must occur.2 Such a feat can only be achieved through significant improvements in activity and durability. However, there exists a lack of fundamental understanding in how catalyst properties correlate to performance, thus hindering optimization efforts. The phenomena of catalyst activity/durability are frequently treated with purely empirical approaches, and thus the foundational knowledge needed for improved catalyst design—such as understanding how crystallinity and oxidation states impact performance in a membrane electrode assembly (MEA)—has not been well investigated.3 This work serves to bridge this gap in knowledge by correlating extensive structural characterization data with MEA activity and durability for six commercial IrOx catalysts. Properties such as oxidation states, chemical composition, local atomic/electronic configuration, crystallinity, surface area, and particle size distribution were elucidated for each catalyst in powder and/or MEA form. Following MEA conditioning, catalyst activity was benchmarked via polarization curves and Tafel analysis. Lastly, durability was evaluated by performing a 500h accelerated stress test (adapted from the H2New consortium), with electrochemical characterization conducted every 100h. The presence of amorphous character and the Ir3+ oxidation state was the best determinant of activity. Durability, on the other hand, was associated with greater crystalline character and more redox-stable cyclic voltammogram profiles. Correlations regarding chemical composition, local atomic/electronic configurations, particle size, and surface area will be discussed as well. Smolinka, T.; Wiebe, N.; Sterchele, P.; Palzer, A.; Lehner, F.; Jansen, M.; Kiemel, S.; Miehe, R.; Wahren, S.; Zimmermann, F. Studie IndWEDe: Industrialisierung Der Wasserelektrolyse in Deutschland: Chancen Und Herausforderungen Für Nachhaltigen Wasserstoff Für Verkehr, Strom Und Wärme.; 2018.Clapp, M.; Zalitis, C. M.; Ryan, M. Perspectives on Current and Future Iridium Demand and Iridium Oxide Catalysts for PEM Water Electrolysis. Catal Today 2023, 420 (March), 114140. https://doi.org/10.1016/j.cattod.2023.114140.Lazaridis, T.; Stühmeier, B. M.; Gasteiger, H. A.; El-Sayed, H. A. Capabilities and Limitations of Rotating Disk Electrodes versus Membrane Electrode Assemblies in the Investigation of Electrocatalysts. Nat Catal 2022, 5 (5), 363–373. https://doi.org/10.1038/s41929-022-00776-5.

Integrating renewable energy with fuel synthesis: Conceptual framework and future directions

The integration of renewable energy sources with fuel synthesis represents a transformative approach to addressing the twin challenges of energy sustainability and climate change. This review presents a conceptual framework for coupling renewable energy technologies, such as solar, wind, and biomass, with fuel synthesis processes to produce sustainable, zero-carbon fuels. The framework emphasizes the use of renewable electricity for water splitting and carbon dioxide reduction, key steps in synthesizing hydrogen and other synthetic fuels. The conceptual framework highlights the importance of advanced catalysts in enhancing the efficiency and selectivity of these chemical reactions. Innovations in nanostructured catalysts, hybrid materials, and biomimetic approaches are discussed for their potential to significantly improve the performance and durability of catalytic processes. Additionally, the framework underscores the role of advanced characterization techniques and computational modeling in understanding and optimizing catalyst behavior. This integration necessitates addressing technical challenges associated with scaling up production processes from laboratory to industrial levels. These challenges include ensuring the stability and longevity of catalysts under operational conditions, managing the intermittency of renewable energy sources, and developing robust systems for capturing and utilizing carbon dioxide. Furthermore, the economic viability of these integrated systems is critical, requiring cost-effective solutions that leverage earth-abundant materials and optimize the overall energy efficiency. The environmental benefits of integrating renewable energy with fuel synthesis are substantial, offering a pathway to significantly reduce carbon emissions and reliance on fossil fuels. The production of synthetic fuels using renewable energy can lead to a closed carbon cycle, thereby mitigating the impact on climate change and contributing to a sustainable energy future. Future directions in this field involve interdisciplinary research to further enhance catalyst performance, develop new materials, and refine process integration strategies. A roadmap for future development includes prioritizing areas such as improved catalyst design, efficient CO2 capture technologies, and the integration of electrochemical and photochemical systems. This abstract concludes by underscoring the transformative potential of renewable energy-fuel synthesis integration, envisioning a future where sustainable energy practices become the cornerstone of global energy systems. Keywords: Integrating, Renewable Energy, Fuel Synthesis, Future Directions, Framework.

Operando Raman spectroscopy uncovers hydroxide and CO species enhance ethanol selectivity during pulsed CO2 electroreduction

Pulsed CO2 electroreduction (CO2RR) has recently emerged as a facile way to in situ tune the product selectivity, in particular toward ethanol, without re-designing the catalytic system. However, in-depth mechanistic understanding requires comprehensive operando time-resolved studies to identify the kinetics and dynamics of the electrocatalytic interface. Here, we track the adsorbates and the catalyst state of pre-reduced Cu2O nanocubes ( ~ 30 nm) during pulsed CO2RR using sub-second time-resolved operando Raman spectroscopy. By screening a variety of product-steering pulse length conditions, we unravel the critical role of co-adsorbed OH and CO on the Cu surface next to the oxidative formation of Cu-Oad or CuOx/(OH)y species, impacting the kinetics of CO adsorption and boosting the ethanol selectivity. However, a too low OHad coverage following the formation of bulk-like Cu2O induces a significant increase in the C1 selectivity, while a too high OHad coverage poisons the surface for C-C coupling. Thus, we unveil the importance of co-adsorbed OH on the alcohol formation under CO2RR conditions and thereby, pave the way for improved catalyst design and operating conditions.

Nano-Cu Derived from a Copper Nitride Precatalyst for Reductive Coupling of Nitroaromatics to Azo Compounds.

The study of structural reconstruction is vital for the understanding of the real active sites in heterogeneous catalysis and guiding the improved catalyst design. Herein, we applied a copper nitride precatalyst in the nitroarene reductive coupling reaction and made a systematic investigation on the dynamic structural evolution behaviors and catalytic performance. This Cu3N precatalyst undergoes a rapid phase transition to nanostructured Cu with rich defective sites, which act as the actual catalytic sites for the coupling process. The nitride-derived defective Cu is very active and selective for azo formation, with 99.6% conversion of nitrobenzene and 97.1% selectivity to azobenzene obtained under mild reaction conditions. Density functional theory calculations suggest that the defective Cu sites play a role for the preferential adsorption of nitrosobenzene intermediates and significantly lowered the activation energy of the key coupling step. This work not only proposes a highly efficient noble-metal-free catalyst for nitroarenes coupling to valuable azo products but also may inspire more scientific interest in the study of the dynamic evolution of metal nitrides in different catalytic reactions.

Enhancing CO2 Hydrogenation Using a Heterogeneous Bimetal NiAl-Deposited Metal-Organic Framework NU-1000: Insights from First-Principles Calculations.

The hydrogenation of CO2 to high-value-added liquid fuels is crucial for greenhouse gas emission reduction and optimal utilization of carbon resources. Developing supported heterogeneous catalysts is a key strategy in this context, as they offer well-defined active sites for in-depth mechanistic studies and improved catalyst design. Here, we conducted extensive first-principles calculations to systematically explore the reaction mechanisms for CO2 hydrogenation on a heterogeneous bimetal NiAl-deposited metal-organic framework (MOF) NU-1000 and its catalytic performance as atomically dispersed catalysts for CO2 hydrogenation to formic acid (HCOOH), formaldehyde (H2CO), and methanol (CH3OH). The present results reveal that the presence of the NiAl-oxo cluster deposited on NU-1000 efficiently activates H2, and the facile heterolysis of H2 on Ni and adjacent O sites serves as a precursor to the hydrogenation of CO2 into various C1 products HCOOH, H2CO, and CH3OH. Generally, H2 activation is the rate-determining step in the entire CO2 hydrogenation process, the corresponding relatively low free energy barriers range from 14.5 to 15.9 kcal/mol, and the desorption of products on NiAl-deposited NU-1000 is relatively facile. Although the Al atom does not directly participate in the reaction, its presence provides exposed oxygen sites that facilitate the heterolytic cleavage of H2 and the hydrogenation of C1 intermediates, which plays an important role in enhancing the catalytic activity of the Ni site. The present study demonstrates that the catalytic performance of NU-1000 can be finely tuned by depositing heterometal-oxo clusters, and the porous MOF should be an attractive platform for the construction of atomically dispersed catalysts.

Electro-Oxidative Valorization of Biomass-Derived Furanics

Electrocatalysis poses many potential advantages for distributed scale biomass valorization. Furanic biomass derivatives such as furfural and 5-hydroxymethylfurfural (HMF) can provide access to a number of value-added chemicals by partial oxidation, including furoic acid, maleic acid, and 2,5-furandicarboxylic acid (FDCA). Here, we have utilized differential reactor studies with online electrochemical mass spectrometry (OLEMS), as well as in-situ attenuated total reflectance surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS), to probe these reaction pathways on various metal electrodes. Experimental insights are combined with computational results to piece together plausible mechanisms. We find tradeoffs between decarbonylation activity and self-assembly of furoate intermediates on late transition metals to be critical selectivity-determining and rate-determining process. We also characterize oxidative dehydrogenation paths for furanic aldehydes, which co-produce (anodic) hydrogen gas. Strategies for improved catalyst design will be discussed.

Crystal-Phase Engineering in Heterogeneous Catalysis.

The performance of a chemical reaction is critically dependent on the electronic and/or geometric structures of a material in heterogeneous catalysis. Over the past century, the Sabatier principle has already provided a conceptual framework for optimal catalyst design by adjusting the electronic structure of the catalytic material via a change in composition. Beyond composition, it is essential to recognize that the geometric atomic structures of a catalyst, encompassing terraces, edges, steps, kinks, and corners, have a substantial impact on the activity and selectivity of a chemical reaction. Crystal-phase engineering has the capacity to bring about substantial alterations in the electronic and geometric configurations of a catalyst, enabling control over coordination numbers, morphological features, and the arrangement of surface atoms. Modulating the crystallographic phase is therefore an important strategy for improving the stability, activity, and selectivity of catalytic materials. Nonetheless, a complete understanding of how the performance depends on the crystal phase of a catalyst remains elusive, primarily due to the absence of a molecular-level view of active sites across various crystal phases. In this review, we primarily focus on assessing the dependence of catalytic performance on crystal phases to elucidate the challenges and complexities inherent in heterogeneous catalysis, ultimately aiming for improved catalyst design.

Processing renewable and waste-based feedstocks with fluid catalytic cracking: Impact on catalytic performance and considerations for improved catalyst design.

Refiners around the globe are either considering or are actively replacing a portion of their crude oil inputs originating from fossil sources with alternative sources, including recycled materials (plastics, urban waste, mixed solid waste) and renewable materials (bio-mass waste, vegetable oils). In this paper, we explore such replacement, specifically focusing on the fluid catalytic cracking (FCC) operation. Five pyrolysis oils, obtained from municipal solid waste (MSW) and biogenic material (olive stones/pits), were fully characterized and tested at 10% loading against a standard fluid catalytic cracking (FCC) vacuum gasoil (VGO) feed in a bench scale reactor using an industrially available fluid catalytic cracking catalyst based on ultrastable Y zeolite to simulate fluid catalytic cracking co-processing. Despite having unique feed properties, including high Conradson carbon (e.g., up to 19.41wt%), water (e.g., up to 5.7wt%), and contaminants (e.g., up to 227ppm Cl) in some cases, the five pyrolysis oils gave similar yield patterns as vacuum gasoil. Gasoline was slightly (ca. 1wt%) higher in all cases and LPG slightly (ca. 1wt%) lower. Olefinicity in the LPG streams were unchanged, bottoms and light cycle oil (LCO) showed no significant changes, while dry gas was slightly (up to -0.2wt%) lower. Coke selectivity was also unchanged (maximum -7.7wt%, relatively), suggesting minimal to no heat balance concerns when co-processing in an industrial fluid catalytic cracking unit. The results demonstrate the applicability of municipal solid waste and biogenic originating pyrolysis oils into a refinery. A catalyst design concept is explored, based on higher rare Earth oxide exchange and/or utilization of ZSM-5 zeolite, that would further minimize the impacts of replacing fossil oils with pyrolysis oils, namely one that shifts the 1% higher gasoline into LPG.

Cholinium-based ionic liquid catalysts for polyethylene terephthalate glycolysis: understanding the role of solvent and a reappraisal of the cation contribution

A combined computational and experimental study has identified a new PET degradation pathway using cholinium-based ionicliquids, leading to a re-evaluation of the cholinium unit's role in catalysis and improved catalyst design.

Selectivity control in alkyne semihydrogenation: Recent experimental and theoretical progress

Researchers have been attempting to characterize heterogeneous catalysts in situ in addition to correlating their structures with their activity and selectivity in spite of many challenges. Here, we review recent experimental and theoretical advances regarding alkyne selective hydrogenation by Pd-based catalysts, which are an important petrochemical reaction. The catalytic selectivity for the reaction of alkynes to alkenes is influenced by the composition and structure of the catalysts. Recent progress achieved through experimental studies and atomic simulations has provided useful insights into the origins of the selectivity. The important role of the subsurface species (H and C) was revealed by monitoring the catalyst surface and the related catalytic performance. The atomic structures of the Pd catalytic centers and their relationship with selectivity were established through atomic simulations. The combined knowledge gained from experimental and theoretical studies provides a fundamental understanding of catalytic mechanisms and reveals a path toward improved catalyst design.

Favoring the Methane Oxychlorination Reaction over EuOCl by Synergistic Effects with Lanthanum.

The direct conversion of CH4 into fuels and chemicals produces less waste, requires smaller capital investments, and has improved energy efficiency compared to multistep processes. While the methane oxychlorination (MOC) reaction has been given little attention, it offers the potential to achieve high CH4 conversion levels at high selectivities. In a continuing effort to design commercially interesting MOC catalysts, we have improved the catalyst design of EuOCl by the partial replacement of Eu3+ by La3+. A set of catalytic solid solutions of La3+ and Eu3+ (i.e., LaxEu1–xOCl, where x = 0, 0.25, 0.50, 0.75, and 1) were synthesized and tested in the MOC reaction. The La3+–Eu3+ catalysts exhibit an increased CH3Cl selectivity (i.e., 54–66 vs 41–52%), a lower CH2Cl2 selectivity (i.e., 8–24 vs 18–34%), and a comparable CO selectivity (i.e., 11–28 vs 14–28%) compared to EuOCl under the same reaction conditions and varying HCl concentrations in the feed. The La3+–Eu3+ catalysts possessed a higher CH4 conversion rate than when the individual activities of LaOCl and EuOCl are summed with a similar La3+/Eu3+ ratio (i.e., the linear combination). In the solid solution, La3+ is readily chlorinated and acts as a chlorine buffer that can transfer chlorine to the active Eu3+ phase, thereby enhancing the activity. The improved catalyst design enhances the CH3Cl yield and selectivity and reduces the catalyst cost and the separation cost of the unreacted HCl. These results showcase that, by matching intrinsic material properties, catalyst design can be altered to overcome reaction bottlenecks.

Versatile in situ/operando Setup for Studying Catalysts by X‐Ray Absorption Spectroscopy under Demanding and Dynamic Reaction Conditions for Energy Storage and Conversion

AbstractX‐ray absorption spectroscopy (XAS) is one of the powerful operando tools to track structural variations in heterogeneous catalysts. The nature of active sites in catalyst research is of great relevance, especially given the growing importance of energy storage using CO2 as feedstock and the need for dynamic availability of electric power. Due to the pressure/temperature prerequisite of catalyst performance, the characterization of catalyst structure during catalysis under such high‐pressure reaction conditions is important to further improve catalyst design at a molecular level. Investigating catalysts in a controlled reaction atmosphere, while probing with X‐rays, offers an excellent opportunity for developing infrastructure at the synchrotron. Herein, a mobile setup with a robust spectroscopic cell for in situ and operando XAS applications, including a high‐pressure gas dosing equipment for such catalytic systems, is presented. The in situ/operando cell is operational for both the transmission and the fluorescence XAS mode at up to 50 bar and 450 °C. The setup comes with a protective box with Kapton windows, which holds the cell and serves as a miniature fume hood, and on‐line product analysis. Furthermore, the gas dosing equipment is compact, light‐weighted and can be easily transported to different synchrotrons and allows an optimum pre‐mix of gas flows and pressure build‐up. Methanol and Fischer‐Tropsch syntheses are used as examples for the highly flexible instrumentation.

X-Ray Absorption Spectroscopy Studies of Ir-Oxide Based Oxygen Evolution Catalysts Revisited

Hydrogen plays a pivotal role in the future decarbonization of the energy sector [1], but its production in a sustainable way is crucial for it to have a positive environmental impact. Due to its high power density, quick start-up and response time as well as pressurized hydrogen delivery, polymer electrolyte membrane water electrolysis (PEMWE) is perfectly suited to facilitate H2 production from renewable electricity [2]. However, at large scale application, the use of scarce and expensive, Ir-based catalysts in PEM water electrolyser anodes limits the proliferation of this technology [3, 4]. For this reason, significant research activities are being conducted to better understand the oxygen evolution reaction (OER) mechanism on benchmark IrO2 based catalysts, as to further improve catalyst design and decrease the efficiency losses related to this reaction.When trying to elucidate a reaction mechanism, the use of operando and/or in situ techniques is often beneficial, and thus in last decades the OER mechanism on Ir-based materials has been extensively investigated through operando / in-situ X-ray absorption as well as X-ray photoelectron spectroscopy (XAS, XPS) [5-10]. Despite enormous efforts in this research area, there is still a lack of consensus regarding the Ir oxidation state under OER conditions and the nature of the OER-active sites. In line with this, in this study we employed operando XAS to investigate the Ir oxidation state in commercial IrO2 (Umicore®) catalyst under OER polarization curve conditions. These XAS measurements were performed both in transmission and fluorescence modes; for the former, electrodes with loadings ≈ 40 fold higher than those used in rotating disk electrode (RDE) measurements were required in order to achieve appropriate XAS data quality. In fluorescence mode, however, thinner electrodes with only four times higher loadings than in RDE could be investigated. Prior to the operando XAS measurement, the utilization of these IrO2 catalyst layers in the operando flow cell (FC) was assessed to ensure that the acquired spectroscopic data was representative of the processes occurring under real conditions. Achieving a good catalyst layer utilization was especially important in the case of the thick electrodes used in transmission XAS measurement, since their resistance is much higher compared to that in thin film RDE measurements. The so obtained results were additionally affected by beam damage of the Nafion ionomer used as the catalyst layer binder. All these factors can further lead to data misinterpretation. Regarding the beam damage, reducing the beam flux helped to prevent this effect and allowed us to obtain reliable results. Additionally, the use of thin catalyst layers in the operando FC and its combination of time-resolved XAS (so called “quickXAS”) in fluorescence mode led to novel insight on the effects of evolved O2 bubbles on the spectroscopic results and subsequent interpretation thereof.In summary, this contribution will provide an overview of common pitfalls and good practices encountered when conducting operando XAS studies of OER-electrocatalysts.

Electro-Oxidation Pathways for Biomass-Derived Furans

Electrocatalysis poses many potential advantages for distributed scale biomass valorization. Furanic biomass derivatives such as furfural and 5-hydroxymethylfurfural (HMF) can provide access to a number of value-added chemicals by partial oxidation, including furoic acid, maleic acid, and 2,5-furandicarboxylic acid (FDCA). Here, we have utilized differential reactor studies with online electrochemical mass spectrometry (OLEMS), as well as in situ attenuated total reflectance-surface-enhanced infrared reflection-absorption spectroscopy (ATR-SEIRAS), to probe these reaction pathways on various metal electrodes. Experimental insights are combined with computational results to piece together plausible mechanisms. In particular we find tradeoffs between decarbonylation activity on Pt-group electrodes and and self-assembly of furoate intermediates on noble metals to be critical selectivity and rate determining steps. Strategies for improved catalyst design will be discussed.

Enantioselective N-heterocyclic carbene-catalysed intermolecular crossed benzoin condensations: improved catalyst design and the role of in situ racemisation.

The enantioselective intermolecular crossed-benzoin condensation mediated by novel chiral N-heterocyclic carbenes derived from pyroglutamic acid has been investigated. A small library of chiral triazolium ions were synthesised. Each possessed a tertiary alcohol H-bond donor and a variable N-aryl substituent. It was found that increasing both the steric requirement and the electron-withdrawing characteristics of the N-aryl ring led to more chemoselective, efficient and enantioselective chemistry, however both quenching the reaction at different times and deuterium incorporation experiments involving the product revealed that this is complicated by product racemisation in situ (except in the case of benzoin itself), which explains the dependence of enantioselectivity on the electrophilicity of the reacting aldehydes common in the literature. Subsequent protocol optimisation, where one reacting partner was an o-substituted benzaldehyde, allowed a range of crossed-benzoins to be synthesised in moderate-good yields with moderate to excellent enantioselectivity.

Spiers Memorial Lecture: Understanding reaction mechanisms in heterogeneously catalysed reactions.

Heterogeneous catalysis lies at the heart of the chemical and fuel manufacturing industries and hence is a cornerstone of many economies. Many of the commercially operated heterogeneous catalysts have remained basically unchanged for decades, undergoing small but important optimisation of their formulations. Yet we all acknowledge that there is a continuous drive towards improved catalysts or designing new ones. At the heart of these studies has been the need to gain an improved understanding of the reaction mechanism for these important reactions since this can unlock new ways to improve catalyst design and, of course, the ultimate aim is to design catalysts based on the detailed understanding of the reaction mechanism. These advanced studies have been aided in the last decade by two key factors, namely: (a) access to advanced characterisation techniques based on synchrotron methods and aberration-corrected microscopy that can probe the nature of the active site, and (b) the application of high-level computational methods to understand how the reactants and products interact at the active site. In this paper this theme will be explored using two examples to bring out the complexity in gaining an understanding of a reaction mechanism. Using the zeolite H-ZSM-5 as an example of a single site catalyst, the mechanism of the conversion of methanol to the first hydrocarbon carbon-carbon bond will be discussed. In this section the use of model reactants and reaction probes will be used to try to differentiate between different mechanistic proposals. The second example explores the use of gold catalysts for CO oxidation and acetylene hydrochlorination. In both these examples the importance of advanced characterisation and theory will be highlighted.

Carbohydrate-Based Chiral Iodoarene Catalysts: A Survey through the Development of an Improved Catalyst Design.

Iodoarene catalysts can be applied in versatile reactions, for instance in the construction of complex chiral molecules via dearomatization of simple aromatic compounds. Recently, we reported the synthesis of the first carbohydrate-based chiral iodoarene catalysts and their application in asymmetric catalysis. Here we describe the synthesis of some new and improved catalysts. An account on how we got to the improved catalyst design, as well as the X-ray structure of one of the carbohydrate-based iodoarenes, is given.

Deciphering key intermediates in the transformation of carbon dioxide into heterocyclic products

The identification of catalytic intermediates in the conversion of carbon dioxide is vital for improved catalyst design and optimization of structure–reactivity relationships, but remains elusive. Here, we report that intermolecular hydrogen bonding interactions between an epoxy alcohol, water and the catalyst structure are crucial towards the formation of a cyclic carbonate from carbon dioxide. A combination of multiple in situ and ex situ techniques including substrate labelling, kinetic studies, computational analysis, operando infrared spectroscopy and X-ray diffraction was applied to identify and support the structural connectivities of several previously unknown intermediates. An epoxy alcohol–water cluster formed by hydrogen bonding was identified as the initial intermediate able to trap CO2 and an elusive alkyl carbonate anion was also detected. The synergistic spectroscopic and computational analysis shown here offers a unique insight under operando conditions, as well as a useful analytical blueprint for key suggested intermediates in other mechanistically related CO2 conversion processes. One of the major routes for the use of CO2 in chemical production is the formation of carbonates via cycloaddition of CO2 to epoxides. This work uses a range of experimental and computational techniques to map out the elusive key intermediates in this process.

Computational Multinuclear NMR Characterization of Metal-Doped Amorphous Silica Catalysts

Metal-doped amorphous silica has shown strong catalytic activity in a number of industrial applications, including lignin depolymerization, ethanol dehydration, and olefin metathesis. The metal dopant is essential to the catalyst’s reactivity, and although an increased metal concentration typically results in increased reactivity, it is the structure of the metal site that determines the activity strength. However, the structure of the active site is difficult to characterize experimentally as it is influenced by the irregular, amorphous silica support. Insights from computational simulations can greatly aid the characterization of these materials, which in turn may lead to improved catalyst design. In this study, we focus on a primary technique for the experimental investigation of solid materials, i.e., solid state nuclear magnetic resonance spectroscopy. We use density functional theory simulations to obtain nuclear magnetic resonance (NMR) spectra and quadrupolar coupling constants of metal-doped amor...