Surface Reactions and Catalytic Activities for Small Alcohols over LaMnO3(100) and La0.7Sr0.3MnO3(100): Dehydrogenation, Dehydration, and Oxidation
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99 GENERAL AND MISCELLANEOUS↗
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Controlling Hydrocarbon (De)Hydrogenation Pathways with Bifunctional PtCu Single-Atom Alloys
The conversions of surface-bound alkyl groups to alkanes and alkenes are important steps in many heterogeneously catalyzed reactions. On the one hand, while Pt is ubiquitous in industry because of its high activity toward C–H activation, many Pt-based catalysts tend to overbind reactive intermediates, which leads to deactivation by carbon deposition and coke formation. On the other hand, Cu binds intermediates more weakly than Pt, but activation barriers tend to be higher on Cu. We examine the reactivity of ethyl, the simplest alkyl group that can undergo hydrogenation and dehydrogenation via β-elimination, and show that isolated Pt atoms in Cu enable low-temperature hydrogenation of ethyl, unseen on Cu, while avoiding the decomposition pathways on pure Pt that lead to coking. Lastly, we confirm the predictions of our theoretical model and experimentally demonstrate that the selectivity of ethyl (de)hydrogenation can be controlled by changing the surface coverage of hydrogen.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Toward Efficient Entropic Recycling by Mastering Ring–Chain Kinetics
Traditional chemical recycling approaches for condensation polymers suffer compounding energy losses and CO 2 emissions across multiple polymerization and depolymerization cycles. Entropic recycling can address these energy losses by entrapping free energy within the deconstruction products. Entropic recycling involves depolymerization to macrocyclic monomers, but such processes have not been feasible due to the high dilutions typically required to generate macrocyclic compounds. Here, we leverage selective catalysis to allow entropic recycling at concentrations 20–2000× higher than typical for macrocyclization reactions. We find that Ru-based olefin metathesis catalysts containing bulky iodine ligands significantly bias the ring–chain kinetic product distribution during ring-closing metathesis (RCM) toward the formation of oligomeric cycloalkenes. Further improvements in reaction concentration and macrocycle yield are obtained by using high catalyst loadings and by predisposing the alkene substrates to undergo favorable macrocyclization. These RCM optimizations translate effectively to cyclodepolymerization (CDP) of an olefin-containing polymer, with RCM and CDP affording similar macrocycle product distributions under identical reaction conditions. Macrocycle polymerization by entropy-driven ring-opening metathesis provides much higher molecular weight polymers than condensation polymerization of linear analogues, reducing the time to achieve high molecular weight from hours to minutes and enabling polymerization at room temperature. Finally, our findings re-emphasize the importance of energy consumption during a polymer’s lifecycle and provide a framework for the design of efficient entropic recycling systems.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Elucidating the Roles of Amorphous Alumina Overcoat in Palladium-Catalyzed Selective Hydrogenation
Amorphous alumina overcoats generated by atomic layer deposition (ALD) have been shown to improve the selectivity and durability of supported metal catalysts in many reactions. Several mechanisms have been proposed to explain the enhanced catalytic performance, but the accessibilities of reactants through the amorphous overcoats remain elusive, which is crucial for understanding reaction mechanisms. Here, we show that an AlO x ALD overcoat is able to improve the alkene product selectivity of a supported Pd catalyst in acetylene (C 2 H 2 ) hydrogenation. We further demonstrate that the AlO x ALD overcoat blocks the access of C 2 H 2 (kinetic diameter of 0.33 nm), O 2 (0.35 nm), and CO (0.38 nm) but allows H 2 (0.29 nm) to access Pd surfaces. A H–D exchange experiment suggests that H 2 might dissociate heterolytically at the Pd–AlO x interface. These findings are in favor of a hydrogen spillover mechanism.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Supported Platinum Nanoparticles Catalyzed Carbon–Carbon Bond Cleavage of Polyolefins: Role of the Oxide Support Acidity
Supported platinum nanoparticle catalysts are known to convert polyolefins to high-quality liquid hydrocarbons using hydrogen under relatively mild conditions. To date, few studies using platinum grafted onto various metal oxide (M x O y ) supports have been undertaken to understand the role of the acidity of the oxide support in the carbon-carbon bond cleavage of polyethylene under consistent catalytic conditions. Specifically, two Pt/M x O y catalysts (M x O y = SrTiO 3 and SiO 2 -Al 2 O 3 ; Al = 3.0 wt %, target Pt loading 2 wt % Pt similar to 1.5 nm), under identical catalytic polyethylene hydrogenolysis conditions (T = 300 degree celsius, P(H 2 ) = 170 psi, t = 24 h; M w = similar to 3,800 g/mol, M n = similar to 1,100 g/mol, D = 3.45, N branch/100C = 1.0), yielded a narrow distribution of hydrocarbons with molecular weights in the range of lubricants (M w = < 600 g/mol; M n < 400 g/mol; D = 1.5). While Pt/SrTiO 3 formed saturated hydrocarbons with negligible branching, Pt/SiO 2 -Al 2 O 3 formed partially unsaturated hydrocarbons (<1 mol % alkenes and similar to 4 mol % alkyl aromatics) with increased branch density (N branch/100C = 5.5). Further investigations suggest evidence for a competitive hydrocracking mechanism occurring alongside hydrogenolysis, stemming from the increased acidity of Pt/SiO 2 -Al 2 O 3 compared to Pt/SrTiO 3 . Additionally, the products of these polymer deconstruction reactions were found to be independent of the polyethylene feedstock, allowing the potential to upcycle polyethylenes with various properties into a value-added product.
36 MATERIALS SCIENCE↗
Ethanol Conversion over La 0.7 Sr 0.3 MnO 3–x (100): Autocatalysis, Adjacent O-Vacancies, Disproportionation, and Dehydrogenation
The mechanism for catalytic conversion of ethanol over La 0.7 Sr 0.3 MnO 3– x (100) surface to acetaldehyde and ethene was investigated. Pre-exposure temperature-programmed reaction (PE-TPR) experiments were performed in which ethanol was introduced to oxidized or reduced surfaces followed by heating. In particular, sequential PE-TPR experiments were conducted to incrementally and gradually reduce the surface. The products and their ratios were investigated as a function of surface reduction. The data show that acetaldehyde and ethene production is catalyzed with hydrogen abstraction and oxygen abstraction reactions occurring by intermediates in vacancies at various temperatures >400 K. Adsorption of acetaldehyde followed by a temperature-programmed reaction does not produce ethene, indicating that acetaldehyde is not an intermediate to ethene and that the hydrogen and oxygen abstraction from ethanol to ethene are decoupled steps. Further evidence for this mechanistic nuance was obtained using isotopically labeled ethanol (CD 3 CH 2 OH), which produces CD 3 CHO and CD 2 CH 2 . Additionally, the ratio of aldehyde production to alkene production increases with reduction, suggesting that aldehyde is produced from a disproportionation reaction between ethoxy species in adjacent O-vacancies, while ethene is produced from a dehydrogenation reaction with ethoxy species in vacancies without requiring adjacent O-vacancies. Counterintuitively, this finding indicates that the more oxygenated product (aldehyde vs ethene) is favored with more vacancies and that the net alcohol conversion is autocatalytic. Density functional theory calculations were able to find the previously unknown disproportionation pathway between ethoxies in adjacent O-vacancies, and kinetic Monte Carlo simulations support this interpretation by reproducing experimental selectivities. The activation energies for these pathways are estimated as 132 ± 10 kJ/mol for the disproportionation reaction (when occurring between ethoxies in adjacent vacancies) and as 148 ± 11 kJ/mol for the direct dehydrogenation reaction of an ethoxy in a vacancy. Based on these results, a mechanism with operative pathways based on elementary steps in O-vacancies is reported.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Reactive Species and Reaction Pathways for the Oxidative Cleavage of 4-Octene and Oleic Acid with H 2 O 2 over Tungsten Oxide Catalysts
The oxidative cleavage of carbon-carbon double bonds (C=C) in alkenes and fatty acids produces aldehydes and acids valued as chemical intermediates. Solid tungsten oxide catalysts are low cost, non-toxic, and selective for the oxidative cleavage of C=C bonds with hydrogen peroxide (H 2 O 2 ) and are, therefore, a promising option for continuous processes. Despite the relevance of these materials, the elementary steps involved and their sensitivity to the form of W sites present on surfaces have not been described. In this work, we combine in situ spectroscopy and rate measurements to identify significant steps in the reaction, the reactive species present on catalysts, and examine differences between the kinetics of this reaction on isolated W atoms grafted to alumina and on those exposed on crystalline WO 3 nanoparticles. Raman spectroscopy shows that W-peroxo complexes (W-(η 2 -O 2 ) formed from H 2 O 2 ) react in a kinetically relevant step to produce epoxides, which undergo hydrolysis at protic surface sites. Subsequently, the CH 3 CN solvent deprotonates diols to form alpha hydroxy ketones that react to form aldehydes and water following nucleophilic attack of H 2 O 2 . Turnover rates for oxidative cleavage, determined by in situ site titrations, on WO x -Al 2 O 3 are 75% greater than those on WO 3 at standard conditions. These differences reflect activation enthalpies (ΔH ‡ ) for oxidative cleavage of 4-octene that are much lower for the isolated WO x sites (36±3 and 60±6 kJ∙mol -1 for WO x -Al 2 O 3 and WO 3 , respectively) and correlate strongly with the difference between enthalpies of adsorption for epoxyoctane (ΔH ads,epox ), which resembles the transition state for epoxidation. The WO x -Al 2 O 3 catalysts mediate oxidative cleavage of oleic acid with H 2 O 2 following a mechanism comparable to that for 4-octene. The WO 3 materials, however, form only the epoxide and do not cleave the C-C bond or produce aldehydes and acids. These differences reflect the distinct site requirements for these reaction pathways and indicate that acid sites required for diol formation are strongly inhibited by oleic acids and epoxides on WO 3 whereas the Al 2 O 3 support provides sites competent for this reaction and increase the yield of the oxidative cleavage products.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Catalytic Light Alkanes Conversion through Anaerobic Ammodehydrogenation
Catalytic transformation of light alkanes could have considerable practical value, yet remains one of the most challenging areas in catalysis research due to the inertness of the C–H bond. Here, we proposed an efficient ammodehydrogenation (ADeH) catalytic system for the direct C–N linkage between light alkanes and ammonia for CH 3 CN and H 2 (CO x free) production. This breakthrough is achieved over bifunctional metal-modified HZSM-5 catalysts, through the tandem dehydrogenation–amination–dehydrogenation mechanism. We show that ethane ADeH over the Pt/HZSM-5 catalyst can be realized under atmospheric pressure at temperatures as low as 350 °C. The specific rate of CH 3 CN is ~60 μmol/(g min), and the selectivity is up to 99% under such mild conditions. The yield of CH 3 CN increases with increasing temperature; however, the selectivity decreases due to the formation of HCN, C 2 H 4 , and CH 4 . Additionally, the Pt/HZSM-5 catalyst is coke-resistant during the ADeH owing to the strong interaction between NH 3 and the acid sites of the catalyst. So, we anticipate that the proposed ADeH could be extended for the transformation of various n/iso-alkanes with tunable selectivity to alkene and nitriles.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Deactivation by Potassium Accumulation on a Pt/TiO 2 Bifunctional Catalyst for Biomass Catalytic Fast Pyrolysis
Biomass-derived feedstocks bring significant challenges to the longevity of the catalysts used for their conversion, and alkali metals, for example, K, in the feedstock have been widely ascribed as one of the important factors causing catalyst deactivation. To address this challenge, it is critical to understand the mechanism of catalyst deactivation caused by K accumulation to guide the improvement of catalysts and processes and the development of catalyst regeneration strategies. In this work, we report a deep understanding of the impact of K on a bifunctional Pt/TiO 2 catalyst, which is an efficient catalyst for the ex situ catalytic fast pyrolysis of biomass. We simulated the K-poisoning of Pt/TiO 2 catalysts by purposely loading different amounts of K (100-6000 ppm by weight) on the catalysts. A series of characterization approaches, including scanning transmission electron microscopy, Fourier transform infrared spectroscopy, and chemical titration, were combined with a kinetic assessment of multiple probe reactions to elucidate the mechanism of Pt/TiO 2 deactivation by K accumulation. At low K loadings (<800 ppm), K preferentially poisons the strong Lewis acid sites, leading to significantly reduced activity for acid-catalyzed alcohol dehydration. However, acetone condensation is less sensitive to the poisoning of strong Lewis acid sites. Reactions that occur on Pt sites or at the metal-support interface, including alkene hydrogenation, m-cresol hydrodeoxygenation (HDO), and CO oxidation, were not impacted. At high K loadings (>800 ppm), K starts to accumulate on the Pt-TiO 2 interfacial area, poisoning the interfacial active sites for HDO and CO oxidation reactions. We further found that the poisoning of the Pt/TiO 2 catalyst by K is reversible, and water washing can successfully remove the accumulated K and recover the activities for both alcohol dehydration and m-cresol HDO reactions.
09 BIOMASS FUELS↗
Hydrogen Adsorption, Reactivity, and Catalysis on Colloidal Iron Carbide Nanoparticles
Supported iron carbide particles have long served as catalysts for CO hydrogenation (the Fischer Tropsch synthesis, FTS) and continue to be attractive. Despite this, little is known about their chemistry. Reported here is a colloidal Fe x C nanoparticle (NP) model system that allows direct observation of surface hydrogen and CO, as well as quantification of the surface H. Dodecylamine-capped Fe x C NPs (DDA-Fe x C NPs) were synthesized through solution-phase carburization of Fe NPs and form stable colloids in low-polarity organic solvents. Treatment of these colloids with H 2 or D 2 produced highly hydrogenated materials, and FTIR spectra of DDA-Fe x C-D n showed that most of the D binds to carbides, with at least four distinct v(C-D) modes. The surface C-H(D) bonds were all reactive, transferring hydrogen to alkenes and other reagents in solution. Titration and ICP measurements showed a 0.17:1 ratio of added H:total Fe, or roughly. 40 H per 1.8 nm DDA-Fe x C NP. Conversely, CO was preferentially bound to surface Fe sites, with FTIR spectra showing a single broad v(CO) that shifted with CO coverage or co-adsorption of H 2 . The DDA-Fe x C NPs were active catalysts for both olefin hydrogenation and the FTS, under mild conditions and without catalyst pre-treatment. The CO hydrogenation reactions yielded a broad distribution of long-chain linear paraffins and olefins. Though quantitative comparisons with typical FTS results are not possible because of our use of sealed batch reactors and other factors, the observations of high catalytic reactivity demonstrate the relevance of this model system to iron-carbide catalysis. DFT calculations on model slab surfaces with varying iron carbide stoichiometries revealed that the thermodynamically preferred surface adsorption sites are C for H ads and Fe for CO ads . A variety of binding sites and binding energies were found for each adsorbate. We are unaware of previous studies indicating that a diverse array of C-H bonds is the primary source of reactive H on iron carbides. Experimentally, the diversity of *C-H sites was evident in reactions with H-atom donors and abstractors of different strengths, from both the reaction stoichiometries and IR spectra. The different surface–H binding energies correlate with the v(C-D) stretching frequencies. Furthermore, these insights into complex iron carbide surfaces and catalysis could assist catalyst design, and they showcase the importance of stoichiometric studies of reaction intermediates.
08 HYDROGEN↗
Transforming Boron Carbon Nitride: A Carbon-to-Oxygen Switch to Boost Propane Oxidative Dehydrogenation
Hexagonal boron nitride (h-BN) catalysts exhibit high alkene selectivity in the oxidative dehydrogenation of propane (ODHP). Nevertheless, the conversion-selectivity trade-off persisted primarily due to the low density of oxygen-containing boron active species, while simple and controllable modification strategies for h-BN still face challenges. Herein, we developed an in situ carbon-to-oxygen switch strategy within a tailored boron carbon nitride (BCN) framework, in which uniformly embedded B–C 3 were transformed into B–O 3 via oxidative treatment (denoted as BNO x ). The structural evolution from B–C 3 to B–O 3 was well characterized by spectroscopy and soft X-ray absorption techniques. The resulting BNO x catalysts, enriched with B–O 3 units, demonstrated performance in ODHP, achieving a propane conversion of 50.4% with 32.7% olefin yield at 500 °C. Density functional theory (DFT) calculations confirmed that B–O 3 species preferentially lower activation barriers, rendering the process thermodynamically more favorable. In conclusion, this work introduced an in situ reconstruction method for atomic-level heteroatom-engineered h-BN catalysts, opening an avenue for advanced catalyst design across energy conversion systems.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Mechanistic Insights toward Accelerated Selenium-Catalyzed Allylic and Propargylic C–H Amination
Catalytic allylic and propargylic C–H aminations present valuable opportunities for the late-stage modification of pharmacophores in drug discovery. However, modern methodology is limited by reliance on expensive transition metal catalysts or slow reactivity. While selenium-catalyzed methods avoid some of these issues, in their current state, they require high catalyst loadings (15 mol %), superstoichiometric quantities of the amine and oxidant source, and long reaction times. Furthermore, our understanding of the mechanism remains incomplete: e.g., what is the catalytically active species, how is the precatalyst converted to it, and what is the role of the ligand? Here, in this paper, we report an N-heterocyclic carbene selenide (NHC-Se) that allows for substantially reduced loadings of selenium without sacrificing reaction time, improves conversions and yields for challenging substrates, and even exhibits the capacity to catalyze 1,4-allylic diamination of alkenes. To understand the origin of the enhanced activity compared to the state-of-the-art NHC-Se precatalyst, we conducted a mechanistic study that supports ligand-free selenium diimide as the active enophile in these systems, while the NHC-derived byproducts, like the corresponding urea, facilitate turnover. We also isolate and structurally characterize NHC-Se mono- and diimido species and explore their mechanistic role. Thus, this work advances C–H amination methodology, our understanding of its mechanistic underpinnings, and selenium chemistry at large.
allylic amination↗
Confinement of Lewis Acid–Base Sites by Microporous Silica Layers on Titania for Enhanced Alkanol Dehydration Reactivity
Alkanol dehydration offers a pathway to upgrade biomass-derived short-chain oxygenates into alkenes, essential chemical building blocks widely used in industrial applications. Transition metal oxides with Lewis acid-base site pairs are attractive catalysts due to their high reactivity and cost-effectiveness. This work demonstrates a synthetic pathway to manipulate local environments around active Lewis acid-base pairs in anatase TiO 2 to enhance their reactivity in alkanol dehydration. Microporous SiO 2 layers with an average pore diameter of ~0.6 nm and a controlled thickness of 0.8-33 nm are deposited on anatase TiO 2 powders by using a molecular templated SiO 2 deposition method. The Lewis acid-base strength of accessible Ti-O pairs remains unchanged, as shown by temperature-programmed surface reactions of surface-bound formic acid-derived species and temperature-programmed desorption of pyridine. However, measured alkanol dehydration rates on confined Ti-O pairs are much higher (by up to 7-fold) than those on TiO 2 . The extent of rate enhancements depends on the reactant size and functional group positioning, suggesting that the rate enhancements reflect the interactions between the guest molecules (reactants and transition states) and the surrounding SiO 2 micropore environments. By providing a detailed synthetic procedure to tailor the local environments around active sites in bulk oxides, this approach offers an additional avenue for enhancing catalytic performance.
09 BIOMASS FUELS↗
Anthraquinone Flow Battery Reactants with Nonhydrolyzable Water-Solubilizing Chains Introduced via a Generic Cross-Coupling Method
Water-soluble anthraquinones (AQs) hold great promise serving as redox-active species in aqueous organic flow batteries. Systematic investigations into how the properties of redox molecules depend on the water-solubilizing groups (WSGs) and the way in which they are bound to the redox core are, however, still lacking. We introduce WSGs linked to anthraquinone by C=C bonds via a cross-coupling reaction and convert C=C to C–C bonds through hydrogenation. The anthraquinone and the WSGs are connected via (un)branched chains with (un)saturated bonds. We investigate the influence of chains and ionic ending groups on the redox potentials of the molecules and identify three important trends: (1) The electron-withdrawing ending groups can affect the redox potentials of AQs with two unsaturated hydrocarbons on the chains through π-conjugation. (2) For chains with two (un)saturated straight hydrocarbons, WSGs increase the redox potentials of the AQs in the order PO 3 2– < CO 2 – < SO 3 – . (3) AQs with (un)saturated chains at high pH possess desirably low redox potentials, high solubilities, and high stability. Disproportionation leads to the formation of anthrone, which can be regenerated to anthraquinone. Tautomerization results in the saturation of alkene chains, stabilizing the structure. Here, we utilize these observations to identify a potentially low-cost and long-lifetime negative electrolyte that demonstrates a temporal fade rate as low as 0.0128%/day when paired with a potassium ferrocyanide positive electrolyte.
25 ENERGY STORAGE↗
Investigating Particle Phase State Dependencies during a Historic Pacific Northwest Wildfire Event
The function and lifetime of an atmospheric particle are greatly dependent upon its phase state. Studying particle phase states from specific ambient source types is often challenging due to uncontrolled environmental conditions and multiple source contributions. However, a historic Pacific Northwest wildfire event occurred in September 2020, providing a rare opportunity to study a pseudo-single particle type ambient sample (i.e., wildfire) over time. Sampling was performed in Richland, Washington, capturing aged particles from shifting wildfire sources. In addition to source variability, temporal variation in wildfire particle phase state was observed from single particle analyses. Despite this, single particle elemental compositions were homogenous over time (=87% carbonaceous) with no significant temporal variation in organic functional group abundances within individual particles either (e.g., 4% relative standard deviation in alkene contributions). While particle composition is indeed known to affect phase state, water uptake appeared to be the most significant contributor to phase state variability amongst single particles here, as particle aspect ratios (related to phase state) linearly correlated with ambient relative humidity during sampling (R2 = 0.65). Therefore, while limited to a case study, meteorological considerations are found to convey greater comparative importance than particle composition for aged particle phase state predictions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Solvent-Free Dimerization of Isoprene at Ambient Temperature: A Green Route to Biofuel-Range Hydrocarbons
In order to achieve a net-zero carbon footprint by 2050, the global aviation industry must reduce its dependence on fossil fuels. In this regard, there is a global challenge to produce sufficient sustainable aviation fuel (SAF) from renewable sources. Isoprene is an intermediate molecule that can be derived from multiple biomass-based or biosynthetic routes. Here, in this work, we report a green route for the catalytic conversion of isoprene to hydrocarbons that are suitable for aviation fuel. By using an Amberlyst-15 catalyst without metal loading at ambient temperature (19–23 °C), as well as 40 °C, 50 °C, and 60 °C, isoprene was converted into olefinic precursors for SAF and/or blending with conventional aviation fuels. Specifically, at ambient temperature, the process achieved approximately 70 wt % conversion of isoprene with over 50 mol % carbon selectivity toward the aviation fuel range. The resulting SAF-range hydrocarbons were composed of iso-alkenes, branched olefinic monocyclic compounds, and bicyclic compounds, covering a wide range of aviation fuel components. Our work demonstrates, for the first time, the formation of diverse hydrocarbon families for SAF and/or aviation fuel blending at ambient temperature from isoprene.
09 BIOMASS FUELS↗
Isotopic Studies for Tracking Biogenic Carbon during Co-processing of Biomass and Vacuum Gas Oil
Co-processing bio-oils with petroleum-derived feeds in the existing multitrillion dollar refining and distribution infrastructure is an attractive option for introducing renewable energy into the fuels marketplace. Considerable research on co-processing bio-oils and vacuum gas oil (VGO) in fluid catalytic cracking units (FCC) using equilibrium catalysts (E-Cats) demonstrated that biomass-derived molecules decreased activity of and increased carbon laydown on E-Cat. In this work, 13 C-labeled biomass was co-processed with VGO using either an E-Cat or a proprietary zeolite Johnson Matthey catalyst (CP758), which is optimzed for upgrading biomass vapors in a riser reactor, to evaluate the fate of biogenic carbon in FCC products. The results from both catalysts indicate that biogenic carbon was incorporated into alkenes and aromatic hydrocarbons. While no biogenic carbon was found in linear alkanes, it was observed in cycloalkanes during experiments with E-Cat but not with CP758. All produced CO2 was biogenic as was most of the carbon laydown on the catalysts. Several partially deoxygenated biomass compounds, such as alkylphenols and benzofurans, unexpectedly contained small amounts of carbon from VGO. Although this study was conducted with labeled biomass and not bio-oil, it provides insights to reaction mechanisms for co-processing bio-oil and VGO in an FCC, which is required to develop catalysts that efficiently convert bio-oil components during FCC co-processing. This work also demonstrates that comprehensive catalyst development utilizing both biomass- and fossil-derived feeds is required to maximize the incorporation of biogenic carbon into transportation fuels.
09 BIOMASS FUELS↗
Thermodynamics and Mechanism of a Photocatalyzed Stereoselective [2 + 2] Cycloaddition on a CdSe Quantum Dot
Colloidal quantum dots (QDs) have shown promise over the last few decades for a range of applications including single photon emission, in vivo imaging and photocatalysis. Recent experiments demonstrated that QDs impart stereoselectivity to triplet excited-state [2+2] cycloaddition reactions of alkenes photocatalyzed by the QD through self-assembly of the reagent molecules on the QD surface, but these experiments did not reveal the precise geometries of surface-bound molecules or their interactions with surface atoms. Here, a theoretical mechanistic approach is used to study such interactions for [2+2] cycloadditions of 4-vinylbenzoic acid derivatives on CdSe QDs. Spin-polarized periodic density functional theory (DFT) and non-periodic DFT calculations are deployed to determine the origin of the selectivity for the syn diastereomer of the resultant tetrasubstituted cyclobutane product via atomistic modelling of the CdSe surface and substrates, and determination of the thermodynamic energies of reactions for each step, the intermolecular interactions between the substrates, and the triplet state reaction paths. The calculations indicate that reaction selectivity arises from preferred binding of pairs through intermolecular interactions of substrate molecules on the QD surface in a syn-precursor structure followed by dimerization after triplet excitation. Further, these mechanisms are generalizable to other metal-enriched QD surfaces that have a similar surface structure to CdSe, such as InSe or CdTe. Design principles for anti diastereomer derivatives are also discussed.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗