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Chloroaluminate ionic liquids selectively transform (waste) polyolefins into gasoline-range alkanes through tandem cracking-alkylation at temperatures below 100 °C. Further improvement of this process necessitates a deep understanding of the nature of the catalytically active species and the correlated performance in the catalyzing critical reactions for the tandem polyolefin deconstruction with isoalkanes at low temperatures. Here, we address this requirement by determining the nuclearity of the chloroaluminate ions and their interactions with reaction intermediates, combining in situ 27Al magic-angle spinning nuclear magnetic resonance spectroscopy, in situ Raman spectroscopy, Al K-edge X-ray absorption near edge structure spectroscopy, and catalytic activity measurement. Cracking and alkylation are facilitated by carbenium ions initiated by AlCl3-tert-butyl chloride (TBC) adducts, which are formed by the dissociation of Al2Cl7− in the presence of TBC. The carbenium ions activate the alkane polymer strands and advance the alkylation cycle through multiple hydride transfer reactions. In situ 1H NMR and operando infrared spectroscopy demonstrate that the cracking and alkylation processes occur synchronously; alkenes formed during cracking are rapidly incorporated into the carbenium ion-mediated alkylation cycle. The conclusions are further supported by ab initio molecular dynamics simulations coupled with an enhanced sampling method, and model experiments using n-hexadecane as a feed. The catalytic conversion of polyolefins into gasoline-range alkanes requires a comprehensive understanding of the catalytically active species and their corresponding performance. Here the authors tackle this need by examining the nuclearity of the chloroaluminate ions and their interactions with reaction intermediates. [ABSTRACT FROM AUTHOR]

Understanding the adsorption and reactivity of carboxylic acids on oxide surfaces is of great interest in catalysis for biomass upgrading via ketonization, a carbon–carbon coupling reaction. Herein, we investigate the adsorption and reaction of acetic acid on anatase TiO2(101) using scanning tunneling microscopy, infrared spectroscopy, temperature programmed reaction, and density functional theory calculations. We demonstrate the adsorption of acetic acid can form two intermediates: (1) dissociated, bidentate acetate with an associated bridging hydroxyl, and (2) molecular, monodentate acetic acid. The coexistence of ordered phases with increasing monolayer (ML) saturation coverages consisting of (1) pure acetate (0.5 ML), (2) mixed acetate/acetic acid (0.67 ML), (3) mixed acetate/acetic acid (1.0 ML) and (4) pure acetic acid demonstrates similar energetics for both acetate and acetic acid species. Under ultra-high vacuum conditions, the presence of both monodentate acetic acid and bidentate acetate was observed below room temperature, while solely bidentate acetate was observed up to 575 K. The deprotonation of acetic acid produces water at 280 K, while the thermal decomposition of bidentate acetate produces ketene and acetic acid at 645 K. This model study provides detailed insight into the stability and reactivity of carboxylic acid surface-bound intermediates, which could participate during ketonization reactions for biomass upgrading. [ABSTRACT FROM AUTHOR]

The analogy between single‐atom catalysts (SACs) and molecular catalysts predicts that the specific catalytic activity of these systems is constant. We provide evidence that this prediction is not necessarily true. As a case in point, we show that the specific activity over ceria‐supported single Pd atoms linearly increases with metal atom density, originating from the cumulative enhancement of CeO2 reducibility. The long‐range electrostatic footprints (≈1.5 nm) around each Pd site overlap with each other as surface Pd density increases, resulting in an observed deviation from constant specific activity. These cooperative effects exhaust previously active O atoms above a certain Pd density, leading to their permanent removal and a consequent drop in reaction rate. The findings of our combined experimental and computational study show that the specific catalytic activity of reducible oxide‐supported single‐atom catalysts can be tuned by varying the surface density of single metal atoms. [ABSTRACT FROM AUTHOR]

Keywords: CO oxidation; electrostatic effects; Pd/CeO2; reducible oxide supports EN CO oxidation electrostatic effects Pd/CeO2 reducible oxide supports 23028 23028 1 10/06/21 20211011 NES 211011 B Just like a well-played pool game b , single atom catalysts lead to novel and exciting catalytic routes. Back Cover: Surface Density Dependent Catalytic Activity of Single Palladium Atoms Supported on Ceria (Angew. CO oxidation, electrostatic effects, Pd/CeO2, reducible oxide supports. [Extracted from the article]

Sung June Cho, Roger Rousseau, Janos Szanyi, Ja Hun Kwak et al. stellen in ihrem Forschungsartikel auf S. 22951 eine kombinierte experimentelle und theoretische Studie vor, die die Rolle von Pd-Einzelatomen auf CeO SB 2 sb und die elektronischen Effekte in der CO-Oxidation beleuchtet. CO oxidation, electrostatic effects, Pd/CeO2, reducible oxide supports Keywords: CO oxidation; electrostatic effects; Pd/CeO2; reducible oxide supports EN CO oxidation electrostatic effects Pd/CeO2 reducible oxide supports 23212 23212 1 10/06/21 20211011 NES 211011 B Wie bei einem Billardspiel b können Einzelatomkatalysatoren zu neuen und aufregenden katalytischen Reaktionspfaden führen. [Extracted from the article]

Transforming polyolefin waste into liquid alkanes through tandem cracking-alkylation reactions catalyzed by Lewis-acid chlorides offers an efficient route for single-step plastic upcycling. Lewis acids in dichloromethane establish a polar environment that stabilizes carbenium ion intermediates and catalyzes hydride transfer, enabling breaking of polyethylene C-C bonds and forming C-C bonds in alkylation. Here, we show that efficient and selective deconstruction of low-density polyethylene (LDPE) to liquid alkanes is achieved with anhydrous aluminum chloride (AlCl3) and gallium chloride (GaCl3). Already at 60 °C, complete LDPE conversion was achieved, while maintaining the selectivity for gasoline-range liquid alkanes over 70%. AlCl3 showed an exceptional conversion rate of 5000 gLDPEmolcat-1h-1, surpassing other Lewis acid catalysts by two orders of magnitude. Through kinetic and mechanistic studies, we show that the rates of LDPE conversion do not correlate directly with the intrinsic strength of the Lewis acids or steric constraints that may limit the polymer to access the Lewis acid sites. Instead, the rates for the tandem processes of cracking and alkylation are primarily governed by the rates of initiation of carbenium ions and the subsequent intermolecular hydride transfer. Both jointly control the relative rates of cracking and alkylation, thereby determining the overall conversion and selectivity., (© 2024 Wiley-VCH GmbH.)

Increasing atmospheric concentrations of greenhouse gases due to industrial activity have led to concerning levels of global warming. Reducing carbon dioxide (CO 2 ) emissions, one of the main contributors to the greenhouse effect, is key to mitigating further warming and its negative effects on the planet. CO 2 capture solvent systems are currently the only available technology deployable at scales commensurate with industrial processes. Nonetheless, designing these solvents for a given application is a daunting task requiring the optimization of both thermodynamic and transport properties. Here, we discuss the use of atomic scale modeling for computing reaction energetics and transport properties of these chemically complex solvents. Theoretical studies have shown that in many cases, one is dealing with a rich ensemble of chemical species in a coupled equilibrium that is often difficult to characterize and quantify by experiment alone. As a result, solvent design is a balancing act between multiple parameters which have optimal zones of effectiveness depending on the operating conditions of the application. Simulation of reaction mechanisms has shown that CO 2 binding and proton transfer reactions create chemical equilibrium between multiple species and that the agglomeration of resulting ions and zwitterions can have profound effects on bulk solvent properties such as viscosity. This is balanced against the solvent systems needing to perform different functions (e.g., CO 2 uptake and release) depending on the thermodynamic conditions (e.g., temperature and pressure swings). The latter constraint imposes a "Goldilocks" range of effective parameters, such as binding enthalpy and p K a , which need to be tuned at the molecular level. The resulting picture is that solvent development requires an integrated approach where theory and simulation can provide the necessary ingredients to balance competing factors., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

The analogy between single-atom catalysts (SACs) and molecular catalysts predicts that the specific catalytic activity of these systems is constant. We provide evidence that this prediction is not necessarily true. As a case in point, we show that the specific activity over ceria-supported single Pd atoms linearly increases with metal atom density, originating from the cumulative enhancement of CeO 2 reducibility. The long-range electrostatic footprints (≈1.5 nm) around each Pd site overlap with each other as surface Pd density increases, resulting in an observed deviation from constant specific activity. These cooperative effects exhaust previously active O atoms above a certain Pd density, leading to their permanent removal and a consequent drop in reaction rate. The findings of our combined experimental and computational study show that the specific catalytic activity of reducible oxide-supported single-atom catalysts can be tuned by varying the surface density of single metal atoms., (© 2021 Wiley-VCH GmbH.)