Benchtop-Stable Carbyl Iminopyridyl Ni Complexes for Olefin Polymerization.

Design of catalysts for Ni-catalyzed olefin polymerization predominantly focuses on ligand design rather than the activation process when attempting to achieve a broader scope of polyolefin micro- and macrostructures. Air-stable alkyl-or aryl-functionalized Ni precatalysts were designed which eliminate the need of in situ alkylating processes and are activated solely by halide abstraction to generate the cationic complex for olefin polymerization. These complexes represent an emerging class of olefin polymerization catalysts, enabling the study of various cocatalysts forming either inner- or outer-sphere ion pairs.

Rational design of nanoscale stabilized oxide catalysts for OER with OC22.

The efficiency of H production water electrolysis is limited by the sluggish oxygen evolution reaction (OER). As such, significant emphasis has been placed upon improving the rate of OER through the anode catalyst. More recently, the Open Catalyst 2022 (OC22) framework has provided a large dataset of density functional theory (DFT) calculations for OER intermediates on the surfaces of oxides.

Tailored Platinum Group Metal/Spinel Oxide Catalysts for Dynamically Enhanced Methane Oxidation.

A combined experimental and molecular modeling study identifies a family of spinel oxides that in combination with PGM (platinum group metals) provide enhanced methane oxidation activity. With a reduction in greenhouse gas (GHG) emissions urgently needed, there is renewed interest in the use of natural gas vehicles (NGVs) and engines (NGEs) for transportation, commerce, and industrial applications. NGVs and NGEs emit less CO than their petroleum-derived counterparts but may emit uncombusted methane, an even more potent GHG.

Deciphering the Olefin Isomerization-Polymerization Paradox of Palladium(II) Diimine Catalysts: Discovery of Simultaneous and Independent Pathways of Olefin Isomerization and Living Polymerization.

This work elucidates a long-standing unexplained paradox commonly observed within the polymerization of α-olefin using palladium (Pd)(II)-diimine catalysts, in which isomerization and living polymerization of α-olefins are both observed. With a classical mechanistic understanding of these complexes, this behavior is often dismissed and interpreted as experimental error. Herein, we present a comprehensive mechanistic investigation into this phenomenon that supports the existence of a novel mechanistic pathway for Pd(II)-diimine complexes.

Platinum Graphene Catalytic Condenser for Millisecond Programmable Metal Surfaces.

Accelerating catalytic chemistry and tuning surface reactions require precise control of the electron density of metal atoms. In this work, nanoclusters of platinum were supported on a graphene sheet within a catalytic condenser device that facilitated electron or hole accumulation in the platinum active sites with negative or positive applied potential, respectively. The catalytic condenser was fabricated by depositing on top of a -type Si wafer an amorphous HfO dielectric (70 nm), on which was placed the active layer of 2-4 nm platinum nanoclusters on graphene.

Spatiotemporal Coke Coupling Enhances -Xylene Selectivity in Highly Stable MCM-22 Catalysts.

Identifying zeolite catalysts that can simultaneously optimize -xylene selectivity and feed utilization is critical to toluene alkylation with methanol (TAM). Here, we show that zeolite MCM-22 (MWW) has an exceptional catalyst lifetime in the TAM reaction at high operating pressure, conversion, and selectivity. We systematically probe the catalytic behavior of active sites in distinct topological features of MCM-22, revealing that high -xylene yield and catalyst stability are predominantly attributed to sinusoidal channels and supercages, respectively.

Atomic Properties of Monoclinic AgSe Thin Film Grown on SrTiO Substrate by Molecular Beam Epitaxy.

Silver chalcogenides have attracted a great deal of interest due to their promise for exhibiting novel topological properties. Using scanning tunneling microscopy/spectroscopy (STM/S), we have characterized the atomic structure and electronic properties of a monoclinic AgSe thin film, similar to β-AgTe, grown on a SrTiO (STO)(001) substrate by molecular beam epitaxy (MBE). Three different types of AgSe atomic terminations are observed on the surface: (i) homogeneous hexagonal-like, (ii) rough mixed, and (iii) flat zigzag-striped structures.

Kinetics of H Adsorption at the Metal-Support Interface of Au/TiO Catalysts Probed by Broad Background IR Absorbance.

H adsorption on Au catalysts is weak and reversible, making it difficult to quantitatively study. We demonstrate H adsorption on Au/TiO catalysts results in electron transfer to the support, inducing shifts in the FTIR background. This broad background absorbance (BBA) signal is used to quantify H adsorption; adsorption equilibrium constants are comparable to volumetric adsorption measurements.

Ethylene Dehydroaromatization over Ga-ZSM-5 Catalysts: Nature and Role of Gallium Speciation.

Bifunctional catalysis in zeolites possessing both Brønsted and Lewis acid sites offers unique opportunities to tailor shape selectivity and enhance catalyst performance. Here, we examine the impact of framework and extra-framework gallium species on enriched aromatics production in zeolite ZSM-5. We compare three distinct methods of preparing Ga-ZSM-5 and reveal direct (single step) synthesis leads to optimal catalysts compared to post-synthesis methods.

Water Poisons H Activation at the Au-TiO Interface by Slowing Proton and Electron Transfer between Au and Titania.

Understanding the dynamic changes at the active site during catalysis is a fundamental challenge that promises to improve catalytic properties. While performing Arrhenius studies during H oxidation over Au/TiO catalysts, we found different apparent activation energies () depending on the feedwater pressure. This is partially attributed to changing numbers of metal-support interface (MSI) sites as water coverage changes with temperature.

Stabilizing the Interface between Sodium Metal Anode and Sulfide-Based Solid-State Electrolyte with an Electron-Blocking Interlayer.

Sulfide-based Na-ion conductors are promising electrolytes for all-solid-state sodium batteries (ASSSBs) because of high ionic conductivity and favorable formability. However, no effective strategy has been reported for long-duration Na cycling with sulfide-based electrolytes because of interfacial challenges. Here we demonstrate that a cellulose-poly(ethylene oxide) (CPEO) interlayer can stabilize the interface between sulfide electrolyte (NaSbS) and Na by shutting off the electron pathway of the electrolyte decomposition reaction.

H Oxidation over Supported Au Nanoparticle Catalysts: Evidence for Heterolytic H Activation at the Metal-Support Interface.

Water adsorbed at the metal-support interface (MSI) plays an important role in multiple reactions. Due to its importance in CO preferential oxidation (PrOx), we examined H oxidation kinetics in the presence of water over Au/TiO and Au/AlO catalysts, reaching the following mechanistic conclusions: (i) O activation follows a similar mechanism to that proposed in CO oxidation catalysis; (ii) weakly adsorbed HO is a strong reaction inhibitor; (iii) fast H activation occurs at the MSI, and (iv) H activation kinetics are inconsistent with traditional dissociative H chemisorption on metals. Density functional theory (DFT) calculations using a supported Au nanorod model suggest H activation proceeds through a heterolytic dissociation mechanism, resulting in a formal hydride residing on the Au and a proton bound to a surface TiOH group.

Finite Size Effects in Submonolayer Catalysts Investigated by CO Electrosorption on Pt/Pd(100).

A combination of scanning tunneling microscopy, subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS), and density functional theory (DFT) is used to quantify the local strain in 2D Pt clusters on the 100 facet of Pd and its effect on CO chemisorption. Good agreement between SNIFTIRS experiments and DFT simulations provide strong evidence that, in the absence of coherent strain between Pt and Pd, finite size effects introduce local compressive strain, which alters the chemisorption properties of the surface. Though this effect has been widely neglected in prior studies, our results suggest that accurate control over cluster sizes in submonolayer catalyst systems can be an effective approach to fine-tune their catalytic properties.

Synthesis Strategies for Ultrastable Zeolite GIS Polymorphs as Sorbents for Selective Separations.

Designing zeolites with tunable physicochemical properties can substantially impact their performance in commercial applications, such as adsorption, separations, catalysis, and drug delivery. Zeolite synthesis typically requires an organic structure-directing agent to produce crystals with specific pore topology. Attempts to remove organics from syntheses to achieve commercially viable methods of preparing zeolites often lead to the formation of impurities.

Synergistic Effects in Bimetallic Palladium-Copper Catalysts Improve Selectivity in Oxygenate Coupling Reactions.

Condensation reactions such as Guerbet and aldol are important since they allow for C-C bond formation and give higher molecular weight oxygenates. An initial study identified Pd-supported on hydrotalcite as an active catalyst for the transformation, although this catalyst showed extensive undesirable decarbonylation. A catalyst containing Pd and Cu in a 3:1 ratio dramatically decreased decarbonylation, while preserving the high catalytic rates seen with Pd-based catalysts.

Epitaxial Growth of ZSM-5@Silicalite-1: A Core-Shell Zeolite Designed with Passivated Surface Acidity.

The design of materials with spatially controlled chemical composition has potential advantages for wide-reaching applications that span energy to medicine. Here, we present a method for preparing a core-shell aluminosilicate zeolite with continuous translational symmetry of nanopores and an epitaxial shell of tunable thickness that passivates Brønsted acid sites associated with framework Al on exterior surfaces. For this study, we selected the commercially relevant MFI framework type and prepared core-shell particles consisting of an aluminosilicate core (ZSM-5) and a siliceous shell (silicalite-1).

The critical role of water at the gold-titania interface in catalytic CO oxidation.

We provide direct evidence of a water-mediated reaction mechanism for room-temperature CO oxidation over Au/TiO2 catalysts. A hydrogen/deuterium kinetic isotope effect of nearly 2 implicates O-H(D) bond breaking in the rate-determining step. Kinetics and in situ infrared spectroscopy experiments showed that the coverage of weakly adsorbed water on TiO2 largely determines catalyst activity by changing the number of active sites.

Water-mediated proton hopping on an iron oxide surface.

The diffusion of hydrogen atoms across solid oxide surfaces is often assumed to be accelerated by the presence of water molecules. Here we present a high-resolution, high-speed scanning tunneling microscopy (STM) study of the diffusion of H atoms on an FeO thin film. STM movies directly reveal a water-mediated hydrogen diffusion mechanism on the oxide surface at temperatures between 100 and 300 kelvin.