Ruthenium-Substituted Polyoxoanion Serves as Redox Shuttle and Intermediate Stabilizer in Selective Electrooxidation of Ethylene to Ethylene Glycol.

The high carbon intensity of present-day ethylene glycol (EG) production motivates interest in electrifying ethylene oxidation. Noting poor kinetics in prior reports of the organic electrooxidation of small hydrocarbons, we explored the design of mediators that activate and simultaneously stabilize light alkenes. A ruthenium-substituted polyoxometalate (Ru-POM, {Si[Ru(HO)WO]}) achieves 82% faradaic efficiency in EG production at 100 mA/cm under ambient conditions.

Integrated CO Capture and Conversion by a Robust Cu(I)-Based Metal-Organic Framework.

Metal-organic frameworks (MOFs) have shown promise in both capturing CO under flue gas conditions and converting it into valuable chemicals. However, the development of a single MOF capable of capturing and selectively converting CO has remained elusive due to a lack of a harmonious combination of selectivity, water stability, and reactivity. For example, Cu(I)-based MOFs are particularly effective for CO conversion, but they do not typically exhibit selective CO adsorption and often suffer from instability in the presence of air and moisture.

Atomically Precise Single-Site Catalysts via Exsolution in a Polyoxometalate-Metal-Organic-Framework Architecture.

Single-site catalysts (SSCs) achieve a high catalytic performance through atomically dispersed active sites. A challenge facing the development of SSCs is aggregation of active catalytic species. Reducing the loading of these sites to very low levels is a common strategy to mitigate aggregation and sintering; however, this limits the tools that can be used to characterize the SSCs.

Selective visible-light photocatalysis of acetylene to ethylene using a cobalt molecular catalyst and water as a proton source.

The production of polymers from ethylene requires the ethylene feed to be sufficiently purified of acetylene contaminant. Accomplishing this task by thermally hydrogenating acetylene requires a high temperature, an external feed of H gas and noble-metal catalysts. It is not only expensive and energy-intensive, but also prone to overhydrogenating to ethane.

Catalytic Degradation of Polyethylene Terephthalate Using a Phase-Transitional Zirconium-Based Metal-Organic Framework.

Polyethylene terephthalate (PET) is utilized as one of the most popular consumer plastics worldwide, but difficulties associated with recycling PET have generated a severe environmental crisis with most PET ending its lifecycle in landfills. We report that zirconium-based metal-organic framework (Zr-MOF) UiO-66 deconstructs waste PET into the building blocks terephthalic acid (TA) and mono-methyl terephthalate (MMT) within 24 hours at 260 °C (total yield of 98 % under 1 atm H and 81 % under 1 atm Ar). Extensive structural characterization studies reveal that during the degradation process, UiO-66 undergoes an intriguing transformation into MIL-140A, which is another Zr-MOF that shows good catalytic activity toward PET degradation under similar reaction conditions.

Engineering Dendrimer-Templated, Metal-Organic Framework-Confined Zero-Valent, Transition-Metal Catalysts.

We describe and experimentally illustrate a strategy for synthesizing reactant-accessible, supported arrays of well-confined, sub-nanometer to 2 nm, metal(0) clusters and particles-here, copper, palladium, and platinum. The synthesis entails (a) solution-phase binding of metal ions by a generation-2 poly(amidoamine) (PAMAM) dendrimer, (b) electrostatic uptake of metalated, solution-dissolved, and positively charged dendrimers by the negatively charged pores of a zirconium-based metal-organic framework (MOF), NU-1000, and (c) chemical reduction of the incorporated metal ions. The pH of the unbuffered solution is known to control the overall charges of both the dendrimer guests and the hierarchically porous MOF.

Constant Change: Exploring Dynamic Oxygen Evolution Reaction Catalysis and Material Transformations in Strontium Zinc Iridate Perovskite in Acid.

While iridium-based perovskites have been identified as promising candidates for the oxygen evolution reaction (OER) in proton exchange membrane (PEM) electrolyzer applications, an improved fundamental understanding of these highly dynamic materials under reaction conditions is needed to inform more robust future catalyst design. Herein, we study the highly active SrIrZnO perovskite for the OER in acid by employing electrochemical experiments with and characterization techniques to understand the dynamic nature of this material at both short and long time scales. We observe initial intrinsic OER activity improvement with electrochemical cycling as well as an initial increase of Ir oxidation state under OER conditions via X-ray absorption spectroscopy.

Pushing the Limits on Metal-Organic Frameworks as a Catalyst Support: NU-1000 Supported Tungsten Catalysts for o-Xylene Isomerization and Disproportionation.

Acid-catalyzed skeletal C-C bond isomerizations are important benchmark reactions for the petrochemical industries. Among those, o-xylene isomerization/disproportionation is a probe reaction for strong Brønsted acid catalysis, and it is also sensitive to the local acid site density and pore topology. Here, we report on the use of phosphotungstic acid (PTA) encapsulated within NU-1000, a Zr-based metal-organic framework (MOF), as a catalyst for o-xylene isomerization at 523 K.

Size Effect of the Active Sites in UiO-66-Supported Nickel Catalysts Synthesized via Atomic Layer Deposition for Ethylene Hydrogenation.

Ni(II) ions have been deposited on the Zr nodes of a metal-organic framework (MOF), UiO-66, via an ALD-like process (ALD = atomic layer deposition). By varying the number of ALD cycles, three Ni-decorated UiO-66 materials were synthesized. A suite of physical methods has been used to characterize these materials, indicating structural and high-surface-area features of the parent MOF are retained.

Fine-Tuning the Activity of Metal-Organic Framework-Supported Cobalt Catalysts for the Oxidative Dehydrogenation of Propane.

Few-atom cobalt-oxide clusters, when dispersed on a Zr-based metal-organic framework (MOF) NU-1000, have been shown to be active for the oxidative dehydrogenation (ODH) of propane at low temperatures (<230 °C), affording a selective and stable propene production catalyst. In our current work, a series of promoter ions with varying Lewis acidity, including Ni(II), Zn(II), Al(III), Ti(IV) and Mo(VI), are anchored as metal-oxide,hydroxide clusters to NU-1000 followed by Co(II) ion deposition, yielding a series of NU-1000-supported bimetallic-oxo,hydroxo,aqua clusters. Using difference envelope density (DED) analyses, the spatial locations of the promoter ions and catalytic cobalt ions are determined.

Bridging Zirconia Nodes within a Metal-Organic Framework via Catalytic Ni-Hydroxo Clusters to Form Heterobimetallic Nanowires.

Metal-organic frameworks (MOFs), with their well-ordered pore networks and tunable surface chemistries, offer a versatile platform for preparing well-defined nanostructures wherein functionality such as catalysis can be incorporated. Notably, atomic layer deposition (ALD) in MOFs has recently emerged as a versatile approach to functionalize MOF surfaces with a wide variety of catalytic metal-oxo species. Understanding the structure of newly deposited species and how they are tethered within the MOF is critical to understanding how these components couple to govern the active material properties.

Metal-Organic Framework Supported Cobalt Catalysts for the Oxidative Dehydrogenation of Propane at Low Temperature.

Zr-based metal-organic frameworks (MOFs) have been shown to be excellent catalyst supports in heterogeneous catalysis due to their exceptional stability. Additionally, their crystalline nature affords the opportunity for molecular level characterization of both the support and the catalytically active site, facilitating mechanistic investigations of the catalytic process. We describe herein the installation of Co(II) ions to the Zr nodes of the mesoporous MOF, NU-1000, via two distinct routes, namely, solvothermal deposition in a MOF (SIM) and atomic layer deposition in a MOF (AIM), denoted as Co-SIM+NU-1000 and Co-AIM+NU-1000, respectively.

Sintering-Resistant Single-Site Nickel Catalyst Supported by Metal-Organic Framework.

Developing supported single-site catalysts is an important goal in heterogeneous catalysis since the well-defined active sites afford opportunities for detailed mechanistic studies, thereby facilitating the design of improved catalysts. We present herein a method for installing Ni ions uniformly and precisely on the node of a Zr-based metal-organic framework (MOF), NU-1000, in high density and large quantity (denoted as Ni-AIM) using atomic layer deposition (ALD) in a MOF (AIM). Ni-AIM is demonstrated to be an efficient gas-phase hydrogenation catalyst upon activation.

A Hafnium-Based Metal-Organic Framework as a Nature-Inspired Tandem Reaction Catalyst.

Tandem catalytic systems, often inspired by biological systems, offer many advantages in the formation of highly functionalized small molecules. Herein, a new metal-organic framework (MOF) with porphyrinic struts and Hf6 nodes is reported. This MOF demonstrates catalytic efficacy in the tandem oxidation and functionalization of styrene utilizing molecular oxygen as a terminal oxidant.

High activity carbide supported catalysts for water gas shift.

Nanostructured carbides are refractory materials with high surface areas that could be used as alternatives to the oxide materials that are widely used as support materials for heterogeneous catalysts. Carbides are also catalytically active for a variety of reactions, offering additional opportunities to tune the overall performance of the catalyst. In this paper we describe the synthesis of molybdenum carbide supported platinum (Pt/Mo(2)C) catalysts and their rates for the water gas shift reaction.

Communications: Developing relationships between the local chemical reactivity of alloy catalysts and physical characteristics of constituent metal elements.

We have used X-ray absorption spectroscopy and quantum chemical density functional theory calculations to identify critical features in the electronic structure of different sites in alloys that govern the local chemical reactivity. The measurements led to a simple model relating local geometric features of a site in an alloy to its electronic structure and chemical reactivity. The central feature of the model is that the formation of alloys does not lead to significant charge transfer between the constituent metal elements in the alloys, and that the local electronic structure and chemical reactivity can be predicted based on physical characteristics of constituent metal elements in their unalloyed form.