Enabling Ethanol Dehydrogenation Catalysis by Postsynthetic Anion Exchange of Triazolate-Based Metal-Organic Frameworks.

Materials containing soft, polarizable elements are expanding the boundaries of catalytic properties, offering unique electronic communication and stability characteristics compared with their harder counterparts due to the enhanced covalent nature of metal-ligand interactions. However, integrating soft components like sulfur into metal-organic frameworks (MOFs) for catalytic applications remains a largely underexplored challenge. Here, we report the synthesis of a family of triazole-based MOFs and expand upon established postsynthetic anion exchange methods to incorporate sterically encumbered polarizable elements, such as alkyl thiolates.

Introducing metal-sulfur active sites in metal-organic frameworks via post-synthetic modification for hydrogenation catalysis.

Metal-sulfur active sites play a central role in catalytic processes such as hydrogenation and dehydrogenation, yet the majority of active sites in these compounds reside on the surfaces and edges of catalyst particles, limiting overall efficiency. Here we present a strategy to embed metal-sulfur active sites into metal-organic frameworks (MOFs) by converting bridging or terminal chloride ligands into hydroxide and subsequently into sulfide groups through post-synthetic modification. We apply this method to two representative MOF families: one featuring one-dimensional metal-chloride chains and another containing discrete multinuclear metal clusters.

Effect of surface modification on silica supported Ti catalysts for cyclohexene oxidation with vapor-phase hydrogen peroxide.

Surface modification grafting of organic moieties on a Lewis acid catalyst (silica supported Ti catalyst, Ti-SiO) alters the activation of HO in vapor-phase cyclohexene epoxidation. Grafting a fluorous group (1,1-perfluoro-octyl) suppresses activity of Ti-SiO. Conversely, grafting either a nonpolar group (octyl) or a polar aprotic group (triethylene glycol monomethyl ether) enhances rates and shifts selectivity toward -1,2-cyclohexanediol.

Precise Modulation of CO Sorption in TiCe-Oxo Clusters: Elucidating Lewis Acidity of the Ce Metal Sites and Structural Flexibility.

Investigating the structure-property correlation in porous materials is a fundamental and consistent focus in various scientific domains, especially within sorption research. Metal oxide clusters with capping ligands, characterized by intrinsic cavities formed through specific solid-state packing, demonstrate significant potential as versatile platforms for sorption investigations due to their precisely tunable atomic structures and inherent long-range order. This study presents a series of TiCe-oxo clusters with subtle variations in coordinated linkers and explores their sorption behavior.

Enhanced Catalytic Performance of a Ce/V Oxo Cluster through Confinement in Mesoporous SBA-15.

To increase catalytic efficiency, mesoporous supports have been widely applied to immobilize well-defined metal oxide clusters due to their ability to stabilize highly dispersed clusters. Herein, a redox-active heterometallic CeV-oxo cluster (CeV) was first presynthesized and then incorporated into mesoporous silica, SBA-15, via a straightforward impregnation method. Scanning transmission electron microscopy (STEM) and Fourier transform infrared spectroscopy (FTIR), in concert with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), verified the successful introduction of the CeV cluster inside the pore of SBA-15.

Interfacial Unit-Dependent Catalytic Activity for CO Oxidation over Cerium Oxysulfate Cluster Assemblies.

Atomically precise cerium oxo clusters offer a platform to investigate structure-property relationships that are much more complex in the ill-defined bulk material cerium dioxide. We investigated the activity of the MCe torus family (M = Cd, Ce, Co, Cu, Fe, Ni, and Zn), a family of discrete oxysulfate-based Ce rings linked by monomeric cation units, for CO oxidation. CuCe emerged as the best performing MCe catalyst among those tested, prompting our exploration of the role of the interfacial unit on catalytic activity.

Mechanistic Investigation of Enhanced Catalytic Selectivity toward Alcohol Oxidation with Ce Oxysulfate Clusters.

Ceria-based materials have been highly desired in photocatalytic reactions due to their redox properties and strong oxygen storage and transfer ability. Herein, we report the structures of one CeCe oxysulfate cluster and four MCe clusters (M = Cu, Ni, Co, and Fe) with the same Ce core. As noted, single-crystal X-ray diffraction confirmed the structures of CeCe and the MCe series, while Raman spectroscopy indicated an increase in oxygen defects upon the introduction of Cu and Fe ions.

Exploring mechanistic routes for light alkane oxidation with an iron-triazolate metal-organic framework.

In this work, we computationally explore the formation and subsequent reactivity of various iron-oxo species in the iron-triazolate framework Fe(μ-OH)(bbta) (Hbbta = 1,5-benzo(1,2-:4,5-')bistriazole) for the catalytic activation of strong C-H bonds. With the direct conversion of methane to methanol as the probe reaction of interest, we use density functional theory (DFT) calculations to evaluate multiple mechanistic pathways in the presence of either NO or HO oxidants. These calculations reveal that a wide range of transition metal-oxo sites - both terminal and bridging - are plausible in this family of metal-organic frameworks, making it a unique platform for comparing the electronic structure and reactivity of different proposed active site motifs.

Modulating Chemical Environments of Metal-Organic Framework-Supported Molybdenum(VI) Catalysts for Insights into the Structure-Activity Relationship in Cyclohexene Epoxidation.

Solid supports are crucial in heterogeneous catalysis due to their profound effects on catalytic activity and selectivity. However, elucidating the specific effects arising from such supports remains challenging. We selected a series of metal-organic frameworks (MOFs) with 8-connected Zr nodes as supports to deposit molybdenum(VI) onto to study the effects of pore environment and topology on the resulting Mo-supported catalysts.

MOF-enabled confinement and related effects for chemical catalyst presentation and utilization.

A defining characteristic of nearly all catalytically functional MOFs is uniform, molecular-scale porosity. MOF pores, linkers and nodes that define them, help regulate reactant and product transport, catalyst siting, catalyst accessibility, catalyst stability, catalyst activity, co-catalyst proximity, composition of the chemical environment at and beyond the catalytic active site, chemical intermediate and transition-state conformations, thermodynamic affinity of molecular guests for MOF interior sites, framework charge and density of charge-compensating ions, pore hydrophobicity/hydrophilicity, pore and channel rigidity flexibility, and other features and properties. Collectively and individually, these properties help define overall catalyst functional behaviour.

Heterometallic Ce/ V Oxo Clusters with Adjustable Catalytic Reactivities.

Heterometallic Ce/M oxo clusters are underexplored yet and can benefit from synergistic properties from combining cerium and other metal cations to produce efficient redox catalysts. Herein, we designed and synthesized a series of new CeV oxo clusters with different capping ligands: , (OTs: toluenesulfonic acid), and (NBSA: nitrobenzenesulfonic acid). Single crystal X-ray diffraction (SCXRD) for all three structures reveals a CeV cubane core formulated [Ce(VO)O] with cerium on the edges of the cube, vanadyl capping the faces, and sulfate on the corners.

Tandem InO-Pt/AlO catalyst for coupling of propane dehydrogenation to selective H combustion.

Tandem catalysis couples multiple reactions and promises to improve chemical processing, but precise spatiotemporal control over reactive intermediates remains elusive. We used atomic layer deposition to grow InO over Pt/AlO, and this nanostructure kinetically couples the domains through surface hydrogen atom transfer, resulting in propane dehydrogenation (PDH) to propylene by platinum, then selective hydrogen combustion by InO, without excessive hydrocarbon combustion. Other nanostructures, including platinum on InO or platinum mixed with InO, favor propane combustion because they cannot organize the reactions sequentially.

Vapor-Phase Cyclohexene Epoxidation by Single-Ion Fe(III) Sites in Metal-Organic Frameworks.

Heterogeneous catalysts supported on metal-organic frameworks (MOFs), which possess uniform porosity and crystallinity, have attracted significant interest for recent years due to the ease of active-site characterization via X-ray diffraction and the subsequent relation of the active site structure to the catalytic activity. We report the syntheses, structures, and oxidation catalytic activities of single-ion iron catalysts incorporated into the zirconium MOF . Single-ion iron catalysts with different counteranions were anchored onto the Zr node through postsynthetic solvothermal deposition.

Comparing GGA, GGA+U, and meta-GGA functionals for redox-dependent binding at open metal sites in metal-organic frameworks.

Metal-organic frameworks (MOFs) with open metal sites have been widely investigated for the selective adsorption of small molecules via redox mechanisms where charge transfer can take place between the binding site and the adsorbate of interest. Quantum-chemical screening methods based on density functional theory have emerged as a promising route to accelerate the discovery of MOFs with enhanced binding affinities toward various adsorbates. However, the success of this approach is linked to the accuracy of the underlying density functional approximations (DFAs).

High-Valent Metal-Oxo Species at the Nodes of Metal-Triazolate Frameworks: The Effects of Ligand Exchange and Two-State Reactivity for C-H Bond Activation.

Through quantum-chemical calculations, we investigate a family of metal-organic frameworks (MOFs) containing triazolate linkers, M X (BBTA) (M=metal, X=bridging anion, H BBTA=1H,5H-benzo(1,2-d:4,5-d')bistriazole), for their ability to form terminal metal-oxo sites and subsequently activate the C-H bond of methane. By varying the metal and bridging anion in the framework, we show how to significantly tune the reactivity of this series of MOFs. The electronic structure of the metal-oxo active site is analyzed for each combination of metal and bridging ligand, and we find that spin density localized on the oxo ligand is not an inherent requirement for low C-H activation barriers.

Tuning the Redox Activity of Metal-Organic Frameworks for Enhanced, Selective O Binding: Design Rules and Ambient Temperature O Chemisorption in a Cobalt-Triazolate Framework.

Metal-organic frameworks (MOFs) with coordinatively unsaturated metal sites are appealing as adsorbent materials due to their tunable functionality and ability to selectively bind small molecules. Through the use of computational screening methods based on periodic density functional theory, we investigate O and N adsorption at the coordinatively unsaturated metal sites of several MOF families. A variety of design handles are identified that can be used to modify the redox activity of the metal centers, including changing the functionalization of the linkers (replacing oxido donors with sulfido donors), anion exchange of bridging ligands (considering μ-Br, μ-Cl, μ-F, μ-SH, or μ-OH groups), and altering the formal oxidation state of the metal.

The Synthesis Science of Targeted Vapor-Phase Metal-Organic Framework Postmodification.

The postmodification of metal organic frameworks (MOFs) affords exceedingly high surface area materials with precisely installed chemical features, which provide new opportunities for detailed structure-function correlation in the field of catalysis. Here, we significantly expand upon the number of vapor-phase postmodification processes reported to date through screening a library of atomic layer deposition (ALD) precursors, which span metals across the periodic table and which include ligands from four distinct precursor classes. With a large library of precursors and synthesis conditions, we discern trends in the compatibility of precursor classes for well-behaved ALD in MOFs (AIM) and identify challenges and solutions to more precise postsynthetic modification.

Direct Visualization of Independent Ta Centers Supported on Two-Dimensional TiO Nanosheets.

Highly dispersed, supported oxides are ubiquitous solid catalysts but can be challenging to characterize with atomic precision. Here, it is shown that crystalline anatase TiO nanosheets (∼5 nm thick) are ideal supports for imaging highly dispersed active sites. Ta cations were deposited by several routes, and high-resolution high angle annular dark-field scanning transmission electron microscopy was used to determine the location of Ta with respect to the TiO lattice and quantify Ta-Ta distances.

Identifying promising metal-organic frameworks for heterogeneous catalysis via high-throughput periodic density functional theory.

Metal-organic frameworks (MOFs) are a class of nanoporous materials with highly tunable structures in terms of both chemical composition and topology. Due to their tunable nature, high-throughput computational screening is a particularly appealing method to reduce the time-to-discovery of MOFs with desirable physical and chemical properties. In this work, a fully automated, high-throughput periodic density functional theory (DFT) workflow for screening promising MOF candidates was developed and benchmarked, with a specific focus on applications in catalysis.

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.

Photo-Initiated Reduction of CO by H on Silica Surface.

The reduction of CO is a promising route to produce valuable chemicals or fuels and create C-neutral resource cycles. Many different approaches to CO reduction have been investigated, but the ability of vacuum UV (VUV) irradiation to cleave C-O bonds has remained largely unexplored for use in processes that convert CO into useful products. Compared with other photo-driven CO conversion processes, VUV-initiated CO reduction can achieve much greater conversion under common photochemical reaction conditions when H and non-reducible oxides are present.

Predicting NO Catalysis by Quantifying Ce from Surface and Lattice Oxygen.

Our work introduces a novel technique based on the magnetic response of Ce and molecular oxygen adsorbed on the surface of nanoceria and ceria-based catalysts that quantifies the number and type of defects and demonstrates that this information is the missing link that finally enables predictive design of NO catalysis in ceria-based systems. The new insights into ceria catalysis are enabled by quantifying the above for different ceria nanoparticle shapes (i.e.

Stable Metal-Organic Framework-Supported Niobium Catalysts.

Developing structurally well-defined, supported oxide catalysts remains a significant challenge. Here, we report the grafting of Nb(V) oxide sites onto the nodes of the Zr-based metal organic framework (MOF) NU-1000 as a stable, well-defined catalyst support. Nb(V) oxide was deposited with loadings up to 1.