Toward Base Heterogenization: A Zirconium Metal–Organic Framework/Dendrimer or Polymer Mixture for Rapid Hydrolysis of a Nerve-Agent Simulant

The base heterogenization is crucial for the practical applications of metal–organic frameworks (MOFs) as catalytic filters, such as masks or protective suits, for the deconstruction of chemical warfare agents (CWAs). Here, we performed the hydrolysis of a phosphate-based nerve agent simulant in the presence of different amine-based bases (i.e., a small organic molecule, dendrimers, and linear and branched polymers) using a Zr-MOF, NU-901, with 4,8-connected scu topology. Remarkably, the catalytic performances of NU-901 using the less-volatile branched polymers and dendrimers are comparable to the volatile N-ethylmorpholine solution

Linker Competition within a Metal–Organic Framework for Topological Insights

Efforts toward predictive topology within the design and synthesis of metal–organic frameworks (MOFs) have been extensively studied. Herein, we report an investigation of a linker competition for the nucleation of a Zr6-based mixed linker MOF. By varying the relative additions of two linkers and introducing prior seeding to the system, we discern that the scu topology is the kinetic product of the two competing linkers. Elemental mapping analysis indicates that the competing linkers are uniformly distributed throughout the MOF. The final ratios of the linkers in the dissolved MOFs align well with the initial synthetic ratio. Through the introduction of a prior nucleation phase to seed the system, the thermodynamic csq product is more readily achieved. The results reported will enhance the understanding of MOF growth process

Heteroatom-Doped Porous Carbons as Effective Adsorbers for Toxic Industrial Gasses

Ammonia (NH3), often stored in large quantities before being used in the production of fertilizer, and sulfur dioxide (SO2), a byproduct of fossil fuel consumption, particularly the burning of coal, are highly toxic and corrosive gases that pose a significant danger to humans if accidentally released. Therefore, developing advanced materials to enable their effective capture and safe storage is highly desired. Herein, advanced benzimidazole-derived carbons (BIDCs) with an exceptional capacity for NH3 and SO2 have been designed and tested. These heteroatom-doped porous carbon adsorbents were synthesized by thermolysis of imidazolate-potassium salts affording high surface area and controlled heteroatom content to optimize for rapid NH3 and SO2 gas uptake and release under practical conditions. According to gas uptake measurements, these nitrogen-doped carbons exhibit exceptional gas adsorption capacity, with BIDC-3-800 adsorbing 21.42 mmol/g SO2 at 298 K and 1 bar, exceeding most reported porous materials and BIDC-2-700 adsorbing 14.26 mmol/g NH3 under the same conditions. The NH3 uptake of BIDC-2-700 surpassed reported activated carbons and is among the best adsorbents including metal organic frameworks (MOFs). Our synthetic method allows for control over both textural and chemical properties of the carbon and enables heteroatom functionality to be incorporated directly into the carbon framework without the need for postsynthetic modification. These materials were also tested for recyclability; all adsorbents showed almost complete retention of their initial gas uptake capacity during recyclability studies and maintained their structural integrity and their previous adsorption capacity of both NH3 and SO2, highlighting their potential for practical application

Mechanistic Study on the Origin of the <i>Trans</i> Selectivity in Alkyne Semihydrogenation by a Heterobimetallic Rhodium–Gallium Catalyst in a Metal–Organic Framework

A heterobimetallic Rh-Ga active site installed onto the Zr6-oxide nodes of the metal organic framework (MOF) NU-1000 was previously shown to catalyze the semihydrogenation of alkynes to alkenes and, of interest, internal alkynes to trans-alkenes with high selectivity. A suite of mechanistic organometallic techniques and periodic density functional theory calculations have been applied to probe the semihydrogenation of diphenylacetylene (DPA) to (E)-stilbene, as a model catalytic reaction. Initial rates confirm that both DPA syn hydrogenation and cis- to trans-stilbene isomerization are faster than (E)-stilbene hydrogenation to bibenzyl by factors of 3 and 4.6, respectively. The semihydrogenation catalysis is first order with respect to catalyst and H2. For diphenylacetylene, the reaction is first order at low concentration but undergoes a sharp switchover to zeroth order when the alkyne concentration exceeds ∼40 equiv per Rh-Ga active site. The kinetic isotope effect for the reaction of diphenylacetylene with H2/D2 is 1.72(7), even though isotopic scrambling between H2 and D2 is facile under catalytic conditions. The Hammett study of p-X­(C6H4)­CCPh substrates, where X is NH2, OMe, CH3, F, CN, or NO2, yielded a small ρ value of −0.69(3), which is consistent with a concerted transition state in the rate-limiting step. The results collectively indicate that alkyne insertion into the Rh–H bond is rate limiting. An isotope labeling study of the cis- to trans-stilbene isomerization lends strong evidence that H2 is directly involved and is consistent with a β-hydride elimination pathway that sets the overall trans selectivity

Mechanistic Study on the Origin of the <i>Trans</i> Selectivity in Alkyne Semihydrogenation by a Heterobimetallic Rhodium–Gallium Catalyst in a Metal–Organic Framework

A heterobimetallic Rh-Ga active site installed onto the Zr6-oxide nodes of the metal organic framework (MOF) NU-1000 was previously shown to catalyze the semihydrogenation of alkynes to alkenes and, of interest, internal alkynes to trans-alkenes with high selectivity. A suite of mechanistic organometallic techniques and periodic density functional theory calculations have been applied to probe the semihydrogenation of diphenylacetylene (DPA) to (E)-stilbene, as a model catalytic reaction. Initial rates confirm that both DPA syn hydrogenation and cis- to trans-stilbene isomerization are faster than (E)-stilbene hydrogenation to bibenzyl by factors of 3 and 4.6, respectively. The semihydrogenation catalysis is first order with respect to catalyst and H2. For diphenylacetylene, the reaction is first order at low concentration but undergoes a sharp switchover to zeroth order when the alkyne concentration exceeds ∼40 equiv per Rh-Ga active site. The kinetic isotope effect for the reaction of diphenylacetylene with H2/D2 is 1.72(7), even though isotopic scrambling between H2 and D2 is facile under catalytic conditions. The Hammett study of p-X­(C6H4)­CCPh substrates, where X is NH2, OMe, CH3, F, CN, or NO2, yielded a small ρ value of −0.69(3), which is consistent with a concerted transition state in the rate-limiting step. The results collectively indicate that alkyne insertion into the Rh–H bond is rate limiting. An isotope labeling study of the cis- to trans-stilbene isomerization lends strong evidence that H2 is directly involved and is consistent with a β-hydride elimination pathway that sets the overall trans selectivity

Influence of Pore Size on Hydrocarbon Transport in Isostructural Metal–Organic Framework Crystallites

Hydrocarbon separations using porous materials such as metal–organic frameworks (MOFs) have been proposed to reduce the energy demands associated with current distillation-based methods. Despite the potential of these materials to distinguish hydrocarbons through thermodynamic or kinetic mechanisms, experimental data quantifying hydrocarbon transport in MOFs is lacking. Such mass transfer measurements are vital to elucidate structure–property relationships and design future high-performing separation materials. In this work, we aim to isolate the influence of pore size on hydrocarbon diffusion by studying a pair of isoreticular MOFs, Co2Cl2BBTA and Co2Cl2BTDD. We use a volumetric method to extract mass transport coefficients for six hydrocarbon probe molecules of varying size and chemical functionality. From these nonequilibrium mass transport measurements, we determine the rate-limiting diffusion mechanism and identify trends in hydrocarbon surface permeabilities in the MOFs based on pore size, hydrocarbon chain length, and temperature

Rapid Quantification of Mass Transfer Barriers in Metal–Organic Framework Crystals

Although mass transfer of molecules in and out of porous materials such as zeolites and metal–organic frameworks impacts many applications, the fast and reproducible measurement of intracrystalline diffusion and surface permeability in porous materials remains challenging. Here, we demonstrate how a commercially available volumetric adsorption instrument can be used to reliably obtain guest mass transfer rates in nanoporous materials. The measurements are rapid and allow for the determination of intracrystalline diffusion coefficients and surface permeabilities in multiple adsorbents simultaneously, as well as the parallel collection of their adsorptive properties. In addition to describing the experimental procedures in detail, we provide a user-friendly code to facilitate the data analysis to obtain the transport parameters from adsorption uptake experiments and to determine the rate limiting process. Using the metal–organic frameworks MOF-808, NU-1000, and UiO-66, we illustrate the reproducibility of this technique for different sample masses across a variety of pressures. Wider adoption of this methodusing commonly available equipmentshould contribute to a better understanding of mass transport in nanoporous materials

Ammonia Capture within Isoreticular Metal–Organic Frameworks with Rod Secondary Building Units

The efficient removal, capture, and recycling of ammonia (NH3) constitutes a demanding process; thus, the development of competent adsorbent materials is highly desirable. The implementation of metal–organic frameworks (MOFs), known for their tunability and high porosity, has attracted much attention for NH3 adsorption studies. Here, we report three isoreticular porphyrin-based MOFs containing aluminum (Al-PMOF), gallium (Ga-PMOF), and indium (In-PMOF) rod secondary building units with Brønsted acidic bridging hydroxyl groups. NH3 sorption isotherms in Al-PMOF demonstrated reversibility in isotherms. In contrast, the slopes of the adsorption isotherms in Ga-PMOF and In-PMOF were much steeper than those of Al-PMOF in lower pressure regions, with a decrease of NH3 adsorbed amounts observed between first cycle and second cycle measurements. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) suggested that the strength of the Brønsted acidic −OH sites was controlled by the identity of the metal, which resulted in stronger interactions between ammonia and the framework in Ga-PMOF and In-PMOF compared to Al-PMOF