Computational Prediction of Metal Organic Frameworks Suitable for Molecular Infiltration as a Route to Development of Conductive Materials

The development of metal organic frameworks (MOFs) with high porosity, large surface area, and good electrical properties would offer opportunities for producing functionalized porous materials suitable for energy storage, conversion, and utilization. Realizing these applications remains challenging because of the limited numbers of electrically conductive porous MOFs that are known. We apply density functional theory (DFT) to assess a large number of potentially electrically conductive MOFs generated by infiltrating known materials with conjugated and redox-active 7,7,8,8-tetracyanquinododimethane (TCNQ) molecules. DFT results demonstrate that TCNQ coordinating with dimeric Cu paddlewheels can create molecular chains in a variety of MOFs. Several of these materials feature the formation of multiple dimensional conducting chains, making the materials promising for electrical conductivity

Theoretical Insights into the Selective Oxidation of Methane to Methanol in Copper-Exchanged Mordenite

Selective oxidation of methane to methanol is one of the most difficult chemical processes to perform. A potential group of catalysts to achieve CH₄ partial oxidation are Cu-exchanged zeolites mimicking the active structure of the enzyme methane monooxygenase. However, the details of this conversion, including the structure of the active site, are still under debate. In this contribution, periodic density functional theory (DFT) methods were employed to explore the molecular features of the selective oxidation of methane to methanol catalyzed by Cu-exchanged mordenite (Cu-MOR). We focused on two types of previously suggested active species, CuOCu and CuOOCu. Our calculations indicate that the formation of CuOCu is more feasible than that of CuOOCu. In addition, a much lower C–H dissociation barrier is located on the former active site, indicating that C–H bond activation is easily achieved with CuOCu. We calculated the energy barriers of all elementary steps for the entire process, including catalyst activation, CH₄ activation, and CH₃OH desorption. Our calculations are in agreement with experimental observations and present the first theoretical study examining the entire process of selective oxidation of methane to methanol

Ultrathin Cobalt Oxide Overlayer Promotes Catalytic Activity of Cobalt Nitride for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) plays a crucial role in various energy devices such as proton-exchange membrane fuel cells (PEMFCs) and metal–air batteries. Owing to the scarcity of the current state-of-the-art Pt-based catalysts, cost-effective Pt-free materials such as transition metal nitrides and their derivatives have gained overwhelming interest as alternatives. In particular, cobalt nitride (CoN) has demonstrated a reasonably high ORR activity. However, the nature of its active phase still remains elusive. Here, we employ density functional theory calculations to study the surface reactivity of rocksalt (RS) and zincblend (ZB) cobalt nitride. The performances of the catalysts terminated by the facets of (100), (110), and (111) are studied for the ORR. We demonstrate that the cobalt nitride surface is highly susceptible to oxidation under ORR conditions. The as-formed oxide overlayer on the facets of CoN_RS(100) and CoN_ZB(110) presents a significant promotional effect in reducing the ORR overpotential, thereby increasing the activity in comparison with those of the pure CoNs. The results of this work rationalize a number of experimental reports in the literature and disclose the nature of the active phase of cobalt nitrides for the ORR. Moreover, they offer guidelines for understanding the activity of other transition metal nitrides and designing efficient catalysts for future generation of PEMFCs

Identification of High-CO₂‑Capacity Cationic Zeolites by Accurate Computational Screening

Solid porous materials such as cationic zeolites have shown great potential in energy-efficient separation processes. Conventional adsorbent design involves ad-hoc and inefficient experimental evaluation of a large structural and compositional space. We developed a computational methodology to screen cationic zeolites for CO₂ separation processes with quantitative accuracy, and identified a number of novel high-performing materials. This study enabled us to develop an intuitive design workflow for selecting optimal materials and dramatically accelerate the development of industrially relevant separation processes

Nano-sized Metallic Nickel Clusters Stabilized on Dealuminated beta‑Zeolite: A Highly Active and Stable Ethylene Hydrogenation Catalyst

Supported Ni catalysts were synthesized using the beta-zeolite framework, with and without the framework Al, as a platform for dispersing Ni. The silanol nest sites of dealuminated zeolite beta provide isolated cationic Ni sites that can be reduced under relatively mild conditions to create highly dispersed metal clusters. Compared to the Ni sites present in Ni-[Al]-beta-19, Ni-[DeAl]-beta exhibit a 20-fold increase in the apparent reaction rate for C2H4 hydrogenation and is stable, with little deactivation over 16 h of catalysis. Ni K-edge X-ray absorption spectroscopy (XAS), as well as CO adsorption monitored with Fourier transform infrared spectroscopy, shows that in the oxidized Ni-[DeAl]-beta catalyst Ni reoccupies vacant silanol nests produced from dealumination. After reductive treatment, XAS shows that approximately 50% of Ni is reduced to metallic Ni, forming clusters that are approximately 1 nm in size. Scanning transmission electron microscopy images are consistent with the absence of large (>1 nm) metallic Ni clusters. These results indicate that [DeAl]-beta can be used to synthesize isolated cationic Ni sites as well as stabilize highly dispersed metal clusters that can be used as a highly active and stable C2H4 hydrogenation catalyst

Nature of Lone-Pair–Surface Bonds and Their Scaling Relations

We investigate the (surface) bonding of a class of industrially and biologically important molecules in which the chemically active orbital is a 2<i>p</i> electron lone pair located on an N or O atom bound via single bonds to H or alkyl groups. This class includes water, ammonia, alcohols, ethers, and amines. Using extensive density functional theory (DFT) calculations, we discover scaling relations (correlations) among molecular binding energies of different members of this class: the bonding energetics of a single member can be used as a descriptor for other members. We investigate the bonding mechanism for a representative (H₂O) and find the most important physical surface properties that dictate the strength and nature of the bonding through a combination of covalent and noncovalent electrostatic effects. We describe the importance of surface intrinsic electrostatic, geometric, and mechanical properties in determining the extent of the lone-pair–surface interactions. We study systems including ionic materials in which the surface positive and negative centers create strong local surface electric fields, which polarize the dangling lone pair and lead to a strong “electrostatically driven bond”. We emphasize the importance of noncovalent electrostatic effects and discuss why a fully covalent picture, common in the current first-principles literature on surface bonding of these molecules, is not adequate to correctly describe the bonding mechanism and energy trends. By pointing out a completely different mechanism (charge transfer) as the major factor for binding N- and O-containing unsaturated (radical) adsorbates, we explain why their binding energies can be tuned independently from those of the aforementioned species, having potential implications in scaling-driven catalyst discovery