Metallated porphyrinic metal−organic frameworks for CO2 conversion to HCOOH: A computational screening and mechanistic study

Microscopic Insights into the Catalytic Activity-Stability Trade-Off on Copper Nanoclusters for CO2 Hydrogenation to HCOOH

Lowly coordinated copper clusters are the most cost-effective benchmark catalysts for CO2 hydrogenation, but there is a meticulous balance between catalytic activity and stability. Herein, density functional theory (DFT) calculations are implemented to examine the catalytic performance of Cun nanoclusters (n = 4, 8, 16, 32) in CO2-to-HCOOH conversion. Facile activation of H2 is observed with significant electron transfer from Cun to antibonding orbitals of H2; conversely, the C-O bond of CO2 is poorly activated due to a low degree of orbital overlap. During the reaction, structural fluxionality occurs on Cu4 and Cu8 because of the low stability; however, negligible deformation is observed on Cu16 and Cu32. In addition, Cu16 achieves a good balance between the kinetics of each elementary reaction, which is, however, difficult to be maintained on Cu4, Cu8, and Cu32. Therefore, Cu16 satisfies the trade-off between activity and stability in CO2-to-HCOOH conversion. Energy decomposition analysis clarifies that the activation barrier of the second hydrogenation originates from the energy of hydride desorption, the electronic repulsion energy due to hydroxyl group formation, as well as the energy for local Cu-O bond cleavage. The high energy demand on the second hydrogenation is mainly sourced from the last term. From the bottom up, this work provides microscopic insights into the catalytic activity-stability trade-off in CO2 hydrogenation to HCOOH and would facilitate the rational design of advanced catalysts for the high-value utilization of CO2 exhaust gas.

Computational Exploration on Coupling Formic Acid Production with Propylene Synthesis via Catalytic Transfer Hydrogenation: The Role of 2 beyond Reverse Water Gas Shift Reaction

CO2-assisted propane dehydrogenation (CO2-ODHP) is emerging as an alternative route to the direct dehydrogenation of propane. Previous studies on CO2-ODHP have shown that the role of CO2 is to shift the reaction equilibrium toward the product side by consuming the produced H2 molecules via reverse water gas shift (RWGS) reaction. Since the ultimate fate of CO2 is to get reduced, we herein propose another pathway of CO2 reduction in the realm of CO2-ODHP─CO2 hydrogenation to formic acid (FA). With the objective of investigating the feasibility of this process, we, for the first time, carry out a computational investigation on coupling propane dehydrogenation with CO2 hydrogenation using a Ti-alkoxide-functionalized UiO-67 metal-organic framework. Analysis using the distortion/interaction model confirms that CO2 hydrogenation to FA is a preferred pathway over the RWGS reaction and hence can be realized in practice. Our study also highlights the importance of intersystem crossing, which provides an opportunity to access nonground state potential energy surfaces while undergoing chemical transformations. Again, subsequent addition of water molecules has shown to ease product desorption by 41 kcal/mol. Our study, therefore, hints at an unexplored role of CO2 beyond the RWGS reaction in oxidative propane dehydrogenation.

Metalation of metal-organic frameworks: fundamentals and applications

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.

An Update in Computational Methods for Environmental Monitoring: Theoretical Evaluation of the Molecular and Electronic Structures of Natural Pigment-Metal Complexes

Metals are beneficial to life, but the presence of these elements in excessive amounts can harm both organisms and the environment; therefore, detecting the presence of metals is essential. Currently, metal detection methods employ powerful instrumental techniques that require a lot of time and money. Hence, the development of efficient and effective metal indicators is essential. Several synthetic metal detectors have been made, but due to their risk of harm, the use of natural pigments is considered a potential alternative. Experiments are needed for their development, but they are expensive and time-consuming. This review explores various computational methods and approaches that can be used to investigate metal-pigment interactions because choosing the right methods and approaches will affect the reliability of the results. The results show that quantum mechanical methods (ab initio, density functional theory, and semiempirical approaches) and molecular dynamics simulations have been used. Among the available methods, the density functional theory approach with the B3LYP functional and the LANL2DZ ECP and basis set is the most promising combination due to its good accuracy and cost-effectiveness. Various experimental studies were also in good agreement with the results of computational methods. However, deeper analysis still needs to be carried out to find the best combination of functions and basis sets.

Computational Design of Single-atom Modified Ti-MOFs for Photocatalytic CO2 Reduction to C1 Chemicals

In this work, density functional theory (DFT) calculations were conducted to investigate a series of transition metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Ru, Rh, Pd, Ag, Hf, Ta, Os, Ir, and Pt) as single-atom components introduced into Ti-BPDC (BPDC=2,2'-bipyridine-5,5'-dicarboxylic acid) as catalysts (M/Ti-BPDC) for the photocatalytic reduction of CO2 . The results show that Fe/Ti-BPDC is the most active candidate for CO2 reduction to HCOOH due to its small limiting potential (-0.40 V). Ag, Cr, Mn, Ru, Zr, Nb, Rh, and Cu modified Ti-BPDC are also active to HCOOH since their limiting potentials are moderate although the reaction mechanisms are different across these materials. Most of the studied catalysts show poor activity and selectivity to CO product because the stability of *COOH/*OCOH intermediates is significantly weaker than *OCHO/*HCOO species. The moderate binding strength of *CO on Pd/Ti-BPDC is responsible for its superior catalytic activity toward CH3 OH generation. Electronic structural analysis was performed to uncover the origin of the activity trend for CO2 reduction to different products on M/Ti-BPDC. The calculation results indicate that the activity and selectivity of CO2 photoreduction can be effectively tuned by designing single-atom metal-based MOF catalysts.

Modulating the Energetics of C-H Bond Activation in Methane by Utilizing Metalated Porphyrinic Metal-Organic Frameworks

In recent years, much effort has been directed toward utilizing metal-organic frameworks (MOFs) for activating C-H bonds of light alkanes. The energy demanding steps involved in the catalytic pathway are the formation of metal-oxo species and the subsequent cleavage of the C-H bonds of alkanes. With the intention of exploring the tunability of the activation barriers involved in the catalytic pathway of methane hydroxylation, we have employed density functional theory to model metalated porphyrinic MOFs (MOF-525(M)). We find that the heavier congeners down a particular group have high exothermic oxo-formation enthalpies ΔH_O and hence are associated with low N₂O activation barriers. Independent analyses of activation barriers and structure-activity relationship leads to the conclusion that MOF-525(Ru) and MOF-525(Ir) can act as an effective catalysts for methane hydroxylation. Hence, ΔH_O has been found to act as a guide, in the first place, in choosing the optimum catalyst for methane hydroxylation from a large set of available systems.