Preferred Pathway Research Articles

Rational design of Mo2C nanosheets anchored on hierarchically porous carbon for boosting electrocatalytic N2 reduction to NH3

Electrocatalytic nitrogen reduction reaction (NRR) is promising for achieving ammonia (NH3) synthesis under ambient conditions, but restricted by the lack of efficient catalysts. Herein, 3D hierarchical architectures of Mo2C nanosheets supported on porous carbon matrix (Mo2C@C) are rationally designed for boosting the electrocatalytic NRR. The morphology engineering endows Mo2C@C electrocatalysts with hierarchically porous architectures, which can sufficiently expose the surface-active sites and enhance the mass diffusion and electron transfer. Moreover, the composition modulation strategy can not only retain the adequate adsorption of N2, but also restrict the hydrogen evolution reaction (HER). Accordingly, Mo2C@C electrocatalysts exhibit a high NH3 yield rate of 12.55 ± 1.04 μg/h/mg at −0.20 V vs. RHE and a well-balanced Faradaic efficiency. Theoretical calculations further confirm the strong N2 adsorption/activation on the Mo2C catalyst and the NRR mechanism of the preferred distal pathway. The morphology engineering and composition modulation strategies can be extended to other materials, guiding the rational design of efficient NRR catalysts.

Theoretical and Experimental Investigation of the Antioxidation Mechanism of Loureirin C by Radical Scavenging for Treatment of Stroke.

Recent pharmacological studies have shown that dragon's blood has an anti-cerebral ischemia effect. Loureirin C (LC), a kind of dihydrochalcone compound in dragon's blood, is believed to be play an important role in the treatment of ischemia stroke, but fewer studies for LC have been done. In this paper, we report the first experimental and theoretical studies on the antioxidation mechanism of LC by radical scavenging. The experimental studies show that LC has almost no effect on cell viability under 15 μM for the SH-SY5Y cells without any treatments. For the SH-SY5Y cells with oxygen and glucose deprivation-reperfusion (OGD/R) treatment, LC increased the viability of SH-SY5Y cells. The results of 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) and MitoSox Red experiments indicate that LC is very efficient in inhibiting the generation of the intracellular/mitochondrial reactive oxygen species (ROS) or removing these two kinds of generated ROS. The density functional theory (DFT) calculations allowed us to elucidate the antioxidation mechanisms of LC. Fukui function analysis reveals the radical scavenging of LC by hydrogen abstraction mechanism, the complex formation by e-transfer, and radical adduct formation (RAF) mechanism. Among the H-abstraction, the complex formation by e-transfer, and radical adduct formation (RAF) reactions on LC, the H-abstraction at O-H35 position by OH• is favorable with the smallest energy difference between the product and two reactants of the attack of OH• to LC of -0.0748 Ha. The bond dissociation enthalpies (BDE), proton affinities (PA), ionization potential (IP), proton dissociation enthalpy (PDE), and electron transfer enthalpy (ETE) were calculated to determine thermodynamically preferred reaction pathway for hydrogen abstraction mechanism. In water, IP and the lowest PDE value at O3-H35 position are lower than the lowest BDE value at O3-H35 position; 41.8986 and 34.221 kcal/mol, respectively, indicating that SEPT mechanism is a preferred one in water in comparison with the HAT mechanism. The PA value of O3-H35 of LC in water is -17.8594 kcal/mol, thus the first step of SPLET would occur spontaneously. The minimum value of ETE is higher than the minimum value of PDE at O3-H35 position and IP value, 14.7332 and 22.4108 kcal/mol, respectively, which suggests that the SEPT mechanism is a preferred one in water in comparison with the SPLET mechanism. Thus, we can draw a conclusion that the SEPT mechanism of is the most favorite hydrogen abstraction mechanism in water, and O-H35 hydroxyl group has the greatest ability to donate H-atoms.

Spatially and temporally understanding dynamic solid-electrolyte interfaces in carbon dioxide electroreduction.

The ubiquity of solid-liquid interfaces in nature and the significant role of their atomic-scale structure in determining interfacial properties have led to intensive research. Particularly in electrocatalysis, however, a molecular-level picture that clearly describes the dynamic interfacial structures and organizations with their correlation to preferred reaction pathways in electrochemical reactions remains poorly understood. In this review, CO2 electroreduction reaction (CO2RR) is spatially and temporally understood as a result of intricate interactions at the interface, in which the interfacial features are highly relevant. We start with the discussion of current understandings and model development associated with the charged electrochemical interface as well as its dynamic landscape. We further highlight the interactive dynamics from the interfacial field, catalyst surface charges and various gradients in electrolyte and interfacial water structures at interfaces under CO2RR working conditions, with emphasis on the interfacial-structure dependence of catalytic reactivity/selectivity. Significantly, a probing energy-dependent "in situ characterization map" for dynamic interfaces based on various complementary in situ/operando techniques is proposed, aiming to present a comprehensive picture of interfacial electrocatalysis and to provide a more unified research framework. Moreover, recent milestones in both experimental and theoretical aspects to establish the correct profile of electrochemical interfaces are stressed. Finally, we present key scientific challenges with related perspectives toward future opportunities for this exciting frontier.

Understanding the different deoxygenation reaction pathways of lauric acid over alumina-supported Ni and Co catalysts

Ni/Al2O3 and Co/Al2O3 perform differently in the conversion of aliphatic acids as evidenced by the preferred reaction pathways for both catalysts.

First-principles study on unidirectional proton transfer on anatase TiO2 (101) surface induced by external electric fields.

The electric field (EF) effect on hydrogen or proton transfer (PT) via hydroxyl groups on an anatase TiO2 (101) surface is examined using first-principles density functional theory and the modern theory of polarization. This study focuses on unidirectional surface PT caused by external EFs at various orientations toward the surface. The preferred PT pathway can change depending on the magnitude and direction of the EF. Detailed analysis reveals that the variation in the energy profile with the EF is significantly different from that determined by the classical electric work of an EF carrying a point charge. The EF effect on the energy profile of the PT is governed by the rearrangement of the chemical bond network at the interface between the water molecules and the surface.

Pyrazolone-type compounds (part II): in vitro and in silico evaluation of antioxidant potential; structure-activity relationship.

The pyrazolone class comprises a variety of hybrid compounds displaying diverse biological actions. Although studied for decades, these compounds are still of interest due to their facile chemical transformations. In our previous work, we presented the synthetic route of functionalised pyrazolone derivatives. The presence of pyrazolone structural motif in many drugs, such as edaravone, prompted us to investigate the antioxidant features of the selected compounds. In this paper, we provide an extensive in vitro and in silico description of the antioxidant properties of selected pyrazolone analogues. The obtained in vitro results revealed their great antiradical potency against the DPPH radical (IC50 values in the 2.6-7.8 μM range), where the best results were obtained for analogues bearing a catechol moiety. Density functional theory (DFT) was used to assess their antioxidant capacity from the thermodynamic aspect. Here, good agreement with in vitro results was achieved. DFT was employed for the prediction of the most preferable radical scavenging pathway, also. In polar solvents, the SPLET mechanism is a favourable scavenging route, whereas in nonpolar solvents the HAT is slightly predominant. Furthermore, antioxidant mechanisms were studied in the presence of relevant reactive oxygen species. The obtained values of the reaction enthalpies with the selected radicals revealed that HAT is slightly prevailing in polar solvents, while the SPLET mechanism is dominant in nonpolar solvents. Regarding the well-known antioxidant features of the drug edaravone, these findings represent valuable data for this pyrazolone class and could be used as the basis for further investigations.

On the mechanistic complexity of oxygen evolution: potential-dependent switching of the mechanism at the volcano apex.

The anodic four-electron oxygen evolution reaction (OER) corresponds to the limiting process in acidic or alkaline electrolyzers to produce gaseous hydrogen at the cathode of the device. In the last decade, tremendous efforts have been dedicated to the identification of active OER materials by electronic structure calculations in the density functional theory approximation. Most of these works rely on the assumption that the mononuclear mechanism, comprising the *OH, *O, and *OOH intermediates, is operative under OER conditions, and that a single elementary reaction step (most likely *OOH formation) governs the kinetics. In the present manuscript, six different OER mechanisms are analyzed, and potential-dependent volcano curves are constructed to comprehend the electrocatalytic activity of these pathways in the approximation of the descriptor Gmax(U), a potential-dependent activity measure based on the notion of the free-energy span model. While the mononuclear description mainly describes the legs of the volcano plot, corresponding to electrocatalysts with low intrinsic activity, it is demonstrated that the preferred pathway at the volcano apex is a strong function of the applied electrode potential. The observed mechanistic complexity including a switch of the favored pathway with increasing overpotential sets previous investigations aiming at the identification of reaction mechanisms and limiting steps into question since the entire breadth of OER pathways was not accounted for. A prerequisite for future atomic-scale studies on highly active OER catalysts refers to the evaluation of several mechanistic pathways so that neither important mechanistic features are overlooked nor limiting steps are incorrectly determined.

A new insight on the NO-CO reaction at the electronic level: homogeneous, E-R, and L-H mechanisms.

Carbonaceous surface, as one of the major carriers in coal combustion, was found to exert great influence on the nitric oxide with carbon monoxide (NO-CO) reaction. Although there have been some studies addressing the NO-CO reaction, the inherent mechanism remains obscure. In this work, some updated mechanisms with details were proposed at the electronic level. Using density functional theory calculations, the preferred pathways were identified with three channels consisting of homogeneous, Eley-Rideal (E-R), and Langmuir-Hinshelwood (L-H) heterogeneous reactions. The reasons for the difference in energy barrier among the three mechanisms were revealed by analyzing the chemical bond and electronic transfer. Results show that among these channels, the NO-CO reaction is more likely to occur along the E-R mechanism, due to its lower energy barrier of the rate-determining step. Compared to the L-H mechanism, there is a higher degree of electronic localization between NO molecules at the initial stage of the E-R mechanism. As a result, the NO dimer formation of the E-R mechanism has a lower energy barrier than that of the L-H mechanism. Meanwhile, a large number of electrons floods into the N-N, N-O, and O-O bonds of NO dimer in the homogeneous reaction, which certainly gets more difficult for the dissociation of O atoms in the gas phase. Accordingly, the following stage of N2 formation in the homogeneous reaction has a higher energy barrier than that in both the E-R and L-H reactions. Compared to the L-H mechanism, the E-R mechanism exhibits a lower degree of electronic localization between N2O and carbonaceous surface, suggesting that the interfacial interaction in the E-R mechanism is weaker. As a result, N2 is easier to remove from the carbonaceous surface in the E-R mechanism than in the L-H mechanism. To sum up, the results deepen the knowledge about the NO-CO reaction, which will help to further develop the oxy-fuel combustion technology.

Theoretical study on the free radical scavenging potency and mechanism of natural coumestans: Roles of substituent, noncovalent interaction and solvent

The free radical scavenging potency and mechanisms of seven representative natural coumestans were systematically evaluated using density functional theory (DFT) approach. Thermodynamic feasibility of different mechanisms was assessed by various physio-chemical descriptors involved in the double (2H+/2e‒) radical-trapping processes. Energy diagram and related transition state structures of the reaction between wedelolactone (WEL) and hydroperoxyl radical were constructed to further uncover the radical-trapping details. Results showed that the studied coumestans prefer to scavenge radicals via formal hydrogen atom transfer (fHAT) mechanism in the gas phase and non-polar environment, whereas sequential proton loss electron transfer (SPLET) is favored in polar media. Moreover, the feasibility of second fHAT and SPLET processes was also revealed. Sequential double proton loss double electron transfer (SdPLdET) mechanism represents the preferred pathway in aqueous solution at physiological pH. Our findings highlight the essential role of ortho-dihydroxyl group, noncovalent interaction and solvents on radical-trapping potency. 4′-OH in D-ring was found to be the most favorable site to trap radical for most of the studied coumestans, whereas 3-OH in A-ring for lucernol (LUN).

Moderating carbon dynamics in black soil by combined application of biochar and an artificial humic substance

AbstractThe mineralization and humification of organic matter triggered by added exogenous carbon are relevant to soil organic matter (SOM) turnover and stability. Biochar (BC) and artificial humic substance (A‐HS), two typical exogenous carbon materials, have not been jointly applied to seek to improve the soil carbon pool, which is contributed by the development of A‐HS which has not yet been used on a large‐scale. We surmise that the dynamic interactions occurring in combined application of BC and A‐HS are complex and deserve detailed attention. Herein, a continuous incubation experiment including relevant weather events (freezing, freezing–thawing, warming climates) was conducted for 180 days to observe the development of SOM in the different stages and under separate and mixed applications of A‐HS and BC. After 45 d cultivation period and the freezing phase, the relative mineralization rate of SOM was up to 6.4% (120 ml/kg A‐HS), 4.9% (2% BC) and 13.3% (for the combination of 120 ml/kg A‐HS and 2% BC), suggesting that the presence of A‐HS triggers an enhanced mineralization of SOM throughout freezing. However, the remaining SOM turned out to be more strongly humified and more stable, preserving the SOM through the warming season, as shown by ultraviolet fluorescence and high‐throughput sequencing. Overall, the dynamic interactions between BC and A‐HS are shown to be mainly mediated by biological activity and alterations of microbial community structure and the related metabolic preferred pathways, which vice versa can be influenced by the added carbon sources.

Nickel-Catalyzed N-Arylation of Sulfinamides: A Comparative Study versus Analogous Sulfonamide Cross-Couplings

Despite recent progress regarding the metal-catalyzed C–N cross-coupling of (hetero)aryl (pseudo)halides with NH substrates, such transformations involving sulfinamide nucleophiles are underdeveloped. Herein we report on Ni-catalyzed C–N cross-couplings of this type, employing primarily tert-butanesulfinamide (i.e., Ellman’s sulfinamide) as a test nucleophile. Inexpensive and abundant (hetero)aryl chlorides proved to be suitable reaction partners in such reactions when using (L)Ni(o-tol)Cl (L = CyPAd-DalPhos or PhPAd-DalPhos) precatalysts. We also present results of an experimental and computational study focusing on C–N reductive elimination involving newly prepared and isolated sulfinamido (L)Ni(o-tol)(NHS(O)tBu) complexes, in which deprotonation leading to the formation of the putative anionic nitrene species [(L)Ni(o-tol)(NS(O)tBu)]− represents the preferred pathway for C–N reductive elimination, in keeping with our past study of related sulfonamido complexes.

The role of coverage effects on the structure–sensitivity of formic acid electrooxidation on Pd surfaces

Direct formic acid (FA) fuel cells (DFAFCs) with Pd anode catalysts are promising for small portable applications. During the electrooxidation of formic acid (FAO), CO accumulates on the Pd electrocatalyst, thereby decreasing its performance. In this work, we use density functional theory (DFT; RPBE) to elucidate the significance of coverage effects on the structure–sensitivity of FAO over four low–index Pd surfaces: Pd(111), Pd(100), Pd(110), and Pd(211). We construct coverage–dependent Gibbs free energy diagrams and in agreement with experiment, predict that Pd(100) and Pd(211) are the most active surfaces. Additionally, we find that the presence of CO spectator species can alter the preferred electrooxidation pathway under different applied potentials. Such pathway transitions appear to be critical for rationalizing experimental trends regarding electrocatalytic activity and are only captured when coverage effects are accounted for. Insights derived from this work may facilitate the design of improved FAO electrocatalysts.

Individuals' preference on reading pathways influences the involvement of neural pathways in phonological learning.

Existing behavioral and neuroimaging studies revealed inter-individual variability in the selection of the two phonological routes in word reading. However, it is not clear how individuals' preferred reading pathways/strategies modulate the involvement of a certain brain region for phonological learning in a new language, and consequently affect their behavioral performance on phonological access. To address this question, the present study recruited a group of native Chinese speakers to learn two sets of artificial language characters, respectively, in addressed-phonology training (i.e., whole-word mapping) and assembled-phonology training conditions (i.e., grapheme-to-phoneme mapping). Behavioral results showed that the more lexical pathways participants preferred, the better they performed on newly-acquired addressed characters relative to assembled characters. More importantly, neuroimaging results showed that participants who preferred lexical pathway in phonological access show less involvement of brain regions for addressed phonology (e.g., the bilateral orbitofrontal cortex and right pars triangularis) in the processing of newly-acquired addressed characters. These results indicated that phonological access via the preferred pathway required less neural resources to achieve better behavioral performance. These above results provide direct neuroimaging evidence for the influence of reading pathway preference on phonological learning.

DFT Simulation-Based Design of 1T-MoS2 Cathode Hosts for Li-S Batteries and Experimental Evaluation.

The main challenge in lithium sulphur (Li-S) batteries is the shuttling of lithium polysulphides (LiPSs) caused by the rapid LiPSs migration to the anode and the slow reaction kinetics in the chain of LiPSs conversion. In this study, we explore 1T-MoS2 as a cathode host for Li-S batteries by examining the affinity of 1T-MoS2 substrates (pristine 1T-MoS2, defected 1T-MoS2 with one and two S vacancies) toward LiPSs and their electrocatalytic effects. Density functional theory (DFT) simulations are used to determine the adsorption energy of LiPSs to these substrates, the Gibbs free energy profiles for the reaction chain, and the preferred pathways and activation energies for the slow reaction stage from Li2S4 to Li2S. The obtained information highlights the potential benefit of a combination of 1T-MoS2 regions, without or with one and two sulphur vacancies, for an improved Li-S battery performance. The recommendation is implemented in a Li-S battery with areas of pristine 1T-MoS2 and some proportion of one and two S vacancies, exhibiting a capacity of 1190 mAh/g at 0.1C, with 97% capacity retention after 60 cycles in a schedule of different C-rates from 0.1C to 2C and back to 0.1C.

Oxygen dissociation on the C3N monolayer: A first-principles study

The oxygen dissociation and the oxidized structure on the pristine C3N monolayer in exposure to air are the inevitably critical issues for the C3N engineering and surface functionalization yet have not been revealed in detail. Using the first-principles calculations, we have systematically investigated the possible O2 adsorption sites, various O2 dissociation pathways and the oxidized structures. It is demonstrated that the pristine C3N monolayer shows more O2 physisorption sites and exhibits stronger O2 adsorption than the pristine graphene. Among various dissociation pathways, the most preferable one is a two-step process involving an intermediate state with the chemisorbed O2 and the barrier is lower than that on the pristine graphene, indicating that the pristine C3N monolayer is more susceptible to oxidation than the pristine graphene. Furthermore, we found that the most stable oxidized structure is not produced by the most preferable dissociation pathway but generated from a direct dissociation process. These results can be generalized into a wide range of temperatures and pressures using ab initio atomistic thermodynamics. Our findings deepen the understanding of the chemical stability of 2D crystalline carbon nitrides under ambient conditions, and could provide insights into the tailoring of the surface chemical structures via doping and oxidation.

Rapid Screening of Mechanistic Pathways for Oxygen‐Reduction Catalysts

AbstractOxygen reduction reaction (ORR) corresponds to the limiting process in fuel cells to convert gaseous hydrogen and oxygen from the air into electricity. Most commonly, electronic structure calculations in the density functional theory (DFT) approximation are applied to comprehend the elementary reaction steps on the atomic scale, including the identification of limiting reaction steps and approximation of electrocatalytic activity. A major challenge in the modeling of the ORR refers to the complexity of the mechanistic pathways given that a plethora of different descriptions, ranging from the mononuclear to OOH dissociation mechanisms, dissociative and oxide pathways, have been reported in the literature. In the present work, the adsorption free energy of the *OH intermediate, ΔG1, is introduced as an effective descriptor for rapid screening of ORR mechanisms. By applying a rigorous thermodynamic analysis in conjunction with a descriptor‐based approach, it is demonstrated how the calculation of a single binding energy in terms of ΔG1 can be used to identify the energetically favored mechanistic description for any ORR catalyst by analyzing the location of the material in the volcano plot. The introduced procedure may support future DFT‐based studies in that the preferred pathway is not missed when modeling the four‐electron ORR by a binding‐energy approach.

Insights into the complexation and oxidation of quercetin and luteolin in aqueous solutions in presence of selected metal cations

Flavonoids are natural antioxidants that can be used for the chelation of metal ions to treat metal toxicity. Ideal chelators should form stable metal complexes and be resistant to oxidative degradation reactions in aqueous solutions at physiological conditions (pH 7.4 and 37 °C). In this work, the complexation and oxidation of quercetin and luteolin with selected metal cations (i.e. Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), and Al(III)) in aqueous solutions at pH 4 and 7.4 is discussed. Using UV–Vis, RP-UHPLC-PDA-MS, ESI-MS and 1H NMR, information about the complexing ability, stoichiometry, and the preferred metal binding sites was obtained. At pH 7.4, all metal ions were complexed by luteolin and quercetin, whereas at pH 4 both flavonoids only formed complexes with the trivalent metal cations (i.e. Cr(III), Fe(III), and Al(III)). No clear preference for any of the complexation sites was observed for quercetin and luteolin. UV–Vis and RP-UHPLC-PDA-MS showed that, at pH 7.4, chelation of quercetin was followed by metal-mediated oxidation resulting in degradation of quercetin. On the contrary, luteolin complexes with metal cations were stable and no oxidative degradation of luteolin was observed. The oxidative degradation pathway of quercetin was investigated by incubation in H218O, which showed that the oxidation occurs via both oxygenation and hydroxylation mechanisms, the latter being the preferred pathway for the trivalent metal ions.Our results indicate that luteolin is a more suitable chelating agent of Al(III) and first-row transition metal cations due to its higher oxidative stability and its ability to form stable complexes in aqueous solutions at pH 7.4.

Two Theorems and Important Insight on How the Preferred Mechanism of Free Radical Scavenging Cannot Be Settled. Comment on Pandithavidana, D.R.; Jayawardana, S.B. Comparative Study of Antioxidant Potential of Selected Dietary Vitamins; Computational Insights. Molecules 2019, 24, 1646.

Totally ignoring that the five enthalpies of reaction-bond dissociation enthalpy (BDE), adiabatic ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA), and electron transfer enthalpy (ETE)-characterizing the three free radical scavenging mechanisms-direct hydrogen atom transfer (HAT), sequential electron transfer proton transfer (SET-PT), and stepwise proton loss electron transfer (SPLET)-are not independent of each other, a recent publication on the antioxidant activity of dietary vitamins compared various vitamins and "found" different quantities, which should be strictly equal by virtue of energy conservation. Aiming to clarify this point, as well as to avoid such mistakes in future studies and to unravel errors in the previous literature, in the present paper we formulate two theorems that any sound results on antioxidation should obey. The first theorem states that the sums of the enthalpies characterizing the individual steps of SET-PT and SPLET are equal: IP+PDE = PA+ETE (=H2). This is a mathematical identity emerging from the fact that both the reactants and the final products of SET-PT and SPLET are chemically identical. The second theorem, which is also a mathematical identity, states that H2 - BDE = IPH > 0, where IPH is the ionization potential of the H-atom in the medium (e.g., gas or solvent) considered. Due to their general character, these theorems may/should serve as necessary sanity tests for any results on antioxidant activity, whatever the method employed in their derivation. From a more general perspective, they should represent a serious word of caution regarding attempts to assign the preferred free radical scavenging pathway based merely on thermochemical descriptors.

Mechanistic Impacts of Metal Site and Solvent Identities for Alkene Oxidation over Carboxylate Fe and Cr Metal–Organic Frameworks

Isolated Fe(III) and Cr(III) sites contained in nanoporous voids of isoreticular carboxylate MIL-101(Fe) and MIL-101(Cr) are interrogated for their reactivity and selectivity of liquid-phase styrene oxidation by hydrogen peroxide (H2O2). Batch kinetic measurements in acetonitrile (MeCN) at 323 K showcase that both metal-normalized oxygenate production and H2O2 consumption rates are O(101) higher for MIL-101(Fe) than MIL-101(Cr). Thermodynamically consistent reaction pathways, constructed through spiking experiments, reveal complex interconnectivities between primary (styrene oxide, benzaldehyde) and secondary (styrene glycol, benzoic acid, phenylacetaldehyde) oxygenates. Though benzaldehyde is the majority product for both MIL-101(Fe) and MIL-101(Cr), isoconversion (Xstyrene = 7%) product distributions suggest intrinsic differences in preferred reaction pathways. Apparent energy barriers for all pathways are lower over MIL-101(Fe) than for MIL-101(Cr), conferred by metal electron affinity differences for primary oxygenate selectivity, while secondary (inter)conversion rates trend with acid site densities. Fitted rate laws, radical trapping, adsorption experiments, and complementary DFT calculations indicate surface-mediated reactions by H2O2-derived surface species that outcompete bound styrene, product oxygenate, solvent, and water molecules for both MIL-101(Fe) and MIL-101(Cr) in MeCN. Extracted enthalpic and entropic effects from temperature-dependent experiments (318–328 K) in MeCN and MeOH showcase the ability of hydrogen bonding solvents in locally hydrophilic environments to selectively stabilize primary oxygenate transition states and indicate additional confinement effects from microporous substructures in MIL-101(Fe) and MIL-101(Cr). Simplified rate expressions are expanded to encompass first-order catalyst deactivation rates through temporal metal leaching experiments and assert that metal leaching dominates MIL-101(Cr) catalyst inefficiencies, while a combination of metal leaching and other (ir)reversible site changes are present for MIL-101(Fe). Overall, this work combines kinetic, spectroscopic, numerical, and computational approaches to rigorously define reaction and deactivation mechanisms for styrene oxidation by H2O2 over isoreticular MIL-101(Fe) and MIL-101(Cr).

Reaction of CHCl[rad]− with HCHO and H2O: A theoretical study

To compare the ion–molecule reaction mechanism of CHCl− with HCHO and H2O, the DFT-BHandHLYP level of theory with the aug-cc-pVDZ basis set was used. Our theoretical findings show that the H-abstraction reaction pattern identified pathway 5 as the preferred pathway for the reactions of CHCl− + H2O. When the direct H- and O-abstraction data are examined, the intramolecular SN2 reaction pattern appears to be the preferred pathway for the CHCl− + HCHO reaction. The reaction between CHCl− and H2O should be less competitive based on the principal reactive pathways of CHCl− + HCHO. As a result, in the atmospheric process the reaction of HCHO with CHCl− may not be appreciably accelerated by the breakdown of HCHO with and without the H2O molecule.