Favorable Reaction Pathway Research Articles

Contrasting Kinetics of Highly Similar Chloroalkane Reductive Dehalogenases.

Chloroform and trichloroethanes are pervasive groundwater contaminants for which bioremediation has been an effective treatment strategy. Reductive dehalogenase (RDase) enzymes from organohalide-respiring bacteria are essential for their remediation under anaerobic conditions. RDases are responsible for dehalogenating these chlorinated solvents, leading to their removal. This work explores the kinetic characteristics of three closely related Dehalobacter chloroalkane-reductases─TmrA, CfrA, and AcdA─and identifies differences between their activity on chloroform (CF), 1,1,1-trichloroethane (TCA), and 1,1,2-TCA. The side-by-side comparison of these enzymes has emphasized that TmrA and AcdA are specialized toward CF with both having a 4-fold higher maximum specific activity (Vmax) on CF than 1,1,1-TCA, whereas CfrA has very similar rates on both CF and 1,1,1-TCA. AcdA is the most sensitive to substrate inhibition by CF and 1,1,2-TCA and inhibition by a common cocontaminant trichloroethene. Finally, the reduction of 1,1,2-TCA, which can produce both 1,2-dichloroethane and vinyl chloride, was assessed for each enzyme. Interestingly, each enzyme has a distinct preference for the major product it produces, indicating a favored reaction pathway. Despite over 95% sequence identity, TmrA, CfrA, and AcdA exhibit substantial differences in kinetic behavior, highlighting the importance of understanding such nuances for informed bioremediation strategies.

Precisely Engineering of Ångström‐Scale Dual Single Atom Drive [Co‐O] Spin‐Orbit Coupling to Boost Lithium–Oxygen Batteries Electrocatalysis

AbstractDual‐atom catalysts (DACs) have emerged as a novel area of investigation in lithium–oxygen (Li‐O2) batteries due to their distinctive synergistic mechanisms. However, achieving precise control of the active site structure and unraveling the synergistic effects of bimetallic species remains a significant challenge. Here, the study reports a pre‐encapsulated pyrolysis strategy using a Co‐based Robson‐type binuclear complex as a precursor to mediate the synthesis of dual single‐atom Co (Co‐DAC) with precise angstrom‐scale inter‐site distance configuration, serving as an efficient catalyst for Li‐O2 batteries. The tailored structure induces significant charge redistribution, reducing crystal field splitting energy (ΔO). The high‐spin Co species generate a strong electronic driving force, forming flexible σ and δ‐like bonds with the crucial oxygen intermediate (*O). Simultaneously, enhanced Co‐O spin‐orbit coupling facilitates electron transport along the bridging O‐channel, forming highly active Co‐O‐O‐Co electron chains that synergistically adsorb *O, establishing a favorable reaction pathway. Significant optimization of Li‐O2 batteries redox kinetics is achieved based on the well‐defined local structure of dual single‐atom Co sites. This work enhances the understanding of the dependence between rational design of custom structures and corresponding electron transfer dynamics, while providing new strategies and theoretical guidance for DACs to help develop high‐performance Li‐O2 batteries.

Silver- and gold-catalyzed azide−alkyne cycloaddition by functionalized NHC-based polynuclear catalysts: Computational investigation and mechanistic insights

This study evaluated the catalytic efficiency of Au(I), Ag(I), and Cu(I) complexes in the azide‒alkyne cycloaddition (AAC) reaction through density functional theory (DFT) calculations. Cu(I) complexes exhibit superior catalytic performance, with lower energy barriers (8.8 kcal/mol) and a favorable Gibbs free energy of -0.9 kcal/mol in the key cycloaddition step, significantly outperforming Ag and Au complexes. Structural analysis revealed that shorter M−C bond lengths in the Cu complex contributed to increased stability. Additionally, the copper complex has a more negative Gibbs free energy for the formed metallacycle, indicating a thermodynamically favorable reaction pathway. Noncovalent interaction (NCI) and reduced density gradient (RDG) analyses of the Cu, Ag, and Au systems highlighted distinct interaction patterns influencing the reactivity. Furthermore, electron localization function (ELF) and localized orbital locator (LOL) analyses revealed bonding characteristics in those complexes. This study offers valuable insights into the mechanistic differences among Au(I), Ag(I), and Cu(I) complexes, paving the way for future research on enhancing the catalytic activity of copper, silver and gold complexes through ligand modification.

Kinetics and simulation of biodiesel production using a geopolymer heterogenous catalyst

This work aims to develop a comprehensive kinetic and simulation study of biodiesel production using waste cooking oil (WCO) catalyzed by blast furnace slag geopolymer (BFSG) as a heterogeneous catalyst. The kinetic investigation was established following the pseudo-first and second-order model using three reaction parameters, namely, the reaction temperature (40–60 °C), reaction time (4–8 h) and catalyst ratio (6–14 wt.%), while maintaining a constant methanol-to-oil composition of 40 wt.%. The geopolymer-catalyzed transesterification process was simulated using ChemCAD version 8.1.0, which incorporates the four major triglycerides (triolein, tripalmitin, tristearin and triolein) of WCO. The results of the transesterification reaction of WCO in a kinetic plug flow reactor (PFR) demonstrated a good fit of the data, with an R 2 above 0.96 in both cases. The pseudo-first-order (PFO) model revealed a more favorable reaction pathway, with an activation energy of 58.876 kJ.mol−1, as opposed to the value of 131.369 kJ.mol−1 obtained from the pseudo-second-order (PSO) analysis. The catalytic activity of BFSG yielded a maximum conversion of 99.18% at a 12 wt.% catalyst ratio. The study results demonstrated the effectiveness of the transesterification process catalyzed by BFSG as a promising low-cost technology for the biodiesel industry.

Near‐Unity Photothermal CO2 Hydrogenation to Methanol based on a Molecule/Nanocarbon Hybrid Catalyst

Solar‐driven CO2‐to‐methanol conversion provides an intriguing route for both solar energy storage and CO2 mitigation. For scalable applications, near‐unity methanol selectivity is highly desirable to reduce the energy and cost endowed by low‐value byproducts and complex separation processes, but so far has not been achieved. Here we demonstrate a molecule/nanocarbon hybrid catalyst composed of carbon nanotube‐supported molecularly dispersed cobalt phthalocyanine (CoPc/CNT), which synergistically integrates high photothermal conversion capability for affording an optimal reaction temperature with homogeneous and intrinsically‐efficient active sites, to achieve a catalytic activity of 2.4 mmol gcat‐1 h‐1 and selectivity of ~99% in direct photothermal CO2 hydrogenation to methanol reaction. Both theoretical calculations and operando characterizations consistently confirm that the unique electronic structure of CoPc and appropriate reaction temperature cooperatively enable a thermodynamic favorable reaction pathway for highly selective methanol production. This work represents an important milestone towards the development of advanced photothermal catalysts for scalable and cost‐effective CO2 hydrogenation.

Near-Unity Photothermal CO2 Hydrogenation to Methanol Based on a Molecule/Nanocarbon Hybrid Catalyst.

Solar-driven CO2-to-methanol conversion provides an intriguing route for both solar energy storage and CO2 mitigation. For scalable applications, near-unity methanol selectivity is highly desirable to reduce the energy and cost endowed by low-value byproducts and complex separation processes, but so far has not been achieved. Here we demonstrate a molecule/nanocarbon hybrid catalyst composed of carbon nanotube-supported molecularly dispersed cobalt phthalocyanine (CoPc/CNT), which synergistically integrates high photothermal conversion capability for affording an optimal reaction temperature with homogeneous and intrinsically-efficient active sites, to achieve a catalytic activity of 2.4 mmol gcat -1 h-1 and selectivity of ~99 % in direct photothermal CO2 hydrogenation to methanol reaction. Both theoretical calculations and operando characterizations consistently confirm that the unique electronic structure of CoPc and appropriate reaction temperature cooperatively enable a thermodynamic favorable reaction pathway for highly selective methanol production. This work represents an important milestone towards the development of advanced photothermal catalysts for scalable and cost-effective CO2 hydrogenation.

Palladium-Catalyzed [7 + 5] and Higher-Order Annulations of Oxa-1,n-dipoles: Synthesis of 12- to 15-Membered Lactones.

Macrolactones are commonly found in natural products and pharmaceuticals. Herein, we present Pd-catalyzed [7 + 5] and higher-order annulations between unprecedented oxa-1,n-dipoles (n = 7-9) with active enol lactones. This protocol enables the rapid synthesis of complex 12 to 15-membered lactones bearing internal E-alkenes. Density functional theory calculations have revealed the favorable reaction pathway and identified coordination interactions between active enol lactones and palladium centers of π-allyl dipole species as key factors in manipulating these dipoles in annulations.

Exploring carbon-based Cu-ZnO catalyst and substitutes for enhanced selective methanol production from CO2: An integrated experimental and computational study

Methanol, produced through the hydrogenation of carbon dioxide, is an essential intermediate compound that plays a crucial function in the production of various organic chemicals. Enhancing the design of copper-containing catalysts for the transformation of CO2 to methanol is a popular strategy in scientific literature, although challenges persist in advancing the efficiency of carbon dioxide transformation and the selectivity of methanol production. This research aims at creating CuZnO-M/rGO (M = Mg, Mn, and Cr) catalysts using an efficient method for selectively converting CO2 to methanol. By optimizing the operational parameters of this system, methanol productivity and CO2 conversion efficiency are enhanced. Under optimal conditions, a CO2 conversion rate of 23.5%, methanol selectivity of 90%, and a space-time yield of 0.47 gMeOH.gcat−1.h−1 were achieved with the CuZnO-MgO (5)/rGO catalyst. These levels were maintained over a 100-h period, demonstrating the stability of the catalyst system. These findings are highly consistent with the density functional theory (DFT) calculations, revealing that the CuZnO-MgO (5)/rGO catalyst possesses a −0.35 eV adsorption energy for CO2 and a favorable reaction pathway with the overpotential of 1.16 V towards methanol production emphasizing the high conversion and selectivity obtained.

Theoretically predicted innovative palladium stripe dopingcobalt(1 1 1) surface with excellent catalytic performance for carbon monoxide oxidative coupling to dimethyl oxalate

Pd-based catalysts are extensively employed to catalyze CO oxidative coupling to generate DMO, while the expensive price and high usage of Pd hinder its massive application in industrial production. Designing Pd-based catalysts with high efficiency and low Pd usage as well as expounding the catalytic mechanisms are significant for the reaction. In this study, we theoretically predict that Pd stripe doping Co(1 1 1) surface exhibits excellent performance than pure Pd(1 1 1), Pd monolayer supporting on Co(1 1 1) and Pd single atom doping Co(1 1 1) surface, and clearly expound the catalytic mechanisms through the density functional theory (DFT) calculation and micro-reaction kinetic model analysis. It is obtained that the favorable reaction pathway is COOCH3–COOCH3 coupling pathway over these four catalysts, while the rate-controlling step is COOCH3+CO+OCH3→2COOCH3 on Pd stripe doping Co(1 1 1) surface, which is different from the case (2COOCH3→DMO) on pure Pd(1 1 1), Pd monolayer supporting on Co(1 1 1) and Pd single atom doping Co(1 1 1) surface. This study can contribute a certain reference value for developing Pd-based catalysts with high efficiency and low Pd usage for CO oxidative coupling to DMO.

Are (100) facets of transition metal carbonitrides suitable as electrocatalysts for nitrogen reduction to ammonia at ambient conditions?

Sustainable and energy-efficient ammonia production requires facile nitrogen reduction for hydrogen preservation and inorganic fertilizers. A nitrogen reduction apparatus with optimal stability, selectivity, and activity for ambient temperatures and pressure is needed to catalyze ammonia synthesis. This paper describes the investigation of using transition metal carbonitrides as catalyst to reduce molecular nitrogen electrochemically to NH3 at room temperature and atmospheric pressure. Density functional theory calculations determine the competition among associative, dissociative, and Mars-van Krevelen mechanisms where in most cases the Mars-van Krevelen is a more favorable reaction pathway. VCN and NbCN are the best candidates for ammonia production via the Mars-van Krevelen mechanism at low onset potentials of −0.52 V and −0.53 V vs reversible hydrogen electrode on the (100) facets. These carbonitrides are predicted to favor nitrogen reduction reaction rather than hydrogen evolution reaction.

Promotional effect and mechanism of SiO2 on Cr-Al2O3 catalysts for N2O-assisted oxidative dehydrogenation of ethylbenzene

A series of Cr-SiO2-Al2O3 (abbreviated as Cr-Si-Al) catalysts were synthesized using an evaporation induced self-assembled (EISA) method and applied to the N2O-assisted dehydrogenation of ethylbenzene (EB), offering a versatile solution for greenhouse gas recycling and a novel pathway for styrene (ST) production. Notably, the Cr-5Si-Al catalyst calcinated at 850 °C exhibited remarkable performance with a high EB conversion of 71% and a good ST selectivity of 62%, resulting in an optimal ST yield of nearly 44%. To elucidate the impact of calcination temperature and reveal the underlying promoting mechanism, numerous types of characterization particularly in-situ DRIFTS were used. Results indicated that the Cr-5Si-Al-850 catalyst possessed a distinctively ordered mesoporous structure, which improved the specific surface area and facilitated the dispersion of active species. The interaction among the multiple species in the catalyst was enhanced under the high calcination temperatures, leading to an increased ratio of Cr6+ and Oα, and thus promoting the dehydrogenation of EB. Furthermore, in situ DRIFTS revealed two favorable reaction pathways: one involving the reaction between adsorbed N2O and EB, and the other involving the reaction between adsorbed EB and N2O. These pathways led to the formation of a similar intermediate, observed at a wavenumber of 1285 cm−1. The improved adsorption of EB played a pivotal role in the excellent catalytic performance of the Cr-5Si-Al-850 catalyst.

Barium concentration controlled phase evolution in molecular solution processing of Cu2BaSnS4 thin films for solar cells with improved optical and electrical properties

Recently, Cu2BaSnS4 (CBTS) has emerged as a leading candidate to improve cationic ordering, which limits performance of solar cells, in Cu2ZnSnS4 (CZTS) absorber layers. While non-toxic solution based approaches appear very attractive for the deposition of the CBTS layers, the formation of secondary phases stemming from poor control of composition must be suppressed. While preparing CBTS thin films from 2-methoxy ethanol based molecular solutions, we find critical dependence of phase evolution on the Ba concentration in the solution. From the systematic variation in molar concentration of cations and sulfurization parameters we have established the favourable reaction pathway leading to the formation of the single phase CBTS via intermediate solid-state binary and tertiary compounds. The resultant films exhibited significantly reduced effects of cation antisite disorder compared to CZTS as reflected from a symmetric room temperature photoluminescence peak. The films had a band gap of ∼2.0 eV and showed considerable white light sensitivity. Detailed electrical and electro-impedance measurements were carried out that revealed p-type conductivity with a carrier concentration of 1.7×1014 cm−3.

Descriptor‐Based Volcano Relations Predict Single Atoms for Hydroxylamine Electrosynthesis

AbstractHydroxylamine (NH2OH) is an important feedstock in fuels, pharmaceuticals, and agrochemicals. Nanostructured electrocatalysts drive green electrosynthesis of hydroxylamine from nitrogen oxide species in water. However, current electrocatalysts still suffer from low selectivity and manpower‐consuming trial‐and‐error modes, leaving unclear selectivity/activity origins and a lack of catalyst design principles. Herein, we theoretically analyze key determinants of selectivity/activity and propose the adsorption energy of NHO (Gad(*NHO)) as a performance descriptor. A weak *NH2OH binding affinity and a favorable reaction pathway (*NHO pathway) jointly enable single‐atom catalysts (SACs) with superior NH2OH selectivity. Then, an activity volcano plot of Gad(*NHO) is established to predict a series of SACs and discover Mn SACs as optimal electrocatalysts that exhibit pH‐dependent activity. These theoretical prediction results are also confirmed by experimental results, rationalizing our Gad(*NHO) descriptor. Furthermore, Mn−Co geminal‐atom catalysts (GACs) are predicted to optimize Gad(*NHO) and are experimentally proved to enhance NH2OH formation.

Descriptor-Based Volcano Relations Predict Single Atoms for Hydroxylamine Electrosynthesis.

Hydroxylamine (NH2OH) is an important feedstock in fuels, pharmaceuticals, and agrochemicals. Nanostructured electrocatalysts drive green electrosynthesis of hydroxylamine from nitrogen oxide species in water. However, current electrocatalysts still suffer from low selectivity and manpower-consuming trial-and-error modes, leaving unclear selectivity/activity origins and a lack of catalyst design principles. Herein, we theoretically analyze key determinants of selectivity/activity and propose the adsorption energy of NHO (Gad(*NHO)) as a performance descriptor. A weak *NH2OH binding affinity and a favorable reaction pathway (*NHO pathway) jointly enable single-atom catalysts (SACs) with superior NH2OH selectivity. Then, an activity volcano plot of Gad(*NHO) is established to predict a series of SACs and discover Mn SACs as optimal electrocatalysts that exhibit pH-dependent activity. These theoretical prediction results are also confirmed by experimental results, rationalizing our Gad(*NHO) descriptor. Furthermore, Mn-Co geminal-atom catalysts (GACs) are predicted to optimize Gad(*NHO) and are experimentally proved to enhance NH2OH formation.

Single-atom tailored atomically-precise nanoclusters for enhanced electrochemical reduction of CO2-to-CO activity

The development of facile tailoring approach to adjust the intrinsic activity and stability of atomically-precise metal nanoclusters catalysts is of great interest but remians challenging. Herein, the well-defined Au8 nanoclusters modified by single-atom sites are rationally synthesized via a co-eletropolymerization strategy, in which uniformly dispersed metal nanocluster and single-atom co-entrenched on the poly-carbazole matrix. Systematic characterization and theoretical modeling reveal that functionalizing single-atoms enable altering the electronic structures of Au8 clusters, which amplifies their electrocatalytic reduction of CO2 to CO activity by ~18.07 fold compared to isolated Au8 metal clusters. The rearrangements of the electronic structure not only strengthen the adsorption of the key intermediates *COOH, but also establish a favorable reaction pathway for the CO2 reduction reaction. Moreover, this strategy fixing nanoclusters and single-atoms on cross-linked polymer networks efficiently deduce the performance deactivation caused by agglomeration during the catalytic process. This work contribute to explore the intrinsic activity and stability improvement of metal clusters.

Diffusion-based generative AI for exploring transition states from 2D molecular graphs

The exploration of transition state (TS) geometries is crucial for elucidating chemical reaction mechanisms and modeling their kinetics. Recently, machine learning (ML) models have shown remarkable performance for prediction of TS geometries. However, they require 3D conformations of reactants and products often with their appropriate orientations as input, which demands substantial efforts and computational cost. Here, we propose a generative approach based on the stochastic diffusion method, namely TSDiff, for prediction of TS geometries just from 2D molecular graphs. TSDiff outperforms the existing ML models with 3D geometries in terms of both accuracy and efficiency. Moreover, it enables to sample various TS conformations, because it learns the distribution of TS geometries for diverse reactions in training. Thus, TSDiff finds more favorable reaction pathways with lower barrier heights than those in the reference database. These results demonstrate that TSDiff shows promising potential for an efficient and reliable TS exploration.

Mechanistic Insight into Lewis Acid-Catalyzed Cycloaddition of Bicyclo[1.1.0]butanes with Ketene: Bicyclo[1.1.0]butanes Serving as an Electrophile.

Lewis acid-catalyzed cycloaddition between bicyclo[1.1.0]butanes (BCBs) and unsaturated substrates has recently been demonstrated to be a powerful strategy for synthesizing bicyclo[2.1.1]hexanes. However, their reaction mechanisms remain elusive. This computational work explored the recently developed TMSOTf-catalyzed cycloaddition of BCB ketone to ketene and determined the rate-determining step as the activation of BCB ketone. Contrary to the previous proposal of BCB enolate as the active species, this work instead identified the catalytically active species to be a partially Lewis acid-activated BCB cation, which shows a greater electrophilicity and larger orbital interactions with ketene compared to those of the pristine BCB. The most favorable reaction pathway uniquely utilizes this activated BCB species as an electrophile to react with ketene as a nucleophile, while the previously proposed enolate is relatively inactive. Moreover, the in situ-generated TfO anion is revealed to be non-innocent, and its coordination mode and orientation could affect the reaction kinetics.

Mechanistic insights into NH3-assisted selective reduction of NO on CeO2: a first-principles microkinetic study on selectivity and activity.

To understand the activity- and selectivity-limiting factors of selective catalytic reduction of NO with NH3 (NH3-SCR) catalyzed by CeO2-based oxides, a molecular-level mechanistic exploration was performed on CeO2(110) using a first-principles microkinetic study. Herein, the favored reaction pathway for N2 formation on CeO2(110) is unveiled, which includes three key subprocesses. (i) NH3 adsorbs on the Cecus site and dissociates into *NH2 assisted by Olat; (ii) *NH2 preferentially couples with NO adsorbed on Olat (ONO#), forming *NH2NO on the Cecus site; (iii) *NH2NO undergoes dehydrogenation into *NHNO, which can be easily anchored by Ovac and can then decompose into N2. The quantitative microkinetic results show that the transfer of NHNO from Cecus to Ovac, rather than the further conversion of N2O to N2 on Ovac, emerges as the N2 selectivity-determining step on CeO2, in which Ovac plays a key role. The number of Ovac is an important factor determining the N2 selectivity of CeO2-based catalysts. The sensitivity analysis reveals that NH2NO formation, i.e., *NH2 + ONO# → *NH2NO + O#, is the rate-determining step for NH3-SCR on the CeO2 catalyst; accordingly, enhancing NH3 adsorption could be an effective strategy to boost the catalytic activity of CeO2 for NH3-SCR. In general, creating Ovac on CeO2 and introducing components (e.g., WO3) with strong NH3 adsorption would be efficient for designing CeO2-based catalysts with superior N2 selectivity and activity. These results could provide a consolidated theoretical basis for understanding and optimizing CeO2-based catalysts for NH3-SCR.

Urban waste upcycling to a recyclable solid acid catalyst for converting levulinic acid platform molecules into high-value products

The conversion of levulinic acid (LA) into alkyl levulinates is highly significant due to the wide range of applications for these products, including their use as fuel additives, solvents, and fragrances. In order to meet the growing need for environmentally friendly chemical production, this study takes a circular economy approach by upcycling a common urban waste, i.e., pine needles, to synthesize a robust heterogeneous acid catalyst, subsequently used to efficiently upgrade LA into levulinates. By utilizing a single-step procedure under mild operating conditions, the resulting PiNe–SO3H catalyst demonstrated good performances and flexibility in synthesizing diverse bio-derived levulinates. In fact, the catalyst showed an exceptionally broad range of applicability, resulting in isolated yields ranging from ̴ 46% to ̴ 93%, which is an unprecedented achievement. The catalyst's ability to be reused was tested, revealing remarkable performance for up to 10 consecutive cycles with negligible loss in efficiency. Additionally, a significant focus was directed towards developing a method that minimizes waste during the isolation process. This involved optimizing reaction conditions and rationalizing work-up procedures, resulting in low Environmental factor (E-factor) values ranging from 1.2 to 8.9. To comprehensively assess the overall environmental sustainability of the process, various additional green metrics were calculated, and the Ecoscale tool was employed as well. Furthermore, mechanistic investigations elucidated the favored reaction pathway, underscoring that, under the optimized conditions, the prevailing mechanism entails direct esterification, as opposed to the generation of a pseudo-ester intermediate.

Active MoS2-based electrode for green ammonia synthesis

Nitrogen electro-reduction under mild conditions is one promising alternative approach of the energy-consuming Haber-Bosch process for the artificial ammonia synthesis. One critical aspect to unlocking this technology is to discover the catalysts with high selectivity and efficiency. In this work, the N2-to-NH3 conversion on the functional MoS2 is fully investigated by density functional theory calculations since the layered MoS2 provides the ideal platform for the elaborating copies of the nitrogenase found in nature, wherein the functionalization is achieved via basal-adsorption, basal-substitution or edge-substitution of transition metal elements. Our results reveal that the edge-functionalization is a feasible strategy for the activity promotion; however, the basal-adsorption and basal-substitution separately suffer from the electrochemical instability and the NRR inefficiency. Specifically, MoS2 functionalized via edge W-substitution exhibits an exceptional activity. The energetically favored reaction pathway is through the distal pathway and a limiting potential is less than 0.20 V. Overall, this work escalates the rational design of the high-effective catalysts for nitrogen fixation and provides the explanation why the predicated catalyst have a good performance, paving the guidance for the experiments.