Low Activation Energy Barrier Research Articles

Direct and efficient catalytic conversion of biomass-derived 2-methyltetrahydrofuran to 1,3-pentadiene via acid-base coupling of lanthanum phosphate

It is critical to increase the reaction selectivity and atom economy, avoid side reactions during the catalytic process, and achieve the desired single-target product. Here, an efficient and novel method of producing 1,3-pentadiene via the acid-base coupling of rare-earth phosphate-catalyzed dehydra-decyclization of 2-methyltetrahydrofuran (2-MTHF) is reported, resulting in a previously unreported 1,3-pentadiene yield of 97.2% at 350 ℃. This method efficiently addresses two significant problems encountered in the dehydra-decyclization of 2-MTHF to generate 1,3-pentadiene research: the occurrence of retro-Prins condensation and the competitive reaction of 1,4-pentadiene. Density-Functional-Theory calculations demonstrated that 2-MTHF was adsorbed on the surface of rare-earth phosphate catalysts in a multi-site parallel mode, resulting in a lower apparent activation energy and ring-opening energy barrier. Space-time investigations and in situ diffuse reflectance infrared Fourier transform spectroscopy provided evidence for direct synthesis of pentadiene on rare-earth phosphate catalysts with Lewis acid-base sites. The acid-base coupling catalysis was demonstrated by poisoning experiments. In-situ self-regeneration of Brønsted acid sites was confirmed by infrared spectroscopy of adsorbed pyridine, facilitating the isomerization of 1,4-pentadiene to 1,3-pentadiene. Therefore, a unique reaction pathway for the dehydra-decyclization of 2-MTHF on the surface of rare-earth phosphates was proposed, and a new rotational isomer was discovered.

Dearomative [2 + 1] Spiroannulation of Bromophenols with Electron-Deficient Alkenes.

A base-assisted dearomative [2 + 1] spiroannulation of p/o-bromophenols with activated olefins (methylenemalonates) to construct various cyclopropyl spirocyclohexadienone skeletons is reported. Furthermore, several other halophenols (X = Cl, I) were also tolerated in this process. Control experiments reveal a dearomative Michael addition of phenols at their halogenated positions to methylenemalonates, followed by intramolecular radical-based SRN1 dehalogenative cyclopropanation. However, according to the density functional theory (DFT) calculations, an SN2 dehalogenative cyclopropanation with the same low activation energy barrier should not be excluded. The utility of this method is showcased by gram-scale syntheses and transformations of the dearomatized products.

Synergetic Manipulation Mechanism of Single-Atom M-N4 and M-OH (M = Mn, Fe, Co, Ni) Sites for Ozone Activation: Theoretical Prediction and Experimental Verification.

Carbon-based single-atom catalysts (SACs) have been gradually introduced in heterogeneous catalytic ozonation (HCO), but the interface mechanism of O3 activation on the catalyst surface is still ambiguous, especially the effect of a surface hydroxyl group (M-OH) at metal sites. Herein, we combined theoretical calculations with experimental verifications to comprehensively investigate the O3 activation mechanisms on a series of conventional SAC structures with N-doped nanocarbon substrates (MN4-NCs, where M = Mn, Fe, Co, Ni). The synergetic manipulation effect of the metal atom and M-OH on O3 activation pathways was paid particular attention. O3 tends to directly interact with the metal atom on MnN4-NC, FeN4-NC, and NiN4-NC catalysts, among which MnN4-NC has the best catalytic activity for its relatively lower activation energy barrier of O3 (0.62 eV) and more active surface-adsorbed oxygen species (Oads). On the CoN4-NC catalyst, direct interaction of O3 with the metal site is energetically infeasible, but O3 can be activated to generate Oads or HO2 species from direct or indirect participation of M-OH sites. The experimental results showed that 90.7 and 82.3% of total organic carbon (TOC) was removed within 40 min during catalytic ozonation of p-hydroxybenzoic acid with MnN4-NC and CoN4-NC catalysts, respectively. Phosphate quenching, catalyst characterization, and EPR measurement further supported the theoretical prediction. This contribution provides fundamental insights into the O3 activation mechanism on SACs, and the methods and ideals could be helpful for future studies of environmental catalysis.

Mechanistic insights into the incorporation of higher alpha-olefins into acrylate copolymers via photoATRP

Visible light-driven SR & NI photoATRP with CuIIBr2/L yielded acrylate-α-olefin copolymers (Đ ≤ 1.13) incorporating up to 30% α-olefins. DFT revealed low activation energy barriers (14.3 kcal mol−1 and 17.8 kcal mol−1) for PCA2 and PCB2 formation.

Advancing Gold Redox Catalysis: Mechanistic Insights, Nucleophilicity-Guided Transmetalation, and Predictive Frameworks for the Oxidation of Aryl Gold(I) Complexes.

Gold redox catalysis, often facilitated by hypervalent iodine(III) reagents, offers unique reactivity but its progress is mainly hindered by an incomplete mechanistic understanding. In this study, we investigated the reaction between the gold(I) complexes [(aryl)Au(PR3 )] and the hypervalent iodine(III) reagent PhICl2 , both experimentally and computationally and provided an explanation for the formation of divergent products as the ligands bonded to the gold(I) center change. We tackled this essential question by uncovering an intriguing transmetalation mechanism that takes place between gold(I) and gold(III) complexes. We found that the ease of transmetalation is governed by the nucleophilicity of the gold(I) complex, [(aryl)Au(PR3 )], with greater nucleophilicity leading to a lower activation energy barrier. Remarkably, transmetalation is mainly controlled by a single orbital - the gold dx 2 -y 2 orbital. This orbital also has a profound influence on the reactivity of the oxidative addition step. In this way, the fundamental mechanistic basis of divergent outcomes in reactions of aryl gold(I) complexes with PhICl2 was established and these observations are reconciled from first principles. The theoretical model developed in this study provides a conceptual framework for anticipating the outcomes of reactions involving [(aryl)Au(PR3 )] with PhICl2 , thereby establishing a solid foundation for further advancements in this field.

Unlocking power of neighboring vacancies in boosting hydrogen evolution reactions on two-dimensional NiPS3 monolayer

This study investigates the effect of defect engineering on the catalytic activity of a NiPS3 monolayer catalyst for the hydrogen evolution reaction (HER). Three different types of vacancies on the basal plane of the monolayer are explored through a multi-step mechanism involving the dissociative adsorption of a water molecule and subsequent electrochemical adsorption of the dissociated proton. Co-formation of vacancies in both Ni and S sites is found to be the most effective in enhancing the catalytic performance of the monolayer. A key resource for the reaction thermodynamics is the S-substitution-like physisorption of a water molecule on a vacant S site, followed by the dissociative occupation of OH and H into vacant sites of S and Ni elements, boosted by the NiS di-vacancy configuration with low activation energy barriers. Investigation reveals the highest contribution of bonding orbitals to the monolayer-H bond makes it the most desirable defect engineering approach for transition metal phosphorus chalcogenides with high HER activities. Overall, this study highlights the significance of controlled defect engineering in augmenting the catalytic performance of NiPS3 monolayer catalysts for HER.

Contributions of CO2, O2, and H2O to the Oxidative Stability of Solid Amine Direct Air Capture Sorbents at Intermediate Temperature.

Aminopolymer-based sorbents are preferred materials for extraction of CO2 from ambient air [direct air capture (DAC) of CO2] owing to their high CO2 adsorption capacity and selectivity at ultra-dilute conditions. While those adsorptive properties are important, the stability of a sorbent is a key element in developing high-performing, cost-effective, and long-lasting sorbents that can be deployed at scale. Along with process upsets, environmental components such as CO2, O2, and H2O may contribute to long-term sorbent instability. As such, unraveling the complex effects of such atmospheric components on the sorbent lifetime as they appear in the environment is a critical step to understanding sorbent deactivation mechanisms and designing more effective sorbents and processes. Here, a poly(ethylenimine) (PEI)/Al2O3 sorbent is assessed over continuous and cyclic dry and humid conditions to determine the effect of the copresence of CO2 and O2 on stability at an intermediate temperature of 70 °C. Thermogravimetric and elemental analyses in combination with in situ horizontal attenuated total reflection infrared (HATR-IR) spectroscopy are performed to measure the extent of deactivation, elemental content, and molecular level changes in the sorbent due to deactivation. The thermal/thermogravimetric analysis results reveal that incorporating CO2 with O2 accelerates sorbent deactivation using these sorbents in dry and humid conditions compared to that using CO2-free air in similar conditions. The in situ HATR-IR spectroscopy results of PEI/Al2O3 sorbent deactivation under a CO2-air environment show the formation of primary amine species in higher quantity (compared to that in conditions without O2 or CO2), which arises due to the C-N bond cleavage at secondary amines due to oxidative degradation. We hypothesize that the formation of bound CO2 species such as carbamic acids catalyzes C-N cleavage reactions in the oxidative degradation pathway by shuttling protons, resulting in a low activation energy barrier for degradation, as probed by metadynamics simulations. In the cyclic experiment after 30 cycles, results show a gradual loss in stability (dry: 29%, humid: 52%) under CO2-containing air (0.04% CO2/21% O2 balance N2). However, the loss in capacity during cyclic studies is significantly less than that during continuous deactivation, as expected.

CO2 methanation over Ni nanoparticles inversely loaded with CeO2 and Cr2O3: Catalytic functions of metal oxide/Ni interfaces

Interfaces between active metal and metal oxide in a heterogenous catalyst often play an important role in catalysis. In this work, we intentionally synthesized a series of inverse CeO2-Cr2O3/Ni model catalysts with the formation of controlled CeO2-Ni and Cr2O3-Ni interfacial structures and investigated the roles of the oxide-metal interfaces in CO2 methanation performance through excluding the normal support effect. Experimental and DFT calculation results reveal that the formate pathway tends to occur on the catalyst with only CeO2-Ni interfaces. The Cr2O3-Ni interface formed after introducing Cr oxide alters the nearby CeO2-Ni interface by electron transfer through Ni, which brings an additional reaction pathway (CO pathway) on CeO2-Cr2O3/Ni. Furthermore, it shows a relatively lower CO2 absorption energy and activation energy barrier for CO2 dissociation to CO at the Cr2O3-Ni interface, favorable for CO2 activation and further hydrogenation, thus leading to excellent low-temperature activity.

Understanding the Activation of Anionic Redox Chemistry in Ti4+-Substituted Li2MnO3 as a Cathode Material for Li-Ion Batteries

Layered Li-rich oxides, demonstrating both cationic and anionic redox chemistry being used as positive electrodes for Li-ion batteries, have raised interest due to their high specific discharge capacities exceeding 250 mAh/g. However, irreversible structural transformations triggered by anionic redox chemistry result in pronounced voltage fade (i.e., lowering the specific energy by a gradual decay of discharge potential) upon extended galvanostatic cycling. Activating or suppressing oxygen anionic redox through structural stabilization induced by redox-inactive cation substitution is a well-known strategy. However, less emphasis has been put on the correlation between substitution degree and the activation/suppression of the anionic redox. In this work, Ti4+-substituted Li2MnO3 was synthesized via a facile solution-gel method. Ti4+ is selected as a dopant as it contains no partially filled d-orbitals. Our study revealed that the layered “honeycomb-ordered” C2/m structure is preserved when increasing the Ti content to x = 0.2 in the Li2Mn1–xTixO3 solid solution, as shown by electron diffraction and aberration-corrected scanning transmission electron microscopy. Galvanostatic cycling hints at a delayed oxygen release, due to an improved reversibility of the anionic redox, during the first 10 charge–discharge cycles for the x = 0.2 composition compared to the parent material (x = 0), followed by pronounced oxygen redox activity afterward. The latter originates from a low activation energy barrier toward O–O dimer formation and Mn migration in Li2Mn0.8Ti0.2O3, as deduced from first-principles molecular dynamics (MD) simulations for the “charged” state. Upon lowering the Ti substitution to x = 0.05, the structural stability was drastically improved based on our MD analysis, stressing the importance of carefully optimizing the substitution degree to achieve the best electrochemical performance.

Asymmetric Photoreactions in Supramolecular Assemblies.

ConspectusStereochemical control of excited-state asymmetric photoreactions has been one of the most challenging topics of modern photochemistry. The short-lived character of electronically excited photosubstrates and their low activation energy barriers to form both enantiomers are the major obstacles to achieving significant enantioselectivity in excited-state asymmetric photochemistry. Recent research demonstrated that the supramolecular strategy is promising to control the stereochemical outcome of asymmetric photoreaction through relatively strong and long-lasting noncovalent interaction at both ground and excited states. In this methodology, chiral hosts/assemblies provide the chiral environment for photochemically transferring chirality to the complexed photosubstrate in both the ground and the excited states by virtue of relatively strong supramolecular interactions, such as hydrogen bonding, van der Waals, π-π, electrostatic, and hydrophobic interactions. The orientation and conformation of the photosubstrate can be critically manipulated by the supramolecular complexation to ensure the subsequent effective stereoselective photochemical conversion.This Account describes our recent advance in asymmetric photoreactions in supramolecular assemblies. Several chiral photoreactions, including photoisomerization of cycloolefins and photocyclodimerization of anthracene and naphthalene derivatives, have been mediated by various supramolecular hosts, such as cyclodextrin (CD), cucurbituril, pillararene, and chiral polymer. The following advantages of supramolecular asymmetric photochemistry were evidenced: (1) The improvement of stereoselectivity can be enabled by the careful design and fabrication of chiral host molecules. (2) Supramolecular complexation could effectively regulate the orientation and conformation of photosubstrates, thus resulting in novel reaction pathways which create unusual photoproducts that are not achievable through traditional reaction conditions. (3) Asymmetric photoreactions in supramolecular systems showed strong correlations with the external environmental variants, such as temperature, solvent, irradiation wavelength, and pressure, which therefore provide a powerful tool for the regulation of stereoselectivities of excited-state photoreactions. (4) Utilizing supramolecular complexation can dramatically speed up photoreactions, a combination of appropriate photosensitizers/photocatalysts being able to drive catalyzed chiral photoreactions effectively. (5) Photoisomerization in chiral supramolecular systems has been applied to chiroptical molecular devices, which exhibited multiple stimulus-response functions and advanced switching performances. We believe that these concepts, methods, and principles derived therefrom are instructive in designing chiral supramolecular hosts, elucidating the stereodifferentiation mechanisms in the ground and excited states, and analyzing and improving the stereochemical outcomes of a diverse range of supramolecular chiral photoreactions.

Development of a Trimethylamine-Catalyzed Novel Synthesis of Azoxystrobin

We report the development of a novel method for the synthesis of Azoxystrobin, which employs trimethylamine as a catalyst. This appealing catalytic system offers several advantages, including low cost, excellent reactivity, easy recovery, and the ability to be used repeatedly with minimal environmental impact. Mechanistic studies and density functional theory (DFT) calculations suggest that the involvement of a highly active quaternary ammonium salt intermediate is likely responsible for the efficient catalysis. This can be attributed to the low steric hindrance, flexible bare nature of the lone pair of electrons on the nitrogen atom, and low activation energy barrier of trimethylamine. These findings hold great promise for the mass production of Azoxystrobin.

Cascade Anchoring Strategy for Fabricating High-Loading Pt Single Atoms as Bifunctional Catalysts for Electrocatalytic Hydrogen Evolution and Oxygen Reduction Reactions.

Carbon supports containing single-atomically dispersed metal-Nx (denoted as MSAC-NxCy, x, y: coordination number) have attracted increasing attention due to their superb performance in heterogeneous catalysis. However, large-scale controllable preparation of single-atom catalysts (SACs) with high concentration of supported metal-Nx is still a big challenge because of the metal atom agglomeration during synthesis at high density and temperatures. Herein, we report a stepwise anchoring strategy from a 1,10-o-phenanthroline Pt chelate to an Nx-doped carbon (NxCy) with isolated Pt single-atom catalysts (PtSAC-NxCy) containing Pt loadings up to 5.31 wt % measured via energy-dispersive X-ray spectroscopy (EDS). The results show that 1,10-o-phenanthroline Pt chelate predominantly contributes to the formation of chelate single metal sites that bind tightly to platinum ions to prevent metal atoms from aggregating, resulting in high metal loading. The high-loading PtSAC-NxCy exhibits a low hydrogen evolution (HER) overpotential of 24 mV at 0.010 A cm-2 current density with a relatively small Tafel gradient of 60.25 mV dec-1 and excellent stable performance. In addition, the PtSAC-NxCy catalyst shows excellent oxygen reduction reaction (ORR) catalytic activity with good stability, represented by the fast ORR kinetics under high-potential conditions. Theoretical calculations show that PtSAC-NC3 (x = 1, y = 3) offers a lower H2O activation energy barrier than Pt nanoparticles. The adsorption free energy of a H atom on a Pt single-atom site is lower than that on a Pt cluster, which is easier for H2 desorption. This study provides a potentially powerful cascade anchoring strategy in the design of other stable MSAC-NxCy catalysts with high-density metal-Nx sites for the HER and ORR.

Water decontamination via nonradical process by nanoconfined Fenton-like catalysts

There is an urgent need to develop effective and sustainable solutions to reduce water pollution. Heterogeneous Fenton-like catalysts are frequently used to eliminate contaminants from water. However, the applicability of these catalysts is limited due to low availability of the reactive species (RS). Herein, nanoconfinement strategy was applied to encapsulate short-lived RS at nanoscale to boost the utilization efficiency of the RS in Fenton-like reactions. The nanoconfined catalyst was fabricated by assembling Co3O4 nanoparticles in carbon nanotube nanochannels to achieve exceptional reaction rate and excellent selectivity. Experiments collectively suggested that the degradation of contaminants was attributed to singlet oxygen (1O2). Density functional theory calculations demonstrated the nanoconfined space contributes to quantum mutation and alters the transition state to lower activation energy barriers. Simulation results revealed that the enrichment of contaminant on the catalyst reduced the migration distance and enhanced the utilization of 1O2. The synergy between the shell layer and core-shell structure further improved the selectivity of 1O2 towards contaminant oxidation in real waters. The nanoconfined catalyst is expected to provide a viable strategy for water pollution control.

Multisite Porphyrinic Metal–Organic Frameworks for Biomass Valorization: Computational Design and Mechanistic Investigation

Renewable chemicals and fuels have received significant attention for sustainable economic development. Our aim in this work is to investigate a porphyrinic metal–organic framework (MOF), namely, MOF-525 for the transfer hydrogenation of methyl levulinate (ML) to γ-valerolactone (GVL) through density functional theory calculations. We computationally design five multisite defect-engineered MOF-525(M) (M = CrIII, FeIII, RuIII, RhIII, and IrIII) and examine their catalytic performance for the transformation of ML to methyl valerate (MV) via catalytic transfer hydrogenation (CTH), subsequently for the cyclization of MV to GVL by anchoring a SO3H group as a Brønsted acid site on the metallated linker M-TPP-Cl. The CTH involves three pathways (two concerted and one stepwise) on the defective Zr node and two pathways (one stepwise and one concerted) on the metallated linker, respectively. It is revealed that a stepwise Meerwein–Ponndorf–Verley pathway is energetically preferred on the defective Zr node. A similar stepwise pathway on Ru-TPP-Cl is also found to be favorable, while a concerted pathway is more favorable on Rh-TPP-Cl and Ir-TPP-Cl. The rate-determining activation barriers on M-TPP-Cl are rationalized by geometry analysis, second-order perturbation theory analysis, and the noncovalent interactions. Among the five metallated MOF-525(M), Ru, Rh, and Ir are predicted to be active for the transformation of ML to MV. However, the defective Zr-SBU is found to have a lower activation energy barrier compared to M-TPP-Cl, suggesting its dominant role in CTH. In addition, the Brønsted acid-catalyzed cyclization appears to be rate-determining on the defective Zr node, Rh-TPP-Cl, and Ir-TPP-Cl. This study suggests that MOF-525 might be potentially used as a multisite catalyst platform for the conversion of ML to GVL and would assist in the future rational design of new MOFs for biomass valorization.

Mechanism insight into the facet-dependent photoaging of polystyrene microplastics on hematite in freshwater

Hematite, as an extensive natural mineral with multiple crystal facets, profoundly affects the migration and transformation of pollutants in the natural environment. However, little is known about the photochemical behavior of microplastics on different facets of hematite in the aquatic environment. In this work, the photoaging of polystyrene microplastics (PS-MPs) on different crystal planes ({001}, {100}, and {012} facets) and related mechanisms were studied. Two-dimensional correlation spectroscopy analysis illustrated that the reaction pathways of PS-MPs photoaging on hematite tended to preferential chemical oxidization. The stronger performance of PS-MPs photoaging, expressed by particle size reduction and surface oxidation, was observed on the {012} crystal facet. Under irradiation, {012} facet-dominated hematite with a narrower bandgap (1.93 eV) reinforced the photogenerated charge carrier separation, and the lower activation energy barrier (1.41 eV calculated from density functional theory) led to effective •OH formation from water oxidation. These findings elucidate the underlying photoaging mechanism of MPs on hematite with different mineralogical phases.

Lattice Mismatch Guided Nickel‐Indium Heterogeneous Alloy Electrocatalysts for Promoting the Alkaline Hydrogen Evolution

AbstractThe immiscibility of crystallographic facets in multi‐metallic catalysts plays a key role in driving the green H2 production by water electrolysis. The lattice mismatch between tetragonal In and face‐centered cubic (fcc) Ni is 14.9 % but the mismatch with hexagonal close‐packed (hcp) Ni is 49.8 %. Hence, in a series of Ni−In heterogeneous alloys, In is selectively incorporated in the fcc Ni. The 18–20 nm Ni particles have 36 wt % fcc phase, which increases to 86 % after In incorporation. The charge transfer from In to Ni, stabilizes the Ni0 state and In develops a fractional positive charge that favors *OH adsorption. With only 5 at% In, 153 mL h−1 H2 is evolved at −385 mV with mass activity of 57.5 A g−1 at—400 mV, 200 h stability at −0.18 V versus reversible hydrogen electrode (RHE), and Pt‐like activity at high current densities, due to the spontaneous water dissociation, lower activation energy barrier, optimal adsorption energy of OH− ions and the prevention of catalyst poisoning.

Lattice Mismatch Guided Nickel-Indium Heterogeneous Alloy Electrocatalysts for Promoting the Alkaline Hydrogen Evolution.

The immiscibility of crystallographic facets in multi-metallic catalysts plays a key role in driving the green H2 production by water electrolysis. The lattice mismatch between tetragonal In and face-centered cubic (fcc) Ni is 14.9 % but the mismatch with hexagonal close-packed (hcp) Ni is 49.8 %. Hence, in a series of Ni-In heterogeneous alloys, In is selectively incorporated in the fcc Ni. The 18-20 nm Ni particles have 36 wt % fcc phase, which increases to 86 % after In incorporation. The charge transfer from In to Ni, stabilizes the Ni0 state and In develops a fractional positive charge that favors *OH adsorption. With only 5 at% In, 153 mL h-1 H2 is evolved at -385 mV with mass activity of 57.5 A g-1 at-400 mV, 200 h stability at -0.18 V versus reversible hydrogen electrode (RHE), and Pt-like activity at high current densities, due to the spontaneous water dissociation, lower activation energy barrier, optimal adsorption energy of OH- ions and the prevention of catalyst poisoning.

Double-Heterostructured Nickel Phosphate-Phosphides as High-Activity Electrocatalyst for Ammonia Borane Electrooxidation.

The direct electrooxidation reaction of ammonia borane (ABOR) as the anodic reaction of direct ammonia borane fuel cells (DABFCs) is greatly dependent on the properties of electrocatalysts. Both the active sites and charge/mass transfer characteristics are the key to promoting the processes of kinetics and thermodynamics, which can further improve the electrocatalytic activity. Hence, the catalyst double-heterostructured Ni2 P/Ni2 P2 O7 /Ni12 P5 (d-NPO/NP) with the optimistic redistribution of electrons and active sites is prepared for the first time. The d-NPO/NP-750 catalyst obtained after pyrolysis at 750°C shows the outstanding electrocatalytic activity toward ABOR with an onset potential of -0.329V vs RHE which is better than all the published catalysts. The density functional theory (DFT) computations illustrate that the Ni2 P2 O7 /Ni2 P acts as the activity enhancement heterostructure with a high d-band center (-1.60eV) and the low activation energy barrier, while the Ni2 P2 O7 /Ni12 P5 acts as the conductivity enhancement heterostructure with the highest density of valence electrons.

Effects of Barium‐Copper‐Cobalt oxide composites supported on reduced graphene oxide in the thermolysis of ammonium perchlorate and 3‐nitro‐1,2,4‐triazol‐5‐one

AbstractSynthesis method of nanocrystalline Barium‐Copper‐Cobalt oxide (BCC) and its composite with reduced graphene oxide (rGO) was provided. The size of nanocrystalline (∼13 nm) materials (BCC and BCC/rGO) was confirmed using powder X‐ray diffraction patterns. The effect of rGO, BCC, and BCC/rGO on the thermal decomposition of 3‐Nitro‐1,2,4‐triazol‐5‐one (NTO) and ammonium perchlorate (AP) was investigated using simultaneous thermal analysis. Non‐isothermal isoconversion method was used to calculate the activation energy of AP and NTO with and without rGO, BCC, and BCC/rGO. The thermal analysis suggests that in the presence of BCC and BCC/rGO, the thermal decomposition exotherm of NTO was lowered to ∼259, and ∼228 °C, respectively, and that of AP was lowered to 355, and 345 °C, respectively. BCC and BCC/rGO exhibit very good catalytic activity for the thermal decomposition of NTO by lowering NTO's activation energy barrier by ∼179 and 261 kJ mol−1, respectively. The activation energy calculations for low thermal decomposition and high thermal decomposition of AP (∼95 kJ mol−1 average) do not provide conclusive evidence to confirm the catalytic influence of BCC and BCC/rGO. The composition NTO+BCC has a lower activation energy barrier (∼121 kJ mol−1) than pure NTO which makes the thermal decomposition of NTO+BCC more favorable than pure NTO making its application in insensitive munitions more favorable. AP+BCC decomposes within a short temperature range and hence, it can be used in solid rocket propellants requiring faster decomposition of AP in place of pure AP.

Quantum chemical study of tautomeric equilibriums, intramolecular hydrogen bonds, and π-electron delocalization in the first singlet and triplet excited states of 2-selenoformyl-3-thioxo-propionaldehyde

In the present study, the tautomeric process, intramolecular hydrogen bonding (IMHB), and π-electron delocalization (π-ED) of 2-selenoformyl-3-thioxo-propionaldehyde (STP) in the first singlet and triplet excited states were investigated by CIS and TD-DFT methods. The relative energies of hydrogen-bonded tautomers in both excited states indicate that the thiol/enol conformers are the most/least stable forms. In this regard, a detailed analysis of various tautomeric equilibriums, different types of hydrogen bonds, and π-electron delocalization was performed. The electronic energies of different tautomers indicate the thermodynamic preference of thiol with respect to the other forms. Furthermore, the low activation energy barriers of thione⇄thiol equilibrium also show the kinetic preference of thiol. On the other hand, the estimation of different hydrogen bond energies emphasizes the stronger IMHB of enol. Moreover, the evaluation of π-ED by the structural parameter of Gilli (λ) represents the significance of electron mobility in the enol conformers. Consequently, the duality between the IMHB and π-ED with the thermodynamic stability order of tautomers indicates that the tautomeric phenomenons play a dominant role in determining the stability of the benchmark structures in both singlet and triplet excited states.