The RhCo 3 catalyst exhibits bimetallic synergy and spin effects via Rh–Co d–d orbital coupling, facilitating efficient N 2 activation for ammonia synthesis in the septet state.

The synthesis of ammonia (NH3) from nitrogen (N2) under mild conditions is a great challenge, in which the electron-donating ability of the catalyst is the key for N2 activation. In this work, the above process was studied using quantum chemical calculations using the density functional method. The results show that Rh and Co exhibit unsaturated d-electron configurations, with d-d orbital coupling occurring within the RhCo3 metal cluster, resulting in bimetallic synergy and spin effects. The Rh atom serves as an electron modulation center and active site for reactant activation, while the Co metal synergistically enhances electron back-donation effects. The RhCo3 cluster exhibits different adsorption and kinetic behaviors across the triplet, quintet, and septet potential energy surfaces, among which the septet state shows the most favorable catalytic performance. Energy span (δE) model analysis further indicates that, at low and moderate temperatures, the N2 adsorption is the key factor governing the catalytic activity of RhCo3. At 298 K, the reaction displays a δE value of 2.03 eV, and the catalytic activity increases with the temperature. However, at higher temperatures, the NH3 desorption becomes the rate-determining process, shifting the turnover-determining transition state beyond the turnover-determining intermediate, and the energy span increases to 2.95 eV. These findings elucidate the temperature-dependent catalytic mechanism of RhCo3 and provide theoretical insights for the rational design of efficient bimetallic catalysts for ammonia synthesis.

The adsorptive removal of methylene blue (MB) from aqueous solution is often executed by attapulgite (ATP) due to its unique one-dimensional nanoscale structure and low-cost, abundant, eco-friendly advantages. Another commonly used material for this job is activated carbon. In this study, a novel composite porous ceramsite was prepared by combining activated carbon and ATP clay to remove MB from an aqueous solution. The composite porous ceramsite, calcined at 450 °C (CPC-450), was characterized by SEM, FT-IR, XRD, and BET specific surface area measurements. It possessed a high specific surface area of 313.606 m2/g and exhibited superior adsorption capacity toward MB than that of raw ATP. Consequently, a 99.6

Theoretical calculation not only is a powerful tool to deeply explore photophysical processes of the emitters but also provides a theoretical basis for material renewal and design strategy in the future. In this work, the interconversion and decay rates of the thermally activated delayed fluorescence (TADF) process of the rigid Ag(dbp)(P2-nCB) complex are quantitatively calculated by employing the optimally tuned range-separated hybrid functional (ω*B97X-D3) method combined with the path integral approach to dynamics considering the Herzberg-Teller and the Duschinsky rotation effects within a multimode harmonic oscillator model. The calculated results show that the small energy splitting ΔE(S1-T1) = 742 cm-1 (experimental value of 650 cm-1) of the lowest singlet S1 and triplet T1 state and proper vibrational spin-orbit coupling interactions facilitate the reverse intersystem crossing (RISC) processes from the T1 to S1 states. The k RISC rate is estimated to be 1.72 × 108 s-1 that is far more than the intersystem crossing rate k ISC of 7.28 × 107 s-1, which will greatly accelerate the RISC process. In addition, the multiple coupling routes of zero-field splitting (ZFS) interaction can provide energetically nearby lying states, to speed up the RISC pathway, and restrict the phosphorescence decay rate. A smaller ZFS D-tensor of 0.143 cm-1, E/D ≈ 0.094 ≪ 1/3, and Δg > 0 are obtained, indicating that the excited singlet states are hardly mixed into the T1 state; thus, a lower phosphorescence decay rate (k p = 9.29 × 101 s-1) is expected to occur, and the T1 state has a long lifetime, which is helpful for the occurrence of the RISC process. These works are in excellent agreement with the experimental observation and are useful for improving and designing efficient TADF materials.

This work fabricated the zirconium-modified attapulgite (Zr@ATP) for removing Cr(vi) ions in aqueous solutions. According to X-ray diffraction, scanning electron microscopy, TEM, Fourier transform infrared, and X-ray photoelectron spectroscopy analyses, Zr was successfully grafted onto the attapulgite rod surface. Cr(vi) adsorption onto Zr@ATP surface fitted well with the Langmuir isotherm and pseudo-second-order kinetic models, which suggested that the adsorption is primarily chemisorption. When the pH of the aqueous solution is 3, Zr@ATP achieved the highest Cr(vi) absorption, of about 32.84 mg/g. Density functional theory studies revealed that the hydroxyl functional group introduced through the modification process supplies more active sites to form the hydrogen bond with CrO(2)(4- )and CrO4-.

The two-state reaction mechanism of NH3 synthesis from N-2 and H-2 catalyzed by Ru are theoretical studied on the singlet, triplet and quintet potential energy surface, and the density functional theory (DFT) UB3LYP methods was used, which is a typical two-state reaction. We calculated spin-orbital coupling constant (H-soc) and intersystem crossing probability (P-ISC) at minimum energy crossing point (MECP) respectively, for MECP1: H-soc= 508.34 cm(-1), P-2(ISC)=0.85; for MECP9: H-soc=269.21 cm(-1), P-2(ISC)=0.27. We used energy span model to determine that turnover frequency (TOF)-determining transition state (TDTS) of the reaction is (3)TS2-3 and TOF-determining intermediate (TDI) of the reaction is (3)IM9.

Quantitative predictions of the photophysical processes for a next generation thermally activated delayed fluorescence molecule are calculated by considering the Herzberg–Teller and the Duschinsky rotation effects within a multimode harmonic oscillator model.

In order to further explore the detailed reaction mechanism of carbon dioxide activated by [Re(CO)(2)](+) complex, CCSD(T) methods was performed to determine related potential energy surface (PES). Crossing point is determined by using a partially optimized method. The result shows that larger spin-orbital coupling (155.37 cm(-1)) and intersystem crossing probabilities in spin-forbidden region causes the electron to spin flip at the minimum energy crossing point and access to the lower singlet PES. Nonadiabatic rate constant k is estimated to be quite rapid, so transition state ((1)TS1) is rate-controlled steps. In addition, the electronic structure of oxygen-atom transfer process is further analyzed by localized molecular orbital and Mayer bond order. The analysis finds that the form of main bonding orbital is the electron contribution from the p(O) in CO2 to the empty d(Re) orbital.

采用密度泛函理论(DFT)研究了Pdn(n=1～4)团簇催化N2 O和CO的反应机理.该反应分两步进行:首先N2 O在Pdn(n=1～4)团簇上还原并分解,形成活性氧并释放出N2;接着CO被氧化形成CO2.势能面分析表明,对于Pd2,Pd3和Pd4,CO的氧化是整个反应的决速步骤,其中Pd3团簇对N2 O分解和CO氧化表现出高的催化活性,决速步骤的能垒仅为61.36 kJ·mol-1.NPA电荷分析表明,电子从Pdn(n=1～4)团簇转移到N2O促进了N—O键的解离,团簇的尺寸效应对反应具有很大的影响.这些结果丰富了我们对基于Pd基催化剂的N2 O催化离解和CO氧化机理的理解.

Ru-based catalysts show high activity and stability to produce ammonia. Herein, the two-state reaction mechanism of Ru catalyzes N2 and H2 to synthesize NH3 are theoretical studied with the density functional theory(DFT)UB3LYP methods. The spin-orbital coupling constant(Hsoc) and intersystem crossing probability(Pisc) at minimum energy crossing point(MECP) were calculated, respectively. its are: Hsoc,MECP1=508.34cm-1，P2,MECP1ISC=0.85，MECP2：Hsoc,MECP2=269.21cm-1， P2,MECP2ISC=0.27. Used energy span model to determined TOF-determining transition state(TDTS) as 3TS2-3 and TOF-determining intermediate(TDI) as 3IM9 of reaction.In addition, the charge decomposition analysis(CDA), spin population analysis and frontier molecular orbital(FMO) theory were used to analyzed reaction mechanism.

Investigations of the detailed photophysical processes are of great significance for future material improvements and novel designing strategies. Herein, the interconversion and decay rates of the first excited singlet state (S-1) and triplet state (T-1) for the Cu2I2(P<^>N)(3) complex are calculated using the thermal vibration correlation function (TVCF) theory, combined with the optimally tuned range-separated hybrid functional (OT-omega B97XD) method at different temperature. A methodology with the building different ONIOM models, was carried over into simulation of crystal environment. All calculated results perfectly match the experimentally available data, demonstrating the validity of our applied theoretical approach. It has been found that the reverse intersystem crossing (RISC) rate k(RISC) from T-1 to S-1 is 3.11 x 10(-10) s(1) at 300 K, about 7 order of magnitude larger than the phosphorescence rate k(r)(T) = 3.71 x 10(3) s(-1), and far more than ISC rate k(ISC)(T-1-S-0) of 6.38 s(-1). The S-1 state can be an efficient thermal population from the T-1 state by the RISC pathway, leading to an occurrence of thermally activated delayed fluorescence (TADF), and the estimated delayed time of tau(TADF) = 10 mu s. On the other hand, the T-1 state also exhibits stronger admixtures with higher lying singlet states due to stronger SOC, having a larger ZFS of 17 cm(-1), thus, a relatively fast phosphorescence decay rate of k(r)(T) = 8.542 x 10(-3) s(-1) estimated by Einstein emission formula is observed. Further calculation results show that the emission intensities are stemming by 91% from the S-1 state as TADF and by 9% as phosphorescence from the T-1 state at 300 K, which indicates the ambient temperature emission represents the combined luminescence of TADF and phosphorescence. Our work would be useful for improving and designing the luminescent material combined high-efficiency TADF with phosphorescence.

A series of complexes (HNgMX3), formed from superhalogen MX3 (M = Be-Ca, X = F-Br) noble gas (Ar-Rn) and the hydrogen atom, were investigated via combined high-level ab initio and DFT calculations. The high vertical electron detachment energy (VDE) of the superhalogen part will lead to charge transfer from the noble gas hydride to it. This charge transfer gives rise to attractive ionic interaction between the two components and to the existence of these complexes as local minima on the potential energy surface eventually. However, the VDE value of the superhalogen part is not always monotonically correlated with the thermodynamic/kinetic stability of the whole complexes. Therefore the superhalogen itself might not be enough to provide information for the correct prediction of the properties of the whole composites. Although there are exothermic channels of dissociation, the existence of energy barrier might ensure the existence of these Ng hydrides under certain conditions. Our analysis indicates the existence of two important factors, functioning in opposite directions, for the energy barriers along the exothermic channel. To achieve a high energy barrier, the attractive interaction between superhalogen and the H atom in the TS, which lowers the barrier, needs to be suppressed effectively. An understanding of the superhalogen-based composites will provide valuable information on the functional properties and potential application of superhalogens. The details of the interaction between different parts of these composites should be one of the areas of focus in these studies.

Density functional theory (DFT)UB3LYP methods was used for FeO catalytic N2 and H2 to synthesize ammonia in the quintet and triplet spin-state potential energy surfaces (PESs). By noncovalent interactions to predict reaction sites, the bonding properties of part of the species along the reaction were analyzed by electron localization function (ELF) and atoms in molecules (AIM), and the mechanism of minimum energy cross point (MECP) was analyzed by frontier molecular orbital theory. The spin-orbit coupling (SOC) and probability of intersystem crossing of different potential surfaces were discussed. In addition, this work demonstrated the reaction rate-determining step and calculated TOF by applying the energetic span model in theory.

本文采用密度泛函理论(DFT)UB3LYP方法对FeO在基态五重态及第一激发态三重态势能面上催化N2与H2反应生成NH3的两态反应机理进行了研究,运用非共价作用预测反应位点,并运用分子中的原子(AIM)、电子定域化函数(ELF)及前线分子轨道理论对部分最低能量路径及最低能量交叉点(MECP)的机理进行了分析.计算了MECP处的自旋轨道耦合值(Hsoc)及系间窜越几率(PISC),通过应用能量跨度模型(energetic span model)确定了反应决速态,并从理论层面计算得到了反应中FeO的催化转化频率(TOF).

Accurate research of the photophysical processes is of great significance for the rational design of excellent thermally activated delayed fluorescence (TADF) materials. Herein, the interconversion and decay rates of the first excited singlet state (S1) and triplet states (T1) in the Cu(pop)(pz2BH2) complex are computed using the thermal vibration correlation function (TVCF) theory at different temperature. For consideration of the solid-state environment, a methodology that is based on the ONIOM model, combined with the optimally tuned range-separated hybrid functional (CAM-B3LYP*) method, was applied. Our calculated results are in excellent agreement with the experimentally available data. It has been found that the energy dissipation of the nonradiative processes from the S1 to ground state is promoted by low frequency vibrational modes in the solution phase, resulting in the high knr(S) = 1.68 × 108 s-1 at 300 K. However, for the crystal phase, they are easily hindered through intermolecular interactions, knr(S) is predicted to be decreased by about 5 orders of magnitude upon aggregation (2.98 × 103 s-1). With temperature increase, the reverse intersystem crossing (RISC) rate kRISC from T1 to S1 is drastically increased to 6.12 × 104 s-1 at 300 K, while the change of other rates is still small, which can compete with the radiative decay rate of kr(T) = 4.75 × 104 s-1 and nonradiative intersystem crossing rate of kISC(T1-S0) = 6.63 × 102 s-1 at the T1 state. This implies that the S1 state can be an efficient thermal population from the T1 state, leading to an occurrence of delayed fluorescence, and the complexes exhibit high emission quantum yields, 58.7%. But, at low temperature T < 100 K, the RISC rate is sharply change, kRISC ≪ kr(T) or kISC, which cannot induce an occurrence of delayed fluorescence. Our investigation would be helpful for designing novel, high-efficiency TADF materials.

The reaction mechanisms for acetylene cyclotrimerization using TiO2 and Ti catalysts were studied by the density functional theory (DFT) method. Interestingly, the reaction catalysed by TiO2 occurs on the potential energy surface (PES) with a singlet state. For the same reaction catalysed by Ti, spin-orbit coupling (SOC) calculations were performed to discuss spin inversion between the triplet and singlet PESs. The chance that an electron hops in the vicinity of the minimum-energy crossing point (MECP) was verified regarding the Landau-Zener model. The possibilities of single (P1ISC) and double (P2ISC) at MECP1 (SOC = 253.38 cm(-1)) are about 0.35 and 0.46, respectively. The energetic span model developed by Kozuch was applied in the above reactions. The turnover frequency (TOF)-determining transition state (TDTS) and TOF-determining intermediate (TDI) were verified. The TOF value indicates that Ti is a more active catalyst compared with TiO2 in C2H2 cyclotrimerization.

In a recent experimental research, the formation of naphthalene has been demonstrated by La-mediated acetylene bicyclo-oligomerization in the gas phase, and this is the first report of metal-activated acetylene bicyclo-oligomerization to form the naphthalene. In this work, the complete reaction mechanism has been systematically analyzed on the doublet potential energy surface by employing density functional theory (DFT), the results showed that the computational results were consistent with experimental dates. Among them, two possible reaction pathways were identified: (1) LaC4H2 is formed by a second addition of acetylene molecule to LaC2H2 followed by dehydrogenation (path (a)). (2) First, dehydrogenation of LaC2H2, followed by the addition of a second acetylene molecule (path (b)), we found that the optimum pathway was path (a). According to the thermodynamic point of view, the reaction is highly exothermic and favorable. In addition, sequential acetylene additions coupled with dehydrogenation showed that the bicycle-oligomerization reaction can occur. For further analysis of the observed kinetic behavior, the energetic span model was utilized and confirmed the TOF-determining transition state (TDTS) and TOF-determining intermediate (TDI) of the overall reaction. Finally, the optimum path was found and demonstrated.

To explore the mechanisms for Ni-based oxide-catalyzed oxidative dehydrogenation (ODH) reactions, we investigate the reactions of C2H6 with NiO+ using density functional calculations. Two possible reaction pathways are identified, which lead to the formation of ethanol (path 1), ethylene and water (path 2). The proportion of products is discussed by Curtin-Hammett principle, and the result shows that path 2 is the main reaction channel and the water and ethylene are the main products. In order to get a deeper understanding of the titled reaction, numerous means of analysis methods including the atoms in molecules (AIM), electron localization function (ELF), natural bond orbital (NBO), and density of states (DOS) are used to study the properties of the chemical bonding evolution along the reaction pathways.

A quantitative understanding of photophysical processes is fundamental for designing novel thermally activated delayed fluorescence (TADF) materials. Taking a Cu(pop)(pz2Bph2) crystal as a typical TADF molecular model, we computed the conversion and decay rates of the first excited singlet state (S1) and triplet state (T1) at different temperatures by employing the thermal vibration correlation function (TVCF) approach. For the consideration of the solid-state environment, a methodology, which is based on the combination of a nonempirical, optimally tuned range-separated hybrid functional with the polarizable continuum model, was applied. Our calculated results are in excellent agreement with the experimentally available data. It is found that the reverse intersystem crossing (RISC) from T1 to S1 proceeds at a rate of kRISC = 6.34 × 105 s-1 and can compete with the radiative decay rate (k = 3.29 × 103 s-1) and nonradiative intersystem crossing rate (k = 1.48 × 102 s-1) of T1 at 300 K. This implies that the S1 state can be repopulated from the T1 state, TADF should be observed and the TADF decay time was found to be τ (300 K) = 9.68 μs by fitting calculations. In addition, the calculations indicate that the free rotation of the phenylene ring in the pop ligand can provide an important channel to energy conversion between T1 and S1. But, at a low temperature of T < 100 K, the situation will experience a larger change. The RISC rate becomes very small, kRISC ≪ k or kISC, and it cannot induce an occurrence of delayed fluorescence. As a consequence, Cu(pop)(pz2Bph2) is a highly attractive candidate for applications of TADF.

The exchange coupling (J) and magnetic dipole (D) interactions of thermally activated delayed fluorescence copper(I) thiolate complex have been investigated by employing computational chemistry methods. The situation of strict orthogonality of the "hole”–“electron" orbitals with the overlap integral 〈ϕ175α|ϕ175β〉 = 0 leads to small J and excessive triplet T1 population, and is unfavorable to the formation of singlet S1 state via the exchange coupling induced reverse intersystem crossing in the triplet state T1. In magnetic dipole interactions, the mutually perpendicular orbitals provides a significant one-center heavy atomic contribution to the SOC, 〈1φ|hySO|3φ〉 = -41.76 and 〈1φ|hzSO|3φ〉 = −63.14 cm−1, which will enhance the probability of intersystem crossing from the T1 to S1, but system needs to overcome a large intersystem crossing barrier height of 11.05 kcal/mol relative to that of the T1 state at the CAM-B3LYP/def2-TZVP(-f) level. Under magnetic field limit, S1−T0, S1−T+1, and S1−T-1 mixing are all inefficient because the large energy gap between T1 and S1, |2J| » gβB prohibits significant mixing in the triplet state T1, but for the S1/T1 crossing point, the S1−T-1 energy gap is comparable to that of the S1−T0 energy gap, allowing for mixing of S1 with T-1 and T0, |Tz〉 = 56%|1, 0〉 + 20%|1, −1〉 + 16%|0, 0〉.