Study Of Reaction Mechanism Research Articles

Cp*Co(III)-Catalyzed Selective C8-Olefination and Oxyarylation of Quinoline N-Oxides with Terminal Alkynes.

Herein we report Cp*Co(III)-catalyzed site-selective (C8)-H olefination and oxyarylation of quinoline N-oxides with terminal alkynes. The selectivity for C8-olefination and oxyarylation is sterically and electronically controlled. In the case of quinoline N-oxides (unsubstituted at the C2 position), only the olefination product was obtained irrespective of the nature of the alkynes. In contrast, oxyarylation was observed exclusively when 2-substituted quinoline N-oxides were reacted with 9-ethynylphenanthrene. However, alkynes with electron-withdrawing groups provided only olefination products with 2-substituted quinoline N-oxides. The developed strategy allowed a facile functionalization of quinoline N-oxides bearing natural molecules and an estrone-derived terminal alkyne to deliver the corresponding olefinated and oxyarylated products. To understand the reaction mechanism, control experiments, deuterium-labeling experiments, and kinetic isotope effect (KIE) studies were performed.

Molecular basis and functional development of enzymes related to amino acid metabolism.

Enzymology, the study of enzyme structures and reaction mechanisms can be considered a classical discipline. However, enzymes cannot be freely designed to catalyze desired reactions yet, and enzymology is by no means a complete science. I have long studied the reaction mechanisms of enzymes related to amino acid metabolism, such as aminotransferases and racemases, which depend on pyridoxal 5'-phosphate, a coenzyme form of vitamin B6. During these studies, I have often been reminded that enzymatic reactions are extremely sophisticated processes based on chemical principles and enzyme structures, and have often been amazed at the evolutionary mechanisms that bestowed them with such structures. In this review, I described the reaction mechanism of various pyridoxal enzymes especially related to d-amino acids metabolism, whose roles in mammals have recently attracted attention. I hope to convey some of the significance and interest in enzymology through this review.

Highly effective electrocatalytic reduction of N-nitrosodimethylamine on Ru/CNT catalyst

N-Nitrosodimethylamine (NDMA) is a commonly identified carcinogenic and genotoxic pollutant in water. In this study, we prepared Ru catalysts supported on carbon nanotube (Ru/CNT) and studied the electrocatalytic reduction of N-nitrosamines on Ru/CNT electrode in a three-electrode system. The results show that Ru-based catalyst exhibits a high activity of 793.3 μmol L−1 gCat−1 h−1 for electrochemical reduction of NDMA. Reaction mechanism study discloses that the electrocatalytic reduction of NDMA is accomplished by both direct electron reduction and atomic H* mediated indirect reduction pathways. Further product analysis indicates that NDMA is finally reduced to dimethylamine (DMA) and ammonia. The reduction efficiency of NDMA strongly relies on cathode potential, initial NDMA concentration and solution pH. To verify the universality of Ru/CNT electrode, electrocatalytic reduction of three dialkyl N-nitrosamines with different alkyl groups was performed and Ru catalyst has high catalytic activities for the three N-nitrosamines, while the catalytic efficiency differs with their structures. Simultaneous electrochemical reduction of the three N-nitrosamines indicates that the reduction rates of N-nitrosamines follow the same order in the multiple-component system as that in the single-component system. Catalyst recycling results demonstrate that after 5 consecutive recycling runs Ru/CNT electrode remains almost identical catalytic activity to the fresh catalyst, manifesting the high catalytic stability of Ru/CNT electrode.

Quantum-chemical study of organic reaction mechanisms. XI.*1 Biologically active 4-substituted 1,2,4-triazoles from diformylhydrazine and aminophenols

Quantum-chemical study of organic reaction mechanisms. XI.*1 Biologically active 4-substituted 1,2,4-triazoles from diformylhydrazine and aminophenols

Single Ni-inserted Cu (1 1 1) surface: A DFT study of adsorption and reaction mechanisms of methanol steam reforming

Modeling of a bimetallic catalyst surface and DFT calculations of its adsorption capacity, as well as methanol steam reforming (MSR) pathways, are of great theoretical achievements in the search for efficient hydrogen-production catalysts. Herein, the single Ni-embedded model (NiCu(111)) and single Ni-adsorbed model (A-NiCu(111)) are built, and DFT calculations are carried out to determine different adsorption capabilities. The results show that adding Ni atoms can improve adsorption performance significantly, which is beneficial to the interaction between reactant molecules and catalyst surfaces. The adsorption energies on the A-NiCu(111) surface are much greater than those on the NiCu(111) surface. Further, some key elementary reactions of MSR are carried out to evaluate the catalytic performances and carbon deposition effects of two surfaces. The stepwise dehydrogenation of methanol molecules, the decomposition of water molecules, and other reactions of some intermediates are analyzed in detail. On the A-NiCu(111) surface, the activation energy barriers of stepwise dehydrogenation of methanol molecules and water decomposition are reduced. The NiCu(111) surface shows advantages in inhibiting the surface carbon deposition. This can provide theoretical ideas for the design of high-efficiency Cu-Ni alloy catalysts in the future.

Reaction mechanism study on transesterification in synthesis of thermotropic liquid crystalline polymer catalyzed by zinc(II) carboxylate: A combination of DFT and kinetics analyses

A deep insight into the reaction mechanism is essential to control the polymerization process with the desired macromolecular structure for high-performance thermotropic liquid crystalline polymer. In this work, density functional theory (DFT) was used to investigate the catalytic polymerization mechanism for the synthesis of thermotropic liquid crystalline polymer catalyzed by zinc(II) carboxylate. The polymerization of 4-acetoxybenzoic acid was studied as a typical reaction. Based on DFT calculations, the rate-limiting step is located in the transesterification between phenol and anhydride acid. The energetically favored pathway was found with the free energy barrier of 51.84 kcal/mol in the presence of zinc acetate, which is significantly lower than the energy barrier without a catalyst. In addition, the effects of the carboxylate group of zinc(II) carboxylate on the catalytic efficiency were revealed by DFT calculations and experiments. Compared with zinc acetate, zinc pivalate has a higher catalytic activity with the rate constant of 1.69 × 10-2 min−1∙M−1 fitted with a second-order reaction model. The HOMO-LUMO gap of zinc pivalate was the smallest among the chosen catalyst, indicating that the chemical activity was strengthened by the methyl substituted. Furthermore, due to the enhanced orbital interactions and the decreased distortion energy in the transition state using zinc pivalate, the energy barrier of the rate-limiting step decreased to 51.36 kcal/mol. These results provide valuable guidance for modeling the catalytic mechanism in aromatic polyester systems.

A Vanadium‐Based Fluoroxide Cathode Material for Lithium‐Ion Storage with High Energy Density

AbstractHigh‐performance lithium‐ion batteries (LIBs) are required for the rising energy storage demand, while their development depends mainly on cathode materials. Vanadium‐based compounds are considered to be promising due to the feasibility of multielectron reactions arising from the rich valence states of vanadium (+2 to +5). Herein, for the first time the electrochemical properties of a vanadium‐based fluoroxide, β‐KVOF3, as a cathode for LIBs, are reported. After optimization, a reversible capacity as high as 274 mAh g−1, a stable 300 cycles lifetime, and an energy density comparable to LiFePO4 (650 vs 550 Wh kg−1) are achieved. Experiments and simulation study of reaction mechanism illustrate that such performance originates from the reversible V3+/V5+ redox reaction, high structural stability of β‐KVOF3, and the pseudocapacitive process during charging and discharging. This study reveals that β‐KVOF3 is a promising cathode for Li‐ion storage and provides a new design idea for developing high‐performance LIBs cathode materials.

Morphology and crystal–plane dependence of CeO2–TiO2 catalysts: Activity and mechanism for the selective catalytic reduction of NOx with NH3

CeO2–TiO2 catalysts with four different morphologies were successfully synthesized by a hydrothermal method and tested for selective catalytic reduction of NOx with NH3 (NH3–SCR). For the four catalysts, CeO2–TiO2 nanocubes (CT–NC) and nanorods (CT–NR) preferentially exposed {100} and {110} facets, respectively; furthermore, nanosheets (CT–NS) and nanospheres (CT–NH) mainly exposed {111} facet. Interestingly, CT–NH catalyst showed the best NH3–SCR performance and the NOx conversion exceeded 97% at 325 °C. Through a series of characteristic methods manifested that the short–range ordered structure of Ce–O–Ti in CT–NH catalyst provided stronger surface acidic sites to promote the high–temperature activity. Moreover, the abundant Ce3+ species and appropriate reduction ability on {111} facet of CT–NH catalyst also caused outstanding deNOx activity. Reaction mechanism study showed that the Langmuir–Hinshelwood (L–H) mechanism and Eley–Rideal (E–R) mechanism existed simultaneously on all catalysts in NH3–SCR reaction. Meaningfully, two types of E–R mechanism were present on CT–NH catalyst, while L–H mechanism was dominant.

Spontaneous Biphasic System with Lithium Chloride Hydrate for Efficient Esterification of Levulinic Acid

AbstractAn efficient approach for synthesis of levulinate from biomass‐derived levulinic acid (LA) and n‐butyl alcohol (BuOH) in molten salt hydrates (MSH) with microwave irridiation was reported. A series of molten salt hydrates were evaluated in terms of their catalytic activity and pH value without any additional catalyst. Introduction of AlCl3 greatly increased the yield of butyl levulinate(BL). As high as 95.5 % BL yield was obtained in LiCl ⋅ 3H2O+AlCl3 system. Reaction mechanism study shows that LiCl ⋅ 3H2O can promote the esterification of LA with BuOH by enhancing the protonation of LA. LiCl is able to expel the formed BL into organic‐phase, and then boost up esterification efficiency. Both separation of BL and strong hygroscopicity of LiCl ⋅ 3H2O promoted the esterification reaction equilibrium. High‐efficient esterification of LA with BuOH realized separation of LA from MSH. Activation energies of BL formation are 70.9 kJ/mol in LiCl ⋅ 3H2O and 31.8 kJ/mol in AlCl3+LiCl ⋅ 3H2O.

A DFT study of the oxygen reduction reaction mechanism on be doped graphene

Graphene despite its high surface area has very limited activity towards the oxygen reduction reaction (ORR), demonstrating selectivity towards the unfavorable two-electron mechanism. We have employed the spin polarized density functional theory method to investigate the oxygen reduction reaction activity of the heteroatom p-type beryllium (Be) doped graphene in gas and aqueous media. The preferred doping sites, active sites and reaction mechanisms available on the doped graphene surfaces were investigated with increasing Be concentrations of 0.03 ML, 0.06 ML and 0.09 ML. Our results reveal that oxygen is physisorbed on bare graphene, however, Be at the lattice sites provides site for oxygen adsorption and ORR. Generally, Be concentration increase in a single honey-comb of graphene from 1 to 2, increasing oxygen activation and dissociation on graphene, compared to their isolated defective counterparts. Considering the conjugated Be defective surfaces, oxygen binds dissociatively on the doped surfaces preferentially in the order 0.06 ML > 0.09 ML > 0.03 ML. Whereby strong binding at the 0.06 ML doped surface corresponds to least charge loss to oxygen. Surfaces with the least affinity for O*, OH* and H2O*, and can transfer the most charges to O2 leading to dissociation (as seen on the 0.03 ML surface), shows the highest reaction activity towards the ORR. From these results surfaces that bind O2 weakly and dissociatively could hold promise for the ORR reaction. Single atom catalyst of Be, based on graphene is promising for the ORR. Graphical abstract

Selective Photoelectrocatalytic Glycerol Oxidation to Dihydroxyacetone via Enhanced Middle Hydroxyl Adsorption over a Bi2O3-Incorporated Catalyst.

Photoelectrocatalytic (PEC) glycerol oxidation offers a sustainable approach to produce dihydroxyacetone (DHA) as a valuable chemical, which can find use in cosmetic, pharmaceutical industries, etc. However, it still suffers from the low selectivity (≤60%) that substantially limits the application. Here, we report the PEC oxidation of glycerol to DHA with a selectivity of 75.4% over a heterogeneous photoanode of Bi2O3 nanoparticles on TiO2 nanorod arrays (Bi2O3/TiO2). The selectivity of DHA can be maintained at ∼65% under a relatively high conversion of glycerol (∼50%). The existing p-n junction between Bi2O3 and TiO2 promotes charge transfer and thus guarantees high photocurrent density. Experimental combined with theoretical studies reveal that Bi2O3 prefers to interact with the middle hydroxyl of glycerol that facilitates the selective oxidation of glycerol to DHA. Comprehensive reaction mechanism studies suggest that the reaction follows two parallel pathways, including electrophilic OH* (major) and lattice oxygen (minor) oxidations. Finally, we designed a self-powered PEC system, achieving a DHA productivity of 1.04 mg cm-2 h-1 with >70% selectivity and a H2 productivity of 0.32 mL cm-2 h-1. This work may shed light on the potential of PEC strategy for biomass valorization toward value-added products via PEC anode surface engineering.

Synthesis of Highly Substituted 2-Aminopyridines with Vinyl Azides, Isonitriles, and Ketones.

We developed a facile, efficient method for synthesizing highly substituted 2-aminopyridines from unstable vinyl carbodiimides generated in situ in a one-pot transformation. A series of novel highly substituted 3-functionalized 2-aminopyridines were produced in good yields. Reaction mechanism studies, which included control experiments and density-functional theory (DFT) calculations, demonstrated that Rh and potassium carbonate played key roles in the cyclization step.

Synthesis of new hybrid composite based on TiO2 for photo-catalytic degradation of sulfamethoxazole and pharmaceutical wastewater, optimization, performance, and reaction mechanism studies

In this study photo-catalytic degradation of sulfamethoxazole (SMX) from aqueous solutions using carbon quantum dot (CQD)-decorated Cu-TiO2 was investigated. The as-prepared photo-catalyst samples were characterized by various FTIR, XRD, FE-SEM, TEM, EDX, BET, and DRS techniques. The investigation of effective photo-catalytic operational parameters confirmed that the complete removal of SMX (20mg/L) can be accomplished at pH: 6.0 and light intensity: 75 mW/cm2 over a 30-min reaction time. DRS analysis demonstrated adding CQD to the Cu-TiO2 reduced its bandgap energy from 2.97 to 2.90eV. The photo-catalytic degradation kinetics of SMX fit well with the pseudo-first-order model. The radical trapping experiment indicates that HO• and O2•- active species were more effective species for SMX degradation, and the higher inhibition effect on the SMX degradation efficiency was assigned to O2•- ions. The water matrix species-inhibited effect in SMX removal was as follows: SO42- > Cl- > NO3- > CO3- > no ions. The synthesized photo-catalyst could be recycled after six consecutive cycles of SMX degradation with an insignificant decrease in performance. The total organic carbon (TOC) analysis suggested the mineralization of SMZ by composite photo-catalysts. The minimum inhibitory concentration (MIC) for Escherichia coli remained at 12.5mg L-1 SMX. A possible mechanism and pathway of SMX degradation in the photo-catalytic system was presented.

Effects of foreign metal doping on the step-by-step oxidation process in M-OMS-2 catalyzed activation of PMS

Various metal cations M (M = Mg2+, Ca2+, Zn2+, Cu2+, Fe3+) were doped into the tunnel of manganese octahedral molecular sieve (OMS-2). Redox-inactive metal (Ca, Mg and Zn) doped OMS-2 exhibited better peroxymonosulfate (PMS) catalytic activity than redox metal-doped Cu-OMS-2 and Fe-OMS-2. Redox-inactive metals doping improves the conductivity and reducibility of the catalyst, while transition metal doping reduces the dispersion of manganese. More importantly, the degradation of ACE can be divided into two stages. In the first stage, ACE was oxidized dominantly through mediated electron transfer process. Subsequently, singlet oxygen (1O2) gradually dominated oxidative degradation in the second stage, which was derived from the reaction between superoxide radical (O2•-) and metastable manganese intermediates. The long half-life of O2•- on the surface of OMS-2 ensured the delay generation of 1O2. This study not only provides a new idea for improving the efficiency of heterogeneous catalysts activation of PMS, but also meaningful for the in-depth study of multiple reaction mechanisms in PMS activation processes.

Experimental investigation on biomass gasification mechanism in supercritical water for poly-generation of hydrogen-rich gas and biochar

Supercritical water gasification (SCWG) technology can realize efficient utilization of biomass. But the gasification mechanism of real biomass is relatively complicated, and complete gasification only can be realized at a relatively high temperature. Identifying reaction mechanism and realize resource utilization of biomass via SCWG technology at a more moderate condition is necessary for industrialization of this technology. In this paper, biomass gasification experiment was conducted, and the gasification mechanism was analyzed. Experiment in quartz tube reactor showed that gasification efficiency and hydrogen yield increased with time and temperature, which reached 90% 14.95 mol/kg at temperature of 700℃, reaction time of 30 min. Carbon distribution study showed that more than 90% carbon was distributed in gas and biochar, proving that SCWG could realize cogeneration of hydrogen and biochar. Thus, experiment was conducted in batch tank reactor to obtain enough liquid and solid products for further study. Reaction mechanism study showed that soybean stem was decomposed to cellulose, hemicellulose, and lignin; then cellulose and hemicellulose were converted to small molecule sugar, which can be further converted to gas; as for lignin, it was decomposed to its monomers first, then it went through de-methoxy reactions and formed gases and phenol; phenol was difficult to be decomposed and could form biochar easily. Study of pore structure evolution of biochar showed that gasification in SCW could produce abundant pore structure, and with gasification proceeding, content of pores increased greatly. Pore size of biochar obtained from gasification of 15 min mainly focused on 6.5 nm and 16 nm. More mesopore were formed at the higher temperature and the diameter of macropore size increased with temperature due to the release of volatiles.

Study of combustion and NO chemical reaction mechanism in ammonia blended with DME

Ammonia (NH3) has been supposed to be the potential alternative energy source towards carbon neutrality. However, it has several unfavorable combustion characteristics, such as the slow combustion rate, poor combustion stability, high ignition energy and so on. As a renewable fuel, dimethyl ether (DME) is also considered to be a favorable carbon–neutral fuel, which can improve the combustion process of ammonia. To investigate the combustion and emission mechanism for the NH3/DME dual-fuel combustion, a detailed chemical reaction mechanism with 221 species and 1597 reactions was developed based on the previous relevant work. The laminar burning velocity (LBV) and ignition delay time (IDT) of ammonia, DME and NH3/DME combustion under a wide range of initial conditions were validated in 0-D and 1-D models. The process of NO formation and reduction reaction was also studied under the laminar burning combustion and ignition model, and it was found that fuel NOx still dominates the total NOx production in NH3/DME combustion, and the DME addition in ammonia up to 50% promotes the NO formation reaction, producing more NO. In order to analyze the effect of DME addition on NO formation mechanism, the analyses of chemical reaction pathway, sensitivity analysis on NO, typical active radical evolution behaviors and rate of production (ROP) were conducted in detail. In comparison with D50 (50%NH3/50%DME), D25(75%NH3/25%DME) with higher ammonia content generates more NH and NH2 radicals, and therefore, promoting the NO reduction reaction. Lower DME content in D25 also generates less H/O/OH active radicals, which inhibits the generation of NO. It is reduced by 9% approximately in total at equivalence ratio of 0.7. In addition, CH3 generated from DME could also partly promote the conversion of HNO and NO2 to NO, slightly increasing the NO production.

Mechanistic insights into catalysis of in-situ iron on pyrolysis of waste printed circuit boards: Comparative study of kinetics, products, and reaction mechanism

Pyrolysis is a potential recovery method for waste printed circuit boards (WPCBs), but the organic brominated products are toxic and hazardous. Iron has been used as a catalyst for debromination from pyrolysis oil, but the effects of in-situ iron on WPCBs pyrolysis is still not well understood. Herein, the pyrolysis mechanism for laminates of PCBs in the absence and presence of iron was studied via analyzing pyrolysis characteristics, kinetics, and products. According to the thermogravimetry experiments, pyrolysis of all samples could be divided into four stages, and iron accelerated the pyrolysis reaction by decreasing the activation energy as calculated using the Starink method. Volatiles released during the heating process were continuously determined by TG-FTIR-MS, and products generated at different pyrolysis temperatures were collected and characterized. The obtained results exhibited that iron promoted the generation of gaseous products and facilitated the conversion of organic bromides to inorganic bromides. Therefore, retaining iron was beneficial to energy saving and environmental protection for WPCBs pyrolysis. In addition, the decomposition mechanisms of brominated epoxy resin with and without iron were proposed. This work would contribute to the improvement and application of WPCBs pyrolysis technology.

The Comparative Study of Reaction Mechanisms and Catalytic Performances of Cu–SSZ-13 and Fe–SSZ-13 for the NH3-SCR Reaction

The Comparative Study of Reaction Mechanisms and Catalytic Performances of Cu–SSZ-13 and Fe–SSZ-13 for the NH3-SCR Reaction

Highly active Fe36Co44 bimetallic nanoclusters catalysts for hydrolysis of ammonia borane: The first-principles study

In this paper, Fe36Co44 nanocluster structure is used to catalyze the hydrolysis reaction of ammonia borane to produce H2. Firstly, we complete the construction of Fe36Co44 cluster structure and calculate the electronic properties of the cluster. By comparing the adsorption process of Ammonia Borane (AB) in active sites of the cluster, which have different Effective Coordination Number (ECN), the qualitative relationship between ECN and the catalytic activation of AB is clarified, and the optimal catalytic active site is obtained. Then, from the perspective of different reaction paths, we study the hydrolysis reaction of AB in multiple paths, and obtain 5 different reaction paths and energy profiles. The calculation results show that in the case of NH bond priority break (path 5), the reaction has the minimum rate-determining step (RDS) barrier (about 1.02 eV) and the entire reaction is exothermic (about 0.40 eV). So, path 5 is an optimal catalytic reaction path. This study will have an important guiding significance for the study of the AB hydrolysis reaction mechanism.

Reaction mechanism and reservoir simulation study of the high-temperature nitrogen injection in-situ oil shale process: A case study in Songliao Basin, China

China’s oil shale reserves are 739.1 billion tons and 45 per cent of which are in Songliao Basin. Therefore, a pilot project is conducted in Songliao Basin, aimed at technical preparation for commercial in-situ oil shale processes production. Because N2 is readily accessible and has no damage to the formation, the high-temperature nitrogen injection in-situ conversion process (HNICP) is the most basic convection heating technique, which is used in the pilot project. In this study, the Wellington reaction model is adjusted to describes the pyrolysis behavior and characteristics of shale in Songliao Basin, China. Based on the geological data and production date of the pilot project in Songliao Basin, a simulation model matching the production test scheme is established to investigate subsequent production performance and the evolution of reservoir physical properties for 550 days. Finally, the effect of injection temperature, total organic carbon (TOC), and enclosing area on the recovery factor is analyzed. The results show that the oil production rate can be divided into four stages for the HNICP of oil shale. In the third stage, prechar accumulation is very severe in the main fracture. However, the prechar accumulation relieves the heat short problem in the main fracture. The high temperature is beneficial to the production of oil, HC, and prechar. The formation plugging in the low TOC shale formation is more serious. Because of the spontaneous imbibition of oil in the formation away from the main fracture, the small enclosing area is beneficial to the production of oil.