Detailed Reaction Mechanism Research Articles

Electrocatalytic water oxidation with manganese phosphates

As inspired by the Mn4CaO5 oxygen evolution center in nature, Mn-based electrocatalysts have received overwhelming attention for water oxidation. However, the understanding of the detailed reaction mechanism has been a long-standing problem. Herein, homologous KMnPO4 and KMnPO4•H2O with 4-coordinated and 6-coordinated Mn centers, respectively, are prepared. The two catalysts constitute an ideal platform to study the structure-performance correlation. The presence of Mn(III), Mn(IV), and Mn(V) intermediate species are identified during water oxidation. The Mn(V)=O species is demonstrated to be the substance for O−O bond formation. In KMnPO4•H2O, the Mn coordination structure did not change significantly during water oxidation. In KMnPO4, the Mn coordination structure changed from 4-coordinated [MnO4] to 5-coordinated [MnO5] motif, which displays a triangular biconical configuration. The structure flexibility of [MnO5] is thermodynamically favored in retaining Mn(III)−OH and generating Mn(V)=O. The Mn(V)=O species is at equilibrium with Mn(IV)=O, the concentration of which determines the intrinsic activity of water oxidation. This study provides a clear picture of water oxidation mechanism on Mn-based systems.

The Use of the Titanium Tetrachloride (Ticl4) Catalysts as a Reagent for Organic Synthesis

Abstract: TiCl4 is a widely utilized reagent in organic synthesis, often functioning through Lewis’s acid-promoted transformations. This review explores the potential for TiCl4 to catalyse various examples, adhering to the classic catalyst definition and allowing for the use of sub-stoichiometric quantities of the catalyst relative to the substrate. The use of metal catalysts in organic synthesis has witnessed a surge in interest due to their ability to facilitate a wide range of chemical reactions. This review article highlights the significance of titanium metal catalysts via comparison with other metal catalysts like Pd [NO3]2, IrO4, Au/Fe2O3, SnCl2, and AlCl3. Among these catalysts, titanium tetrachloride (TiCl4) has gained considerable popularity for its cost-effectiveness, eco-friendliness, enhancing reaction efficiency, and ability to accelerate reactions while reducing reaction times. This comparison helps in determining the most suitable catalyst for different chemical processes, considering efficiency, safety, and economic factors. TiCl4 operates as a non-consumable catalyst, allowing for the use of sub-stoichiometric quantities relative to the substrate. This review discusses TiCl4's applications, efficiency, and mechanisms in organic synthesis. It distinguishes itself by presenting new applications and comparative efficiencies of TiCl4, delving into detailed reaction mechanisms, and discussing its environmental, economic, and safety aspects. TiCl4's role in pivotal chemical reactions, such as Friedel-Crafts acylation and alkylation, epoxidation, cyclization, Mannich reactions, Suzuki-Miyaura reactions, Pechmann condensation, Knoevenagel condensation, anti-Markovnikov hydration, pinacol coupling, and Diels-Alder reactions. These reactions have led to the synthesis of biologically active compounds like zolmitriptan, ropinirole, risperidone, and rivastigmine. TiCl4-catalyzed reactions are characterized by their mild conditions, high efficiency, and selectivity, making them an attractive choice for modern organic cyclic, acyclic, and heterocyclic synthesis.

One‐Pot N‐Alkylation of Amines over Ni(II) Embedded Reusable Porous Organic Polymer via Borrowing Hydrogen Strategy

AbstractThe first‐of‐its‐kind, one‐pot N‐alkylation reaction of amines over Ni(II) impregnated porous organic polymer of highly dense N‐rich skeleton is reported. The primeval Ni(II) decorated hollow spherical porous polymer is synthesized and employed in a series of catalytic reactions involving C−N bond formation. The catalytic reactions are optimised to yield the desired product highlighting the role of different substituents present on the reactants towards the overall selectivity and efficiency. The detailed reaction mechanism is corroborated with computation validating a three‐step arrow formalism viz. dehydrogenation of the alcohol, condensation with amines to generate the imine as intermediate followed by hydrogenation by a borrowing strategy to yield the final product. The role of the bare support material in the first step and that of the Ni(II) centres of the support material in the third step is marked as pivotal for the forward reaction to proceed with enriching sustainability and feasibility.

Electro-chemical effects on combustion chemistry in electric field fire suppression

In order to investigate the role played by electro-chemical effects in the combustion of flames under an external electric field, it is necessary to simulate the chain effect brought about by the increase of electron energy during the combustion reaction by modifying the electron energy according to the ethanol combustion mechanism containing ionic chemical reaction. Due to the large amount of computation involved in carrying out numerical simulations using detailed chemical reaction mechanisms, the mechanisms are simplified in this paper in order to save computational resources. Combining the simplified mechanism, a finite rate chemical reaction model is used to simulate the chemical reaction of ions during the transverse electric field fire extinguishing process, and the relationship between the concentration of intermediate components in ethanol air diffusion combustion and temperature is analyzed.

Study on inhomogeneous hydrogen–air mixture flame acceleration and deflagration-to-detonation transition

This paper discusses the effect of obstacle spacing on flame acceleration (FA) and deflagration-to-detonation transition (DDT) in inhomogeneous hydrogen–air mixture using the OpenFOAM open-source code and large eddy simulation technology based on the unsteady compressible reacting flow Navier–Stokes equation and the detailed chemical reaction mechanism of 9 species and 21 steps. The results show that the obstacle spacing has a more significant impact on the rapid deflagration state, manifested as an inverse relationship between the flame propagation speed and the obstacle spacing due to the negative correlation between the interference intensity of obstacles to the flow within a unit channel length and the obstacle spacing. In addition, under all conditions considered in this paper, the main mechanisms of FA and DDT are the same. Further analysis reveals that the detonation initiation dynamics portrayed in this study seem more aligned with the mechanisms proposed by Liberman and akin to the shock wave amplification mechanism of coherent energy release models. As the obstacle spacing increases, the run-up distance and the acceleration time of supersonic flames and DDT also increase. This paper also observes that the flame structure during explosion flame propagation has typical self-similarity, and the turbulence level in the obstacle area is higher, resulting in a larger fractal dimension. During flame acceleration, there is a mode transition from the “thin reaction zone” to the “broken reaction zone.”

Ab Initio Density Functional Theory Calculation: Americium Hydrolysis Mechanism.

The hydrolysis mechanism of americium was calculated using density functional theory, and the detailed microscopic reaction mechanism was obtained. The results show that americium reacts with water along the octet state to produce oxides and H2, and that this reaction is exothermic. The interaction between Am and O atoms gradually changes from initially electrostatic interaction to covalent interaction, and continues to strengthen. During the reaction process, Am atoms always lose electrons, the 5f orbital is obviously involved, and there is df orbital hybridization. This study provides the necessary theoretical data support for the theoretical and experimental study of the actinide system.

Study on the Inhibition Effect of C6F12O on Charged Particles in the Flame of Transformer Oil Discharge Gas

ABSTRACT The accidental combustion of insulating oil poses a significant risk in the event of transformer failure. The charged particles generated through the combustion ionization reaction exert considerable influence on the combustion speed and stability of the flame. Therefore, the detailed chemical reaction mechanism including neutral matter and charged particle is simplified. The two-dimensional finite rate reaction model is established. The theoretical calculation investigates the suppressive effect of the novel fire extinguishing agent C6F12O on charged particles in the flame resulting from transformer oil decomposition. The analysis encompasses changes in flame temperature, free radicals, and charged particles in the decomposition gas of transformer oil under C6F12O concentrations ranging from 0% to 4%. The findings reveal that the addition of C6F12O exerts a discernible inhibitory effect on the flame temperature of the transformer oil exhaust gas. The large reduction of charged particles in the flame caused by C6F12O is achieved by its consumption of large amounts of O and OH radicals in the flame. It hampers key elementary reactions responsible for charged particle generation. In conclusion, C6F12O demonstrates a pronounced inhibitory effect on charged particles in the flame resulting from transformer oil decomposition.

Detailed kinetic modeling of catalytic oxidative coupling of methane

The oxidative coupling of methane (OCM) at high temperature over monolithic Pt-based catalysts operated at short contact times is investigated as an attractive method for methane upgrading to higher value products like ethylene and acetylene. An experimental measurement campaign aiming at elucidating the effect of operation parameters on the catalyst performance revealed that lower N2 dilution, lower CH4/O2 ratio, and higher space velocities promote high C2 yields. A maximum C2 yield of 10 % with 94 % CH4 conversion was obtained at a CH4/O2 ratio of 1.1, 50 % N2 dilution, and a space velocity of 4.5 × 105 h−1. Since both heterogenous and homogenous gas-phase chemistry together are required for determining C2 formation pathways, a detailed OCM surface reaction mechanism over Pt is presented consisting of 26 species and 86 reactions that are consistent from the view of thermodynamics and micro-kinetic reversibility. The combination of this OCM surface mechanism with a detailed gas-phase mechanism allows a numerical micro-kinetic description of the experimental measurements. The simulations presented in this study suggest that C2 formation takes place in the gas-phase at temperature above 1200 K with both oxidative and pyrolytic pathways for methane dehydrogenation to form CH3 radicals, whose coupling results in C2H6, C2H4 and C2H2 formation. Furthermore, the simultaneous presence of sufficient oxygen content and heat are vital for high C2 species yields.

Photoelectrochemical Glycerol Oxidation Coupled with Hydrogen Production

AbstractThe catalytic oxidation of glycerol, a surplus byproduct of biodiesel, has received increasing attention due to the popular applications of its oxidation products, such as aldehydes, ketones, and carboxylates. Photoelectrochemical (PEC) methods provide a clean and sustainable pathway for glycerol oxidation and upgrading. However, selective oxidation of glycerol is a challenge due to its complex oxidation path, where the cleavage of C−O or C−C bonds at different positions can lead to a variety of products. This concept aims to describe the recent advances in PEC selective glycerol oxidation for the preparation of multiple high value‐added products, and discuss the reaction mechanism and selective production strategies in detail. Finally, the remaining challenges and future prospects for the PEC glycerol oxidation system are presented.

Investigations of the reaction mechanism of sodium with hydrogen fluoride to form sodium fluoride and the adsorption of hydrogen fluoride on sodium fluoride monomer and tetramer.

The reaction between Na and HF is a typical harpooning reaction which is of great interest due to its significance in understanding the elementary chemical reaction kinetics. This work aims to investigate the detailed reaction mechanisms of sodium with hydrogen fluoride and the adsorption of HF on the resultant NaF as well as the (NaF)4 tetramer. The results suggest that the reaction between Na and HF leads to the formation of sodium fluoride salt NaF and hydrogen gas. Na interacts with HF to form a complex HF···Na, and then the approaching of F atom of HF to Na results in a transition state H···F···Na. Accompanied by the broken of H-F bond, the bond forms between F and Na atoms as NaF, then the product NaF is yielded due to the removal of H atom. The resultant NaF can further form (NaF)4 tetramer. The interaction of NaF with HF leads to the complex NaF···HF; the form I as well as II of (NaF)4 can interact with HF to produce two complexes (i.e., (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF), but the form III of (NaF)4 can interact with HF to produce only one complex (NaF)4(III)···HF. These complexes were explored in terms of noncovalent interaction (NCI) and quantum theory of atoms in molecules (QTAIM) analyses. NCI analyses confirm the existences of attractive interactions in the complexes HF···Na, NaF···HF, (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF, and (NaF)4(III)···HF. QTAIM analyses suggest that the F···Na interaction forms in the HF···Na complex while the F···H hydrogen bonds form in NaF···HF, (NaF)4(I-1)···HF, (NaF)4(I-2)···HF, (NaF)4(II-1)···HF and (NaF)4(II-2)···HF, and (NaF)4(III)···HF complexes. Natural bond orbital (NBO) analyses were also applied to analyze the intermolecular donor-acceptor orbital interactions in these complexes. These results would provide valuable insight into the chemical reaction of Na and HF and the adsorption interaction between sodium fluoride salt and HF. The calculations were carried out at the M06-L/6-311++G(2d,2p) level of theory which were performed using the Gaussian16 program. Intrinsic reaction coordinate (IRC) calculations were carried out at the same level of theory to confirm that the obtained transition state was true. The molecular surface electrostatic potential (MSEP) was employed to understand how the complex forms. Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) analysis was used to know the topology parameters at bond critical points (BCPs) and intermolecular interactions in the complex and intermediate. The topology parameters and the BCP plots were obtained by the Multiwfn software.

6-Amino-4-aryl-7-phenyl-3-(phenylimino)-4,7-dihydro-3H-[1,2]dithiolo[3,4-b]pyridine-5-carboxamides: Synthesis, Biological Activity, Quantum Chemical Studies and In Silico Docking Studies.

New [1,2]dithiolo[3,4-b]pyridine-5-carboxamides were synthesized through the reaction of dithiomalondianilide (N,N'-diphenyldithiomalondiamide) with 3-aryl-2-cyanoacrylamides or via a three-component reaction involving aromatic aldehydes, cyanoacetamide and dithiomalondianilide in the presence of morpholine. The structure of 6-amino-4-(2,4-dichloro- phenyl)-7-phenyl-3-(phenylimino)-4,7-dihydro-3H-[1,2]dithiolo[3,4-b]pyridine-5-carboxamide was confirmed using X-ray crystallography. To understand the reaction mechanism in detail, density functional theory (DFT) calculations were performed with a Grimme B97-3c composite computational scheme. The results revealed that the rate-limiting step is a cyclization process leading to the closure of the 1,4-dihydropyridine ring, with an activation barrier of 28.8 kcal/mol. Some of the dithiolo[3,4-b]pyridines exhibited moderate herbicide safening effects against 2,4-D. Additionally, ADMET (Absorption, Distribution, Metabolism, Excretion, Toxicity) parameters were calculated and molecular docking studies were performed to identify potential protein targets.

The mechanism and kinetics of the atmospheric oxidation of CF3(CF2)2CHCH2 (HFC-1447fz) by hydroxyl radicals: ab initio investigation.

The oxidation of 3,3,4,4,5,5,5-heptafluoro-1-pentene (HFC-1447fz) by hydroxyl radicals plays a crucial role in atmospheric conditions. By employing the CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level of theory, the detailed reaction mechanism, kinetics and atmospheric implications of the degradation of HFC-1447fz by hydroxyl radicals were investigated. Compared to H-abstraction channels, the OH addition reaction is determined to be more favorable initial pathways in the degradation processes of HFC-1447fz. The overall rate coefficient of the degradation of HFC-1447fz by OH radicals is estimated to be 1.66 × 10-12 cm3 molecule-1 s-1 and the lifetime of HFC-1447fz is found to be 7 days at 298 K, which are in good agreement with the reported experimental results. The global warming potential (GWP) for HFC-1447fz on the 50, 100 and 500-year time horizons is estimated using the calculated rate coefficient. Furthermore, the mechanisms of the subsequent reactions of two OH-addition adducts have also been investigated. By TD-DFT calculations, it was found that eleven species can undergo photodissociation, while ten other species are photolytically stable under sunlight.

Recent advances in CO2 reduction with renewable reductants under hydrothermal conditions: towards efficient and net carbon benefit CO2 conversion.

The ever-growing atmospheric CO2 concentration threatening the environmental sustainability of humankind makes the reduction of CO2 to chemicals or fuels an ideal solution. Two priorities are anticipated for the conversion technology, high efficiency and net carbon benefit, to ensure the mitigation of the CO2 problem both promptly and sustainably. Until now, catalytic hydrogenation or solar/electro-chemical CO2 conversion have achieved CO2 reduction promisingly while, to some extent, compromising to fulfill the two rules, and thus alternative approaches for CO2 reduction are necessary. Natural geochemical processes as abiotic CO2 reductions give hints for efficient CO2 reduction by building hydrothermal reaction systems, and this type of reaction atmosphere provides room for introducing renewable substances as reductants, which offers the possibility to achieve CO2 reduction with net carbon benefit. While the progress in CO2 reduction has been abundantly summarized, reviews on hydrothermal CO2 reduction are relatively scarce and, more importantly, few have focused on CO2 reduction with renewable reductants with the consideration of both scale of efficiency and sustainability. This review provides a fundamental and critical review of metal, biomass and polymer waste as reducing agents for hydrothermal CO2 reduction. Various products including formic acid, methanol, methane and multi-carbon chemicals can be formed, and effects of operational parameters such as temperature, batch holding time, pH value and water filing as well as detailed reaction mechanisms are illustrated. Particularly, the critical roles of high temperature and pressure water as reaction promotor and catalyst in hydrothermal CO2 conversion are discussed at the mechanistic level. More importantly, this review compares hydrothermal CO2 reduction with other methods such as catalytic hydrogenation and photo/electrocatalysis, evaluating their efficiency and potential for net carbon benefit. The aim of this review is to promote the understanding of CO2 activation under a hydrothermal environment and provide insights into the efficient and sustainable strategy of hydrothermal CO2 conversion for future fundamental research and industrial applications.

Mechanism and origin of enantioselectivity for organocatalyzed asymmetric heteroannulation of alkynes in the construction of axially chiral C2-arylquinoline.

Axially chiral C2-arylquinoline has been successfully constructed via asymmetric heteroannulation of alkynes catalyzed by chiral phosphoric acid with high yield and high enantioselectivity. Inspired by this intriguing work, theoretical calculations have been carried out, and the detailed reaction mechanism has been elaborated, in which the whole reaction can be divided into steps including hydrogen transfer, C-N bonding, annulation reaction and the final dehydration processes. The initial hydrogen-transfer reaction has two possible pathways, while the subsequent C-N bonding process has eight possible pathways. Then, after the annulation reaction and the final dehydration processes, the major product and byproduct were formed. QTAIM and IGMH analyses were used to illustrate the role of weak intermolecular interactions in the catalytic process, and the distortion/interaction and EDA analyses provided a deeper understanding of the origin of enantioselectivity. The calculated results are consistent with the experimental results. This work would provide valuable insights into asymmetric reactions catalyzed by chiral phosphoric acid.

Redox reactions of a pyrazine-bridged RuIII(edta) binuclear complex: spectrochemical, spectroelectrochemical and theoretical studies.

The redox reactions of a pyrazine-bridged binuclear [(edta)RuIIIpzRuIII(edta)]2- (edta4- = ethylenediaminetetraacetate; pz = pyrazine) have been investigated spectrochemically and spectroelectrochemically for the first time. The kinetics of the reduction of [(edta)RuIIIpzRuIII(edta)]2- (RuIII-RuIII) with the ascorbic acid anion (HA-) was studied as a function of ascorbic concentration and temperature at a fixed pH 6.0. The overall reaction of RuIII-RuIII was found to consist of two-steps involving the initial formation of the mixed-valence [(edta)RuIIpzRuIII(edta)]3- (RuII-RuIII) intermediate complex (λmax = 462 nm, εmax = 10 000 M-1 cm-1), which undergoes further reduction by ascorbic acid to produce the [(edta)RuIIpzRuII(edta)]4-(RuII-RuII) ultimate product complex (λmax = 540 nm, εmax = 20 700 M-1 cm-1). Our studies further revealed that the RuII-RuIII and RuII-RuII species are formed in the electrochemical reduction of the RuIII-RuIII complex at 0.0 and -0.4 V (vs. SHE), respectively. Formation of RuII-RuIII and RuII-RuII was further corroborated by magnetic moment measurements and DFT calculations. Kinetic data and activation parameters are interpreted in terms of a mechanism involving rate-determining outer-sphere electron transfer between Ru(III) and the ascorbate monoanion (HA-) at pH 6.0. A detailed reaction mechanism in agreement with the spectral, spectro-electrochemical and kinetic data is presented. The results of the spectral and kinetic studies of the reaction of the RuII-RuII complex with molecular oxygen (O2) reveal the ability of the RuII-RuII species to effect the oxygen reduction reaction (ORR) leading to the formation of H2O2, a partial reduction product of dioxygen (O2).

A comprehensive experimental and kinetic modeling study of methyl tert-butyl ether combustion

A comprehensive understanding of the combustion chemistry of methyl tert‑butyl ether (MTBE) is of key importance in its application as an additive in gasoline fuels. Ignition delay times (IDTs) of MTBE/air mixtures have been measured in both a high-pressure shock tube (HPST) and in a rapid compression machine (RCM) at equivalence ratios of 0.5, 1.0, and 2.0 in air, at pressures of 10 and 30 bar over the temperature range 600 – 1350 K. Species profiles for MTBE oxidation were obtained in a jet-stirred reactor (JSR) at 1 bar, at equivalence ratios of 0.5, 1.0, and 2.0 in the temperature range 700 – 1100 K.A detailed reaction mechanism, comprising 813 species and 4319 reactions, has been developed and predicts well all of the experimental data obtained in this work and also texisitng literature data. Pressure- and temperature-dependent rate constants for the MTBE unimolecular elimination reaction producing isobutene and methanol were calculated using high-level ab-initio calculations. A sensitivity analysis reveals that this elimination reaction is important, and significantly inhibits fuel reactivity at temperatures above 1300 K. At intermediate temperatures (850 – 1300 K), the reaction MTBE + ȮH = TĊ4H8OCH3 + H2O plays a crucial role in promoting the reactivity of MTBE oxidation, whereas the reaction MTBE + ȮH = TC4H9OĊH2 + H2O is the most inhibiting reaction. At low temperatures (600 – 850 K), the isomerization reaction of TC4OCȮ2–1 ⇌ TĊ4OCO2H-2 significantly promotes the reactivity. Conversely, the reaction 2TC4OCȮ2–1 ↔ 2TC4OCȮ-1 + O2 inhibits reactivity the most. The NTC behavior in MTBE oxidation can be explained by the competition between the reactions involving the formation and consumption of cyclic ethers from TĊ4H8OCH3 radicals and the reactions associated with the formation and consumption of carbonyl hydroperoxide species.

Detailed mechanism and kinetics of reactions of anti- and syn-CH3CHOO with HC(O)OH: infrared spectra of conformers of hydroperoxyethyl formate.

The reaction of CH3CHOO with HC(O)OH has a large rate coefficient so that it might play a significant role in the formation of secondary organic aerosols (SOA) in the atmosphere. We investigated the detailed mechanism and kinetics of the reactions of Criegee intermediate anti- and syn-CH3CHOO with HC(O)OH with a step-scan Fourier-transform infrared spectrometer by recording time-resolved absorption spectra of transient species and end products produced upon irradiation at 308 nm of a flowing mixture of CH3CHI2/O2/HC(O)OH at 298 K and 60 Torr. Thirteen bands of hydroperoxyethyl formate [HC(O)OCH(CH3)OOH, HPEF], the hydrogen-transferred adduct of CH3CHOO and HC(O)OH, were observed. Careful analysis deconvoluted these bands into absorption of three conformers of HPEF: a transient HPEF (P2*/P3*), a more stable open-form HPEF (mainly P2), and a stable intramolecularly hydrogen-bonded HPEF (mainly P1). At a later period, the end-product formic acetic anhydride [CH3C(O)OC(O)H, FAA], a dehydrated product of HPEF, was observed; this end-product is the same as that observed in CH2OO + CH3C(O)OH. Theoretical calculations on the reaction pathway scheme were performed to elucidate these reaction paths. Syn-CH3CHOO + HC(O)OH produced conformers P2*/P3* initially, followed by conversion to conformers P2, whereas anti-CH3CHOO + HC(O)OH produced conformers P2 and P1 directly. We derived a rate coefficient for the reaction CH3CHOO + HC(O)OH to be k = (2.1 ± 0.7) × 10-10 cm3 molecule-1 s-1 at 298 K and 40-80 Torr; the rate coefficient appeared to show insignificant conformation-specificity. We also found that FAA was produced mainly from the dehydration of the open-form HPEF (P2) with a rate coefficient k = (1420 ± 70) s-1; the intramolecularly hydrogen-bonded HPEF (P1) is stable.

DFT study of electron donor-acceptor (EDA) complexes: mechanism exploration and theoretical prediction.

Organic synthesis methods initiated by visible light have received increasing attention from synthetic chemists. Reactions initiated by EDA complexes do not require the use of toxic or expensive photoredox catalysts, unlike traditional photoreaction processes. However, this kind of reaction requires a particular structure for the substrate, so it is important to study the detailed and systematic reaction mechanism for its design. EDA complexes of substituted 1H-indole and substituted benzyl bromide derivatives were studied by density functional theory (DFT). The difference between EDA complexes with substituents of different kinds and locations were compared by theoretical study and a new EDA complex was predicted.

Surface kinetics and pressure dependence of propane oxidation over platinum

The catalytic total oxidation of propane over platinum was investigated experimentally and numerically at pressures of 1–7 bar and catalyst temperatures up to 700 K. A wire microcalorimeter was employed to determine the global rate parameters of the catalytic reaction within the kinetically controlled regime. For 1 bar pressure, the dissociative adsorption of C3H8 on Pt and its subsequent decomposition were modeled as two lumped steps based on global reaction parameters. A detailed and thermodynamically consistent catalytic mechanism was constructed by incorporating these lumped steps with an existing atmospheric-pressure H-C2 elementary reaction model. Two-dimensional CFD simulations using the developed global and detailed reaction mechanisms closely reproduced the measured heat release rates. The intricate dependence of catalytic ignition and reactivity on pressure was further elucidated. Ignition temperatures were found to be linearly correlated to pressures, due to the weaker net adsorption of oxygen compared to that of propane, which progressively aggravated at higher pressures and in turn hindered ignition. More importantly, a non-monotonic pressure dependence of the C3H8 catalytic reactivity on Pt, which gradually diminishes with increasing temperatures, is reported for the first time. The temperature range of this non-monotonic behavior (< 650 K) is of special importance for part-load and idling operations of gas turbines using hybrid hetero-/homogeneous combustion approaches and for normal operations of recuperative microreactors. Thus, this work provides key information for the design and optimization of such devices utilizing Pt as catalyst.

Copper/ruthenium relay catalysis for stereodivergent construction of 1,4-nonadjacent stereocenters: mechanistic investigation using DFT calculations

DFT calculations were used to explore the detailed reaction mechanism, and the origins of stereodivergence, in the Cu/Ru dual-catalyzed hydroalkylation of racemic allylic alcohols and racemic ketimine esters.