Eley-Rideal Reaction Mechanism Research Articles

Nox impact on mercury removal based on TAC: A comprehensive DFT and XAFS analysis

The simplification of surface chemical reactions is crucial for comprehending the role of nitrogen oxides (NOx) in the adsorption behavior of elemental mercury (Hg0) onto carbon-based sorbents, thereby contributing to technological advancements in reducing mercury emissions. In this study, we developed two fundamental models for activated carbon and investigated the interactions among the carbon surface, NO/NO2, and Hg0 using density functional theory (DFT) calculations. Additionally, thermally-treated activated carbon (TAC) was utilized for Hg0 adsorption, and X-ray absorption fine structure (XAFS) analysis was conducted to examine the morphology and bonding environment of captured Hg. The results suggest that the carbon surface exhibits weak physisorption towards Hg0, but effectively adsorbs NO/NO2. Adsorption of NO/NO2 on the carbon surface with a zigzag edge leads to a decrease in the ADCH charge and surrounding electrostatic potential (ESP) of neighboring carbon vertices, thereby enhancing Hg0 adsorption in those regions through the Eley-Rideal reaction mechanism. The interaction between Hg0 and the surface with ZNO1, ZNO2, or ZNOO2 configurations involves electron transfer and subsequent formation of Hg-C ionic bonds, resulting in adsorption energies ranging from −91.33 to −87.56 kJ/mol. Notably, the adsorption of Hg0 onto the surface with ZNOO1 configuration results in a more extensive electron transfer, facilitating the formation of a robust Hg-O ionic bond and leading to a further reduction in Hg0 adsorption energy to −430.02 kJ/mol. XAFS analysis confirms that predominant formation of Hg-O species occurs following Hg0 adsorption on TAC under syngas containing NO2.

Preparation of fibrous ceramic-based catalytic membranes by microwave heating and their structural properties and dust and NO removal characteristics

Different drying methods were used to prepare catalytic membranes for the simultaneous removal of dust and NO to explore their effect on the distribution of active components, with the structural properties, filtration performance, catalytic performance, and working mechanism of the preferred prepared catalytic membrane systematically investigated. The results indicated that microwave drying, in contrast to traditional electric drying with blasting, effectively inhibited the migration of the precursor solution to achieve uniform loading of active components, thus endowing the catalytic membrane with excellent catalytic activity. Meanwhile, the pore structure of the fibrous ceramic substrate was not almost affected by the loaded catalyst and still exhibited high porosity. These characteristics contributed to the development of a catalytic membrane with good filtration and catalytic performance, as well as superior adaptable NO concentration and filtration velocity properties. Therefore, fibrous ceramic-based catalytic membranes prepared using microwave assistance offer considerable application prospects for integrated purification of high-temperature flue gases. Furthermore, the removal of dust and NO was determined to follow the Eley–Rideal reaction mechanism and surface filtration mechanism of the residual dust cake, respectively.

Substitutional Coinage Metals as Promising Defects for Adsorption and Detection of Gases on MoS2 Monolayers: A Computational Approach.

Defective molybdenum disulfide (MoS2) monolayers (MLs) modified with coinage metal atoms (Cu, Ag and Au) embedded in sulfur vacancies are studied at a dispersion-corrected density functional level. Atmospheric constituents (H2, O2 and N2) and air pollutants (CO and NO), known as secondary greenhouse gases, are adsorbed on up to two atoms embedded into sulfur vacancies in MoS2 MLs. The adsorption energies suggest that the NO (1.44 eV) and CO (1.24 eV) are chemisorbed more strongly than O2 (1.07 eV) and N2 (0.66 eV) on the ML with a cooper atom substituting for a sulfur atom. Therefore, the adsorption of N2 and O2 does not compete with NO or CO adsorption. Besides, NO adsorbed on embedded Cu creates a new level in the band gap. In addition, it was found that the CO molecule could directly react with the pre-adsorbed O2 molecule on a Cu atom, forming the complex OOCO, via the Eley-Rideal reaction mechanism. The adsorption energies of CO, NO and O2 on Au2S2, Cu2S2 and Ag2S2 embedded into two sulfur vacancies were competitive. Charge transference occurs from the defective MoS2 ML to the adsorbed molecules, oxidizing the later ones (NO, CO and O2) since they act as acceptors. The total and projected density of states reveal that a MoS2 ML modified with copper, gold and silver dimers could be used to design electronic or magnetic devices for sensing applications in the adsorption of NO, CO and O2 molecules. Moreover, NO and O2 molecules adsorbed on MoS2-Au2s2 and MoS2-Cu2s2 introduce a transition from metallic to half-metallic behavior for applications in spintronics. These modified monolayers are expected to exhibit chemiresistive behavior, meaning their electrical resistance changes in response to the presence of NO molecules. This property makes them suitable for detecting and measuring NO concentrations. Also, modified materials with half-metal behavior could be beneficial for spintronic devices, particularly those that require spin-polarized currents.

Interaction mechanism between CO and H2S over CuFe2O4 oxygen carrier during chemical-looping combustion: A DFT study

During the chemical-looping combustion process, CO as an important part of syngas and H2S as a common sulfur compound inevitably coexist in the fuel. Based on the density functional theory and periodic structure model, the interaction mechanism between CO and H2S over the O-defective CuFe2O4 surface was comprehensively investigated. The results show that the adsorption energies of adsorbates on the O-defective surface are in the order of S* (−205.42 kJ/mol) > HS* (−191.37 kJ/mol) > CO (−44.88 kJ/mol) > H2S* (−28.97 kJ/mol). CO adsorption over the O-defective surface is dominant as compared to H2S adsorption. The adsorption energies of CO in the presence of H2S, HS* and S* are − 73.21, −255.98 and − 105.35 kJ/mol, respectively. The adsorption strength of CO over the O-defective surface was enhanced in the presence of HS* or S*. The presence of CO* will greatly limit the H2S dehydrogenation process, especially for the second dehydrogenation step. The energy barriers of CO oxidation with the participation of H2S*, HS* and S* are 69.66, 51.42 and 14.19 kJ/mol, respectively. COS may be produced form the reaction between CO and S* with an energy barrier of 27.13 kJ/mol, following the Eley–Rideal reaction mechanism. CuFe2O4 oxygen carrier exhibits good anti-sulfur ability because the reaction of CuFe2O4 with CO and H2S kinetically prefers the CO oxidation pathway rather than the COS formation pathway.

Identification of High‐Performance Single‐Atom MXenes Catalysts for Low‐Temperature CO Oxidation

AbstractOn the basis of first‐principles calculations, Fe, Co, Ni, Cu, Zn, Ru, Rh, Ag, Ir, Pt, and Au decorated Mo2CO2−δ monolayers are investigated as potential single‐atom catalyst (SAC) candidates for low‐temperature CO oxidation reaction. From a first screening based on intuitive criteria concerning metal sintering, CO poisoning, and O2 adsorption strength, the Zn/Mo2CO2−δ system is selected for further scrutiny by means of reactivity calculations for different CO concentrations. A lower barrier is found for Eley–Rideal reaction mechanism than for the Langmuir–Hinshelwood mechanism. The low Eley–Rideal barrier (0.15 eV) is attributed to the fact that the Zn atom weakens the O‐O bond considerably and the electrophilic attack of CO weakens it further. The main conclusion is that this system is a promising low‐temperature SAC candidate with a lower energy barrier for CO oxidation than noble metal and other 2D SAC systems investigated.

Kinetics of Gas Phase Synthesis of Ethyl-tert-butyl Ether (ETBE) on H3PW12O40/MCM-41 Catalyst

The mechanism and kinetics of gas phase synthesis of ethyl-tert-butyl ether (ETBE) in the reaction between tert-butyl alcohol (TBA) and ethanol (EtOH) were investigated performing the reaction in a continuous flow quartz reactor at different temperatures and atmospheric pressure, using a heteropoliacid catalyst with 30wt% loading, dispersed on MCM-41. The Eley-Rideal reaction mechanism was previously proposed based on experimental observations that showed the rate of ETBE increased when partial pressure of tert-butyl alcohol increased, and the partial pressure of ethanol decreased, without significant effects on product selectivity. The kinetic model based on the Eley-Rideal mechanism was proposed and successfully employed to model accurately the experimental data at three different temperatures. The apparent activation energy and the frequency factor of the etherification reaction were 39.42 kJ/mol and 1.69 x 108 mol/kg . h . bar, respectively.

Catalytic synthesis of fatty acid methyl esters from Madhuca indica oil in supercritical methanol

Fatty acid methyl esters (FAMEs) that are used as biodiesel can be synthesized in supercritical methylating agents such as supercritical methanol. While the synthesis can be conducted both non-catalytically and catalytically, the synthesis in the presence of oxides is significantly faster. In this study, FAMEs were synthesized by transesterification of a non-edible oil (Mahua, Madhuca indica) in supercritical methanol with a wide variety of oxides. The reaction was extensively studied with eleven different oxides, synthesized using the solution combustion method, as catalysts. In addition, the best two catalysts, namely MgO and Mn3O4, were synthesized using four different fuels in the combustion synthesis. The catalytic effect of all these oxides was investigated and conversions ranging from 5% to 100% were obtained over the investigated range of temperature from 503 K to 583 K, and with reaction time varying between 2 min and 80 min. Among all the catalysts, MgO synthesized with ascorbic acid as the fuel for the solution combustion gave the best results. Therefore, this catalyst was chosen and the influence of operating temperature for the transesterification reaction (503–583 K) on the rate of the reaction was studied. A pseudo first order kinetic model was obtained based on the proposed Eley-Rideal reaction mechanism and, the rate constants were obtained. The rate constants varied between 1.61 × 10−3 s−1 to 4.93 × 10−3 s−1 with an activation energy of 36 kJ/mol and a pre-exponential factor of 9.33 s−1. The rate constant obtained for the non-catalytic supercritical transesterification with oxide as catalyst was significantly higher than the rate constant of 9.9 × 10−5 s−1 obtained for the non-catalytic reaction at 523 K. The activation energy for the catalyzed reaction (36 kJ/mol) was notably lower than the activation energy (75 kJ/mol) for the uncatalyzed reaction indicating the efficacy of the catalyst.

Supercritical water syntheses of transition metal-doped CeO2 nano-catalysts for selective catalytic reduction of NO by CO: An in situ diffuse reflectance Fourier transform infrared spectroscopy study

In the present study, we synthesized CeO2 catalysts doped with various transition metals (M = Co, Fe, or Cu) using a supercritical water hydrothermal route, which led to the incorporation of the metal ions in the CeO2 lattice, forming solid solutions. The catalysts were then used for the selective catalytic reduction (SCR) of NO by CO. The Cu-doped catalyst exhibited the highest SCR activity; it had a T50 (i.e., 50% NO conversion) of only 83 °C and a T90 (i.e., 90% NO conversion) of 126 °C. Such an activity was also higher than in many state-of-the-art catalysts. In situ diffuse reflectance Fourier transform infrared spectroscopy suggested that the MOx-CeO2 catalysts (M = Co and Fe) mainly followed an Eley-Rideal reaction mechanism for CO-SCR. In contrast, a Langmuir-Hinshelwood SCR reaction mechanism occurred in CuO-CeO2 owing to the presence of Cu+ species, which ensured effective adsorption of CO. This explains why CuO-CeO2 exhibited the highest activity with regard to the SCR of NO by CO.

CO oxidation on Mn-N4 porphyrin-like carbon nanotube: A DFT-D study

First-principle calculations based on dispersion-corrected density functional theory (DFT-D) are carried out to reveal the elementary steps of CO oxidation on Mn-N4 porphyrin-like carbon nanotube (MnN4-CNT). The stability of MnN4-CNT is confirmed by the first-principles molecular dynamics simulation. According to the energetic calculations, CO and O2 prefer to anchor at the MnN4 site and the adsorption of CO is slightly more favorable than O2. The three reaction mechanisms of CO oxidation on the MnN4-CNT are explored, namely, Eley-Rideal, Langmuir–Hinshelwood, and a “new” termolecular Eley-Rideal, respectively. It is found that the termolecular Eley-Rideal reaction mechanism is the most favorable one and the energy barrier for the rate-limiting step is merely 0.69eV. Our results suggest the high catalytic activity of MnN4-CNT for CO oxidation at room temperature.

A kinetic study on methylation of naphthalene over Fe/ZSM-5 zeolite catalysts

2,6-Dimethylnaphthalene is an important dimethylnaphthalene isomer which can be used in the production of polyethylene naphthalate. The novelty of this study is to reveal Langmuir–Hinshelwood and Eley–Rideal reaction rate equations for the methylation of naphthalene over Fe/ZSM-5 zeolite catalysts besides the proposed reaction rate equation. To investigate the kinetics and mechanisms of naphthalene methylation, the methylation experiments were carried out in a gas–solid catalytic fixed-bed reactor in the presence of Fe/ZSM-5 zeolite catalysts at two different temperatures (450 and 500 °C) and five different weight hourly space velocities (0.5, 1.0, 1.5, 2.0, 2.5, 3.0 h−1). A naphthalene:methanol:1,2,4-trimethyl benzene mixture having a 1:3:10 molar ratio was used as a feed stream. The methylation products were identified by using GC–MS. For the methylation kinetics of naphthalene, the reaction rates depending on the naphthalene and methanol concentration were determined. Furthermore, the effects of temperature and weight hourly space velocity on the conversion of naphthalene, the selectivity of 2,6-dimethylnaphthalene, and the ratio of 2-methylnaphthalene/1-methylnaphthalene were determined. The results of this study demonstrate that the Langmuir–Hinshelwood reaction mechanism for naphthalene methylation is more compatible at 450 °C and the Eley–Rideal reaction mechanism at 500 °C. Moreover, in addition to 2,6-dimethylnaphthalene, other dimethylnaphthalene and tri-methylnaphthalene isomers were formed in the methylation of naphthalene. The conversion of naphthalene reached approximately 70%. Moreover, the highest selectivity of 2,6-dimethylnaphthalene was almost 40%. The ratios of 2-methylnaphthalene/1-methylnaphalene demonstrate that the methylation of naphthalene to 2-methynaphthalene is much higher than to 1-methynaphthalene.

Impact of HCl and O2 on removal of elemental mercury by heat-treated activated carbon: Integrated X-ray analysis

Treated activated carbons, prepared by heat treatment of activated carbon sorbents under the protection of argon (Ar), were subjected to synthetic flue gases to investigate its elemental mercury (Hg0) capture and the specific role of HCl and O2. To elucidate the adsorption mechanisms & binding properties, subsequent sorbents were characterized by X-ray photoelectron spectroscopy and X-ray absorption fine structure spectroscopy. The results suggest that Hg0 capture on the heat treated activated carbon (TAC) under HCl atmosphere mainly follows Eley-Rideal reaction mechanism, where, HCl reacts with the basic active carbon sites on the TAC leading to the formation of Cl-containing active sites, subsequently gaseous Hg0 heterogeneously reacts with these Cl-containing active sites through electron-transfer and forms HgClx compounds. Both the 2.42Å and 2.39Å bonding distance of Hg-Cl shows that only one of the two valence electrons on mercury bond with Cl, while the other electron bonds with the basic active carbon site covalently. In presence of HCl and O2, the synergistic effect of O2 on Hg0 adsorption might attribute to the O2 adsorption and the subsequent formation of oxygen-containing functional groups (OFGs) on TAC, which increase the amount of effective activated sites for Hg0 adsorption and at the same time enhance the adsorbing kinetics of adjacent Cl-containing sites.

Dynamic molecular oxygen production in cometary comae

Abundant molecular oxygen was discovered in the coma of comet 67P/Churyumov–Gerasimenko. Its origin was ascribed to primordial gaseous O2 incorporated into the nucleus during the comet’s formation. This thesis was put forward after discounting several O2 production mechanisms in comets, including photolysis and radiolysis of water, solar wind–surface interactions and gas-phase collisions. Here we report an original Eley–Rideal reaction mechanism, which permits direct O2 formation in single collisions of energetic water ions with oxidized cometary surface analogues. The reaction proceeds by H2O+ abstracting a surface O-atom, then forming an excited precursor state, which dissociates to produce O2−. Subsequent photo-detachment leads to molecular O2, whose presence in the coma may thus be linked directly to water molecules and their interaction with the solar wind. This abiotic O2 production mechanism is consistent with reported trends in the 67P coma and raises awareness of the role of energetic negative ions in comets.

Performance of Fe-ZSM-5 for selective catalytic reduction of NOx with NH3: Effect of the atmosphere during the preparation of catalysts

Fe-ZSM-5 catalysts for selective catalytic reduction (SCR) of NOx with ammonia were prepared by ion exchange under different atmospheres and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Temperature-programmed desorption of NH3 and NO (NH3-TPD and NO-TPD), Ultraviolet–visible (UV–vis) spectroscopy and in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). The results show that the atmosphere during ion exchange and calcination significantly affects the cation exchange capacity and the nature of the Fe species in Fe-ZSM-5 catalysts. An air atmosphere was conducive to improving the ability of ZSM-5 zeolites for Fe ionic exchange. However, isolated Fe3+ sites were dominant in Fe-ZSM-5 catalyst (Fe-Z(N2)) prepared under a N2 atmosphere, and small oligomeric FexOy clusters and FexOy nano-particles were markedly increased in Fe-ZSM-5 catalyst prepared in air, resulting in the higher SCR activity and wide temperature window of Fe-Z(N2). Moreover, Fe-Z(N2) catalyst possessed more Brønsted acid sites and could adsorb more NH3 species, promoting its SCR activity. In situ DRIFT studies showed that NH3 can be adsorbed on both Brønsted and Lewis acid sites on Fe-ZSM-5 catalyst, and this adsorbed NH3 can react with gaseous NOx. Additionally, NOx can be adsorbed on Fe-ZSM-5 catalyst, mainly as a bidentate nitrate, but these nitrate species cannot be confirmed to react with gaseous NH3 because of the overlap with the strong absorption band of adsorbed NH3 species. Based on the IR results and weak adsorption of NOx over Fe-ZSM-5 catalysts, it was concluded that NH3-SCR over this Fe-ZSM-5 catalyst predominantly follows the Eley-Rideal reaction mechanism.

Direct Hydrogenation of Dinitrogen and Dioxygen via Eley–Rideal Reactions

AbstractMost Eley–Rideal abstraction reactions involve an energetic gas‐phase atom reacting directly with a surface adsorbate to form a molecular product. Molecular projectiles are generally less reactive, may dissociate upon collision with the surface, and thus more difficult to prove that they can participate intact in abstraction reactions. Here we provide experimental evidence for direct reactions occurring between molecular N2+ and O2+ projectiles and surface‐adsorbed D atoms in two steps: first, the two atoms of the diatomic molecule undergo consecutive collisions with a metal surface atom without bond rupture; and second, the rebounding molecule abstracts a surface D atom to form N2D and O2D intermediates, respectively, detected as ions. The kinematics of the collisional interaction confirms product formation by an Eley–Rideal reaction mechanism and accounts for inelastic energy losses commensurate with surface re‐ionization. Such energetic hydrogenation of dinitrogen may provide facile activation of its triple bond as a first step towards bond cleavage.

Direct Hydrogenation of Dinitrogen and Dioxygen via Eley-Rideal Reactions.

Most Eley-Rideal abstraction reactions involve an energetic gas-phase atom reacting directly with a surface adsorbate to form a molecular product. Molecular projectiles are generally less reactive, may dissociate upon collision with the surface, and thus more difficult to prove that they can participate intact in abstraction reactions. Here we provide experimental evidence for direct reactions occurring between molecular N2 (+) and O2 (+) projectiles and surface-adsorbed D atoms in two steps: first, the two atoms of the diatomic molecule undergo consecutive collisions with a metal surface atom without bond rupture; and second, the rebounding molecule abstracts a surface D atom to form N2 D and O2 D intermediates, respectively, detected as ions. The kinematics of the collisional interaction confirms product formation by an Eley-Rideal reaction mechanism and accounts for inelastic energy losses commensurate with surface re-ionization. Such energetic hydrogenation of dinitrogen may provide facile activation of its triple bond as a first step towards bond cleavage.

Kinetics and Mechanism of Ethyl Acetate Production Using Eco-Benign Solid Catalyst

The kinetics and mechanism of an eco-benign clay catalyst employed in the production of ethyl acetate was evaluated. The results obtained revealed that the conversion of acetic acid was dependent on the catalyst weight, reaction time and mole ratio. The maximum conversion of acetic acid was obtained for mole ratio (acid: alcohol) of 2:1 with optimum catalyst weight of 2.0g at a reaction temperature of 363K and 150 minutes time on-stream. Kinetic studies revealed that the esterification reaction was second-order and followed the single step Eley-Rideal reaction mechanism.

Theoretical Study of Inorganic Carbonaceous Species Reaction with the Surfaces of BaTiO3(001)

Due to the variety of component elements and their high chemical stability at elevated temperatures, various perovskite oxide materials have been used to replace catalyst containing precious metals as oxidation catalysts or oxygen-activated catalysts (1). Additionally, because of their oxygen mobility through the material the C accumulation is not promoted. Such is the case of the resistance towards C deposition of Ni/BaTiO3-Al2O3 when employed as catalyst for low temperature dry reforming of CH4 (2). During the CH4 reforming, the C deposition is caused mainly due the CH4 decomposition or the CO disproportionation reaction that will lead to the formation of CO2 and C. On the other hand, one of the drawbacks of some perovskite materials such as BaTiO3 is that in the presence of CO2 the formation of a localized stable carbonate phase on the surface is possible (3). This carbonate phase will affect not only the catalytic activity of the material, but also may influence in its electronic properties. In this study the density functional theory (DFT) will be employed to analyze from a theoretical point of view the interaction of CO2 and the CO disproportionation reaction on the surfaces of BaTiO3(001). Our first approach with the BaO-terminated surface revealed that the CO molecule chemisorbs on the surface O atom. Additionally, if another CO molecule from the gas phase will interact with the already adsorbed CO molecule (Eley-Rideal reaction mechanism), the formation of trioxydehydroethene showed high spontaneity and the least stable but still probable to occur is the formation of CO2 and C that chemisorbs on top of an O atom (disproportionation reaction). Moreover, for the CO2 reaction with the BaO-terminated surface, the formation of CO3 anion showed to be quite stable. Furthermore, the CO2 reaction and CO disproportionation reaction will be also analyzed for the TiO2-terminated surface. References J. T. S. Irvine, in Perovskite Oxide for Solid Oxide Fuel Cells, T. Ishihara, Ed., p. 167, Springer, Fukuoka (2008).X. Li, Q. Hu, Y. Yang, Y. Wang, and F. He, Appl. Catal. A, 413– 414, 163, (2012).M. Wegman, L. Watson, A. Hendry, J. Am. Ceram. Soc., 87, 371 (2004).

Theoretical Study of Inorganic Carbonaceous Species Reaction with the Surfaces of BaTiO3(001)

In this study, the density functional theory was employed to analyze from a theoretical point of view the reaction of CO and CO2 with the surfaces of BaTiO3(001). Our results showed that the adsorption of CO is more stable on the TiO2-terminated than on the BaO-terminated slab. Additionally, this interaction led to the stable formation of CO3 on the TiO2-terminated slab. Similarly, the chemisorption of CO2 on both surfaces showed to be high stable, and it led to the CO3 formation on the BaOT slab. Moreover, in order to investigate the possibility of carbon deposition, the CO disproportionation reaction was considered to occur via the Eley-Rideal reaction mechanism. However, it was observed that the carbon deposition is quite energetically demanding, more challenging for the BaO-terminated surface than for the TiO2-terminated, and might not occur at the operating conditions of the solid oxide fuel cells.

Determination of methanolysis rate constants for low and high fatty acid oils using heterogeneous surface reaction kinetic models

Catalytic methanolysis of soybean oil with Amberlyst A26-OH basic ion-exchange resin was studied in the presence and absence of free fatty acids. Catalytic methanolysis of soybean oil is a key step in the biodiesel production process. The use of the heterogeneous Amberlyst A26-OH basic resin to catalyze this conversion is of interest due to the resin’s ability to be recovered, regenerated, and reused. This current research modeled methanolysis on the surface of the heterogeneous catalyst using both the Eley–Rideal and Langmuir–Hinshelwood–Hougen–Watson reaction kinetic models. For all experiments, soybean oil (with and without 5 % oleic acid incorporated) was reacted with methanol at a molar ratio of 1:10 soybean oil to methanol in the presence of Amberlyst A26-OH (added at 20 % by weight of oil). The reaction was carried out over multiple investigations in a batch reactor where the reactants were mixed at 550 rpm and held at 50 °C and atmospheric pressure. The resulting data demonstrated that the Eley–Rideal reaction mechanism offered the best description of the surface interactions occurring on the resin. Based upon Eley–Rideal model fitting, the mean (± standard deviation) methanolysis rate constant (the rate at which methanol was consumed during the reaction) was determined to be 7.48 × 10−4 (±4.05 × 10−5) h−1 with free fatty acid absent and 1.94 (± 1.25 × 10−1) h−1 with free fatty acid present.

CO Oxidation on the Pd(111) Surface

Under technologically relevant oxygen-rich conditions, the reaction mechanism of CO oxidation over transition metals can be complicated by the formation of oxides. Questions of whether the active surface for CO oxidation is a pristine metal, a surface oxide, or a bulk oxide is still under active debate. In this study, density functional theory calculations are used to model CO oxidation on the Pd(111) surface. Our results show that a thin layer of Pd5O4 surface oxide is stable under catalytically relevant gas-phase conditions. Three-fold oxygen atoms in the surface are found to react with gas-phase CO molecules following an Eley–Rideal reaction mechanism. Such CO oxidation reduces the surface oxide, but the oxide can be replenished by O2 dissociation. Kinetic analysis shows that experimentally observed reaction conditions, that are uninhibited by CO and limited only by mass transfer, correspond to a surface oxide phase with CO oxidation occurring though the Eley–Rideal mechanism. Under steady-state operating conditions, the continuous formation and decomposition of the surface oxide is expected and is key to the high CO oxidation rate on Pd(111).