Hydrocarbon Oxidation Reactions Research Articles

Recyclable Ni(II), Cu(II), and Co(II) complexes containing Schiff base immobilized on nanosilica as catalysts in oxidation of hydrocarbons

Metal complexes (M=Ni, Cu, and Co) containing Schiff base have been synthesized and characterized using the usual coordination chemistry techniques. The complexes were immobilized in silica nanoparticle functionalized with a Schiff base (SB) and the heterogeneous catalysts were characterized by infrared spectroscopy, Scanning electron microscopy (SEM) and determination of the surface area (BET). Thermogravimetric analysis (TGA) of metal concentration was conducted using atomic absorption spectroscopy. The catalysts were studied in the oxidation reaction of hydrocarbons at 50 °C using H2O2 or tert-butyl hydroperoxide (TBHP) as oxidant. The heterogeneous catalysts NPs-SiO2-SB-Co(II) (catalyst 1), NPs-SiO2-SB-Cu(II) (catalyst 2), and NPs-SiO2-SB-Ni(II) (catalyst 3) showed moderate activities in the oxidation of cyclohexane, toluene, and benzene using H2O2 as oxidant. The results indicated that catalyst 2 displayed better activity in the oxidation of cyclohexane, toluene, and benzene. The best activity was obtained at 50 °C with the following conversions: 88 %, 78 %, and 66 % for cyclohexane, toluene and benzene, respectively. The results of the recycling experiment revealed that the copper complex immobilized in mesoporous silica nanoparticle maintains its catalytic activity after 4 cycle.

Investigating Ligand Sphere Perturbations on MnIII-Alkylperoxo Complexes.

Manganese catalysts that activate hydrogen peroxide carry out several different hydrocarbon oxidation reactions with high stereoselectivity. The commonly proposed mechanism for these reactions involves a key manganese(III)-hydroperoxo intermediate, which decays via O-O bond heterolysis to generate a Mn(V)-oxo species that institutes substrate oxidation. Due to the scarcity of characterized MnIII-hydroperoxo complexes, MnIII-alkylperoxo complexes are employed to understand factors that affect the mechanism of the O-O cleavage. Herein, we report a series of novel complexes, including two room-temperature-stable MnIII-alkylperoxo species, supported by a new amide-containing pentadentate ligand (6Medpaq5NO2). We use a combination of spectroscopic methods and density functional theory computations to probe the effects of the electronic changes in the ligand sphere trans to the hydroxo and alkylperoxo units to thermal stability and reactivity. The structural characterizations for both MnII(OTf)(6Medpaq5NO2) and [MnIII(OH)(6Medpaq5NO2)](OTf) were obtained via single-crystal X-ray crystallography. A perturbation to the ligand sphere allowed for a marked increase in reactivity towards an organic substrate, a modest change in the distribution of the O-O cleavage products from homolytic and heterolytic pathways, and little change in thermal stability.

Temperature-Dependent Selectivity and Detection of Hidden Carbon Deposition in Methane Oxidation.

Reaction products in heterogeneous catalysis can be detected either on the catalyst surface or in the gas phase after desorption. However, if atoms are dissolved in the catalyst bulk, then reaction channels can become hidden. This is the case if the dissolution rate of the deposits is faster than their formation rate. This might lead to the underestimation or even overlooking of reaction channels such as, e.g., carbon deposition during hydrocarbon oxidation reactions, which is problematic as carbon can have a significant influence on the catalytic activity. Here, we demonstrate how such hidden deposition channels can be uncovered by carefully measuring the product formation rates in the local gas phase just above the catalyst surface with time-resolved ambient pressure X-ray photoelectron spectroscopy. As a case study, we investigate methane oxidation on a polycrystalline Pd catalyst in an oxygen-lean environment at a few millibar pressure. By ramping the temperature between 350 and 525 °C, we follow the time evolution of the different reaction pathways. Only in the oxygen mass-transfer limit do we observe CO production, while our data suggests that carbon deposition also happens outside this limit.

Theoretical study of the local environment of Co-NxCy structure for selective oxidation of benzene to phenol

Adjusting the local environment of single-atom catalysts (SACs) is a promising approach to enhance the catalytic performance in benzene oxidation reaction (BOR). Herein, a range of Co-based SACs with N2/3/4-coordination numbers on graphene were constructed to investigate the effect of the electronic structure of SACs on BOR via density function theory (DFT). Expectedly, the electron density and charge amount of the Co active sites in the overall reaction path on the CoNxCy catalyst can be regulated by coordination environment. In particular, the as-formed *O=CoN4=O* intermediate displays the strongest electron interaction between Co atom and O*, thus O* has the largest electron density and the most negative charge number, resulting in a lower energy barrier of 0.69 eV for the rate-determining step of CO bond formation. The methodology in this work provides a certain theory supporting and guidance for developing highly efficient SACs with controllable coordination structures to enhance hydrocarbon oxidation reactions.

Abatement of photochemical smog precursors through complete hydrocarbon oxidation over commercial Pd catalysts under fuel-lean conditions with NO promoting effect

Currently, severe environmental issues have led to a great transition in the automotive industry from internal combustion engine vehicles to electric vehicles, but this transition will take time more than 10 years, which still requires the use of internal combustion engine vehicles. However, these vehicles emit a significant amount of hydrocarbons, in addition to nitrogen oxides (NOx), due to incomplete fuel combustion. They contribute to the formation of photochemical smog when they react with NOx in the presence of sunlight. To effectively remove these hydrocarbons from the exhaust gas of turbo-gasoline engines or diesel engines, we investigated the abatement of propane and iso-pentane, two typical hydrocarbons. In particular, we studied commercial Pd catalysts and revealed how the Pd loading and aging process simulating 4k and 100k mileage affected hydrocarbon abatement abilities, and their phases were identified using characterization technique, including CO chemisorption, X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HR-TEM). We also suggested the reaction pathway for the complete oxidation of propane over Pd catalyst based on the reaction orders of propane and oxygen: Propane adsorbs on O atoms of PdO, and the kinetically relevant C–H bond cleavage step occurs by the interaction with abundant neighboring O atoms of PdO. Finally, the propane and iso-pentane abatement ability of the Pd catalyst aged for 100k mileage were evaluated under realistic exhaust gas conditions, and the effect of each gas component in the realistic exhaust gas was identified; water inhibits the catalytic reaction of hydrocarbons by occupying the active sites, whereas NO catalyzes the hydrocarbon oxidation reaction by either changing the reaction pathway or active sites under fuel-lean conditions. These findings enable us to effectively reduce environmental pollution and facilitate a smoother transition from internal combustion engine vehicles to electric vehicles.

Effects of gold and platinum on the activity of catalysts for the complete oxidation reaction of hydrocarbons and carbon monoxide

This study presents synthesis results of catalysts made of perovskite-like oxide La2-xSrxCuO4 (x=0.0, 0.5, 1.0) using the citrate method and crystallisation at 800°C. The structure of the catalysts was characterised by X-ray diffraction (XRD). The perovskite-like oxide catalyst activity was enhanced with gold (Au) and platinum (Pt). Au was mounted on the perovskite-like oxide catalysts by the sol-gel method. The activity of the perovskite-like oxide La2-xSrxCuO4 (x=0.0, 0.5, 1.0) and the perovskite catalyst LaMnO3/LaCuO3 was evaluated by complete oxidation of volatile hydrocarbons (HCs) in a mixture of toluene and methyl ethyl ketone (MEK) and carbon monoxide (CO) in a microflow analysis system combined with gas chromatography. The results showed that the light-off temperature (the 50% conversion temperature of the catalysts) of the Pt, Au/perovskite catalyst samples decreased significantly. The light-off temperature of the Au/LaSrCuO4 Au nanoparticle catalysts in the complete CO oxidation reaction reached a temperature of 150°C, lower than the Pt/LaSrCuO4 catalyst (170°C), allowing replacement of previous Pt catalysts with Au nanoparticle catalysts. The LaSrCuO4 catalyst had better oxidising activities than the La2CuO4 catalyst, indicating that the addition of strontium (Sr) has increased the catalyst activity, and demonstrates the potential for application in catalytic converters in motorcycles.

Effect of molecular structure change on the properties of persistent free radicals during coal oxidation

This study is aimed at exploring the effect of molecular structure changes on the properties of persistent free radicals in coal during the heating process of coal spontaneous combustion (CSC). Therefore, the persistent free radicals and main functional groups variation characteristics in the process of coal oxidation were analyzed by means of in situ electron spin resonance and in situ infrared spectroscopy, and the change relationship between the molecular structure of coal and the persistent free radicals in coal during the reaction was further discussed by correlation analysis. The results showed that the concentration of persistent free radicals showed a stage change of “first decreasing, then increasing and then decreasing”. The g-factor decreases gradually and the heteroatom free radicals are consumed continuously. Dehydrogenation oxidation reaction causes the weakening of the “electron-proton” interaction, which narrows the line-width (ΔH) of free radicals. The phenolic hydroxyl as the electron donating group is converted into -CO functional group through dehydrogenation and oxidation reaction, which promotes the formation and accumulation of persistent free radicals in coal. Under the influence of phenolic hydroxyl, the relationship between the stretching vibration strength of aromatic ring CH and the properties of persistent free radicals in coal shows a similar change law with phenolic hydroxyl. In addition, the chain structure represented by –CH2-, –CH3/–CH2- is continuously consumed in the oxidative dehydrogenation reaction, triggering a series of free radical reactions. The free radicals formed in this process are affected by the steric hindrance of polymer networks and the electron delocalization of aromatic group in coal, so the persistent free radicals can be formed and accumulated. The dehydrogenation and oxidation reaction of the active group led to the reduction of g-factor and ΔH. Persistent free radicals play an important role in the free radical chain reaction that triggers CSC, so preventing the dehydrogenation and oxidation reaction of hydroxyl (especially phenolic hydroxyl) and aliphatic hydrocarbons (especially –CH2- and –CH3/–CH2-) is the key to prevent CSC.

Electronic structure contributions to O-O bond cleavage reactions for MnIII-alkylperoxo complexes.

Synthetic manganese catalysts that activate hydrogen peroxide perform a variety of hydrocarbon oxidation reactions. The most commonly proposed mechanism for these catalysts involves the generation of a manganese(III)-hydroperoxo intermediate that decays via heterolytic O-O bond cleavage to generate a Mn(V)-oxo species that initiates substrate oxidation. Due to the paucity of well-defined MnIII-hydroperoxo complexes, MnIII-alkylperoxo complexes are often employed to understand the factors that affect the O-O cleavage reaction. Herein, we examine the decay pathways of the MnIII-alkylperoxo complexes [MnIII(OOtBu)(6Medpaq)]+ and [MnIII(OOtBu)(N4S)]+, which have distinct coordination environments (N5- and N4S-, respectively). Through the use of density functional theory (DFT) calculations and comparisons with published experimental data, we are able to rationalize the differences in the decay pathways of these complexes. For the [MnIII(OOtBu)(N4S)]+ system, O-O homolysis proceeds via a two-state mechanism that involves a crossing from the quintet reactant to a triplet state. A high energy singlet state discourages O-O heterolysis for this complex. In contrast, while quintet-triplet crossing is unfavorable for [MnIII(OOtBu)(6Medpaq)]+, a relatively low-energy single state accounts for the observation of both O-O homolysis and heterolysis products for this complex. The origins of these differences in decay pathways are linked to variations in the electronic structures of the MnIII-alkylperoxo complexes.

Novel Nanosized Spinel MnCoFeO4 for Low-Temperature Hydrocarbon Oxidation.

The present paper reports on MnCoFeO4 spinels with peculiar composition and their catalytic behavior in the reactions of complete oxidation of hydrocarbons. The samples were synthesized by solution combustion method with sucrose and citric acid as fuels. All samples were characterized by powder X-ray diffraction, N2-physisorption, scanning electron microscopy, thermal analysis, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy. The catalytic properties of the spinels with Mn:Co:Fe = 1:1:1 composition were studied in reactions of complete oxidation of methane, propane, butane, and propane in the presence of water as model pollutants. Both prepared catalysts are nanosized materials. The slight difference in the compositions, structure, and morphology is due to the type of fuel used in the synthesis reaction. The spinel, prepared with sucrose, shows a higher specific surface area, pore volume, higher amount of small particles fraction, higher thermal stability, and as a result, more exposed active sites on the sample surface that lead to higher catalytic activity in the studied oxidation reactions. After the catalytic tests, both samples do not undergo any substantial phase and morphological changes; thus, they could be applied in low-temperature hydrocarbon oxidation reactions.

Effect of products of low temperature oxidation reaction on NOx reduction in HC-SCR system

Fuel reforming technology using a low temperature oxidation reaction was applied to improvement of NOx reduction efficiency of hydrocarbons selective catalytic reduction (HC-SCR) system, which does not require urea. The low temperature oxidation reaction of hydrocarbons produces oxygenated hydrocarbons which has high NOx reduction ability such as aldehydes. A pre-evaporation and premixing-type fuel reformer was developed in order to generate uniform fuel/air premixed gas. To prevent from hot-flame ignition, the reaction chamber of the fuel reformer has a high surface/volume ratio and the wall temperature of the reaction chamber was controlled. As a fundamental study, NOx reduction experiments and elementary reaction calculation were carried out to investigate the suitable fuel reformer temperature and reforming equivalence ratio for the promotion of NOx reduction on the surface of the catalyst. It was found that the reforming fuel gas has a higher NOx reduction efficiency than the fuel vapor in the catalyst temperature range from 473 to 773 K. The NOx reduction efficiency was highest at the reforming temperature of 673 K. The NOx reduction efficiency at the catalyst temperature of 723 K increases with the increase in the reforming equivalence ratio. It was suggested that alcohols predominantly affect NOx reduction reaction at low catalyst temperatures, and aldehydes at high catalyst temperatures.

Fe-CONTAINING CARBON NANOTUBES AS CATALYSTS IN THE AEROBIC OXIDATION REACTIONS OF DECALIN AND TETRADECANE

This article studies the catalytic activity of multi-walled carbon nanotubes (MWCNTs) in the oxidation reactions of aliphatic and polycyclic hydrocarbons is studied. In order to determine the catalytic activity, MWCNTs catalysts containing 22.8% Fe each were used. Catalyst samples were synthesized from propane gas under optimal conditions determined by CVD method. The experiments were performed at 5 different temperatures (60, 80, 100, 120, 1400C) for 2 hours. No significant change in the oxidation reaction of both hydrocarbons was observed at relatively low temperatures. In the oxidation of decalin, when the reaction temperature rises to 1200C and 1400C, oxidation has already taken place, and the rate of the reaction is directly proportional to the increase in temperature. The same trend can be seen in the oxidation reaction of tetradecane at MWCNTs with temperatures of 120 and 1400C. However, unlike decalin, the MWCNTs sample in tetradecane oxidation showed optimal catalytic performance at 1200C. However, at these temperatures, where oxidation occurs, the oxidation of decalin and tetradecane in an environment without a catalyst is almost non-existent

Modulating the Electronic Metal‐Support Interactions in Single‐Atom Pt1−CuO Catalyst for Boosting Acetone Oxidation

AbstractThe development of highly active single‐atom catalysts (SACs) and identifying their intrinsic active sites in oxidizing industrial hazardous hydrocarbons are challenging prospects. Tuning the electronic metal‐support interactions (EMSIs) is valid for modulating the catalytic performance of SACs. We propose that the modulation of the EMSIs in a Pt1−CuO SAC significantly promotes the activity of the catalyst in acetone oxidation. The EMSIs promote charge redistribution through the unified Pt−O−Cu moieties, which modulates the d‐band structure of atomic Pt sites, and strengthens the adsorption and activation of reactants. The positively charged Pt atoms are superior for activating acetone at low temperatures, and the stretched Cu−O bonds facilitate the activation of lattice oxygen atoms to participate in subsequent oxidation. We believe that this work will guide researchers to engineer efficient SACs for application in hydrocarbon oxidation reactions.

Modulating the Electronic Metal‐Support Interactions in Single‐Atom Pt1−CuO Catalyst for Boosting Acetone Oxidation

The development of highly active single-atom catalysts (SACs) and identifying their intrinsic active sites in oxidizing industrial hazardous hydrocarbons are challenging prospects. Tuning the electronic metal-support interactions (EMSIs) is valid for modulating the catalytic performance of SACs. We propose that the modulation of the EMSIs in a Pt1 -CuO SAC significantly promotes the activity of the catalyst in acetone oxidation. The EMSIs promote charge redistribution through the unified Pt-O-Cu moieties, which modulates the d-band structure of atomic Pt sites, and strengthens the adsorption and activation of reactants. The positively charged Pt atoms are superior for activating acetone at low temperatures, and the stretched Cu-O bonds facilitate the activation of lattice oxygen atoms to participate in subsequent oxidation. We believe that this work will guide researchers to engineer efficient SACs for application in hydrocarbon oxidation reactions.

Induced Near-Infrared Emission and Controlled Photooxidation based on Sulfonated Crown Ether in Water.

Regulation of physio-chemical properties and reaction activities via noncovalent methodology has become one of increasingly significant topics in supramolecular chemistry and showed inventive applications in miscellaneous fields. Herein, we demonstrate that sulfonated crown ether can form very stable host-guest complexes with a series of push-pull-type photosensitizers, eventually leading to the dramatic fluorescence enhancement in visible and near-infrared regions. Meanwhile, severe suppression in singlet oxygen (1 O2 ) production is found, mainly due to the higher energy barriers between the excited single and triple states upon host-guest complexation. Moreover, such complexation-induced tuneable 1 O2 generation systems has been utilized in adjusting the photochemical oxidation reactions of polycyclic aromatic hydrocarbons (anthracene) and sulfides ((methylthio)benzene) in water. This supramolecularly controlled photooxidation based on the selective molecular binding of crown ether with photosensitizers may provide a feasible and applicable strategy for monitoring and modulating many photocatalysis processes in aqueous phase.

Zeolites and Related Materials as Catalyst Supports for Hydrocarbon Oxidation Reactions

Catalytic oxidation is a key technology for the conversion of petroleum-based feedstocks into useful chemicals (e.g., adipic acid, caprolactam, glycols, acrylates, and vinyl acetate) since this chemical transformation is always involved in synthesis processes. Millions of tons of these compounds are annually produced worldwide and find applications in all areas of chemical industries, ranging from pharmaceutical to large-scale commodities. The traditional industrial methods to produce large amounts of those compounds involve over-stoichiometric quantities of toxic inorganic reactants and homogeneous catalysts that operate at high temperature, originating large amounts of effluents, often leading to expensive downstream processes, along with nonrecovery of valuable catalysts that are loss within the reactant effluent. Due to the increasingly stringent environmental legislation nowadays, there is considerable pressure to replace these antiquate technologies, focusing on heterogeneous catalysts that can operate under mild reactions conditions, easily recovered, and reused. Parallelly, recent advances in the synthesis and characterization of metal complexes and metal clusters on support surfaces have brought new insights to catalysis and highlight ways to systematic catalysts design. This review aims to provide a comprehensive bibliographic examination over the last 10 years on the development of heterogeneous catalysts, i.e., organometallic complexes or metal clusters immobilized in distinct inorganic supports such as zeolites, hierarchical zeolites, silicas, and clays. The methodologies used to prepare and/or modify the supports are critically reviewed, as well as the methods used for the immobilization of the active species. The applications of the heterogenized catalysts are presented, and some case-studies are discussed in detail.

THE USE OF MODIFIED ZEOLITES AS CATALYSTS IN THE GAS-PHASE OXIDATION OF OLEFINIC HYDROCARBONS

The results of studies on the creation of highly dispersed metal zeolite systems and the study of their catalytic action in the oxidation of lower olefinic hydrocarbons (ethylene to acetaldehyde, propylene to acetone) are presented. It has been established that the selectivity of the action of these catalysts is determined by the optimal combination of the metal component in them with the acidity and structure of the zeolite. Based on the results of experimental studies of the kinetic regularities of the oxidation reactions of lower olefinic hydrocarbons on the synthesized catalysts, their probable stepwise mechanisms are presented and kinetic models of the reactions are developed.

Influence of Cobalt Substitution in LaMnO<sub>3</sub> on Catalytic Propylene Oxidation

Perovskite-type structures LaBO3 with the compositions of LaMn1-xCoxO3 (x = 0.0, 0.3, 0.5, 0.7, and 1.0) were synthesized at 800 °C by a modified co-precipitation precursor technique for total oxidation of propylene, as a model test of the hydrocarbon oxidation reaction. Details concerning the evolution of the crystal structure, morphology, and crystallite size were performed by X-ray diffraction (XRD), Thermo Gravimetry Analysis (TGA)/Differential Scanning Calorimetry (DSC), Fourier Transform Infra-Red (FTIR), Atomic Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM), and Electron Spin Resonance (ESR) techniques. All compositions were identified to be single-phase and are indexed to rhombohedral structures. TG/DSC technique evidenced a temperature of 330 °C needed for the precursor as the start point and 800 °C completion for perovskite phase formation. Slight distortion in XRD diffraction peaks was observed on substituting manganese with cobalt in B-site, and new peaks emerged. An attempt has been made to understand the effect of the B-site substitution of Co3+ ions in the lattice of LaMnO3 and their influence on catalytic total propylene oxidation efficiency. These compounds show a considerable increase in the activity of propylene oxidation to carbon dioxide and water and could be explored for hydrocarbon pollution control.

First of Its Kind Automotive Catalyst Prepared by Recycled PGMs-Catalytic Performance

The production of new automotive catalytic converters requires the increase of the quantity of Platinum Group Metals in order to deal with the strict emission standards that are imposed for vehicles. The use of PGMs coming from the recycling of spent autocatalysts could greatly reduce the cost of catalyst production for the automotive industry. This paper presents the synthesis of novel automotive Three-Way Catalysts (PLTWC, Pd/Rh = 55/5, 60 gPGMs/ft3) and diesel oxidation catalysts (PLDOC, Pt/Pd = 3/1, 110 gPGMs/ft3) from recovered PGMs, without further refinement steps. The catalysts were characterized and evaluated in terms of activity in comparison with benchmark catalysts produced using commercial metal precursors. The small-scale catalytic monoliths were successfully synthesized as evidenced by the characterization of the samples with XRF analysis, optical microscopy, and N2 physisorption. Hydrothermal ageing of the catalysts was performed and led to a significant decrease of the specific surface area of all catalysts (recycled and benchmarks) due to sintering of the support material and metal particles. The TWCs were studied for their activity in CO and unburned hydrocarbon oxidation reactions under a slightly lean environment of the gas mixture (λ > 1) as well as for their ability to reduce NOx under a slightly rich gas mixture (λ < 1). Recycled TWC fresh catalyst presented the best performance amongst the catalysts studied for the abatement of all pollutant gases, and they also showed the highest Oxygen Storage Capacity value. Moreover, comparing the aged samples, the catalyst produced from recycled PGMs presented higher activity than the one synthesized with the use of commercial PGM metal precursors. The results obtained for the DOC catalysts showed that the aged PLDOC catalyst outperformed both the fresh catalyst and the aged DOC catalyst prepared with the use of commercial metal precursors for the oxidation of CO, hydrocarbons, and NO. The latter reveals the effect of the presence of several impurities in the recovered PGMs solutions.

Application of cascade forward neural network and group method of data handling to modeling crude oil pyrolysis during thermal enhanced oil recovery

Oil recovery during in situ combustion is majorly controlled by hydrocarbon oxidation and pyrolysis reactions, which govern fuel formation and heat evolution. Fuel deposition, in turn, can be accurately predicted in part through crude oil pyrolysis using thermogravimetry analysis (TGA). The theoretical models based on TGA runs, however, may be limited to crude oil samples at hand. In this study, we develop more general models to predict the residual mass during crude oil pyrolysis based on multi-layer perceptron (MLP), cascade forward (CFNN), generalized regression (GRNN), and radial basis function (RBF) neural networks. More than 2000 experimental data spanning wide range of weight percentages of asphaltenes and resins as well as o API gravities, heating rates, and temperatures are used. Moreover, six optimization algorithms; including Bayesian regularization (BR), scaled conjugate gradient (SCG), Levenberg-Marquardt (LM), conjugate gradient backpropagation with Fletcher-Reeves updates (CGF), resilient backpropagation (RB), and conjugate gradient backpropagation with Polak-Ribiére updates (CGP) are used to improve the performance and prediction ability of the MLP and CFNN neural networks. The CFNN model optimized with the LM algorithm best fits all the experimental data with a mean absolute percent relative error of 1.04%. Lastly, a mathematical correlation is developed utilizing the group method of data handling (GMDH) to estimate the residual mass of crude oil pyrolysis in TGA. Despite its simplicity, the correlation also provides very good estimates. Sensitivity analysis showed that temperature followed by asphaltenes and resin content showed the highest effect on mass loss during crude oil pyrolysis. Outliers estimation applying the Leverage approach suggested only 1% of the data points could be doubtful. • The residual mass during crude oil pyrolysis is modeled using CFNN, MLP and RBF, GRNN models. • A simple to use correlation is also developed using group method of data handling based on 2000 experimental data. • Six optimization algorithms are used to optimize the models. • The CFNN-LM model best fits all the experimental data with a mean absolute percent relative error of 1.04%. • The leverage approach proved that the CFNN-LM model and experimental data are statistically valid.

Aqueous Electrochemical Partial Oxidation of Hydrocarbons By a Gas Diffusion Electrode Carrying Ru-Doped Covalent Triazine Framework

The oxidative functionalization of organic substrates to valuable chemicals has attracted global interest from both fundamental and practical viewpoints. One of the promising approaches for the C-H oxidative functionalization is an aqueous electrochemical method because it can operate under mild conditions without toxic oxidants or flammable solvents. However, there are two major challenging issues for the further dissemination of electrochemical hydrocarbon oxidation in aqueous solution. The first one is the low solubility of raw organics in aqueous media. Here, we focus on gas diffusion electrodes (GDEs) that have been originally developed for hydrogen/oxygen fuel cells in an attempt to overcome this problem. The other major issue is that highly reactive species on an electrocatalyst are required for the activation of stable C−H bonds of hydrocarbons. Although high-valency ruthenium-oxo species (RuIV=O or RuV=O) are known to catalyze O-atom insertion into stable C-H bonds, Ru-based molecular electrocatalysts generally exhibit poor robustness and also catalyze the competitive oxygen evolution reaction (OER) in aqueous solutions. Our group has recently reported that singly isolated Ru-doped covalent triazine frameworks (Ru-CTF) effectively oxidize benzyl alcohol in aqueous electrolytes without the OER[1]. Besides, Ru-CTF displayed higher stability than an organometallic complex immobilized on an electrode because of the covalently cross-linked structure of CTF. In this study, we attempt to realize the electrochemical oxidation of vaporized hydrocarbons in aqueous solutions using a GDE that supports Ru-CTFs (Ru-CTF/GDE).A mixture of 1.0 g ZnCl2, 100 mg 2,6-dicyanopyridine, and 100 mg Ketjenblack was filled into a vacuum glass tube and then heated at 400 °C for 40 hours to prepare a CTF. Ru atoms were then impregnated into the CTF using 0.91 mM RuCl3 ethanol solution for 6 h at 90 °C. A catalyst ink was prepared by dispersing 4.0 mg Ru-CTF in 38 μL 5% Nafion solution and 400 μL ethanol, which was then added dropwise onto the GDE.Ethylbenzene (EB)-saturated (1.2×103 Pa) argon gas was supplied from the backside of GDE as a model substrate. Reaction products in liquid phases after electrolysis were quantitatively analyzed using high-performance liquid chromatography. When the GDE electrode carrying Ru-CTF was applied at 1.5V vs. RHE, acetophenone was generated as the product of ethylbenzene oxidation. The amount of generated acetophenone reached up to 4.7 µmol after 6 h electrolysis. In contrast, generated acetophenone was almost negligible in the absence of ethylbenzene or for bare CTF (without Ru). These results indicated that the Ru atoms in CTF served as the active center for ethylbenzene oxidation. For comparison, electrochemical measurements of Ru-CTF/GDE with 0.2 mM EB in the electrolyte instead of gaseous EB were also conducted using the same GDE electrochemical cell. In this case, the gas chamber was filled with pure argon gas. Although the EB concentration of 0.2 mM is about one-seventh lower than the saturated concentration (solubility of EB in water: 1.4 mM), the amount of acetophenone generated from gaseous EB was over 40-fold larger than that from the electrolyte. This result demonstrates that a GDE is effective for the aqueous electrochemical oxidation of hydrophobic organic compounds. The stability of Ru-CTF on GDE was investigated by the repeated tests in which an EB oxidation reaction was performed over four consecutive cycles with the replacement of the electrolyte every 12 h. Ru-CTF on GDE had negligible deactivation for both current-time profiles and acetophenone generation with repeated use. These results indicate that Ru-CTF on GDE has good stability at 1.5 V vs. RHE.In summary, gaseous EB was successfully oxidized to acetophenone in aqueous electrolytes using a GDE that supported Ru-CTF. Singly isolated Ru-atoms coordinated with nitrogen atoms in Ru-CTF were converted to high-valency Ru=O by water oxidation, and O-atom insertion into the C-H bond of EB was facilitated. Considering that Ru-CTF is highly stable during the long-term electrolysis in aqueous solution, Ru-CTF is a novel platform as a heterogeneous electrocatalyst for partial hydrocarbon oxidation reactions. This is the first demonstration of electrochemical hydrocarbon oxidation in aqueous electrolytes using GDEs. The three-dimensional microstructures in the GDE maximized the transportation of gaseous hydrocarbons, and the oxidation reaction occurred at the triple-phase boundary. The present results clearly demonstrate that GDEs are a promising approach for the electrochemical oxidative upgrading of hydrophobic organics.Reference:[1] S. Yamaguchi et al. Chem. Commun. 2017, 53, 10437-10440.Figure. (a) Schematic illustration of GDE carrying Ru-CTF (left), Molecular structure of Ru-CTF (right), (b) The amount of acetophenone generated as a function of time with gaseous EB (Black), with 0.2 mM aqueous EB (Gray). Figure 1