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Showing papers on "Reaction rate published in 2021"


Journal ArticleDOI
04 Feb 2021
TL;DR: In this paper, a selective photocatalytic oxidation of methane at room temperature using quantum-sized bismuth vanadate nanoparticles as the catalyst and oxygen as a mild oxidant was reported.
Abstract: The direct oxidation of methane to more desirable, one-carbon oxygenated molecules such as methanol and formaldehyde offers a pathway towards a more sustainable chemical industry as the current commercial reforming process involving two steps features a high carbon footprint and energy consumption. Here, we report the selective photocatalytic oxidation of methane at room temperature using quantum-sized bismuth vanadate nanoparticles as the catalyst and oxygen as a mild oxidant. The reaction offers a high selectivity, of 96.6% for methanol or 86.7% for formaldehyde, under optimum wavelength and intensity of light, reaction time and amount of water solvent. Comprehensive characterizations disclose a multistep reaction mechanism in which the activation of methane by the hydroxyl radical determines the reaction rate. This work broadens the avenue towards the selective conversion of the greenhouse gas methane into desirable chemical products in a sustainable way. The conversion of methane to target one-carbon oxygenates relies on a two-step process that is carbon and energy intensive. Direct oxidation offers a sustainable alternative pathway. Here, the authors report on the selective photocatalytic oxidation of methane at room temperature using bismuth vanadate catalyst, realizing high methanol and formaldehyde selectivity.

90 citations


Journal ArticleDOI
TL;DR: In this article, the incorporation of unreducible metal oxides (MxOy) onto CuO hybrid magnetic nano ferric oxide (Cu@Fe3O4) may alter the reaction pathway in persulfate activation, and increase the reaction rate constant.
Abstract: In this paper, we surprisingly found that the incorporation of unreducible metal oxides MxOy (M = Mg, Zn, Ca, Ba, Al) onto CuO hybrid magnetic nano ferric oxide (Cu@Fe3O4) may alter the reaction pathway in persulfate activation, and increase the reaction rate constant. The activation of peroxymonosulfate (PMS) by Cu@Fe3O4 led to a classic sulfate radical based oxidation process (SR-AOP) with an acetaminophen (ACE) degradation rate constant of 0.004 min−1, while 1O2-dominated nonradical oxidation process was disclosed in CuM@Fe3O4 with wildly fluctuated reaction rate constants from 0.003 to 0.242 min−1. Mechanism studies indicated that singlet oxygen (1O2) derived from the direct oxidation of superoxide anions radicals (O2 −) or the recombination of O2 − was the main reactive oxygen species (ROS) in CuM@Fe3O4/PMS system. A series of characterization experiments (pHpzc tests, XPS, H2-TPR, et al.) and DFT calculation disclosed that the addition of an unreducible metal M yielded many positive effects: (1) the formation of surface oxygen vacancies (OV) raised the zero point charge (pHpzc) of CuM@Fe3O4, thus enhanced the adsorption and activation of PMS; (2) promoting the generation of a new Cu species (Cu3+) on the surface of CuM@Fe3O4, which then participated in the generation of 1O2. The different reducibility of Cu3+ led to differences in the catalytic properties of CuM@Fe3O4. In addition, the effects of various water matrix species and the results of reusability experiment, mineralization experiment, and ecotoxicity test exhibited that CuM@Fe3O4/PMS system possessed excellent practical application value.

83 citations


Journal ArticleDOI
TL;DR: In this article, a low-energy catalytic route for methanolysis to convert PET resin to dimethyl terephthalate (DMT) was developed, and the effects of cosolvents on the catalytic performance were investigated to develop a new decomposition pathway towards DMT at ambient temperature.

77 citations


Journal ArticleDOI
01 Jul 2021-Fuel
TL;DR: In this article, a method to calculate the key parameters of coal oxidation reaction based on temperature-programmed tests was proposed, and a one-step global numerical model for exploring coal oxidation considering the effects of multi-component material was established.

71 citations


Journal ArticleDOI
26 Aug 2021
TL;DR: The physical origin of cation-dependent HER/HOR kinetics can be rationalized by an increase in concentration of cations on the negatively charged Pt surface, altering the interfacial water structure and the H-bonding network, which is supported by classical molecular dynamics simulation and surface-enhanced infrared absorption spectroscopy.
Abstract: The production of molecular hydrogen by catalyzing water splitting is central to achieving the decarbonization of sustainable fuels and chemical transformations. In this work, a series of structure-making/breaking cations in the electrolyte were investigated as spectator cations in hydrogen evolution and oxidation reactions (HER/HOR) in the pH range of 1 to 14, whose kinetics was found to be altered by up to 2 orders of magnitude by these cations. The exchange current density of HER/HOR was shown to increase with greater structure-making tendency of cations in the order of Cs+ < Rb+ < K+ < Na+ < Li+, which was accompanied by decreasing reorganization energy from the Marcus-Hush-Chidsey formalism and increasing reaction entropy. Invoking the Born model of reorganization energy and reaction entropy, the static dielectric constant of the electrolyte at the electrified interface was found to be significantly lower than that of bulk, decreasing with the structure-making tendency of cations at the negatively charged Pt surface. The physical origin of cation-dependent HER/HOR kinetics can be rationalized by an increase in concentration of cations on the negatively charged Pt surface, altering the interfacial water structure and the H-bonding network, which is supported by classical molecular dynamics simulation and surface-enhanced infrared absorption spectroscopy. This work highlights immense opportunities to control the reaction rates by tuning interfacial structures of cation and solvents.

64 citations


Journal ArticleDOI
TL;DR: In this article, a volume-averaged oxygen consumption rate (OCR) was proposed to evaluate the characteristics of the oxidation reaction of coal and showed that increasing the volume fraction of oxygen and the programmed heating rate both can promote the reaction between coal and oxygen and reduce the hysteretic effects of heating in the reaction under external heating.

61 citations


Journal ArticleDOI
28 May 2021-Science
TL;DR: In this paper, the intramolecular dehydration of cyclohexanol on H-MFI zeolites in water has been used to quantitatively show an enhancement of the reaction rate by the presence of high ionic strength.
Abstract: Tailoring the molecular environment around catalytically active sites allows for the enhancement of catalytic reactivity through a hitherto unexplored pathway. In zeolites, the presence of water creates an ionic environment via the formation of hydrated hydronium ions and the negatively charged framework aluminum tetrahedra. The high density of cation-anion pairs determined by the aluminum concentration of a zeolite induces a high local ionic strength that increases the excess chemical potential of sorbed and uncharged organic reactants. Charged transition states (carbocations for example) are stabilized, which reduces the energy barrier and leads to higher reaction rates. Using the intramolecular dehydration of cyclohexanol on H-MFI zeolites in water, we quantitatively show an enhancement of the reaction rate by the presence of high ionic strength as well as show potential limitations of this strategy.

55 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of catalysts on pyrolysis behavior was firstly investigated through thermogravimetric (TG) analysis to determine the kinetics and mechanism of the process and then laboratory scale semi-batch reactor was used to determine distribution and composition of the pyrolynsis products.

52 citations


Journal ArticleDOI
TL;DR: In this article, a citric acid-assisted sol-gel method was used to synthesize Fe0.94Sm0.06Ox catalysts with a homogeneous distribution of Sm in Fe2O3 nanoparticles.

52 citations


Journal ArticleDOI
TL;DR: Results show that H2 addition increases the laminar burning velocity, while it shortens the ignition delay time of H2/CH4/air mixture, which may effectively reduce the explosion hazards.

50 citations


Journal ArticleDOI
TL;DR: In this paper, the authors developed a convenient and reliable approach to generate micromolar level superoxide radical (O 2 ∙ - ) in aqueous solution by photolysis of formate and H2O2.

Journal ArticleDOI
TL;DR: In this paper, a piezo-tunable microcavity was used to reproduce the reported vacuum Rabi splitting but failed to observe any change in the reaction rate as the cavity thickness is tuned in and out of the strong coupling regime during a given experiment.
Abstract: One of the most exciting and debated aspects of polariton chemistry is the possibility that chemical reactions can be catalyzed by vibrational strong coupling (VSC) with confined optical modes in the absence of external illumination. Here, we report an attempt to reproduce the enhanced rate of cyanate ion hydrolysis reported by Hiura et al. [chemRxiv:7234721 (2019)] when the collective OH stretching vibrations of water (which is both the solvent and a reactant) are strongly coupled to a Fabry-Perot cavity mode. Using a piezo-tunable microcavity, we reproduce the reported vacuum Rabi splitting but fail to observe any change in the reaction rate as the cavity thickness is tuned in and out of the strong coupling regime during a given experiment. These findings suggest that there are subtleties involved in successfully realizing VSC-catalyzed reaction kinetics and therefore motivate a broader effort within the community to validate the claims of polariton chemistry in the dark.

Journal ArticleDOI
TL;DR: In this paper, a Pt/re-Mg4Al-LDH-based catalysts for selective oxidation reaction of furfural to furoic acid was reported.
Abstract: Catalytic oxidation conversion of biomass-derived resource to high value-added products has evoked considerable interest. Herein, we report a Pt atomic clusters catalyst (size: 1.3 nm) supported on rehydrated layered double hydroxides (denoted as Pt/re-Mg4Al-LDHs), which exhibits great catalytic behavior towards selective oxidation reaction of furfural to furoic acid (conversion: 99 %; yield: 97 %; reaction rate: 676.57 mmol gPt−1 h−1). This result stands at the highest standard compared with reported Pt-based catalysts. A combination research confirms the formation of surface Ptδ− species, due to the local electron transfer from support to Pt atomic clusters. LDHs provide a confined effect to achieve tunable size and highly-stabilized metal clusters, which imposes influence on catalytic performance via metal-support interactions. Both experimental methods (In situ DRIFTS, Raman, EPR and Isotope Labelling MS) and theoretical calculations reveal that the negatively-charged Pt active site plays a crucial role in determining catalytic behavior: C O bond undergoes activation adsorption on Ptδ− site, followed by reaction with H2O (Aldehyde-Water Shift); subsequently, oxygen is activated to generate reactive oxide species (O2−) that serves as a hydrogen acceptor (Oxidative Dehydrogenation) to produce furoic acid. This work displays a valuable paradigm for preparation of noble metal atomic clusters catalysts based on memory effect of LDHs support, which would pave a way for the development of heterogeneous catalysts toward selective oxidation reactions.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a kinetic model based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism for CO2 hydrogenation to methanol over a highly effective indium oxide (In2O3) catalyst.

Journal ArticleDOI
TL;DR: In this paper, thermal stability and microstructural evolution of Yb2Si2O7 were studied in high-temperature high-velocity water vapor at temperatures between 1200-1400 °C.
Abstract: Thermochemical stability and microstructural evolution of Yb2Si2O7 was studied in high-temperature high-velocity water vapor at temperatures between 1200–1400 °C. Two reactions were shown to occur in the steam environment: Yb2Si2O7 reaction to form Yb2SiO5, and further Yb2SiO5 reaction to form Yb2O3. Parabolic rates of both reactions were observed, and similar reaction enthalpies were determined for each reaction; 207 kJ/mol and 205 kJ/mol, respectively. Densification of the product phase Yb2SiO5 shut off pore connectivity for gas transport to the reaction interface at gas velocities exceeding 115−125 m/s and for temperatures of 1300 °C and 1400 °C, resulting in reduced reaction rates at higher velocities. Outward gas diffusion by a silicon hydroxide species is predicted to govern ytterbium silicate reactions with high temperature water vapor. Microstructure changes at high temperatures and velocities were shown to greatly impact the long-term stability of Yb2Si2O7.

Journal ArticleDOI
04 Mar 2021-Langmuir
TL;DR: In this article, a simple modification of the PSO rate equation was proposed, yielding d q t d t = k'C t ( 1 - q t q e ) 2.
Abstract: The development of new adsorbent materials for the removal of toxic contaminants from drinking water is crucial toward achieving the United Nations Sustainable Development Goal 6 (clean water and sanitation). The characterization of these materials includes fitting models of adsorption kinetics to experimental data, most commonly the pseudo-second-order (PSO) model. The PSO model, however, is not sensitive to parameters such as adsorbate and adsorbent concentrations (C0 and Cs) and consequently is not able to predict changes in performance as a function of operating conditions. Furthermore, the experimental conditionality of the PSO rate constant, k2, can lead to erroneous conclusions when comparing literature results. In this study, we analyze 103 kinetic experiments from 47 literature sources to develop a relatively simple modification of the PSO rate equation, yielding d q t d t = k ' C t ( 1 - q t q e ) 2 . Unlike the original PSO model, this revised rate equation (rPSO) provides the first-order and zero-order dependencies upon C0 and Cs that we observe empirically. Our new model reduces the residual sum of squares by 66% when using a single rate constant to model multiple adsorption experiments with varying initial conditions. Furthermore, we demonstrate how the rPSO rate constant k' is more appropriate for comparing literature studies, highlighting faster kinetics in the adsorption of arsenic onto alumina versus iron oxides. This revised rate equation should find applications in engineering studies, especially since the rPSO rate constant k' does not show a counter-intuitive inverse relationship with increasing reaction rates when C0 is increased, unlike the PSO rate constant k2.

Journal ArticleDOI
TL;DR: In this paper, the photodegradation tendencies of mixed and isolated VOCs, e.g., benzene, toluene, and p-xylene were studied using TiO2 P25 as a model photocatalyst.
Abstract: The photodegradation tendencies of mixed and isolated VOCs, e.g., benzene, toluene, and p-xylene were studied using TiO2 P25 as a model photocatalyst. The degradation of VOCs in the mixture is significantly affected by the existence of different organic pollutants. For example, benzene only showed 10% degradation efficiency in the mixture whilst 67% in the isolated mode. The conversion efficiency of benzene was 20% and 27% when mixed with p-xylene and toluene, respectively. It shows that the degradability of benzene is influenced more by the presence of p-xylene than toluene. The dynamic adsorption-desorption experiments and DFT calculations on stoichiometric and defective TiO2 surface revealed that benzene only weakly interacts with the stoichiometric TiO2 surface than toluene and p-xylene. This behavior could be the fundamental factor for the lower degradation efficiency of benzene. Furthermore, the presence of oxygen vacancy (Ov) in TiO2 surface tremendously improved the overall adsorption of VOCs. Several Langmuir-Hinshelwood kinetic models, which are based on different reaction dynamic assumptions, were used to determine rates of reactions, water adsorption equilibrium constant, and VOCs adsorption equilibrium constant. The results indicated that the oxidation of VOCs occurred on the catalyst surface, and the adsorption equilibrium constant of VOCs was higher than water adsorption equilibrium constant. The intermediate formation and hydroxyl groups consumption were further rationalized via in-situ FTIR study. This work provides a comprehensive analysis of VOCs degradation in the mixed and isolated mode, which will increase the possibility of implementing the photocatalytic oxidation technology for the VOCs abatement.

Journal ArticleDOI
TL;DR: In this article, the microscopic parameters of each model were calculated by density functional theory (DFT), and the elementary reaction pathways and thermodynamic parameters of hydroxyl groups were explored, and the results of intrinsic reaction coordinate (IRC) indicated that hydrogen captured by oxygen is endothermic, while the ·OH free radical capturing hydrogen is exothermic.

Journal ArticleDOI
TL;DR: In this paper, the separation of water from mixtures containing CO2, hydrogen and water at suitable temperatures for hydrogenation of CO2 to methanol was tested with several zeolite membranes.


Journal ArticleDOI
TL;DR: In this paper, the mechanism and kinetics in catalytic hydrodeoxygenation of palmitic acid under hydrothermal conditions (310, 340 and 370°C), in which 5% Pt/C serves as catalyst and formic acid is used for in-situ H2 generation.

Journal ArticleDOI
08 Apr 2021-Chem
TL;DR: In this article, the reactivity of 1,3-Dimethyl-2-(4-(dimethylamino)phenyl)-2,4-dihydro-1H-benzoimidazole, N-DMBI-H, is investigated with a variety of imide- and amide-containing semiconductor molecules that have reduction potentials in the range −0.54 to −1.10

Journal ArticleDOI
TL;DR: In this paper, a multi-step, aqueous phase hydrogenation kinetics of furfural (FUR) to furfuryl alcohol (FA), 2-methylfuran (2MF), tetrahydrofurfury l alcohol (THFA), and 5-hydroxy-2-pentanone (5H2P) over Pd-TiO2 on an activated carbon catalyst (derived from a monolith structure) was studied.

Journal ArticleDOI
TL;DR: The catalytic performance of Ni-supported Ni catalysts for the methanation of CO2 has been investigated using different crystalline phases of TiO2 (rutile and anatase) as mentioned in this paper.

Journal ArticleDOI
TL;DR: Based on Electron spin resonance (ESR) and Fourier transform infrared (FTIR) spectroscopy, an analysis was made on the influence of different oxygen concentrations on the reaction activity of micro-groups during low-temperature coal oxidation as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, a simple demonstration of the influence of the specific surface area of a catalyst on the rate of a catalytic reaction is presented, based on a model reaction of hydrogen peroxide decomposition catalyzed by cobalt spinel (Co3O4).
Abstract: Heterogeneous catalysis plays an important role in many chemical reactions, especially those applied in industrial processes, and therefore, its theoretical foundations are introduced not only to students majoring in chemical engineering or catalysis but also as part of general chemistry courses. The consideration of catalytic activity of various solids and mechanisms of catalytic reactions requires the introduction of the concept of an active site, which together with the catalyst specific surface area are discussed as key parameters controlling the reaction rate. There are many known demonstrations of heterogeneous catalysis phenomena that can be performed live in a lecture hall, but all of them focus only on the general idea of catalytic processes and are not suitable for quantitative analysis. Therefore, herein we present a simple demonstration of the influence of the specific surface area of a catalyst on the rate of a catalytic reaction. This demonstration is based on a model reaction of hydrogen peroxide decomposition catalyzed by cobalt spinel (Co3O4) calcined at various temperatures. The differences in reaction rates can be monitored visually, and the obtained data can be used directly for a simple kinetic analysis, including comparison of numerical values of the reaction rate constants.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the differences in kinetic characteristics and PCE state of the CO2 dissociation and CH4 reforming reactions in a dielectric barrier discharge reactor (DBD), how these are mutually affected when combining both gases in the dry reforming of methane (DRM) reaction, and how they change when a packing material (nonporous SiO2) is added to the reactor.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated a steam reactor powered by propane fuel consisting of a shell and tube heat exchanger, and the results showed that the hydrogen production yield can vary from 77.5 % to 92.2 %.

Journal ArticleDOI
TL;DR: In this article, Koutecky-Levich and Butler-Volmer analyses yield electrochemical rate constants and transfer coefficients, which informed mixedpotential models that treat each nanoparticle as a short-circuited electrochemical cell.
Abstract: We examine relationships between H2O2 and H2O formation on metal nanoparticles by the electrochemical oxygen reduction reaction (ORR) and the thermochemical direct synthesis of H2O2. The similar mechanisms of such reactions suggest that these catalysts should exhibit similar reaction rates and selectivities at equivalent electrochemical potentials (μi), determined by reactant activities, electrode potential, and temperature. We quantitatively compare the kinetic parameters for 12 nanoparticle catalysts obtained in a thermocatalytic fixed-bed reactor and a ring-disk electrode cell. Koutecky-Levich and Butler-Volmer analyses yield electrochemical rate constants and transfer coefficients, which informed mixed-potential models that treat each nanoparticle as a short-circuited electrochemical cell. These models require that the hydrogen oxidation reaction (HOR) and ORR occur at equal rates to conserve the charge on nanoparticles. These kinetic relationships predict that nanoparticle catalysts operate at potentials that depend on reactant activities (H2, O2), H2O2 selectivity, and rate constants for the HOR and ORR, as confirmed by measurements of the operating potential during the direct synthesis of H2O2. The selectivities and rates of H2O2 formation during thermocatalysis and electrocatalysis correlate across all catalysts when operating at equivalent μi values. This analysis provides quantitative relationships that guide the optimization of H2O2 formation rates and selectivities. Catalysts achieve the greatest H2O2 selectivities when they operate at high H atom coverages, low temperatures, and potentials that maximize electron transfer toward stable OOH* and H2O2* while preventing excessive occupation of O-O antibonding states that lead to H2O formation. These findings guide the design and operation of catalysts that maximize H2O2 formation, and these concepts may inform other liquid-phase chemistries.

Journal ArticleDOI
TL;DR: FRR-EF is proposed, which is operated by applying the optimal potential of ferric iron reduction reaction (FRR) rather than that of 2e-ORR on cathode for EF, thus improving the comprehensive efficiency of EF.