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•A micro-kinetic model is developed by involving a set of coverage dependence factors to accurately describe the catalytic oxidation of C2H4 and CH4 on the Pt surface.•Experiments are ...performed in an isothermal Pt microtube reactor to validate the model.•The formation of hydrocarbon oxygenates is important for the effective catalytic activity of the Pt surface.
The kinetics of ethylene (C2H4) and methane (CH4) on platinum (Pt) is investigated in an isothermal Pt microtube. A micro-kinetic model of C1 and C2 hydrocarbon oxidation on the Pt(111) surface established using density functional theory is tuned and validated based on experimental results obtained from the Pt microtube. Density functional theory (DFT) modelling is carried out to evaluate the Pt(111) surface coverage of selected species on the thermochemistry and kinetics. The model reasonably predicts the conversion temperature and carbon selectivity of C2H4 and CH4 oxidation under various fuel-oxygen ratios. Micro-kinetic analysis based on this model illustrates that the formation of hydrocarbon oxygenates intermediates is essential, which makes the activity of surface oxygen species decisive in the catalytic activity.
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•Determination of activation energies rationalizes the high selectivity to methanol.•Promoting and inhibiting effects of reactants and (by)products are elucidated.•In2O3-x(1 1 1) is ...identified as the main active facet empirically and experimentally.•DFT shows heterolytic H2 splitting and hydride-proton transfer as key for mechanism.•The experimental kinetic parameters are correlated to an ab initio microkinetic model.
Indium oxide has emerged as a highly effective catalyst for methanol synthesis by direct CO2 hydrogenation. Aiming at gathering a deeper fundamental understanding, mechanistic and (micro)kinetic aspects of this catalytic system were investigated. Steady-state evaluation at 5 MPa and variable temperature indicated a lower apparent activation energy for CO2 hydrogenation than for the reverse watergas shift reaction (103 versus 117 kJ mol−1), which is in line with the high methanol selectivity observed. Upon changing the partial pressure of reactants and products, apparent reaction orders of −0.1, 0.5, −0.2, and −0.9 were determined for CO2, H2, methanol, and water, respectively, which highlight a strong inhibition by the latter. Co-feeding of H2O led to catalyst deactivation by sintering for partial pressures exceeding 0.125 MPa, while addition of the byproduct CO to the gas stream could be favorable at a total pressure below 4 MPa but was detrimental at higher pressures. Density Functional Theory simulations conducted on In2O3(1 1 1), which was experimentally and theoretically shown to be the most exposed surface termination, indicated that oxygen vacancies surrounded by three indium atoms enable the activation of CO2 and split hydrogen heterolytically, stabilizing the polarized species formed. The most energetically favored path to methanol comprises three consecutive additions of hydrides and protons and features CH2OOH and CH2(OH)2 as intermediates. Microkinetic modeling based on the DFT results provided values for temperature and concentration-dependent parameters, which are in good agreement with the empirically obtained data. These results are expected to drive further optimization of In2O3-based materials and serve as a solid basis for reactor and process design, thus fostering advances towards a potential large-scale methanol synthesis from CO2.
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•Another available source of C1 species is by HCO → CH + O, apart from CO → C + O.•Thermo stability of CH2 species is a dominant factor in the CH4 formation.•Different mechanisms of ...C1 + C1 couplings are found on the Fe surfaces.•Exposition of the Fe facets could tune CH4 selectivity.
To tune CH4 selectivity of Fe-based Fischer-Tropsch synthesis (FTS) in the initial stage is of prime scientific and industrial importance to further improve the catalyst performance. Herein, distribution of CH4 selectivity on the metallic Fe nanoparticle is predicted by DFT calculations and micro-kinetics analysis about the competition between C1 hydrogenations and C1 + C1 couplings on abundant Fe surfaces including Fe(1 0 0), Fe(1 1 0), Fe(1 1 1), Fe(2 1 1), and Fe(3 1 0). The results show that HCO mechanism (HCO → CH + O) is an available source of C1 species apart from CO direct dissociation. These Fe surfaces exhibit high effective barriers for CH4 formation, which is linearly correlated to the thermal stability of CH2 species. However, carbon chain prolongation on the more stable surfaces greatly depends on the coupling of C and CH species. On the less stable Fe(1 1 1) surface, the CO + C coupling is the main route for chain prolongation. Utilizing the effective barrier difference between the CH4 formation and the most feasible C1 + C1 coupling as a descriptor of CH4 selectivity, it is quantified that CH4 selectivity decreases in sequence of Fe(1 0 0) > Fe(2 1 1) > Fe(1 1 0) > Fe(3 1 0) > Fe(1 1 1). It is revealed that thermal stability of the CH2 species and exposition of the Fe facets could play essential roles in tuning CH4 selectivity. Trying to expand the area of Fe(2 1 1), Fe(3 1 0) and especially Fe(1 1 1) surfaces would greatly suppress CH4 selectivity without a decrease of activity. This work provides new insights and design principles for the Fe-based FTS catalysts.
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•Tetralin, naphthalene and 1-methylnaphthalene conversion over HZSM-5 was modelled.•Hydrogenation, isomerization, dehydrogenation, and cracking reactions were included.•Kinetic rate ...parameters were optimized using experimental data with good agreement.•Model was expanded with coke formation reactions and validated by experimental data.•Sensitivity analysis was performed for a better insight into the surface mechanisms.
Biomass tar chemical model compounds (tetralin, naphthalene and 1-methylnaphthalene) have been previously extensively investigated over alumina, various zeolite materials and metal(s)-modified rate catalysts. In this mechanistic work, the relationship between cascade molecular structures, intermediates and reactivity was examined as a first time quantification through detailed micro-kinetic modelling. Herein, systematic measurement-based kinetics, consisting of the 17 gas phase species, 23 bonded adsorbed molecules and sites with the 41 reactions between them, are reported. System was tested based on the obtained experimental data for 1,2,3,4-tetrahydronaphthalene, aromatics and isomer hydrocracking, hydrogenation, and isomerization processes. Proposed derived representation exhibited a good consistent agreement with statistical numerical variation only, including hydrogen-activated hydrocarbon conversion, BTX (benzene, toluene and xylenes) selectivity and coking. Experiments have been before carried out in a packed bed reactor over the H-beta, H-mordenite, H-USY, H-Y and H-ZSM-5, or (Ga, Nb, Ni, NiMo, Sn, W, Zr or H3P(W3O10)4)/ZSM-5 without the sulphide standard procedures in the functional temperature range of 370–500 °C under applied atmospheric pressure. The most promising yield was achieved over H-ZSM-5. Plug flow reactor (PFR), ideal continuous stirred tank (CSTR) vessel, and coupling the PFR with diffusion was considered, where the 1st one is found as the most fitting to results. The influence of the feedstock on catalytic activity performance was also studied. Deactivation was detected due to stable coke formation, stability was decreased, but predictability was shown. A technique sensitivity analysis was also performed BTX products. Simulations indicated that heat or mass transfer resistances, either intra- or inter-particle, were negligible.
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•Experimental and in-silico study on HDO of bio-based furfural.•Directly comparable kinetic parameters and TOF for Pd, Ru, and Ni catalysts.•Adsorption and desorption kinetics ...obtained from TPD analysis.•Ring hydrogenation was more prevalent than ring opening on all catalysts.•Interfacial sites increased activity on alumina-supported catalysts.
The furfural hydro-treatment process over Ni/Al2O3, Ni/SiO2, Pd/Al2O3, Pd/SiO2, Ru/Al2O3 and Ru/SiO2 was investigated in a three-phase batch reactor operation at 150 °C, 175 °C and 200 °C, 60 barg hydrogen and tetrahydrofuran as solvent. The strength and rate of adsorption and desorption to/from acidic, metallic and interface site structures were determined, using H2 temperature-programmed reduction (H2-TPR), CO (CO-TPD) and NH3 (NH3-TPD) desorption experiments, and subsequent regression analysis of the results by numerical modelling and optimisation. To quantify the contribution of transport, active metal materials and support effect relationship, a generalized micro-kinetic model was postulated, which has been shown to describe experimental result outcomes well. Mechanistic description and regression analysis were applied to evaluate the role of the support (Al2O3 or SiO2) on the catalytic element (Ni, Pd or Ru) atoms, their energy impact on the individual steps and selectivity. Evaluation of morphological and structural characteristics, and sorption or intrinsic reaction kinetics has indicated that the coverage of acidic sites (on alumina or silica) facilitated yielding ring hydrogenation, inhibited deoxygenation, decarbonylation and cyclic compound opening, and supressed etherification. The rates for aromatics or aldehyde functional groups were, nonetheless, affected in a different order. Understanding the chemistry of bio-based furanic derivatives mechanistically is vital and can improve the process of their conversion into of mono- or di-alcohols.
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•Non-oxidative methane conversion to C2 products was carried out over stable Pt/CeO2 catalyst.•The catalyst was stable for 245 h of time on stream.•Micro-kinetic model was developed ...for a reaction in a packed bed reactor.•Sensitivity analysis was performed and most important elementary reaction steps were elucidated.
A single atom Pt/CeO2 catalyst for the direct non-oxidative methane coupling (NOCM) operation to C2 hydrocarbon product species was prepared, mechanisms were evaluated, and kinetics based on elementary step reaction scheme equations were determined. The catalyst was characterized by a number of techniques; scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were implemented. CO DRIFTS showed the presence of single Pt atoms. Temperature, CH4 flow and functional weight hourly space velocity were varied in the ranges of 780–910 °C, 0.9–2.6 mL min-1 and 0.094–0.29 h−1, respectively. The applied total pressure, used was 1.5 bar. The highest reactant conversion achieved was 4.3 mol.%, the selectivity to C2 was 60 mol.%, and to ethene alone, maximally 80 mol.% among C2 products. Also some coke was forming, but processing remained stable for 245 h of the time on stream. System’s kinetic parameters were fitted to quantitative data values, non-linear regression analyses were being reiterated, and a relatively good agreement with the space–time point sets for CH4, ethylene, acetylene and hydrogen was reached. The sensitivity analysis of fixed rate constants showed which reaction steps influence reacting CH4, the reactivity towards transformed C2 and yields the most. It was shown that the important physico-chemical transformations are CH4 adsorption, the abstraction of the first H• from its neutral CH4 molecule on the surface and the sorption/desorption of H2. Fast C–C bond processes only have a limited measurable effect on CH4 converted. C2 are primarily affected by the Pt adhesion/release of CH4, synthesized C2 and H2. Modelling may be translated to other catalytic NOCM understanding, designing and optimizing, as an alternative to steam methane reforming.
•Energy-efficient electrowinning-coupled CO2 capture (ECC) system was provided.•Electrochemical mechanism and kinetics of ECC process was investigated to provide valuable insights into its practical ...operation.•Micro-kinetics model was developed and validated by bench-scale ECC operation, which achieved energy requirements of 47.1–50.2 kJe/mol CO2.•The process modeling was an effective and efficient way to screen various experimental parameters of ECC and save experimental investment.
The emerging electrochemical CO2 captures are energy-intensive or inefficient (operated at low current density). Here, we proposed a promising electrowinning-coupled CO2 capture (ECC) system using copper (Cu) as electrochemical mediator and ammonia (NH3) as CO2 absorbent to advance the electrically-driven approach. The Cu-mediated ECC process used the electro-active competitor of Cu(NH)42+/Cu to achieve efficient electrochemical CO2 desorption and NH3 regeneration at desirable energy consumption. To elucidate the electrochemical behavior of the CO2 desorption and NH3 regeneration, we performed experimental electrochemical analysis. This inspired us that to ensure a desired electrodissolution-coupled competitive complexation of Cu2+, CO2 with NH3 and electrodeposition-coupled separation of Cu2+ from NH3, efficient redox-active reaction of Cu(NH)42+/Cu should be achieved. We developed micro-kinetics process model, which achieved energy requirements of 47.1–50.2 kJe/mol CO2. This energy performance was competitive with the 100–500 kJe/mol of other advanced electrochemical CO2 capture approaches. The modeling energy consumption was very close to that of the value obtained from bench-scale ECC electrolysis. It is anticipated that the Cu-mediated ECC process would provide an energy-efficient pathway with desirable Faradaically-driven operational efficiency, ultimately advancing electrochemical CO2 capture towards industrial application.
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Electrodissolution-coupled hafnium alkoxide synthesis (EHS) is a promising pathway for efficient electro- synthesis. It employs simultaneous heterogeneous reactions of Hf dissolution and ethanol ...dehydrogenation, and spontaneous solution-based combination reaction between Hf4+ cations and alkoxy anions. To elucidate the mechanism and kinetics of EHS process, the electrochemical behaviors of anodic Hf dissolution and cathodic ethanol dehydrogenation were explored through electrochemical measurements, SEM observations, gas chromatography, and micro-kinetics modeling. The results indicated the supporting electrolytes of tetraethylammonium chloride (Et4NCl) to be preferable, which facilitated a passive-film-punctured pitting mechanism for Hf dissolution and a two-stage dehydrogenation mechanism. Three indicators related to passive rate, sensitivity towards puncture of the passive film, and pitting rate were extracted to quantify the kinetics of passive puncture and Hf corrosion. Micro-kinetics models were developed to evaluate the Et4NCl-based EHS process, which achieved electric energy requirements of 1.53–1.83 kW·h/kg Hf(OC2H5)4.
We present a novel procedure for computing washcoat diffusional effects in monolith reactors with detailed micro-kinetic models. First, we show that the short time scales associated with the ...adsorption/desorption steps of micro-kinetic models requires using a significantly larger number of mesh points within the washcoat to obtain a solution that is independent of the mesh size. Next, we present a multi-mode reduced order model that eliminates the degrees of freedom associated with species diffusion in the washcoat using the local property dependent internal mass transfer coefficient matrix. This matrix is shown to be diagonal for most micro-kinetic models of practical interest and can be calculated accurately. We illustrate the new approach with an example of H2/CO/C3H6 oxidation over a Pt/Al2O3 catalyst with a 20 step micro-kinetic model. Even for this simple single site model, the small time (and length) scales associated with the species adsorption steps make the computation of the mesh size independent solution of the 1＋1D model time consuming. However, the reduced order model leads to an accurate solution while speeding-up calculations by about three orders of magnitude.
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•A method is presented to include washcoat diffusional effects with micro-kinetics.•Various approximations for washcoat diffusional effects are compared.•Examples are provided to illustrate the utility of the proposed method.•The proposed method can speed-up the calculations by orders of magnitude.
Membrane reactor processes can be used to overcome the constraints of the chemical rate equilibrium of methanol (MeOH) synthesis products. In this thermodynamics-limited work, three different ...selective sulfonated poly(ether ketones) (SPEEK) membranes were applied in an engineered unit operation with a commercial Cu/ZnO/Al2O3/MgO surface catalyst for several CO2/CO-involving chemistries. A detailed mathematical model with micro-kinetics was developed, optimised and utilised to assess the vessel with barrier by using CERRES (Chemical Reaction and Reactor Engineering Simulations). Scaled separation tests were described by the integrated reference values of permeance. The permeability for all compound molecules (H2, H2O, CO, CO2, MeOH) was determined by adjusting parameters to account for the experimental gas composition on the permeate, interface and retention segment side after reduction. The specific kinetic characteristics of the mechanism of elementary step reactions were analysed in fixed bed design. A comparison of the estimated data prediction for the packed system with related definite numbers showed excellent statistical agreement. Similarly, a very good reliability was obtained between the results for 3 SPEEK membrane cases. Thus, the defined particular evaluations of derived theoretical expressions were benchmarked accurately. Although (validated) performance, i.e. the yield of MeOH, was overestimated, discrepancy was not so large so as to simulate behaviour verily. The (3-aminopropyl)triethoxysilane (polyamide) over a SPEEK layer performed best for intensification. Herein, the pressurised (>50 bar) CO2 hydrogenation pathway was not only shifted by in situ removal as a proof of concept, but also modelled intrinsically, considering transport phenomena resistances, adsorption and desorption as well. The storage of hydrogen can benefit from MeOH production reengineering.
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•Membrane reactors can overcome thermodynamic constraints in methanol production.•A model of membrane reactor with micro-kinetics for CO2 conversion on CuZn catalyst.•Introducing CERRES (Chemical Reaction and Reactor Engineering Simulations).•Utilizing (3-aminopropyl)triethoxysilane (polyamide) over a SPEEK layer membranes.
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