Model Of Catalytic Reactor Research Articles

Ligand Many-Body Expansion as a General Approach for Accelerating Transition Metal Complex Discovery.

Methods that accelerate the evaluation of molecular properties are essential for chemical discovery. While some degree of ligand additivity has been established for transition metal complexes, it is underutilized in asymmetric complexes, such as the square pyramidal coordination geometries highly relevant to catalysis. To develop predictive methods beyond simple additivity, we apply a many-body expansion to octahedral and square pyramidal complexes and introduce a correction based on adjacent ligands (i.e., the cis interaction model). We first test the cis interaction model on adiabatic spin-splitting energies of octahedral Fe(II) complexes, predicting DFT-calculated values of unseen binary complexes to within an average error of 1.4 kcal/mol. Uncertainty analysis reveals the optimal basis, comprising the homoleptic and mer symmetric complexes. We next show that the cis model (i.e., the cis interaction model solved for the optimal basis) infers both DFT- and CCSD(T)-calculated model catalytic reaction energies to within 1 kcal/mol on average. The cis model predicts low-symmetry complexes with reaction energies outside the range of binary complex reaction energies. We observe that trans interactions are unnecessary for most monodentate systems but can be important for some combinations of ligands, such as complexes containing a mixture of bidentate and monodentate ligands. Finally, we demonstrate that the cis model may be combined with Δ-learning to predict CCSD(T) reaction energies from exhaustively calculated DFT reaction energies and the same fraction of CCSD(T) reaction energies needed for the cis model, achieving around 30% of the error from using the CCSD(T) reaction energies in the cis model alone.

Al(III) and Ga(III) triflate complexes as solvate ionic liquids: speciation and application as soluble and recyclable Lewis acidic catalysts.

This work reports on the first solvate ionic liquids (SILs) based on aluminium(III) and gallium(III) triflates, M(OTf)3, and triglyme (G3). Liquid-phase speciation of these new SILs was studied by multinuclear NMR spectroscopy. Across the compositional range of G3 : M(OTf)3 mixtures, both metals were found to be in a hexacoordinate environment, with both G3 and [OTf]- ligands present in the first coordination sphere, and apparently exchanging through a dynamic equilibrium. The Lewis acidity was quantified by the Gutmann acceptor number (AN) and compared to the performance of SILs as Lewis acidic catalysts in model [3 + 3] cycloadditions. Despite saturated coordination, AN values were relatively high, reaching AN = ca. 71-83 for Al-SILs and ca. 80-93 for Ga-SILs, corroborating the labile nature of the metal-ligand bonding. In a model catalytic reaction, SILs were fully soluble in the reaction mixtures, in contrast to the corresponding triflate salts. The catalytic performance of SILs exceeded that of the corresponding triflate salts, and Ga-SILs were more active than Al-SILs, in agreement with AN measurements. In conclusion, the new Group 13 SILs can be considered as soluble and catalytically active forms of their corresponding metal triflates, with potential uses in catalysis.

Development of Air–Ti Gas-Surface Reaction Mechanisms and Rate Calculations

Gas-surface reaction mechanisms and rates were developed for an air–titanium surface to support finite-rate catalytic surface reaction models used in computational fluid dynamics. For the surface dissociation/recombination reactions, a two-step reaction method was applied based on the assumption that two atoms must be positioned in adjacent cells to recombine. Transition state theory was used to calculate the surface reactions for adsorbed diatomic molecules to dissociate to the adjacent unit cell or atoms located in the adjacent cells to recombine into diatomic molecules. For the second step, atoms located in the adjacent cells are allowed to further dissociate to another cell (total separation), or totally separated atoms recombine into the adjacent cells. A stochastic gas-surface kinetics simulation code, STOKIN, was developed to simulate gas-surface reactions and to calculate the equilibrium constants of second molecular dissociation ⇌ recombination processes. Thermodynamic properties of the adsorbates (enthalpies, entropies, and heat capacities) were calculated using density functional theory along with statistical mechanics assuming no rotational and translational contributions to the entropies and heat capacities due to the adsorbates’ inability to freely move or rotate on the surface.

Elusive supported surface M2Ox dimer active site (M = Re, W, Mo, Cr, V, Nb, and Ta)

Supported transition metal oxide catalysts are extensively used as heterogeneous catalysts for various energy, chemical, and environmental applications. The molecular structures of dehydrated surface metal oxide phases are crucial for understanding structure-activity/selectivity relationships that guide the design of enhanced catalysts. Some early studies suggested that dimeric (aka binuclear) surface metal oxide sites were more active/selective than monomeric (aka mononuclear) sites, prompting interest in synthesizing catalysts with supported dimeric metal oxide structures. This review examines the literature on dehydrated silica-based supported group 7-5 MOx catalysts (ReOx, WOx, MoOx, CrOx, VOx, NbOx, and TaOx on SiO2, MCM-41, AlOx/SiO2, and H-ZSM-5) for their surface metal oxide structures. In situ Raman, extended x-ray absorption fine structure, and ultraviolet-visible spectroscopy indicate that monomeric surface MOx structures predominate in all such catalysts. Therefore, the cursory use of dimeric surface M2Ox sites in catalytic mechanisms and reaction models in heterogeneous catalysis by supported metal oxides is questionable, and moving forward, the invoking of supporting dimeric surface M2Ox sites should be critically examined and backed up with direct spectroscopic methods.

Impact of mixed boundary conditions and nonsmooth data on layer‐originated nonpremixed combustion problems: Higher‐order convergence analysis

AbstractThis work explores the theoretical and computational impacts of mixed‐type flux conditions and nonsmooth data on boundary/interior layer‐originated singularly perturbed semilinear reaction–diffusion problems. Such problems are prevalent in nonpremixed combustion models and catalytic reaction models. The inclusion of arbitrarily small diffusion terms results in boundary layers influenced by specific flux conditions normalized by perturbation parameters. We have demonstrated theoretically that the sharpness of the boundary layer is significantly reduced when this normalization is independent of the diffusion parameter. In addition, the presence of a nonsmooth source function gives rise to an interior layer in the current problem. We show that using upwind discretizations for mixed boundary fluxes achieves nearly second‐order accuracy if the first derivatives are not normalized concerning perturbation parameters. This outcome arises from the bounds of a prior derivative of the continuous solution. Furthermore, it is theoretically shown that nearly second‐order uniform accuracy can be attained for reaction‐dominated semilinear problems using a hybrid scheme at the discontinuity point. To ensure the uniform stability of the discrete solution, a transformation is necessary for the corresponding discrete problem. Theoretical results are supported by various experiments on nonlinear problems, illustrating the pointwise rates and highlighting both linear and higher‐order accuracy at specific points.

Thermal Truncation of Heptamethine Cyanine Dyes.

Cyanine dyes are a class of organic, usually cationic molecules containing two nitrogen centers linked through conjugated polymethine chains. The synthesis and reactivity of cyanine derivatives have been extensively investigated for decades. Unlike the recently described phototruncation process, the thermal truncation (chain shortening) reaction is a phenomenon that has rarely been reported for these important fluorophores. Here, we present a systematic investigation of the truncation of heptamethine cyanines (Cy7) to pentamethine (Cy5) and trimethine (Cy3) cyanines via homogeneous, acid-base-catalyzed nucleophilic exchange reactions. We demonstrate how different substituents at the C3' and C4' positions of the chain and different heterocyclic end groups, the presence of bases, nucleophiles, and oxygen, solvent properties, and temperature affect the truncation process. The mechanism of chain shortening, studied by various analytical and spectroscopic techniques, was verified by extensive ab initio calculation, implying the necessity to model catalytic reactions by highly correlated wave function-based methods. In this study, we provide critical insight into the reactivity of cyanine polyene chains and elucidate the truncation mechanism and methods to mitigate side processes that can occur during the synthesis of cyanine derivatives. In addition, we offer alternative routes to the preparation of symmetrical and unsymmetrical meso-substituted Cy5 derivatives.

Gas–Liquid Mass Transfer Intensification for Selective Alkyne Semi-Hydrogenation with an Advanced Elastic Catalytic Foam-Bed Reactor

The Elastic Catalytic Foam-bed Reactor (EcFR) technology was used to enhance a model catalytic hydrogenation reaction by improving gas–liquid mass transfer. This advanced technology is based on a column packed with a commercial elastomeric polyurethane open-cell foam, which also acts as a catalyst support. A simple and efficient crankshaft-inspired system applied in situ compression/relaxation movements to the foam bed. For the first time, the catalytic support parameters (i.e., porosity, tortuosity, characteristic length, etc.) underwent cyclic and controlled changes over time. These dynamic cycles have made it possible to intensify the transfer of gas to liquid at a constant energy level. The application chosen was the selective hydrogenation of phenylacetylene to styrene in an alcoholic solution using a palladium-based catalyst under hydrogen bubble conditions. The conversion observed with this EcFR at 1 Hz as cycle frequency was compared with that observed with a conventional Fixed Catalytic Foam-bed Reactor (FcFR).

Modeling and numerical analysis for cylindrical flow-through catalytic membrane reactor with power-law reaction kinetics: Revealing dead-core phenomena

Cylindrical flow-through catalytic membrane reactors, employing porous membranes impregnated with catalysts, offer enhanced selectivity and yield in chemical reactions. This work focuses on the mathematical modeling and numerical analysis of a cylindrical flow-through catalytic membrane reactor. The proposed reactor model addresses a critical gap in research by incorporating realistic geometries of porous catalytic membranes. This model simulates a series of irreversible reactions following power-law kinetics under non-isothermal conditions within the reactor, formulated using a system of non-linear differential equations to account for mass and heat balances.The paper investigates the occurrence of dead zones within the membrane reactor as a result of rapid reactant depletion, a phenomenon that has not been extensively studied in prior literature for cylindrical membrane reactors. Problems with fractional reaction exponents require efficient numerical solvers since conventional iterative solvers encounter difficulties due to the fact that the power-law reaction term with fractional reaction exponent is not differentiable at the vanishing concentration. A novel time-marching scheme specifically designed for the cylindrical catalytic flow-through membrane reactor is developed and applied for simulations to get valuable insights into dead-core phenomena.The effects of dimensionless process parameters, including Thiele modulus, Peclet numbers, reaction exponent, Prater number, and a membrane geometrical parameter on the concentration and temperature profiles, as well as dead zone formation, are extensively investigated. The simulation results demonstrate that these parameters affect the occurrence of dead zones and their size. Finally, the effect of convective flow on the reactor performance indicators is presented.

Recovered carbon black from tires as carbon carrier in metal oxide catalytic systems

Pyrolysis is one of the most common methods of end-of-life tires (ELTs) recycling. This study considered the use of carbon black from pyrolysis of ELTs as a carbon carrier for metals (Co, Ni, Cu, Fe) and their oxides to produce catalytic systems. The synchronous thermal analysis showed the positive effect of metal oxides/recovered carbon black (MOs/rCB) on ammonium perchlorate thermolysis. It was selected as a model catalytic reaction. Metal oxides/recovered carbon black (MOs/rCB) catalysts facilitated a reduction in the thermal decomposition phases of ammonium perchlorate, resulting in a significant narrowing of the decomposition interval. The greatest narrowing (22.7 °C) was observed at 103.5 °C for non-catalytic process. All tri-metallic catalytic systems showed high catalytic efficiency, providing a narrowing of the decomposition interval on average 2.5 times more in comparison with mono-metallic catalysts. Trioxide catalyst CuO/CoO/FeO/rCB showed the most significant shift in the high-temperature decomposition stage by 13% (from 334.0 °C to 293.2 °C). The activity of di-, tri-, and tetra-metallic catalytic systems was further enhanced by the synergistic effect induced by the addition of a second (or more) metal to the system. Efficient use of rCB for impregnated catalyst systems production could improve the economic efficiency of ELTs pyrolysis.

Mathematical Modeling of a Self-Oscillating Catalytic Reaction in a Flow Reactor

Mathematical Modeling of a Self-Oscillating Catalytic Reaction in a Flow Reactor

Oriented Exfoliating 3D Metal–Organic Frameworks into Ultrathin Metal–Organic Nanosheets with Different Crystal Faces

AbstractManufacturing two‐dimensional (2D) materials or nanosheets with desired crystal faces originating from an established intrinsic 3D structure is a significant challenge. Herein, an intrinsic t3D metal–organic frameworks (MOFs) can be exfoliated into ultrathin metal–organic nanosheets with (001) and (101) crystal faces, which is regulated by the solute's shard and soft acid−base and pH value in the exfoliating solution. The inorganic ligands (with different charges) possessing the similar hardness of Lewis acid‐base of metal center can replace some of the organic ligands along the established crystal faces of the 3D MOFs with different electrostatic potentials, resulting in the exfoliating of the 3D MOFs into metal–organic nanosheets with different crystal faces. Using the Knoevenagel reaction as the catalytic reaction model, the catalytic activity of (001) crystal faces is three times that of (101) crystal faces, which is determined by the different locations of open metal sits in the 3D lamellar structure, further confirming the occurrence of oriented exfoliation.

A CFD model of natural gas steam reforming in a catalytic membrane reactor: Effect of various operating parameters on the performance of CMR

The use of hydrogen as an energy carrier has increased for reasons related to its environmentally friendly characteristics. The most common and low-cost method of producing hydrogen from natural gas (or CH4) is the steam reforming process. The 2-D axisymmetric catalytic membrane reactor (CMR) model is developed for pure hydrogen production from real natural gas (NG) using a Pd–Ru membrane with a Ni/Al2O3 catalyst. In this paper, a CFD model is prepared to investigate the performance of a catalytic membrane reactor through natural gas conversion and hydrogen production under various operation parameters, i.e., temperature of reaction in the range of 600, 700, 800, 900, and 1000 K, gas hourly space velocity GHSV with a range of 500, 700, 1000, 2000, and 3000 h−1, and sweep gas flow rate (Re No.) 1, 50, 100, 150, and 250. The results of the simulation show that the CMR exhibits a high permeation rate of hydrogen on the permeate side (tube side) and achieves a high methane conversion rate of approximately 99.9 % at 1000 K on the retentate side. The hydrogen flux exhibits a decline as the temperature increases from 900 to 1000 K, despite the achievement of complete (NG) conversion. Hence, it can be concluded that the performance of the catalytic membrane reactor (CMR) process exhibits a pattern of increase when the other parameters, such as (GHSV) and (Re.No.), are increased.

DFT study of the moiré pattern of FeO monolayer on Au(111).

Metal oxides are a class of material of particular interest for catalytic purposes. Among them the iron oxide as a monolayer supported on gold, FeO/Au, stands out for its capability to promote the CO oxidation and the dissociation of O2 and H2. In this work, we use density functional theory calculations to characterize interfacial properties of this heterostructure. We consider a FeO/Au realistic model system, managing to reproduce the moiré pattern experimentally found. Specific features of the high-symmetry domains of the moiré are identified, providing a robust ground for establishing a structure-activity relationship and guessing how the surface would behave in catalytic conditions. We also describe a strategy to model smaller systems representative of each high-symmetry domains of the moiré, which will be useful in the future to model catalytic reaction mechanisms.

“Click” Chemistry Assisted Synthesis of Magnetite‐CNT Nanohybrid Supported Gold Nanoparticles for Enhanced Catalytic Reduction of 4‐Nitrophenol

AbstractThe magnetite (Fe3O4) nanoparticles were strategically tethered over carbon nanotube (CNT) templates by using UV light‐induced thiol‐yne “click” chemistry approach which was followed by immobilization of chitosan stabilized gold nanoparticles (Au NPs) onto this surface through electrostatic interactions. Their application as a magnetically recyclable catalyst was explored through the study of the model catalytic reaction of reduction of 4‐nitrophenol (4‐NP) in the presence of an excess of NaBH4. Kinetic studies on the reduction of 4‐nitrophenol revealed Au/Fe3O4−CNT ternary nanohybrids to serve as better catalytic systems compared to Au NPs. The catalytic reduction of 4‐NP was found to occur through the formation of active gold hydride (Au−H) species. The formation of Au−H species was facilitated by Au−Fe3O4 interaction through the transfer of hydride ions via dissociation of the B−H bond of the adsorbed borohydride ions [BH4]− and the heterolytic dissociation of molecular hydrogen (H2), produced on hydrolysis of NaBH4 on the surface of Au/Fe3O4. Moreover, the π–π interactions between the nitroaromatic ring of 4‐NP and the CNT surface are believed to facilitate their proximity. Further, on visible light irradiation, dissociation of H2 on the gold surfaces was enhanced by the localized surface plasmon resonance (LSPR)‐induced hot electrons.

Simple Model of an Industrial Catalytic Cracking Riser Reactor

Simple Model of an Industrial Catalytic Cracking Riser Reactor

A pore-level 3D lattice Boltzmann simulation of mass transport and reaction in catalytic particles used for methane synthesis

Three-dimensional lattice Boltzmann (LB) simulations were carried out to investigate the mass transport and reaction inside and around catalytic porous particles used in fluidized beds for the synthesis of methane from biogas (H2/CO mixtures). The 3D internal porous structure of a real particle with a size ∼200 μm was assessed with Synchrotron-based X-ray tomography (XTM). Pore-resolved simulations with a suitable LB model for catalytic reactions in microflows revealed that the preferential diffusion of H2 and the resulting inability of CO to penetrate deep inside the pores led to segregated distributions of the two species, hindering reaction in the downstream parts of the particle and rendering CO the deficient reactant. The implications for practical fluidized beds are that, for specific bed zones with a high dense-phase (solid-phase) volume fraction and a predominant flow direction, CO starvation may occur and may thus limit the methane yields. Subsequent parametric studies of spherical particles with a diameter 2R=150 μm and an artificially generated porosity allowed comparisons of LB results with radially symmetric analytical continuum-model solutions. The LB simulations revealed appreciable angular variations in the CO concentration at the external surface (r=R) and the outer layers of particle, especially at the higher investigated Damköhler numbers, which were however diminished as the core of the particle (r→0) was approached. The large angular variations, in conjunction with the skewed CO distributions towards their lower values, led to LB-computed particle effectiveness factors ∼30% lower than the corresponding analytical solutions.

Criteria for the use of 1D and 2D models in catalytic membrane reactor modeling

A criterion was developed to determine the necessity of using 1D or 2D methods for modeling a concentric tubular membrane reactor for hydrogen-producing reactions. Four dimensionless parameters were defined to provide a complete description of the physical and chemical systems, and the effects of each parameter on the difference between a 1D and 2D model were explored. The membrane reactor geometry consisted of a tube-and-shell configuration with a catalyst bed in the tubular section and a perm-selective membrane in the interphase. The four dimensionless parameters consisted of the Damköhler number (Da), which relates the reaction and axial convection rates, the Péclet number (Pe), which relates the radial diffusion and axial convection rates, the transport parameter (θ), which relates the axial convection and membrane permeation rates, and the equilibrium parameter (ε), which is a measure of the favorability of the reaction. A cutoff at which 1D and 2D model results have less than a 1% difference in final concentrations was used to define a critical Pe value, or Pecrit. Then, a criterion equation was fitted using non-linear regression so that any system can be calculated and compared against Pecrit. Using this criterion, a model above the cutoff (Pe > Pecrit) can reduce computation time by selectively calculating a simple 1D model for conditions, while a model below the cutoff (Pe ≤ Pecrit) should use a more computationally expensive 2D model to assure accuracy. The final criterion was validated against literature data for both 1D and 2D models.

Palladium-Catalyzed Modular Assembly of P-Stereogenic and Axially Chiral Phosphinooxazoles (PHOX) Ligands by C-P Bond Cleavage/Intermolecular C(sp2)-H Bond Functionalization.

Chiral P,N-ligands are of great interest and importance in the fields of metal-catalyzed enantioselective transformations and have found numerous applications spanning drug and polymer synthesis. Here, modular assembly of diverse P-stereogenic and axially chiral phosphinooxazoles ligands is achieved through palladium-catalyzed asymmetric cleavage of C-P bond/intermolecular C-H bond functionalization in high atroposelectivities and diastereoselectivities of up to >99% ee and >25:1 dr. This protocol features broad substrate scope and provides an avenue for facile construction of new P-stereogenic and axially chiral phosphinooxazoles ligands directly from the phosphonium salts and benzoxazoles/benzothiazoles. Evaluation of the synthesized P-stereogenic and axially chiral phosphinooxazoles ligands in two model catalytic asymmetric reactions illustrates the potential of our strategy to access valuable chiral molecules.

Tethered particle motion of the adaptation enzyme CheR in bacterial chemotaxis

Bacteria perform chemotactic adaptation by sequential modification of multiple modifiable sites on chemoreceptors through stochastic action of tethered adaptation enzymes (CheR and CheB). To study the molecular kinetics of this process, we measured the response to different concentrations of MeAsp for the Tar-only Escherichia coli strain. We found a strong dependence of the methylation rate on the methylation level and established a new mechanism of adaptation kinetics due to tethered particle motion of the methylation enzyme CheR. Experiments with various lengths of the C-terminal flexible chain in the Tar receptor further validated this mechanism. The tethered particle motion resulted in a CheR concentration gradient that ensures encounter-rate matching of the sequential modifiable sites. An analytical model of multisite catalytic reaction showed that this enables robustness of methylation to fluctuations in receptor activity or cell-to-cell variations in the expression of adaptation enzymes and reduces the variation in methylation level among individual receptors.

Simple Rate Expression for Catalyzed Ammonia Decomposition for Fuel Cells.

This paper examines NH3 decomposition rates based on a literature-proven six-step elementary catalytic (Ni-BaZrO3) mechanism valid for 1 × 105 Pa pressure in a 650-950 K range. The rates are generated using a hypothetical continuous stirred tank catalytic reactor model running the literature mechanism. Excellent correlations are then obtained by fitting these rates to a simple overall kinetic expression based on an assumed slow step, with the remaining steps in fast pseudo-equilibria. The robust overall simple rate expression is then successfully demonstrated in various packed bed reactor applications. This expression facilitates engineering calculations without the need for a complex, detailed mechanism solver package. The methodology used in this work is independent of the choice of catalyst. It relies on the availability of a previously published and validated elementary reaction mechanism.