Reaction Of Propane Research Articles

Monomolecular Cracking of Propane: Effect of Zeolite Confinement and Acidity.

The effect of zeolite pore geometry and intrinsic acidity on the activation energy of propane monomolecular cracking was investigated for six topologically distinct zeolites with different pore sizes. Periodic density functional theory calculations were used to calculate the activation energy, while cluster models were used to calculate deprotonation energies. The computed intrinsic activation energies showed a smaller variation with topology than the adsorption energies. No correlation was found between the computed deprotonation and ammonia adsorption energies at the acid site and the intrinsic activation energy. Detailed analysis of the computed structures and properties suggests that acid sites with different pore topologies impose geometrical constraints on the ion-pair formed by the ammonium molecule, which differs significantly from those that affect the propane reaction.

The reactions of propanal/acetone with hydroperoxyl radicals: A theoretical and modeling study

Propanal (C2H5CHO) and acetone (CH3COCH3), the C3 carbonyl compound isomers, are the main byproducts of bio-alcohol combustion. In this work, the reaction rate coefficients between propanal/acetone and hydroperoxyl radicals (HO2) over 500–2000 K and 0.01–100 atm were obtained by the RRKM/master equation method based on high-level quantum chemical calculations. The competition relationship among the H-abstraction, HO2 addition, addition-dissociation reaction pathways and their temperature and pressure dependence were explored. The results show that for propanal + HO2, the aldehydic H-abstraction reaction is highly favored over the addition-dissociation and other abstraction channels, while for acetone + HO2, the H-abstraction reaction is comparable with those of addition-dissociation reactions at low temperature. At temperatures ≤ 700 K and pressures ≥ 1 atm, collisional stabilization of the peroxy-alcohol radical is the dominant channel. To reveal the impact of the studied reactions on model predictions, the rate coefficients of various reaction channels calculated in this work and those of peroxy-alcohol radicals + HO2 from the literature were incorporated into a recently proposed low-temperature mechanism of propanal. The results show that the aldehydic H-abstraction reaction of propanal by HO2 greatly contributes to the combustion behavior in the negative temperature coefficient regime. The peroxy-alcohol radical favors its decomposition channel with temperatures ranging from 500 to 900 K at 1 atm in a JSR. Modified Arrhenius representations of the calculated rate coefficients are given and should be valuable for the future development of low-temperature oxidation mechanisms for aldehydes, ketones, and alcohols.

In-depth study on propane dehydrogenation over Al2O3-based unconventional catalysts with different crystal phases

Al2O3 has been demonstrated to possess relatively high activity for alkane dehydrogenation, but there is short of in-depth understanding of the effect of its crystal phase on the dehydrogenation performance. In this study, γ-Al2O3, δ-Al2O3, θ-Al2O3 and α-Al2O3 samples have been synthesized and evaluated for propane dehydrogenation. With the phase transformation from γ-Al2O3 to α-Al2O3, propane conversion decreases gradually, while the selectivity to propene increases except for the inactive α-Al2O3. According to systemic characterization and deep analysis, phase transformation cannot change the type of active components for propane dehydrogenation, but influences its surface density, thus leading to the variation of the catalytic behaviors. Furthermore, the active sites have a close relationship with the difficultly removed hydroxyl groups on the surface of Al2O3, i.e. some specific Lewis acid sites (such as the coordinatively unsaturated AlⅣ species), but abundant acid sites will result in the secondary reactions of propene and decreased selectivity. From this perspective, the difference in propene selectivity with the phase transformation is probably caused by the change in the relative content of the active sites for propane dehydrogenation.

Pyrolysis and oxidation of a light naphtha fuel and its surrogate blend

An experimental and kinetic study on pyrolysis and oxidation of a real light naphtha fuel and its surrogate blend were conducted. Based on the chemical functional group method, a three-component surrogate blend for the target naphtha was formulated, which contains 64.2 mol% iso-pentane, 21.0 mol% n-hexane, and 14.8 mol% methylcyclopentane. The pyrolysis and oxidation characteristics of the target naphtha fuel and the formulated surrogate were compared using a jet-stirred reactor (JSR) at the equivalence ratios of 0.5, 1.0, 2.0 and ∞, across the temperature range from 700 to 1100 K, and at atmospheric pressure. Mole fractions of the three components, oxygen, hydrogen, CO, CO2, and C1-C4 hydrocarbons were measured by gas chromatograph. Similar global reactivities between the two test fuels were observed in both pyrolysis and oxidation experiments. In addition, a detailed chemical kinetic model was constructed and validated against the species mole fraction profiles measured in JSR experiments. The present model can provide reasonable prediction of the experimental measurements of the species mole fractions in pyrolysis and oxidation of the surrogate blend. Uncertainty-weighted sensitivity analysis indicates that the model prediction of the consumption of the three components of the surrogate blend in pyrolysis are dominated by the rate constants for H-abstraction reactions of isopentane, n-hexane, methylcyclopentane and propene by H atom and methyl radical. The model predictions of the oxidation reactivity of the surrogate blend mainly depend on H-abstraction reactions from the three surrogate components by HO2 radical at 800 K, while the H-abstraction reactions from aldehyde and alkene intermediates become more significant at 950 K.

2+2] Cycloaddition or β-hydrogen elimination?—a DFT study of the reactions of propylene catalyzed by (PDI)Fe-metallacycle

The origin of the chemoselectivity of [2+2] cycloaddition reactions catalyzed by different (PDI)Fe-metallacycles is due to the different groups (N2 or CH3) coordinated with the Fe metal.

Oxidative Dehydrogenation of Propane over Nanostructured Mesoporous VOx/CexZr1-xO2 Catalysts

High-surface-area mesoporous CexZr1-xO2 materials synthesized through a surfactant-assisted approach of nanocrystalline particle assembly are utilized as a promising support for VOx-based catalysts. The catalytic properties of the resultant VOx/CexZr1-xO2 nanocatalysts are evaluated by the oxidative dehydrogenation of propane using a microreactor-GC system. It is indicated that the catalyst particles are on a nanoscale, having a mesoporous structure with uniform pore-size distribution and high surface area. The catalytic behavior of these mesoporous nanostructured VOx/CexZr1-xO2 catalysts for the oxidative dehydrogenation of propane reaction relies on the vanadia loading amount, the calcination temperature, the surface area and the Ce/Zr ratio of the supports, the particle size of active compounds, and the additional contribution to the propylene formation derives from the contribution of the catalytic dehydrogenation of propane under oxygen-lean conditions. The catalyst prepared with 8 wt% vanadia loading on Ce0.2Zr0.8O2 exhibits high and stable catalytic performance in the oxidative dehydrogenation of propane reaction. 

Design of MFI Type Aluminum- and Titanium-Containing Zeolites

HZSM-5 (MFI type) of composition (Hx)[Al3+xSi12−xO24] × wH2O and nanocomposites NA/HZSM-5, NA:M/HZSM-5 (NA—nanoscale anatase; M = V, Ni, Ag) with Si/Al = 12, 25, 40, 300 (sp.gr. Pnma or P21/n; z = 8), as well as zeolites [(Ti4+xSi12−xO24] × wH2O (TS) with Si/Ti = 47, 53, 73.5 (sp.gr. Pnma) were studied by XRPD, XAS, FTIR-spectroscopy, BET, XPS, SEM, EDX, TPD, UV–VIS-spectroscopy, UV–DRS, and chemiluminescence methods. The results obtained together with photocatalytic, adsorption, antimicrobial, catalytic properties were analyzed using crystallochemical concepts and literature data. It was shown that NA or NA:M introduction into HZSM-5 leads, respectively, to the photodegradation of MeO dye in the UV region or difenoconazole in the visible range, and contributes to the appearance in the dark of adsorption (almost complete extraction of P(V), As(V), and Se(V) from aquatic environment) and bacteriostatic properties in respect to Staphylococcus epidermidis, Bacillus antracoides, and Escherichia coli for NA:Ag/HZSM-5(40, 300). The presence of titanium ions in NA nanoparticles on the HZSM-5 surface improves the catalytic activity in ethanol and propane (the best performance for NA/HZSM-5(25) and NA/HZSM-5(40), respectively) conversion. Determination of the composition (surface and bulk) and structure (statistical and local) of TS zeolites together with the found correlations made it possible to propose new catalysts in the reactions of propane, ethanol, and allyl chloride conversion.

Nitrogen-Doped Graphene Monolith Catalysts for Oxidative Dehydrogenation of Propane.

It’s of paramount importance to develop renewable nanocarbon materials to replace conventional precious metal catalysts in alkane dehydrogenation reactions. Graphene-based materials with high surface area have great potential for light alkane dehydrogenation. However, the powder-like state of the graphene-based materials seriously limits their potential industrial applications. In the present work, a new synthetic route is designed to fabricate nitrogen-doped graphene-based monolith catalysts for oxidative dehydrogenation of propane. The synthetic strategy combines the hydrothermal-aerogel and the post thermo-treatment procedures with urea and graphene as precursors. The structural characterization and kinetic analysis show that the monolithic catalyst well maintains the structural advantages of graphene with relatively high surface area and excellent thermal stability. The homogeneous distributed nitrogen species can effectively improve the yield of propylene (5.3% vs. 1.9%) and lower the activation energy (62.6 kJ mol−1 vs. 80.1 kJ mol−1) in oxidative dehydrogenation of propane reaction comparing with un-doped graphene monolith. An optimized doping amount at 1:1 weight content of the graphene to urea precursors could exhibit the best catalytic performance. The present work paves the way for developing novel and efficient nitrogen-doped graphene monolithic catalysts for oxidative dehydrogenation reactions of propane.

Different roles of MoO3 and Nb2O5 promotion in short-chain alkane combustion over Pt/ZrO2 catalysts

Pt/ZrO2 catalysts promoted with MoO3 and Nb2O5 were tested for the combustion of short-chain alkanes (namely, methane, ethane, propane, and n-hexane). For short-chain alkane combustion, the inhibition of MoO3 (for the methane reaction) dramatically transformed to promotion (for the ethane, propane, and n-hexane reactions) as the carbon chain length increased, whereas the remarkable promotion of Nb2O5 gradually weakened with an increase in the carbon chain length. Based on a detailed study of the oxidation reactions of methane and propane over the catalysts, the different roles of the promoters in the reactions were ascribed to differences in the acidic properties of the surface and the oxidation or reduction states of the Pt species. The MoO3 promoter could decorate the surface of the Pt species for a Pt-Mo/ZrO2 catalyst, whereas the Nb2O5 promoter on the support could be partially covered by Pt particles for a Pt-Nb/ZrO2 catalyst. The formation of accessible Pt-MoO3 interfacial sites, a high concentration of metallic Pt species, and a high surface acidity in Pt-Mo/ZrO2 were responsible for the enhanced activity for catalytic propane combustion. The lack of enough accessible Pt-Nb2O5 interfacial sites but an enhanced surface acid sites in Pt-Nb/ZrO2 explained the slight improvement in activity for catalytic propane combustion. However, the stabilized Ptn+ species in Pt-Nb/ZrO2 were responsible for the much-improved activity for methane combustion, whereas the Ptn+ species in Pt-Mo/ZrO2 could be reduced during the oxidation reaction, and the fewer exposed surface Pt species because of MoO3 decoration accounted for the inhibited activity for methane combustion. In addition, it can be concluded that MoO3 promotion is favorable for the activation of C–C bonds, whereas Nb2O5 promotion is more beneficial for the activation of C–H bonds with high energy.

Synergistic Effect Between Ca4V4O14 and Vanadium‐Substituted Hydroxyapatite in the Oxidative Dehydrogenation of Propane

AbstractThe present work reports on a new type of V‐based catalysts, namely V‐substituted hydroxyapatites, and the influence of the synthesis conditions on their catalytic performance in the oxidative dehydrogenation of propane (ODHP) reaction. Vx‐substituted hydroxyapatite materials prepared with the periodic addition of ammonia during the maturation step (Vx‐HAp‐pH‐per) were shown to exhibit a Ca4V4O14 phase in addition to the V‐substituted hydroxyapatite phase for x greater than or equal to 3.5. TEM characterization of the biphasic samples allowed us to demonstrate that the Ca4V4O14 phase was grown epitaxially on the Vx‐HAp nanorods. The close intimacy between the two phases was confirmed by NMR suggesting the involvement of V4+ species. Consistently EPR data of the fresh and spent samples showed that V4+ species may be stabilized at the boundaries of these two phases. The strong promotion of the oxidative dehydrogenation reaction to propene observed from 723 K for the V4‐HAp‐pH‐per composition is attributed to a synergistic effect between the Vx‐HAp nanorods that enable the activation of propane and the Ca4V4O14 phase that helps the redox exchanges. This synergy may be attributed to an easier electron delocalization on the V4O14 units located at the phases’ boundaries.

Total oxidation of propane over Co3O4-based catalysts: Elucidating the influence of Zr dopant

A series of Zr-doped Co3O4 catalysts (x% Zr-Co3O4), prepared by citrate sol-gel method with a low doping amount of zirconium, was applied in the catalytic oxidation of 1000 ppm propane at a weight hourly space velocity of 40,000 mL g−1 h−1. Different techniques were used to characterize the catalysts. The results showed that the physicochemical properties and catalytic performances of the x% Zr-Co3O4 catalysts were significantly influenced by the addition of zirconium. Only a small part of Zr could be doped into the Co3O4 lattice and the spare Zr would prefer to aggregate on the surface to form zirconium oxide. In the x% Zr-Co3O4 catalysts, Zr disordered Co3O4 spinel is formed by entering into the Co3O4 lattice and forming Co-O-Zr species, resulting in smaller Co3O4 crystallite size, larger specific surface area, better low-temperature reducibility, higher surface Co2+ concentration, and higher content of surface oxygen vacancies and active oxygen species. The best performance was achieved on 1% Zr-Co3O4 for propane oxidation, with 90% propane conversion at 241 °C. The most active catalyst showed excellent performance in toluene and propene oxidation as well. Propane reaction tests, carried out without oxygen in the gas stream, indicated the promoting effect of the low amount of Zr on the oxygen mobility of x% Zr-Co3O4 catalysts. Durability tests of propane oxidation showed that stable conversion could be achieved over 1% Zr-Co3O4, thus being a potential active catalyst for practical application.

Plasma Tuning Local Environment of Hexagonal Boron Nitride for Oxidative Dehydrogenation of Propane.

Hexagonal boron nitride (h-BN) has lately received great attention in the oxidative dehydrogenation (ODH) reaction of propane to propylene for its extraordinary olefin selectivity in contrast to metal oxides. However, high crystallinity of commercial h-BN and elusive cognition of active sites hindered the enhancement of utilization efficiency. Herein, four kinds of plasmas (N2 , O2 , H2 , Ar) were accordingly employed to regulate the local chemical environment of h-BN. N2 -treated BN exhibited a remarkable activity, i.e., 26.0 % propane conversion with 89.4 % selectivity toward olefins at 520 °C. Spectroscopy demonstrated that "three-boron center" N-defects in the catalyst played a pivotal role in facilitating the conversion of propane. While the sintering effect of the "BOx " species in O2 -treated BN, led to the suppressed catalytic performance (12.4 % conversion at 520 °C).

Plasma Tuning Local Environment of Hexagonal Boron Nitride for Oxidative Dehydrogenation of Propane

AbstractHexagonal boron nitride (h‐BN) has lately received great attention in the oxidative dehydrogenation (ODH) reaction of propane to propylene for its extraordinary olefin selectivity in contrast to metal oxides. However, high crystallinity of commercial h‐BN and elusive cognition of active sites hindered the enhancement of utilization efficiency. Herein, four kinds of plasmas (N2, O2, H2, Ar) were accordingly employed to regulate the local chemical environment of h‐BN. N2‐treated BN exhibited a remarkable activity, i.e., 26.0 % propane conversion with 89.4 % selectivity toward olefins at 520 °C. Spectroscopy demonstrated that “three‐boron center” N‐defects in the catalyst played a pivotal role in facilitating the conversion of propane. While the sintering effect of the “BOx” species in O2‐treated BN, led to the suppressed catalytic performance (12.4 % conversion at 520 °C).

The role of the compositions of HZSM-5 zeolites modified with nanosized anatase in propane and ethanol conversion

For the first time catalytic systems based on HZSM-5 zeolites (Si/Al=12, 25, 40) with nanosized anatase (NA) were obtained in situ by a modified hydrothermal method and a sol-gel method. Initial HZSM-5 and NA/HZSM-5 were characterized (XRPD, XAS, FT-IR, DSC, BET, XPS, SEM, TPD) and analyzed in the reactions of propane (liquefied petroleum gas) conversion (РС; temperature range 200–870 °С) with the formation of the main products propylene (C3H6, PP) and ethylene (C2H4, ETH) and liquid ethanol conversion (EC; temperature range 150–360 °C) with the formation of diethyl ether ((C2H5)2O, DEE) and ETH. In the PC reaction the maximum selectivity (SETH = 75%) and conversion (αP = 65%) were obtained on HZSM-5(40) (650 °С). With an increase in the NA content in NA/HZSM-5 SETH value increases up to 85%. In the EC reaction SDEE/ETH~98–99% was reached on HZSM-5(25) (200 °C) and HZSM-5(40) (300 °C); the αE to ETH is comparable (94%) for all HZSM-5 (300 °C). Modification of HZSM-5 with NA leads to a shift in the EC reaction temperature to lower temperature region (αE to ETH ~98% at 280 °C) with SDEE/ETH~94–100% for NA/HZSM-5(25) and NA/HZSM-5(12) obtained by a modified hydrothermal method. It was established the relationship between HZSM-5 and NA/HZSM-5 catalytic activity and their characteristics: Si/Al, NA content and Ti coordination number (NA/HZSM-5), the content of "zeolite water" with OH groups, specific surface area, meso- and micropores volume and spherical particles size (HZSM-5), surface energy of adsorption centers (HZSM-5 and NA/HZSM-5), and hence the content of acid sites, the strength of which is also determined by the temperature of the catalytic reaction. The reaction mechanisms have been presented. The obtained NA/HZSM-5 catalysts have a higher or comparable catalytic activity to commercial ones, but low cost, ease of preparation, and versatility.

Large Anharmonic Effects on Tunneling and Kinetics: Reaction of Propane with Muonium

Calculations of kinetic isotope effects (KIEs) provide challenging tests of quantal mass effects on reaction rates, and muonium KIEs are the most challenging. Here, we show that it can be very important to include reaction-coordinate-dependent vibrational anharmonicity along the whole reaction path to calculate tunneling probabilities and KIEs. For the reaction of propane with Mu, this decreases both the height and width of the vibrationally adiabatic potential barrier, with both effects increasing the rate constants. Our results agree well with the experimental observations.

Kinetic Studies on Both Synthesis of Methacrolein Catalyzed by an Ionic Liquid and Catalyst Deactivation

Diethylamine acetate as an ionic liquid is used as a catalyst for the Mannich reaction of propanal and formaldehyde to produce methacrolein. However, catalyst deactivation remains a serious problem...

Catalytic performance of different zeolites for propane and CO2 coupling to propylene

CO2 hydrogenation to light olefins is an exothermic reaction, while propane dehydrogenation to propylene is an endothermic reaction, and with generating of hydrogen. Coupling of the two reactions can break the equilibrium limit of thermodynamics and dynamics of the single reaction and improve yield of propylene. Therefore, the effects of different crystalline zeolites (HZSM-5, SAPO-34 and Al-SBA-16) on the reactivity of propane coupled with CO2 to propylene were investigated. The properties of different zeolites were characterized by means of XRD, SEM, NH3-TPD, N2 desorption and TG, and the catalytic performance of the three different zeolites in the reaction of propane and carbon dioxide coupling to propylene was investigated in a fixed bed reactor. The experimental results showed that HZSM-5 zeolite had high content of weak acid, large specific surface area and excellent catalytic activity. Typically the propane conversion rate is 10.5%, the CO2 conversion is 3.0%, the propylene selectivity is 38.4% and the yield is 4.0% when the volume ratio of propane to CO2 is 1:4, the reaction pressure is 0.1 MPa, the reaction temperature is 580°C, the catalyst mass is 0.2 g and the space velocity is 6000 mL/(gcat·h).

Does crystallite size dominate MTP performance over Silicalite-1 zeolite in methanol to propene?

The relations of crystallite sizes over Silicalite-1 zeolite with the silanols distribution and catalytic performance in methanol to propene (MTP) reaction were determined. The catalytic lifetime and the formation of ethene was independent of the crystallite size, but was attributed to the silanols distribution. The internal isolated silanol groups (I) affects the diffusion restrictions of intermediate species. The external isolated silanols (E) determined the tolerance for coke capacity on the external surface. Propene and the initial catalytic activity was dominated by the amount of Brønsted acid sites.

СОЗДАНИЕ МАТЕМАТИЧЕСКО-КОМПЬЮТЕРНЫХ МОДЕЛЕЙ ДИНАМИКИ РАСПРОСТРАНЕНИЯ ПЛАМЕНИ АЭРОВЗВЕСЕЙ ТВЕРДЫХ ВЕЩЕСТВ В РАЗЛИЧНЫХ ГОРНЫХ ПОРОДАХ В СРЕДЕ MATLAB

The propagation of transient, air-suspended solids in a vented explosion chamber is numerically investigated by a dynamic formulation for the Concentration Limit of Flame Propagation (CLFP) with the GUI MATLAB environment. The geomechanics is modeled by a one-step overall reaction, which simulates the reaction of a stoichiometric propane– air-suspended solids. The CLFP modeling in the reaction rate model is numerically employed with mathematical models on basis Antoine's equation. This is based on an empirical correlation of the velocity fluctuations and implemented as interface with input-output data with graphic realization. The computer modeling show that the dynamic CLFP models provide superior results as general implementation of physical process of flame propagation and could be used for different rocks (f.e. granite, limestone, sandstone etc).

Ultrafast synthesis of high-silica Beta zeolite from dealuminated MOR by interzeolite transformation for methanol to propylene reactions

A novel interzeolite transformation method was developed to synthesize the large pore Beta zeolite with high Si/Al ratio. and less defects within 3 h. Such high-silica Beta showed a long lifetime in comparison to the high-silica Beta prepared via the post-synthesis method (Beta-DA) and hydrothermal method in F medium (Beta-F), owing to its nano-size and defect-less crystal.