Reactions Of C3H8 Research Articles

A Theoretical Study of NH2 Radical Reactions with Propane and Its Kinetic Implications in NH3-Propane Blends’ Oxidation

The reaction of NH2 radicals with C3H8 is crucial for understanding the combustion behavior of NH3/C3H8 blends. In this study, we investigated the temperature dependence of the rate coefficients for the hydrogen abstraction reactions of C3H8 by NH2 radicals using high-level theoretical approaches. The potential energy surface was constructed at the CCSD(T)/cc-pV(T, Q)//M06-2X/aug-cc-pVTZ level of theory, and the rate coefficients were computed using conventional transition state theory, incorporating the corrections for quantum tunneling and hindered internal rotors (HIR). The computed rate coefficients showed a strong curvature in the Arrhenius behavior, capturing the experimental literature data well at low temperatures. However, at T > 1500 K, the theory severely overpredicted the experimental data. The available theoretical studies did not align with the experiment at high temperatures, and the possible reasons for this discrepancy are discussed. At 300 K, the reaction of NH2 with C3H8 predominantly occurs at the secondary C-H site, which accounts for approximately 95% of the total reaction flux. However, the hydrogen abstraction reaction at the primary C-H site becomes the dominant reaction above 1700 K. A composite kinetic model was built, which incorporated the computed rate coefficients for NH2 + C3H8 reactions. The importance of NH2 + C3H8 reactions in predicting the combustion behavior of NH3/C3H8 blends was demonstrated by kinetic modeling.

Insights into catalyst structure, kinetics and reaction mechanism during propane dehydrogenation on Pt-Ge bimetallic catalysts

In the present work, in-depth characterization techniques combined with kinetic analyses were used to develop a deep understanding of the remarkable catalytic performance observed during propane dehydrogenation (PDH) over Ge-promoted Pt/SiO2. Following our previous work on Pt-Ge/Al2O3, we found Ge to significantly affect Pt catalytic performance, reaction mechanism and kinetics, regardless of the nature of the support. The synthesized catalysts were characterized using XAS, XPS, TPR, TGA, C3H6/C3H8-TPD, HRTEM, CO-chemisorption, BET, and CO-DRIFT. Upon Ge promotion to Pt nanoparticles supported on a large, neutral, SiO2 surface area, the bimetallic samples showed higher activation energy, lower desorption energy of C3H6, lower coke formation rates, and higher C3H6 selectivity as compared to the results from using the unpromoted catalyst. Ruling out the neutral SiO2’s support effect, the kinetic study indicates the C3H8 reaction order remains close to 1 for all the samples, while the H2 reaction order decreases from 0.04 to − 0.52 with increasing Ge loading from 0 wt% to 5 wt%. According to the kinetic analysis, the first C-H bond cleavage seems to be the rate-determining step. The addition of Ge enhances the adsorption of hydrogen, which explains the change of the hydrogen reaction order and the apparent activation energy exhibited by the bimetallic samples.

Key role of NO + C3H8 reaction for the elimination of NO in automobile exhaust by three-way catalyst.

Pd-only three-way catalysts with improved catalytic activity for NO elimination were prepared. In order to explore the catalytic reaction rules of NO reduction under a three-way catalytic system, a series of single reactions related to NO reduction were evaluated. It was found that the reaction temperatures of NO + H2 or NO + CO or NO + C3H6 reactions were below 250°C, while that of NO + C3H8 was up to 350°C. Thus, the reaction NO + C3H8 served as the key reaction in determining the purification efficiency of NO at the high-temperature stage. By in situ FTIR, we proposed that three possible steps were involved in NO + C3H8 reaction. The first step was the oxidation of C3H8 and NO to acetone and nitrate species by active oxygen species, respectively (C3H8 + O* → C3H6O, NO + O* → NO3-). XPS results revealed that the amount of active oxygen species in Pd/CeO2-ZrO2-Al2O3 (Pd/CZA, 73.7%) was much higher than that in Pd/CexZr1-xO2+Al2O3 (Pd/CZ+A, 64.1%). This was in line with the higher reaction efficiency of the first step over Pd/CZA. Then the NO + C3H8 reaction was accelerated by the first step, which consequently contributed to the higher NO elimination efficiency of Pd/CZA.

A low temperature investigation of the N(2D) + CH4, C2H6 and C3H8 reactions.

The gas-phase reactions between metastable nitrogen atoms, N(2D) and saturated hydrocarbons CH4, C2H6 and C3H8 have been investigated using a supersonic flow reactor over the 296-75 K temperature range. N(2D) was generated as a product of the C(3P) + NO → N(2D) + CO reaction, with C(3P) atoms created in situ by pulsed laser photolysis of CBr4. The kinetics of N(2D) loss were followed by vacuum ultraviolet laser induced fluorescence. The measured rate constants for the N(2D) + CH4 reaction are in good agreement with earlier work and extend the available kinetic data for this process down to 127 K. The measured rate constants for the N(2D) + C2H6 and N(2D) + C3H6 reactions are in reasonable agreement with previous work at room temperature and extend the available kinetic data for these processes down to 75 K. The rate constants for all three reactions decrease as the temperature falls, indicating the presence of activation barriers for these processes. While the recommended values for the low temperature rate constants of the N(2D) + CH4 reaction are close to those reported here, the previous recommendations for the other saturated hydrocarbon reactions significantly overestimate the rate constants for these processes. The effects of the new rate constants on a coupled ion-neutral photochemical model of Titan's atmosphere are discussed.

Hydrogen production via propane dry reforming: Carbon deposition and reaction-deactivation study

Carbon deposition during carbon dioxide reforming reaction of C3H8 has been studied over alumina-supported bimetallic Mo/CoNi catalysts. To better understand the carbon-induced deactivation during the reforming reaction, changes in catalyst morphology and carbon deposition kinetics were examined. Different characterization techniques were used for both fresh and rejuvenated catalysts including liquid nitrogen adsorption/desorption, chemisorption via hydrogen, ammonia and CO2 desorption, and thermogravimetric measurement of the coked catalysts. The time dependant reaction rate profiles indicated that MoNi catalyst has higher syngas (H2/CO) formation rates with lower CO2 rate of consumption compared to CoNi catalyst. However, the H2:CO ratio values were almost the same for both catalysts suggesting similarity in the product formation pathway. Conversion-time analysis showed that MoNi catalyst was more stable and active during a 72-h run while CoNi suffered noticeable deactivation after 30 h on-stream. Reaction-deactivation models implicated a higher deactivation coefficient (kd) with activation energy of Ed = 78.1 kJ mol−1 for the cobalt-containing Ni catalyst, while the Ni catalyst with molybdenum had a lower deactivation coefficient with smaller activation energy of just under 70 kJ mol−1. Post-mortem analysis (TPR-TPO dual cycle and TOC) of spent catalysts confirmed that the surface of CoNi catalyst has more carbon residue than the MoNi sample which was consistent with the higher deactivation of CoNi.

Raman spectroscopic study of cracking and hydrolysis of propane in fused silica capillary capsules between 300 and 400 °C

Isothermal experiments on C3H8, with or without water, in fused silica capillary capsules were conducted at temperatures (Ts) between 300 and 400 °C for durations up to 322 hours. Reaction progresses were evaluated with Raman spectroscopy at room T before and after heating. After an initial experiment, some samples were reheated to the same T for total durations up to 821 hours. Consumption of water was monitored by calculating the changes in relative volumes of the vapor, aqueous, and C3H8 liquid phases from the lengths of the phases in the capillary. Reactions of C3H8 without water produced a small amount of CH4, reaching a steady state after about 100 hours of heating at T < 360 °C. Reactions with water appear to be largely hydrolysis, generating a CH4‐rich vapor phase and methanol and ethanol in the aqueous phase. At fixed T, Raman spectra showed that concentrations of alcohols increased steadily with time as water was consumed. Our observations show that, without iron‐bearing mineral buffers, the reactions between propane and water are relatively limited, forming alcohols without further oxidation to propanoic or ethanoic acid and/or CO2. This observation suggests that during deep burial, hydrocarbon gases may be more stable in iron‐poor reservoirs like quartz arenites or carbonate grainstones than in mudstones or arkoses that are rich in redox‐reactive iron‐bearing siliciclastic and diagenetic minerals. Copyright © 2017 John Wiley & Sons, Ltd.

Theoretical Study on Mechanism and Kinetics of Reaction of O(3P) with Propane

The reaction of C3H8+O(3P)→C3H7+OH is investigated using ab initio calculation and dynamical methods. Electronic structure calculations for all stationary points are obtained using a dual-level strategy. The geometry optimization is performed using the unrestricted second-order Møller-Plesset perturbation method and the single-point energy is computed using the coupled-cluster singles and doubles augmented by a perturbative treatment of triple excitations method. Results indicate that the main reaction channel is C3H8+O(3P)→i-C3H7+OH. Based upon the ab initio data, thermal rate constants are calculated using the variational transition state theory method with the temperature ranging from 298 K to 1000 K. These calculated rate constants are in better agreement with experiments than those reported in previous theoretical studies, and the branching ratios of the reaction are also calculated in the present work. Furthermore, the isotope effects of the title reaction are calculated and discussed. The present work reveals the reaction mechanism of hydrogen-abstraction from propane involving reaction channel competitions is helpful for the understanding of propane combustion.

A detailed combined experimental and theoretical study on dimethyl ether/propane blended oxidation

In this paper, a binary fuel model for dimethyl ether (DME) and propane is developed, with a focus on engine-relevant conditions (10–50atm and 550–2000K). New rapid compression machine (RCM) data are obtained for the purpose of further validating the binary fuel model, identifying reactions important to low-temperature propane and DME oxidation, and understanding the ignition-promoting effect of DME on propane. It is found that the simulated RCM data for DME/propane mixtures is very sensitive to the rates of C3H8+OH, which acts as a radical sink relative to DME oxidation, especially at high relative DME concentrations. New rate evaluations are conducted for the reactions of C3H8+OH=products as well as the self-reaction of methoxymethyl peroxy (in competition with RO2=QOOH isomerization) of 2CH3OCH2O2=products. Accurate phenomenological rate constants, k(T, P), are computed by RRKM/ME methods (with energies obtained at the CCSD(T)-F12a/cc-pVTZ-F12 level of theory) for several radical intermediates relevant to DME. The model developed in this paper (120 species and 711 reactions) performs well against the experimental targets tested here and is suitable for use over a wide range of conditions. In addition, the reaction mechanism generator software RMG is used to explore cross-reactions between propane and DME radical intermediates. These cross-reactions did not have a significant effect on simulations of the conditions modeled in this paper, suggesting that kinetic models for high- and low-reactivity binary fuel mixtures may be assembled from addition of their corresponding submodels and a small molecule foundation model.

Reactions of propane with CO2 over Au catalysts

The decomposition of C3H8 and its reaction with CO2 have been investigated on Au deposited on ZnO, MgO and Al2O3. The reactions proceeded above 650–700K. The conversion of C3H8 was only few percents on Au/MgO and Au/Al2O3, even at 873K, but reached ∼17% on Au/ZnO. The selectivity of propylene formation was about 56%. CO2 only slightly affected the reaction of C3H8 on Au/Al2O3 and Au/MgO, but significantly enhanced the conversion of C3H8 on Au/ZnO catalyst. The formation of large amount of CO indicates the involvement of CO2 in the reaction of C3H8. From the product distribution it was inferred that beside the oxidative dehydrogenation and dry reforming reaction, the decomposition of C3H8 into CH4 and surface carbon also occurred. The effect of ZnO is explained by an electronic interaction between n-type ZnO and Au particles leading to a formation of reactive CO2−.

Possibility of Copper-Ion-Exchanged MFI-Type Zeolite as C–H Bond Activation Material for Propane and the Driving Force for Activation

The dehydrogenation of propane (C3H8) utilizing solid catalysts is expected to be a promising method for producing propene (C3H6) selectively and economically. Propene is useful as a raw material to produce other valuable materials. To push forward the dehydrogenation reaction of C3H8, it is essential to find catalysts that work effectively in the activation of the C–H bonds in C3H8. To this end, we investigated the interaction of C3H8 with the copper-ion-exchanged MFI-type zeolite (CuMFI) at room temperature. The C3H8 adsorption properties of CuMFI were remarkable, compared with those of the sodium-form MFI-type zeolite (NaMFI); CuMFI exhibited irreversible adsorption, even at room temperature, whereas NaMFI exhibited reversible adsorption. Correspondingly, the CuMFI had an adsorption energy of 110 kJ mol–1 in the initial adsorption region, whereas the NaMFI had an adsorption energy of 50 kJ mol–1. Furthermore, a peculiar feature was observed in the appearance of the characteristic infrared (IR) absorpti...

Promotion of a Pd/Al2O3 close-coupled catalyst by Ni

The influence of a nickel promoter on the catalytic behavior of a modified alumina supported Pd close-coupled catalyst was investigated. Doping with nickel improved the catalytic activity for the reactions of C3H8, especially over the aged catalyst. T50 and T90 of the aged Pd catalyst were decreased by 31 and 30 °C, respectively. The single reaction results revealed that doping with Ni promoted the catalytic activity for the C3H8 + NO reaction. The fresh and aged catalysts were characterized by H2-temperature-programmed reduction, CO chemisorption, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy, which revealed that the doping with Ni inhibited the sintering of active PdOx species and the formation of undesired metallic Pd0, and led to improved reducibility of active PdOx and increased the surface area of PdOx species.

A highly efficient Rh-modified Pd/Al2O3 close-coupled catalyst

The close-coupled catalysts Pd/Al2O3 and Rh-Pd/Al2O3 were prepared by the impregnation method and characterized by H2 temperature-programmed reduction, CO chemisorption, and X-ray photoelectron spectroscopy. Both overall catalytic activity and specific reactions associated with C3H8 elimination were assessed. The light-off temperature and complete conversion temperature decreased by 23 and 18 °C, respectively, upon addition of Rh to the Pd/Al2O3 catalyst. The addition of Rh promotes the catalytic activity during C3H8 reactions, particularly in the presence of NO. The introduction of Rh not only inhibits sintering of PdOx and increases the dispersion of these same species, but also changes the electronic state of the PdOx in the catalyst.

Reaction mechanism and product branching ratios of the CH + C₃H₈ reaction: a theoretical study.

The C4H9 potential energy surface accessed by the reaction of methylidyne radical, CH (X(2)Π), with propane, C3H8, including possible intermediates, transition states and dissociation products, has been studied by ab initio and density functional calculations at the CCSD(T)/CBS//B3LYP/6-311G(d,p) level of theory. The computed relative energies and molecular parameters were utilized to calculate collision-energy-dependent unimolecular rate constants at the zero-pressure limit for isomerization and dissociation channels of the C4H9 adducts formed in the entrance reaction channels. The rate constants were used to evaluate the product branching ratios in the CH + C3H8 reaction under single-collision conditions. The results show that the reaction can produce mostly ethene (C2H4) + ethyl radical (C2H5) and propene (C3H6) + methyl radical (CH3), and up to 14% of various butene isomers (C4H8) + H. The product branching ratios are sensitive to the initial reaction adduct (a butyl radical, C4H9) formed in the entrance channels via barrierless insertion of the CH radical into the terminal and middle C-H bonds of propane or, possibly, into the single C-C bonds. A more definite answer on relative contributions of various available CH insertion channels can be obtained through ab initio quasiclassical trajectory calculations, which are proposed for the future. The results allowed us to conclude that the CH + C3H8 reaction does not result in major amounts in the direct growth of the carbon-skeleton to four-carbon C4H8 products via the CH-for-H exchange because C-C bond cleavages in C4H9 radicals are generally more preferable than C-H bond cleavages.

Sensing performance of zirconia-based gas sensor using titania sensing-electrode added with palladium

The sensing characteristics of a yttria-stabilized zirconia (YSZ)-based sensor using a sensing electrode (SE) consisting of rod-shaped TiO2 added with 1 wt.% of nano-sized Pd particles (abbreviated as TiO2(+ Pd)-SE) were evaluated, aiming at selective detection of hydrocarbons. The rod-shaped TiO2-SE without Pd addition (TiO2-SE) was found to give high sensitivities to both C3H8 and C3H6 which were used as representatives of alkane and alkene groups, respectively, in hydrocarbons (HCs), while TiO2(+ Pd)-SE gave selective detection of C3H8. The evaluation of catalytic activity to the gas-phase oxidation of HCs for the SE materials revealed that the oxidation of C3H6 was largely promoted by the Pd addition, leading to the high selectivity to C3H8 for the sensor using TiO2(+ Pd)-SE. From the results of polarization-curve measurements, the current value for the cathodic reaction of O2 was found to be slightly decreased by the Pd addition, while those for the anodic reaction of C3H8 and C3H6 were largely decreased. This is presumably due to the decrease in the actual concentration of C3H8 and C3H6 at the SE/YSZ interface owing to the promoted gas-phase oxidation of these HCs through the TiO2(+ Pd)-SE layer. XRD measurements as well as SEM observations confirmed that the added Pd particles were existing as PdO particles on the surface of the rutile-type TiO2 rods after the SE fabrication process. The stability test revealed that the C3H8 sensitivity of the sensor using TiO2(+ Pd)-SE gradually increased and reached the stable value after the 12 day operation. By considering the results of the complex-impedance analysis, we believed that this gradual increase in sensitivity was due to the decrease in the catalytic activity against the gas-phase oxidation of C3H8 in the TiO2(+ Pd)-SE layer.

Staged O2 Introduction and Selective H2 Combustion during Catalytic Reactions of Alkanes on Cation-Exchanged H-ZSM5

Stoichiometric reactions can be used to remove H2 and the associated kinetic and thermodynamic barriers that lead to low dehydrocyclodimerization selectivity during alkane reactions on cation-modified H-ZSM5. O2 co-reactants can form H2O in exothermic reactions that balance the enthalpy of endothermic dehydrogenation steps. O2 reacts preferentially with H2 via homogeneous and heterogeneous pathways, but also with hydrocarbons as H2 is depleted; thus, it must be gradually introduced as H2 forms in dehydrogenation reactions. Staged O2 protocols significantly increased aromatics yields during C3H8 reactions on unexchanged and on Ga- and Zn-exchanged H-ZSM5. On Ga/H-ZSM5, the maximum aromatic yields increased from 54% to 68% and aromatization/cracking selectivity ratios increased from 2.1 to 3.9 when O2 was introduced gradually into a gradientless batch reactor as H2 formed. O2 introduced was converted to H2O with >95% selectivity; an equivalent amount of O2 initially added with C3H8 led to low H2O selectivit...

Isotopic Tracer and Kinetic Studies of Oxidative Dehydrogenation Pathways on Vanadium Oxide Catalysts

Kinetic analysis and isotopic tracer studies were used to identify elementary steps and their reversibility in the oxidative dehydrogenation of propane on VOx/ZrO2 catalysts with VOx surface densities between 1.6 and 6 VOx/nm2. Competitive reactions of C3H6 and CH313CH2CH3 showed that CO forms via secondary combustion of propene intermediates. CO2 formed via this reaction and also via the direct combustion of propane. Reactions of 18O2/C3H8 mixtures on supported V216O5 led to the preferential initial appearance of lattice 16O atoms in all oxygen-containing products, as expected if lattice oxygens were required for the activation of C–H bonds. Isotopically mixed O2 species were not detected during reactions of C3H8–18O2–16O2 reactant mixtures. Therefore, dissociative O2 chemisorption steps are irreversible. Similarly, C3H8–C3D8–O2 reactants undergo oxidative dehydrogenation without forming C3H8−xDx mixed isotopomers, suggesting that C–H bond activation steps are also irreversible. Normal kinetic isotopic effects (kC–H/kC–D=2.5) were measured for primary oxidative dehydrogenation reactions. Kinetic isotope effects were slightly lower for propane and propene combustion steps (1.7 and 2.2, respectively). These data are consistent with kinetically relevant steps involving the dissociation of C–H bonds in propane and propene. C3H6–D2O and C3D6–H2O cross exchange reactions occur readily during reaction; therefore, OH recombination steps are reversible and nearly equilibrated. These isotopic tracer results are consistent with a Mars–van Krevelen redox mechanism involving two lattice oxygens in irreversible C–H bond activation steps. The resulting alkyl species desorb as propene and the remaining O–H group recombines with neighboring OH groups to form water and reduced V centers. These reduced V centers reoxidize by irreversible dissociative chemisorption of O2. The application of pseudo-steady-state and reversibility assumptions leads to a complex kinetic rate expression that describes accurately the observed water inhibition effects and the kinetic orders in propane and oxygen when surface oxygen and OH groups are assumed to be the most abundant surface intermediates.

Angular Distributions for the Cl + C2H6 → HCl + C2H5 Reaction Observed via Multiphoton Ionization of the C2H5 Radical

The title reaction has been studied by observing the ethyl radical product by means of resonance-enhanced multiphoton ionization (REMPI) that proceeds at 242 nm via highly dissociative Rydberg states. The method of core extraction was employed to measure the speed and spatial anisotropy distributions of the C2H5 product from which the differential cross section and the internal energy distribution of the products were deduced. The C2H5 product exhibits broad scattering that peaks sideways, and the internal modes of this product are not significantly excited. These results agree closely with those found from a previous study of the title reaction in which the HCl product was detected by REMPI under the same conditions. Additionally, we report REMPI detection of the propyl radical product in the analogous Cl + C3H8 reaction.

Statistical Modeling of Gas-Phase Organometallic Reactions Based on Density Functional Theory: Ni+ + C3H8

Density functional theory in its B3LYP variant has been used to explore quantitative details of the adiabatic potential energy surface leading from Ni+ + C3H8 reactants through a deep Ni+(C3H8) well to NiC2H4+ + CH4 and NiC3H6+ + H2 elimination products. The lowest energy path to CH4 elimination involves facile CC bond insertion followed by a high multicenter transition state (MCTS) leading directly to the exit-channel complex Ni+(C2H4)(CH4). The lowest energy path to H2 elimination involves comparably facile secondary CH insertion followed by a comparably high MCTS leading directly to the Ni+(C3H6)(H2) complex. Primary CH insertion leads to significantly higher barriers to both CH4 and H2 elimination; in particular, β-methyl migration is energetically very costly. These results support a mechanism significantly different from the stepwise mechanisms invoked earlier but the same as that found in recent calculations on the Fe+ + C3H8 reaction by Holthausen and Koch. The geometries suggest that agostic inte...

Infrared Absorption Probing of the Cl + C2H4 Reaction: Direct Measurement of Arrhenius Parameters for Hydrogen Abstraction

The laser photolysis/infrared long path absorption technique has been used to study the reaction of Cl atoms with C2H4. The time-resolved population of HCl produced in the reaction is monitored by continuous infrared absorption after pulsed photolytic generation of Cl atoms. At room temperature, the reaction proceeds principally through addition to form a chloroethyl radical, and the HCl production at 10 Torr is almost exclusively via secondary reactions. Above 500 K the abstraction channel dominates the HCl production, allowing direct extraction of Arrhenius parameters for the hydrogen abstraction. The abstraction rates are extracted by correcting the total rate by the HCl yield, which is determined by comparison with the Cl + C3H8 reaction. The abstraction reaction is well-described between 500 and 800 K by the simple Arrhenius expression k(T) = (6.2 ± 1.4) × 10-11e-(3400±450)/T cm3 molecule-1 s-1 (2σ). The activation energy determined in the present work would yield a heat of formation of the vinyl radical of ΔH°f,298(C2H3) = 71.3 ± 1.3 kcal mol-1 when combined with an extrapolation of published 298−495 K measurements of the HCl + C2H3 activation energy. A third-law analysis at 500 K yields ΔH°f,298(C2H3) = 71.6 ± 0.3 kcal mol-1.

Atomic probe imaging of β-SiC thin films grown on (100) Si

Atomic-scale imaging has been achieved on β-SiC surfaces using scanning tunneling microscopy in air. SiC films were grown on Si (100) substrates by chemical vapor deposition using the carbonization reaction of the surface with C3H8, followed (for films thicker than 100 nm) by the reaction of C3H8 and SiH4. For a relatively thick SiC (∼6 μm) film, the average nearest-neighbor surface atomic spacing measured was 3.09 Å, which is very close to the nominal value of 3.08 Å. Several of the thinner (<100 nm) SiC films exhibited significantly larger atomic spacings, indicating the strong effect of the larger atomic spacing (nominally 3.84 Å) of the Si substrate.