Vacuum-ultraviolet photolysis of ethane films.
Vacuum UV photolysis of solid ethane films, measuring product distributions, presenting evidence for quenching of excited ethane and ethylene
ETHANE↗
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Nickel/gallium modified HZSM-5 for ethane aromatization: Influence of metal function on reactivity and stability
Bimetallic catalysts often outperform their monometallic counterparts due to the synergistic effect. Here we reported that the Ni/Ga co-functionalized HZSM-5 catalyst, specifically with Ni 1 /Ga 1 stoichiometric ratio, shows significantly improved selectivity (above 80 %) and stability than the Ni/HZSM-5 catalyst and higher activity (with identical selectivity) than the Ga/HZSM-5 catalyst in ethane aromatization. According to the transient experiment, the Ga and Ni 1 Ga 1 /HZSM-5 catalysts show an induction period of a few minutes. However, for Ni/HZSM-5 and Ni 1 Ga 1/3 /HZSM-5, the induction period increased to >10 min and >30 min, respectively, where up to 100 % of ethane was converted into methane and coke through cracking/hydrogenolysis. Furthermore, based on the generalized power-law equation model, a modified model for deactivation kinetic was proposed. Consequently, the influence of the metal function on the kinetic parameters was discussed. We anticipate the formation of Ni 3 Ga intermetallic alloy and its synergy with the exchanged Ga δ+ to be responsible for optimal BTX formation.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Stable isotope equilibria in the dihydrogen-water-methane-ethane-propane system. Part 1: Path-integral calculations with CCSD(T) quality potentials
Isotopic compositions of alkanes are typically assumed to be kinetically controlled, but recently is has been proposed that alkanes can isotopically equilibrate for both C and H isotopes during natural gas generation. Evaluation of this requires knowledge of the isotopic equilibrium between alkanes and other common hydrogen and carbon bearing species. Here, in this study, we calculate isotopic equilibria within and between gaseous dihydrogen (H 2 ), water (H 2 O), methane (CH 4 ), ethane (C 2 H 6 ) and propane (C 3 H 8 ), including isotope fractionation among molecules, clumped isotope effects, as well as among sites of propane (i.e., the site-specific isotope effects) from 0°C to 500°C using a path-integral method paired with high-level descriptions of molecular potentials and the diagonal correction to the Born Oppenheimer approximation. While path-integral calculations with high- level CCSD(T) potentials are available for the isotopic equilibria involving methane, the path-integral calculations for ethane and propane have only been performed based on lower-level descriptions of the molecular potentials. We analyze the relative importance of various approximations that are commonly employed when isotopic equilibria are evaluated. We find that clumped isotope effects can be calculated to the same accuracy using computationally inexpensive combination of the Bigeleisen-Mayer-Urey model with the molecular potential from density functional theory. In contrast, fractionation and site preferences of both deuterium and carbon-13 benefit from the use of the higher level CCSD(T) potentials and accounting for anharmonic effects. Additionally, for fractionation and site preference of deuterium corrections to Born-Oppenheimer approximation can also be important.
03 NATURAL GAS↗
Study of the Hydrogen Pretreatment of Gallium and Platinum Promoted ZSM-5 for the Ethane Dehydroaromatization Reaction
Here, the performances of gallium and platinum promoted ZSM-5 catalysts, fresh and reduced, were studied for the dehydroaromatization of ethane to aromatics. Fresh and reduced 2% Ga/ZSM-5, 1.5% Ga–0.5% Pt/ZSM-5, and 0.5% Pt/ZSM-5 were tested in a fixed-bed reactor system at 615 °C for 2 h time on stream. It was observed that the hydrogen reduction of the fresh Pt-containing catalysts led to an increase in catalytic conversion. The addition of platinum to the gallium catalyst resulted in an increase in the reducibility of the Ga species on the surface of the zeolite. The GaPt catalysts exhibited an increase in ethane conversion and the stability of aromatic production selectivity over the Ga and Pt catalysts. The as-prepared fresh catalysts were characterized by ICP and BET methods. The fresh and reduced catalysts were further analyzed by XRD, H 2 -TPR, XPS, pyridine DRIFTS, TGA, and TEM.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Phase Behavior of Methane–Ethane Mixtures in Nanopores
The behavior of fluids in confined spaces is important in several research fields, including the oil and gas industry, because of the importance of confined hydrocarbons in unconventional shale reservoirs. A large percentage of the hydrocarbons are contained in nanoscale shale pores, and as a result, interactions between fluid molecules and the pore walls become significant to the fluid behavior and cause deviations of the fluid properties from bulk properties. In this work, classical molecular dynamics (MD) simulations and grand canonical Monte Carlo (GCMC) simulations are performed to model kerogen pores in shale reservoirs and their effect on adsorption selectivity and phase equilibria of hydrocarbon mixtures in a wide range of temperatures and pressures. A slit pore made of graphite walls is used to represent the basic unit where a fluid may be stored in shale reservoirs. The separation between graphite layers is varied to observe the effect of confinement on the adsorption selectivity and phase equilibrium of methane-ethane mixtures. Results from GCMC and MD simulations show that ethane is preferred over methane in the confined system. Moreover, most fluid molecules in the confined system tend to be adsorbed on the pore walls instead of remaining in the gas phase. Preferential interactions between the fluid molecules and the pore walls induce changes in the phase diagram in the confined system. Furthermore, the results from GCMC simulations show shifts with respect to the bulk pressure-composition phase diagram that becomes more pronounced as the pore size decreases.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Efficient Implementation of NOCI-MP2 Using the Resolution of the Identity Approximation with Application to Charged Dimers and Long C–C Bonds in Ethane Derivatives
An efficient implementation of the perturb-then-diagonalize nonorthogonal configuration interaction method with second-order Møller-Plesset perturbation theory (NOCI-MP2) is introduced. Relative to other low scaling multireference perturbation theories, NOCI-MP2 often requires a much smaller active space because of the use of nonorthogonal reference configurations. Reworking the NOCI-MP2 equations with the resolution of the identity (RI) approximation enables the method to have the same memory requirements and computational scaling as single reference RI-MP2. The working equations are extended to include single substitutions as required when the reference determinants do not satisfy the Hartree-Fock equations. A detailed computational algorithm is presented along with timings to establish the performance of the implementation. NOCI-MP2 is applied to the binding energy and charge resonance energy in dication and monocation π dimers, as well as didiamantane ethane, and hexaphenylethane. A well-defined set of nonorthogonal determinants are obtained using absolutely localized molecular orbitals (ALMOs), as solutions to the self-consistent field for molecular interactions (SCF-MI) equations corresponding to covalent and ionic determinants. Agreement with experimental information where available, and other multireference methods, is satisfactory, with the use of an 0.3 au level shift to guard against large MP2 amplitudes. For didiamantane ethane and hexaphenylethane, large dispersion forces help stabilize the molecules despite the steric repulsion. However, in the case of hexaphenylethane, the energy penalty from the geometric distortion of the fragments critically weakens the bond.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Gas-Phase Hydrogen-Atom Measurement above Catalytic and Noncatalytic Materials during Ethane Dehydrogenation
The role of a solid surface for initiating gas-phase reactions is still not well understood. The hydrogen atom (H) is an important intermediate in gas-phase ethane dehydrogenation and is known to interact with surface sites on catalysts. However, direct measurements of H near catalytic surfaces have not yet been reported. Here, we present the first H measurements by laser-induced fluorescence in the gas-phase above catalytic and noncatalytic surfaces. Measurements at temperatures up to 700 °C show H concentrations to be at the highest above inert quartz surfaces compared to stainless steel and a platinum-based catalyst. Additionally, H concentrations above the catalyst decreased rapidly with time on stream. Furthermore, these newly obtained observations are consistent with the recently reported differences in bulk ethane dehydrogenation reactivity of these materials, suggesting H may be a good reporter for dehydrogenation activity.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Transient Pulse-Response Time-of-Flight Mass Spectrometry for Complex, Deactivating Heterogeneous Catalytic Systems: Application to Ethane Dehydroaromatization
The study of complex, multistep bond-forming and -breaking reactions in heterogeneous catalytic systems often encounters challenges associated with the involvement of large numbers of intermediates among branching pathways. Kinetic information obtained from traditional steady-state measurements can be complemented with that from time-resolved methods to uncover details of the underlying chemistry. Herein, we describe an approach for tracking the complete time-resolved chemical composition (ca. 4–200 u) of a reactor effluent in response to a reactant pulse. We use a six-port rotary valve with a metered sampling loop to pulse reactants at ambient pressure into a flow reactor packed with a catalyst bed within the isothermal region of a heated furnace. The temporal evolution of effluent species is tracked using time-resolved molecular-beam time-of-flight mass spectrometry. We highlight the possibilities that this method has to offer by studying the complex bifunctional mechanism of ethane dehydroaromatization over an HZSM-5-supported platinum catalyst. We demonstrate that energy-tunable ionization sources, which facilitate isomer resolution, enable the measurement of the full mass spectral time-dependent system response. This includes the evolution of major products and mechanistically relevant reactive intermediates such as 1,3-butadiene and cyclopentadiene; these species have not previously been observed from this reaction. In additional studies, we also assess the role of platinum in the catalyst by examining temporal responses to ethane and ethylene feeds. Results show that two temporally distinct formation pathways exist for methane and benzene, and that their importance depends on both catalyst composition and reactant identity. Additionally, characteristics of catalyst deactivation are uniquely observable in the time-resolved mass spectral response, including the selective deactivation of a benzene formation pathway. The combination of time-of-flight mass spectrometry with tunable ionization enables the simultaneous observation of all effluents in a complex mixture of intermediates with isomer/isobar differentiation capabilities that can be applied to any complex reaction system.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Oxygenate Production from Plasma-Activated Reaction of CO 2 and Ethane
Upgrading ethane with CO 2 as a soft oxidant represents a desirable means of obtaining oxygenated hydrocarbons. This reaction is not thermodynamically feasible under mild conditions and has not been previously achieved as a one-step process. Non-thermal plasma was implemented as an alternative means of supplying energy to overcome activation barriers, leading to the production of alcohols, aldehydes, and acids as well as C 1 -C 5+ hydrocarbons under ambient pressure, with a maximum total oxygenate selectivity of 12%. A plasma chemical kinetic computational model was developed and found to be in good agreement with the experimental trends. Results from this study illustrate the potential to use plasma for the direct synthesis of value-added alcohols, acids, and aldehydes from ethane and CO 2 under mild conditions.
54 ENVIRONMENTAL SCIENCES↗
Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis
The application of bimolecular reductive elimination to the activation of iron catalysts for alkene–diene cycloaddition is described. Key to this approach was the synthesis, characterization, electronic structure determination, and ultimately solution stability of a family of pyridine(diimine) iron methyl complexes with diverse steric properties and electronic ground states. Both the aryl-substituted, ( Me PDI)FeCH 3 and ( Et PDI)FeCH 3 ( R PDI = 2,6-(2,6-R 2 -C 6 H 3 N=CMe) 2 C 5 H 3 N), and the alkyl-substituted examples, ( Cy APDI)FeCH 3 ( Cy APDI = 2,6-(C 6 H 11 N=CMe) 2 C 5 H 3 N), have molecular structures significantly distorted from planarity and S = 3/2 ground states. The related N-arylated derivative bearing 2,6-di-isopropyl aryl substituents, ( iPr PDI)FeCH 3 , has an idealized planar geometry and exhibits spin crossover behavior from S = 1/2 to S = 3/2 states. At 23 °C under an N 2 atmosphere, both ( Me PDI)FeCH 3 and ( Et PDI)FeCH 3 underwent reductive elimination of ethane to form the iron dinitrogen precatalysts, [( Me PDI)Fe(N 2 )] 2 (μ-N 2 ) and [( Et PDI)Fe(N 2 )] 2 (μ-N 2 ), respectively, while ( iPr PDI)FeCH 3 proved inert to C–C bond formation. By contrast, addition of butadiene to all three iron methyl complexes induced ethane formation and generated the corresponding iron butadiene complexes, ( R PDI)Fe(η 4 -C 4 H 6 ) (R = Me, Et, i Pr), known precatalysts for the [2+2] cycloaddition of olefins and dienes. Kinetic, crossover experiments, and structural studies were combined with magnetic measurements and Mössbauer spectroscopy to elucidate the electronic and steric features of the iron complexes that enable this unusual reductive elimination and precatalyst activation pathway. Furthermore, transmetalation of methyl groups between iron centers was fast at ambient temperature and independent of steric environment or spin state, while the intermediate dimer underwent the sterically controlled rate-determining reaction with either N 2 or butadiene to access a catalytically active iron compound.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Oxidation of a Monomethylpalladium(II) Complex with O 2 in Water: Tuning Reaction Selectivity to Form Ethane, Methanol, or Methylhydroperoxide
We report photochemical aerobic oxidation of n -Pr 4 N[(dpms)Pd II Me(OH)] ( 5 ) and (dpms)Pd II Me(OH 2 ) ( 8 ) (dpms = di(2-pyridyl)methanesulfonate) in water in the pH range of 6–14 at 21 °C was studied and found to produce, in combined high yield, a mixture of MeOH, C 2 H 6 , and MeOOH along with water-soluble n -Pr 4 N[(dpms)Pd II (OH) 2 ] ( 9 ). By changing the reaction pH and concentration of the substrate, the oxidation reaction can be directed toward selective production of ethane (up to 94% selectivity) or methanol (up to 54% selective); the yield of MeOOH can be varied in the range of 0–40%. The source of ethane was found to be an unstable dimethyl Pd IV complex (dpms)Pd IV Me 2 (OH) ( 7 ), which could be generated from 5 and MeI. For shedding light on the role of MeOOH in the aerobic reaction, oxidation of 5 and 8 with a range of hydroperoxo compounds, including MeOOH, t -BuOOH, and H 2 O 2 , was carried out. The proposed mechanism of aerobic oxidation of 5 or 8 involves predominant direct reaction of excited methylpalladium(II) species with O 2 to produce a highly electrophilic monomethyl Pd IV transient that is involved in subsequent transfer of its methyl group to 5 or 8 , H 2 O, and other nucleophilic components of the reaction mixture.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ethane dehydrogenation on pristine and AlO x decorated Pt stepped surfaces
In this work, ethane dehydrogenation on pristine and AlO x decorated Pt surfaces was studied using density functional theory (DFT) calculations and reaction kinetics experiments. Following the study of adsorption of fourteen distinct C 2 H x and CH x species, the whole reaction network for ethane dehydrogenation on the terrace and the step of the pristine Pt(433) surface was systematically analyzed using DFT. We show that the under-coordinated step edge sites bind C 2 H x and CH x species more strongly than terrace sites. These under-coordinated step sites facilitate deep dehydrogenation, resulting in accumulation of coke precursors on the surface and catalyst deactivation. We demonstrate that by decorating the step with AlO x species the step edge sites can be blocked, leading to substantial suppression of deep dehydrogenation and coke formation. These findings were corroborated by reaction kinetics experiments where a four-fold enhancement of the turnover frequency for ethylene formation was measured on 10-cycle atomic layer deposited (ALD) alumina overcoated Pt/γ-Al 2 O 3 catalyst compared to Pt/γ-Al 2 O 3 without decoration with ALD-alumina. Our results suggest that AlO x decorated Pt is a promising catalyst for alkane dehydrogenation and could have applications, including in endothermic cooling in hypersonic flights.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
A novel low-thermal-budget approach for the co-production of ethylene and hydrogen via the electrochemical non-oxidative deprotonation of ethane
Here, the oversupply of ethane, a major component of natural gas liquids, has stimulated the wide applications of ethylene since the shale gas revolution. However, ethylene production is energy-intensive and represents the most energy-consuming single process in the chemical industry. In this communication, we report, for the first time, a novel low-thermal-budget process for the co-production of ethylene and pure hydrogen using a proton-conducting electrochemical deprotonation cell. At a constant current density of 1 A cm –2 , corresponding to a hydrogen production rate of 0.448 mol cm –2 per day, and 400 °C, a close to 100% ethylene selectivity was achieved under an electrochemical overpotential of 140 mV. Compared to an industrial ethane steam cracker, the electrochemical deprotonation process can achieve a 65% saving in process energy and reduce the carbon footprint by as much as 72% or even more if renewable electricity and heat are used. If the heating value of produced hydrogen is taken into account, the electrochemical deprotonation process actually has a net gain in processing energy. The electrochemical deprotonation process at reduced temperatures in the present study provides a disruptive approach for petrochemical manufacturing, shifting the paradigm from thermal chemical practice to a clean energy regime.
04 OIL SHALES AND TAR SANDS↗
First-order and gradual phase transitions of ethane confined in MCM-41
The first-order phase transition of ethane confined in MCM-41, i.e., capillary condensation, has been measured using an isochoric cooling procedure by differential scanning calorimetry (DSC) under conditions ranging from 206 K and 1.1 bar up to the pore critical point (PCP). The PCP has also been determined using the three-line method developed earlier based on the vanishing heat of phase transition. As in the bulk phase, no first-order phase transition can occur above the critical point, which also implies that vapor can transform into liquid gradually by following a path around the critical point through the supercritical region. For the first time, the gradual phase transition is demonstrated with ethane in MCM-41, which is achieved through a multistep process with paths proceeding around the PCP without crossing the capillary-condensation curve. Finally, the occurrence of the gradual phase transition in nanopores, thus the confined supercriticality, is confirmed while our consistent DSC measurements are also well demonstrated.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ethane dehydrogenation over manganese oxides supported on ZSM-5 zeolites
Mn-ZSM5 catalysts are shown to have high reaction rates, C 2 H 4 selectivity and stability for the ethane dehydrogenation reaction. The specific reaction rate increases with the Mn loading until the optimal Mn amount of 3.4 wt% for zeolites with a Si/Al ratio of 12. Structure characterizations and spectra analysis have unveiled that this catalyst contains MnO 2 nanoparticles on the zeolite external surface and (MnOH) + groups on the external surface of the zeolite. The MnO 2 nanoparticles contain the catalytic sites for ethane dehydrogenation while the (MnOH) + groups help stabilize the oxide particles, leading to the high stability of the Mn-ZSM5 catalyst for EDH. As a result, the Mn-ZSM5 samples can catalyze EDH for over 150 h at 600 °C with a high reaction rate (>10 mmol C 2 H 6 g cat –1 h –1 ) and high C 2 H 4 selectivity (>98%). Finally, the spent catalyst can also be regenerated by calcination in dry or wet air (3% steam).
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
On the mechanisms of ethane dehydrogenation on silica-supported mononuclear Fe
We explore ethane dehydrogenation over Fe( ii ) and Fe( iii ) sites on amorphous SiO 2 . Ethane dehydrogenation occurs through a heterolytic cleavage mechanism over Fe( ii ), and a redox mechanism over Fe( iii ) with lower energetic barrier.
Satyanand, Sakshi [Department of Chemical and Biom↗
Molecular frame photoelectron angular distributions for core ionization of ethane, carbon tetrafluoride and 1,1-difluoroethylene
Molecular frame photoelectron angular distributions (MFPADs) are measured in this paper in electron–ion momentum imaging experiments and compared with complex Kohn variational calculations for carbon K-shell ionization of carbon tetrafluoride (CF 4 ), ethane (C 2 H 6 ) and 1,1-difluoroethylene (C 2 H 2 F 2 ). While in ethane the polarization averaged MFPADs show a tendency at low energies for the photoelectron to be emitted in the directions of the bonds, the opposite effect is seen in CF 4 . A combination of these behaviors is seen in difluoroethylene where ionization from the two carbons can be distinguished experimentally because of their different K-shell ionization potentials. Excellent agreement is found between experiment and simple static-exchange or coupled two-channel theoretical calculations. Finally, however, simple electrostatics do not provide an adequate explanation of the suggestively simple angular distributions at low electron ejection energies.
74 ATOMIC AND MOLECULAR PHYSICS↗
Ethane-xenon mixtures under shock conditions
Mixtures of light elements with heavy elements are important in inertial confinement fusion. We explore the physics of molecular scale mixing through a validation study of equation of state (EOS) properties. Density functional theory molecular dynamics (DFT-MD) at elevated temperature and pressure is used to obtain the thermodynamic state properties of pure xenon, ethane, and various compressed mixture compositions along their principal Hugoniots. In order to validate these simulations, we have performed shock compression experiments using the Sandia Z-Machine. A bond tracking analysis correlates the sharp rise in the Hugoniot curve with the completion of dissociation in ethane. Furthermore, the DFT-based simulation results compare well with the experimental data along the principal Hugoniots and are used to provide insight into the dissociation and temperature along the Hugoniots as a function of mixture composition. Interestingly, we find that the compression ratio for complete dissociation is similar for several compositions suggesting a limiting compression for C-C bonded systems.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗