Methane benchmarking

The simplest hydrocarbon, methane, has posed a wealth of challenges to experimentalists and theoreticians seeking to discern its combustion mechanism. Methane s reactions have been explored in a wide variety of contexts over the past several decades. We have discussed these briefly the interested reader is referred to the reviews cited in our previous discussion for further details. Due to the scope of this review, we are primarily interested in these reactions insofar as they provide useful benchmarks for the reactions of larger alkylperoxy (RO2 ) and alkoxy (RO ) systems. With respect to the reactive intermediates present in methane combustion and their implications for larger systems, Lightfoot has published a review on the atmospheric role of these species, while Wallington et al. have provided multiple overviews of gas-phase peroxy radical chemistry. Lesclaux has provided multiple reviews of developments in peroxy radical chemistry. Batt published a review of the gas-phase decomposition reactions available to the alkoxy radicals. ... 

The nature of the methanol-zeolite interaction has been shown to be sensitive to a number of parameters and as such has proved to be a good benchmark for judging the reliability of quantum chemical methods. Not only are there a number of possible modes whereby one and two molecules interact with an acidic site (245), the barrier to proton transfer is small and sensitive to calculation details. Recent first-principles simulations (236-238) suggest that the nature of adsorbed methanol may be sensitive to the topology of the zeolite pore. The activation and reaction of methane, ethane, and isobutane have been characterized by using reliable methods and models, and realistic activation energies for catalytic reactions have been obtained. 

Adams and Schoenherr [29] achieved most of these benchmarks by formulating an adhesive consisting of a 40 wt % solids solution of kraft lignin in phenol-methanal-sodium hydroxide. This fluid had a viscosity of 10 Pa/s and thus was a very thick and energy-consuming adhesive to spread. However, when this binder was used in the manufacture of three ply panels of Douglas... 

A hierarchical series of ab initio methods was applied to obtain benchmark potential energy surface for the oxidative addition of methane to the Pd atom. The best estimate of kinetic and thermodynamic parameters is -8.1 kcal mol for the formation of the reactant complex, 5.8 kcal mol for the activation energy relative to the separate reactants, and 0.8 kcal mol for the reaction energy. The values agree well with those obtained by Siegbahn et al. with the PCI-80 method. Calculations were based on a model reaction involving the f --C,H transition state. 

Fuel flexibility of the fuel reforming subsystem was demonstrated using methane, propane, butane, methanol, ethanol, isooctane, and benchmark gasoline. A 1000-hour catalyst and reactor durability test was completed using benchmark gasoline. Warm transient response of less than 5 seconds was achieved for 10 to 90% of full reformer capacity. A three-fold increase in reformer productivity was achieved compared to the previous year, due to improved catalyst performance and more uniform flow within the reactor. Reactor concepts that would meet FreedomCAR s rapid start-up targets were developed. 

Abstract The singlet-triplet splittings of the di-radicals methylene, trimethylene-methane, ortha-, meta- and para-benzynes, and cyclobutane-l,2,3,4-tetrone have become test systems for the applications of various multi-reference (MR) coupled-cluster methods. We report results close to the basis set limit computed with double ionization potential (DIP) and double electron attachment (DBA) equation-of-motion coupled-cluster methods. These diradicals share the characteristics of a 2-hole 2-particle MR problem and are commonly used to assess the performance of MR methods, and yet require more careful study unto themselves as benchmarks. Here, using our CCSD(T)/6-311G(2d,2p) optimized geometries, we report DIP/DEA-CC results and single-reference (SR) CCSD, CCSD(T), ACCSD(T) and CCSDT results for comparison. 

The computed AEs are found 1.3, 2.6, and 2.9 kJmol" below the ATcT reference values for CH, CH4, and C2H6, respectively. One reason for these discrepancies is that in the present work, we have only included (except for the hindered-rotor treatment) the harmonic ZPVE. For example, the anharmonic correction to the ZPVE of CH amounts to 0.9 kJrnoR at the ae-CCSD(T)/cc-pCVTZ level [107]. Taking this anharmonic correction into account would have produced a theoretical AE for CH of 1209.3 kJrnoR within 0.4 kJ mol of the experimental value. The total ZPVE contribution would have been —77.4 kJrnoR, in good agreement with the value (—77.6 kJmol" ) of Schwenke [113]. For methane, Schwenke s value [114] amounts to —116.1 kJ mol whereas our harmonic value is —117.9 kJ mol Taking Schwenke s value in place of ours would reduce the error in the calculated AE of methane from 2.6 to 0.8 kJ mol k For ethane, an accurate (anharmonic) ZPVE contribution of —194.1 kJmol" is available from benchmark calculations performed by Karton and co-workers [115], This contribution is 2.6 kJmol" smaller in magnitude than our harmonic value, which makes up for almost all of the error of 2.9 kJ mol k Eurthermore, our fc-CCSD(T) value of 2972.5 kJ mol compares well with the value of 2973.7 kJ mol obtained at the W4 level [116[ by these authors. 

A microchannel reactor for high-temperature steam reforming of methane, isooctane and a benchmark fuel was developed by Whyatt et al. [41]. The main... 

Diedrich et al. could demonstrate with calculations on the dimers of methane, ammonia, and water, as well as the benzene dimer, that DMC performs very well on the whole range of interactions from pure dispersive to mainly electrostatic. " They used pseudopotentials and HF orbitals. With a similar approach, Korth et al. calculated the full S22 test set of dimers and the pairs of nucleic adds both in the Watson-Crick and the stacked conformation. The benchmark calculations revealed a mean absolute deviation for the binding energy of only 0.68kcal/mol. Very accurate results for the parallel displaced benzene dimer were obtained by Sorella et al. who obtained a binding energy of 2.2kcal/mol. These authors used their AGP approach with a Jastrow function and carefully optimized wave function parameters. 

Table 5 presents benchmark, estimated CCSD(T) binding energies for several noncovalent complexes and the errors for the MP2, SCS-MP2, and SCSN-MP2 methods. Also included are local versions of the SCS-type methods (SCS-LMP2 and SCSN-LMP2). As already mentioned, in every case but the methane dimer, the MP2 method greatly overbinds in the CBS limit. The SCS-MP2 results are greatly improved over MP2 for all cases but the methane dimer, where the error increases from 0.04 to 0.27kcal mol. This remains a... 

PCN-11, another benchmark MOF, that shows very high excess methane uptake [171 cm (STP)/cm ]... 

We first present some recent results on small hydrocarbons methane, acetylene, and the methyl cation CH. Benchmark calculations have been performed on the determination of the equilibrium geometries of these species in their ground electronic state. These systems identified in numerous planetary atmospheres and interstellar medium present a renewed astrophysical interest [66, 102] and are extensively studied in high resolution laboratory experiments [14, 51]. 

Despite much effort exerted to identify new 16-electron fragments capable of reacting with C—H bonds in methane and other saturated hydrocarbons, only a few such systems are known. The benchmark remains [Cp ML] (M = Rh, Ir L = PMea, CO). These complexes continue to appear in the literature in mechanistic and application studies. The activation of ethane by irradiation of [Cp Ir(CO)2] in supercritical C02(SC—CO2) is greatly accelerated in solutions saturated with The extremely photolabile... 

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