Search

Acceptorless dehydrogenation into carbonyls and molecular hydrogen is an attractive strategy to valorize (biobased) alcohols. Using 2-octanol dehydrogenation as benchmark reaction in a continuous reactor, a library of metal-supported catalysts is tested to validate the predictive level of catalytic activity for combined DFT and micro-kinetic modeling. Based on a series of transition metals, scaling relations are determined as a function of two descriptors, i.e. the surface binding energies of atomic carbon and oxygen. Then, a volcano-shape relation based on both descriptors is derived, paving the way to further optimization of active catalysts. Evaluation of 294 diluted alloys but also a series of carbides and nitrides with the volcano map identified 12 promising candidates with potentially improved activity for alcohol dehydrogenation, which provides useful guidance for experimental catalyst design. Further screening identifies β-Mo2N and γ-Mo2N exposing mostly (001) and (100) facets as potential candidates for alcohol dehydrogenation.

First-principles based kinetic modeling is essential to gain insight into the governing chemistry of nitrogen-containing compounds over a wide range of technologically important processes, e.g. pyrolysis, oxidation and combustion. It also enables the development of predictive, fundamental models key to improving understanding of the influence of nitrogen-containing compounds present as impurities or process additives, considering safety, operability and quality of the product streams. A prerequisite for the generation of detailed fundamental kinetic models is the availability of accurate thermodynamic properties. To address the scarcity of thermodynamic properties for nitrogen-containing compounds, a consistent set of 91 group additive values and three non-nearest-neighbor interactions has been determined from a dataset of CBS-QB3 calculations for 300 species, including 104 radicals. This dataset contains a wide range of nitrogen-containing functionalities, i.e. imine, nitrile, nitro, nitroso, nitrite, nitrate and azo functional groups. The group additivity model enables the approximation of the standard enthalpy of formation and standard entropy at 298 K as well as the standard heat capacities over a large temperature range, i.e. 300–1500 K. For a test set of 27 nitrogen-containing compounds, the group additivity model succeeds in approximating the ab initio calculated values for the standard enthalpy of formation with a MAD of 2.3 kJ mol−1. The MAD for the standard entropy and heat capacity is lower than 4 and 2 J mol−1 K−1, respectively. For a test set of 11 nitrogen-containing compounds, the MAD between experimental and group additivity approximated values for the standard enthalpy of formation amounts to 2.8 kJ mol−1. [ABSTRACT FROM AUTHOR]

New group additivity values are presented to enable the modeling of a broad range of intermolecular hydrogen abstraction reactions involving nitrogen-containing compounds. From a dataset of 316 reaction rate coefficients calculated at the CBS-QB3 level of theory in the high-pressure limit, 76 group additivity values and 14 resonance corrections have been estimated. The influence of substituents on both the attacked hydrogen and attacking radical, being a carbon or nitrogen atom, has been investigated systematically. The new group additivity models can be applied to approximate the Arrhenius parameters of hydrogen abstraction reactions of nitrogen-containing compounds by hydrogen atoms, carbon-centered and nitrogen-centered radicals in the 300–1800 K temperature range. Complementary to the group additivity model, correlations for the tunneling coefficients, which depend on both the temperature and the activation energy of the reaction in the exothermic direction, have been generated. The good performance of the new group additivity schemes has been demonstrated using a test set of reactions. At 1000 K, the rate coefficients for all test set reactions are approximated on average within a factor of 1.45, 1.47 and 1.34, for the hydrogen abstractions with a reactive center of the type H–H–N, N–H–N and C–H–N respectively. [ABSTRACT FROM AUTHOR]

Secondary reactions in radical polymerization pose a challenge when creating kinetic models for predicting polymer structures. Despite the high impact of these reactions in the polymer structure, their effects are difficult to isolate and measure to produce kinetic data. To this end, we used solvation-corrected M06-2X/6-311+G(d,p) ab initio calculations to predict a complete and consistent data set of intrinsic rate coefficients of the secondary reactions in acrylate radical polymerization, including backbiting, β-scission, radical migration, macromonomer propagation, mid-chain radical propagation, chain transfer to monomer and chain transfer to polymer. Two new approaches towards computationally predicting rate coefficients for secondary reactions are proposed: (i) explicit accounting for all possible enantiomers for reactions involving optically active centers; (ii) imposing reduced flexibility if the reaction center is in the middle of the polymer chain. The accuracy and reliability of the ab initio predictions were benchmarked against experimental data via kinetic Monte Carlo simulations under three sufficiently different experimental conditions: a high-frequency modulated polymerization process in the transient regime, a low-frequency modulated process in the sliding regime at both low and high temperatures and a degradation process in the absence of free monomers. The complete and consistent ab initio data set compiled in this work predicts a good agreement when benchmarked via kMC simulations against experimental data, which is a technique never used before for computational chemistry. The simulation results show that these two newly proposed approaches are promising for bridging the gap between experimental and computational chemistry methods in polymer reaction engineering. [ABSTRACT FROM AUTHOR]

Basic oxides such as CaO and MgO were added to a γ-Al2O3 support in NiCu-catalyzed hydrodeoxygenation of anisole. A commercial CaO-MgO-γ-Al2O3 was compared to a benchmark γ-Al2O3 and in-house variants with sequential oxide impregnation prior to NiCu impregnation. CaO did not have a significant impact on activity compared to the benchmark, while MgO improved NiCu dispersion, enhancing activity. Co-impregnation of CaO and MgO resulted in intermediate activity. Despite decreased demethoxylation, likely due to moderated support acidity, both CaO-modified and the commercially supported catalysts showed improved stability over 48 h Time On Stream. [ABSTRACT FROM AUTHOR]

The thermodynamics and kinetics studies of hydrogen abstraction between methyl radicals and simple hydrocarbons or [H.sub.2] are described. The best experimental rate coefficients of five hydrogen abstraction reactions were obtained with CBS-QB3 method.