Elementary reaction

About: Elementary reaction is a research topic. Over the lifetime, 2972 publications have been published within this topic receiving 76110 citations.

The structure of laminar alkane-, alkene-, and acetylene flames

Abstract: The detailed knowledge of combustion mechanisms is important for example for the control of (kinetically determined) pollutant formation (e.g., NO, hydrocarbons, soot), or for the extrapolation to technologically important but experimentally inaccessible conditions. By suitable separation and elimination of unimportant reactions, a mechanism is developed with the aid of the present kinetic data for the elementary reactions involved. This mechanism explains, without fitting, the currently available experimental results for laminar premixed flames of alkanes, alkenes, and acetylene (flame velocity and structure of free flames, concentration and temperature profiles in burner-stabilized flames). These experimental results are simulated by the solution of the corresponding conservation equations with suitable models describing diffusion and heat conduction in the multicomponent mixture considered. In lean and moderately rich flames the hydrocarbon is attacked by O, H, and OH, in the first step. These radicals are produced by the chain-branching steps of the oxyhydrogen reaction. The alkyl radicals formed in this way always decompose to smaller alkyl radicals by fast thermal elimination of alkenes. Only the relatively slow thermal decomposition of the smallest alkyl radicals (CH 3 and C 2 H 5 ) competes with recombination and with oxidation reactions by O atoms and O 2 . This part of the mechanism is rate-controlling in the combustion of alkanes and alkenes, and is therefore the reason for the similarity of all alkane and alkene flames.

Unraveling the reaction mechanisms governing methanol-to-olefins catalysis by theory and experiment

Abstract: The conversion of methanol to olefins (MTO) over a heterogeneous nanoporous catalyst material is a highly complex process involving a cascade of elementary reactions. The elucidation of the reaction mechanisms leading to either the desired production of ethene and/or propene or undesired deactivation has challenged researchers for many decades. Clearly, catalyst choice, in particular topology and acidity, as well as the specific process conditions determine the overall MTO activity and selectivity; however, the subtle balances between these factors remain not fully understood. In this review, an overview of proposed reaction mechanisms for the MTO process is given, focusing on the archetypal MTO catalysts, H-ZSM-5 and H-SAPO-34. The presence of organic species, that is, the so-called hydrocarbon pool, in the inorganic framework forms the starting point for the majority of the mechanistic routes. The combination of theory and experiment enables a detailed description of reaction mechanisms and corresponding reaction intermediates. The identification of such intermediates occurs by different spectroscopic techniques, for which theory and experiment also complement each other. Depending on the catalyst topology, reaction mechanisms proposed thus far involve aromatic or aliphatic intermediates. Ab initio simulations taking into account the zeolitic environment can nowadays be used to obtain reliable reaction barriers and chemical kinetics of individual reactions. As a result, computational chemistry and by extension computational spectroscopy have matured to the level at which reliable theoretical data can be obtained, supplying information that is very hard to acquire experimentally. Special emphasis is given to theoretical developments that open new perspectives and possibilities that aid to unravel a process as complex as methanol conversion over an acidic porous material.

Comprehensive Mechanism for Methanol Oxidation

Abstract: A detailed chemical kinetic mechanism, involving 26 chemical species and 84 elementary reactions, is proposed for the oxidation of methanol Within the scope of this mechanism, turbulent flow reactor and shock tube experimental data are used to determine rate expressions for several of the important reactions involving CH3OH and its intermediate product species, CH2OH Calculations using the proposed mechanism and elementary reaction rates accurately reproduce experimental results over a combined temperature range of 1000-2180K, for fuel-air equivalence ratios between 005 and 30 and for pressures between 1 and 5 atmospheres The resulting chemical kinetic model is then employed, together with an unsteady, one-dimensional numerical model for flame propagation, to predict the laminar flame speed of a stoichiometric methanol-air mixture The calculated laminar flame speed is 44+ 2 cm/ sec and is in good agreement with experimentally observed values