We develop and validate detailed reaction mechanisms to represent the oxidative coupling of methane (OCM) over a La2O3/CeO2 nanofabric catalyst. The reaction mechanism includes 39 reversible gas‐phase reactions and 52 irreversible surface reactions between 22 gas‐phase species and 11 surface species. We use a model‐based interpretation of spatially resolved concentration and temperature profiles measured by using a laboratory‐scale packed‐bed reactor. The reaction mechanisms are validated for inlet feed compositions in the range of 7≤CH4/O2≤11. The results are supported by a reaction pathway analysis that provides insight into the relative contributions of the gas‐phase and surface reactions to form the desired C2+ and the undesired COx products. The results provide new quantitative insights into the complex nature of the OCM chemistry, which can assist practical process and reactor development.

Oxidative coupling of methane (OCM) is a high-temperature process involving the transformation of methane into ethane and ethylene, which are valuable intermediates for the chemical processing industry.[1] Despite decades of long research that has resulted in thousands of papers and hundreds of patents, OCM still remains at the research stage. Although many OCM catalysts have been reported, [2] there appears to be an upper limit for the yield of C 2 + products of approximately 25 % per reactor pass, for which the kinetic reasons are largely unknown. It has been recognized that to make progress in the OCM an improved quantitative understanding of the underlying detailed chemical kinetic mechanisms (DCKMs) of the coupled surface and gas-phase reactions must be developed and validated over the very broad range of conditions encountered in the process. [3][4][5][6] DCKMs comprise a comprehensive description of chemical transformations in terms of irreducible chemical events or elementary reactions for which independent rate coefficient parameters, frequently expressed in the form k = AT n exp(ÀE/RT), are either available from direct measurements or estimated from theoretical considerations. [3,[5][6][7] DCKMs are then combined with models describing the transport phenomena for the realistic simulation of the performance of the OCM reactors. [3,5,7] With the availability of DCKMs, we will then be in a better position to identify improved OCM conditions, superior reactor configurations, and new leads for catalytic materials that are needed to exceed the 25 % limit for C 2 + product yields.[3]Validation of DCKMs requires experimental data of high information content because of the presence of a large number of species participating in an even larger number of elementary reactions. Although DCKMs for OCM have been reported in the past, [3,6] they were all validated by using integral reactor data, that is, reactor exit conditions. However, this is not a particularly demanding test for mechanism validation. In fact, different DCKMs can readily predict similar OCM reactor exit concentrations, as estimated kinetic parameters are used for many of the elementary reactions. Therefore, the performance of more comprehensive validation tests such as the prediction of the absolute concentration profiles of all the major and minor species within the catalytic packed-bed reactors is necessary for the development of truly predictive DCKMs for the OCM process. However, we are not aware of such information-rich data sets in the open OCM literature.Herein, we report, for the first time, the spatially resolved comprehensive species concentrations and temperature profiles in a fixed-bed OCM reactor by using microprobe sampling. Although microprobe sampling techniques have long been used in high-temperature flame-combustion research to obtain spatial temperature and concentration profiles, [8][9][10] their adaptation to and use in heterogeneous catalysis is relatively recent. One of the earliest applications of microprobe sampling to cataly...

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Oxidative coupling of methane (OCM) is a complex surface catalysis and gas‐phase reaction process to transform methane into ethane, ethylene and higher molecular weight hydrocarbons (C2+). However, the C2+ product yields in single‐pass fixed‐bed reactors have been limited by the intrusion of gas‐phase combustion reactions. To remedy this problem, a dual‐bed OCM reactor configuration was explored in which the O2 feed was distributed between two sequential packed bed reactors with interstage cooling using La2O3–CeO2 nanofiber fabric catalysts. At the overall CH4/O2 feed ratio of 4.0, the dual‐bed reactor configuration with split O2 introduction resulted in the ultimate C2+ product yield of 21%, which is significantly higher than the 16% observed in the single‐bed OCM reactor. In addition, spatially resolved species concentration and temperature profiles along the entire length of the dual‐bed reactor were also acquired by using in situ microprobe sampling.

The discovery of the RuO2–CuO–NaCl/SiO2 catalyst for the direct gas‐phase epoxidation of propylene to propylene oxide created a potentially promising path towards developing a high‐performing catalyst of substantial commercial value and opened a new challenge in catalysis research. In this work, studies following up this discovery are presented to reveal critical insight into the catalytic mechanism on the trimetallic catalyst. Small crystalline CuO particles, in close proximity of RuO2, were determined from temperature‐programmed reduction and high‐resolution transmission electron microscopy studies to be the site for propylene oxide synthesis. In addition, the presence of NaCl was confirmed to suppress the formation of CO2.