A Homogeneous‐Heterogeneous Kinetic Study of Oxidative Coupling of Methane (OCM) on La₂O₃/CeO₂ Catalyst

Abstract

A La 2 O 3 /CeO 2 catalyst was synthesized and achieved 19 % C 2 + yield with 65 % C 2 + selectivity at 650 °C. The doping of CeO 2 not only enhanced catalytic performance, but also improved catalyst stability in the presence CO 2 and H 2 O. This study investigated the kinetics on La 2 O 3 /CeO 2 over a wide range of operating conditions. Planar laser-induced fluorescence was implemented to directly observe the presence of formaldehyde, as the first time reported in OCM. A packed bed reactor model was constructed based on the dimensions of experimental setup and catalyst characterization. Rather than using a tuned gas phase model, the experimentally validated mechanism NUIGMech1.1 was implemented. The proposed homogeneousheterogeneous OCM mechanism kinetic model was validated against experimental data under isothermal conditions, and the results show good agreement with measured species. The rate of production (ROP) was performed to identify the important reactions and prove the necessity of surface reactions for the OCM process.

Consequence of products from oxidative coupling of methane in a non-oxidative high temperature environment

“…However, because the resulting hydrocarbons can be easily activated compared to CH 4 due to their weaker C-H bond strength, their overoxidation to CO x is a challenge, which results in a loss of selectivity and the resulting yield at high CH 4 conversion. [8][9][10] Various catalysts, such as Li/MgO-, La 2 O 3 -, and Sm 2 O 3 -based catalysts, were investigated to improve the process's selectivity and reaction rate, [11][12][13][14][15] One of the most studied catalysts is alkali metal-based tungstate, such as Na 2 WO 4 , due to its high C 2 selectivity. The unique feature of the tungstate catalysts is that the addition of H 2 O in the reactant stream improves the CH 4 conversion rate and the selectivity to C 2 products.…”

Improved Homogeneous–Heterogeneous Kinetic Mechanism Using a Langmuir–Hinshelwood-Based Microkinetic Model for High-Pressure Oxidative Coupling of Methane

“…Later, Karakaya et al utilized the same reaction network to explore the kinetic behavior under non-isothermal conditions, which captured the significant temperature rise within the catalyst bed associated with the high exothermicity of OCM under low pressure. , Recently, various reported gas-phase mechanisms were compared to better describe the gas-phase experiments in the presence of CH 4 and O 2 to utilize in the OCM microkinetic study . The findings in the gas-phase mechanism were introduced in the microkinetic study on the La 2 O 3 –CeO 2 catalyst with a reported surface mechanism under low pressure (total 101 kPa) …”

“…The La 2 O 3 –CeO 2 catalyst was also found to be coke-tolerant, which is beneficial for industrial application. The doping of CeO 2 into La 2 O 3 can improve the catalytic performance as well as the stability in the presence of CO 2 and H 2 O …”

“…26 The findings in the gas-phase mechanism were introduced in the microkinetic study on the La 2 O 3 −CeO 2 catalyst with a reported surface mechanism under low pressure (total 101 kPa). 27 Most of the previously proposed surface elementary reactions are based on equivalent gas-phase reactions, with the hydrocarbon reacting directly from the gas phase onto an adsorbed oxygen species (e.g., CH 4 + O* ⇌ CH 3 •+ OH*). Yet, chemisorptions of hydrocarbons (CH 4 , C 2 H 4 , C 2 H 6 , etc.)…”

“…The doping of CeO 2 into La 2 O 3 can improve the catalytic performance as well as the stability in the presence of CO 2 and H 2 O. 27 Industrial processes are typically beneficial at elevated pressures to increase productivity and reduce capital costs, 38 so understanding OCM at higher pressures is an important goal of kinetic modeling. This study aims to improve the kinetic mechanism to describe catalytic behavior under various conditions using the La 2 O 3 −CeO 2 catalyst, which was obtained from the industry, specifically by introducing explicit adsorption terms for all relevant hydrocarbons.…”