Oxidative coupling of methane over strontium‐doped neodymium oxide: Parametric evaluations

Abstract

Since its discovery in 1982, oxidative coupling of methane (OCM) has been considered one of the most promising approaches for the on-purpose synthesis of ethylene.The development of more selective catalysts is essential to improve process economics. In this work, undoped neodymium oxide as well as neodymium oxide doped with high (20%) and low (2.5%) levels of strontium were tested in a high-throughput fashion covering a wide range of operating conditions. The catalysts were shown to be able to achieve greater than 18% C 2 + yield. Space velocity was shown to play a significant role in C 2 + selectivity. For a methane to oxygen feed ratio of 3.5, selectivity increased with increasing space velocity, reaching a maximum of 62% at a methane conversion of 30% at an optimal space velocity of $250,000 ml/h/g. The difference in activity between the three samples was linked to the contribution of different oxygen centers.

Divide to Conquer: On the Use of Distributed Feed Strategies in Oxidative Coupling of Methane

“…Another approach is to combine Li + with alkali earth metals such as Mg, Ca, and Sr, , as the presence of basic sites benefits the reaction. Other examples include combining Li + with lanthanides. ,, Another type of catalytic system that shows a promising performance is a trimetallic system based on Mn–Na–W/SiO 2 . ,, However, this catalyst system shows a high ignition temperature as will be highlighted in the following paragraphs. , Perovskite-type and fluorite-type catalysts have also been shown to be active for OCM. , Catalysts based on lanthanides, such as La 2 O 3 , Nd 2 O 3 , Gd 2 O 3 , and Sm 2 O 3 , generally show satisfactory performance with excellent thermal stability and appropriate ignition-extinction properties. − …”

High‐Performance Mn2O3‐Na2WO4/SiO2‐TiO2 Catalyst for the Oxidative Coupling of Methane: TiO2‐Modulated MnTiO3 Formation for Enhanced Low‐Temperature Performance

“…[24,25] For this purpose, various simple, complex, and mixed oxides of alkaline, alkalineearth, and rare-earth elements have been investigated, with some of these showing high activity. [26][27][28][29][30][31] One such typical early catalyst is Li/MgO, with the Li + O À species on the surface able to generate CH 3 • from CH 4 efficiently; however, these are also subject to rapid deactivation owing to the loss of Li. [32] Another representative class of catalysts is the lanthanide oxides, [33,34] whose surface oxygen vacancies are responsible for generating the reactive oxygen, but with relatively lower C 2 À C 3 selectivity.…”

“…Thus, it is essential for the ideal catalyst to have selective surface oxygen ion radicals with suitable mobility, [21–23] enabling them to function as active sites for methyl radical generation while avoiding deep oxidation on the surface [24,25] . For this purpose, various simple, complex, and mixed oxides of alkaline, alkaline‐earth, and rare‐earth elements have been investigated, with some of these showing high activity [26–31] . One such typical early catalyst is Li/MgO, with the Li + O − species on the surface able to generate CH 3 ⋅ from CH 4 efficiently; however, these are also subject to rapid deactivation owing to the loss of Li [32] .…”

Fundamentals of Unanticipated Efficiency of Gd2O3‐based Catalysts in Oxidative Coupling of Methane

“…[2] Catalysts based on oxides of lanthanides are also promising for OCM. [3][4][5][6] La 2 O 3 , [7] Sm 2 O 3 [8] or Nd 2 O 3 [9] can activate CH 4 below 700 °C but have low selectivity to the desired products.…”