Codoping Mg-Mn Based Oxygen Carrier with Lithium and Tungsten for Enhanced C₂ Yield in a Chemical Looping Oxidative Coupling of Methane System

Abstract

Oxidative coupling of methane (OCM) is a compelling strategy for the direct conversion of methane to C2+ hydrocarbons in order to produce fuels and value-added chemicals. Nevertheless, it remains challenging to achieve the high C2+ yield that is desirable in industrial synthesis. Here, a lithium, tungsten-codoped Mg-Mn based oxygen carrier, (Li,W)-Mg6MnO8, is prepared for the chemical looping oxidative coupling of methane (CLOCM) technology. The designed codoped oxygen carrier exhibits an improved OCM performance with a C2+ yield of 28.6% at 850 °C, which is 80% higher than the combined yields of the single Li- and W-doped oxygen carriers, and 330% higher than that of the undoped Mg6MnO8 oxygen carrier. The enhanced activity has also been demonstrated over 50 redox cycles in the CLOCM system. In combination with solid characterization, density functional theory calculations reveal that, as compared to the single-metal-doped Mg6MnO8, the Li and W codopants work synergistically which not only enhances CH3 dimerization but also inhibits CO2 formation. This effect was attributed to the suppressed formation of unselective oxygen vacancies, which in turn leads to the C2+ yield enhancement. As a result, (Li,W)-Mg6MnO8 was found to be one of the best performing oxygen carriers as compared to other oxygen carriers reported in the literature. These findings provide new insights into the understanding of the codoping effect on the activity of a Mg-Mn based oxygen carrier for C2+ production and can open new avenues to design an environmentally and economically feasible CLOCM system.

Mixed oxides as multi-functional reaction media for chemical looping catalysis

“…Addition of dopants and/or modulating the metal-oxygen bonding strength on the surface have been shown be effective to enhance the selectivity towards light olefins for a number of redox oxides and reactions. 106,150 This section focuses on presenting a more ''generalized strategy'' for surface modification of mixed oxide in the context of oxidative dehydrogenation of hydrocarbons: instead of doping or impregnation of small amount of heteroatoms on the surface, we reasoned that complete or near-complete coverage of a non-selective oxide surface with a catalytically active layer would effectively suppress side reactions. This approach was first validated in our group for methane partial oxidation reactions, 122,151,152 and was recently extended to a series of ODH reactions using various core and shell materials, as illustrated in Fig.…”

“…52–94 Furthermore, marrying the chemical looping strategy with oxidative catalysis offers a unique opportunity to intensify the production of a few important commodity chemicals with substantially decreased energy consumption and CO 2 emissions. 95–136 Given that separation processes consume ∼60% of the total energy usage in chemical and petroleum industries and heterogeneous catalysts are responsible for >80% of all chemical products worldwide, chemical looping catalysis (CLCa) in this article, has the potential to facilitate process intensification throughout the chemical manufacturing sector by combining catalytic reactions with separations. 120,137–142 The abovementioned chemical looping process types are summarized in Table 1.…”

Over 90% C2+ Selectivity in Kalium-Doped Manganese Perovskite Oxygen Carriers for Chemical Looping Oxidative Coupling of Methane with Plasma Assistance

“…Chemical looping oxidative coupling of methane (CLOCM) is a process that uses metal oxides to selectively convert methane into higher-value hydrocarbons. , CLOCM is based on the use of a solid oxygen carrier that can transfer oxygen between a fuel (methane) and an oxidant (air) . Solid oxygen carriers provide lattice oxygen for the reaction and avoid the problem of gaseous oxygen being present in the reaction. , The reaction process is shown in Figure . The oxygen carriers are first reduced by the fuel in a fuel reactor, producing metal oxides and the desired product .…”

Co and Mo Co-doped Fe2O3 for Selective Ethylene Production via Chemical Looping Oxidative Dehydrogenation

“…Chemical looping, which splits a one-step redox reaction process into two sub-steps via a solid intermediate, has been recognized as a promising way for energy conversion and upgradation. , In the past decades, the chemical looping concept has been widely investigated under the contexts of chemical looping combustion, , reforming, − CO 2 splitting, , H 2 production, , air separation, , ammonia synthesis, oxidative coupling, epoxidation, etc. Similarly, the chemical looping concept can be applied to the ethane ODH process, known as chemical looping ODH (CL-ODH) .…”