A noble-metal-free, nickel(II)-doped MgO/Al2O3 catalyst for highly selective photothermal coupling of methane to ethane
Tianyang ShenZelin WangSimin XuXiaoliang SunGuihao LiuSha BaiJiaxin LiZiheng SongLirong ZhengYu‐Fei Song
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Abstract:
Selective coupling of methane into high-value-added chemicals under mild conditions is a grand challenge since activation of the inert C–H bonds and inhibition of methane from over-oxidation are simultaneously required. Here, we report the fabrication of a noble-metal-free, Ni2+-doped MgO/Al2O3 photocatalyst where the Ni2+ ions are isomorphically doped into an MgO cell. By involving trace amounts of water, photothermal conversion of methane to ethane can be accomplished in a flow reactor with a high ethane production rate of 454.30 μmol g−1 h−1 and a superior selectivity of 97.8%. Detailed characterizations reveal that the electron-enriched oxygen species are the active sites in methane activation. The involved H2O repairs the oxygen defects generated during the reaction process and induces the reaction into the coupling conductive pathway, resulting in an increased catalytic stability and C2H6 selectivity.Keywords:
Noble metal
Aromatization
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Methane is the predominant component of natural gas, from which many kinds of chemicals can be produced. Over the past two decades, extensive efforts have been made in indirect and direct conversion of methane into valuable products. One of the attractive applications of methane is the oxidative coupling of methane (OCM) to C2 hydrocarbons, especially ethylene.
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Introduction Methane is the main component of natural gas and its utilization amounts to ca. 1.7 × 109 tons of oil equivalent per year [1]. Since the present reserve of methane is located in remote places, its transportation is a major problem. Methane coupling to form C2+ hydrocarbons is, therefore, of a primary importance because before transportation methane should be converted into hydrocarbons with higher boiling points, such as ethane, propane, etc. The catalytic conversion of methane can be carried out in several ways which have excellently been reviewed in Refs. 1 and 2. Basically, three routes exist: (i) the indirect route in which methane is first converted into syngas in presence of water (steam reforming), CO2 (carbon dioxide reforming), or oxygen (partial oxidation) and the resultant syngas can be utilized in the traditional way; (ii) direct coupling in the presence of oxygen (oxidative coupling of methane, OCM) or hydrogen (two-step polymerization); and (iii) direct conversion in the presence of oxygen to oxygenates (CH3OH, HCOH), in the presence of Cl2, HCI to methane chlorides, in the presence of ammonia to HCN, etc.
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Propane
Partial oxidation
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The partial oxidation of methane to ethane over a model Li/MgO catalyst has been studied using combined surface science techniques/elevated pressure kinetic measurements. The results indicate that [Li+O−] centers are not likely directly involved in the methane activation step. Rather, addition of lithium promotes the production of F centers which are considered to be responsible for this key step in the methane coupling reaction.
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Atmospheric temperature range
Alkane
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Atmospheric temperature range
Alkane
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