Recent Progress in Direct Conversion of Methane to Methanol Over Copper-Exchanged Zeolites

Abstract

The conversion of methane into an easily transportable liquid fuel or chemicals has become a highly sought-after goal spurred by the increasing availability of cheap and abundant natural gas. While utilization of methane for the production of syngas and its subsequent conversion via an indirect route is typical, it is cost-intensive, and alternative direct conversion routes have been investigated actively. One of the most promising directions among these is the low-temperature partial oxidation of methane to methanol over a metal-loaded zeolite, which mimics facile enzymatic chemistry of methane oxidation. Thus mono-, bi-, and trinuclear oxide compounds of iron and copper stabilized on ZSM-5 or mordenite, which are structurally analogous to those found in methane monooxygenases, have demonstrated promising catalytic performances. The two major problems of theses metal-loaded zeolites are low yield to methanol and batch-like non-catalytic reaction systems challenging to extend to an industrial scale. In this mini-review, attention was given to the direct methane oxidation to methanol over copper-loaded zeolite systems. A brief introduction on the catalytic methane direct oxidation routes and current status of the applied metal-containing zeolites including the ones with copper ions are given. Next, by analyzing the extensive experimental and theoretical data available, the consensus among the researchers to achieve the target of high methanol yield is discussed in terms of zeolite topology, active species, and reaction parameters. Finally, the recent efforts on continuous methanol production from the direct methane oxidation aiming for an industrial process are summarized.

Selective Oxidation of Methane over Fe-Zeolites by In Situ Generated H2O2

“…The partial oxidation of methane has been mainly investigated either in the gas phase at relatively high temperatures or in the liquid phase at low temperatures. The gas-phase partial oxidation of methane has been reported over metal ion-exchanged zeolites [4][5][6] using O 2 [7,8], N 2 O [9,10], and H 2 O [11,12]. The liquid-phase partial oxidation of methane has been demonstrated over several catalyst systems including Pt [13][14][15][16], Pd [17,18], Rh [19,20], Os [21], Hg [22], Cu [23], V [24], Fe [25,26], Eu [27], and Co [28,29] using different oxidants such as SO 3 [17,23], K 2 S 2 O 8 [30], and H 2 O 2 [24][25][26].…”

High H2O2 Utilization Promotes Selective Oxidation of Methane to Methanol at Low Temperature

“…To address this problem, increasing effort has been devoted to the direct conversion of methane, a more economical and environmentally friendly route to utilize methane (Tang et al, 2014;Schwach et al, 2017). Among them, the direct oxidation of methane to methanol has been one of the major challenges for many decades (Palkovits et al, 2009;Grundner et al, 2015;Shan et al, 2017;Sushkevich et al, 2017;Cui et al, 2018;Park et al, 2019;Jin et al, 2020).…”

Bioinspired chemistry at MOF secondary building units

“…Overall, these studies complement additional investigations of copper-mediated and catalyzed methane oxidation chemistry within other porous materials. [48][49][50][51] Unlike pMMO, where the nuclearity of the active site is still debated, the hydroxylase subunit of soluble methane monooxygenase (sMMO) is generally agreed to feature a dimeric Fe active site. 40 The compatibility of MIL-53(Al, Fe) with H 2 O 2 underscores two important distinctions between biomimetic MOFs and the enzymes they emulate.…”