Liquid-Phase Selective Oxidation of Methane to Methane Oxygenates

Abstract

Methane is an abundant and relatively clean fossil fuel resource; therefore, its utilization as a chemical feedstock has a major impact on the chemical industry. However, its inert nature makes direct conversion into value-added products difficult under mild conditions. Compared to the gas-phase selective oxidation of methane, there have been several recent advances in the liquid-phase conversion of methane. This review categorizes the reports on the liquid-phase selective oxidation of methane according to the solvent and oxidant used. The advantages and disadvantages of each approach are discussed. High yields of methyl bisulfate as a methanol precursor can be achieved using SO3 in sulfuric acid; however, more attention should be paid to the separation process and overall economic analysis. However, the aqueous-phase selective oxidation of methane with in situ generated H2O2 is quite promising from an environmental point of view, provided that an economical reducing agent can be used. Based on the current state-of-the-art on this topic, directions for future research are proposed.

Recent Advances in the Use of Controlled Nanocatalysts in Methane Conversion Reactions

“…However, methane conversion is a huge topic that has been widely investigated for over a century, influencing numerous books which have deep approached each specific topic. We recommend some recent review articles to delve deeper into each catalytic reaction, such as the nonoxidative conversion of methane [52][53][54][55][56][57][58], methane oxidation [4,53,[59][60][61][62], methane-to-methanol [49,53,59,[63][64][65][66], the oxidative coupling of methane [47,50,53,[67][68][69][70], methane steam reforming [25,53,60,[71][72][73][74][75], the dry reforming of methane [4,24,25,28,32,53,60,73,74,[76][77][78][79]<...…”

“…Figure 4A illustrates the overall reaction mechanism for the methane-to-methanol cycle. Initially, the metal center undergoes oxidation via N 2 O to create a metal oxide anionic unit (Equation ( 1)) [49,59]. Following this, the methane reacts with the metal oxide anion (MO − ) to generate either HOMCH 3 − or MOH − , interacting with a methyl radical, MOH − .…”

“…The oxidative coupling of methane (OCM) process presents an opportunity to generate ethene (C 2 H 4 ), which holds significant value across various industrial sectors [50,101]. It serves as a vital monomer for polyethylene production and as a primary component in fuels such as gasoline (C 5 -C 10 ) or diesel (C 10 -C 20 ) [47,50,59,68]. However, the oxidative coupling of the methane process involves a complex series of surface and gas-phase reactions that are not fully understood and can be summarized as a single global reaction, as shown in Equation (4) [47,50].…”

Simple Fabrication of Hydrophobicity-Controlled Fe-ZSM-5 for Aqueous-Phase Partial Oxidation of Methane with Hydrogen Peroxide

“…The aqueous-phase selective oxidation of hydrocarbons has attracted considerable attention as an environmentally friendly route to produce value-added products. In particular, the selective oxidation of methane in water with hydrogen peroxide has been intensively studied over the last decade because methane is a relatively clean and abundant resource [6][7][8]. Inspired by enzymes (e.g., soluble and particulate methane monooxygenases) that can oxidize methane into methanol with dioxygen in the presence of reducing agents under ambient conditions [9], various biomimetic heterogeneous catalysts, such as Fe-and Cu-zeolites, have been examined for the aqueous-phase oxidation of methane with H 2 O 2 [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] or in situ-generated H 2 O 2 from H 2 and O 2 [28][29][30][31][32][33].…”