Abstract
Methane is an abundant resource and its direct conversion into value-added chemicals has been an attractive subject for its efficient utilization. This method can be more efficient than the present energy-intensive indirect conversion of methane via syngas, a mixture of CO and H2. Among the various approaches for direct methane conversion, the selective oxidation of methane into methane oxygenates (e.g., methanol and formaldehyde) is particularly promising because it can proceed at low temperatures. Nevertheless, due to low product yields this method is challenging. Compared with the liquid-phase partial oxidation of methane, which frequently demands for strong oxidizing agents in protic solvents, gas-phase selective methane oxidation has some merits, such as the possibility of using oxygen as an oxidant and the ease of scale-up owing to the use of heterogeneous catalysts. Herein, we summarize recent advances in the gas-phase partial oxidation of methane into methane oxygenates, focusing mainly on its conversion into formaldehyde and methanol.
Highlights
Petroleum, coal, and natural gas are important fossil fuels and feedstocks for various products, including plastics, clothing, and pharmaceuticals [1]
MoO3 nanoparticles mainly existed on the surface of KIT-6 in the form of Mo-O-Mo bonds, which could cause the over-oxidation of methane owing to the polymeric MoOx species, facilitating the decomposition of formaldehyde to generate CO
The peculiar structure of iron, tetrahedral Fe3+ isolated by phosphate groups, in the FePO4 nanoclusters contributes to enhancing the selectivity of formaldehyde, and the one-pass yield of formaldehyde over the P-FeOx -stoichiometric clusters [(V2 O5 )n (SiO2) (P/Fe = 0.5) catalyst up to 2.4% at 898 K, which is consistent with studies showing that the support of FePO4 onto SiO2 boosted the conversion of methane [124,125]
Summary
Coal, and natural gas are important fossil fuels and feedstocks for various products, including plastics, clothing, and pharmaceuticals [1]. Various approaches have been reported for the direct conversion of methane (Figure 1) They can be classified as liquid- and gas-phase reactions. The development of highly active catalysts capable of selectively converting methane into the desired product under mild conditions is necessary for commercializing processes of its direct conversion. We focus on the recent advances and forthcoming challenges in the gas-phase partial oxidation of methane into methane oxygenates in the past decades. They are classified into two categories based on the product (e.g., formaldehyde and methanol): selective oxidation of methane into formaldehyde and selective oxidation of methane into methanol
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