Transformation of Methane to Propylene: A Two‐Step Reaction Route Catalyzed by Modified CeO₂ Nanocrystals and Zeolites

Abstract

The utilization of methane, which is the main constituent of natural gas, coal-bed gas, shale gas, and the vast gas hydrate resources, for the production of chemicals is one of the most important research targets in catalysis. The current technology for chemical utilization of methane involves high-temperature steam reforming to produce syngas, and the subsequent conversion of syngas to methanol, followed by methanol transformation. However, steam reforming of methane is an energy-and cost-intensive process. The direct transformation of methane to valuable chemicals would be the most desirable route, however, despite many efforts it remains difficult to achieve.[1] The development of novel catalytic routes for the transformation of methane is of high significance from both practical and fundamental points of view.Monohalogenomethanes (CH 3 Cl or CH 3 Br) could be alternative platform molecules for the conversion of CH 4 to chemicals. Olah et al. reported the catalytic monohalogenation of CH 4 by Cl 2 or Br 2 over supported superacids or noble metals, followed by hydrolysis of methyl halides to methanol and dimethyl ether.[2] Zhou et al. disclosed the conversion of CH 4 or C 2 H 6 to alkyl bromides by using Br 2 , and the subsequent conversion to oxygenates through stoichiometric reactions with metal oxides.[3] GRT, Inc. developed a technology for the transformation of CH 4 to various products, particularly liquid hydrocarbon fuels, through the reaction with Br 2 via methyl bromides, and claimed that this is a costeffective route.[4] In these processes, the generated HCl, HBr, or metal bromides must be oxidized to Cl 2 or Br 2 to complete the catalytic cycle. HBr was demonstrated to be useful for the oxidative bromination of CH 4 in the presence of O 2 instead of Br 2 over supported Ru or Rh catalysts, [5] but the high cost and limited availability of noble metals may hinder the large-scale application of this system. Zn-MCM-48-supported hydrated dibromo(dioxo)molybdenum(VI), which might generate Br 2 during reaction, catalyzed the oxidation of CH 4 to methanol and dimethyl ether, but the long-term stability of this system was not confirmed.[6] SiO 2 -supported FePO 4 was stable for the oxidative bromination of CH 4 , which provided CH 3 Br with a selectivity of approximately 50 %.[7] Only a few studies have been devoted to the oxidative chlorination of CH 4 to CH 3 Cl, although HCl is cheaper than HBr. Lercher and co-workers found that LaCl 3 was a superior catalyst for this reaction, which provided CH 3 Cl with a selectivity of around 55 % at a CH 4 conversion of 12 % at 748 K.[8]Herein, we present a novel catalytic route for the conversion of CH 4 to propylene via monohalogenomethane. Propylene is one of the most important bulk chemicals, and currently, it is mainly produced as a coproduct of ethylene through the cracking of naphtha. However, the demand for propylene is growing much faster than the demand for ethylene.[9] The development of novel routes for the production of propylene, for example, dehydrogenat...

Methane activation: the past and future

“…73 Metal oxides were also found to be promising catalysts in these reactions. 74,75 The detailed reaction results are shown in Table 2. High yields of halogenated methane and their polar bonds make them potential new platform molecules from methane chemistry.…”

“…76,77 Third, CH 3 Cl and CH 3 Br can be directly transformed into higher hydrocarbons using zeolitic materials. 72,75,78 However, although halogenated methane can be transformed into a series of useful chemicals under quite mild conditions with high yields, the severe corrosivity and toxicity of the reactants and products hinder the application of these chemical processes. In order to overcome these problems, the oxidative halogenation of methane, shown in eqn (14) and (15), was developed.…”

Onion‐Like Graphene Carbon Nanospheres as Stable Catalysts for Carbon Monoxide and Methane Chlorination

“…It should be noted that there is great interest in the conversion of methane to olefins and gasoline by mono‐halogen alkanes, as an alternative route to methanol conversion 41–45. Carbon materials offer an interesting alternative to metal oxides, which may form volatile halogenides46 and have problems with long‐term stability related to the volatility of MeCl x species.…”

Structure and phase analysis of one-pot hydrothermally synthesized FePO4-SBA-15 as an extremely stable catalyst for harsh oxy-bromination of methane

“…However, FePO 4 /SiO 2 gradually deactivated after an induction period due to coke deposition [11]. Recently, He et al [12] studied modified CeO 2 nanocrystals for the oxyhalogenations of methane with a relatively high selectivity of CH 3 X (X = Cl, Br), but long-term (>100 h) stability test was needed. It still remains a challenge to develop an efficient and stable catalyst that could stand the severe chemical ambience under the OBM reaction.…”