Continuous selective oxidation of methane to methanol over Cu- and Fe-modified ZSM-5 catalysts in a flow reactor

Abstract

Please cite this article in press as: J. Xu, et al., Continuous selective oxidation of methane to methanol over Cu-and Fe-modified ZSM-5 catalysts in a flow reactor, Catal. Today (2015), http://dx. a b s t r a c tThe selective oxidation of methane to methanol is a key challenge in catalysis. Iron and copper modified ZSM-5 catalysts are shown to be effective for this reaction using H 2 O 2 as the oxidant under continuous flow operation. Co-impregnation of ZSM-5 with Fe and Cu by chemical vapour impregnation yielded catalysts that showed high selectivity to methanol (>92% selectivity, 0.5% conversion), as the only product in the liquid phase. The catalysts investigated did not deactivate during continuous reaction, and methanol selectivity remained high. The effect of reaction pressure, temperature, hydrogen peroxide concentration and catalyst mass were investigated. An increase in any of these led to increased methane conversion, with high methanol selectivity (≥73%) maintained throughout. Catalysts were characterised using DR-FTIR, DR-UV-Vis and 27 Al MAS-NMR spectroscopy.

Die direkte katalytische Oxidation von Methan zu Methanol – eine kritische Beurteilung

“…[161] Eisenhaltige Zeolithe wie Eisensodalith zeigten 70 % Selektivitätf ürM ethanol bei 5.7 %M ethanumsatz bei 689 K. [162] Siliciumdioxid-fixiertes Eisenoxid mit annähernd dem gleichen Eisengehalt wie der Eisensodalith war bei einem Methanumsatz von etwa 4% weit weniger selektiv für Methanol. [167] Tabelle 4z eigt die Ergebnisse von Studien mit dem Batch-Reaktor und dem Durchflussreaktor. Diese Resultate hielten Forscher jedoch nicht davon ab,a uch nicht-zeolithische Materialien zu untersuchen.…”

“…Batch-Reaktor [112] Durchflussreaktor [167] ZSM-5 KatalysatorZ SM-5 0. [184] Ein typischer Prozess bestand aus einer Sauerstoff-unterstützten Aktivierung, gefolgt von einer Reaktion mit Methan unter hohem Druck und anschließenden Online-Extraktion mit Wasser,w obei alle Schritte bei der gleichen Te mperatur durchgeführt wurden.…”

“…Eine aktuelle Studie zeigt die Mçglichkeit auf,M ethan anaerob mit Wasser als Oxidationsmittel in Methanol zu überführen. [46,48,112,167,119,[211][212][213] DMTM-Prozesses infolge der zugrunde liegenden Thermodynamik sind die schlechten methanbezogenen Ausbeuten; dies kann auch nicht durch die Wahl von geeigneten Homogen-oder Heterogenkatalysatoren überwunden werden. [214] Allerdings vermeiden es die meisten Forschungsarbeiten, den Methanumsatz zu bestimmen.…”

Selective Oxidation of Methane with Hydrogen Peroxide Towards Formic Acid in a Micro Fixed‐Bed Reactor

“…In contrast to the harsh reaction conditions employed in many methane oxidation processes [16], methanotrophic bacteria are able to convert methane highly selective into methanol under ambient conditions using methane monooxygenase enzymes (MMOs) [17,18]. The reaction was switched to continuous operation with the same catalyst [21]. Recently, the selective catalytic oxidation of methane was carried out by Hutchings et al using H 2 O 2 as oxidant at 70°C and 3 bar in a batch reactor [20].…”

“…Inspired by the fact that the active sites of these enzymes contain diiron or dicopper centers [19], many researchers tried to develop catalysts containing Cu and/ or Fe and performed the oxidation reaction at a low temperature (< 250°C) [3, 4, 6, 10, 20 -22]. However, turnover frequency dropped by nearly two orders of magnitude compared to the batch reactor which let the authors assume that severe mass transport limitations occur during the reaction [21]. With a physical mixture of Cu-silicalite-1 and Fe-silicalite-1 as catalyst, denoted in the following as Cu-Fe-silicalite-1, a methane conversion of 10.1 % with a methanol selectivity of 93 % was obtained.…”