Cu-ZSM-5 Zeolites for the Formation of Methanol from Methane and Oxygen: Probing the Active Sites and Spectator Species

Abstract

A series of Cu-ZSM-5 zeolites was prepared by varying nature of the charge compensating cation, copper precursor, copper loading, and pH. The materials were tested for the oxidation of methane to methanol using oxygen. A linear relationship between the amount of methanol produced over Cu-ZSM-5 zeolites from methane and oxygen and a UV-Vis-NIR DRS charge transfer band at 22,700 cm -1 is reported irrespective of the synthesis route used. The absolute intensity of the 22,700 cm -1 band is always low, indicating a low number of active sites in the samples. In all studied Cu-ZSM-5 zeolites at least two copper species were present: (a) Cu-O clusters dispersed on the outer surface of ZSM-5 and (b) highly dispersed copper-oxo species inside the channels, a minority fraction in the sample. By relating catalytic activity to FT-IR data of adsorbed pivalonitrile, visualizing Cu-O particles on the outer surface of the zeolite, and subsequently adsorbed NO, indicative of the Cu-O species inside the zeolite channel, it was concluded that Cu-O species on the outer surface are not involved in the oxidation reaction, while copper inside the channels are responsible for the selective conversion of methane to methanol.Keywords Methanol Á Methane activation Á Cu-ZSM-5 Á l-Oxo dicopper cluster Á UV-Vis spectroscopy Á FT-IR with pivalonitrile and NO

Recent Advances in Catalytic/Biocatalytic Conversion of Greenhouse Methane and Carbon Dioxide to Methanol and Other Oxygenates

“…at remote locations) would be the direct methane partial oxidation to methanol. Furthermore, it should be noted that methanol, being a precursor to ethylene and propylene, is a primary raw material for the chemical industry (Olah et al, 2009;Beznis et al, 2010aBeznis et al, , 2010b. It is produced in large quantities as an intermediate for the production of a wide range of chemicals including formaldehyde, methyl tert-butyl ether and acetic acid, most of which are subsequently used to produce many important industrial products such as paints, resins, adhesives, antifreezes and plastics (Olah et al, 2009).…”

“…These workers confirmed that the oxygen activated Cu core is defined as bent mono-(µ-oxo)dicupric cluster (Cu II -O-Cu II ) (Woertink et al, 2009). Subsequent investigations by Beznis et al (Beznis et al, 2010a) have now established a linear relationship between the intensity of the UV-Vis-NIR DRS charge transfer (CT) band at 22,700 cm -1 and the amount of methanol produced irrespective of the synthesis route used.…”

“…At least two Cu species were identified to be present in all Cu-ZSM-5 zeolites, namely Cu-O clusters dispersed on the outer surface of ZSM-5 and highly dispersed copper-oxo species inside the channels which are only a minority fraction in the sample (Beznis et al, 2010a). Catalytic experiments and FTIR measurements of adsorbed pivalonitrile revealed that the Cu-O species on the outer surface are inactive for methanol production while the copper species inside the channels are responsible for the selective oxidation of methane to methanol (Beznis et al, 2010a).…”

An Attempt to Selectively Oxidize Methane over Supported Gold Catalysts

“…Direct methane valorisation, surpassing the costly syngas production, still attracts major attention in both academia and industry [8][9][10][11][12][13][14][15][16][17][18][19]. Although proof-of-principle studies have been successful, it has not led to any commercial application yet, mainly due to the low yields and high costs.…”

Aluminium Phosphate Supported Copper Phosphate Catalytic Converter to Reduce Nitrous Oxides and Particulate Matter from Engine Emission

“…Cu-ZSM-5 Zeolite has been proved to be one of the catalysts to detoxify gas emissions 2 . Such catalysts however have not been commercialized due to hectic ion exchange of ZSM-5 with Cu, which involves a huge volume of water 3 .…”