Direct Methylation of Benzene with Methane Catalyzed by Co/MFI Zeolite

Abstract

Cobalt‐loaded MFI zeolite showed distinct activity for direct methylation of benzene with methane into toluene. High activity was found at around 0.6 of Co/Al molar ratio. Incorporation of carbon from methane into the methyl group of toluene was confirmed with isotope tracer experiments and mass spectroscopy. Ammonia infrared‐mass spectroscopy temperature‐programmed desorption, transmission electron microscopy, X‐ray absorption near edge spectroscopy and extended X‐ray absorption fine structure indicated that Lewis acidic divalent (+II of oxidation state) Co species mono‐atomically dispersed on the ion exchange site of MFI zeolite was the active species.

Reactivity of Methane and Benzene over Metal/MFI Zeolite Analyzed with Temperature‐Programmed Reaction Technique

“…The signal at m/z =91 is ascribed to the fragment C 7 H 7 + formed in the mass spectrometer mainly from toluene as already detailed in our previous paper . The formation of toluene and its reaction rate have been confirmed using a gas chromatograph (GC) . The signal at m / z =91 (C 7 H 7 + ) directly shows the presence of tropylium ion, which can be formed from xylene and other methyl derivatives of benzenes.…”

“…On Co‐0.6 (Figure (b)), the ion current at m/z =78, the parent signal of benzene, showed decrease of intensity at >800 K. The formation of toluene ( m/z =91) was apparent at >673 K. The parent peak with m/z =92 assigned to C 7 H 8 + was also observed, and here the largest signal at m/z =91 is shown. The signal at m/z =91 is ascribed to the fragment C 7 H 7 + formed in the mass spectrometer mainly from toluene as already detailed in our previous paper . The formation of toluene and its reaction rate have been confirmed using a gas chromatograph (GC) .…”

“…(1)]. We have recently found that Co supported by MFI type zeolite, hereafter Co/MFI, had distinct catalytic activity for the methylation of benzene with methane at K …”

“…The catalytic activity for (1) was found to be negligible on various kinds of elements loaded on MFI zeolite, while only Co showed high activity . It should be noteworthy that little activities were found on Ni, which generally shows chemical nature to Co, and noble metals, which are generally active for hydrogenation/dehydrogenation type reactions (Ni is also active), although the reaction (1) is one kind of dehydrogenation.…”

“…It is therefore considered that the high catalytic performance requires high selectivity and long catalyst life [durability against the coverage of active site with carbonaceous formed by (2)], as well as the high ability for activation of methane, which has been known to be a chemically stable molecule. The activity, selectivity and life should be complicatedly dependent on the reaction temperature, although our previous study was carried out at a limited temperature, 773 K . Therefore, the analysis was here carried out over a wide range of reaction temperature.…”