Understanding Methane Aromatization on a Zn‐Modified High‐Silica Zeolite

Abstract

It takes two: A high level of conversion of 13C atoms of methane into the products of methane/propane coaromatization on zeolite Zn/H‐BEA has been demonstrated by 13C solid‐state NMR spectroscopic analysis and GC‐MS. The isotope‐labeling experiments show the mechanism consists of the methylation of aromatic compounds formed from the propane followed by ring‐expansion/contraction (see scheme).

Recent progress in methane dehydroaromatization: From laboratory curiosities to promising technology

“…(1) Regarding that the zeolites HZSM-5 and HMCM-22 containing molybdenum exhibit higher CH 4 conversion and selectivity to benzene than other types of zeolites, improvements may be made by modifying both the zeolite and the active phase. (2) Regarding the reaction mechanism, Mo-zeolite acts as a bifunctional catalyst.…”

“…Since then, many catalysts based on metal ions dispersed on various supports have been investigated. They include Zn [3,4], W [5−12], Re [13−18], Cu [19,20], Mn [21], Ni, Cr, V, and Ga [22,23]. Table 1 shows that Mo-based catalysts exhibit the highest activity in the conversion of methane to aromatics, while catalysts containing W, Re, and Co-Ga also perform well.…”

“…Most researchers prepare Mo/zeolite catalysts for MDA by an impregnation method, using (NH 4 [66], some of which migrates into zeolite channels as the temperature increases [67]. Molybdenum oxides are the direct precursors of MoC x , although there is no consensus about the precise molybdenum species active in methane dehydroaromatization.…”

“…The carburized molybdenum species derived from the ionexchanged Mo species were presumed to be the active centers for MDA reaction. Savinelli et al [90] compared the structures of Mo species present in Mo/HZSM-5 with those of MgMoO 4 and MgMo 2 O 7 using Wavelet Transform EXAFS, and they concluded that dimolybdate ions are the major Mo species present at low loadings, while monomolybdates are also present at higher loadings.…”

“…The direct conversion of methane becomes thermodynamically favorable with the assistance of oxidants, and therefore it has received much attention from researchers. One widely-pursued strategy has focused on finding an effective method for direct and selective oxidation of CH 4 to methanol or/and formaldehyde. Unfortunately, it has not yet been successful in making direct conversion competitive with indirect reforming via synthesis gas.…”