A Fourier-transform infrared spectral study of H-ZSM-5 surface sites and reactivity sequences in methanol conversion

One-Step Synthesis of Dimethyl Ether from Syngas with Fe-Modified Zeolite ZSM-5 as Dehydration Catalyst

“…The sharp band at 3702 cm À1 , observed in the sample HAl-30, can be attributed to the t(OH) band of free OH groups of water species adsorbed on the Brønsted acid sites as reported by Wakabayashi et al [19]. In addition, the broad band at 3565 cm À1 may be assigned to the vibrations of hydrogen-bonded silanols or hydroxyl groups on Brønsted acid sites although any unquestionable explanation has not been brought forward [19,20]. This broad band disappeared on the spectra of HFeAl-S1 and shifted to 3589 cm À1 on the spectra of HFeAl-S2.…”

Direct synthesis of DME from syngas on hybrid CuZnAl/ZSM-5 catalysts: New insights into the role of zeolite acidity

“…Since, as discussed before, the main effect of the acid treatment was the selective removal of EFAL species with the concomitant decrease in the amount of EFAL-related strong Lewis acid sites, it may be readily inferred that these sites could also be active for methanol dehydration at the relatively low STD temperature of 260ºC. In this respect, previous studies did also point towards an active participation of zeolitic Lewis acid sites associated to non-skeletal Al species in the formation of DME from methanol in the context of methanol-to-hydrocarbons reactions [24,34]. A further consequence of the correlation depicted in Fig.…”

“…By contrast, Xia et al suggested that extralattice Al species, which are typically associated to the development of Lewistype acidity in zeolites, do promote the formation of hydrocarbons during the STD reaction [21]. In preceding studies, however, evidences were presented that Lewis acid sites in HZSM-5 are at the origin of catalytic activity in the conversion of methanol to DME [24]. By studying the effect of water addition on the methanol dehydration activity over different solid acids, Xu et al concluded that both Brønsted and Lewis acid sites in HZSM-5 are active for DME formation, though obviously the former ones generally present in greater amounts in zeolites do contribute the most to the overall dehydration activity [19].…”

Research on the Acidity of the Double-function Catalyst for DME Synthesis from Syngas

“…Typically, a mixed doublefunction catalyst was used in STD process, which composed of a methanol synthesis catalyst (Cu/Zn/Al, Cu/Zn/Cr, Cu/Zn/Zr, etc) and a methanol dehydration catalyst (zeolite [6,7] or c-alumina [8,9]). The acidity of the methanol dehydration catalyst is very important to influence the rate of reaction (2) [10][11][12]. Kim et al [13] investigated NaZSM-5 and HZSM-5 with three Si/Al ratios (30,50,100) and concluded that the acid strength of ZSM-5 increased with a decrease in the Si/Al ratios and the methanol dehydration rate was dependent on the acid strength of the ZSM-5, the difference of acid strength would change the optimal ratio of the two components, because the relative rate of intrinsic methanol synthesis and methanol dehydration was changed.…”