27Al and 29Si solid-state NMR studies of dealuminated mordenite

Abstract

27AI and 29Si MAS and CP MAS NMR have been used to monitor structural modifications of mordenite subjected to hydrothermal dealumination, acid leaching and calcination. Six, four-and possibly five-coordinate extraframework aluminium species are formed upon expulsion of aluminium from the framework. 'H-29Si CP MAS NMR monitors the creation of Si-OH defect sites. Calcination of dealuminated mordenite greatly reduces the number of such defects, indicating that they are substantially 'healed' by silicon atoms from other parts of the crystal, and also via dehydration of hydroxy groups to form bridging oxygen sites. The occupancies of crystallographically inequivalent Si(0AI) sites calculated from 29Si MAS NMR spectra of dealuminated mordenite show that aluminium atoms occupy some of the T2 tetrahedral sites in the parent material.

Infrared Study of Acetophenone Adsorption on Mordenite and Dealuminated Mordenite

“…2) were at 55 ppm due to tetrahedral framework aluminum and at 0 ppm due to octahedral extraframework aluminum (14). In accordance with results of Barras et al (14) the concentrations of both framework and extraframework aluminum were considerably reduced by acid leaching.…”

“…Dealumination by acid leaching (14) considerably enhanced the latter at the expense of the former (Fig. 1).…”

“…The 29 Si NMR spectrum of mordenite contained two peaks at Ϫ106 and Ϫ112 ppm which may be ascribed to Si(1Al) and Si(OA1) species, respectively (11,13,14). Dealumination by acid leaching (14) considerably enhanced the latter at the expense of the former (Fig.…”

Synthesis of nano-SSZ-13 and its application in the reaction of methanol to olefins

“…Information about the structural defects and different Si coordination is given in the 29 Si NMR spectra (Fig.S4). The samples show resonances at -112, -106 corresponding to Si(4Si), Si(3Si 1Al), and other signal at -102 that has been assigned to Si-OH(defects) 47 . The presence of mesoporosity in nano-SSZ-13 is reflected in a decrease in the -106 signal while the signal at -102 ppm due to structural defects increases comparing to the standard SSZ-13(see in Table 2).…”

Coking on micrometer- and nanometer-sized mordenite during dimethyl ether carbonylation to methyl acetate

“…Figure 3 shows the NMR spectra of the two mordenites. The 29 Si MAS NMR spectra were deconvoluted into two Gaussian peaks at δ = -113 and -107, which were assigned to Si(0Al) and Si(1A1) units, respectively [32]. The Si/Al ratios were estimated to be 18 for HMOR-C and 22 for HMOR-N.…”