Characterization of extra-framework species of steamed and acid washed faujasite by MQMAS NMR and IR measurements

Hydrogenation of tetralin on silica–alumina-supported Pt catalysts I. Physicochemical characterization of the catalytic materials

“…A new resonance at approximately 30 ppm was observed. In the literature, peaks at this position have been assigned to strongly distorted tetrahedral [14,22,23] or pentavalent aluminum species [24][25][26][27]. In the present case, the MQMAS spectrum contained a contribution at δ F 2 = 43 ppm, which allows the unambiguous assignment of this resonance to 5-fold coordinated aluminum.…”

“…Whereas the observation of pentavalent Al has been discussed in various publications [22][23][24][25][26][27], to date most studies have focused on proving or disproving its existence. Probably the most detailed discussion has been given by De Witte et al [24], suggesting that penta-coordinated aluminum is present as a highly disordered interface connecting an alumina domain with a silica or silica-alumina domain.…”

Bimetallic Pt–Pd/silica–alumina hydrotreating catalysts – Part I: Physicochemical characterization

“…Due to the high alumina content (55 wt.%) in ASA(55/45), the peak at 57 is probably composed of the signal corresponding to tetrahedral Al in pure alumina (67 ppm) and the signal of diluted Al in the neighborhood of a central Al atom (51 ppm). The peak at 29 ppm was assigned to pentavalent aluminum species [28][29][30][31] or strongly distorted tetrahedral [32,33]. The aluminum species in octahedral environment were observed at 4 ppm.…”

Influence of steam-calcination and acid leaching treatment on the VGO hydrocracking performance of faujasite zeolite

“…Nevertheless, a significant amount of EFAl species (penta-and hexacoordinated Al) resisted acid leaching. According to literature, acid leaching removes preferentially amorphous material and Al linked to the framework [37,38]. The changes in the NMR spectra therefore indicate that a separate extraframework silica-alumina phase is removed by acid leaching.…”

“…The signals at 60 and 0 ppm are due to Al nuclei in tetrahedral and octahedral coordination environment, respectively [33][34][35]. The signal at 30 ppm is assigned to distorted tetrahedral or five-coordinated Al species [35][36][37]. Increasing the temperature of hydrothermal treatment from 500 to 600°C increases the 30 ppm band (Fig.…”