| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 74634 | Microporous and Mesoporous Materials | 2011 | 6 Pages |
A series of H-ZSM-5 samples (Si/Al = 14) were modified by impregnation with phosphoric acid and consecutive calcination. The influence of this modification was investigated by FT-IR and 27Al and 31P MAS NMR spectroscopy, temperature-programmed desorption of ammonia with coupled in situ FT-IR.Phosphoric acid treatment influences strongly the textural properties of H-ZSM-5. A decreasing optical density indicates that phosphoric acid treatment is accompanied by a reduction of the short distance order caused by the reaction between phosphoric acid and zeolite framework species during calcination. 27Al MAS NMR exhibited a clear decrease of framework aluminum forming intermediated pentacoordinated aluminum and finally non-classical octahedral coordinated aluminum. Classical extra-framework aluminum disappears with increasing phosphorus content. A frequency shift for silanol groups was observed due to the modification of the environment of initially free silanol groups. Strong evidence for this assumption is the appearance of a vibration band at 1557 cm−1 which is typical for Si–NH2 groups resulting from the reaction of NH3 with modified silanol groups.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Phosphorus impregnation results in a modification of the silanol groups. ► Evidence for modified silanol groups is the appearance of Si-NH2-groups during ammonia adsorption. ► Textural and structural properties can be restored by washing with hot water prior calcination. ► During dealumination intermediate pentacoordinated aluminum is formed. ► Dealumination results in non-classical octahedral aluminum.
