W. Lutz

Determination of the framework and non-framework [SiO2] and [AlO2] species of steamed and leached faujasite type zeolites: calibration of IR, NMR, and XRD data by chemical methods

Abstract Zeolite Y was thermochemically dealuminated (DAY) by steaming for 7 h at 873 K. The total concentrations of the [SiO2] and [AlO2] building units of zeolites Y, DAY and its acid-(DAYacid), alkaline-(DAYalkaline), and successively alkaline- and acid-(DAYalkaline+acid) leached forms, separately for their dissolved and solid components, were determined wet chemically. Non-framework species of the solids were quantified using the molybdate and ferron chemical methods and they were identified as aluminosilicate (DAY, DAYalkaline) and silica gels (DAYacid, DAYalkaline+acid). Chemical mass balances were used to calibrate IR, NMR and XRD data to the Si/Al ratios of the zeolite framework without superimposition of the framework with non-framework species.

Phase Transformations in Alkaline and Acid Leached Y Zeolites Dealuminated by Steaming

The steaming of zeolite Y (here at 873 K for 7 hours) leads to the formation of an amorphous aluminium aluminosilicate in addition to the dealuminated zeolite (DAY). An alkaline treatment of DAY causes the transformation of the non-framework phase into an alkali aluminosilicate and the partial desilication of the DAY framework. The alkali aluminosilicate is decomposed by a moderate acid leaching under the formation of silica gel. The 29Si MAS NMR and IR spectra of DAY and its chemically treated modifications are superimposed by the signals of the crystalline zeolite framework and the amorphous non-framework materials whereas XRD measurements only characterize the current state of the framework. Phasenumwandlungen in thermochemisch dealuminierten Y-Zeolithen bei alkalischer und saurer Behandlung Bei der thermochemischen Dealuminierung von Y-Zeolithen wird neben dem dealuminierten Zeolithgerust (DAY) ein amorphes Aluminium-Alumosilicat als Nicht-Gerust-Phase gebildet. In alkalischer Losung geht die Nicht-Gerust-Phase in ein Alkali-Alumosilicat uber, das nachfolgend in saurer Losung unter Abscheidung von Silica zersetzt werden kann. Wahrend der Zeolith von der sauren Behandlung unbeeinflusst bleibt, erzeugt die alkalische Behandlung einen gewissen Strukturabbau. Weil die 29Si MAS NMR- und IR-Spektroskopie uberlagerte Signale der Gerust- und Nicht-Gerust-Phase liefern, sind die Veranderungen der Zeolithstruktur nur mit XRD-Untersuchungen eindeutig nachweisbar.

Investigations of the mechanism of dealumination of zeolite y by steam: Tuned mesopore formation versus the Si/Al ratio

Abstract The hydrothermal treatment of zeolite NH4Y was investigated as a function of steaming time in the range between 0.5 h and 20 h at 773 K, 873 K and 973 K, respectively. The evolution of the lattice parameter (ao) and the frequency of the double ring vibration mode in the infrared absorption spectra (wDR) show saturation effects for the Si/Al ratios of about 4 and 5 at 773 K and 873 K, respectively. The average crystal size remains in this case temperature and time independent between about 90 and 110 nm. Short time steaming, i.e. up to 5 h at 973 K, also indicates a saturation of the Si/Al ratio at about 7, which is accompanied by a strong decrease in the average crystal size. The Si/Al ratios calculated using the results of 29Si MAS NMR show similar dependecies on the steaming temperature and time as the data obtained by the IR spectroscopy. However, the absolute values of the Si/Al ratios obtained by the former method are significantly larger than those obtained by the latter. This difference is attributed to the sensitivity of the MAS NMR data to the presence of non-framework species, which leads to the overestimation of the Si/Al ratios. The steaming-time dependences of the micropore volume and micropore surface area are closely related to the steaming-time dependences of the Si/Al ratios. At 773 K and 873 K there is an increasing formation of mesopores with increasing steaming time. However, the increase in the steaming temperature up to 973 K does not lead to a faster development of the mesopore surface area, which implies that a suitable fine tuning of mesopores in steam is only possible at the lower temperatures.

Formation of Alkali-Aluminosilicate Layers on Thermochemically Dealuminated Y Zeolites by Alkaline Leaching

Zeolite Y was steamed at 873 K for 7 h. This thermochemical treatment increases the Si/Al ratio of the zeolite framework from 2.4 to 3.8 under the formation of non-framework aluminium species. Successive leaching in 0.25 M KOH at 353 K for 24 h decreases the Si/Al ratio of the zeolite to 2.6 due to the formation of a X-ray amorphous potassium aluminosilicate surface layer.

13-P-15-Determination of the Si/Al ratio of faujasite-type zeolites

Publisher Summary This chapter presents the determination of the silicon/aluminium (Si/Al) ratio of faujasite-type zeolites. Zeolites Y dealuminated by Si/Al substitution using tetrachlorosilane (SiCl4) (DAY-S) and dealuminated thermochemically in steam (DAY-T) are investigated by X-ray powder diffraction, infrared spectroscopy, and wet chemical methods. The dependence of lattice constants (a) on the molar ratio x = (1+Si/A1)-1 show nonideal solid solution behavior. In a first approximation, the change in a (in nm) can be described as a = 0.187x+2.412, for 0.1

Burning out of di-n-propylamine template from MeAPO-31 materials studied by thermal analysis

Conditions for oxidative burning out of template, di-n-propylamine, from MeAPO-31 materials have been studied by means of thermal analysis. The materials were doped with very low amounts of Cu, Cd, Co, Mn, Mg, and Zn, ranging from 0.04 to 0.63 wt.%. These low contents of heteroatoms have significantly determined the observed effects. The same holds for the stability of the microporous ATO (aluminophosphate thirty-one) type structure. Grinding of the crystallites leads to more efficient exchange of atmosphere and the gaseous products and thus results in a tendency to lower calcination temperature. This observation may be useful when considering a lower thermal stability of higher doped microporous MeAPO-31 materials.