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Lutz W.,TU Brandenburg | Weber M.,SCW Process Technology Development GmbH | Bertram R.,Leibniz Institute For Kristallzuchtung | Kurzhals R.,Sud Chemie Zeolites GmbH | Kryukova G.,RAS Boreskov Institute of Catalysis
Zeitschrift fur Anorganische und Allgemeine Chemie | Year: 2011

Commercial silica gels of the pyrogenic and precipitated types were hydrothermally treated for 72 hours at temperatures between 90 °C and 210 °C in water of autogenous pressure. The samples were characterised by IR spectroscopy, water and nitrogen adsorption. Stability and sorption capacity run similarly. The more Q4 (Si(OSi)4) building units the framework of a silica gel contained, the lower was its sorption capacity. Sorption capacity increased with rising number of structural defects characterised by the presence of Q3 (Si(OSi)3OH) and Q2 (Si(OSi)2(OH)2) groups. Simultaneously, the hydrothermal stability of the silica material dropped off. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Lutz W.,TU Brandenburg | Bertram R.,Leibniz Institute For Kristallzuchtung | Heidemann D.,Humboldt University of Berlin | Kurzhals R.,Sud Chemie Zeolites GmbH | And 2 more authors.
Zeitschrift fur Anorganische und Allgemeine Chemie | Year: 2011

Zeolites of type USY (ultra-stable Y) were obtained by steaming of NH 4NaY modification. Samples were modified by subsequent alkaline treatment in KOH solution. USY and USY-KOH were characterised by chemical element analysis, XRD, IR, 29Al and 29Si MAS NMR spectroscopic measurements. Correct silicon to aluminium ratios (Si/Al) were determined by XRD and IR (double ring vibration wDR) data whereas values calculated according to data of 29Si MAS NMR and IR spectroscopy (asymmetrical TOT valence vibration wTOT) appeared to be too high., In the latter case, the signals of the zeolite framework were strongly superimposed by that of extra-framework silica gel (EFSi) formed during steaming. It was found that alkaline leaching induces desilication of silicon-rich area of the zeolite framework and partial dissolution of EFSi. Silicate ions of both react with likewise dissolved extra-framework aluminium (EFAl) to form X-ray amorphous aluminosilicate. Consequently, the superposition of the 29Si MAS NMR signals of the zeolite framework by silica gel was reduced for Q4(0Al) but increased for Q4 (2Al) and Q4(3Al) structure units. A reinsertion of EFAl into the zeolite framework has not been observed. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Lutz W.,TU Brandenburg | Kurzhals R.,Sud Chemie Zeolites GmbH | Kryukova G.,RAS Boreskov Institute of Catalysis | Enke D.,Martin Luther University of Halle Wittenberg | And 2 more authors.
Zeitschrift fur Anorganische und Allgemeine Chemie | Year: 2010

Steaming of NH4Y zeolite at 723 K and 873 K is accompanied by the formation of extra-framework amorphous aluminosilicate and silica gel in addition to earlier observed extra-framework aluminum species. Their occurrence is directly associated with the formation of mesopores. Bulk (intracrystalline) mesopores occur inside the crys- tallite nuclei and surface intercrystalline) mesopores are located nearby the crystallite surface. Corrosion of the zeolite framework results in a loss of crystallinity and, consequently, decreased catalytic activity of the USY catalysts synthesized. Analysis of the reasons of mesopore formation may help to reduce these disadvantages. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Lutz W.,TU Brandenburg | Heidemann D.,Humboldt University of Berlin | Kurzhals R.,Sud Chemie Zeolites GmbH | Kryukova G.,RAS Boreskov Institute of Catalysis
Zeitschrift fur Anorganische und Allgemeine Chemie | Year: 2010

Dealuminated Y zeolites (DAY) were obtained by steaming of NH 4NaY at temperatures between 450 °C and 700 °C. They were characterised by means of 27Al and 29Si MAS NMR, IR spectroscopic and XRD measurements. The Si/Al framework ratios of samples were calculated using the 29Si MAS NMR signal intensities, the wave numbers of the double-ring vibration band WDR and the asymmetrical TOT valence vibration WTOT of IR spectra as well as the XRD lattice constant a0. In contrast to actual Si/Al ratio obtained from W DR and a0, the NMR spectroscopic and WTOT values were determined to be too high because of the superposition of the signals coming from dealuminated zeolite framework and silica gel which forms in the zeolite as a result of steaming. The differently determined Si/AI. ratios characterise the siliceous extra-framework species. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Lutz W.,TU Brandenburg | Enke D.,University of Leipzig | Einicke W.-D.,University of Leipzig | Taschner D.,Sud Chemie Zeolites GmbH | Kurzhals R.,Sud Chemie Zeolites GmbH
Zeitschrift fur Anorganische und Allgemeine Chemie | Year: 2010

Zeolites of type NaY synthesised by use of seed-solution and zeolite X-seeds to initialise the crystallisation were compared. A different homogeneity of the internal framework structure related to the Si/Al ratio was expected. Thus, the formation of closed bulk mesopores should be influenced during treatment of NH4NaY modification for 7 hours at 450 °C and 600 °C, respectively, in the water steam of 1 bar. Occurrence of different mesopores was actually observed in obtained ultra-stable USY zeolites using nitrogen adsorption. Whereas USY prepared by use of seed-solution contains only open mesopores at the crystal surface, the X-seed synthesised material contains open and closed mesopores at the surface and in the nuclei of samples, respectively. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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