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. 2014 Aug 18;4(3):712-725.
doi: 10.3390/nano4030712.

High-Temperature Synthesis of Ordered Mesoporous Aluminosilicates from ZSM-5 Nanoseeds with Improved Acidic Properties

Xuan Hoan Vu  1 , Reinhard Eckelt  2 , Udo Armbruster  3 , Andreas Martin  4
Affiliations

High-Temperature Synthesis of Ordered Mesoporous Aluminosilicates from ZSM-5 Nanoseeds with Improved Acidic Properties

Xuan Hoan Vu et al. Nanomaterials (Basel). .

Abstract

Ordered mesoporous SBA-15 analogs with different Si/Al ratios were successfully prepared in a two-step process from self-assembly of ZSM-5 nanoseeds at high temperature in mildly acidic media (473 K, pH 3.5). The obtained products were characterized as SAXS, XRD, N₂ sorption, FTIR, TEM, NH₃-TPD, AAS and ICP. The results show that the initial Si/Al molar ratio of ZSM-5 precursors strongly affects the final materials' properties. A highly condensed, well-ordered mesoporous SBA-15 analog with improved hydrothermal stability and acidic properties can be prepared from low aluminum containing ZSM-5 precursors (Si/Al ≥ 20). Reducing the initial Si/Al molar ratio to 10, however, leads to the formation of a disordered mesoporous SBA-15 type material accompanied by degraded textural and acidic properties. The gas phase cracking of cumene, carried out as probe reaction to evaluate Brønsted acidity, reveals that an increased density of Brønsted acid sites has been achieved over the SBA-15 analogs compared to conventional Al-SBA-15 due to the preservation of zeolite building units in the mesopore walls of the SBA-15 analogs.

Keywords: SBA-15 analogs; acidity; cumene cracking; hydrothermal stability; zeolite nanoseeds.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Small angle X-ray Scattering (SAXS); (b) X-ray diffraction (XRD) patterns; and (c) Fourier transform infrared (FTIR) spectra of SAZ materials, Al-SBA-15 and H-ZSM-5.
Figure 2
Figure 2
(a) N2 sorption isotherms; and (b) corresponding pore size distributions of SAZ and Al-SBA-15 materials.
Figure 3
Figure 3
Temperature-programmed desorption of ammonia (NH3-TPD) profiles of SAZ solids compared to reference samples Al-SBA-15 and H-ZSM-5.
Figure 4
Figure 4
Effect of steaming on the structural and textural properties of SAZ-30: (a) SAXS patterns, (b) N2 sorption isotherms.
Figure 5
Figure 5
TEM images of (a) fresh and (b) steamed SAZ-30 viewed along [110] direction.
Figure 6
Figure 6
(a) Cumene conversion over SAZ materials compared to Al-SBA-15 and H-ZSM-5 as a function of time-on-stream; (b) cumene conversion over SAZ materials after 1 h on-stream and their total acidity plotted against the initial Si/Al ratio.
See this image and copyright information in PMC

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