Single-Step Delamination of a MWW Borosilicate Layered Zeolite Precursor under Mild Conditions without Surfactant and Sonication

Abstract

Layered borosilicate zeolite precursor ERB-1P (Si/B = 11) is delaminated via isomorphous substitution of Al for B using a simple aqueous Al(NO_3)_3 treatment. Characterization by PXRD shows loss of long-range order, and TEM demonstrates transformation of rectilinear layers in the precursor to single and curved layers in the delaminated material. N_2 physisorption and base titration confirm the expected decrease of micropore volume and increase in external surface area for delaminated materials relative to their calcined 3D zeolite counterpart, whereas FTIR and multinuclear NMR spectroscopies demonstrate synthesis of Brønsted acid sites upon delamination. Comparative synthetic studies demonstrate that this new delamination method requires (i) a borosilicate layered zeolite precursor, in which boron atoms can be isomorphously substituted by aluminum, (ii) neutral amine pore fillers instead of rigid and large quaternary amine SDAs, and (iii) careful temperature control, with the preferred temperature window being around 135 °C for ERB-1P delamination. Acylation of 2-methoxynaphthalene was used as a model reaction to investigate the catalytic benefits of delamination. A partially dealuminated delaminated material displays a 2.3-fold enhancement in its initial rate of catalysis relative to the 3D calcined material, which is nearly equal to its 2.5-fold measured increase in external surface area. This simple, surfactant- and sonication-free, mild delamination method is expected to find broad implementation for the synthesis of delaminated zeolite catalysts.

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