The inorganic chemistry of guest-mediated zeolite crystallization: a comparison of the use of boron and aluminum as lattice-substituting components in the presence of a single guest molecule during zeolite synthesis

A comparison of two zeolite systems was made with trivalent element substitution for the use of N-benzyl-DABCO as the structure-directing agent (SDA). Boron and aluminum were used at the same initial concentrations. One reason for the study was awareness that a higher number of new zeolite structures are being found when researching borosilicate reaction mixtures. The borosilicate system studied produces SSZ-42 (IFR) while the aluminosilicate system yields beta zeolite (BEA). We focused on comparisons of the kinetics and found that the borosilicate system crystallized more rapidly, kept most of the boron in solution before incorporation into the crystal, and added mass even at the point where all solids were crystalline. In contrast, the aluminosilicate gel remained almost entirely in the solid phase through a long induction period and the mass of solids was relatively constant. The kinetics were followed by using a variety of techniques including powder XRD, pH changes, elemental analyses, partitioning in centrifugation and effects of dilution. The reaction systems were followed via NMR techniques. The transformation to crystalline could be seen by NMR for both the aluminosilicate and borosilicate reactions. Proton NMR changes were followed for both sets of solids. In addition, a profile for removal of boron from solution and towards the growing SSZ-42 was quantified by NMR. An unusual tetrahedral doublet for B-11 was found in the SSZ-42 product. No such doublet was observed for tetrahedral aluminum in the case of beta zeolite formation. (C) 2003 Elsevier Science Inc. All rights reserved.