The distribution of framework aluminium in Beta zeolite plays an important role in determining its acidic properties and catalytic behavior. Organic structure-directing agents (OSDAs) offer a means of regulating aluminium incorporation during zeolite crystallization. In this work, tetraethylammonium hydroxide (TEAOH) and dimethyldiethylammonium hydroxide (DMDEAOH) were used as dual OSDAs to investigate the effect of their relative proportions on aluminium distribution in Beta zeolite. A series of samples was hydrothermally synthesized at 160 °C for 120 h by varying the TEAOH/DMDEAOH ratio while maintaining a constant total OSDA content and nominal gel Si/Al ratio. The organic species occluded in the as-made samples and the local aluminium environments were examined using ¹³C and ²⁷Al nuclear magnetic resonance (NMR) spectroscopy, respectively. The ¹³C NMR spectra show increasingly prominent signals characteristic of DMDEAOH with increasing DMDEAOH content in the synthesis gel, supporting its incorporation into the as-made zeolites. Deconvolution of the ²⁷Al NMR spectra reveals a systematic change in the relative contributions assigned to the T1-T2 and T3-T9 aluminium sites. Specifically, the proportion attributed to T1-T2 sites increases from approximately 52% to 62% as the DMDEAOH content increases, accompanied by a corresponding decrease in the T3-T9 contribution. These results indicate that the relative proportions of the two OSDAs influence the preferential incorporation of aluminium into different framework environments. This study demonstrates a practical strategy for tuning aluminium distribution in Beta zeolite through dual-OSDA synthesis and provides a basis for further tailoring its acid-site distribution.

 

Beta zeolite; dual organic structure-directing agents; aluminium distribution;