γ-Aminobutyric acid-promoted crystallization of Beta zeolite and its application for direct amination of isobutene with ammonia

Beta zeolite is a significant catalyst used in petroleum refining and fine chemical course. We report a novel way to considerably shorten the crystallization time of Beta zeolite by adding γ-aminobutyric acid (GABA) as a ‘promoter’. The synthesis parameters are systematically investigated to unveil the promotion effect of GABA on Beta zeolite synthesis via a range of characterization skills, such as XRD, SEM, TEM, TG-DTG, NH₃-TPD, Py-IR and NMR. The results demonstrate that under hydrothermal synthesis at 140 °C (initial Si/Al₂ = 43), the addition of GABA has been shown to result in a significant reduction in crystallization time, from 130 h to 18 h, while concurrently enhancing product yield from 51.7 % to 76.1 %. The resulting Si/Al₂ ratio increases from 22.6 to 33.1, suggesting that GABA regulates aluminum incorporation kinetics during zeolite nucleation. GABA can break the hydration layer round TEA⁺ and aluminosilicate, and consequently, the formation of 5Rs structure and the nucleation process are accelerated. Meanwhile, the Hoffmann decomposition of TEAOH is inhibited as well. In comparison with the conventionally synthesized counterpart, the fast-synthesized Beta zeolite possessing high product yield and high Si/Al₂ ratio, exhibits comparable or even better catalytic performance in the direct amination of isobutene (i-C₄H₈) with ammonia (NH₃), due to its relatively high concentration of weak acid site.