Investigation of a liquid-mediated defect-healing treatment in zeolite beta

We report the application of a liquid-mediated defect-healing treatment based on tetraethylammonium (TEA+) hydroxide and ammonium fluoride, and variants thereof, to the H+ form of zeolite beta. Through comparison between H-beta of high (730) and lower (28.6) SiO2: Al2O3 ratios, and characterisation of the treated samples before and after calcination, insights into the interaction of TEA+ and F− with H-beta under hydrothermal conditions were gained. In general, the treatments resulted in the loss of crystallinity and the generation of relatively large mesopores in the more siliceous samples, but improvements in long-range order and the development of relatively small mesopores in the less siliceous samples. The healing of silanol defects was observed for most of the treatments. A partial mechanism is proposed to explain the action of defect-healing treatments based on pore-occupying cations and F−; fluorine may be essential in some cases because it balances the charge of the organic cations, preventing the “trapping” of silanol groups as charge-balancing silanolate groups which resist healing. [Display omitted] •Application of a liquid mediated defect-healing treatment (TEAOH + NH4F) and variants thereof to commercial zeolite Beta of high and lower SiO2/Al2O3 ratio (SAR).•Different TEA+: anion pairs can be identified in the materials and their concentration and type vary with the treatment and the parent zeolite SAR.•Defect healing as judged by a reduction in silanol defect density was shown to increase with decreasing density of TEA + balanced silanolate groups.