Lewis acid metal ion-exchanged MAPO-36 molecular sieve: Characterisation and catalytic activity

Magnesium aluminophosphate-36 (MAPO-36) molecular sieve was synthesised hydrothermally and subjected to wet ion-exchange with Fe³⁺, Zn²⁺, La³⁺ or Ce³⁺. They were characterised by using XRD, SEM, temperature programmed desorption (TPD) of ammonia and thermogravimetric analysis (TGA). The XRD patterns of ion-exchanged MAPO-36 exhibit similar features to that of MAPO-36, which revealed no structural degradation during ion-exchange. TPD (ammonia) showed selective ion-exchange of strong acid sites for Fe³⁺, La³⁺ and Ce³⁺ but not for Zn²⁺. Based on the results of TGA the actual species involved in the ion-exchange is suggested to be M(OH)₂⁺, which upon calcination converted to MO⁺ where M is Fe³⁺, La³⁺ or Ce³⁺. tert-Butylation of phenol was carried out in the vapour phase as a probe reaction to examine the catalytic activity of MAPO-36 and ion-exchanged MAPO-36 molecular sieves. The ion-exchanged catalysts were found to be more active than the parent MAPO-36 and also showed higher selectivity to 4-tert-butylphenol.