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.

MAPO-36 was ion-exchanged with Fe3+, Zn2+, La3+ and Ce3+ ions. Vapour phase tert-butylation of phenol was carried over ion-exchanged and parent catalysts. The major product was found to be p-tert-butylphenol. The main active site was suggested to be MO+ (M = Fe3+, La3+ and Ce3+).Figure optionsDownload as PowerPoint slide