On the Sn(II) and Sn(IV) incorporation into the AFI-structured AlPO4-based framework: the first significantly acidic SnAPO-5

Abstract

Both Sn(II) and Sn(IV) chlorides were tested as sources for tin incorporation into an AlPO4-5 framework. N-Methyldicyclohexylamine (MCHA) was chosen as a structure-directing agent, taking advantage of its reported high specificity towards AFI-structured AlPO4-based materials. Pure AFI materials were successfully produced, irrespective of the Sn source in a wide range of gel compositions. Whereas the different characterization techniques of the Sn(IV)APO-5 materials certify the unfavourable (or at least low-quality) incorporation of Sn, as expected from previous studies, there is no doubt about the right Sn(II) incorporation into the AlPO4 framework. The amount of Sn(II) able to be properly incorporated into the AlPO4-5 structure is significantly higher than that described in the literature for Sn(IV)APO-5 materials as well as for the Sn(IV)APO-5 materials prepared in this work. For the first time, AlPO4-based microporous catalysts were tested in the Friedel–Crafts acylation of anisole. Supporting the characterization results, Sn(IV)APO-5 and especially Sn(II)APO-5 were active catalysts in such reactions which require acid centers to take place. Since all tested AlPO4-based materials (pure AlPO4-5, SAPO-5 and SnAPO-5) possess an AFI structure and similar surfaces areas, the extent of the acylation of anisole was taken as indirect proof of acidic strength. The conversion given by pure AlPO4-5 was negligible in comparison with Sn(II)APO-5, which overcomes the activity of the SAPO-5 and even that of a standard zeolite H-beta.