Synthesis of Sn–silicalite from hydrothermal conversion of SiO2–SnO2 xerogels

For the first time, the synthesis of Sn–zeolites starting from SiO2–SnO2 xerogels is described. The influence of several synthesis parameters in the physico–chemical properties of the xerogels and the zeolites subsequently generated has been investigated. Two different tin sources were assayed in the synthesis of xerogels (anhydrous SnCl4 and SnCl4 · 5H2O) as well as two gelation agents (NH3 and TPAOH). Though both bases led SiO2–SnO2 xerogels mainly showing tetrahedrally coordinated tin centres, regardless the tin source, only TPAOH derived materials were easily transformed into MFI-type zeolites showing tin incorporation. On the other hand, NH3 gelified xerogels were difficult to crystallize, being this fact attributed to the retention of NH3 species in the xerogels because of the tin Lewis acidity, avoiding its inclusion in the zeolite crystalline framework. Studies on the crystallization time and temperature allowed to optimize the transformation of TPAOH gelified SiO2–SnO2 xerogels into tin-containing MFI zeolites showing isomorphically incorporated tin centres. The so-obtained materials were compared with conventionally synthesized SnS-1 zeolite showing better quality in terms of tin incorporation.