Hydrothermal synthesis of MWW-type stannosilicate and its post-structural transformation to MCM-56 analogue

A series of novel stannosilicates with the MWW topology, Sn-MWW, was hydrothermally synthesized in alkali medium using boric acid as a crystallization-supporting agent. The Sn-MWW lamellar precursors with a high crystallinity were obtained from the synthetic gels even at Si/Sn ratio of 60. UV-visible and ¹¹⁹Sn MAS NMR characterizations verified that the Sn species were incorporated in the framework, occupying mainly the tetrahedral sites. A mild acid treatment was conducted on the precursors to induce a structural transformation to tin-containing materials structurally analogous to MCM-56. Sn-MCM-56 thus post-synthesized comprised partially delaminated MWW sheets, and possessed larger external surface as well as more open reaction space. Sn-MCM-56 analogue alleviated effectively the steric restriction and diffusion limitation to bulky molecules that the microporous zeolite catalysts usually encountered. It appeared to be more efficient than Sn-MWW in the Baeyer-Villiger oxidation of 2-adamantanone with H ₂O ₂. Moreover, Sn-MCM-56 turned to be more active than Sn-Beta when tert-butyl hydroperoxide was employed as an oxidant.