In the search for new environmentally friendly processes Sn-Beta has been developed as a heterogeneous catalyst. Its reactivity is different from similar materials, i.e. titanium containing molecular sieves. The origin of its singularity is described by means of density functional theory (DFT), in situ IR spectroscopy of deuterated acetonitrile and catalytic studies. All results point to a bi-functional active site that involves a Lewis acid tin centre and an adjacent oxygen atom capable to accept hydrogen bonding from water or hydrogen peroxide. The catalyst may be employed for Baeyer-Villiger oxidations taking part in InUlti-step synthesis of' industrial interest, achieving more than 10,000 turnovers per tin centre. (c) 2006 Elsevier B.V. All rights reserved.