A novel ammonium triflate-functionalized silica (NH4+OTf- @SiO2, ATFS) has been prepared and characterized by simple operation from commercially available and relatively cheap starting materials. Various types of aldehydes as well as cyclic ketones were selectively converted to the corresponding 1,3-dioxanes in the presence of ethyl orthoformate, 1,3-propanediol and a catalytic amount of ATFS catalyst via an in situ acetal-exchange process. The catalyst can be recovered and reused for at least six reaction cycles without considerable loss of its reactivity. (C) 2007 Elsevier B.V. All rights reserved.