Zeolitc 5 A molecular sieve was doped with iron ions Fe3+ by ion exchange and the catalytic activity of lie obtained solids for the formaldehyde oxidation was investigated. The catalysts are able to oxidize formaldehyde (if a very low concentration at moderate temperatures, The light-off temperatures were about 70-100 C and the temperatures for the complete oxidation were about 100 190 C,The oxidation reaction product contains HCOOH, and its formation is associated with the silanol groups on the catalyst structure, The pH value of the suspension during the ion exchange and the temperatures at which the catalysts were calcined has profound influence on the amount of the silanols. in the catalysts. Ferric species are also active sites on the zeolite, which are more active at higher temperature than silanols and responsible for producing carbon dioxide. (c) 2005 Elsevier B.V. All rights reserved.