Adsorption and transformation of chloromethane over SAPO-34 catalyst were studied using deuterated CD3Cl as probe by in situ FTIR spectroscopy and compared with CH3Cl. The detection of the deuterated hydroxyls Si(OD)Al indicated the existence of the H and D exchange reaction due to the interaction of Si(OH)Al and DCI molecules produced by CD3Cl conversion. The reversible breaking of Al-O-P bonds as a result of the interaction of Al-O-P with the produced DCI molecules has been clearly evidenced by the observation of P-OD and P-OD-Al species. Increasing CD3Cl loading favors C=C generation and higher hydrocarbons formation. A possible surface species evolution and formation during CD3Cl transformation over SAPO-34 catalyst is proposed. (C) 2007 Elsevier B.V. All rights reserved.