A new process for oxidation of toxic compounds in liquids has been demonstrated. The concept is based on the same principles as catalytic wet air oxidation (CWAO), but the metal catalyst is fixed to a ceramic porous membrane in a catalytic membrane reactor of the contactor type (CMR-C). Air is flowing along the surface of the contactor, and the waste liquid is supplied from the other side of the contactor through the porous contactor wall. In this way, the gas and liquid phases are driven to contact in the porous network of the catalytic contactor separating them. Fifty percent of conversion of formic acid model solution (5 g/l) was obtained in initial reactor experiments at 150 degreesC and 10 bar pressure, but the observed oxidation rate was low: about 0.13 mmol/s per g(pt). TEM and EDS investigations of the contactor showed that 5-10 nm Pt particles were evenly distributed close to the surface of the mesoporous TiO2 top layer. After the experiments, a 10-50 nm thick aluminium-rich amorphous deposit was observed in the porous structure. The low conversion rate has been attributed to this deposit causing deactivation by encapsulation of the catalyst and plugging of the mesoporous layer of the contactor. The deposits are believed to be caused by chemical instability of alpha-Al2O3 in acidic aqueous environment at elevated temperature. alpha-Al2O3 is present in the coarse-grained membrane support. (C) 2003 Elsevier Science B.V. All rights reserved.