The catalytic behavior of Pd (2 wt.%) catalysts supported on CeO2 and promoted with La2O3 was investigated for methanol decomposition. The addition of lanthana significantly improved the catalytic activity for methanol decomposition. Over LaPd/Ce-1.00 catalyst, a 100% conversion of methanol can be achieved at around 275 degreesC, which is about 40 degreesC lower than the temperature needed for Pd/CeO2. TPR results showed that the presence of lanthana shifted the reduction temperature of CeO2 to lower values, while it hindered the reduction of PdO due to an accelerated diffusion of oxygen ions in the ceria-lanthana interface. Pddelta+-like species were formed on the catalyst surface due to the SMSI effect. Moreover, an increase of Pddelta+/Pd-0 ratio accompanied by the shift of the conversion profile to the lower temperature with increase of lanthana loading indicated that the low-temperature decomposition of methanol was very sensitive to the valence of palladium. The reasons for the formation of such Pddelta+-like species caused by lanthana addition are discussed in detail based on XRD, BET and XPS results. A simplified hypothesis about side reactions. which might occur during methanol decomposition to form by-products in this work, is also proposed. (C) 2004 Elsevier B.V. All rights reserved.