CO hydrogenation on supported Pd catalysts was investigated using steady-state isotopic transient kinetic analysis (SSITKA) in order to explore the differences in catalytic behavior which have been previously reported by others to result from using different supports and Pd precursors. In this study, two different precursors [PdCl2 and Pd(NO3)(2)] and three supports [SiO2, Al2O3, and SiO2-Al2O3] Were investigated. The dispersion of the Pd particles on the prepared catalysts, as evaluated by CO chemisorption, was not affected by either the Pd precursor or the support used. In addition, for a given support the catalysts exhibited almost the same selectivities during CO hydrogenation toward methane, methanol [MeOH], and dimethyl ether [DME]. However, catalysts prepared using PdCl2 showed higher overall activities than those prepared using Pd(NO3)(2) for a given support. The nature of the support altered significantly the activity and the selectivity of the Pd. The order of activities at steady-state for a given precursor was Al2O3 > SiO2-Al2O3 > SiO2. The activity of the Pd/SiO2-Al2O3 was lower than expected probably due to the relatively high level of S (500 ppm) present in the support as an impurity. It was found that Pd/SiO2 produced essentially only MeOH. The use of acidic supports [Al2O3 and SiO2-Al2O3] resulted in the formation of DME due to the secondary reaction of MeOH on acid sites of the supports. DME production was found to be limited by the amount of MeOH formed. Pd on the acidic supports also produced significant amounts of methane. SSITKA results showed [after considering readsorption effects] that the Pd precursor used, or more specifically its anion [Cl- and NO3-], had a slight effect on the intrinsic activity of the sites producing methane (1/tau(methane)) [Cl- > NO3-] and a significant effect on the surface coverage of the intermediates leading to methane (N-methane) [Cl- > NO3-]. On the other hand, the precursor used had little or no effect on the intrinsic activity of the sites producing MeOH (1/tau(MeOH)) or the surface coverage of MeOH intermediates (N-MeOH) The nature of the support altered only slightly the intrinsic activities of the sites producing methane and MeOH. However, the number of surface intermediates leading to methane and MeOH were significantly affected by the support used and were in the order Al2O3 > SiO2-Al2O3 and Al2O3 > SiO2-Al2O3 > SiO2, respectively. It is, thus, the effect of the support on the concentration of active sites/intermediates on Pd that determines the impact of the support on the reaction rate.