A series of supported Ni catalysts (similar to 2 wt% Ni) were tested for the dry reforming of propane to synthesis gas reaction at 600 degrees C, C3H8:CO2:H-2:N-2 (%) = 10:30:10:50, 1 atm and GHSV = 13333 Nml/(hg(cat)). The support systems studied range from acidic (SiO2) to amphoteric [Al2O3, Mg(Al)O] to basic oxides [MgO, CaO], with BET areas of 100, 100 (131 and 173), 117, and 16 m(2)/g, respectively. Ni particle size and reduction state was investigated by magnetic measurements, performed before and during catalytic testing. Support basicity was measured by CO2 TPD. It was observed that the intrinsic activity of the catalysts (TOF) depends strongly on the Ni particle size (D) in the size range of 4.5-11 nm. As such, a TOF versus D plot showed an exponential inverse relationship, much more pronounced than previously reported for the methane dry reforming reaction. In turn, a volcano-type correlation was found between intrinsic catalyst activity and support basicity. As a result, the best catalytic performance, including a low selectivity to methane, was observed on the most dispersed Ni particles supported on Mg(Al)O. Key mechanistic features were derived from these observations. (C) 2007 Elsevier Inc. All rights reserved.