The effect of the type of fuel (diesel or biodiesel) on the characteristics of the soot produced, affecting the non-catalytic and catalytic combustion, has been studied. For this comparison, two copper-based catalysts (5% Cu/Al(2)O(3) and Sr(0.8)K(0.2)Ti(0.9)Cu(0.1)O(3)) have been selected. The results of soot characterization by DRIFTS, XRD, Raman spectroscopy and TEM do not reveal significant differences between both soot samples, which present the expected features for this type of carbon materials. It has been observed that the use of biodiesel fuel has a double positive effect because, in addition to the expected reduction in the soot production rate, the reactivity of biodiesel soot is higher than that observed for diesel soot. The higher reactivity of biodiesel soot is mainly attributed to both, metals with catalytic activity (mainly Mg, Cu, K and Cr) which come from the raw materials and from the synthesis process and, to the higher oxygen content of the biodiesel soot. For biodiesel soot, the soot production rate and the uncatalyzed combustion rate at 515 degrees C are equal, and the copper catalysts tested lower this temperature to around 450 degrees C. For conventional diesel soot, much higher temperatures are required to balance the production and combustion rates. (C) 2011 Elsevier B.V. All rights reserved.