Combustion of carbonaceous materials by Cusingle bondKsingle bondV based catalysts: II. Reaction mechanism

In Part I the chemical and microstructural nature of Cusingle bondKsingle bondV catalysts for diesel soot combustion was assessed. In this second communication the reaction mechanism of these catalysts is studied by testing their activity through either differential scanning calorimetry (DSC) or temperature-programmed oxidation (TPO), performed on catalyst-carbon mixtures. The following parameters were varied: the particle size of both the catalyst and the carbon powders, the catalyst-to-carbon weight ratio, the catalyst composition (besides the standard Cusingle bondKsingle bondV catalyst defined in Part I, binary catalysts based on a single copper or potassium vanadate + KCl were also considered). On the basis of the obtained results the presence of liquid eutectic phases (whose formation was detected via DSC runs performed in the absence of carbon) is found to be a key factor in determining the catalytic activity of all tested catalysts since it dramatically improves the catalyst-carbon contact. Once liquid phases are formed at suitable temperatures (ranging from 330 to 480°C depending on the catalyst nature), the catalytic combustion likely proceeds according to redox mechanisms.