“…The homogeneous SO 3 formation, like its catalytic counterpart, clearly shows a temperature-dependent behaviour (Belo et al, 2014;Fleig et al, 2011b). Both reaction mechanisms are relatively slow (Belo et al, 2014;Walsh et al, 2006), which is the reason why in a practical firing systems, no equilibrium concentrations of SO 3 can be observed.…”