With pure acid zeolites the density of the acid sites
seems to be the main parameter determining the rate of
coke oxidation. Radical cations formed through reaction
of molecular oxygen on coke molecules adsorbed
on protonic sites were proposed as intermediates in
coke oxidation [35]. The pore structure of the zeolite
and the coke content have only a limited effect on the
rate of coke oxidation. Combustion accelerators (such
as platinum or palladium) can be introduced in low
amounts in the zeolite catalysts in order to obtain an
easier elimination of coke and to convert CO, thus
produced, into CO2. This is generally done in FCC
catalysts with the advantages of a greater activity of
the regenerated catalysts, a shorter residence time in
the regenerator and no need for a CO afterburner [29].
A lower temperature for complete removal of coke
from zeolite catalysts can also be expected with a less
detrimental effect of regeneration.