Plastic degradation in presence of a reforming catalyst is
explained differently. The reforming catalysts are said to be
bifunctional, in view of the two kinds of active sites playing
different roles. The metallic sites catalyze hydrogenation and
dehydrogenation reactions, while the acidic sites on the support
catalyze isomerization reactions. A proper combination of these
two functions can promote a variety of reforming reactions such as
isomerization where straight-chain paraffins are isomerized to
branched-chain molecules, dehydrocyclization where straightchain
paraffins are converted to cycloparaffins, and dehydrogenation
in which naphthenes are dehydrogenated to aromatics; the
octane numbers of gasoline-range hydrocarbons are improved
without changing their carbon numbers. The most commonly used
reforming catalyst is Pt/SiO2-Al2O3 with about 0.5 wt% Pt only. The
following overall reaction scheme for n-pentane isomerization
illustrates the reforming reaction