JCATAL 294-2012-128

Ir/Pt-HZSM5 for n-pentane isomerization: Effect of iridium loading on the
properties and catalytic activity

The effects of iridium loading on the properties of Ir/Pt-HZSM5 and n-pentane isomerization were studied.
XRD, IR, and NMR results indicated that increasing iridium loading did not much change the properties
of catalysts, but eliminated the perturbed silanol groups at 3700 and 3520 cm1, whereas IR and ESR
spectroscopy confirmed that increasing iridium loading continuously decreased the permanent Lewis and
Brønsted acid sites and inhibited the formation of protonic acid sites induced by hydrogen. At low iridium
loading (0–0.3 wt%), cracking process proceed through dimerization-cracking step, whereas high iridium
loading (0.5–2.0 wt%) reduces the contribution of dimerization-cracking step and promotes the contribution
of hydrogenolysis. The excessive amount of iridium loading, with the presence of a low amount of
active protonic acid sites and hydrogen gas, accelerated the hydrogenolysis process. The activity of
Ir/Pt-HZSM5 was marginal in the absence of hydrogen, showing the dependence of activity on promotive
effect of hydrogen.