Adsorption and surface reactions of acetonitrile on Al2O3-supported noble metal catalysts

The adsorption and surface reactions of acetonitrile on Al2O3-supported noble metal (Pt, Rh, Au) catalysts at 300–673 K were studied by FT-IR and mass spectrometry. It was found that acetonitrile adsorbs molecularly in different forms on these surfaces: besides the H-bridge-bonded and physisorbed forms monodentate CH3CN (on strong and weak Lewis acid sites) and η2(C, N)CH3CN-adsorbed species were formed at 300 K. CH3CN, on the other hand, dissociates producing CN(a) species even at this temperature. Among the gas phase products formed during the heat treatments of adsorbed CH3CN layer methylamine (CH3NH2) was detected, the amount of which depended on the nature of the surfaces. The appearance of gas phase NH3 can be connected with the rupture of CN bond in CN(a). In the presence of oxygen the formation of isocyanate (NCO) surface species was observed on Pt/Al2O3, Rh/Al2O3 and (in a very small extent) on Al2O3 at and above 473 K; no NCO formation was found on Au/Al2O3.