Acetonitrile on silica-magnesia mixed oxides. Temperature-programmed desorption and infrared study

The adsorption of acetonitrile on silica, silica-magnesia mixed oxides and magnesia was studied by means of temperature-programmed desorption (t.p.d.) and infrared spectroscopy. With t.p.d. three types of desorption behaviour were distinguished. On silica, only one comparatively narrow peak was detected (type 1), the mixed oxides containing up to 50 mol % magnesia showed one broad peak with pronounced high-temperature tailing (type 2) and the mixed oxides containing 60-90 mol % magnesia showed up to 4 peaks (type 3). The i.r. results gave evidence for at least 3 adsorption structures: acetonitrile bound to surface hydroxyl groups, acetonitrile bound to cations and a surface carboxamide. Assignments of desorption peaks to the different adsorption structures of acetonitrile are suggested.