Evidence by in situ FTIR spectroscopy and isotopic effect of new assignments for isocyanate species vibrations on Ag/Al2O3

Ethyl isocyanate has been introduced on prereduced and preoxidised Ag(2%)/Al2O3 catalysts and on Ag(2%)/SiO2 for comparison at 573 K. Its decomposition on preoxidised silica catalyst gives IR bands at 2294 and 2204 cm(-1) whereas on prereduced catalyst vibrations at 2294 and 2243 cm(-1) are observed. The 2294 cm(-1) feature is attributed to isocyanates on SiO2 while the 2204 and 2243 cm(-1) bands are assigned to Ag-I-NCO and Ag-0-NCO vibrations respectively. When alumina replaces silica, we show using isotopic substitutions that the bands observed at 2229 and 2256 cm(-1) are characteristic of -NCO groups coordinated on two different sites of alumina.