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

Abstract

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 Ag⁰–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.