Adsorption and decomposition of CH3NO2 on a polycrystalline Pt foil using TPD, MBRS, XPS and FT-RAIRS

Abstract

The adsorption and decomposition of nitromethane (CH ₃ NO ₂ ) on a polycrystalline Pt foil has been studied using a combination of temperature-programmed desorption (TPD), molecular beam reactive scattering (MBRS), and X-ray photoelectron (XPS) and Fourier-transform-reflection/absorption IR (FT-RAIRS) spectroscopies. Adsorption at 100 K is predominantly molecular, with multilayers of physisorbed CH ₃ NO ₂ desorbing at 140 K and the first monolayer at 170 K. Adsorption at 300 K leads to complete dissociation of nitromethane to yield CO, NO, and H ₂ as major desorption products, C ₂ N ₂ , and CH ₄ , H ₂ O and CO ₂ as minor desorption products. MBRS experiments reveal that some molecular H ₂ O is also formed following adsorption at 300 K, but the surface lifetime of H ₂ O at 300 K is relatively short and spontaneous desorption occurs at this temperature. The possible involvement of a nitrite intermediate in the thermal decomposition at 300 K and also under XPS acquisition conditions at lower temperatures is discussed.