Microcalorimetric and IR spectroscopic studies of CO adsorption on molybdenum nitride catalysts

Abstract

The adsorption of CO on both nitrided and reduced passivated Mo2N catalysts in either alumina supported or unsupported forms was studied by adsorption microcalorimetry and infrared (IR) spectroscopy. The CO is adsorbed on nitrided Mo2N catalysts on three different surface sites: 4-fold vacancies, Moδ+ (0 < δ < 2) and N sites, with differential heats of CO adsorption decreasing in the same order. The presence of the alumina-support affects the energetic distribution of the adsorption sites on the nitrided Mo2N, i.e. weakens the CO adsorption strength on the different sites and changes the fraction of sites adsorbing CO in a specific form, revealing that the alumina supported Mo2N phase shows lower electron density than pure Mo2N. On reduced passivated Mo2N catalysts the CO was found to adsorb mainly on Mo4+ sites, although some slightly different surface Moδ+ (0 < δ < 2) sites are also detected. The nature, density and distribution of surface sites of reduced passivated Mo2N/γ-Al2O3 were similar to those on reduced MoO3/γ-Al2O3.