Nature of acid-base sites on molybdenum nitride catalysts: Effect of nitrogen and oxygen content

Abstract

The presence of nitrogen and oxygen sites was shown to have a direct impact on the acid-base properties of Mo2N. The gas phase reaction of 2-methyl-3-butyn-2-ol (MBOH), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) were used to characterize the Mo2N catalyst. The acid-base character of Mo2N was impacted by synthesis and surface pretreatment methods prior to analysis. The basic character of passivated Mo2N increased after the following pretreatment: degassing in helium < reduction in hydrogen < in-situ unpassivated < renitridation. The CO2 desorbed during TPD increased from 0 to 128.8 × 1016 molecules/m2 for the degassed and renitrided Mo2N, while NH3 desorption decreased from 134 to 13.2 × 1016 molecules/m2, respectively. Acid-base character was linked to N/O atomic ratio using XPS. The renitrided Mo2N surface exhibited the highest N/O atomic ratio, base site density, highest acetylene selectivity, while displaying the lowest acid site density and activity.