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

• Published in: Applied catalysis. A, General Vol. 605; p. 117777
• Main Authors: McGee, Randolph C.V., Thompson, Levi T.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05.09.2020; Elsevier Science SA
• Subjects: Acetylene; Acid-base; Acids; Ammonia; Catalysts; Degassing; Density; Desorption; MBOH reaction; Methylbutynol; Molybdenum nitride; Nitrogen; Oxygen content; Photoelectrons; Pretreatment; Selectivity; Surface pretreatments; TPD; Vapor phases; X ray photoelectron spectroscopy; XPS; Molybdenum nitride; TPD; MBOH reaction; XPS; Methylbutynol; Acid-base
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2020.117777

[Display omitted] •Acid-base properties of Mo2N correlate to presence of nitrogen and oxygen sites.•Pretreatment conditions impact the density and nature of acid-base sites on Mo2N.•Basic activity of passivated Mo2N increases with H2 reduction and renitridation.•Base site density and basic character of Mo2N is suppressed by passivation.•Acid character of Mo2N decreased proportionately with increasing basic properties. 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.