Surface properties and fractal approach to molybdenum nitrides and their surface activity for hydrodenitrogenation

The surface structure of the Mo nitrides was determined by N2 adsorption using a volumetric adsorption apparatus and XRD, and estimated by fractal dimensions from a gravimetric adsorption with a series of molecules of various sizes. The relationship between the fractal dimension of the Mo nitride and the catalytic activity for the hydrodenitrogenation of carbazole was determined. The BET surface area of the Mo nitrides had the maximum at the nitriding temperature of 973 K and significantly decreased at 1073 and 1173 K, while the fractal dimension had the maximum at 1073 K (2.6) with a slight decreasing at 973 and 1173 K (2.5). The 873 and 973 K-nitrided samples had the mesopores/macropore areas of 15.5 and 16.5 m2 g−1, respectively, based on the t-plot calculation and, therefore, the micropore areas of the two samples were 26.9 and 42.9% of the BET surface areas, respectively. The 973 K-nitrided sample significantly exhibited the micropores of γ-Mo2N. The fractal dimension can estimate the surface irregularity better than the N2 adsorption in terms of the adsorption of the relatively large adsorbent and was related to the activity of the Mo nitrides for the hydrogenation of carbazole during the hydrodenitrogenation.