Active site distribution analysis of hydrodenitrogenation catalyst using Fredholm integral equation Original Research Article

A non-parametric analysis using the Fredholm integral equation of the first kind exploits the distribution of the catalytic active sites during the hydrodenitrogenation (HDN) of carbazole on nitrided and reduced 12.5% Mo/Al2O3 catalysts. The approach was combined with the reactivity data and the surface property measurements. The equation describes two kinds of active sites (Site 1 with a small rate coefficient and Site 2 with a high rate coefficient) on the catalysts. The 1173 K-nitrided catalyst had a high activity and large Site 1 population along with a very low population and the highest value of Site 2, while the treatment at 773 K with NH3 or H2 produced less Site 1 than Site 2. The 973 K-nitrided catalyst had the highest k2·x2 value of the four catalysts, showing that it was superior to the other catalysts for Site 2. Based on the reaction product selectivity, Site 1 of the nitrided catalyst was responsible for the hydrogenation of carbazole, while Site 2 was responsible for the C–N hydrogenolysis of perhydrocarbazole. The turnover frequency (carbazole disappearance rate divided by the CO adsorption) was correlated to the k1x1 value, but not to the k2x2 value, showing that Site 1 facilitated the HDN reaction controlled by the carbazole hydrogenation. The two sites and mechanism for the carbazole HDN are discussed.