N-N Self-Inhibition Effect of Aromatic N-Heterocyclic Compounds on Niws Supported Γ-Al2o3 Hydrotreating Catalyst

Abstract

The nature of high-difficulty nitrogen removal in petroleum fractions was investigated from the main thought of “Catalyst property - Nitrides reaction behavior - DFT theoretical calculation”. The catalyst characterization results showed that the NiW active metals exhibited good dispersion and sulfidation degrees on the Al2O3 support surface, and the active phase had roughly one CUS per 2.9 metal atoms at the edge region. The kinetic experiments in fixed-bed reactor revealed that although THQ1 and DHQ, OEA exhibited relatively high yields in the HDN reaction of quinoline and indole respectively, they were all able to show high conversions and HDN rates when reacted as feedstocks alone. The study of product normalizations in the reaction system of the mixed feedstocks demonstrated that the difficulty of conversion of THQ1 and DHQ in quinoline HDN was mainly due to the inhibition effect of quinoline feedstock. While in the HDN of indole, the presence of the intermediate product OEA was the main factor for the low conversion of indole. This phenomenon of inhibition originating from within the molecular reaction network was proposed as the N-N self-inhibition effect for the first time. The DFT calculations suggested that the inhibition of quinoline on THQ1 could be attributed to the adsorption advantage of quinoline, while the inhibition on DHQ was mainly due to the steric hindrance effect of DHQ itself. And the inhibition effect of OEA on indole stems from the low basicity and adsorption capacity on the active sites of the inhibited molecule (indole) and the high yield due to the lowest adsorption energy of the inhibiting molecule (OEA) among the hydrogenation intermediates.

Keywords: Hydrodenitrogenation, NiWS active phase, Kinetic reaction, DFT, N-N self-inhibition effect