N-N self-inhibition effect of aromatic N-heterocyclic compounds on NiWS supported -Al2O3 hydrotreating catalyst

The reason for high-difficulty nitrogen removal of aromatic N-heterocyclic compounds in petroleum fractions was investigated from the main thought of "NiWS property - Reaction behavior - DFT calculation". The properties of the used catalyst were characterized by a series of techniques with the aim of providing the basis for model construction in the DFT calculations. The kinetic experiments in fixed-bed reactor revealed that although 1,2,3,4tetrahydroquinoline (THQ1) and decahydroquinoline (DHQ), o-ethylaniline (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 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 can be mainly attributed to its greater nucleophilicity and stronger adsorption ability on the active sites compared with IND.