SINOPEC Dalian Research Institute of Petroleum and Petrochemicals Co., Ltd., Dalian 116041, China.
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China.
Int J Mol Sci. 2023 Feb 3;24(3):3044. doi: 10.3390/ijms24033044.
Hydrodenitrogenation (HDN) experiments and density functional theory (DFT) calculations were combined herein to study the substituent effects of the nitrogen heterocycle on the HDN behaviors of indole and quinoline. Indole (IND), 2-methyl-indole (2-M-IND), 3-methyl-indole (3-M-IND), quinoline (QL), 2-methyl-quinoline (2-M-QL) and 3-methyl-quinoline (3-M-QL) were used as the HDN reactant on the NiMo/γ-AlO catalyst. Some key elementary reactions in the HDN process of these nitrogen compounds on the Ni-Mo-S active nanocluster were calculated. The notable difference between IND and QL in the HDN is that dihydro-indole (DHI) can directly convert to O-ethyl aniline via the C-N bond cleavage, whereas tetrahydro-quinoline (THQ) can only break the C-N single bond via the full hydrogenation saturation of the aromatic ring. The reason for this is that the -NH and C=C groups of DHI can be coplanar and well adsorbed on the Ni-Mo-edge simultaneously during the C-N bond cleavage. In comparison, those of THQ cannot stably simultaneously adsorb on the Ni-Mo-edge because of the non-coplanarity. Whenever the methyl group locates on the α-C or the β-C atom of indole, the hydrogenation ability of the nitrogen heterocycle will be evidently weakened because the methyl group increases the space requirement of the sp carbon, and the impaction of the C=C groups on the Ni-S-edge cannot provide enough space. When the methyl groups are located on the α-C of quinoline, the self-HDN behavior of 2-M-QL is similar to quinoline, whereas the competitive HDN ability of 2-M-QL in the homologs is evidently weakened because the methyl group on the α-C hinders the contact between the N atom of 2-M-QL and the exposed metal atom of the coordinatively unsaturated active sites (CUS). When the methyl group locates on the β-C of quinoline, the C-N bond cleavage of 3-methyl-quinoline becomes more difficult because the methyl group on the β-C increases the steric hindrance of the C=C group. However, the competitive HDN ability of 3-M-QL is not evidently influenced because the methyl group on the β-C does not evidently hinder the adsorption of 3-M-QL on the active sites.
本文通过加氢脱硫（HDN）实验和密度泛函理论（DFT）计算相结合的方法，研究了氮杂环取代基对吲哚和喹啉加氢脱硫行为的影响。吲哚（IND）、2-甲基吲哚（2-M-IND）、3-甲基吲哚（3-M-IND）、喹啉（QL）、2-甲基喹啉（2-M-QL）和 3-甲基喹啉（3-M-QL）被用作 NiMo/γ-Al2O3 催化剂上的加氢脱硫反应原料。计算了这些氮化合物在 Ni-Mo-S 活性纳米簇加氢脱硫过程中一些关键的基元反应。IND 和 QL 在加氢脱硫过程中的显著区别在于，二氢吲哚（DHI）可以通过 C-N 键断裂直接转化为 O-乙基苯胺，而四氢喹啉（THQ）只能通过芳环的完全加氢饱和来断裂 C-N 单键。原因是在 C-N 键断裂过程中，DHI 的-NH 和 C=C 基团可以共面并同时很好地吸附在 Ni-Mo 边缘上。相比之下，由于非共面性，THQ 的那些基团不能稳定地同时吸附在 Ni-Mo 边缘上。无论甲基位于吲哚的α-C 还是β-C 原子上，氮杂环的加氢能力都会明显减弱，因为甲基增加了 sp 碳的空间要求，并且 C=C 基团对 Ni-S 边缘的撞击不能提供足够的空间。当甲基位于喹啉的α-C 时，2-M-QL 的自加氢脱硫行为与喹啉相似，而 2-M-QL 在同系物中的竞争加氢脱硫能力明显减弱，因为α-C 上的甲基阻碍了 2-M-QL 的 N 原子与配位不饱和活性位（CUS）暴露金属原子之间的接触。当甲基位于喹啉的β-C 时，3-甲基喹啉的 C-N 键断裂变得更加困难，因为β-C 上的甲基增加了 C=C 基团的空间位阻。然而，3-M-QL 的竞争加氢脱硫能力并没有明显受到影响，因为β-C 上的甲基并没有明显阻碍 3-M-QL 在活性位上的吸附。
