氮化物对NiW/Al_2O_3上DBT和4,6-DMDBT加氢脱硫反应活性的影响

EFFECT OF NITROGEN COMPOUNDS ON THE HYDRODESULFURIZATION OF DIBENZOTHIOPHENE AND 4,6-DIMETHYLDIBENZOTHIOPHENE OVER ALUMINA-SUPPORTED NiW CATALYST

以碱性氮化物喹啉和非碱性氮化物吲哚为杂质模型化合物,考察其对DBT和4,6-DMDBT在NiW/Al_2O_3上的加氢脱硫活性和选择性的影响。结果表明:氮化物对DBT和4,6-DMDBT的加氢脱硫反应存在截然不同的作用结果;氮化物存在条件下,DBT的加氢脱硫反应通过直接脱硫路线活性的提高得到改善,而4,6-DMDBT的加氢脱硫反应由于氮化物的存在受到抑制,这主要是因为氮化物在加氢活性位上的吸附抑制了硫化物在加氢活性位上的吸附,从而抑制了加氢路线的进行;但氮化物作用下催化剂表面结构重排使硫化物氢解活性提高成为可能,此时硫化物的分子大小和分子结构起到了决定性作用;DBT由于分子体积小、通过S原子与氢解活性位接触容易而提高氢解活性,4,6-DMDBT由于分子体积大和4、6位的位阻效应以及氮化物的拥塞效应,其氢解活性随N含量的升高而减小。

Effect of basic nitrogen compound （quinoline） and nonbasic nitrogen compound （indole） on the catalytic activity and product selectivity of the hydrodesulfurization （HDS） reactions of dibenzothiophene （DBT） and 4, 6-dimethyldibenzothiophene （4, 6 DMDBT） were investigated over sulfided NiW/Al2O3 catalyst. The results for DBT and 4,6-DMDBT were varied. With the existence of nitrogen compounds,the HDS reactions of DBT enhanced due to the improved DI）S reaction activity, yet for 4, 6-DMDBT, its HDS reaction activity decreased significantly. The adsorption of nitrogen compounds on the hydrogenation active sites of catalyst could inhibit the adsorption of sulfur compounds, resulting in the suppression of HYD reactions,and simultaneously, the accessible active sites on the catalyst surface seemed to be redistributed. In this case, the molecule size and stereo structure of the sulfur compounds become essential. Smaller size DBT molecules could access hydrogenolysis active sites via sulfur atom easily and its hydrogenolysis activity improved; large 4,6-DMDBT molecules were suffocated by overcrowding nitrogen compounds to access active sites, thus the hydrogenolysis activity of 4,6 DMDBT decreased with the increase of nitrogen content.