Fe基催化剂的酸性调控及其对加氢脱硫反应路径选择性的影响

Acidity regulation of Fe-based catalysts and its effect on the selectivity of HDS reaction pathways

以Fe作为主活性金属、Zn作为助活性金属,制备了Y型分子筛改性的Fe基加氢脱硫(HDS)催化剂。采用低温氮气物理吸附、X射线衍射(XRD)、氢气程序升温还原(H_(2)-TPR)、氨气程序升温脱附(NH_(3)-TPD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和吡啶红外(Py-IR)等表征方法对改性前后Fe基催化剂的形貌、孔结构、分散性、还原性、电子缺陷结构以及酸性等变化进行了研究,并使用固定床反应器对Fe基催化剂的HDS性能进行了评价。结果表明,Y型分子筛的引入提供了Bronsted(B)酸中心,使得Fe基催化剂的脱硫率提高了10.7%-34.1%。同时,B酸中心提高了催化剂的直接脱硫(DDS)反应路径的选择性。此外,B酸中心在促进DDS反应路径选择性增加的同时,抑制了预加氢脱硫(HYD)反应路径中四氢二苯并噻吩(THDBT)和六氢二苯并噻吩(HHDBT)更进一步的深度加氢,从而在保证脱硫率提升的同时又降低了氢耗。其根本原因可能是Y型分子筛的引入增强了催化剂的酸性,特别是B酸中心和活性金属之间的相互作用促进了电子转移,从而调节了Fe物种的电子缺陷结构,进而提升了催化剂的HDS性能。

An Fe-based hydrodesulfurization(HDS)catalyst modified by Y zeolite was developed using Fe as the main active metal and Zn as a promoter.The change of morphology,pore structure,dispersity,reducibility,electronic defect structure and acidity of the Fe-based catalysts before and after modification were investigated using low-temperature nitrogen physical adsorption,X-ray diffraction(XRD),H_(2)-temperature programmed reduction(H_(2)-TPR),NH_(3)-temperature programmed desorption(NH_(3)-TPD),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS)and pyridine infrared spectroscopy(Py-IR).Meanwhile,the HDS performance of the Fe-based catalyst was evaluated using a fixed-bed reactor.The results showed that the introduction of Y zeolite provided the Brønsted(B)acid sites,which increased the sulfur removal rates of Fe based catalysts by 10.7%−34.1%.Meanwhile,the B acid sites improved the selectivity of the direct desulfurization(DDS)reaction pathway.In addition,the B acid sites not only promoted the increase of DDS selectivity but also inhibited further deep hydrogenation of tetrahydrodibenzothiophene(THDBT)and hexahydrodibenzothiophene(HHDBT)in the hydrogenation(HYD)reaction pathway,thereby ensuring an increase in desulfurization efficiency while reducing hydrogen consumption.The fundamental reason was that the introduction of Y zeolite enhanced the acidity of the modified catalyst,especially the interaction between B acid sites and active metal promoted electron transfer,which adjusted the Fe species electronic defect structure,resulting in the improvement of HDS performance.