Essential role of promoter Co on the MoS2 catalyst in selective hydrodesulfurization of FCC gasoline
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摘要: 采用含硫前驱体四硫代钼酸铵直接构建MoS2催化剂，通过调变Co/Mo原子比深入认识Co调变MoS2催化剂的作用本质及其FCC汽油选择性加氢脱硫机理。借助XRD、HRTEM、XPS、H2-TPR和Py-FTIR表征发现，Co/Mo原子比能够影响催化剂的活性相微观结构组成，从而影响催化剂的加氢脱硫活性和选择性。当Co/Mo（atomic ratio） < 0.2时，助剂Co原子倾向于占据MoS2相的边角位而形成CoMoS活性相，明显提高了催化剂的加氢脱硫活性；当0.2 < Co/Mo（atomic ratio） < 0.6时，助剂Co在催化剂表面形成适量的Co9S8相，其产生的溢流氢能提高硫化物的脱除活性而对烯烃饱和活性的影响较小；当Co/Mo（atomic ratio）>0.6时，过量的Co会形成大颗粒的Co9S8相，阻碍硫化物和烯烃与催化剂活性中心的接触，从而降低催化剂的活性和选择性。Abstract: The essential role of Co on the MoS2 catalyst in selective hydrodesulfurization (HDS) of FCC gasoline was investigated with ammonium tetrathiomolybdate supported on alumina modified with various amount of Co sulfide. According to the data obtained by XRD, HRTEM, XPS, H2-TPR and Py-FTIR analysis, the Co species could significantly affect the microstructure and composition proportion of the active phase, and thus induced the enormous differences in catalytic properties. The evaluation results demonstrated that the Co atoms tending to form the CoMoS phase as Co/Mo(atomic ratio) < 0.2 could greatly improve the HDS activity, but slightly improve the hydrogenation (HYD) activity of olefins. The spillover hydrogen produced by the formation of Co9S8 phase as 0.2 < Co/Mo(atomic ratio) < 0.6 greatly improved the HDS activity, but showed almost no effect on the HYD of olefins. The excess Co could inevitably form some large size Co9S8 phase as Co/Mo(atomic ratio) > 0.6, which would hinder the mutual contact of the reactants and the active sites, and thus lead to the decrease of the HDS activity and selectivity. The obtained results were useful for developing highly effective hydrotreating catalyst.
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Key words:
- selective hydrodesulfurization /
- active phase /
- Co/Mo atomic ratio /
- spillover hydrogen
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Figure 1 XRD patterns of the CoMo/γ-Al2O3 catalysts prepared with different Co/Mo atomic ratios
Figure 2 HRTEM images of the sulfided CoMo/γ-Al2O3 catalysts obtained with different Co/Mo atomic ratios
Figure 4 H2-TPR profiles of the sulfided CoMo/γ-Al2O3 catalysts with different Co/Mo atomic ratios
Figure 5 Py-FTIR spectra of pyridine adsorbed on the sulfided CoMo/γ-Al2O3 catalysts with different Co/Mo atomic ratios
Figure 6 Schematic representation of the Co/Mo atomic ratios effect on the structure of the active phase and the HDS selectivity
Table 1 HDS activity and selectivity of the CoMo/γ-Al2O3 catalysts prepared with different Co/Mo atomic ratios
Sample HYD /% kHYD /(g-1· h-1) HDS /% kHDS/(g-1 · h-1) S M(N) 12.8 0.548 35.4 1.748 3.2 Co/Mo(0.1) 13.6 0.585 65.4 4.245 7.3 Co/Mo(0.2) 13.9 0.599 80.5 6.539 10.9 Co/Mo(0.5) 14.1 0.608 91.4 9.814 16.1 Co/Mo(0.56) 14.3 0.617 93.5 10.933 17.7 Co/Mo(0.6) 14.4 0.622 91.9 10.053 16.2 Co/Mo(1) 12.8 0.548 86.2 7.922 14.5 
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Table 2 Characteristics of the morphology of all the catalysts
Sample Average slab length L/nm Average stacking number N M(N) 4.95 3.59 M(HS) 4.77 3.51 Co/Mo(0.2) 4.67 3.82 Co/Mo(1) 4.59 3.85
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Table 3 XPS parameters of the different contributions Co 2p obtained for the sulfided CoMo/γ-Al2O3 catalysts with different Co/Mo atomic ratios
Catalyst Co9S8 CoMoS Co (Ⅱ) E/eV w/% E/eV w/% E/eV w/% Co/Mo(0.1) - - 778.7 80.9 781.5 19.1 Co/Mo(0.2) 778.2 2.3 778.7 85.2 781.5 12.5 Co/Mo(0.5) 778.1 23.9 778.6 50.2 781.4 25.9 Co/Mo(0.56) 778.2 32.3 778.7 44.6 781.5 23.1 Co/Mo(0.6) 778.1 34.2 778.6 41.7 781.4 24.1 Co/Mo(1) 778.1 53.9 778.6 24.7 781.3 21.4
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Table 4 Relative peak areas with dimensionless of the Brønsted acid sites at 1540 cm-1 and Lewis acid sites at 1450 cm-1 of the CoMo/γ-Al2O3 catalysts
Sample AL/gcat AB/gcat Co/Mo(0.1) 21.8 16.4 Co/Mo(0.2) 21.1 17.9 Co/Mo(0.56) 38.1 25.9 Co/Mo(0.6) 38.0 23.6 Co/Mo(1) 30.6 12.6
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