Abstract:

Residue hydrogenation is a diffusion-limited reaction. When the active components are distributed in the outer region of pellet catalysts, namely eggshell distribution, the diffusion resistance of reactants in catalyst particles can be effectively reduced to achieve the best catalytic activity. The adsorption strength of active metals on alumina support was regulated by adjusting the surface properties. Multiple techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), molybdenum equilibrium adsorption, and contact angle, were employed to determine the surface properties of the supports. It was found that the support with more basic hydroxyl group would have stronger adsorption on the active metals, slowing down the diffusion rate of the active components during impregnation. The distribution of active components could be adjusted through the regulation of adsorption and diffusion rates. Dibenzothiophene was chosen as a model compound for the evaluation of the desulfurization performance. The results showed that the eggshell catalyst exhibited an apparent desulfurization rate of 79.3%, with a specific activity 1.2 times higher than the uniform catalyst. It might be attributed to the weaker metal-support interactions on the eggshell catalyst, which facilitates a higher sulfurization degree and the formation of the Ni-Mo-S type Ⅱ active phase during the sulfurizing process. Moreover, eggshell catalyst could remarkably reduce the internal diffusion resistance owing to a short diffusion path of the reactants, thus greatly improving the utilization efficiency of the active components.

Key words: alumina, eggshell catalyst, surface property, hydrodesulfurization, adsorption

摘要：

渣油加氢为扩散限制反应，当活性组分集中分布在催化剂颗粒外层，能有效减少反应物在催化剂中的扩散阻力，提升催化活性。本文利用氧化铝载体表面性质差异，调变活性金属在载体上的吸附强弱。采用X射线衍射、红外、钼平衡吸附法、接触角等表征手段分析载体表面性质。实验结果表明，含有更多碱性羟基的载体会对活性金属产生强吸附，降低浸渍过程活性组分在孔内的扩散速率。通过调控吸附与扩散速率，促进了蛋壳催化剂的形成，实现活性组分可控分布。模型化合物二苯并噻吩的脱硫反应性能评价结果表明，蛋壳催化剂上金属-载体相互作用更弱，利于形成高活性的Ⅱ型Ni-Mo-S活性相，同时蛋壳结构减少了扩散阻力，催化剂表观脱硫率为79.3%，比活性为均匀分布催化剂的1.2倍。

关键词: 氧化铝, 蛋壳催化剂, 表面性质, 加氢脱硫, 吸附