Regulation active components distribution of NiMo/Al2 O3 catalysts for hydrodesulfurization
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.
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