Reactive adsorption desulfurization of model FCC gasoline on Ni-based adsorbents: Effect of active phase dispersion on activity and HDS/HYD selectivity

Abstract

A series of Ni/ZnO-Al2O3 and Ni/ZnO-SiO2 adsorptive-catalytic adsorbents differing in the support composition (the Al2O3, SiO2 and ZnO covered) and nickel surface content have been synthesized. Zinc oxide-based supports and Ni supported adsorbents were characterized using X-ray diffraction (XRD), temperature-programmed reduction (TPR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and N2 physisorption to study their structural properties and morphology. Desulfurization (HDS) and hydrogenation (HYD) activity of the synthesized systems, as well as the HDS/HYD selectivity factor (SF) were determined in the process of reactive adsorption of model FCC gasoline containing thiophene (1000 ppm of sulfur) and 1-hexene (20 wt%) on a fixed-bed flow-type laboratory unit. It has been established that an increase in the nickel surface content and average particle size of the active phase leads to an enhancement of the HDS/HYD selectivity factor regardless of the support used. The Ni/ZnO-SiO2 sample with 8 at Ni/nm2 exhibited the highest HDS/HYD selectivity at a high level of thiophene conversion (> 96%) in the chemisorption mode. The evolution of catalytic properties of Ni-Zn sorbents during FCC gasoline desulfurization process was estimated as well as characteristics of sulfurized samples. Relationships between the turnover frequency number in HDS and HYD reactions, HDS/HYD selectivity factor and size of Ni particles are discussed. DFT calculations of the adsorption thermodynamics were carried out for three model components and adsorption in the diffusion-controlled mode of the feedstock was studied for a series of nickel clusters. The results helped to explain the catalytic behavior of Ni-based sorbents in chemisorption and catalytic (after sulfur saturation) conditions.