Search

The effects of the synthesis method, dopant nature, and porosity on the dibenzothiophene hydrodesulfurization performance of hierarchically porous NiMoS(Si,Zr)/Al2O3catalysts were studied. Si and Zr incorporation was carried out using grafting (G) and sol–gel (SG) methods. The catalysts were characterized using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), N2physisorption, Hg intrusion porosimetry (MIP), X-ray diffraction, hydrogen temperature-programmed reduction (H2-TPR), pyridine-adsorbed Fourier transform infrared spectroscopy (Py-FTIR), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy and then correlated with the kinetic parameters. The experimental results showed that Si- and Zr-modified catalysts promoted different degrees of activity and selectivity. The NMS/A-Zr(G) catalyst displayed the highest HDS activity, followed by NMS/A-Zr(SG), NMS/A, NMS/A-Si(G), and NMS/A-Si(SG) in descending order. The presence of Si and Zr in the catalysts and their incorporation methods were identified as the main reasons for this trend. More active catalysts exhibited an increased total acidity. Furthermore, Lewis sites were positively related to kDDS(CUS sites), while Brönsted sites were related to kHYD(BRIM sites). These modifications were found to enhance various characteristics of the catalysts, such as larger edge sites, Mo and NiMo coordination, and large pores.

Two equilibrium FCC catalysts of the octane-barrel (ECAT-D) and resid (ECAT-R) types were used in the cracking of a typical vacuum gasoil (VGO) and its saturated (SF), aromatic (AF), and resin (RF) fractions. The experiments were carried out in a batch, fluidized bed laboratory CREC Riser Simulator reactor. The reaction temperature was 500 °C, the catalyst-to-oil relationship was 1, with 0.2 g of the catalyst being used in each experiment, and the reaction times were 0.7, 1.5, and 3 s. The ranking of the reactivities of the different feedstocks was SF > VGO > AF > RF over both catalysts. While the AF and RF fractions yielded more gasoline than the SF fraction, the latter showed the highest yields of LPG. The coke forming trend followed the order SF < VGO < AF < RF. Even though catalyst ECAT-D, with a higher and stronger acidity, was more active than catalyst ECAT-R, which has less acidity and better textural properties (higher mesoporosity and pore diameter), the latter was less affected by coke deposition, considering the changes in the specific surface area and acidic properties after use. Coke impacted more severely on Brönsted acid sites than on Lewis sites, particularly when the AF and RF fractions were used. The stronger acid sites were more severely affected by coke, particularly in catalyst ECAT-D. The negative effect on strong acidic sites was consistent with the increasing basic character of the feedstocks, following the order SF < VGO < AF < RF.