Combined Effects of EDTA and Heteroatoms (Ti, Zr, and Al) on Catalytic Activity of SBA-15 Supported NiMo Catalyst for Hydrotreating of Heavy Gas Oil

Abstract

M-SBA-15 (M = Ti, Al, and Zr) materials with a Si/M ratio of 20 were synthesized using a direct synthesis method. M-SBA-15 supported NiMo hydrotreating catalysts with and without EDTA was prepared by an incipient wetness impregnation method. A EDTA/Ni molar ratio of 2 was used for catalysts with EDTA. The hydrotreating activities of these catalysts were measured using Athabasca bitumen derived heavy gas oil, and comparison was done with the performance of NiMo/SBA-15 and NiMo/γ-Al 2 O 3 catalysts. All catalysts were thoroughly characterized by BET, TPR, TPD, CO-chemisorption, XRD, XANES, HRTEM, ICP-MS, and 13 C NMR. Incorporation of Ti, Al, and Zr in SBA-15 framework results in an increase in the surface acidity and metal support interactions in otherwise neutral SBA-15 material. This increases the dispersion, and HDS, HDN and HDA activity of a NiMo/SBA-15 catalyst increases by 12%, 70%, and 22%, respectively, as in the case of a NiMo/Ti-SBA-15 (Cat-Ti) catalyst. EDTA addition helps in better redispersion of molybdenum during sulfidation/activation as indicated by HRTEM and CO chemisorption studies. A XANES Mo LIII-edge study for the oxide state of catalysts reveals that EDTA helps in the formation of a greater number of molybdenum in octahedral structures which are easily reducible during sulfidation as compared to molybdenum in tetrahedral structures. A power law based kinetic study indicates that addition of EDTA lowers the activation energy, which could be due to formation of a more favorable Type II NiMoS active site. The activity studies show that using EDTA increases the HDS, HDN, and HDA activity of a NiMo/M-SBA-15 catalyst by 18%, 36%, and 22%, respectively, as in the case of a NiMo/Ti-SBA-15/2EDTA (Cat-TiE) catalyst. Based on the results from different characterization techniques, the schematic is presented related to the effect of EDTA-Mo-support interactions on dispersion of active metals in catalysts. The results from characterization techniques are in parallel with catalytic activity which follows the order Cat-TiE > Cat-AlE > Cat-ZrE > Cat-Ti. However, the catalytic activity of Cat-TiE is almost comparable to that of a NiMo/γ-Al 2 O 3 catalyst and has the potential for superior hydrotreating catalyst.

Synthesis and characterization of mesoporous aluminas with different pore sizes: Application in NiMo supported catalyst for hydrotreating of heavy gas oil

“…1. This also indicates the presence of P6mm symmetry representing hexagonal ordered mesostructure [2]. However, the H3 type hysteresis shows adsorption at high P/P 0 indicating the presence of large pore size and broad pore size distribution as shown in inset of Fig.…”

“…The CO-chemisorption studies for metal dispersion were carried out in Micromeritics ASAP 2020 Chemisorption system. The following expression was used to calculate the percentage metal dispersion of the active metal available for interaction with the adsorbate [2]:…”

“…The instrumental error in N and S analysis was ±1%. Further details were mentioned in our previous work [2,19].…”

“…The strength of acidic sites was determined on the basis of NH 3 desorption temperature. Ammonia from weak acidic sites desorbs at <200 • C, from moderately acidic sites it desorbs at 200-350 • C and from strongly acidic sites it desorb at >350 • C [2]. It can be seen in Table 4 that all catalysts have weak acidic sites at 150 • C, however the catalysts have difference in the number/strength of strong acidic sites at 375 • C. The catalyst NiMo/Meso-Al-1.25 shows desorption of 155 mol/g NH 3 at 415 • C, indicating the presence of strong acidic sites.…”

“…Actual overall reaction rate Overall reaction rate without internal diffusion (2) where the value of Á ≥ 0.95 signifies that the reaction is kinetic limited and not diffusion limited. The following equations were used to calculate the value of Á [40]:…”