Insights into individual and combined effects of phosphorus and EDTA on performance of NiMo/MesoAl2O3 catalyst for hydrotreating of heavy gas oil

Abstract

The individual and combined effects of phosphorus, EDTA and support modification on hydrotreating of bitumen derived heavy gas oil were studied. The EDTA/Ni molar ratio was varied from 0.5 to 2 for optimization and studying the effect of EDTA on activity of mesoporous alumina supported NiMo catalyst. The phosphorus was impregnated using two different methods: modified co-impregnation (MCI) and sequential impregnation (SI), and their effect on physico-chemical properties was studied. The catalysts were characterized using N2-physisorption, CO-chemisorption, pyridine-FTIR, H2-TPR, NH3-TPD, X-ray diffraction, High resolution-TEM and XANES. HRTEM and XANES techniques were predominantly used to determine the structural changes, and to visualize and measure active metal dispersion. All catalysts were tested for hydrotreating reactions in a continuous trickle-bed reactor at industrial conditions. The activities were measured in terms of hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA). The studies on NiMo/γ-Al2O3 were also performed for comparison purpose. The increase in HDS and HDN activities was observed for NiMo/MesoAl2O3 catalyst and this is assigned to high metal dispersion due to large surface area and pore volume of synthesized mesoporous alumina. The addition of EDTA in NiMo/MesoAl2O3 catalyst resulted in increasing the MoS2 slab length and stacking degree, which resulted in decrease in dispersion, and HDN and HDS activities. However, the catalyst NiMoP/MesoAl2O3(MCI) containing only 2.5wt.% P prepared by modified co-impregnation method showed the best HDS (97wt.%) and HDN (77wt.%) activity among all other studied catalysts. This increase in activity is attributed to the effect of mesoporous alumina and influence of P on reducibility, acidic strength, structural changes and desired molybdenum dispersion.