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•Ni2P shows high HDS activity with less inhibition by S and N compounds.•Smaller Ni2P particles have better resistance to S and N compounds.•Sulfur resistance of Ni2P is attributed to ...stronger interaction between Ni and P.
Catalysts consisting of Ni2P placed on low and high surface area siliceous supports, i.e. SiO2-L, SiO2-H, and Si-MCM-41, were synthesized by TPR (temperature-programmed reduction), and the effect of the sulfur and nitrogen content of the feed on hydrotreating activity was studied. Structural information on the supported Ni2P phase after reaction was obtained by XRD (X-ray diffraction) and EXAFS (extended X-ray absorption fine structure) measurements. The catalytic activity in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) was obtained at 573 and 613K and a pressure of 3.1MPa in an upflow, liquid-gas-solid bed reactor with a feed consisting of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and quinoline dissolved in tridecane as solvent. Using reference compositions of 4,6-DMDBT at levels of 500ppm S, dimethyldisulfide (DMDS) at levels of 6000ppm S, and quinoline at levels of 200ppmN, the order of activity was Ni2P/SiO2-L<Ni2P/SiO2-H<Ni2P/MCM-41, compared on the basis of equal number of sites (230mmol) placed in the reactor. The Ni2P/MCM-41 gave a notably high conversion in HDS of 98% that was substantially above those of a Ni-Mo-S/Al2O3 commercial catalyst which had an HDS conversion of 81%, on a basis of equal quantity of sites (230mmol) placed in the reactor. The sites were titrated by pulse CO uptakes for the phosphides and by pulse O2 adsorption at low temperature for the sulfide. Analysis of the spent samples by EXAFS showed that Ni(2) sites of square pyramidal geometry in Ni2P are bound to sulfur, with a lower NiS coordination, as the particle size decreased, and the order in the number of these sites followed the reactivity Ni2P/SiO2-L<Ni2P/SiO2-H<Ni2P/MCM-41. It is thus concluded that the active Ni(2) site on the highly dispersed Ni2P is much more tolerant to sulfur than the tetrahedral Ni(1) sites also present in the samples.
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•Ni2P/SiO2 catalyst was active for guaiacol hydrodeoxygenation (HDO).•HDO followed direct deoxygenation or prehydrogenation pathway.•Threefold hollow Ni site and neighboring P site in ...Ni2P were active in HDO.•Distribution of H and OH groups on Ni2P surface influenced HDO pathways.
A Ni2P/SiO2 catalyst was prepared by temperature-programed reduction (TPR), and applied for the hydrodeoxygenation of guaiacol. The physical properties of the catalyst samples were characterized by N2 adsorption/desorption isotherms and CO uptake chemisorption. X-ray diffraction (XRD) and extended X-ray absorption fine structure (XAFS) spectroscopy were used to obtain structural properties for the supported Ni2P catalysts. Hydrodeoxygenation (HDO) tests were performed in a continuous flow fixed-bed reactor at 523–573K, and 1 or 8atm, and an LHSV of 2.0h−1. The Ni2P/SiO2 gave an HDO conversion over 90% with two different reaction pathways being identified; at 1atm direct deoxygenation was dominant to produce benzene, and at 8atm prehydrogenation followed by deoxygenation was preferred to produce cyclohexane. A combined X-ray absorption fine structure spectroscopy and density functional theory analysis revealed that the active site of Ni2P catalysts is composed of threefold hollow Ni and P sites which lead to adsorption of H or OH groups. These results suggest that relative populations of H or OH groups on Ni or P sites of Ni2P surface have an impact on overall reaction pathways of the HDO.
The diminishing quality of oil feedstocks coupled with increasingly more stringent environmental regulations limiting the content of sulfur in transportation fuels have given rise to a need for ...improved hydroprocessing technology. This review begins with a summary of the major improvements in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) catalysts and processes that have been reported in recent years. It then describes a new class of hydroprocessing catalysts, the transition metal phosphides, which have emerged as a promising group of high-activity, stable catalysts. The phosphides have physical properties resembling ceramics, so are strong and hard, yet retain electronic and magnetic properties similar to metals. Their crystal structures are based on trigonal prisms, yet they do not form layered structures like the sulfides. They display excellent performance in HDS and HDN, with the most active phosphide, Ni
2P, having activity surpassing that of promoted sulfides on the basis of sites titrated by chemisorption (CO for the phosphides, O
2 for the sulfides). In the HDS of difficult heteroaromatics like 4,6-dimethyldibenzothiophene Ni
2P operates by the hydrogenation pathway, while in the HDN of substituted nitrogen compounds like 2-methylpiperidine it carries out nucleophilic substitution. The active sites for hydrogenation in Ni
2P have a square pyramidal geometry, while those for direct hydrodesulfurization have a tetrahedral geometry. Overall, Ni
2P is a promising catalyst for deep HDS in the presence of nitrogen and aromatic compounds.
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•Oil-soluble V-MoS2 catalysts of 6–8 nm in size were successfully prepared in situ in the VR HCK at 693 K and 9.5 MPa H2.•V-MoS2 catalysts showed better activity than monometallic ...MoS2 or V2S3 catalysts in regard to the C7-ASP conversion and turnover frequencies for the VR HCK.•Formation of V-Mo-S phase was confirmed by the V K-edge XANES and Mo K-edge EXAFS analysis.
The structure and the catalytic activity of the dispersed VxMo(1−x)S2catalysts were investigated for hydrocracking (HCK) of vacuum residue (VR) with the same amount of catalyst loading of 0.113 mmol as a metal basis at 693 K and 9.5 MPa H2. The catalysts were prepared in situ in the reaction using vanadium acetylacetonate and molybdenum hexacarbonyl as V and Mo precursors, respectively. Structural properties of the dispersed catalysts were characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy and transmission electron microscopy, which confirmed the formation of a well-dispersed V-MoS2phase in size range 6–8 nm. Furthermore, it was demonstrated that the V-MoS2catalysts feature higher stability in the catalyst recycle test for the VR HCK in terms of H2 consumption rate (TOF) and asphaltene conversion in comparison to monometallic sulfides of V2S3 or MoS2.
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•Vacuum residue hydrocracking follows parallel reaction pathways to form liquid oils, gas, and coke.•During hydrocracking, the oil-soluble Mo precursor is transformed into a nano-MoS2 ...catalyst.•Dispersed MoS2 catalyst enhanced vacuum residue hydrocracking with liquid oils to over 90%.
The slurry phase hydrocracking (HCK) of vacuum residue (VR) in the presence of dispersed MoS2 catalyst was investigated under varying temperature, pressure, and reaction time. Extended X-ray absorption fine structure (EXAFS) measurements were used to obtain structural information about the dispersed MoS2 phase during the reaction. Under a standard reaction condition of temperature 673K and pressure 10.0MPa in an autoclave batch reactor, kinetic analysis for VR HCK confirmed that the reaction occurs in a parallel manner in the production of 77% liquid oils as major products such as vacuum gas oil and distillates with the generation of gas and of 23% coke in the presence of dispersed MoS2 catalyst (0.113mmol or 360ppm Mo). Although temperatures below 653K at 9.5MPa were found beneficial in coke reduction to less than 1.0wt.% in favor of hydrogenation at 33h of reaction, higher pressures over 15MPa at 673K were more influential in accelerating the VR conversion into liquid products, reaching 90% at 4h of reaction with coke reduction down to 1.2wt.% than the cases under conditions below 10MPa. Analysis of the spent catalysts by EXAFS and TEM demonstrated that the nanosized MoS2 phase was well developed from Mo(CO)6 in the early stage of the reaction, with lower MoS and MoMo coordination verifying the small MoS2 particles having more exposed and defect sites as active phases.
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•Different shapes of oil-dispersed MoS2 were obtained by a ligand stabilization method.•Monoslab MoS2 showed higher activity in vacuum residue hydrocracking than multilayered ...MoS2.•The vacuum residue hydrocracking activity of MoS2 catalysts was well correlated with the rim-site model.
Different morphologies of oil-dispersed MoS2 catalysts were obtained by a ligand stabilization method using Mo(CO)6 as a Mo precursor and trioctylphosphine oxide (TOPO) as a coordinating agent to identify the active site of MoS2 in the hydrocracking (HCK) of vacuum residue (VR). Transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy were used to obtain structural properties of the dispersed catalyst. It was observed that the MoS2 forms a nanoscaled monolayer from 5 to 10 nm in size. The effect of the oil-dispersed MoS2 catalysts having different morphology on the slurry phase HCK of VR was investigated at 673 K and 9.5 MPa H2. The turnover frequency (TOF) of the dispersed MoS2 catalysts in the VR HCK was found to show a good correlation with the rim-site Mo dispersion of the MoS2 slabs based on the same metal loading of 0.113 mmol at 673 K and 9.5 MPa H2.
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•In situ XANES with CV cycles identified the working mechanisms of CoFe-LDH in OER.•Degradation of CoFe-LDH occurs due to the loss of Fe and the formation of β-CoOOH.•Fe-doped ...Co(OH)2/Co enabled high and stable activity even under potential changes.
The activation and degradation mechanisms of CoFe layered double hydroxide (CoFe-LDH) and Fe-decorated Co(OH)2 (Fe-Co(OH)2) have been investigated using in situ X-ray absorption spectroscopy coupled with cyclic voltammetry (CV) in 0–0.9 V (vs Hg/HgO). A series of CoFe-LDH samples have been prepared by co-electrodeposition with varying Co/Fe ratios. Fe-decorating on Co(OH)2 has been applied using 10 ppm of Fe in 1.0 M KOH. Electrochemical impedance spectroscopy (EIS) and CV cycles confirm the degradation of Co(OH)2 and CoFe-LDH due to the irreversible redox of Co(OH)2/CoOOH, and Fe extraction. In contrast, Fe-decorated Co(OH)2 shows high activity and stability in the OER. In situ XANES analysis suggests that the Fe-decorating allows the Co(OH)2 to remain as γ-CoOOH even under potential fluctuations.
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•Oil-dispersed CoWS2 catalysts of 7–10 nm were prepared in situ in VR HCK.•CoWS2 catalysts showed better activity and stability than Co9S8 or WS2.•Formation of Co-WS2 phase was ...confirmed by the Co K-edge XANES analysis.
The bimetallic CoWS2 catalysts were prepared in situ during the slurry phase hydrocracking (HCK) of vacuum residue (VR) using W(CO)6 and Co-octoate as oil soluble precursors to investigate the promotional effect of Co promoters on the dispersed WS2 catalyst for the VR HCK. The morphologies and structural properties of dispersed catalysts were characterized by transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS). The bimetallic CoWS2 catalyst was observed to form well-dispersed monolayers in the size range of 7–11 nm, which showed higher turn-over frequency values (TOF) and C7-asphaltene (C7-ASP) conversions than monometallic WS2 or Co9S8 catalysts in the VR HCK at 693 K and 10.0 MPa H2. Moreover, the extended X-ray fine absorption structure spectroscopy (EXAFS) coupled with the density functional theory (DFT) calculations successfully verified the formation of the Co-W-S phase.
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•A series test of hydrotreating (HDT) and hydrocracking (HDC) of FCC light cycle oil for BTX-rich light aromatics.•In HDT, selective hydrogenation of polyaromatics into mono-aromatics ...at high HDN rate is important.•HDC catalyst, Mo-S/BZ (BZ = H-Beta + H-ZSM-5), exhibited high BTX-rich light aromatics yield close to theoretical yield.•LCO with low contents of refractory alkyl-carbazoles and heavy tri+-aromatics was preferred.
Comprehensive series tests on hydrotreating (HDT) and hydrocracking (HDC) of fluid catalytic cracking (FCC) light cycle oil (LCO) into high-value light aromatics rich in benzene, toluene, and xylenes (BTX) were conducted in a fixed-bed down-flow reactor under medium pressure (6 MPa). Two different LCOs, LCO-1 (a full-range LCO) and LCO-2 (340 °C− LCO which contained a smaller fraction of refractory alkyl(C2+)-carbazoles and heavy tri+-aromatics (three and more rings aromatics) than LCO-1), were used as feedstocks. Comparison of NiW-S, NiMo-S, and CoMo-S supported on γ-Al2O3 and a commercial catalyst (for vacuum gasoil hydrodesulfurization) as LCO HDT catalysts revealed that NiMo-S/γ-Al2O3 allowed for highly selective hydrogenation (HYD) of di+-aromatics (two and more rings aromatics) into mono-aromatics with minimal loss of aromatics at high HDN conversion rates. For HDC catalysts, NiMo-S, CoMo-S, and Mo-S were supported on a hybrid zeolite, BZ(x) (a mixture of H-Beta (B) and H-ZSM-5 (Z) (x wt%)). Since Mo-S exhibited moderate HYD power and H-ZSM-5 promoted the dealkylation of alkyl-aromatics into BTX, Mo-S/BZ(10) yielded the largest amount of BTX in the HDC model of tetralin among the three catalyst analyzed. The HDC of hydrotreated LCO-1 (HDT-LCO-1) over Mo-S/BZ(10) catalyst generated a low yield of BTX-rich light aromatics because of the limited conversion of C11+ heavy aromatics. However, during the HDC of HDT-LCO-2, the yield of BTX-rich light aromatics was close to the theoretical yield (48.4 wt%) over a wide temperature range when Mo-S/BZ(10) was used as catalyst, which indicated the highly selective HDC behavior of Mo-S/BZ(10) for this reaction. Therefore, NiMo-S/γ-Al2O3 and Mo-S/BZ(10), which exhibited well-balanced metallic and/or acidic functions, were promising HDT and HDC catalysts, respectively, for the selective conversion of LCOs into high-value BTX-rich light aromatics at high yields.
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