V.H.J. de Beer

The effect of phosphate on the hydrodenitrogenation activity and selectivity of alumina-supported sulfided Mo, Ni, and Ni-Mo catalysts

Abstract Al 2 O 3 -supported Mo, Ni, NiMo, and Rh catalysts, prepared by sequential aqueous impregnation and in situ sulfidation, were investigated in the hydrodenitrogenation (HDN) of quinoline at 643 K and 3 MPa and in the hydrodesulfurisation (HDS) of thiophene at 673 K and 0.1 MPa. The Ni and Mo catalysts had a very low conversion of quinoline to hydrocarbons which improved only slightly in the presence of phosphate. The Rh catalysts had a high conversion and a high selectivity for propylcyclohexane and showed no deactivation with time. The addition of Ni to MO/Al 2 O 3 and of phosphate to NiMo/Al 2 O 3 and Rh/Al 2 O 3 catalysts increased the HDN conversion significantly. The selectivity for propylbenzene and the apparent HDN activation energy increased with increasing P-loading. Ni increased the thiophene conversion of Mo/Al 2 O 3 , but phosphate had almost no influence on the HDS activity of NiMo/Al 2 O 3 and Rh/Al 2 O 3 . The effect of phosphate is due to a combination of structural and catalytic factors. Phosphate improves the activity by inducing the formation of the type II NiMoS structure, but also, especially at high Ni loading, lowers the activity by inducing a decrease in the dispersion of the NiMoS phases and a segregation of Ni 3 S 2 . Phosphate also promotes the S- and N-elimination reactions, but this only has an influence on the overall catalyst activity if the preceding hydrogenation reactions are not rate determining.

Periodic trends in the hydrodenitrogenation activity of carbon-supported transition metal sulfide catalysts

Periodic trends of transition metals for the catalysis of reactions such as hydrogenation, hydrogenolysis, isomerization and hydrogen oxidation have been well studied. When activity versus position of the transition metal in the periodic table is plotted, quite often these trends are manifested in the form of so-called volcano-type curves. In the present study, the authors have chosen the HDN of quinoline at moderately high pressure as a model reaction, and they have used the same carbon-supported transition metal sulfide catalysts studied by Vissers et al. Results are shown for the following transition metals: V, Cr, Mn, Fe, Co, Ni, Mo, Ru, Rh, Pd, W, Re, Os, Ir, and Pt. 9 references.

The CoO-MoO3-gamma-Al2O3 : VII. Influence of the support

The thiophene hydrodesulfurization activity was measured under continuous flow conditions at 400 °C and atmospheric pressure for Mo- and Co-containing catalysts supported on different materials (γ- and η-Al 2 O 3 and SiO 2 ) and using different methods of preparation. The results showed that all supports having a high specific surface area are suitable in HDS catalyst preparation. Alumina is to be preferred because it inhibits the formation of CoMoO 4 , and thus exerts a beneficial influence on catalyst preparation. The main function of the support is to stabilize a high degree of dispersion of the actual active component MoS 2 . In addition the carrier may facilitate hydrogenation and isomerization reactions.

Roman spectroscopic study of CoMoγ-Al2O3 catalysts

Laser Raman spectroscopy is used to study the structure of molybdenum and cobalt species present in CoMoγ-Al2O3 catalyst systems. From comparison with Raman spectra of Mo and Co in known structures it is derived that these catalyst systems contain Mo and Co in different modifications depending on the degree of surface coverage. In the absence of Co, four different Mo species are found. At low coverages isolated molybdate tetrahedra are observed. Increasing the surface coverage results in formation of a polymolybdate phase in which Mo is octahedrally surrounded. At higher coverages “bulk” aluminum molybdate is formed. At very high coverages formation of “free” MoO3 occurs. In Coγ-Al2O3 samples the color indicates the presence of Co3O4- and CoAl2O4-like species. When Co is introduced in Moγ-Al2O3 (CoMo atomic ratio, 0.64) various effects occur. “Free” MoO3, as well as Al2(MoO4)3, is converted into “CoMoO4.” Cobalt addition results in a decrease of the isolated Mo tetrahedra concentration in favor of the polymeric molybdate form, which apparently is not qualitatively affected by the presence of Co. In CoMoγ-Al2O3 most of the Co is present in a structure comparable to CoAl2O4. The influences of the nature of the support, heat treatment, reduction in hydrogen and the effect of sulfiding are discussed briefly.

The CoO-MoO3-Al2O3 catalyst. IV. Pulse and continuous flow experiments and catalyst promotion by cobalt, nickel, zinc, and manganese

The activities of MoO3Al2O3 catalysts promoted with various amounts of cobalt, nickel, zinc, and manganese have been determined in pulse and continuous flow experiments for the hydrodesulphurization of thiophene at atmospheric pressure and 400 °C. The initial activities of a MoO3Al2O3 and a CoOMoO3Al2O3 catalyst as inferred from pulse experiments are equal. Continuous flow experiments for all catalysts show that the activity decays rapidly and approaches a steady-state level that depends on the promoter and its concentration. Maximum steady-state activity levels are attained for each of the promoter ions at different metal-to-molybdenum ratios. Some models are discussed in an attempt to explain the experimental results. A preliminary investigation of hydrogenation activity of the above-mentioned catalysts is reported. With increasing promoter content a minimum for the initial hydrogenation activity is found. Hydrocarbon saturation at the steady-state is comparatively insensitive to the nature of the promoter ion, which may be associated with the sulphiding of the surface.

Hydrodenitrogenation of quinoline over carbon-supported transition metal sulfides

Transition metal sulfide (TMS) catalysts were prepared by impregnation of an activated carbon support with aqueous solutions of first-, second-, and third-row (group V-VIII) transition metal salts, drying and in situ sulfidation. The catalysts were tested in the hydrodenitrogenation of quinoline (653 K, 5.5 MPa) in microautoclaves and microflow reactors. The first-row transition metal sulfides had low quinoline conversions to hydrocarbons, and their periodic trend formed a U-shaped curve with a minimum at Mn/C and Fe/C and maxima at V/C and Ni/C. The quinoline conversions to hydrocarbons of the second- and third-row TMS formed volcano curves with maxima at Rh/C and Ir/C and with Mo/C and W/C having the lowest conversions. The transition metal sulfide catalysts with a low quinoline hydrogenation (first-row transition metal sulfides, Mo/C and W/C) also had a low quinoline conversion to hydrocarbons. The transition metal sulfides with the highest quinoline conversions to hydrocarbons (Rh/C, Pd/C, Os/C, INC and Pt/C) had a very high quinoline hydrogenation and a high selectivity for propylcyclohexane. Ru/C and especially Re/C had a good quinoline conversion to hydrocarbons, but also an exceptionally high selectivity for propylbenzene.

On the formation of cobalt-molybdenum sulfides in silica-supported hydrotreating model catalysts

Model catalysts, consisting of a conducting substrate with a thin SiO2 layer on top of which the active catalytic phase is deposited by spincoating impregnation, were applied to study the formation of the active CoMoS phase in HDS catalysts. The catalysts thus prepared showed representative activity in the hydrodesulfurization of thiophene, confirming that these models of HDS catalysts are realistic. Combination of the sulfidation behaviour of Co and Mo studied by XPS and activity measurements shows that the key in the formation of the CoMoS phase is the retardation of the sulfidation of Co. Complexing Co to nitrilotriacetic acid complexes retarded the Co sulfidation, resulting in the most active catalyst. Due to the retardation of Co in these catalysts, the sulfidation of Mo precedes that of Co, thereby creating the ideal conditions for CoMoS formation. In the CoMo catalyst without NTA the sulfidation of Co is also retarded due to a Co–Mo interaction. However, the sulfidation of Mo still lags behind that of Co, resulting in less active phase and a lower activity in thiophene HDS.

Phosphorus poisoning of molybdenum sulfide hydrodesulfurization catalysts supported on carbon and alumina

Phosphorus-containing MO sulfide catalysts supported on y-A1203 and activated carbon were evaluated for their thiophene HDS activities. Phosphorus was added as phosphoric acid to the carrier material prior to the molybdenum component. The thiophene HDS activity of the carbonsupported catalysts was strongly decreased by phosphorus, while alumina-supported catalysts were not poisoned by phosphorus when present at moderate contents. The structural characteristics and degree of dispersion of the sulfided carbon-supported catalysts were determined by X-ray photoelectron spectroscopy and dynamic CO chemisorption. The cause of the phosphorus poisoning could not be related to a decrease in active phase dispersion or to incomplete sulfidation of the oxidic precursor catalyst. CO chemisorption revealed that in a phosphorus-containing catalyst anion vacancies were blocked. It was suggested that phosphorus poisoning can be related to phosphine (PH,), created by reduction of phosphate, probably during the presulfiding treatment. The poisoning effect can be explained as resulting from the adsorption of phosphine on the anion vacancies. The fact that alumina-supported catalysts are not poisoned by phosphorus can be explained by the strong interaction of phosphate with the alumina support. Due to this strong interaction, phosphate will not be reduced to phosphine under the sulfiding and reaction conditions

Hydrodenitrogenation of decahydroquinoline, cyclohexylamine and O-Propylaniline over carbon-supported transition metal sulfide catalysts

Carbon-supported transition metal sulfide (TMS) catalysts were prepared by impregnation of an activated carbon support with aqueous solutions of first-, second-, and third-row (group V-VIII) transition metal salts followed by drying and in situ sulfidation. Their activity for the hydrodenitrogenation of decahydroquinoline (5.2–5.5 MPa, 623–653 K), cyclohexylamine (4.8-5.5 MPa, 543–653 K), and o-propylaniline (5.1–5.5 MPa, 593–653 K) was tested in microautoclaves. When plotted versus the position of the transition metal in the Periodic System, the conversions of all three N-containing reactants to hydrocarbons over the first-row transition metal sulfides formed U-shaped curves with a minimum at Mn, while V had the highest conversion. The decahydroquinoline and cyclohexylamine conversions to hydrocarbons over the second- and third-row TMS formed volcano curves with maxima at Rh and Ir, respectively. Disproportionation reactions were found to be important side reactions in the cyclohexylamine hydrodenitrogenation. The activities of the second-row transition metal sulfides for the conversion of o-propylaniline formed a volcano curve with a maximum at Ru or Rh sulfide, whereas the activities of the third-row transition metal sulfides formed a strongly distorted volcano curve. All catalysts and especially Re sulfide had a very high selectivity for propylbenzene.

Application of ASA supported noble metal catalysts in the deep hydrodesulphurisation of diesel fuel

Abstract The potential of Amorphous Silica Alumina (ASA) supported Pt and Pd catalysts for deep hydrodesulphurisation (HDS) of diesel fuels was investigated. It appeared that the ASA supported catalysts exhibit an excellent activity for the conversion of 4-Ethyl, 6-Methyl Dibenzothiophene (4-E, 6-M DBT) under model conditions as compared to conventional HDS catalysts and γ-Al 2 O 3 supported noble metal catalysts. Pt/ASA was also tested under practical conditions using a diesel fuel feed. ThePt/ASA catalyst showed a comparable activity to the NiW/γ-Al 2 O 3 catalyst which was higher than that of the conventional CoMo/γ-Al 2 O 3 catalyst. The main difference of the catalyst was the better hydroconversion of the 4,6 di-alkylated DBTs. The better performance of Pt/ASA in the testing under model conditions as compared to the diesel fuel HDS can be attributed to poisoning of part of the active phase by basic nitrogen compounds like quinoline. It is concluded that ASA supported noble metal catalysts have a promising potentialfor deep HDS processing.