MoS2 morphology and promoter segregation in commercial Type 2 Ni–Mo/Al2O3 and Co–Mo/Al2O3 hydroprocessing catalysts

A series of commercial liquid-phase-sulfided Type 2 Ni–Mo/Al₂O₃ and Co–Mo/Al₂O₃ catalysts used in different trickle-phase reactions has been characterized by (scanning) transmission electron microscopy combined with energy-dispersive X-ray analysis ((S)TEM-EDX) and X-ray diffraction (XRD) analysis. In contrast to what is reported for H₂S/H₂ sulfided Type 2 model catalysts, MoS₂ stacking is not prominent in liquid-phase sulfided Type 2 commercial catalysts. The presence or absence of MoS₂ stacking has been shown to be highly dependent on the sulfidation procedure applied. Although Type 2 commercial Ni–Mo catalysts have high MoS₂ dispersion, there is a significant Ni sulfide segregation. This is not the case for their Co-containing counterparts.     

Activity and thermal stability of sonochemically synthesized MoS2 and Ni-promoted MoS2 catalysts

Sonochemically synthesized MoS₂/Al₂O₃, which had a hydrodesulfurization (HDS) activity that was significantly greater than that of a catalyst prepared by impregnation, exhibited low thermal stability due to sintering of MoS₂ crystallites at high temperatures. The thermal stability was improved when the catalyst was promoted with Ni. In this study, we compared the activity and thermal stability of different Ni-promoted MoS₂ catalysts, which were prepared by addition of Ni to MoS₂ using either impregnation (IMP) or chemical vapor deposition (CVD). After use in the HDS of dibenzothiophene (DBT) at 673 K for 2 h, the initial activity of the un-promoted catalyst was partially lost, while that of the Ni-promoted catalysts was preserved. Ni added by CVD interacted more intimately with MoS₂ than Ni added by impregnation because CVD allowed selective deposition of Ni on the MoS₂ edge sites. Another advantage of the CVD method over the impregnation method is that Ni(CO)₄, which was used as the Ni precursor in the former method, could be decomposed at much lower temperatures than in the case of Ni(NO₃)₂, which was used in the impregnation method. As a result, Ni-promoted catalysts prepared using Ni-CVD showed superior HDS activity compared with those prepared using Ni-impregnation.     

Effect of mixed γ- and χ-crystalline phases in nanocrystalline Al2O3 on the dispersion of cobalt on Al2O3

This paper reports the results of a study into the effect of mixed γ and crystalline phases in Al₂O₃ on the characteristics and catalytic activities for CO hydrogenation of Co/Al₂O₃ catalysts. The catalysts were characterized by X-ray diffraction, N₂ physisorption, transmission electron microscopy, and H₂ chemisorption. Increasing Co loading from 5 to 20 wt% for the mixed phase Al₂O₃-supported Co catalysts resulted in a constant increase in both the number of cobalt metal active sites and the hydrogenation activities. However, for those supported on γ-Al₂O₃, Co dispersion increased up to 15 wt%Co and declined at 20 wt%Co loading. It is suggested that the spherical-shape like morphology of the χ-phase Al₂O₃ prevented agglomeration of Co particles, especially at high Co loadings.     

Mesoporous molecular sieve MCM-41 supported Co–Mo catalyst for hydrodesulfurization of dibenzothiophene in distillate fuels

A mesoporous aluminosilicate molecular sieve with MCM-41 type structure was synthesized using aluminum isopropoxide as the Al source. Supported Co–Mo/MCM-41 catalysts were prepared by co-impregnation of Co(NO₃)₂·6H₂O and (NH₄)₆Mo₇O₂₄ followed by calcination and sulfidation. For comparison, conventional Al₂O₃-supported sulfided Co–Mo catalysts were also prepared using the same procedure. These two types of catalysts were examined at two different metal loading levels in hydrodesulfurization of a model fuel containing 3.5 wt% sulfur as dibenzothiophene in n-tridecane. At 350–375°C under higher H₂ pressure (6.9 MPa), sulfided Co–Mo/MCM-41 catalysts show higher hydrogenation and hydrocracking activities at both normal and high metal loading levels, whereas Co–Mo/Al₂O₃ catalysts show higher selectivity to desulfurization. Co–Mo/MCM-41 catalyst at high metal loading level is substantially more active than the Co–Mo/Al₂O₃ catalysts.     

Properties of unsupported MoS<Subscript>2</Subscript> species produced in the preparation of MoS<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> using a sonochemical method

Unsupported MoS₂ particles, which were produced in the preparation of MoS₂/Al₂O₃ using a sonochemical method, were successfully separated from the prepared sample catalyst by adding oleylamine as an agent for dispersing the unsupported particles. The fraction of the unsupported MoS₂, which was estimated based on Mo balance, varied between 0.03 and 0.4, independent of the Mo loading levels investigated (6–54 wt% of Mo). The activity of the unsupported MoS₂ for the hydrodesulfurization of dibenzothiophene was nearly the same as that of the Al₂O₃-supported MoS₂, indicating that the activity of the prepared catalyst was not affected by the presence of the unsupported MoS₂ particles.     

Nickel Oxide Based Supported Catalysts for the In-situ Reactions of Methanation and Desulfurization in the Removal of Sour Gases from Simulated Natural Gas

Supported nickel oxide based catalysts were prepared by wetness impregnation method for the in-situ reactions of H₂S desulfurization and CO₂ methanation from ambient temperature up to 300 °C. Fe/Co/Ni (10:30:60)–Al₂O₃ and Pr/Co/Ni (5:35:60)–Al₂O₃ catalysts were revealed as the most potential catalysts, which yielded 2.9% and 6.1% of CH₄ at reaction temperature of 300 °C, respectively. From XPS, Ni₂O₃ and Fe₃O₄ were suggested as the surface active components on the Fe/Co/Ni (10:30:60)–Al₂O₃ catalyst, while Ni₂O₃ and Co₃O₄ on the Pr/Co/Ni (5:35:60)–Al₂O₃ catalyst.     

Comparative Study on CO2 Hydrogenation to Higher Hydrocarbons over Fe-Based Bimetallic Catalysts

This paper reports on notable promotion of C₂ ⁺ hydrocarbons formation from CO₂ hydrogenation induced by combining Fe and a small amount of selected transition metals. Al₂O₃-supported bimetallic Fe–M (M = Co, Ni, Cu, Pd) catalysts as well as the corresponding monometallic catalysts were prepared, and examined for CO₂ hydrogenation at 573 K and 1.1 MPa. Among the monometallic catalysts, C₂ ⁺ hydrocarbons were obtained only with Fe catalyst, while Co and Ni catalysts yielded higher CH₄ selectively than other catalysts. The combination of Fe and Cu or Pd led to significant bimetallic promotion of C₂ ⁺ hydrocarbons formation from CO₂ hydrogenation, in addition to Fe–Co formulation discovered in our previous work. CO₂ conversion on Ni catalyst nearly reached equilibrium for CO₂ methanation which makes this catalyst suitable for making synthetic natural gas. Fe–Ni bimetallic catalyst was also capable of catalyzing CO₂ hydrogenation to C₂ ⁺ hydrocarbons, but with much lower Ni/(Ni+Fe) atomic ratio compared to other bimetallic catalysts. The addition of a small amount of K to these bimetallic catalysts further enhanced CO₂ hydrogenation activity to C₂ ⁺ hydrocarbons. K-promoted Fe–Co and Fe–Cu catalysts showed better performance for synthesizing C₂ ⁺ hydrocarbons than Fe/K/Al₂O₃ catalyst which has been known as a promising catalyst so far.     

Investigation of CH4 Reforming with CO2 on Meso-Porous Al2O3-Supported Ni Catalyst

Meso-porous Al₂O₃-supported Ni catalysts exhibited the highest activity, stability and excellent coke-resistance ability for CH₄ reforming with CO₂ among several oxide-supported Ni catalysts (meso-porous Al₂O₃ (Yas1-2, Yas3-8), -Al₂O₃, -Al₂O₃, SiO₂, MgO, La₂O₃, CeO₂ and ZrO₂). The properties of deposited carbons depended on the properties of the supports, and on the meso-porous Al₂O₃-supported Ni catalyst, only the intermediate carbon of the reforming reaction formed. XRD and H₂-TPR analysis found that mainly spinel NiAl₂O₄ formed in meso-porous Al₂O₃ and -Al₂O₃-supported catalysts, while only NiO was detected in -Al₂O₃, SiO₂, CeO₂, La₂O₃ and ZrO₂ supports. The strong interaction between Ni and meso-porous Al₂O₃ improved the dispersion of Ni, retarded its sintering and improved the activated adsorption of CO₂. The coking reaction via CH₄ temperature-programed decomposition indicated that meso-porous Al₂O₃-supported Ni catalysts were less active for carbon formation by CH₄ decomposition than Ni/-Al₂O₃ and Ni/-Al₂O₃.     

Synthesis,characterization and evaluation of Ni–Mo/Zr–Al2O3 catalyst for hydro-conversion of lignite-based heavy carbon resources

NaOH depolymerized products (SDP) of Shengli lignite was used as lignite-based heavy carbon resources in this study. Hydrotreatment of SDP over Ni–Mo/Al₂O₃ and Ni–Mo/Zr–Al₂O₃ catalysts was investigated. It was found that the incorporation of Zr to Ni–Mo/Al₂O₃ catalyst results in the easy reduction of metal oxides and the increase of the stacking degree and length of MoS₂ slabs. Both of Ni–Mo/Al₂O₃ and Ni–Mo/Zr–Al₂O₃ catalysts show better performance for hydrogenation of SDP and can be used repeatedly. The incorporation of Zr to Ni–Mo/Al₂O₃ catalyst significantly inhibits the formation of tetrahydrofuran insolubles (THFI), promotes the formation of two-ring aromatics and increases HS yield compared to that over Ni–Mo/Al₂O₃ catalyst.     

Highly Selective and Active Niobia-Supported Cobalt Catalysts for Fischer–Tropsch Synthesis

The performance of Co/Nb₂O₅ was compared to that of Co/γ-Al₂O₃ for the Fischer–Tropsch synthesis at 20 bar and over the temperature range of 220–260 °C. The C₅₊ selectivity of Nb₂O₅-supported cobalt catalysts was found to be very high, i.e. up to 90 wt% C₅₊ at 220 °C. The activity per unit weight cobalt was found to be similar for Nb₂O₅ and γ-Al₂O₃-supported catalysts at identical reaction temperature. However, due to the low porosity of crystalline Nb₂O₅, the cobalt loading was limited to 5 wt% and consequently the activity per unit weight of catalyst was lower than of Co/γ-Al₂O₃ catalysts with higher cobalt loadings. This low activity was largely compensated by increasing the reaction temperature, although the C₅₊ selectivity decreased upon increasing reaction temperature. Due to the high intrinsic C₅₊ selectivity, Nb₂O₅-supported catalysts could be operated up to ~250 °C at a target C₅₊ selectivity of 80 wt%, whereas γ-Al₂O₃-supported catalysts called for an operation temperature of ~210 °C. At this target C₅₊ selectivity, the activity per unit weight of catalyst was found to be identical for 5 wt% Co/Nb₂O₅ and 25 wt% Co/Al₂O₃, while the activity per unit weight of cobalt was a factor of four higher for the niobia-supported catalyst.     

Oxidative desulfurization of dibenzothiophene over Fe promoted Co–Mo/Al_2O_3 and Ni–Mo/Al_2O_3 catalysts using hydrogen peroxide and formic acid as oxidants

This work reports the enhancing effect of a highly cost effective and efficient metal, Fe, incorporation to Co or Ni based Mo/Al_2O_3 catalysts in the oxidative desulfurization(ODS) of dibenzothiophene(DBT) using H_2O_2 and formic acid as oxidants. The influence of operating parameters i.e. reaction time, catalyst dose, reaction temperature and oxidant amount on oxidation process was investigated. Results revealed that 99% DBT conversion was achieved at 60 °C and 150 min reaction time over Fe–Ni–Mo/Al_2O_3. Fe tremendously enhanced the ODS activity of Co or Ni based Mo/Al_2O_3 catalysts following the activity order: Fe–Ni–Mo/Al_2O_3 NFe–Co–Mo/Al_2O_3 NNi–Mo/Al_2O_3 NCo–Mo/Al_2O_3, while H_2O_2 exhibited higher oxidation activity than formic acid over all catalyst systems. Insight about the surface morphology and textural properties of fresh and spent catalysts were achieved using scanning electron microscopy(SEM), X-ray diffraction(XRD), energy dispersive X-ray(EDX)analysis, Atomic Absorption Spectroscopy(AAS) and BET surface area analysis, which helped in the interpretation of experimental data. The present study can be deemed as an effective approach on industrial level for ODS of fuel oils crediting to its high efficiency, low process/catalyst cost, safety and mild operating condition.     

Stable carbon dioxide reforming of methane over modified Ni/Al2O3 catalysts

CO₂ reforming of methane was studied over modified Ni/Al₂O₃ catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al₂O₃, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO₂ reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even in the absence of diluent gas and the activity changed only slightly during 100 h operation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of support material on the catalytic performance of V2O5/P2O5 catalysts for the selective oxidation of but-1-ene and furan to maleic anhydride and its consecutive nonselective oxidation : I. Results of Catalytic Testing

The performance of Al₂O₃- and TiO₂-supported V₂O₅/P2O5 catalysts was studied with respect to activity and selectivity for the oxidation of but-1-ene and furan to maleic anhydride (MA) and its consecutive nonselective oxidation. TiO₂-supported catalysts result in better selectivities for MA both for but-1-ene and furan oxidation. For both the supports MA selectivity was affected by the amount of V₂O₅ and P₂O₅ loading: An increase of the V₂O₅/P₂O₅ loading resulted in improved MA selectivity for the Al₂O₃ support while the effect was opposite in the case of the TiO₂ support. For the oxidation of but-1-ene and furan the activity of the TiO₂-supported catalyst (V₂O₅/P₂O₅/TiO₂, = 5/ 5/90 mass-%) was higher than the Al₂O₃-supported catalyst (V₂O₅/P₂O₅/Al₂O₃ = 5/ 5/90 mass-%) while for the non-selective oxidation of MA to carbon dioxide the Al₂O₃,-supported catalyst was more active than the TiO₂-supported catalyst.     

Production of Synthesis Gas via Dry Reforming of Methane over Co‐Based Catalysts: Effect on H2/CO Ratio and Carbon Deposition

The effect of support type on synthesis gas production using Co‐based catalysts supported over TiO₂‐P25, Al₂O₃, SiO₂, and CeO₂ was investigated. The catalysts were prepared by the incipient wet impregnation method and characterized by various techniques for comparison. Experiments were performed in a micro tubular reactor. The results revealed that all Co‐supported catalysts produced synthesis gas ratios of 1 and below and, thus, proved to be well‐suited for methanol and Fischer‐Tropsch syntheses. Co catalysts supported over TiO₂‐P25 and Al₂O₃ provided better synthesis gas ratios and stability performances. The promotion of a Co/TiO₂‐P25 catalyst with Ce had a substantial influence on its catalytic activity and the amount of carbon deposit. A Ce‐promoted catalyst diminished markedly the extent of carbon deposition and thus boosted the performance towards better activity and stability.     

The Effect of Surface Acidic and Basic Properties on the Performance of Cobalt-Based Catalysts for Ethanol Steam Reforming

In this study, the effect of surface acidic and basic properties of y-Al₂O₃-, ZrO₂-, and CeO₂-supported cobalt catalysts on their catalytic performance during ethanol steam reforming was investigated using various characterization techniques including temperature programmed desorption, CO₂ and NH₃ pulse chemisorption, and diffuse reflectance infrared fourier transform spectroscopy. The steady-state reaction experiments showed that catalyst exhibited decreasing performance (i.e., less activity and worse stability) by following the order of Co/CeO₂?>?Co/ZrO₂?>?Co/Al₂O₃. Characterization results showed the catalysts had the reverse order of surface acidity (i.e., Co/CeO₂?<?Co/ZrO₂?<?Co/Al₂O₃), indicating that the performance difference could be attributed to the variation of surface acidic and basic properties in addition to the oxygen mobility variations reported previously.     

Isospecific polymerization of styrene with supported nickel acetylacetonate/methylaluminoxane catalysts

Summary The polymerization of styrene with catalysts based on Ni(acac)₂ supported on SiO₂ and Al₂O₃ was investigated. Using catalysts based on MAO supported on silica, a highly isotactic polystyrene was obtained. Nevertheless, the Al₂O₃-supported catalyst can promote isospecific polymerization activated by common. alkyl aluminum compounds even by any prior support treatment with MAO. Received: 3 March 1998/Revised version: 14 April 1998/Accepted: 14 April 1998     

On the mechanisms and the selectivity determining steps in syngas conversion over supported metal catalysts: An IR study

An IR study of syngas and methanol conversion has been performed over Cu–ZnO–Al₂O₃ methanol synthesis catalyst, Ni–Al₂O₃ methanation catalyst and Co–Al₂O₃ Fischer Tropsch catalyst. The data, obtained at low pressure, provide unequivocal evidence of the existence of a way via oxygenated intermediates (formates, possibly dioxymethylene, methoxy groups) in the three cases. In the selectivity determining step, methoxy groups desorb associatively as methanol on Cu–ZnO–Al₂O₃. Methoxy groups are selectively hydrogenolyzed to methane over Ni–Al₂O₃. Over Co–Al₂O₃ oxygenated surface species may be involved in the chain growth to give C₂₊ compounds. It is possible that this mechanism coexists with the via-carbide all-metallic catalysis reported for methanation and FT synthesis, on the basis of studies performed on pure metals.     

Elucidation of hydrodesulfurization mechanism using S radioisotope pulse tracer methods

The sulfidation state in a series of Co-promoted Mo/Al₂O₃ catalysts was investigated using a ³⁵S pulse tracer method. ³⁵S-labeled H₂S ([³⁵S]H₂S) pulses were introduced into catalysts in a nitrogen stream until the radioactivity in the recovered pulse approached the radioactivity of the introduced pulse. From the amount of introduced [³⁵S]H₂S, the amount of sulfur accumulated on the catalyst was estimated. The result indicated that the amounts of sulfur accumulated on the catalysts increased with increasing temperature for all catalysts. Only molybdenum was sulfided in both Co–Mo/Al₂O₃ and Mo/Al₂O₃ catalysts below 300°C, but the sulfided states of the catalysts at 400°C were very close to the stoichiometric states where Co and Mo are present as Co₉S₈ and MoS₂. Further, hydrodesulfurization (HDS) reactions of radioactive ³⁵S labeled dibenzothiophene were carried out over the series of Co-promoted Mo/Al₂O₃ catalysts. The amount of labile sulfur and the release rate constant of H₂S were determined. The promotion effect of cobalt on activity of the molybdenum catalyst was attributed to the formation of more active sites. Moreover, the increase in the catalytic activity with Co/Mo ratio among the promoted catalysts was due to increase in the number of the sites with the same activity.     

Fischer-Tropsch synthesis: Support and cobalt cluster size effects on kinetics over Co/Al2O3 and Co/SiO2 catalysts

The influence of support type and cobalt cluster size (i.e., with average diameters falling within the range of 8-40 nm) on the kinetics of Fischer-Tropsch synthesis (FT) were investigated by kinetic tests employing a CSTR and two Co/γ-Al₂O₃ catalysts having different average pore sizes, and two Co/SiO₂ catalysts prepared on the same support but having different loadings. A kinetic model that contains a water effect constant “m” was used to fit the experimental data obtained with all four catalysts. Kinetic parameters suggest that both support type and average Co particle size impact FT behavior. Cobalt cluster size influenced kinetic parameters such as reaction order, rate constant, and the water effect parameter. In the cluster size range studied, decreasing the average Co cluster diameter by about 30% led to an increase in the intrinsic reaction rate constant k, defined on a per g of catalyst basis, by 62-102% for the γ-Al₂O₃ and SiO₂-supported cobalt catalysts. This increase was due to the higher active Co⁰ surface site density as measured by hydrogen chemisorption. Moreover, less inhibition by adsorbed CO and greater H₂ dissociation on catalysts having smaller Co particles was suggested by the higher a and lower b values obtained for the measured reaction orders. Interestingly, irrespective of support type, the catalysts having smaller average Co particles were more sensitive to water. Comparing the catalysts having strong interactions between cobalt and support (Co/Al₂O₃) to the ones with weak interactions (Co/SiO₂), the water effect parameters were found to be positive (indicating a negative influence on CO conversion) and negative (denoting a positive effect on CO conversion), respectively. No clear trend was observed for b values among the different supports, but greater a and a/b values were observed for both Al₂O₃-supported Co catalysts, implying greater inhibition of the FT rate by strongly adsorbed CO on Co/Al₂O₃ relative to Co/SiO₂. For both supports, the order on P_CO was always found to be negative (i.e., suggesting an inhibiting effect) and positive for P_H2 for all four catalysts. The order of the reaction on P_H2 was close to 0.5, suggesting that dissociated H₂ is likely involved in the catalytic cycle. Finally, in the limited range of average pore diameters studied (13.5 and 18.2 nm), the average pore size of the Al₂O₃-supported Co catalysts displayed no observable impact on the reaction rate or water effect, suggesting either that the reaction is kinetically controlled, or that the pore size difference was not significant enough to elicit a measurable response.     

MgO-supported cluster catalysts with Pt–Ru interactions prepared from Pt3Ru6(CO)21(μ3-H)(μ-H)3

Bimetallic MgO-supported catalysts were prepared by adsorption of Pt₃Ru₆(CO)₂₁(μ₃-H)(μ-H)₃ on porous MgO. Characterization of the supported clusters by infrared (IR) spectroscopy showed that the adsorbed species were still in the form of metal carbonyls. The supported clusters were decarbonylated by treatment in flowing helium at 300 °C, as shown by IR and extended X-ray absorption fine structure (EXAFS) data, and the resulting supported PtRu clusters were shown by EXAFS spectroscopy to have metal frames that retained Pt–Ru bonds but were slightly restructured relative to those of the precursor; the average cluster size was almost unchanged as a result of the decarbonylation. These are among the smallest reported bimetallic clusters of group-8 metals. The decarbonylated sample catalyzed ethylene hydrogenation with an activity similar to that reported previously for γ-Al₂O₃-supported clusters prepared in nearly the same way and having nearly the same structure. Both samples were also active for n-butane hydrogenolysis, with the MgO-supported catalyst being more active than the γ-Al₂O₃-supported catalyst.