Pore Volume Impregnation Research Articles

Hydrogel-derived catalysts. Laboratory results on nickel-molybdenum and cobalt-molybdenum hydrotreating catalysts

Conventional nickel or cobalt modified molybdenum disulfide-containing hydrotreating catalysts are generally prepared by impregnation. While this route has proven to be quite successful and has led to a variety of commercial products, inherent in the pore volume impregnation technique are several potential limitations. These limitations may be chemical or economic in nature. In order to overcome these potential limitations, we have developed a new, one-step route to the oxidic form of these nickel or cobalt modified molybdenum disulfide-containing hydrotreating catalysts. This route consists of reacting the metals solutions directly with a precipitated α-alumina monohydrate (boehmite) hydrogel prior to extrusion. The metals-containing hydrogel is extruded directly to pellet form and subsequently dried and calcined. Catalysts formed appear to have benefits not seen with conventional catalysts. As an example, the metals efficiencies and utilization of these catalysts can exceed conventional catalysts by 25%. Volumetric performances of these catalysts can also be quite good. Surface areas of the new, gel-derived catalysts are significantly higher than conventional catalysts. Crush strengths of the gel catalyst pellets can show improved strength over conventionally-prepared catalysts. Possible reasons for the enhancements in properties are discussed as well as details of the experimental procedures required to prepare these catalysts.

95/01328 Studies on the the F-T performances of Iton-based ultrafine particle catalysts. II. Effects of reaction conditions, stability of catalysts and sulfer poisoning

Carbon-supported iron-molybdenum sulphide catalysts were characterized by means of Mössbauer spectroscopy at temperatures down to 4.2 K. Thiophene hydrodesulphurization (HDS) activity measurements were performed at 673 K in a flow microreactor operating at atmospheric pressure. The molybdenum content was 9.5 wt.-% whereas the iron content varied from 0.6 to 9.0 wt.-%. Sequential deposition (Molybdenum first) by pore-volume impregnation was employed to prepare oxidic catalyst precursors. The oxidic catalyst precursors were dried at 293 K in an air flow, followed by an additional hydrogen treatment up to 393 K. The type and relative particle sizes of the iron compounds present in the oxidic precursors and in the sulphided and reoxidized catalysts were determined by Mössbauer spectroscopy. It was demonstrated that after sulphidation for 4 h at 623 K, the composition of the sulphide catalyst depends on the iron content. Sulphided Fe-Mo/C catalysts contain a mixed “FeMoS” phase and “Fe-sulphide”. The former is responsible for the observed promoting effect toward thiophene HDS. From the temperature dependence of the resonant absorption areas, it was concluded that the iron atoms in the “FeMoS” phase are located at the surface of MoS2 microcrystals. The amount of “Fe-sulphide” present in the catalyst was found to increase with increasing iron content. This “Fe-sulphide” might partly cover the “FeMoS” phase, thus causing a decrease in the promoting effect.

In situ poisoning of the thiophene hydrodesulfurization activity of carbon-supported transition metal sulfide catalysts by phosphorus

Carbon-supported transition metal sulfide catalysts, prepared by pore volume impregnation of an activated carbon support with aqueous solutions of first, second and third row transition metal salts (Group V-VIII), drying and in situ sulfidation, were tested in thiophene hydrodesulfurization (723 K, 0. 1 MPa). In the poisoning experiments a bed of phosphorus compound-containing carbon was placed upstream of the catalyst bed. Under the sulfiding and reaction conditions the phosphorus compound was volatilized and transported to the catalyst bed where it could affect the catalytic properties of the active metal sulfide phase. This poisoning effect was different for the thiophene conversion to hydrocarbons and butene hydrogenation, and depended on the transition metal sulfide. Group VIII transition metal Sulfides were rather resistant towards the poisoning by the phosphorus compound. Only the hydrodesulfurization activity of the carbon-supported nickel catalyst was promoted in the presence of phosphorus. This beneficial effect of phosphorus on nickel might atso explain the gain in activity for the commercial Al 2O 3-supported Ni-Mo-P catalysts.

ZrO 2-Promoted Rh/SiO 2 Catalysts in CO Hydrogenation and Temperature-Programmed Reduction

The hydrogen chemisorption, high-pressure CO hydrogenation, and temperature-programmed reduction of ZrO 2-promoted Rh/SiO 2 catalysts were studied. The promoter decreased the adsorption capacity of the catalysts by covering the metal surface. The covering of Rh by ZrO 2 seemed to occur during reduction. At low ZrO 2 loadings this covering created new active sites for CO hydrogenation, while at higher ZrO 2 loadings both activity and turnover frequency were decreased. The impregnation sequence in the pore volume impregnation had no influence on the catalytic behavior. By applying different calcination procedures, however, the interactions between ZrO 2 and the SiO 2 support, as well as between ZrO 2 and Rh 2O 3, could be intensified and the catalytic behavior altered. When ZrO 2 is in contact with Rh, it can be partly reduced and forms Zr 3+ ions. Thus, the interaction between Rh and ZrO 2 is similar to the strong metal-support interaction.

Reducibility of metals on fluid cracking catalyst

Temperature-programmed reduction (TPR) and high-temperature oxygen titration have been applied to characterize Ni and V in fluid cracking catalysts (FCC) as a function of catalyst composition and the method of metals impregnation and deactivation. The influence of the type of matrix, the level of nickel and vanadium, antimony and oxidation/reduction cycles have been examined. TPR spectra of nickel on cracking catalysts are characterized by a low-temperature peak at 680 °C attributable to supported nickel oxide and a high-temperature peak in the range of 800 to 880 °C attributable to highly dispersed nickel species such as Ni hydroxysilicate and Ni surface spinel. Increasing the alumina content of the catalyst generally leads to a decrease in the intensity of the low-temperature peak and an increase in the reduction temperature of the high-temperature peak. TPR spectra of vanadium on cracking catalysts are characterized by a single peak in the range of 550 to 650 °C. Metals were introduced by pore volume impregnation followed by steaming in an inert or a cyclic oxidizing/reducing environment. Metals, especially vanadium, from pore volume impregnation are generally more easily reduced than metals in equilibrium catalyst. Steaming the metallated catalysts in a cyclic redox environment decreases the amount of reducible nickel and vanadium, increases the temperature required for the reduction of vandium, and decreases the dehydrogenation activity of the metals, especially vanadium. A survey of commercial equilibrium catalysts shows that the reducibility of metals, as measured by high-temperature oxygen titration can be correlated with the coke selectivity.

ADSORPTION OF HEXACHLOROPLATINIC ACID ON γ-ALUMINA COATINGS FOR PREPARATION OF MONOLITHIC STRUCTURE CATALYSTS

The adsorption of hexachloroplatinic acid on γ-Alumina coatings is investigated in order to prepare monolithic structure catalysts for carbon monoxide oxidation. For acid concentrations in the range 0.25-1.5 mM the adsorption is examined in a batch process and a kinetic model is proposed and evaluated. The pH of the solution has a major impact on the adsorption rate and dispersion of Pt on Al2O3 and when acidity becomes lower than 1.5 pH value the deposition of Pt on the catalyst by pore volume impregnation is favourable. The catalytic properties of Pt-alumina as oxidation catalyst for CO depend strongly on the adsorption rate of H2PtCI6. A difference of 80 °C at the light off temperature is observed for catalysts prepared by adsorption from solutions with different acidity.

Cold reduced tubes from nickel-molybdenum stainless powder alloys : Y.V. Manegin et al. (Central Scientific Research Institute for Ferrous metallurgy, Russia.) Stal'. 1991, 76–79. (In Russian.)

Carbon-supported iron-molybdenum sulphide catalysts were characterized by means of Mössbauer spectroscopy at temperatures down to 4.2 K. Thiophene hydrodesulphurization (HDS) activity measurements were performed at 673 K in a flow microreactor operating at atmospheric pressure. The molybdenum content was 9.5 wt.-% whereas the iron content varied from 0.6 to 9.0 wt.-%. Sequential deposition (Molybdenum first) by pore-volume impregnation was employed to prepare oxidic catalyst precursors. The oxidic catalyst precursors were dried at 293 K in an air flow, followed by an additional hydrogen treatment up to 393 K. The type and relative particle sizes of the iron compounds present in the oxidic precursors and in the sulphided and reoxidized catalysts were determined by Mössbauer spectroscopy. It was demonstrated that after sulphidation for 4 h at 623 K, the composition of the sulphide catalyst depends on the iron content. Sulphided Fe-Mo/C catalysts contain a mixed “FeMoS” phase and “Fe-sulphide”. The former is responsible for the observed promoting effect toward thiophene HDS. From the temperature dependence of the resonant absorption areas, it was concluded that the iron atoms in the “FeMoS” phase are located at the surface of MoS2 microcrystals. The amount of “Fe-sulphide” present in the catalyst was found to increase with increasing iron content. This “Fe-sulphide” might partly cover the “FeMoS” phase, thus causing a decrease in the promoting effect.

Ni EXAFS studies of the NiMoS structure in carbon-supported and alumina-supported NiMo catalysts

Sulfided NiS/C, NiMoS/C, and NiMoS/Al 2O 3 catalysts were prepared by pore volume impregnation with a solution containing nitrilotriacetic acid, which gives almost exclusively the NiMoS structure. The catalysts were studied by means of in situ EXAFS measurements at the Ni K-Edge. The Ni in the carbon-supported Ni catalysts was present in a Ni 3S 2-like phase. In the alumina-supported and carbon-supported NiMoS catalysts no bulk Ni sulfide was detected up to a Ni/Mo ratio of about 0.5, and all Ni was present at the NiMoS structure, which is the active phase in hydrodesulfurization. In this structure the Ni atoms are situated in a square pyramid of five S atoms at 2.22 Å, and have Mo neighbors at 2.85 Å. This indicates that the Ni atoms are situated on top of the S 4 squares at the MoS 2 edges in the Mo plane, in millerite-type Ni sites. A NiNi coordination at 3.2 Å was observed at low Ni/Mo ratios, indicating that part of the Ni atoms are present at neighboring sites on the MoS 2 edge. In order to examine the influence of the H 2S partial pressure on the Ni structure, a NiMoS/Al 2O 3 catalyst was exposed to several flushing procedures after sulfidation. When the catalyst was flushed with a mixture of 2% H 2S or less in H 2, the NiS coordination number decreased, indicating that the Ni atoms become uncovered and are made available for catalysis.

Sulphidation of carbon-supported iron-molybdemum oxide catalysts

Carbon-supported iron-molybdenum sulphide catalysts were characterized by means of Mössbauer spectroscopy at temperatures down to 4.2 K. Thiophene hydrodesulphurization (HDS) activity measurements were performed at 673 K in a flow microreactor operating at atmospheric pressure. The molybdenum content was 9.5 wt.-% whereas the iron content varied from 0.6 to 9.0 wt.-%. Sequential deposition (Molybdenum first) by pore-volume impregnation was employed to prepare oxidic catalyst precursors. The oxidic catalyst precursors were dried at 293 K in an air flow, followed by an additional hydrogen treatment up to 393 K. The type and relative particle sizes of the iron compounds present in the oxidic precursors and in the sulphided and reoxidized catalysts were determined by Mössbauer spectroscopy. It was demonstrated that after sulphidation for 4 h at 623 K, the composition of the sulphide catalyst depends on the iron content. Sulphided Fe-Mo/C catalysts contain a mixed “Fe Mo S” phase and “Fe-sulphide”. The former is responsible for the observed promoting effect toward thiophene HDS. From the temperature dependence of the resonant absorption areas, it was concluded that the iron atoms in the “Fe Mo S” phase are located at the surface of MoS 2 microcrystals. The amount of “Fe-sulphide” present in the catalyst was found to increase with increasing iron content. This “Fe-sulphide” might partly cover the “Fe Mo S” phase, thus causing a decrease in the promoting effect.

Influence of pH on the preparation of monometallic rhodium and platinum, and bimetallic Rhodium [sbnd]Platinum Catalysts supported on γ-Alumina

195PtNMR and Raman experiments indicated that H 2PtCl 6 adsorbed monomolecularly on the surface of alumina up to a loading of 1 μmol m −2 during pore volume impregnation. Above this limit crystalline H 2PtCl 6 was formed during the subsequent drying procedure. Adsorption experiments showed that RhCl 3 exhibited the same behaviour, with an even larger monomolecular coverage. The coverage of both metal complexes was dependent on the pH during adsorption and decreased with decreasing pH, due to a shift in the bonding equilibrium between the metal complexes in solution and the complexes adsorbed on the support surface. Because of the acidic properties of RhCl 3 and H 2PtCl 6, the amounts of rhodium and platinum adsorbed during co-adsorption were smaller than during adsorption of the separate metal complexes. The reduction of RhCl 3+H 2PtCl 6 supported on Al 2O 3 was governed by mobile rhodium atoms and small bimetallic clusters. Large metal salt crystals smothered the reduction process.

Influence of support on the availability of nickel in supported catalysts for hydrogen chemisorption and hydrogenation of benzene

Oxides such as SiO2, γ-Al2O3, TiO2(anatase and rutile), ZrO2 and MgO with different properties have been used as supports for loading nickel by the pore volume impregnation method. Catalysts were calcined in air at 723 K for 6 h before reduction at the same temperature. Surface area and acidity measurements, X-ray diffraction and hydrogen and oxygen adsorption measurements along with hydrogenation of benzene were used as tools for characterising the catalyst. A measure of the availability of nickel in the bulk and on the surface of the catalyst is given by the O2/H2 ratio. In a metal–support system there is always a possibility of an interaction. The reducibility of catalysts depends on the availability of nickel ions determined by the support properties and the extent and type of interaction, and follows the order Ni/SiO2 > Ni/TiO2. (R)≈ Ni/ZrO2≈ Ni/TiO2(A) > Ni/γ-Al2O3 Z.Gtc Ni/MgO. The benzene hydrogenation activity was maximum around 433 K and for Ni/TiO2(A) it occurred beyond 473 K. Easily reducible Ni/SiO2 showed the highest activity and difficult-to-reduce Ni/MgO showed no appreciable activity. The turnover number (TON) for benzene hydrogenation is dependent on the available metal area and on the crystallite size. A smooth correlation between TON and the dispersion (Smetal//S,B.E.T.) is observed.

Thermogravimetric study of the interactions of asphaltene with sulphided cobalt-molybdenum on alumina catalysts

A thermogravimetric study of the decomposition of a Safaniya asphaltene deposited on various catalysts is described. The objective was to discern the influence of various functions of the catalyst surface on the evolution of light hydrocarbons and the formation of residual coke. The asphaltene was deposited, by pore-volume impregnation, from a solution in xylene, on sulphided CoMo catalysts supported on pure or sodium- or fluorine-modified γ-Al 2O 3. The presence of a catalyst, except fluorine-modified alumina, always diminishes the weight loss compared with that observed with the pure asphaltenes. The acidity of the support favours cracking to light hydrocarbons. Cobalt and molybdenum sulphides increase coke formation in a N 2 atmosphere, whereas they favour decomposition to light products under H 2/H 2S.

Influence of asphaltene deposition on catalytic activity of cobalt molybdenum on alumina catalysts

A Safaniya asphaltene was deposited on various sulphided catalysts: a typical CoMo A1 20 3 , Mo A1 20 3 , Co A1 20 3 and A1 20 3. Various methods of deposition were investigated: deposition at 30 kg cm −2 and 200–300°C from a solution of asphaltene in xylene, simple physical mixture or pore volume impregnation at room temperature by a solution in xylene. The changes of activity were measured at 300 and 400°C, 30 kg cm −2, with a mixture of cyclohexane, cyclohexene and thiophene. Deposition modifies all catalytic activities, namely hydrogenation- dehydrogenation, desulphurization and isomerization of cyclohexene to methyl- cyclopentene. The results must be explained by both pore blockage and surface poisoning, especially poisoning of acid centres. Besides, a small hydrogenating activity of the products of asphaltene decomposition, presumably vanadium and/or nickel sulphide, is detected.

On the mechanism of Na+ regulation of active species of cobalt oxide supported on γ-alumina catalysts

The influence of Na+ cations, introduced into the support from different compounds, on the formation of cobalt species on γ-alumina surface has been studied. The monitoring of the Co3O4/CoAl2O4 critical ratio has been obtained using diffuse reflectance spectroscopy (DRS). Sodium cations were deposited on the carrier surface by dry impregnation with aqueous solutions of NaNO3, NaOH and CH3COONa as well as with a solution of CH3COONa in CH3COOH. The active phase was mounted on the doped supports by pore volume impregnation with aqueous Co(NO3)2·6H2O solutions. Sodium cations catalyze the solid transformation of Co3O4 into CoAl2O4. The extent of this transformation is nearly independent of the particular sodium compound used.

Effect of sodium on the CoMo/γ-Al2O3 system. Part 2.—Influence of sodium content and preparation methods on the state of dispersion and nature of molybdenum supported on γ-Al2O3

The effect of preparation method, calcination temperature and sodium content on the dispersion of molybdenum on the surface of γ-Al2O3, as well as on the kind of molybdenum species formed thereon, has been studied using diffuse reflectance spectroscopy (d.r.s), X-ray powder analysis (X.r.), X-ray photoelectron spectroscopy (X.p.s.), analytical electron microscopy (a.e.m.) and electron paramagnetic resonance (e.p.r.).Two series of specimens (each series containing 6 samples having various amounts of sodium) containing 12% MoO3 have been prepared by, respectively, wet and incipient wetness impregnations of sodium-doped γ-Al2O3 with ammonium paramolybdate aqueous solution.The adsorption of MoVIvia polymeric species, the presence of MoV after calcination at 300°C and the formation of small amounts of Al2(MoO4)3 after calcination at 500°C and above have been observed for a weakly-doped specimen prepared by pore volume impregnation. The formation of Na2MoO4 is observed only for high Na content, irrespective of the preparation method used.The dispersion of molybdenum, as measured by X.p.s., for calcination temperatures of 500°C, is virtually independent of the sodium content up to 3.6% Na; it decreases above this content. Calcining at 300°C leads to lower dispersion; sodium has no appreciable effect.Some mechanisms explaining the results are proposed.

Physico-chemical characterisation of impregnated and ion-exchanged silica-supported nickel oxide

X-ray analysis, reflectance spectroscopy, analytical electron microscopy and X.p.s. measurements have been used to investigate the influence of the preparation method on the dispersion and interaction of nickel oxide on silica. Two series of solids containing up to 10 wt % NiO were prepared, respectively, by pore volume impregnation and ion-exchange methods. It was found that impregnated samples are poorly dispersed and contain essentially bulk-like NiO crystallites or aggregates. Only in the sample with the lowest nickel content (2 wt % NiO) may the presence of a second nickel species be deduced. Conversely, ion-exchanged samples are well dispersed and give no evidence of the presence of NiO, but rather contain a surface layer of nickel hydrosilicate. The results were used to account for the dramatic difference in the reducibility of impregnated and ion-exchanged samples.