Formation of carbon nanotubes from the carbon monoxide disproportionation reaction over Co/Al2O3 and Co/SiO2 catalysts

The ammonia method has been successfully used for preparing thermostable and well dispersed alumina‐supported catalysts with a surface average size of cobalt particle D _{s= 5.7} nm. The disproportionation reaction of CO over this Co/Al₂O₃ catalyst and a similar Co/SiO₂ catalyst leads to the formation of carbon nanotubes demonstrating the same morphology. The amount of nanotubes over Co/Al₂O₃, however, is much larger than that obtained over Co/SiO₂, because of a faster ageing in the latter solid. Similar support effects have already been reported for other catalytic reactions involving carbon oxides. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of CO2 in the feed stream on the deactivation of Co/γ-Al2O3 Fischer–Tropsch catalyst

The influence of CO₂ on the deactivation of Co/γ-Al₂O₃ Fischer–Tropsch (FT) catalyst in CO hydrogenation has been investigated. The presence of CO₂ in the feed stream reveals a negative effect on catalyst stability and in the formation of heavy hydrocarbons. The CO₂ acts as a mild oxidizing agent on cobalt metal during Fischer–Tropsch synthesis. During FT synthesis on Co/γ-Al₂O₃ of 70 h, the CO conversion and C₅₊ selectivity in the presence of CO₂ decreased more significantly than in the absence of CO₂. CO₂ is found to be responsible for the partial oxidation of surface cobalt metal at FT synthesis environment with the co-existence of generated water.     

Non-oxidative methane transformations into higher hydrocarbons over bimetallic Pt–Co catalysts supported on Al2O3 and NaY

The methane conversion under non-oxidative conditions over Al₂O₃ and NaY supported cobalt, platinum and Pt–Co bimetallic catalysts in a flow system has been investigated. The two-step process was applied in the temperature range between 523 and 673 K and 1 bar pressure and the one-step process was carried out under the conditions of 1073 K and 10 bar pressure. Addition of platinum to NaY and alumina supported cobalt samples results in the formation of metallic Co particles and Pt–Co bimetallic particles. On bimetallic catalysts in the two-step process, the amount of C₂₊ products formed were higher than that on mono-metallic samples. The synergism shown by the bimetallic system can be explained by: (i) enhanced reducibility of cobalt, and (ii) the co-operation of two types of active components (Co facilitates the chain-growth of partially dehydrogenated species produced on Pt in Pt–Co bimetallic particles). The use of higher pressures and high temperature makes it possible to run the process to form primarily ethane (and ethylene) which is predicted from thermodynamic calculations. For NaY as support, significantly enhanced activity and C₂₊ selectivity are obtained compared with Al₂O₃ as support, which can be attributed to the structural differences of metal particles (location, dispersion and reducibility).     

NO2 formation and its effect on the selective catalytic reduction of NO over Co/ZSM-5

Catalytic performance of Co/ZSM-5 with different metal loadings and of HZSM-5 was compared in the NO + O₂, C₃H₈ + O₂, and NO + C₃H₈ + O₂ reactions. It was found that Co/ZSM-5 catalysts containing only isolated cobalt ions in cationic positions are inactive in NO₂ formation. To achieve appreciable NO conversion in the SCR process over these catalysts higher reaction temperatures are required. These results make it possible to suggest that NO₂ formation is not a prerequisite for the SCR of NO with hydrocarbons over Co/ZSM-5. With increasing Co loading, however, Co/ZSM-5 begins to exhibit activity in NO₂ formation. This is explained by the formation of cobalt oxide particles on the zeolite carrier, which are active in the NO₂ formation. Increase in NO₂ formation strongly enhances catalytic activity in SCR of NO at lower reaction temperatures. Comparison of the C₃H₈ conversion in the C₃H₈ + O₂ and C₃H₈ + O₂ + NO reactions provides evidence that NO₂ activates hydrocarbon molecules resulting in the formation of the reaction intermediates of the SCR process.On leave from N.D. Zelinskii Institute of Organic Chemistry, Leninskii Pr. 47, Moscow, Russia.     

Development of a multi-layered micro-reactor coated with Pt–Co/Al2O3 catalyst for preferential oxidation of CO

Pt–Co/Al₂O₃ catalysts were prepared with different Co/Pt weight ratios (0.3–1.8) and their performances for preferential oxidation of CO (PROX) were tested. The activity of the catalyst increased with Co/Pt weight ratio due to the increase of the area of active phase by interaction between Pt and Co species. The 13-layered micro-channel reactor was prepared by stacking the plates coated with Pt–Co/Al₂O₃ catalyst. The reactor was divided into three parts (inlet, middle, and outlet) to evaluate the performance of each part. Most of O₂ supplied was depleted at the inlet part and the temperature gradient of the reactor occurred due to the high exothermicity of oxidations of CO and hydrogen. In order to prevent hot spot and temperature gradient, the reactor with non-uniform distribution of the catalyst (partially coating the catalyst on the channels) was prepared. The prepared reactor showed uniform temperature distribution and exhibited excellent performance for PROX.     

Physico-Chemical Properties of Cobalt–Ruthenium (10% Co–0.5% Ru) Catalysts Supported on Binary Oxides 8.5%ZrO<Subscript>2</Subscript>/Support (SiO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, TiO<Subscript>2</Subscript>) for Fischer-Tropsch Synthesis

The promotion of Fischer-Tropsch catalysts 10%Co/Al₂O₃, 10%Co/SiO₂, 10%Co/TiO₂ by 0.5% Ru and the modification of supports by 8.5 wt% ZrO₂ have been studied. The following properties: catalyst specific surface area as well as reducibility and dispersion of metallic phase were studied by different techniques: BET, TPR, and H₂ chemisorption. The modification of supports by non-reducible ZrO₂, results in a decrease of cobalt oxide reduction on Al₂O₃ and TiO₂ but not on SiO₂ supports. Additionally the enhancement of cobalt dispersion was found for all catalysts with ZrO₂ modified supports. The impact of Ru promotion is likely due to the stabilization of applied supports, prevention or blockage of interaction between surface Co species and support and an increase in cobalt oxide reducibility to the catalytically active metallic cobalt phase.     

Promoting Effect of Pt Addition to V2O5/ZrO2 Catalyst on Reduction of NO by C3H6

The effect of Pt addition to a V₂O₅/ZrO₂ catalyst on the reduction of NO by C₃H₆ has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Pt loading promoted the catalytic activity remarkably. FTIR spectra of NO adsorbed on the catalysts doped with Pt show the presence of two different types of Pt sites, Pt oxide and Pt cluster, on the surface. The amount of these sites depends on Pt contents and the catalyst state. Pt atoms highly disperse on the surface as Pt oxide at low Pt content, being aggregated into Pt metal clusters by increasing Pt amount or reducing the catalysts. The spectral behavior of V=O bands on the surface also supports the formation of Pt clusters. It is concluded that Pt promotes the NO–C₃H₆ reaction through a reduction–oxidation cycle between its oxide and cluster form.     

The influence of an intermediate MoO3 layer on the solid state reaction of cobalt oxide withγ-Al2O3

In view of the importance for Co_xO_y,-MoO₃/-Al₂O₃ hydrodesulphurization (HDS) catalysts, the reactivity of cobalt oxide layers towards cobalt aluminate formation was investigated on both MoO₃-covered and bare -Al₂O₃ substrates. Co₃O₄/MoO₃/-Al₂O₃ and Co₃O₄/-Al₂O₃ systems were prepared by vapour-deposition of MoO₃ (12 × 10¹⁵ Mo atoms/cm²) and Co (400 × 10¹⁵ Co atoms/cm²) layers onto a -Al₂O₃ substrate, followed by oxidation of the Co layer to Co₃O₄. After annealing at 800°C for 40 h, the interfacial reaction to cobalt aluminate was assessed using Rutherford backscattering spectrometry. The presence of molybdenum oxide appeared to enhance cobalt aluminate formation. The Mo atoms, which spread out over the entire cobalt-containing layer, presumably caused a high defect density, which explains the observed higher reaction rate. The amount of MoO₃ was much too low to stabilize all cobalt atoms by cobalt molybdate formation.     

Reaction performance and characterization of Co/Al2O3 Fischer–Tropsch catalysts promoted with Pt, Pd and Ru

A series of noble metal (Pt, Ru or Pd) promoted Co/Al₂O₃ catalysts were prepared by sequential impregnation method. The catalysts were characterized by XRD, TPR, H₂-TPD and TPSR techniques, and their catalytic performance in Fischer–Tropsch synthesis was investigated in a fixed-bed reactor. The results of activity measurements show that the addition of small amounts of noble metal greatly improved the activity of the Co/Al₂O₃ catalyst. TPR experimental results demonstrate that hydrogen spillover from the noble metal to cobalt oxide clusters facilitated the reduction of cobalt oxide and, thus significantly increased the reducibility of Co/Al₂O₃ catalyst. The presence of noble metal increased the amount of chemisorbed hydrogen and weakened the bond strength of Co–H. TPSR results indicate that CO was adsorbed in a more reactive state on the promoted catalysts.     

Partial Oxidation Reforming Catalyst for Fuel Cell-Powered Vehicles Applications

Transition metal oxide formulations for the partial oxidation (POX) reforming of isooctane were investigated for an onboard gasoline fuel processor. Ni/M/MgO/Al₂O₃ systems are more active than a commercial ICI catalyst. These catalysts showed better sulfur tolerance over the commercial ICI catalyst in the POX reforming of isooctane containing sulfur (Cs = 100 ppm). There was no apparent deactivation or modification of structure during 770h onstream. It was found that Ni/(Fe,Co)/MgO/Al₂O₃ catalyst is a promising candidate as POX reforming catalyst for gasoline fuel processor applications.     

乙酰丙酮钴(Ⅱ)对甲苯液相空气氧化反应的催化性能

以乙酰丙酮钴(Co(acac)₂)为催化剂,在1 L高压搅拌反应釜中研究了其对甲苯液相空气氧化反应的催化性能和反应产物分布,考察了催化剂用量对甲苯转化率和苯甲酸收率的影响,并考察了不同温度下不同催化剂用量时的催化剂寿命。结果表明,Co(acac)₂催化甲苯液相氧化是平行连串的复杂反应,Co(acac)₂的催化活性存在"催化-抑制转换"现象,适宜的催化剂用量为0.0044%(质量分数);催化剂的寿命随反应温度变化存在一个最大值,165℃时催化剂寿命最长,反应温度较低(<165℃)时催化剂更容易失活;在165℃、Co(acac)₂用量为0.0044%时,反应4 h,甲苯转化率为19%,苯甲酸收率为80%;与醋酸钴、环烷酸钴等钴盐催化剂相比,Co(acac)₂催化剂具有用量少、催化活性时间长的优点,可有效地减缓钴盐结垢现象,Co(acac)₂催化剂对甲苯液相空气氧化反应具有良好的催化性能。     

Ambient temperature oxidation of carbon monoxide using a Cu2Ag2O3 catalyst

The mixed copper–silver oxide, Cu₂Ag₂O₃, has been prepared by co-precipitation and tested for ambient temperature carbon monoxide oxidation. The catalyst demonstrated appreciable low temperature oxidation activity and the catalyst aged for 4 h was the most active. Carbon monoxide conversion increased with time-on-stream, reaching steady state after ca. 1000 min. Acomparison of the catalytic activity has been made with a representative sample of a high activity hopcalite, mixed copper/manganese oxide catalyst. On the basis of CO oxidation rate data corrected for the effect of catalyst surface area the Cu₂Ag₂O₃, aged for 4 h was at least as active as the hopcalite.     

Preparation and characterization of NiO/MgO/Al2O3 supported CoPcS catalyst and its application to mercaptan oxidation

MgO/Al₂O₃ and NiO/MgO/Al₂O₃ solid bases were prepared by mixing method. The samples were characterized by X-ray diffraction (XRD), CO₂ temperature-programmed desorption (CO₂-TPD) and surface area measurements. After supported sulfonated cobalt phthalocyanine (CoPcS) the catalytic performance of these catalysts was evaluated in the mercaptan oxidation reaction. The effect of Mg/Al mole ratios on activity, crystal structure, basicity and stability in air was discussed. And the mechanism of the effect of NiO was identified. Results show that the base amount of MgO/Al₂O₃ increases with increasing Mg/Al mole ratio and catalyst with high Mg/Al mole ratio has a higher initial activity. NiO/MgO/Al₂O₃–CoPcS shows a higher initial activity and a much longer lifetime than MgO/Al₂O₃–CoPcS. When nickel oxide is doped into the MgO/Al₂O₃ support more crystal defects are generated, which increases the amount and types of basic sites.     

Bi2O3 modified cobalt hydroxide as an electrode for alkaline batteries

Manganese dioxide electrode shows reversible charge storage capacity, if the charge-discharge process is limited to 0.3e⁻ exchange. Addition of small amount of Bi₂O₃ to manganese dioxide induces reversibility with an exchange of 2e⁻/Mn. Nickel hydroxide is known to reversibly exchange 1e⁻. In spite of isostructural relationship between the cobalt hydroxide, nickel hydroxide and manganese dioxide, cobalt hydroxide does not show any electrochemical activity. Bi₂O₃ modified cobalt hydroxide electrodes exchanges 0.3-0.5e⁻/Co during the charge discharge process. The oxidation-reduction process in cobalt hydroxide and Bi₂O₃ modified cobalt hydroxide electrodes were monitored using the PXRD patterns.     

Highly hydrogen-deficient hydrocarbon species for the CO2-reforming of CH4 on Co/Al2O3 catalyst

The dynamics of produced CO and H₂, measured by pulse surface reaction rate analysis (PSRA), revealed that the intermediate hydrocarbon species for the CO₂-reforming of CH₄ was highly hydrogen-deficient (CH_0.75) on supported Co/Al₂O₃ catalyst. It was also found that the species was more reactive than the less hydrogen-deficient one (CH_2.4) on Ni/Al₂O₃ catalyst.     

Perovskite-type oxide ACo0.8Bi0.2O2.87 (A=La0.8Ba0.2): a catalyst for low-temperature CO oxidation

Perovskite-type oxide ACo_0.8Bi_0.2O_2.87 (A=La_0.8Ba_0.2) has been investigated as a catalyst for the oxidation of carbon monoxide. X-ray diffraction results revealed that the catalyst is single-phase and cubic in structure. The results of chemical analysis indicated that in ACo_0.8Bi_0.2O_2.87, bismuth is pentavalent whereas cobalt is trivalent as well as bivalent; in La_0.8Ba_0.2CoO_2.94, cobalt ions exist as Co³⁺ and Co⁴⁺. The substitution of Bi for Co enhanced the catalytic activity of the perovskite-type oxide significantly. Over the Bi-incorporated catalyst, at equal space velocities and with the rise in CO/O₂ molar ratio, the temperature for 100% CO conversion shifted to a higher range; at a typical space velocity of 30000 h^–1 and a CO/O₂ molar ratio of 0.67/1.00, 100% CO conversion was observed at 250°C. Over ACo_0.8Bi_0.2O_2.87, at equal CO/O₂ molar ratio, the temperature for 100% CO conversion decreased with a drop in space velocity; the lowest being 190°C at a space velocity of 5000 h^–1. The result of O₂-TPD study illustrated that the presence of Bi ions caused the lattice oxygen of La_0.8Ba_0.2CoO_3– to desorb at a lower temperature. The results of TPR, ¹⁸O/¹⁶O isotopic exchange, and CO-pulsing investigations demonstrated that the lattice oxygen of the Bi-doped catalyst is highly mobile.     

Ru-Promoted CrO x /Al2O3 Catalyst for the Low-Temperature Oxidative Decomposition of Trichloroethylene in Air

A series of Ru-promoted CrO _x /Al₂O₃ as catalysts for the low-temperature oxidative decomposition of trichloroethylene (TCE) were characterized and evaluated in comparison with an unpromoted CrO _x /Al₂O₃ catalyst. Catalyst characterization was conducted by surface area measurement, X-ray diffraction and X-ray photoelectron spectroscopy. Catalyst performance in the TCE decomposition reaction was evaluated with respect to the initial catalytic activity, the rate of catalyst deactivation, and the product concentrations of CO and Cl₂ under dry or wet air conditions. The presence of a small amount of Ru, as much as 0.4 wt% in a CrO _x /Al₂O₃ catalyst, brought about several beneficial effects on the catalytic reaction performance. As compared with the unpromoted CrO _x /Al₂O₃, this Ru-promoted CrO _x /Al₂O₃ catalyst showed enhanced catalytic activity (249 versus 264 °C in terms of temperature at which 50% of TCE conversion occurred), a reduced concentration of CO (180 versus 325 ppm) in the product, and a decreased propensity to deactivation. Performance improvements of the Ru-promoted CrO _x /Al₂O₃ catalyst were thought to originate from its enhanced oxidation activity due to the coexisting highly-dispersed Ru oxides rendering less active Cr(III) to more active Cr(VI), and facilitating the process of supplying activated oxygen for the reaction system.     

Hydrotreating of Heavy Gas Oil Derived from Athabasca Bitumen Over Co–Mo/γ-Al2O3 Catalyst Prepared by Sonochemical Method

Co–Mo/γ-Al₂O₃ oxide containing 9.8 wt% Mo and 2.9 wt% Co was prepared by high-intensity ultrasonic irradiation of Mo(CO)₆, Co₂(CO)₈, and γ-Al₂O₃ in decahydronapthalene under air flow. The oxidic Co–Mo catalyst thus formed was characterized by elemental analysis, BET N₂ adsorption and XRD. The surface sites on the sulfided Co–Mo/γ-Al₂O₃ catalyst were characterized by infrared spectroscopy of CO adsorption. Hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities were evaluated for heavy gas oil derived from Athabasca bitumen in a trickle bed reaction system using the following conditions: temperatures ranging from 370 to 400 °C, a pressure of 8.8 MPa, a liquid hourly space velocity of 1 h⁻¹, and a H₂/feed ratio of 600 ml/ml. The dispersion, nature of active sites and hydrotreating activity of this catalyst were compared with the conventionally prepared Co–Mo/γ-Al₂O₃ catalyst containing similar wt% of Mo and Co. The Co–Mo catalyst prepared by sonochemical method has higher HDN and HDS rate constants than the conventional catalyst due to an improved dispersion of MoS₂.     

Preparation of MoO3/Al2O3 Catalysts with Sharp Eggshell Mo Distribution by Slurry Impregnation

MoO₃/Al₂O₃ catalysts with eggshell Mo concentration profiles were prepared by reaction of Al₂O₃ extrudates or balls with slurry of MoO₃ in water. The Mo concentration wave penetrating Al₂O₃ particles during this slurry impregnation was almost rectangular. Its height was close to the filled monolayer loading. The thickness of the shell was regulated either by impregnation time or by the MoO₃ amount in the slurry. The hydrodesulfurization activity of Mo species deposited by slurry impregnation was about the same or better (depending on the Al₂O₃ used) as in industrial MoO₃/Al₂O₃ catalyst.     

Electrogeneration of Hydrogen Peroxide in Acid Medium using Pyrolyzed Cobalt-based Catalysts: Influence of the Cobalt Content on the Electrode Performance

Cobalt tetramethoxyphenyl porphyrin (CoTMPP) adsorbed on a high area carbon support (Vulcan XC72-R) and heat-treated at 900 °C under inert atmosphere was studied as electrocatalyst for the reduction of O₂ to H₂O₂ in acid medium. Experiments performed on rotating ring-disc electrode (RRDE) and gas diffusion electrode (GDE) show that the catalyst performance depends on the cobalt loading, going through a maximum at 0.2 wt. % Co. For higher cobalt loadings, a growing part of oxygen is reduced into water, decreasing therefore the selectivity of the catalyst. These results are interpreted in terms of a further reduction of H₂O₂ on Co-based catalytic sites before leaving the catalytic layer. For a GDE polarized at −150 mV vs. saturated calomel electrode (SCE) and loaded with 0.9 μg cm⁻² of 0.2 wt. % Co-based catalyst, a H₂O₂ production rate of 300 μmol h⁻¹ cm⁻² was obtained which is five times higher than the H₂O₂ production rate measured with Vulcan. In these conditions, the selectivity of the Co-based catalyst for H₂O₂ production is 92%. The good agreement observed between RRDE and GDE results confirms the relevance of using RRDE experiment for screening these non-precious metal catalysts for further GDE applications.