Preparation and catalytic performance of Co3O4 catalysts for low-temperature CO oxidation

Without use of any surfactant or oxidant, a series of Co₃O₄ catalysts have been prepared from cobalt nitrate aqueous solution via a very simple liquid-precipitation method with ammonium acid carbonate followed by calcination at various temperatures. The catalytic performance of the Co₃O₄ for CO oxidation has been studied with a continuous flowing laboratory microreactor system. The results show that the CO conversion of all the samples can reach 100% at ambient temperature. The catalyst calcined at 300 °C is able to maintain its activity for CO complete oxidation more than 500 min at 25 °C and about 240 min even at −78 °C. High reaction temperature results in a high catalytic stability, while the catalytic stability decreases with further increasing the reaction temperature. Characterizations with X-ray powder diffraction and transmission electron microscopy suggest that all the samples exist as a pure Co₃O₄ phase with the spinel structure, the samples are apt to aggregate and the specific surface area gradually decreases with increasing the calcination temperature, which directly leads to the decrease of catalytic stability. Furthermore, the amount of active oxygen species measured by CO titration experiments appears to be critical for catalytic performance.     

The catalytic removal of CO and NO over Co-Pt(Pd, Rh)/γ-Al2O3 catalysts and their structural characterizations

A series of Co-Pt(Pd, Rh)/γ- Al₂O₃ catalysts were prepared by successive wetness impregnation. The catalytic activities for CO oxidation, NO decomposition and NO selective catalytic reduction (SCR) by C₂H₄ over the samples calcined at 500°C and reduced at 450°C were determined. The activities of the samples calcined at 750°C and reduced at 450°C for NO selective catalytic reduction (SCR) by C₂H₄ were also determined. All the samples were characterized by XRD, XPS, XANES, EXAFS, TPR, TPO and TPD techniques. The results of activity measurements show that the presence of noble metals greatly enhances the activity of Co/γ-Al₂O₃ for CO or C₂H₄ oxidation. For NO decomposition, the H₂-reduced Co-Pt(Pd, Rh)/γ- Al₂O₃ catalysts exhibit very high activities during the initial period of catalytic reaction, but with the increase of reaction time, the activities decrease obviously because of the oxidation of surface cobalt phase. For NO selective reduction by C₂H₄, the reduced samples are oxidized more quickly by the excess oxygen in reaction gas. The oxidized samples possess very low activities for NO selective reduction. The results of XRD, XPS and EXAFS indicate that all the cobalt in Co-Pt(Pd, Rh)/γ-Al₂O₃ has been reduced to zero valence during reduction by H₂ at 450°C, but in Co/γ-Al₂O₃ only a part of the cobalt has been reduced to zero valence, the rest exists as CoAl₂O₄-like spinel which is difficult to reduce. For the samples calcined at 750°C, the cobalt exists as CoAl₂O₄ which cannot be reduced by H₂ at 450°C and possesses better activities for NO selective reduction. The results of XANES spectra show that the cobalt in Co/γ- Al₂O₃ has lower coordination symmetry than that in Co-Pt(Pd, Rh)/γ-Al₂O₃. This difference mainly results from the distorting tetrahedrally- coordinated Co²⁺ ions which have lower coordination symmetry than Co⁰ in the catalysts. The coordination number for the Co-Co shell from EXAFS has shown that the cobalt phase is highly dispersed on Co-Pt(Pd, Rh)/γ- Al₂O₃ catalysts. The TPR results indicate that the addition of noble metals to Co/γ- Al₂O₃ makes the TPR peaks shift to lower temperatures, which implies the spillover of hydrogen species from noble metals to cobalt oxides. The oxygen spillover from noble metals to cobalt is also inferred from the shift of TPO peaks to lower temperatures and the increased amount of desorbed oxygen from TPD. For CO oxidation, the Co⁰ is the main active phase. For NO decomposition and selective reduction, Co⁰ is also catalytically active, but it can be oxidized into Co₃O₄ by oxygen at high reaction temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of Fischer–Tropsch Cobalt-Based Catalytic Systems (Co/SiO<Subscript>2</Subscript> and Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) by X-ray Diffraction and Magnetic Measurements

Results of the characterization of six Co-based Fischer–Tropsch (FT) catalysts, with 15% Co loading and supported on SiO₂ and Al₂O₃, are presented. Room temperature X-ray diffraction (XRD), temperature and magnetic field (H) variation of the magnetization (M), and low-temperature (5 K) electron magnetic resonance (EMR) are used for determining the electronic states (Co⁰, CoO, Co₃O₄, Co²⁺) of cobalt. Performance of these catalysts for FT synthesis is tested at reaction temperature of 240 °C and pressure of 20 bars. Under these conditions, 15% Co/SiO₂ catalysts yield higher CO and syngas conversions with higher methane selectivity than 15% Co/Al₂O₃ catalysts. Conversely the Al₂O₃ supported catalysts gave much higher selectivity towards olefins than Co/SiO₂. These results yield the correlation that the presence of Co₃O₄ yield higher methane selectivity whereas the presence of Co²⁺ species yields lower methane selectivity but higher olefin selectivity. The activities and selectivities are found to be stable for 55 h on-stream.     

Active species of copper chromite catalyst in C–O hydrogenolysis of 5-methylfurfuryl alcohol

The active sites of copper chromite catalyst, CuCr₂O₄·CuO, were investigated for the condensed-phase hydrogenolysis of 5-methylfurfuryl alcohol to 2,5-dimethylfuran at 220 °C. The bulk and surface features of the catalyst were characterized by XRD, H₂-TPR, N₂ adsorption, CO chemisorption, N₂O titration, NH₃-TPD, XPS, and AES. Maxima of both of the potential active species, Cu⁰ and Cu⁺, occurred after reduction in H₂ at 300 °C compared to 240 and 360 °C. These Cu⁰ and Cu⁺ maxima also coincided with the highest specific rate of reaction based on the surface area of the reduced catalyst. The trends of Cu⁰ and Cu⁺ observed by N₂O titration and CO chemisorption were also observed qualitatively by AES. Correlations between activity and the possible active species suggested that Cu⁰ was primarily responsible for the activity of the catalysts.     

Quantification and redox property of the oxygen-bridged Cu<Superscript>2+</Superscript> dimers as the active sites for the NO decomposition over Cu-ZSM-5 catalysts

For a range of Cu-ZSM-5 catalysts with different Cu-exchange levels on the two kinds of ZSM-5 with different Si/A1 ratios, temperature programmed reduction using CO (CO-TPR) followed by H₂ (H₂-TPR), and temperature programmed desorption of oxygen (O₂-TPD) were conducted using an online mass spectrometer to characterize and quantify the copper species on the catalysts in the calcined state. Copper species on the ZSM-5 were quantitatively characterized as Cu²⁺, (Cu-O-Cu)²⁺ and CuO after calcination in oxygen environment. The N₂ formation activities of the catalysts in the decomposition of NO were well correlated with the quantified catalytic amounts of the Cu²⁺ ions involved in the Cu-dimers, (Cu-O-Cu)²⁺. The mol fraction of the Cu ions present as the Cu-dimers increased at the sacrifice of the isolated Cu²⁺ with increasing Cu ion exchange level, suggesting that the species could be formed between the two Cu²⁺ in close proximity. Oxygen that could be thermally desorbed from the oxidized catalysts in the O₂-TPD was responsible for the reduction of the Cu-dimers. It was concluded that the decomposition of NO over Cu-ZSM-5 catalyst proceeded by the redox of (Cu-O-Cu)²⁺, as active centers. With the temperature programmed surface reaction using N₂O or NO over an oxidized catalyst sample as well as the O₂-TPD, it was possible to estimate the change of the oxidation state of the Cu ions engaged in the Cu-dimers.     

Dependence of n-Butane Activation on Active Site of Vanadium Phosphate Catalysts

The nature and the role of oxygen species and vanadium oxidation states on the activation of n-butane for selective oxidation to maleic anhydride were investigated. Bi–Fe doped and undoped vanadium phosphate catalysts were used a model catalyst. XRD revealed that Bi–Fe mixture dopants led to formation of α_II-VOPO₄ phase together with (VO)₂P₂O₇ as a dominant phase when the materials were heated in n-butane/air to form the final catalysts. TPR analysis showed that the reduction behaviour of Bi–Fe doped catalysts was dominated by the reduction peak assigned to the reduction of V⁵⁺ species as compared to the undoped catalyst, which gave the reduction of V⁴⁺ as the major feature. An excess of the oxygen species (O^2?) associated with V⁵⁺ in Bi–Fe doped catalysts improved the maleic anhydride selectivity but significantly lowering the rate of n-butane conversion. The reactive pairing of V⁴⁺-O^? was shown to be the centre for n-butane activation. It is proposed that the availability and appearance of active oxygen species (O^?) on the surface of vanadium phosphate catalyst is the rate determining step of the overall reaction.     

Enhancement of hydrogen spillover by surface labile oxygen species on oxidized Pt/TiO2 catalyst

TPD, H₂-O₂ titration and TPR techniques have been used to study the effect of the surface oxygen species on hydrogen adsorption in an oxidized Pt/TiO₂ catalyst system. Oxygen desorption peaks in the temperature range of 610–730 K were observed in the O₂-TPD profiles of the Pt/TiO₂ samples oxidized in oxygen at temperatures 573, 673 and 773 K, respectively. They reveal that labile oxygen species were formed on the surfaces of these oxidized catalysts. Much more hydrogen spillover on the oxidized Pt/TiO₂ catalysts was observed at room temperature using H2-O₂ titration. The results from TPR and H₂-TPD experiments further support the proposal that the existence of labile oxygen species enhances hydrogen spillover in the system studied.     

Cobalt and Copper Composite Oxides as Efficient Catalysts for Preferential Oxidation of CO in H2-Rich Stream

A series of Co–Cu composite oxides with different Co/Cu atomic ratios were prepared by a co-precipitation method. XRD, N₂ sorption, TEM, XPS, H₂-TPR, CO-TPR, CO-TPD and O₂-TPD were used to characterize the structure and redox properties of the composite oxides. Only spinel structure of Co₃O₄ phase was confirmed for the Co–Cu composite oxides with Co/Cu ratios of 4/1 and 2/1, but the particle sizes of these composite oxides decreased evidently compared with Co₃O₄. These composite oxides could be reduced at lower temperatures than Co₃O₄ by either H₂ or CO. CO and O₂ adsorption amounts over the composite oxides were significantly higher than those over Co₃O₄. These results indicated a strong interaction between cobalt and copper species in the composite samples, possibly suggesting the formation of Cu _x Co_3?x O₄ solid solution. For the preferential oxidation of CO in a H₂-rich stream, the Co–Cu composite oxides (Co/Cu = 4/1–1/1) showed distinctly higher catalytic activities than both Co₃O₄ and CuO, and the formation of Cu _x Co_3?x O₄ solid solution was proposed to contribute to the high catalytic activity of the composite catalysts. The Co–Cu composite oxide was found to exhibit higher catalytic activity than several other Co₃O₄-based binary oxides including Co–Ce, Co–Ni, Co–Fe and Co–Zn oxides.     

Catalytic removal of methane over thermal-proof nanostructured catalysts for CNG engines

Five spinel-type catalysts AB₂O₄ (Co_0.8Cr₂O₄, CoCr₂O₄, MnCr₂O₄, MgFe₂O₄ and CoFe₂O₄) were prepared and characterized by XRD, BET and FESEM techniques. The activity of these catalysts towards the combustion of methane was evaluated in a Temperature Programmed Combustion (TPC) apparatus. The half conversion temperature of methane over the Co_0.8Cr₂O₄ catalyst was 369 °C with a W/F = 0.12 g s/cm³. On the basis of Temperature Programmed Desorption (TPD) of oxygen as well as of catalytic combustion runs, the prevalent activity of the Co_0.8Cr₂O₄ catalyst could be explained by its higher capability to deliver suprafacial chemisorbed oxygen species. This catalyst, promoted by the presence of 1 wt% of Pd, deposited by wet impregnation, was lined on cordierite monoliths and then tested in a lab-scale test rig. The combination of Pd and Co_0.8Cr₂O₄ catalysts enables half methane conversion at 340 °C (GHSV = 10,000 h⁻¹), a performance similar to that of conventional 4 wt% Pd-γ Al₂O₃ catalysts but guaranteed with just a four-fold lower amount of noble metal. Both the catalysts in powder and the monolith hosting the Co_0.8Cr₂O₄ + 1 wt% Pd catalyst, submitted to a thermal ageing treatment in air at 700 °C for 12 h, displayed a negligible deactivation.     

Fabricating an oxygen-vacancy-rich urchin-like Co3O4 nanocatalyst to boost peroxymonosulfate activation to degrade high-concentration crystal violet

Due to the in-situ generation of reactive oxygen species (ROS), sulfate radical-based advanced oxidation processes (SR-AOPs) have emerged for the oxidative degradation of organic contaminants. Developing highly efficient heterogeneous catalysts is of great importance for SR-AOPs. In this work, an urchin-like Co₃O₄ nanocatalyst with oxygen vacancies (V_O) was elaborately fabricated and employed for enhanced peroxymonosulfate (PMS) activation to degrade the high-concentration active dye crystal violet (CV). The obtained sample was characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and N₂ adsorption/desorption isotherms. Characterization results indicated that this unique V_O-rich urchin-like Co₃O₄ nanocatalyst was endowed with a larger surface area and abundant reactive sites for PMS adsorption and activation. The experimental results of CV degradation showed that nearly complete removal of 100 mg L^?1 CV could be realized within 30 min of reaction time under neutral conditions at room temperature, and the degradation process followed retarded-first-order kinetics. Electron paramagnetic resonance (EPR) spectra accompanied by quenching experiments of radicals demonstrated that the contribution of ROS to CV degradation followed this sequence: ¹O₂ > ?OH > SO₄^?- > O₂^?-. The degradation pathways of CV were proposed by a combination of density functional theory (DFT) calculations along with frontier orbit theory while the toxicity of intermediate products was evaluated by quantitative structure-activity relationship (QSAR) prediction.     

The Nature of Active Sites of Co/Al2O3 for the Selective Catalytic Reduction of NO with C2H4

The effects of Co loading and calcination temperatures on the catalytic activity of Co/Al₂O₃ for selective catalytic reduction (SCR) of NO with ethylene in excess oxygen were investigated. Co/Al₂O₃ showed high and low activities when calcined at high (800 °C) and low (350 °C) temperatures, respectively. The formation and dispersion of cobalt species for catalysts calcined at 350 and 800 °C as well as for Al₂O₃ were studied by XRD, UV–vis and FTIR spectra. Combined with DRIFTS results of ad-species and reaction experiments, it allowed us to correlate the catalytic activity with active sites of Co/Al₂O₃, and the catalytic functions of active cobalt species and support were clarified. Co₃O₄ species contributed to the oxidation of NO to various nitrates and of C₂H₄ to reactive formate species, even in the absence of O₂, whereas the side reaction of ethylene combustion occurred simultaneously when excess oxygen was present. Tetrahedral Co²⁺ ions in CoAl₂O₄, which acted as the active sites, were responsible for the reaction between formate and nitrate species to form organic nitro compound.     

In situ FTIR Study of Cobalt Oxides for the Oxidation of Carbon Monoxide

A high-valance cobalt oxide, CoO _x , was prepared from cobalt nitrate aqueous solution through precipitation with sodium hydroxide and oxidation by hydrogen peroxide. Further, other pure cobalt oxide species were refined from the CoO _x by temperature-programmed reduction (TPR) to 170, 230 and 300 °C. They were characterized by TPR and X-ray diffraction (XRD). Adsorption of CO and the co-adsorption of CO/O₂ over the cobalt oxides were further tested by in situ FTIR. It was shown that Co₃O₄ is quite active for the oxidation of CO at room temperature in the presence of oxygen, leading to the formation of CO₂. The variation in the oxidation of CO was interpreted with a mechanism involving two kinds of oxygen species, i.e., *-O₂ on the CoO _x surface and *-O_L on the surface of Co₃O₄ spinel structure.     

Ethanol Steam Reforming on Co/CeO2: The Effect of ZnO Promoter

A series of ZnO promoted Co/CeO₂ catalysts were synthesized and characterized using XRD, TEM, H₂-TPR, CO chemisorption, O₂-TPO, IR-Py, and CO₂-TPD. The effects of ZnO on the catalytic performances of Co/CeO₂ were studied in ethanol steam reforming. It was found that the addition of ZnO facilitated the oxidation of Co⁰ via enhanced oxygen mobility of the CeO₂ support which decreased the activity of Co/CeO₂ in C–C bond cleavage of ethanol. 3 wt% ZnO promoted Co/CeO₂ exhibited minimum CO and CH₄ selectivity and maximum CO₂ selectivity. This resulted from the combined effects of the following factors with increasing ZnO loading: (1) enhanced oxygen mobility of CeO₂ facilitated the oxidation of CH _x and CO to form CO₂; (2) increased ZnO coverage on CeO₂ surface reduced the interaction between CH _x /CO and Co/CeO₂; and (3) suppressed CO adsorption on Co⁰ reduced CO oxidation rate to form CO₂. In addition, the addition of ZnO also modified the surface acidity and basicity of CeO₂, which consequently affected the C₂–C₄ product distributions.     

NO oxidation over supported cobalt oxide catalysts

NO oxidation was conducted over cobalt oxides supported on various supports such as SiO₂, ZrO₂, TiO₂, and CeO₂. The N₂ physisorption, an inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), NO chemisorptions, the temperature-programmed desorption (TPD) with a mass spectroscopy after NO or CO chemisorptions were conducted to characterize catalysts. Among tested catalysts, Co₃O₄ supported on ceria with a high surface area showed the highest catalytic activity. This catalyst showed superior catalytic activity to unsupported Co₃O₄ with a high surface area and 1 wt% Pt/γ-Al₂O₃. For ceria-supported Co₃O₄, the catalytic activity, the NO uptake at 298 K and the dispersion of Co₃O₄ increased with increasing the surface area of CeO₂. The active participation of the lattice oxygen in NO oxidation could not be observed. On the other hand, the lattice oxygen participated in the CO oxidation over the same catalyst. The deactivation was observed over Co₃O₄/CeO₂ and 1 wt% Pt/γ-Al₂O₃ in the presence of SO₂ in a feed. 1 wt% Pt/γ-Al₂O₃ was deactivated by SO₂ more rapidly compared with Co₃O₄/CeO₂.     

Higher Oxidation State Responsible for Ozone Decomposition at Room Temperature over Manganese and Cobalt Oxides: Effect of Calcination Temperature

The heterogeneous catalytic decomposition of ozone was investigated over unsupported manganese and cobalt oxide at room temperature. All catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption (Brunauer–Emmet–Teller method), H₂-temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic activity test indicated that these oxides had a good activity on ozone conversion meanwhile the catalysts remained highly active over time under reaction conditions. The treated temperature of the catalyst had a significant impact on the performance of ozone abatement and the samples treated at lower temperature showed higher activity. The surface area decreased obviously when developing the calcination temperature and H₂-TPR results demonstrated that much higher oxidation state of metal ions and active oxygen species were maintained on the surface under low treated temperature. XPS analysis showed that there were higher oxidation states of metal ions (Mn⁴⁺ and Co³⁺) and adsorbed oxygen species on the surface of catalysts treated at lower temperature, both of which play a significant role in ozone decomposition. However, the activity of manganese oxide was higher than that of cobalt oxide and the possible reason for this phenomenon was discussed.     

Higher alcohol synthesis from syngas over KCoMoP catalysts

Carbon modified K_xCo_0.75MoP (0 ≤ x ≤ 1.5) catalysts were prepared from a sol–gel method using citric acid as a complexant. The catalysts were evaluated with CO hydrogenation and characterized by XRD, XPS and CO₂-TPD techniques. Results show that the addition of cobalt accelerates the dispersion of catalytic components in phosphide catalysts while the participation of potassium in phosphide catalysts enhances the interaction between MoP and CoMoP and facilitates the rearrangement of electron density in different Mo species. In K₁Co_0.75MoP, a large number of Mo^4 + species resulted in high selectivity to C_2 + higher alcohol.     

Influence of Mg Addition on the Catalytic Activity of Alumina Supported Ag for C3H6-SCR of NO

The influence of different magnesium (Mg) weight percentages (1, 2.5, 5, 7.5 and 10) over silver (3 wt%) impregnated alumina (SA) catalyst was investigated for the reduction of NO by C₃H₆. Mg doped SA catalysts were prepared by conventional impregnation method and characterized by XRD, BET-SA, ICP-MS, XPS, SEM, UV-DRS, H₂-TPR and O₂-TPD. The existence of MgO and MgAl₂O₄ phases on Mg doped SA catalysts were observed from XRD and XPS analyses. Existence of high percentage MgAl₂O₄ phase on 5% Mg doped SA catalyst (Mg (5) SA) enhances the dispersion and stabilization of silver phases (Ag₂O). Mg (5) SA catalyst shows a 51% of high selectivity (NO to N₂) in presence of SO₂ (80 ppm) at low temperatures (350 °C) and maintained high selectivity’s with a wide temperature window (350–500 °C). An optimal high surface availability of Ag⁰ and Ag⁺ species were observed from XPS analysis over Mg (5) SA catalyst. H₂-TPR analysis shows high temperature reduction peak over Mg (5) SA compared to SA catalyst. XPS analysis confirms the high percent availability of MgAl₂O₄ species over Mg (5) SA catalyst. DRIFTS study reveals the molecular evidences for the evolution of enolic species during NO reduction over the highly active Mg (5) SA catalyst at low temperatures. It also confirms further transformation of enolic species into –NCO species with NO + O₂ and finally into N₂ and CO₂.     

Reaction mechanism of NO decomposition over alkali metal-doped cobalt oxide catalysts

The kinetics of NO decomposition were investigated over alkali metal-doped Co₃O₄ catalysts. For all the alkali metal-doped Co₃O₄ catalysts tested, the presence of O₂ caused a decrease in the N₂ formation rate with reaction orders between −0.26 and −0.40. The reaction orders with respect to NO were between 1.21 and 1.47, which are higher than unity, suggesting that NO decomposition proceeds via a bimolecular reaction. The observation by in situ Fourier transform infrared (FT-IR) spectroscopy confirmed the presence of nitrite (NO₂⁻) species on the surface under NO decomposition conditions. Isotopic transient kinetic analysis performed using ¹⁴NO and ¹⁵NO revealed that a surface-adsorbed species, probably NO₂⁻, serves as an intermediate during NO decomposition. We proposed a reaction mechanism in which the reaction is initiated by NO adsorption onto alkali metals to form NO₂⁻ species, which migrates to the interface between the alkali metals and Co₃O₄, the active sites, and then react with the adsorbed NO species to form N₂.     

Hydrocracking of vegetable oil on boron-containing catalysts: Effect of the nature and content of a hydrogenation component

Catalysts based on metals (Pt, Pd) and metal oxides (NiO, Co₃O₄, MoO₃, WO₃), supported on the surface of borate-containing aluminum oxide (B₂O₃–Al₂O₃), in the hydrocracking of sunflower oil at a temperature of 400°C, a pressure 4.0 MPa and a mass hourly space velocity MHSV 5.0 h^–1 are compared. H₂ TPR and IR spectroscopy of adsorbed CO and ESDR show that the hydrogenation catalyst components are Pt⁰ and Pd⁰, a mixture of Ni²⁺ + Ni⁰, Co²⁺ + Co⁰, or a mixture of the highest and partially reduced oxides of Mo and W. It is established that catalysts containing Pt, Pd, NiO and Co₃O₄, ensure complete oil hydrodeoxygenation. The main oxygen removal reactions in Ptand Pd-systems are decarboxylation and hydrodecarbonylation. For catalysts with NiO and Co₃O₄, characteristic reactions are reduction and methanation. The highest yield of the diesel fraction was obtained on Pt/B₂O₃-Al₂O₃ catalysts with metal contents of 0.3–1.0 wt %. Along with n-alkanes, the diesel fractions obtained on these catalysts include cycloalkanes and iso-alkanes (up to around 40 wt %) and aromatic hydrocarbons present in trace amounts. Hydrocracking on the Pt system at 400°C for 20 h with MHSV of 1.0 h^–1 produces a diesel fraction with a yield of at least 82.0 wt % and the content of iso-alkanes at least 76.1 wt %.     

Ruthenium promotion of Co/SBA-15 catalysts with high cobalt loading for Fischer–Tropsch synthesis

30 wt.%Co/SBA-15 catalysts with different ruthenium contents (0.05–0.5 wt.%) were prepared by incipient wetness impregnation and characterized by diffuse reflectance infrared fourier transform spectroscopy, N₂ adsorption-desorption, X-ray diffractometry, temperature-programmed reduction and H₂ desorption, oxygen titration as well as X-ray photoelectron spectroscopy. The addition of a small amount of Ru promoter to Co/SBA-15 shifted the reduction temperature of both steps (Co₃O₄ → CoO and CoO → Co⁰) to lower temperatures and suppressed the formation of Co²⁺ species. After reduction, ruthenium atoms were encapsulated partially with cobalt cluster. There was no strong electronic interaction between metal cobalt and ruthenium, however, hydrogen spillover from ruthenium to cobalt oxide clusters occurred. With increasing ruthenium content, catalyst reducibility increased and the surface was enriched in cobalt atoms. Moreover, the peak intensities of both the linear and bridge types CO adsorption increased with the increase of ruthenium content, enhancing the catalytic activity on Fischer–Tropsch synthesis.