Synergy of ruthenium and cobalt in SiO2-supported catalysts on ethylene hydroformylation

Dynamic hydroformylation of ethylene at atmospheric pressure and 150°C has been studied in a fixed bed reactor over ruthenium- and cobalt-containing SiO₂-supported catalysts (1% Ru loading). Any combination of ruthenium and cobalt precursors leads to significant improvement of hydroformylation activity with respect to those of monometallic catalysts. The optimal atomic ratio of Co:Ru is estimated to be 3:1 for ideal catalytic activity. A catalyst derived from Ru₃(CO)₁₂ and Co₂(CO)₈ is most active. A catalyst derived from metal carbonyls is generally more active than a catalyst prepared from metal salts. Metal chlorides retard the preparation of active catalysts in most cases. The catalysts studied exhibit fairly good catalytic stability. The determined rate enhancement of ethylene hydroformylation suggests a synergy of ruthenium and cobalt, which is understood as catalysis by bimetallic particles or ruthenium and cobalt monometallic particles in intimate contact. The synergy causes high ethylene hydrogenation activity while giving enhanced ethylene hydroformylation activity. Meanwhile, the potential of the ruthenium-based catalysts is evaluated from both catalytic performances and cost by comparison with the corresponding rhodium-based ones.     

SiO2‐supported bimetallic Rh–Co catalysts derived from [Rh(CO)2Cl]2 and cobalt carbonyls

According to the results of IR characterization and catalytic study in ethylene hydroformylation, bimetallic Rh–Co catalysts can be efficiently prepared from [Rh(CO)₂Cl]₂ and cobalt carbonyls by co‐impregnation on SiO₂. The reaction of Co₂(CO)₈ with [Rh(CO)₂Cl]₂ (Rh : Co = 1 : 3 atomic ratio) gives rapidly RhCo₃(CO)₁₂ on the surface of SiO₂. Although Co₄(CO)₁₂ is not reactive with [Rh(CO)₂Cl]₂ on SiO₂ to form directly RhCo₃(CO)₁₂, an equivalent bimetallic catalyst can be easily obtained from ([Rh(CO)₂Cl]₂ + Co₄(CO)₁₂)/SiO₂ or its derivative (Rh⁺ + Co²⁺)/SiO₂ (Rh : Co = 1 : 3 atomic ratio) under reducing conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ethene hydroformylation on Co/SiO2 catalysts

The results from ethene hydroformylation at 173°C showed that a Co(acac)₃/SiO₂ catalyst prepared from Co(acac)₃ precursor by gas‐phase deposition was three times as active as a catalyst prepared by impregnation from cobalt nitrate, but oxo‐selectivities were similar. The high propanal selectivities on the Co(acac)₃/SiO₂ seem to be related to the presence of highly dispersed active sites favouring CO insertion. As dispersion is decreased from 23 to 8% due to increasing metal content (from 5 to 16 wt%), oxo‐selectivity decreased from 39 to 25%. The activity of Co(acac)₃/SiO₂ remained unchanged during 68 h on stream. The gas‐phase deposition technique described here is a promising method for the preparation of active, selective and stable heterogeneous hydroformylation catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Ru addition to Co/SiO2/HZSM-5 catalysts on Fischer–Tropsch synthesis of gasoline-range hydrocarbons

Microporous HZSM-5 zeolite and mesoporous SiO₂ supported Ru–Co catalysts of various Ru adding amounts were prepared and evaluated for Fischer–Tropsch synthesis (FTS) of gasoline-range hydrocarbons (C₅–C₁₂). The tailor-made Ru–Co/SiO₂/HZSM-5 catalysts possessed both micro- and mesopores, which accelerated hydrocracking/hydroisomerization of long-chain products and provided quick mass transfer channels respectively during FTS. In the same time, Ru increased Co reduction degree by hydrogen spillover, thus CO conversion of 62.8% and gasoline-range hydrocarbon selectivity of 47%, including more than 14% isoparaffins, were achieved simultaneously when Ru content was optimized at 1 wt% in Ru–Co/SiO₂/HZSM-5 catalyst.     

Influence of the support on CO2 methanation over Ru catalysts: an FT-IR study

The hydrogenation of CO₂ to methane has been investigated over Ru catalysts supported on zeolite (H-ZSM-5) and on silica. Supported Ru catalysts were very active for the hydrogenation of CO₂. Ru/ZSM-5 was more selective to methane than Ru/SiO₂. On the basis of FT-IR spectra of CO and CO₂ adsorbed on the catalysts, it has been suggested that this behaviour can be related to a higher positive polarization of ruthenium on the zeolite. This leads to a weaker Ru–CO bond on the H-ZSM-5-supported sample with a corresponding increase of the hydrogen surface coverage that favours the transformation of the intermediate CO to methane. This revised version was published online in July 2006 with corrections to the Cover Date.     

CO2 hydrogenation over micro‐ and mesoporous oxides supported Ru catalysts

We prepared relatively uniform supported Ru catalysts by ion‐exchange and CVD methods, using an NaY zeolite and a mesoporous FSM‐16 as substrates, and carried out CO₂ hydrogenation. They showed high activity for CO₂ hydrogenation. A Ru‐ion‐exchanged catalyst showed high activity for methanol production. Co addition promoted methanol formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

A highly active bimetallic supported Rh–Co hydroformylation catalyst prepared from RhCl3 and Co2(CO)8

The preparation of a highly active bimetallic SiO₂‐supported Rh–Co catalyst from RhCl₃ and Co₂(CO)₈ (Rh:Co= 1 : 3 atomic ratio) has been studied by IR spectroscopy and ethylene hydroformylation, etc. Two steps are involved in the preparative process: (1) surface‐mediated synthesis of Rh⁺(CO)₂/SiO₂ from calcined RhCl₃/SiO₂; (2) impregnation of Rh⁺(CO)₂/SiO₂ with a Co₂(CO)₈ solution followed by H₂ reduction at 623 K. The IR results of reductive carbonylation of calcined RhCl₃/SiO₂ have been compared to those of uncalcined RhCl₃/SiO₂ at 373 K. In situ IR observations, extraction results and elemental analysis suggest that approximately 50% of RhCl₃ are transformed to Rh₂O₃ on the SiO₂ surface and that calcined RhCl₃/SiO₂ is converted to a mixture of [Rh(CO)₂Cl]₂ and [Rh(CO)₂O₂ (O_s: surface oxygen) under CO at 373 K. When this SiO₂‐supported mixture was submitted to impregnation with a Co₂(CO)₈ solution at room temperature, IR study and elemental analysis show that [Rh(CO)₂Cl]₂ reacts easily with Co₂(CO)₈ on the surface to give RhCo₃(CO)₁₂, whereas [Rh(CO)₂O₂ does not react with Co₂(CO)₈. Catalytic study in steady‐state ethylene hydroformylation shows that a catalyst thus derived is more active than a catalyst derived from RhCo₃(CO)₁₂/SiO₂ and a catalyst derived by coimpregnation of [Rh(CO)₂Cl]₂ and Co₂(CO)₈ on SiO₂. This result suggests that the high rhodium dispersion of [Rh(CO)₂O₂ plays a crucial role in the formation of highly dispersed bimetallic Rh–Co sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Partial oxidation of methane to synthesis gas over α-Al2O3-supported bimetallic Pt–Co catalysts

The partial oxidation of methane to synthesis gas was studied at atmospheric pressure and in the temperature range of 550–800°C over -Al₂O₃-supported bimetallic Pt–Co, and monometallic Pt and Co catalysts, respectively. Both methane conversion and CO selectivity over a bimetallic Pt_0.5Co₁ catalyst were higher than those over monometallic Pt_0.5 and Co₁ catalysts. Furthermore, the addition of platinum in Pt–Co bimetallic catalysts effectively improved their resistance to carbon deposition with no coking occurring on Pt_0.5Co₁ during 80 h reaction. The FTIR study of CO adsorption observed only linearly bonded CO on bimetallic Pt–Co catalysts. TPR and XPS showed enhanced formation of a cobalt surface phase (CSP) in bimetallic Pt–Co catalysts. The origins of the good coking resistivity of bimetallic Pt–Co catalysts were discussed.     

Promoting effect of noble metals to Co/SiO2 catalysts for hydroformylation of 1-hexene

Small amount of Pt, Pd and Ru promoters in Co/SiO₂ led to great improvement of catalyst activity for hydroformylation of 1-hexene. The 1-hexene conversion as high as 89.7% and oxygenate products selectivity of 88.9% were obtained after 2 h reaction over Pd promoted Co/SiO₂ catalyst. The increasing of reduction degree, the minimizing of cobalt particle size and the enhancement of carbonyl and linear CO adsorption were responsible for the improved performance of the catalyst.     

CH3-modified Co/Ru/SiO2 catalysts and the performances for Fischer–Tropsch synthesis

CH₃-modified Co/Ru/SiO₂ catalysts were prepared and the catalytic performances for Fischer–Tropsch synthesis were investigated. The modified and unmodified catalysts were characterized by FT-IR, N₂ physisorption, TG, XRD, TPR and DRIFTS. FT-IR indicated an effective surface organic modification. TG suggested that modified catalysts had good thermal stability. XRD and TPR showed that modified catalysts had similar reducibility and Co₃O₄ particle size with unmodified catalyst. During reaction tests in a fixed bed reactor it was found that compared with unmodified Co/Ru/SiO₂ catalyst CH₃-modified Co/Ru/SiO₂ catalysts showed higher selectivity to C₅–C₁₁ hydrocarbons, which should be ascribed to hydrophobic surface of CH₃-modified Co/Ru/SiO₂ catalysts.     

Fischer–Tropsch synthesis using Co/SiO2 catalysts prepared from mixed precursors and addition effect of noble metals

Fischer–Tropsch synthesis in Co/SiO₂ catalysts, which were prepared by mixed impregnation of cobalt (II) nitrate and cobalt (II) acetate, was studied under mild reaction conditions (Total pressure=1 MPa, H₂/CO=2, T=513 K). X-ray diffraction indicated that highly dispersed cobalt metal was the main active sites on the catalyst prepared by the same method. It was considered that the metallic crystallines, which were readily reduced from cobalt nitrate, promoted the reduction of Co²⁺ to metallic a state in cobalt acetate by H₂ spillover mechanism during the catalyst reduction process. The reduced cobalt, from cobalt acetate, was highly dispersed one and remarkably enhanced the catalytic activity. The addition of a small amount of Ru to this type of catalyst remarkably increased the catalytic activity and the reduction degree. Its turn over frequency (TOF) increased but the selectivity of CH₄ was unchanged. However, when Pt or Pd were added into catalysts, they exhibited a higher selectivity of CH₄. Although Pt and Pd hardly exerted an effect on cobalt reduction degree, they promoted cobalt dispersion and decreased the value of TOF. Characterization of these bimetallic catalysts suggested that a different contact between Co and Ru, Pt or Pd existed. Ru was enriched on the metallic cobalt surface but, Pt or Pd dispersed well in the form of Pt–Co or Pd–Co alloy.     

Hydrogenolysis of Glycerol to Propanediols Over Highly Active Ru–Re Bimetallic Catalysts

Several supported Ru–Re bimetallic catalysts (Ru–Re/SiO₂, Ru–Re/ZrO₂, Ru–Re/TiO₂, Ru–Re/H-β, Ru–Re/H–ZSM5) and Ru monometallic catalysts (Ru/SiO₂, Ru/ZrO₂, Ru/TiO₂, Ru/H-β, Ru/H–ZSM5) were prepared and their catalytic performances were evaluated in the hydrogenolysis of glycerol to propanediols (1,2-propanediol and 1,3-propanediol) with a batch type reactor (autoclave) under the reaction conditions of 160 °C, 8.0 MPa and 8 h. Compared with Ru monometallic catalysts, the Ru–Re bimetallic catalysts showed much higher activity in the hydrogenolysis of glycerol, and Re exhibited obvious promoting effect on the performance of the catalysts. The supported Ru monometallic catalysts and Ru–Re bimetallic catalysts were characterized by N₂ adsorption/desorption, XRD, TEM-EDX, H₂-TPR and CO chemisorption for obtaining some physicochemical properties of the catalysts, such as specific surface areas, crystal phases, morphologies/microstructure, reduction behaviors and dispersion of Ru metal. The results of XRD and CO chemisorption indicate that the addition of Re component could improve the dispersion of Ru species on supports. The measurements of H₂-TPR revealed that the coexistence of Re and Ru components on supports changed the respective reduction behavior of Re or Ru alone on the supports, indicating the existence of synergistic effect between Ru and Re species on the bimetallic catalysts. The hydrogenolysis of some products (such as 1,2-propanediol, 1,3-propanediol, 1-propanol and 2-propanol) were also examined over Ru and Ru–Re catalysts for evaluating influence of Re–Re on the reaction routes during glycerol hydrogenolysis. The results showed that over Ru–Re catalysts, glycerol was favorable to be converted to 1,2-propanediol, but not favorable to ethylene glycol, while 1,2-propanediol and 1,3-propanediol were favorable to be converted to 1-propanol. The influence of glycerol concentration in its aqueous solution on the catalytic performance was also evaluated over Ru and Ru–Re catalysts.     

Catalytic behavior of silica-supported polyalumazane-Co-Ru bimetallic complex for the hydroformylation of cyclohexene

Summary The cobalt and ruthenium bimetallic complex of an inorganic polymer, polyalumazane (abbr. as Al-N-Co-Ru), was prepared. The catalytic behavior of this complex for the hydroformylation of cyclohexene was studied. The conversion percents were more than 90% in a certain reaction temperature and pressure. Both of the conversion and product composition was also affected by the Ru/Co ratio in catalyst and the CO/H₂ ratio in reactant gas. Aldehyde was firstly formed in the hydroformylation, and then it was further hydrogenated to form the corresponding alcohol. There was no any other by-product formed in the reaction. Compared with the corresponding homogeneous catalyst system, the Al-N-Co-Ru catalyst has higher catalytic activity and stability with lower Ru/Co ratio (1.86). After reused for several times, the catalyst did not lose its activity. The total turnover number was more than 2500 (based on the amount of cobalt used).     

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.     

Influence of noble metals on the performance of Co/SiO2 catalyst for 1-hexene hydroformylation

Effect of small amount of Pt, Pd and Ru promoters on the characteristics and performance of Co/SiO₂ catalyst, which was prepared from the mixture of cobalt nitrate and cobalt acetate, was investigated in the hydroformylation of 1-hexene. It was found that the addition of small amount of a noble metal to the supported cobalt catalyst led into great improvement of catalyst activity for hydroformylation of 1-hexene. The 1-hexene conversion as high as 89.7% and oxygenate products selectivity of 88.9% were obtained after reaction of 2 h over Pd promoted Co/SiO₂ catalyst. The increasing of reduction degree, the minimizing of cobalt particle size and the enhancement of carbonyl and linear CO adsorption were responsible for the improved performance of the catalyst.     

Olefin hydroformylation and selective hydrogenation of acetaldehyde on Mo-promoted Rh/SiO2 catalysts derived from metal salt and heteronuclear cluster precursors

Molybdenum promoted Rh/SiO₂ catalysts have been prepared by using the heteronuclear cluster (C₅H₅)₃RhMo₂(CO)₅ as well as metal salt precursors. The promoting effect of molybdenum has been studied for the hydroformylation of ethene and propene and the hydrogenation of acetaldehyde. It has been found that molybdenum, especially on the cluster-derived catalyst, increases both the hydrogenation and the hydroformylation rate of the olefins. No specific influence on the CO insertion reaction could be obtained. As an explanation, the promotion of the initial step to form intermediate surface alkyl groups has been proposed as the rate determining step for ethene hydroformylation. The promotion of the alcohol formation by bimetallic centers having Rh and Mo in close vicinity has been supported by the results of the hydrogenation of acetaldehyde.     

Selective synthesis of alcohols from syngas and hydroformylation of ethylene over supported cluster-derived cobalt catalysts

Hydroformylation of ethylene and CO hydrogenation were studied over cobalt-based catalysts derived from reaction of Co₂(CO)₈ with ZnO, MgO and La₂O₃ supports. At 433 K a similar activity sequence was reached for both reactions: Co/ ZnO > Co/La₂O₃ > Co/MgO. This confirms the deep analogy between hydroformylation and CO hydrogenation into alcohols. In the CO hydrogenation the selectivity towards alcohol mixture (C₁-C₃) was found to be near 100% at 433 K for a conversion of 6% over the Co/ZnO catalyst; this catalyst showed oxo selectivity higher than 98% in the hydroformylation of ethylene. Magnetic experiments showed that no metallic cobalt particles were formed at 433 K. It is suggested that the active site for the step that is common to both reactions is related to the surface homonuclear Co²⁺/[Co(CO)₄]^– ion-pairing species.     

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).     

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.     

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.