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.     

A mini review on strategies for heterogenization of rhodium-based hydroformylation catalysts

Hydroformylation has been widely used in industry to manufacture high value-added aldehydes and alcohols, and is considered as the largest homogenously catalyzed process in industry. However, this process often suffers from complicated operation and the difficulty in catalyst recycling. It is highly desirable to develop a heterogeneous catalyst that enables the catalyst recovery without sacrificing the activity and selectivity. There are two strategies to afford such a catalyst for the hydrofromylation: immobilized catalysts on solid support and porous organic ligand (POL)-supported catalysts. In the latter, high concentration of phosphine ligands in the catalyst framework is favorable for the high dispersion of rhodium species and the formation of Rh-P multiple bonds, which endow the catalysts with high activity and stability respectively. Besides, the high linear regioselectivity could be achieved through the copolymerization of vinyl functionalized bidentate ligand (vinyl biphephos) and monodentate ligand (3vPPh₃) into the catalyst framework. The newly-emerging POL-supported catalysts have great perspectives in the industrial hydroformylation.

Open image in new window

     

Cobalt(III) Acetylacetonate Chemisorbed on Aluminum-Nitride-Modified Silica: Characteristics and Hydroformylation Activity

Co/AlN/SiO₂ catalysts were prepared by the saturative chemisorption of cobalt(III) acetylacetonate (Co(acac)₃). The support was bare silica or silica that had been modified with aluminum nitride (AlN) by repeated separate, saturated chemisorptions of trimethylaluminum and ammonia two or six times. Chemisorption of Co(acac)₃ occurred on all the supports up to a saturation ligand density of 2.7 acac nm^-2; the amount of bonded cobalt decreased from 2.1 to 1.5 at_Co nm^-2 with increasing extent of AlN modification of the support. Ligand exchange reaction, releasing Hacac, occurred less on AlN-modified silica than on bare silica. This induced difference in the reduction behavior of the catalysts, and catalytic activity in gas-phase hydroformylation of ethene, was lower with Co/AlN/SiO₂ than with Co/SiO₂ catalyst.     

苯乙烯氢甲酰化反应铱基催化剂的改性研究

研究了无机盐对铱基催化剂在苯乙烯氢甲酰化反应中催化性能的改进。结果表明:铱基的羰基配合物Ir2(CO)8对反应具有较好的催化活性和较高的选择性,NaCl对催化剂的改性效果较好。最佳反应条件:甲苯作溶∶PCO=1∶1),NaCl∶Ir2(CO)8=1∶1(摩尔比),苯基丙醛的产率剂,Ir2(CO)8作催化剂,温度100℃,压力5.0MPa(PH2达到64.5%,i/n=2.48。     

Studies on the interaction between ruthenium and cobalt in supported catalysts in favor of hydroformylation

The interaction between ruthenium and cobalt atoms in SiO₂‐supported catalysts prepared from various precursors by H₂ treatment at 350 °C has been studied by ethylene hydroformylation, temperature‐programmed reduction (TPR) technique and IR spectroscopy. Incorporation of cobalt with ruthenium gives a catalyst with remarkably enhanced hydroformylation activity with respect to those of monometallic catalysts, irrespective of the ruthenium and cobalt precursors used. The synergistic effect of ruthenium and cobalt on the catalysis is consistent with TPR and IR results. TPR analysis shows regularly a promoted reduction of cobalt due to the “hydrogen spillover” effect, which indicates that ruthenium and cobalt atoms are in intimate contact in the catalysts. CO adsorption IR study demonstrates a strong decrease of CO chemisorption on Ru in the presence of cobalt, proposing that ruthenium and cobalt atoms interact on the SiO₂ surface to form Ru–Co bimetallic particles. The results suggest that the catalysts thus obtained contain Ru–Co bimetallic particles, at least atoms of the two metals in intimate contact. However, in situ surface IR spectra of ethylene hydroformylation exhibit little modification by the presence of cobalt on Ru/SiO₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Characterization of magnesium promoted Co/SiO2 catalysts

Co/SiO₂, Mg-Co/SiO₂, and Co-Mg/SiO₂ catalysts were prepared from nitrate precursors to get more insight into the effect of magnesium promotion on the cobalt catalyst. The desorption characteristics and reactivity of the catalysts towards synthesis gas were evaluated in a pulse micro reactor connected to an on-line quadrupole mass spectrometer. The presence of MgO both decreased the extent of reduction and increased the dispersion of cobalt. The reactivity results suggested that MgO promotion created new types of active sites, probably at the edge sites of cobalt and magnesium. The highest activity per metallic site available was obtained with a Mg: Co molar ratio of 1/2, i.e. with a high amount of edge sites. In accordance with previous results the formation of CO₂ was clearly suppressed in the presence of MgO, and methanol was formed in trace amounts.     

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.     

The long-term performance of Co/SiO2 catalysts in CO hydrogenation

The activity in terms of conversion of carbon monoxide was determined for Co/SiO₂ catalysts in CO hydrogenation over a reaction time of 120 h. The catalysts were prepared from nitrate (N) and carbonyl (CO) precursors. The conversion decreased rapidly during the first five hours, and thereafter moderately at a rate related to dispersion, i.e. the higher the dispersion the higher the rate of decrease. The active sites were blocked by wax and coke formed in the reaction, although some agglomeration of particles probably took place on the Co(CO)/SiO₂ catalysts. More carbon was accumulated on Co(CO)/SiO₂ than on Co(N)/SiO₂ during the reaction suggesting a need for frequent regeneration. The reduction-oxidation-reduction treatments indicated, however, that the regenerability of the Co(CO)/SiO₂ in terms of hydrogen uptake is poor, although the amounts adsorbed still remained higher than those for Co(N)/SiO₂.     

Preparation and characterization of Co/SiO2, Co-Mg/SiO2 and Mg-Co/SiO2 catalysts and their activity in CO hydrogenation

Co/SiO₂, Mg-Co/SiO₂ and Co-Mg/SiO2 catalysts were prepared from acetate, nitrate or carbonyl precursors. The catalysts were characterized by XRD, XPS, SIMS and TGA. The steady-state activity and product distribution of the catalysts were evaluated in synthesis gas reactions at 0.5 MPa and 235-290°C using 3 : 1 : 3 molar ratio of Ar : CO : H₂. The activity in CO hydrogenation decreased in the precursor order Co₂(CO)₈>Co(NO₃)₂> Co(CH₃COO)₂, and the probability of chain growth decreased in the precursor order Co(NO₃)₂>Co₂(CO)₈>Co(CH₃COO)₂. Alcohol yields were highest with Co₂(CO)₈, and lowest with Co(NO₃)₂, Magnesium promotion influenced the catalyst activity and decreased the CO₂ formation, but the promotion effects were less profound than those of the precursor. Surface studies on partially magnesium covered cobalt foil model catalysts suggested that magnesium promotes CO dissociation and chain growth, neither of which were, however, observed in the supported catalysts.     

Catalytic dehydrogenation of propane over cluster-derived Ir–Sn/SiO2 catalysts

The dehydrogenation of propane was studied in gas-phase at 773 K over two series of silica-deposited Ir–Sn systems: the bimetallic catalysts obtained from Ir–Sn carbonyl clusters precursors and the ones prepared by deposition of a metallorganic Sn precursor onto preformed Ir nanoparticles. In the comparison, cluster-derived catalysts showed good propane conversion, optimal selectivity to propene and high stability under the severe reaction conditions.     

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.     

Methanol synthesis over Cu/SiO2 catalysts

The rates of CO and CO/CO₂ hydrogenation at 4.2 MPa and 523 K are reported for a series of Cu/SiO₂ catalysts containing 2 to 88 wt.% Cu. These catalysts were prepared on a variety of silica sources using several different Cu deposition techniques. In CO/CO₂ hydrogenation, the rate of methanol formation is proportional to the exposed Cu surface area of the reduced catalyst precursor, as determined by N₂O frontal chromatography. The observed rate, 4.2×10^–3 mole CH₃OH/Cu site-sec, is within a factor of three of the rates reported by others over Cu/ZnO and Cu/ZnO/Al₂O₃ catalysts under comparable conditions. These results suggest that the ZnO component is only a moderate promoter in methanol synthesis. Hydrogenation of CO over these catalysts also gives methanol with high selectivity, but the synthesis rate is not proportional to the Cu surface area. This implies that another type of site, either alone or in cooperation with Cu, is involved in the synthesis of methanol from CO.     

Effect of vanadia loading in propane oxidative dehydrogenation on V2O5/SiO2 catalysts

The influence of V₂O₅ loading on the catalytic behaviour of V₂O₅/SiO2₂ catalysts in the oxidative dehydrogenation of propane to propylene (POD) has been investigated. The different activity-selectivity pattern of low (5 wt%) and highly (>10 wt%) loaded V₂O₅/SiO₂ catalysts is explained in terms of different surface vanadia species.     

Support and precursor effects on the preparation of new heterogenized Pt/Sn catalysts for the selective hydroformylation of 1-pentene

New heterogenized Pt/Sn catalysts selective for the hydroformylation of 1-pentene have been synthesized. The complex cis-[PtCl₂(PPh₃)₂] and the SnCl₂.2H₂O or SnC₂O₄ precursors have been anchored on silica-, magnesia- and alumina-carriers. X-ray photoelectron spectroscopy was used to determine the surface composition and the nature of the anchored species. The hydroformylation activity was found to depend on the type of support and tin precursor used. Only the silica supported catalysts were active in the hydroformylation reaction. Samples prepared from SnCl₂-2H₂O were 200-fold more active than those prepared from SnC₂O₄. Selectivity ton-hexanal of the silica-supported catalyst prepared from SnCl₂-2H₂O was as high as 94.4% at 39.2% conversion of 1-pentene.     

Studies on CrO x /La2O3/ZrO2 catalysts modified by Mg

Lanthana–zirconia supported chromium oxide and magnesium chromium mixed oxide catalysts were studied in the dehydrocyclization of n-octane and characterized by temperature-programmed desorption of NH₃, temperature-programmed reduction, XPS and DRIFTS. The Mg-free catalyst shows the highest activity, but suffers from rapid deactivation due to coke formation. The addition of Mg decreases the initial activity of the supported chromium oxide and retards its deactivation. The characterization results reveal that the deactivation retarding effect of Mg species not only consists in the deletion of strong acid sites but also in the decoration and/or dilution of Cr³⁺ oxide cluster, supposedly due to the formation of Mg–Cr surface compounds and, thus, in preventing the formation of coke.     

Conversion of Carbon Monoxide‐Rich Synthesis Gas to Hydrocarbons and Alcohols over Cu/Co/ZnO/SiO2 Catalysts

Catalysts of the type Cu/Co/ZnO/SiO₂ were prepared by impregnation, subsequent calcination and reduction with hydrogen. Characterization of the catalysts was carried out by ICP‐AES, BET measurements and powder X‐ray diffraction analyses. Furthermore, temperature programmed reduction was employed to investigate their reduction behavior. The catalysts were tested in the conversion of synthesis gas to hydrocarbons and alcohols. High CO conversions could be reached in a single reactor pass. Selectivity was highest for methane, and short‐chain hydrocarbons, but alcohols were also formed.     

The formation of cobalt silicates on Co/SiO2 under hydrothermal conditions

A Co/SiO₂ catalyst recovered after both gas and liquid phase Fischer-Tropsch synthesis exhibited significant decreases in the amount of reducible metal. Hydrothermal conditions similar to those occurring during Fischer-Tropsch synthesis were simulated in order to study compound formation in this Co/SiO₂ catalyst. Hydrothermal treatment at 220°C led to a catalyst with lower reducibility, attributable to the formation of both reducible and nonreducible (<900°C) Co silicates. The formation of these compounds occurred only when metallic Co was present, was more pronounced in the presence of hydrogen, and was inhibited by air.     

An in situ high pressure FT-IR study of CO2/H2 interactions with model ZnO/SiO2, Cu/SiO2 and Cu/ZnO/SiO2 methanol synthesis catalysts

In situ FT-IR spectroscopy allows the methanol synthesis reaction to be investigated under actual industrial conditions of 503 K and 10 MPa. On Cu/SiO₂ catalyst formate species were initially formed which were subsequently hydrogenated to methanol. During the reaction a steady state concentration of formate species persisted on the copper. Additionally, a small quantity of gaseous methane was produced. In contrast, the reaction of CO₂ and H₂ on ZnO/SiO₂ catalyst only resulted in the formation of zinc formate species: no methanol was detected. The interaction of CO₂ and H₂ with Cu/ZnO/SiO₂ catalyst gave formate species on both copper and zinc oxide. Methanol was again formed by the hydrogenation of copper formate species. Steady-state concentrations of copper formate existed under actual industrial reaction conditions, and copper formate is the pivotal intermediate for methanol synthesis. Collation of these results with previous data on copper-based methanol synthesis catalysts allowed the formulation of a reaction mechanism.     

Selective vapor phase hydroformylation of ethylene over cluster-derived cobalt catalyst

Vapor phase hydroformylation of ethylene was studied with silica-supported metal catalysts. A cobalt metal catalyst derived from Co₂(CO)₈ gave propanal and its derivatives in as high selectivity of about 36% as Rh/SiO₂ catalyst under the reaction conditions of 1.1 MPa of a gas-mixture of ArCOC₂H₄H₂ = 1333 at 423–503 K. On the other hand, conventional cobalt catalysts derived from cobalt nitrate, chloride, or acetate, and other noble metal catalysts (Pd/SiO₂ and Ir/SiO₂) produced mainly ethane.     

Preparation and characterization of WO3/SiO2 catalysts

Two sets of WO₃/SiO₂ catalysts were prepared from (NH_{4 6}H₂W₁₂O₄₀ (aqueous method) and W(³-C₃H₅)₄ (non-aqueous method). The molecular structures and dispersions of the surface tungsten oxide species for the WO₃/SiO₂ catalysts under ambient and in situ dehydrated conditions were investigated by Raman spectroscopy. The samples prepared from (NH₄)₆H₂W₁₂O₄₀ (aqueous method) exhibit very strong Raman features due to the presence of crystalline WO₃ and the samples prepared from W(³-C₃H₅)₄ (non-aqueous method) do not possess crystalline WO₃. These results suggest that the preparation method exerts an influence on the dispersion of the surface tungsten oxide species on SiO₂. The surface tungsten oxide species under ambient conditions possess polytungstate clusters, W₁₂O ₄₂ ^12– , on the silica support. Upon dehydration at elevated temperatures, the hydrated polytungstate clusters decompose and interact with the silica support via the formation of isolated, octahedrally coordinated tungsten oxide species.