Rhodiumkatalysierte Zweiphasenhydroformylierung von n-Hex-1-en mit Sulfonsäuresalzen des Tris(4-fluorphenyl)phosphins als wasserlösliche Komplexliganden

Rhodium-catalyzed Two-phase Hydroformylation of Hex-1-ene with Sulfonated Tris(4-fluorophenyl)phosphine as Water-soluble Complex Ligands Tris(4-fluorophenyl)phosphine (TFPP) was prepared from 1-bromo-4-fluoro-benzene in 35% yield. This phosphine was quantitatively sulfonated by using a H₂SO₄-SO₃ mixture containing 25,5% SO₃ and a 14-fold excess of SO₃ to phosphine. The desired product was the trisodium salt of the trisulfonated tris(4-fluorophenyl)phosphine (TFPPTS). After 410 hours of sulfonation, hydrolysis and pH-selective separation, the resulting mixture contained 6% TFPPTS and 94% disodium salt of the disulfonated tris(4-fluorphenyl)phosphine (TFPPDS). Hex-1-ene was hydroformylated in a two-phase system by using the water-soluble catalytic systems Rh₄(CO)₁₂ with a mixture of 94% TFPPDS + 6% TFPPTS and Rh₄(CO)₁₂ with the trisodium salt of trisulfonated triphenylphosphine (TPPTS). The TFPP or TFPPTS ligand possesses a stronger π-acidity than the TPP or TPPTS and at low P/Ph-ratios higher selectivities to linear aldehydes are achieved with the Rh/TFPP or Rh/TFPPDS + TFPPTS than with the Rh/TPP or Rh/TPPTS catalytic system. The Rh/TFPPDS + TFPPTS complex is quantitatively recovered by simple separation of the aqueous layer from the organic layer which contains the substrate and the products.     

Hydroformylation of Alkenes with Rhodium Catalyst in Supercritical Carbon Dioxide

1-Octene, 1-decene and styrene have been hydroformylated using a CO₂-philic fluorous ligand associated with a rhodium catalyst. The effect of P/Rh molar ratio, partial pressure of CO/H₂ and total pressure of carbon dioxide were studied. When 1-octene was used as the substrate, high conversion and selectivity in aldehydes were observed using low rhodium concentration and low P/Rh ratios.     

Immobilized Co/Rh Heterobimetallic Nanoparticle‐Catalyzed Pauson–Khand‐Type Reaction

Co/Rh heterobimetallic nanoparticles were prepared from cobalt‐rhodium carbonyl clusters [Co₂Rh₂(CO)₁₂ and Co₃Rh(CO)₁₂] and immobilized on charcoal. HR‐TEM revealed that the size of the heterobimetallic nanoparticles was ca. 2 nm and ICP‐AES analysis showed a 2 : 2 and a 3 : 1 cobalt‐rhodium stoichiometry (Co₂Rh₂ and Co₃Rh₁) in the heterobimetallic nanoparticles. The Co/Rh heterobimetallic nanoparticles immobilized on charcoal were used as a catalyst in the Pauson–Khand‐type reaction under 1 atm of CO. The catalytic reactivity was highly dependent upon the ratio of Co : Rh with the highest reactivity being observed when the ratio was 2 : 2 (Co₂Rh₂). The Co₂Rh₂ immobilized catalyst is quite an effective catalyst for intra‐ and intermolecular Pauson–Khand‐type reactions. When the immobilized Co₂Rh₂ catalyst was used as a catalyst in the Pauson–Khand‐type reaction in the presence of an aldehyde instead of carbon monoxide, the catalytic system was highly efficient. When the reaction was carried out in the presence of chiral diphosphines, ee values up to 87% were observed. The catalytic system can be reused at least five times in the presence of chiral diphosphines without loss of catalytic activity and enantioselectivity. The addition of Hg(0), a known heterogeneous catalyst poison, completely inhibits further catalysis. Thus, an environmentally friendly and sustainable process was developed.     

Hydroformylation of mixed octenes catalyzed by supported rhodium-based catalyst

In order to solve the difficult separation between catalyst and products in homogeneous system, the activated carbon (AC)-supported rhodium-based catalyst (Rh/AC) was prepared. Hydroformylation of mixed octenes catalyzed by Rh/AC was studied, and compared to that catalyzed by RhCl(CO)(TPPTS)₂ [TPPTS: trisodium salt of tris(m-sulphonylphenyl) phosphine], and [Rh(CH₃COO)₂]₂-Ph₃PO (Ph₃PO: triphenyl phosphine oxide). The performance test of the catalysts showed the Rh/AC presented higher catalytic activity, selectivity and air-stability. During the recycle experiments Rh/AC could be used 4 times without significant loss of rhodium. The effects of the supports, rhodium loading and reaction conditions on the catalytic performance of Rh/AC were investigated. The results showed petroleum coke-based activated carbon with higher surface area and more basic groups was advantageous to the formation of aldehydes. The heterogeneous Rh/AC catalyst displayed higher catalytic activity and reusability.     

Electrochemically Induced Oscillations of C2H4 Oxidation Over Thin Sputtered Rh Catalyst Films

The electrochemically promoted induction of self-sustained catalytic rate and potential oscillations during C₂H₄ oxidation was studied over sputtered Rh thin (40 nm catalyst films interfaced with ZrO₂ (8 mol% Y₂O₃). The reaction rate oscillates simultaneously with the catalyst potential, and always in the opposite direction. The electrochemically induced oscillatory rate is typically 60 times larger than the open-circuit catalytic rate and 1000 times larger than the electrochemical rate of O²⁻ supply to the catalyst. The phenomenon is completely reversible and only observed under anodic polarization where the rate oscillates between the values corresponding to metallic Rh and surface Rh₂O₃. The oscillations are caused by the electrochemically controlled backspillover of O²⁻ to the catalyst surface and the concomitant, via repulsive lateral interactions, decomposition of surface rhodium oxide followed by surface reoxidation to Rh₂O₃ by gaseous O₂.     

Rhodium phosphide catalyst for hydrodesulfurization: Low temperature synthesis by sodium addition

Effect of sodium (Na) addition on rhodium phosphide (Rh₂P) formation on MFI zeolite, SiO₂ and Al₂O₃ and hydrodesulfurization (HDS) activity were examined. The TPR results revealed that Na addition enhanced reducibility of phosphates. The XRD results indicated that Rh₂P phase was easily formed on NaMFI support as compared with on HMFI support. The maximum HDS activity of Rh–P/NaMFI catalyst was obtained at lower reduction temperature and this activity was higher than that of Rh–P/HMFI catalyst. We concluded that since Na would weaken interaction between Al and phosphate, high HDS activity of Rh–P/NaMFI catalyst was observed at lower reduction temperature.     

Spectral reconstruction of in situ FTIR spectroscopic reaction data using band-target entropy minimization (BTEM): application to the homogeneous rhodium catalyzed hydroformylation of 3,3-dimethylbut-1-ene using Rh4(CO)12

The homogeneous catalytic hydroformylation of 3,3-dimethylbut-1-ene was studied, starting with Rh₄(σ-CO)₉(μ-CO)₃ as catalyst. The multiple experiment in situ spectroscopic data were preconditioned to subtract the absorbance due to background moisture, carbon dioxide, and solvent. The preconditioned data were then subjected to band-target entropy minimization (BTEM) in order to recover the pure component spectra of the species present—using no libraries and no a priori information. The pure component spectra of the main species present, namely, the organic reactant 3,3-dimethylbut-1-ene, the organic product 4,4-dimethylpentanal, the catalyst precursor Rh₄(σ-CO)₉(μ-CO)₃, and the observable organometallic intermediate RCORh(CO)₄, were all readily recovered. In addition, it was possible to recover the expected minor species, namely 2-methyl-3,3-dimethylbutanal, Rh₆(CO)₁₆, and a recently identified cluster Rh₄(σ-CO)₁₂. The latter two species exist at ppm levels. The new BTEM algorithm shows that successful and detailed in situ spectroscopic system identification for catalytic studies is possible given no prior information.     

Decarbonylation dehydration of fatty acids to alkenes in the presence of transition metal complexes

The catalytic decarbonylation of stearic acid into a mixture of heptadecenes has been accomplished by use of a catalyst system comprised of rhodium trichloride (RhCl₃) and triphenylphosphine. The isomeric composition of the heptadecenes formed was found, by spectroscopic and chemical methods, to be dependent upon the type of rhodium catalyst employed. Anhydrous RhCl₃ produced about the same amount of 2-heptadecene, twice the amount of 3-heptadecene, and about half the amount of 1-heptadecene as hydrated RhCl₃. The active catalytic species formed in situ has been identified as the rhodium I complex [(C₆H₅)₃P]₂Rh(CO)Cl. A mechanistic pathway to account for the observed decarbonylation products employing the above catalyst is presented. Presented at the AOCS Meeting, Dallas, 1975     

H2-Production on New BaTi(1−x)RhxO3 Catalyst via the Steam Reforming of CH4 for H2-SCR Applications

Rh-doped perovskites BaTi_0.9Rh_0.1O₃ and Rh–BaTiO₃ were prepared by a new synthesis method and analyzed by XRD and FE-scanning electron microscopy (SEM). The effect of HCl for sol-formation was studied, HCl improves the sol formation but chlorine remains in the catalyst even after calcination treatment at 1,000 °C. Cl-free catalysts were prepared and analyzed on reactions for H₂ production which can be used for H₂-SCR reactions. The Rh-integrated perovskite BaTi_0.9Rh_0.1O₃ displayed better catalytic performance compared to Rh–BaTiO₃ and Rh–TiO₂ under the studied reaction conditions. Carefull XRD analysis was carried out to demonstrate the incorporation of Rh in the perovskite lattice. Rhodium reacts with the tetragonal perovskite BaTiO₃ to stabilize the hexagonal modification. Mainly, the hexagonal perovskite was found in the catalyst BaTi_0.9Rh_0.1O₃. This modification appears only after Rh-impregnation and calcination of the tetragonal BaTiO₃ thus coexisting the hexagonal perovskite BaTi_(1?x)Rh_xO₃ and the tetragonal BaTiO₃. The catalysts reduction in diluted H₂ containing gas mixtures cause the segregation of Rh° nanoparticles out of the perovskite crystal lattice.     

Organometallic Rhodium Complexes Encapsulated in Mesoporous Molecular Sieves

Rh(III) complexes both dimmer [Cp*RhCl]₂(μ-Cl)₂ and monomer ([RhCp*(S)₃]²⁺) were encapsulated into MCM-41 channels. All silica MCM-41 molecular sieve and aminosililated MCM-41 matrix were used for rhodium complexes accommodation. Reactivity of Cp* rhodium complexes encapsulated in meso structure was estimated on the grounds of their susceptibility to interaction with CO molecules resulting in the formation of carbonyl complexes. Formation of Cp*Rh carbonyls was recorded by means of FTIR spectra. It was found that accommodation of Rh(III) complexes in MCM-41 molecular sieves activated the complex and led to the formation of Rh(III)Cp* carbonyls as a result of contact with CO. Contact of rhodium (III) complexes encapsulated in MCM-41 matrix with CO did not result in rhodium (III) reduction, whereas in the presence of amine groups in aminosililated MCM-41 the reduction of Rh(III) to Rh(I) occurred relatively easily and formation of Cp*Rh(CO)₂ complex containing Rh(I) was noted. Encapsulated rhodium complexes showed some activity in methanol carbonylation reaction carried out under heterogeneous conditions. For the most active catalyst the amount of methyl acetate reached about 8 mol.%, however, deactivation of catalyst occurred and after 2 h on stream methyl acetate was not found in the product.     

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.     

Study on catalysis by carbonyl cluster-derived SiO2-supported rhodium for ethylene hydroformylation

Atmospheric hydroformylation of ethylene was studied under differential conditions over Rh₄(CO)₁₂-derived Rh/SiO₂ catalysts. The specific activities as functions of Rh dispersions show that ethylene hydroformylation is structure sensitive and ethylene hydrogenation structure insensitive. These structural dependences and in situ IR observations show that Rh⁰ is the unique active site for catalytic ethylene hydroformylation on Rh/SiO₂. The reactions of Rh⁰-coordinated CO and Rh⁰-adsorbed CO with C₂H₄ + H₂ at 293 K were monitored by IR spectroscopy. The linear CO adsorbed on Rh⁰/SiO₂ is consumed with formation of propanal, whereas the coordinated CO in Rh₆(CO)₁₆/SiO₂ and its derivative do not participate in CO insertion. IR study of the thermal decomposition of Rh₆(CO)₁₆/SiO₂ indicates that the cluster can be stabilized on the surface up to 548 K by gaseous CO under hydroformylation conditions. Moreover, the Rh₆(CO)₁₆/SiO₂ system exhibits increased catalytic hydroformylation activity with reducing coordinated CO. These results show that coordinative unsaturation on the Rh⁰ surface is necessary for heterogeneously rhodium-catalyzed hydroformylation and that totally decarbonylated Rh⁰/SiO₂ is most effective. In addition, the oxidation of Rh⁰ by surface OH^? is discussed.     

Effect of Aging Atmosphere on Thermal Sintering of Modern Commercial TWCs

The effect of aging atmosphere on the sintering behavior of commercial Pd and Rh catalysts as well as the TWC performance thereof has been investigated under straight oxidizing, reducing and periodic cycling aging conditions, in search of useful guidance in the optimum design of thermally durable TWCs for advanced gasoline engines equipped with the deceleration fuel cutoff technology. Pd and Rh catalysts individually exhibit an opposite trend in the thermal sintering behavior with respect to the aging atmosphere. Under oxidizing conditions, the Pd catalyst becomes more resistant to sintering in higher O₂ concentrations, whereas the Rh catalyst reveals the opposite behavior, regardless of the aging temperature. Physicochemical characterizations by using TGA and CO chemisorption have indicated that the state of Pd (PdO vs. Pd⁰) and Rh (Rh₂O₃ vs. Rh⁰) on the catalyst surface formed during the thermal aging plays an important role for determining the trend of thermal sintering; the positive effect of the O₂ concentration on Pd sintering is attributable primarily to the formation of PdO, while the main cause for severe deactivation of the Rh catalyst under oxidizing conditions is the diffusion of Rh₂O₃ into the support along with the agglomeration of Rh particles.     

Infrared spectroscopic detection of Rh(1) by CO in supported Rh catalyst

The detection limit of Rh(1) in the Rh/Al₂O₃ catalyst in a form of Rh¹(CO)₂ was determined by FTIR spectroscopy. It was demonstrated that at least 0.5 g Rh, corresponding to 0.005 wt% of Rh, can be identified in this way. During synthesis gas conversion the predominant surface species is Rh _x -CO, but a detectable amount of Rh(1) exists on the catalyst up to 473 K.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Hydroformylation of olefins with water-soluble rhodium catalysts in the presence ofα-cyclodextrin

Hydroformylation of hex-1-ene using a water soluble rhodium catalyst HRh(CO)[PPh₂(m-C₆H₄SO₃Na)]₃ (HRh(CO)(TPPMS)₃) (I), gives lower yields when-cyclodextrin is added to the biphasic reaction system implying an interaction between the cyclodextrin and rhodium catalyst.     

The decomposition of NO on CNTs and 1 wt% Rh/CNTs

Carbon nanotubes (CNTs) and CNTs-supported rhodium were tested as catalysts for NO decomposition. For the fresh catalysts, 100% NO conversion was achieved at 600°C over CNTs; when 1 wt% Rh was loaded on CNTs, 100% NO conversion was achieved at 450°C. If the catalysts were pre-reduced in H₂ at or above 300°C, 100% NO conversions were observed at 300°C. XPS investigation indicated that there was still metallic rhodium (BE=307.2 eV) on Rh/CNTs after heating in air at 500°C for 2 h and after the NO decomposition reaction. As for a 1 wt% Rh/Al₂O₃ sample, the rhodium (BE = 308.2 eV) was completely in the form of Rh₂O₃ after similar treatments. These results suggest that compared to γ-Al₂O₃, the CNTs material is more capable of keeping the rhodium in its metallic state. The results obtained in H₂-TPR studies support this conclusion. In addition, TEM investigation revealed that the rhodium particles distributed rather evenly over CNTs with a particle diameter of around 8 nm. We propose that CNTs can be used as a material for the facilitation of NO decomposition. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the kinetics of CO oxidation by O2 over RhI(CO)2 catalytic species anchored to a zeolitic support

The reactivity of Rh^I(CO)₂ towards CO oxidation was studied on a model Rh(0.7 wt%)/HY material. The kinetic results show that Rh^I(CO)₂ exhibit a fairly low activity. It is therefore suggested that the catalytic species responsible for the enhanced activity of Rh/Ce_0.68Zr_0.32O₂ [Manuel et al., J. Catal. 224 (2004) 269] would rather be electron-deficient Rh clusters (Rh _n ^δ+ ).     

Rhodium supported in basic zeolite Y: A selective and stable catalyst for CO hydrogenation

Catalysts prepared by a condensation reaction of Rh(CO)₂(acac) within the supercages of zeolite Y made basic by treatment with NaN₃ are active for CO hydrogenation and selective for low-molecular-weight olefins and methanol. High partial pressures of CO (or CO + H₂) stabilize the catalyst. The predominant species in the catalyst are suggested to be rhodium carbonyl clusters trapped in the zeolite cages.     

A Fixed-Bed Reactor Study of Catalytic Partial Oxidation over Rh/Al2O3: An Indication of a Direct Pathway to CO

Catalytic partial oxidation (CPO) of CH₄ in air was investigated over Rh/Al₂O₃ catalysts (0.01, 0.05, 0.1 and 1 wt% Rh⁰) in co-feed modus in laboratory scale fixed-bed reactors. Main focus was on catalyst stability and selectivity at low temperatures (<700 °C). A particularly high selectivity to CO was observed, indicating existence of a direct pathway.     

The Effect of Polarization and Reaction Mixture on the Rh/YSZ Oxidation State During Ethylene Oxidation Studied by Near Ambient Pressure XPS

In this study, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is applied to investigate an electrochemical cell consisting of a rhodium thin film catalyst supported on an yttria-stabilized zirconia (YSZ) solid electrolyte under various ethylene-oxygen reaction mixtures. The aim of the study is twofold: first to show how the surface oxidation state of the Rh catalyst is correlated with the reactants feed composition and the temperature, and second, to reveal the effect of the anodic polarization on the stability of Rh oxides and the implications on the electrochemical promotion of catalysis. It is clearly shown that even under reducing conditions part of the Rh electrode remains oxidized at temperatures up to 250 °C. Reduction of the oxide can take place by increasing the temperature under C₂H₄ excess, something which is not happening under oxidizing reaction mixtures. Moreover, anodic polarization, i.e. oxygen ion supply to the surface, facilitates reduction of oxidized Rh electrodes over a broad range of ethylene–oxygen reaction mixtures. Remarkably, under mildly reducing conditions a stable ultrathin Rh surface oxide film forms over metallic Rh. This surface Rh oxide film (RhO_x) is associated to higher cell currents, counterintuitive to the case of bulk Rh oxides (Rh₂O₃).