Catalytic Activity Of Rh Research Articles

Methane steam reforming at low steam-to-carbon ratio: The effect of Y doping in Rh substituted lanthanum zirconates

A series of Rh-substituted lanthanum zirconate pyrochlores doped with different loadings of Y (A-site or B-site) were synthesized and studied for methane steam reforming (MSR) under low steam-to-carbon ratios (S/C = 1.0). This study mainly focuses on Y doping in the pyrochlore structure and its potential influence on the catalytic activity of Rh and carbon formation during reaction. XANES data showed that doping Y into the pyrochlore resulted in an occupancy that was predominately located in the B-site, but overall the distribution of Y in each site was similar in all catalysts despite the loadings of Y and stoichiometry of the constituent pyrochlore cations. Activity testing showed that 4 wt% Y doping at La-site led to higher activity at high flow rate and feed dilution, and high selectivity to synthesis gas. This catalyst showed strong resistance to coking under a long-term stability test (300 h) and a series of low S/C ratios MSR.

Reducing-agent-free facile preparation of Rh-nanoparticles uniformly anchored on onion-like fullerene for catalytic applications.

Herein we report a very simple ‘mix and heat’ synthesis of a very fine Rh-nanoparticle loaded carbon fullerene-C60 nanocatalyst (Rh(0)NPs/Fullerene-C60) for the very first time. The preparation method used no reducing agent and capping agent to control the morphology of the nanocatalyst. Transmission electron microscopy (TEM) results confirmed the uniform decoration of small Rh-nanoparticles on the surface of fullerene-C60. The Rh-content in Rh(0)NPs/Fullerene-C60 was found to be 2.89 wt%. The crystalline properties of Rh(0)NPs/Fullerene-C60 were studied by X-ray diffraction (XRD). The metallic state of Rh-nanoparticles in Rh(0)NPs/Fullerene-C60 was confirmed by X-ray photoemission spectroscopy (XPS). Raman results depicted good interaction between Rh-nanoparticles and fullerene-C60. To our delight, the present Rh(0)NPs/Fullerene-C60 showed excellent catalytic activity in the reduction of 4-nitrophenol with NaBH4 in water. Very high kapp, k′ and TOF values of 82.14 × 10−3 min−1, 4107 × 10−3 min−1 and 138 min−1, respectively, were calculated for the Rh(0)NPs/Fullerene-C60 catalyzed reduction of 4-nitrophenol. To the best of our knowledge, this is the most efficient fullerene-based nanocatalyst for the rapid reduction of 4-nitrophenol reported to date. Moreover, the catalytic activity of Rh(0)NPs/Fullerene-C60 was also tested towards Suzuki cross-coupling reactions. Reusability of the Rh(0)NPs/Fullerene-C60 was also tested.

Preparation and detailed characterization of zirconia nanopowder supported rhodium (0) nanoparticles for hydrogen production from the methanolysis of methylamine-borane in room conditions

Uniformly dispersed Rh (0) nanoparticles supported on zirconia nanopowder were synthesized by a two-step and simple ex-situ method summarized by mixing rhodium (III) chloride hydrate with zirconia (nano-ZrO2) aqueous solution in ambient conditions followed by reduction with NaBH4. The ex-situ prepared nano-ZrO2 supported Rh (0) nanoparticles (Rh/nano-ZrO2) were characterized by various spectroscopic methods, including TEM, TEM-EDX, HR-TEM, P-XRD, XPS and ICP-OES. The catalytic activity of Rh (0) nanoparticles is 1050 h−1 in terms of initial turnover frequency (TOF), which is the first study in the literature to produce hydrogen by catalytic methanolysis of methylamine-borane. In addition, the catalytic methanolysis of methylamine-borane by using Rh (0) nanoparticles was carried out in different catalyst/substrate concentrations and different temperatures to reveal rate equation and kinetic parameters. Consequently, Rh (0) nanoparticles are taken into account as an encouraging catalyst for the methanolysis of methylamine-borane and for providing a more fertile hydrogen storage gain in fuel cell operations.

Persulfate activation by magnetic γ-Fe2O3/Mn3O4 nanocomposites for degradation of organic pollutants

Abstract In this work, magnetic γ-Fe2O3/Mn3O4 nanocomposites with various mass ratios were successfully fabricated using a facile two-step method. Then these composites were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microcopy (TEM), X-ray photoelectron spectra (XPS) and vibrating sample magnetometer (VSM) measurements. Besides, the samples were applied to activate persulfate for Rh B degradation. Results showed that the sample with a γ-Fe2O3/Mn3O4 mass ratio of 3:1 exhibited higher activity than other γ-Fe2O3/Mn3O4 nanocomposites, pure γ-Fe2O3 and pure Mn3O4, where 95.1% of Rh B could be decomposed within 150 min in the presence of persulfate. In addition, effects of operational parameters on the catalytic activity of Rh B were also evaluated, which included persulfate concentration, catalyst dosage, reaction temperature and initial pH value. More importantly, the as-fabricated γ-Fe2O3/Mn3O4 nanocomposites revealed magnetism and could be separated conveniently through external magnetic, which was beneficial to recycle the catalysts from the aqueous solution. Finally, the mechanism of activating persulfate by γ-Fe2O3/Mn3O4 nanocomposites was proposed based on the results and literatures, which might provide a reference for further study of heterogeneous catalysis.

The effect of the morpholinium ionic liquid anion on the catalytic activity of Rh (or Pt) complex-ionic liquid systems in hydrosilylation processes.

Studies were performed on the catalytic activity for olefin hydrosilylation shown by three rhodium complexes, [{Rh(μ-OSiMe3)(cod)}2] (I), [{Rh(μ-Cl)(cod)}2] (II) and [RhCl(PPh3)3] (III), and three platinum complexes, [Pt(PPh3)4] (IV), [Pt(PPh3)2Cl2] (V) and PtCl4 (VI), immobilized in a series of different anion-containing morpholinium ionic liquids. The effect of the kind of anion (its nucleophilic character) on the activity, stability and possibility of a catalytic system with multiple uses in the hydrosilylation process has been established. In the case of the best systems it was possible to reuse the same catalyst sample 10 times almost without any decrease in the activity and a TON value over 99 000 was obtained.

The Mechanism of Rh-Catalyzed Transformation of Fatty Acids to Linear Alpha olefins

Linear alpha olefins (LAOs) are key commodity chemicals and petrochemical intermediates that are currently produced from fossil resources. Fatty acids are the obvious renewable starting material for LAOs, which can be obtained via transition-metal-catalyzed decarbonylative dehydration. However, even the best catalysts that have been obtained to date, which are based on palladium, are not active and stable enough for industrial use. To provide insight for design of better catalysts, we here present the first computationally derived mechanism for another attractive transition-metal for this reaction, rhodium. By comparing the calculated mechanisms and free energy profiles for the two metals, Pd and Rh, we single out important factors for a facile, low-barrier reaction and for a stable catalyst. While the olefin formation is rate limiting for both of the metals, the rate-determining intermediate for Rh is, in contrast to Pd, the starting complex, (PPh3)2Rh(CO)Cl. This complex largely draws its stability from the strength of the Rh(I)–CO bond. CO is a much less suitable ligand for the high-oxidation state Rh(III). However, for steric reasons, rhodium dissociates a bulkier triphenylphosphine and keeps the carbonyl during the oxidative addition, which is less favorable than for Pd. When compared to Pd, which dissociates two phosphine ligands at the start of the reaction, the catalytic activity of Rh also appears to be hampered by its preference for high coordination numbers. The remaining ancillary ligands leave less space for the metal to mediate the reaction.

Insights into the effect of coverage on CO adsorption and dissociation over Rh(1 0 0) surface: A theoretical study

The adsorption, dissociation and desorption of CO at different coverage over Rh(100) surface have been systematically investigated using density functional theory method together with the periodic slab model. Our results show that at the coverage less than or equal to 4/12 ML, CO favored the most stable bridge site adsorption, and the adsorption energies of CO have little difference; while at the coverage greater than or equal to 5/12 ML, the lateral repulsive interaction begins to affect the adsorption structures and the corresponding adsorption energies of adsorbed CO molecules, and the interaction will be stronger with the increasing of CO coverage, which leads to CO migration over Rh(100) surface when CO coverage is greater than or equal to 10/12 ML. The adsorption energies of these CO molecules will decrease successively until the saturated adsorption with the CO coverage of 12/12 ML. Further calculations on CO dissociation indicate that when CO coverage is greater than or equal to 3/12 ML, the dissociation of adsorbed CO molecules will be unfavorable both kinetically and thermodynamically, suggesting that only molecule CO adsorption are favored. Considering the catalytic activity of Rh(100) surface toward CO dissociation and the higher CO coverage under the continuous supply of CO in syngas conversion, it is to be expected that only molecule CO adsorption exist on Rh catalyst.

ChemInform Abstract: Chemical Modification of Catalyst Support for Enhancement of Transient Catalytic Activity: Nitric Oxide Reduction by Carbon Monoxide Over Rhodium.

A commercial ceria powder was chemically modified by doping with gadolinia in order to improve its oxygen storage/transport characteristics. The catalytic activity of Rh impregnated on this modified ceria support was measured and compared with those impregnated on conventional ceria or alumina support, using a packed-bed reactor and an isotopic reactant (13CO) for the NO + CO reaction under both cycled- and steady-feed conditions. Results of transient pulse experiments indicated that the oxygen uptakes of both ceria and modified ceria are an order of magnitude greater than that of alumina. This work has demonstrated that the chemical modification of the ceria support can significantly enhance the catalytic activity of Rh for the NO + CO reaction under cycled feedstream conditions at high temperatures above 500°C. This enhancement of catalytic activity of Rh supported on the modified ceria is discussed in light of the oxygen storage and transport characteristics of the modified support.

ChemInform Abstract: Synthesis, Characterization, and Catalytic Activity of Rh(PPh3)2(en)Cl Complex.

Ethylenediamine bis(triphenylphosphine) monochlororhodium has been prepared by the interaction of Wilkinson's catalyst and ethylenediamine in benzene. The complex has been isolated and characterized by conventional and spectroscopic methods. The catalytic activity of the complex was investigated for the hydrogenation of 1-octene as a model reaction at a hydrogen pressure of 1 atmosphere (101 kPa) using methanol as a solvent. The influence of various factors such as catalyst, substrate concentrations and temperature have been studied. The hydrido complex has been identified as an intermediate product by IR and NMR studies. The experimental data are in accordance with a rate expression of the form: .

Hydrogenation of unsaturated hydrocarbons catalyzed by homogeneous and supported Rh, Rh-Co, and Pd, Pd-Ni complexes with oligomeric allene ligands

Mono- and bimetallic Rh and Rh-Co complexes containing oligoallene ligands were synthesized. Their catalytic activity was examined in the hydrogenation of unsaturated compounds, such as isoprene, hexene-1, and toluene. The catalytic activity of Rh(DMA)ol and Rh-Co(DMA)ol was shown to be 16 800 and 23000 mol/(mol h) in the hydrogenation of hexene-1 and 72 and 90 mol/(mol h) in the hydrogenation of toluene, respectively. Isoprene is hydrogenated completely: the rate curves exhibit two portions corresponding to hydrogenation of both double bonds. The catalytic activity of palladium oligodimethylallene complexes deposited on an inorganic support (γ-Al2O3) in isoprene hydrogenation depends on the support preparation procedure, the particle size, and the metal loading on the surface. Heterogenization of the homogeneous mono- and bimetallic Rh and Pd complexes somewhat enhances the catalytic activity in hydrogenation of the given substrates.

Di-, tetra- and polynuclear RhI complexes containing phenylene-1,4-diaminotetra(phosphonite), p-C6H4[N{P(OC6H4OMe-o)2}2]2 and their catalytic investigation towards transfer hydrogenation reactions

The reactions of phenylene-1,4-diaminotetra(phosphonite), p-C(6)H(4)[N{P(OC(6)H(4)OMe-o)(2)}(2)](2) (P(2)N(Ph)NP(2)) () with [Rh(COD)Cl](2) in 1 : 2 and 1 : 1 molar ratio produce tetra- and polymetallic chelate complexes, [Rh(4)(COD)(2)(micro-Cl)(4)(P(2)N(Ph)NP(2))] () and [Rh(2)(micro-Cl)(2)(P(2)N(Ph)NP(2))](n) (), respectively. Similar reaction of with [Rh(COD)Cl](2) in dichloromethane-acetonitrile mixture furnishes a dinuclear complex, [Rh(2)Cl(2)(CH(3)CN)(2)(P(2)N(Ph)NP(2))] (). The reaction of or with CO affords a dinuclear carbonyl derivative, [Rh(2)Cl(2)(CO)(2)(P(2)N(Ph)NP(2))] (). Treatment of with 2 equivalents of pyrazine or 4,4'-bipyridine produce one-dimensional Rh(I) coordination polymers, [Rh(2)Cl(2)(C(4)H(4)N(2))(P(2)N(Ph)NP(2))](n) () and [Rh(2)Cl(2)(C(10)H(8)N(2))(P(2)N(Ph)NP(2))](n) in quantitative yields. The catalytic activity of Rh(I) complexes have been investigated in transfer hydrogenation reactions.

Correlation of Electrochemical Characteristics and Catalytic Activity of Rh2(OAc)4in the Presence of Various Phosphines

To improve the activity of dirhodium complexes in thecatalytic reactions or biological reactions, a variety ofligands can be employed not only at the axial position butalso at the bridging position of dirhodium complexes. Sinceligands at either bridging or axial positions vary the electronicand steric properties of dirhodium complexes, investigationson appropriate ligands through the electrochemical analysishave been demanded. The electrochemical analysis ofdirhodium complexes bearing electronically different ligandshas been reported to account for the different catalyticactivity of dirhodium complexes.

Strong inhibition effect of sulfur impurities in alumina supports on the catalytic activity of Rh in the CH 4–CO 2 reforming reaction

The influence of the sulfur impurity on the CH 4–CO 2 reforming reaction over Rh catalyst was studied. The activity of Rh/Al 2O 3 varied remarkably depending on the kinds of Al 2O 3 support. Based on the EXAFS and TPR measurements, the variations were ascribed to the changes in the reducibility of Rh as a result of the interaction with SO 4 2− present as impurity in the alumina support. In agreement with the assumption, the activity of Rh improved significantly as SO 4 2− was removed from the Al 2O 3 support. Based on the EXAFS analysis, the role of SO 4 2− anion was ascribed to the inhibition of the reduction of RhCl 3 to give metal Rh.

Small-scale hydrogen production from propane

Partial oxidation and oxidative steam reforming of propane were investigated over 0.01 wt.% Rh/Al 2O 3 foam catalysts. High selectivity to hydrogen was obtained for both reactions, but addition of steam to the reactant mixture gave higher selectivity to hydrogen. Stability tests over 7 h revealed that the catalytic activity of Rh was quite stable under partial oxidation conditions. Higher loss in Rh activity was observed when steam was present in the reactant mixture. FE-SEM images showed that Rh particle size and distribution are modified under partial oxidation and oxidative steam reforming conditions. However, these changes were more distinct on the catalyst used for oxidative steam reforming.

Support Effect of Metal Oxide on Rh Catalysts in the CH4-CO2 Reforming Reaction

Rhodium supported on various metal oxides was studied in the dry reforming reaction using methane and carbon dioxide, in order to reveal the effect of support on the catalytic activity of Rh. The TOF (turnover frequency) based on exposed Rh decreased in the following sequence of support: TiO2 > La2O3 = CeO2 > ZrO2 = MgO = SiO2 = MCM-41 > γ-Al2O3. The different TOF could be correlated with the stabilized species of Rh atom. It was concluded that the supports influenced the electronic state of Rh atoms, and that Rh metal catalyzed this reaction as a prominent active species.

ChemInform Abstract: Synthesis, Characterization, and Catalytic Activity of Rh(I) Complexes with (S)‐BINAPO, an Axially Chiral Inducer Capable of Hemilabile P,O‐Heterobidentate Coordination.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis, Characterization, and Catalytic Activity of Rh(I) Complexes with ( S)- BINAPO, an Axially Chiral Inducer Capable of Hemilabile P,O-Heterobidentate Coordination

Synthesis, Characterization, and Catalytic Activity of Rh(I) Complexes with ( S)- BINAPO, an Axially Chiral Inducer Capable of Hemilabile P,O-Heterobidentate Coordination

ChemInform Abstract: Catalytic Activity of Rh, Rh—Co, and Ir—Co Multinuclear Complexes and Application to Organic Syntheses

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Hydrogenation of acetone on technetium catalysts

The catalytic properties of supported mono- and bimetallic catalysts of the Tc/support, M/support, and M-Tc/support types (M=Pt, Pd, Rh, Ru, Ni, Re, Co; supports are γ-Al2O3, MgO, SiO2) were investigated in the acetone hydrogenation. The main products of this reaction are isopropyl alcohol and propane. The catalytic activity in the acetone hydrogenation of the metals studied decreases in the consequence Pt>Tc≈Rh>Pd>Ru >Ni≈Re>Co (with γ-Al2O3 as the support). The influence of support nature on the catalytic activity was investigated for the Rh−Tc system as an example. A nonadditive increase in the catalytic activity of Rh−Tc/γ-Al2O3 in comparison with monometallic catalysts was found. The state of the surface of the catalysts was characterized by the UV-VIS diffuse reflectance spectra.

Liquid-phase hydrogenation of 1-alkenes over Rh/AlPO 4 and Rh/sepiolite catalysts

The catalytic activity of Rh (1 wt.%) catalysts supported on AlPO 4 and sepiolite has been studied in the liquid-phase hydrogenation of linear 1-alkenes. The reaction orders with respect to 1-alkene concentration are negative but are first order with respect to hydrogen, indicating that 1-alkene adsorbs very strongly on Rh sites and alkene and H 2, compete for adsorption sites on the surface. The initial hydrogenation rates increase in the order 1-hexene < 1-heptene < 1-octene, and furthermore, on going from 1-hexene to 1-octene the steric effects (through Δ S ≠) are activating, while electronic effects (from Δ H ≠) deactivate the reaction process. A cis-concerted mechanism taking place in a single step on a Rh site with three coordinative unsaturations which can simultaneously adsorb hydrogen and a π-bonded alkene is suggested.