Alumina-supported Rhodium Catalysts Research Articles

Dry reforming of methane over alumina-supported rhodium catalysts at low temperatures under visible and near-infrared light

An alumina-supported metallic Rh catalyst (Rh/Al2O3) was found to be an effective catalyst in photo-assisted dry reforming of methane at around 473 K under visible and near-infrared light.

X-ray study of titania- and alumina-supported rhodium catalysts for the hydrogenation of hydrocarbons

An X-ray study of titaniaand alumina-supported rhodium catalysts for the hydrogenation of hydrocarbons is performed. Rhodium is shown to be present in the form of highly dispersed oxide, independent of the type of support. The atomic structure of alumina changes, while no change in the real structure of titanium oxide is observed.

Time-resolved, in situ DRIFTS/EDE/MS studies on alumina-supported rhodium catalysts: effects of ceriation and zirconiation on rhodium-CO interactions.

The effects of ceria and zirconia on the structure–function properties of supported rhodium catalysts (1.6 and 4 wt % Rh/γ-Al2O3) during CO exposure are described. Ceria and zirconia are introduced through two preparation methods: 1) ceria is deposited on γ-Al2O3 from [Ce(acac)3] and rhodium metal is subsequently added, and 2) through the controlled surface modification (CSM) technique, which involves the decomposition of [M(acac)x] (M=Ce, x=3; M=Zr, x=4) on Rh/γ-Al2O3. The structure–function correlations of ceria and/or zirconia-doped rhodium catalysts are investigated by diffuse reflectance infrared Fourier-transform spectroscopy/energy-dispersive extended X-ray absorption spectroscopy/mass spectrometry (DRIFTS/EDE/MS) under time-resolved, in situ conditions. CeOx and ZrO2 facilitate the protection of Rh particles against extensive oxidation in air and CO. Larger Rh core particles of ceriated and zirconiated Rh catalysts prepared by CSM are observed and compared with Rh/γ-Al2O3 samples, whereas supported Rh particles are easily disrupted by CO forming mononuclear Rh geminal dicarbonyl species. DRIFTS results indicate that, through the interaction of CO with ceriated Rh particles, a significantly larger amount of linear CO species form; this suggests the predominance of a metallic Rh phase.

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Catalytic partial oxidation of ethanol on alumina-supported rhodium catalysts: An experimental study

The catalytic partial oxidation of ethanol is experimentally studied over an alumina rhodium coated monolithic honeycomb catalyst at short contact times. The product distribution is analyzed as function of carbon-to-oxygen ratio (C/O) for two different space velocities by a variety of simultaneously applied methods such as Fourier transform infrared spectroscopy, sector mass spectrometry, paramagnetic gas analyzer and gas chromatography combined with mass spectrometry. Low C/O resulted in highly selective synthesis gas production, whereas by-products like methane, ethylene, acetaldehyde and diethyl ether became eminent with increasing C/O.

A New Supported Rhodium Catalyst for Selective Hydrogenation of Nitriles to Primary Amines

Nitriles are converted to primary amines with high selectivity using a newly developed alumina-supported rhodium catalyst. The high selectivity is obtained without any additives, which are often used to prevent the formation of higher amines. The catalyst is active under mild conditions in various solvents, which makes it specifically suitable for use in pharmaceutical applications or for other substrates that can react with additives like strong acids or bases.

Enantioselective hydrogenation of ethyl pyruvate catalyzed by alumina support rhodium modified with quinine

Alumina supported rhodium catalyst using cinchonidine as a stabilizer exhibited excellent performance in the asymmetric hydrogenation of ethyl pyruvate with the addition of quinine. Quinine as a chiral modifier can not only induce the enantioselectivity, but also greatly accelerate the reaction. Under the optimum conditions: 293 K, 7.0 MPa of hydrogen pressure and 4.6 × 10 −3 mol/L of quinine concentration in THF, TOF of Rh/2(cinchonidine)-γ-Al 2O 3 as catalyst and ee value of ( R)-ethyl lactate can achieve 894 h −1 and 71.6% ee, respectively.

In situ monitoring of oxide-supported platinum-group metal catalysts by energy dispersive EXAFS

Energy dispersive EXAFS (EDE), using a Laue monochromator on ID24 of the ESRF, and multiple ion monitoring mass spectrometry have been used to monitor the structure and function of alumina-supported rhodium and palladium catalysts within a microreactor. Metallic 5%-Rh/Al2O3 was preformed in situ by hydrogen reduction, and shown to react rapidly with NO at room temperature yielding an oxidised phase. In order for this material to catalyse the reduction of NO by H2 (to N2), it was shown that the metallic phase must be reformed. The “light-off” temperature at which the metallic phase was formed and catalysis commenced varied with NO : H2 stoichiometry, this temperature lowering in more reducing conditions. N2O formation was concomitant with the conversion from the oxidised to the metallic phase.The EDE configuration allowed the simultaneous monitoring of structure at both the rhodium and palladium K-edges. Incorporation of a 20% palladium mole fraction into 5%-Rh-Pd/Al2O3 protected rhodium from oxidation and also reduced the light-off temperature, and this is reflected in low coordination number values for the composite Pd to Rh/Pd shell. This favours palladium being preferentially on the surface of the nanoparticles. At higher temperatures there are changes in coordination numbers than imply a redistribution of metal sites under catalytic conditions. Future plans to include infrared spectroscopy as a third simultaneous technique will be outlined.

Hydrogen Production for Fuel Cells from the Catalytic Ethanol Steam Reforming

Alumina-supported rhodium catalysts were shown to be active, selective and stable catalysts in the catalytic ethanol steam reforming when the reaction is carried out under pressure (1.1 MPa). Both the nature of the metal precursor salt, the metal loading and the reaction conditions were shown to influence the activity, the selectivity and the stability of the catalysts. Some trends observed when the reaction is carried out under moderate pressure were shown to be different from the conclusions drawn from earlier results obtained at atmospheric pressure. In fact, rhodium catalysts derived from a chlorinated metal precursor were shown to be the most active, selective and stable.

Étude de l'effet des additifs Fe, Co, Ni sur l'interaction Rh–toluène sur Rh/Al 2O 3

Effect of added Fe, Co, Ni on Rh–toluene interaction for alumina-supported rhodium catalysts. A series of catalysts Rh–M/Al 2O 3 (M = Fe, Co, Ni, Pb) was prepared by solution-impregnation method. The catalysts modified by Fe, Co, Ni were studied by thermal programmed desorption (TPD) of toluene, then tested in hydrogenation reaction of toluene between 25 and 250 °C. The effect of lead, which is known as a poison of catalyst, was also studied. The results of toluene TPD show a decrease of Rh–toluene interaction strengths in the presence of Fe, Co and Ni, which are represented by a significant increase of the fraction of toluene desorbing molecularly from the rhodium surface. Consequently, these catalysts, modified by Fe, Co and Ni, give a best catalytic activity and stability. However, the lead affects noticeably the activity and stability of Rh/Al 2O 3 catalyst. To cite this article: F. Benseradj et al., C. R. Chimie 7 (2004) .

Effects of Isoflurane of Kinetics of N2O Catalytic Decomposition over Rh/Al2O3 in Medical Operating Rooms.

As a major anesthetic, a mixture of nitrous oxide (N2O), oxygen (O2) and isoflurane (CF3CHClOF2H) is used in medical operating rooms. Catalytic decomposition of N2O over alumina-supported rhodium catalyst (Rh/Al2O3) has been investigated to clean the air contaminated with N2O in medical operating rooms. Although N2O decomposition activities over Rh/Al2O3 were significantly decreased by isoflurane, N2O was completely decomposed at higher temperature. The deactivation effect of isoflurane was investigated and a reaction rate equation was proposed.

The effects of hydrogen pressure and temperature on the methylcyclopentane conversion on Rh catalysts

The effect of hydrogen pressure ( pH 2) and temperature ( T) was investigated on the hydrogenolytic ring opening of methylcyclopentane (MCP) over silica and alumina supported rhodium catalysts. Strong dependence could be seen in the activity and in distribution of ring opening products as a function of reaction conditions. Temperature and hydrogen pressure did not affect the position of the first C–C bond rupture. However, the final ring opening product distribution was largely influenced by the reaction conditions due to the different ability of intermediates to undergo further hydrogenolysis.

Evaluation of the Role of the Metal–Support Interfacial Centers in the Dry Reforming of Methane on Alumina-Supported Rhodium Catalysts

The reforming of CH4 with CO2 (dry reforming) has been studied on a series of Al2O3-supported Rh–Cu catalysts. The reaction has been found to proceed on these systems through a bifunctional mechanism, in which the activation on methane takes place on the rhodium phase while carbon dioxide is activated on the support surface via formate intermediates. The addition of a metal, such as copper, inactive for methane activation, has allowed us to evaluate the role of the interfacial Rh–Al2O3 sites in the reaction. The presence of copper reduces the stability of the catalysts, though it does not have any effect on the initial activity per surface exposed site. It indicates that the dry reforming of methane is not a structure-sensitive reaction and that catalytic activity, largely affected by the alumina support, is dependent on the number of surface exposed rhodium centers.

Decomposition of Acetate Groups on an Alumina-Supported Rhodium Catalyst

The decomposition of adsorbed acetate groups on a 1% Rh/Al2O3catalyst has been investigated by means of temperature-programmed desorption (TPD) at atmospheric pressure, in a microreactor fitted with an on-line mass spectrometer. Under certain conditions of catalyst pretreatment, the adsorbed acetate groups decompose autocatalytically in a process that has been described in the past as a “surface explosion.” The phenomenon of surface explosions has been investigated by various groups and was generally considered to be confined to ultrahigh vacuum regimes using single crystals. It is found, however, that the explosive acetate decomposition reaction actually translates directly to real supported metal catalysts at atmospheric pressure. A description is given involving the influence of adsorbed oxygen and differentiated acetate adsorption sites on the metal, the support, and at the interface between the two. Surface migration of the acetate groups is also involved in determining the intensities of the various TPD peaks.

The Preparation and Characterisation of Fe-Promoted Al2O3-Supported Rh Catalysts for the Selective Production of Ethanol from Syngas

This paper describes the development of a selective alumina-supported rhodium catalyst for the synthesis of ethanol from high pressure (10 bar) CO/H2mixtures. It has been shown that selectivity to ethanol of up to 50% can be achieved with an alumina-supported Rh catalyst containing 2 wt% Rh and promoted by 10 wt% Fe. Characterisation of the Fe-promoted Al2O3-supported Rh catalysts with increasing promoter loadings by selective chemisorption and temperature-programmed reduction (TPR) has provided evidence of a close interaction between the active metal and the promoter oxide especially at higher promoter loadings. The results obtained are consistent with the buildup of a close packed monolayer of the promoter oxide on the support surface which is possible due to the presence of a high surface density of hydroxyl groups on alumina. The influence of the metal precursor and the drying rate on the final metal salt distribution through the pore structure of a preshaped alumina support has also been investigated. It has been shown that impregnation of 1/16′′γ-alumina extrudates with an aqueous solution of iron nitrate causes the iron salt to be deposited at the outer edge of the pore structure. A more uniform distribution can be obtained if a methanolic solution of Fe(NO3)3or an aqueous solution of an organometallic complex is used as the deposited metal precursor.

Surface organometallic chemistry on metals: kinetics of the hydrogenolysis of tetra n-butyl tin on silica and alumina supported rhodium catalysts

The stoichiometry and the kinetics of the hydrogenolysis of tetra n-butyl tin on silica and alumina supported rhodium catalysts has been determined at 298 K in n-heptane. Various Rh/SiO 2 and Rh/Al 2O 3 catalysts have been prepared by exchange from [RhCl(NH 3) 5] (OH) 2 and by impregnation from RhCl 3 respectively. After reduction, metallic dispersions were found to vary from 0.45 to 0.9 as determined by hydrogen chemisorption measurements. Concerning the hydrogenolysis of the organotin complex, the amount of grafted tin was found to depend on the amount of tetra n-butyl tin introduced: since this amount is lower than the value corresponding to a ratio Sn/Rh s of 0.7, all the tin complex is grafted and the amount of grafted tin is directly proportional to the number of surface rhodium atoms; on average, each surface rhodium atom is able to graft 0.8 Sn(n-C 4H 9) x fragment. Above this ratio, the amount of grafted tin is almost independent of the amount of complex introduced. These results strongly support the hypothesis that the reaction occurs selectively on the metallic surface. The stoichiometry of the hydrogenolysis, determined by the amount of butane evolved per mole of grafted tin, depends on the coverage of the rhodium surface: for a low coverage, all the butyl groups are hydrogenolyzed, showing the formation of ‘naked’ tin atoms. For a full coverage, some butyl groups remain fixed on the surface showing the presence of grafted organotin species on the rhodium surface. The stoichiometry of the hydrogenolysis also depends on the reaction time for a given concentration of tetra n-butyl tin: at short reaction times which correspond to low coverages of the metallic particles, all the butyl groups are removed whereas this phenomenon is not observed at longer reaction times for which alkyl groups remain on the metallic surface. Kinetics of the hydrogenolysis indicates that the reaction is first order in ‘free surface adsorption site’ and zero order in tetra n-butyl tin.

Identification of ethylene-derived species on alumina-supported rhodium, iridium, palladium and platinum catalysts by infrared spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIdentification of ethylene-derived species on alumina-supported rhodium, iridium, palladium and platinum catalysts by infrared spectroscopySheher B. Mohsin, Michael Trenary, and Heinz J. RobotaCite this: J. Phys. Chem. 1991, 95, 17, 6657–6661Publication Date (Print):August 1, 1991Publication History Published online1 May 2002Published inissue 1 August 1991https://doi.org/10.1021/j100170a051RIGHTS & PERMISSIONSArticle Views171Altmetric-Citations36LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (671 KB) Get e-Alerts

Effects of cerium addition on the CONO reaction kinetics over alumina-supported rhodium catalysts

Laboratory reactor experiments have shown that the addition of cerium to a low-loaded Rh/Al 2O 3 catalyst gives rise to the following changes in the CONO reaction kinetics: suppression of N 2O formation, decreased apparent activation energy, and a shift to a positive-order dependence of the rate on NO partial pressure. These cerium-induced modifications of the kinetics lead to enhancement of the NO reduction activity at low temperatures. A simple kinetic analysis and temperature-programmed desorption experiments suggest that higher rates for both the NO dissociation and the low-temperature N 2 desorption steps in the presence of Ce may be responsible for the changes in the CONO reaction kinetics observed here.

Steady-state kinetics of the CON 2O reaction over an alumina-supported rhodium catalyst

Kinetics of the rhodium-catalyzed reaction between carbon monoxide (CO) and nitrous oxide (N 2O) were measured in a laboratory plug-flow reactor at temperatures between 550 and 700 K, space times between 0.06 and 0.26 s, and CO and N 2O partial pressures between 0.6 and 7 Torr. A brief comparison was also made between the CON 2O kinetics and kinetics of the CONO and COO 2 reactions. The comparison showed that the CON 2O reaction is an important subreaction of the CONO reaction (i.e., CO reacts initially with NO to produce N 2O which undergoes further reaction is much lower than rates of the CONO and COO 2 reactions (ratio of turnover frequencies at 475 K estimated as 1 (CON 2O) vs 7.1 × 10 2 (CONO) vs 4.4 × 10 5 (COO 2). CON 2O rate measurements under differential conversion conditions at temperatures of 564 and 583 K yielded reaction orders of −1.0 ± 0.15 in CO pressure, 0.65 ± 0.1 in N 2O pressure, and −0.30 ± 0.1 in total (CO + N 2O) pressure. The reaction orders and apparent activation energy (40 ± 2 kcal/gmol) are consistent with a mechanism involving reaction between adsorbed CO and adsorbed N 2O dissociation products. The low rate of the CON 2O reaction compared to the COO 2 and CONO reactions suggests that, under reaction conditions characterized by high CO coverages, the rate of dissociative N 2O adsorption is slow compared to the rates of dissociative O 2 or NO adsorption.

ChemInform Abstract: Controlled Oxygen Chemisorption on an Alumina Supported Rhodium Catalyst. Formation of a New Metal‐Metal Oxide Interface Determined with Extended X‐Ray Absorption Fine Structure Spectroscopy.

AbstractThe EXAFS spectra of Rh/Al2O3 catalysts obtained after oxygen admission at 100 K indicates the beginning of oxidation.