Rh Al2O3 Research Articles

Effect of Functional Groups on Autothermal Partial Oxidation of Bio-oil. Part 1: Role of Catalyst Surface and Molecular Oxygen

Autothermal partial oxidation is a promising technique to upgrade bio-oil into syngas and commodity chemicals. This work aims to clarify preferred chemical routes in an autothermal system by investigating individually two-carbon molecules containing the functional groups found in bio-oil. Acids, alcohols, aldehydes, esters, ethers, and polyols were reacted over Pt– and Rh–Al2O3 catalysts. Also, to investigate thermal effects independent of O2-induced reactions, these molecules were passed over the same catalysts under similar conditions but in the absence of O2. Oxygen and adsorption geometry (the latter deduced from surface science literature) appear to play a key role in reaction initiation (manifested via overall conversion) and in the subsequent reaction of intermediate compounds. The catalyst identity also played a significant role in the observed product spectrum, and conversion was higher over the Rh catalyst. Polyols, ethers, and acids were the least reactive, while esters were the most reactive. ...

Electrocatalytic hydrogenation of catechol on Rh–Al2O3 in different media — pH-Dependent reduction mechanism for intermediate formation

The electrocatalytic hydrogenation of catechol was carried out in aqueous media in different pH ranges with Rh–Al2O3 powder catalyst. The reactions were conducted in an H-cell used as a dynamic cell, with a reticulated vitreous carbon electrode in contact with the catalyst powder as the working electrode. It was shown that the final product is 1,2-cyclohexanediol (cis and trans isomers) and that several intermediates are detected depending on the pH of the solution. Different media, from pH 5 to 13, were studied. One of the intermediates is 1,2-cyclohexanedione, detected at all pH values. The other is 2-hydroxycyclohexan-1-one, only observed at pH ≤ 7. To determine the mechanism of the reactions involved, the electrocatalytic hydrogenation of these intermediates to form the final 1,2-cyclohexanediol product was also conducted, and their UV spectroscopy and cyclic voltammetry data recorded. The influence of the nature of the solution was screened by measuring the Henry constant of each molecule.Key words: electrocatalytic hydrogenation of catechol, pH-dependent reduction mechanism, UV–vis spectroscopy, cyclic voltammetry, Henry constants.

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.

Clean catalytic combustion of nitrogen-bearing gasified biomass

Zero NOx emissions are obtained in the catalytic combustion of simulated biomass mixtures containing substantial amounts of ammonia by optimisation of NH3 oxidation and NOx reduction using a 2%Rh–Al2O3 catalyst.

Diastereoselective hydrogenation of o-toluic acid derivatives over supported rhodium and ruthenium heterogeneous catalysts

Asymmetric hydrogenation of an o-toluic acid derivative to 2-methylcyclohexanoic acid with high optical selectivity (up to 95%) was performed by using (S)-pyroglutamic acid methyl ester as a chiral auxiliary and Rh–Al2O3 as the catalyst.

A Transient Kinetic Study of the Co/H2 Reaction on Rh/Al2O3 Using FTIR and Mass Spectroscopy

The evolution of surface species (their chemical composition and surface coverage) formed during the CO/H2 reaction at 220°C on 1 wt% Rh/Al2O3 catalyst was studied by transient isotopic and various hydrogen titration techniques using both in situ mass spectrometry and FTIR. There is a very small amount of active carbon, CHx (θCHx < 0.03), and a large amount of surface linear and bridged CO species (θCO = 0.93) which participate in the formation of CH4 during reaction. Their amounts stay practically constant with reaction time in CO/H2 even after 1 h on stream. Also present on the Rh surface are some CxHy (alkyl chains) species which largely grow with reaction time (during the first hour on stream) but do not participate in the reaction mechanism of CH4 formation (spectator species). In addition, formate and carbonate (spectator species) build slowly on the alumina support surface even after 1 h of reaction. The surface coverage of hydrogen, θH, is found to be very small, a result consistent with the coverages of CO, CHx, and CxHy species. CO dissociation over the present 1 wt% Rh/Al2O3 (1.5-nm Rh particles) appears to largely control the overall rate of methane formation, a result similar to that previously reported over the 5 wt% Rh Al2O3 (9.0-nm Rh particles) catalyst.

The Promotion Effect of Rare Earth Oxides on the Hydrogenation of Carbon Monoxide over Rh–Al2O3 Catalyst

Abstract The addition of Dy2O3, Nd2O3, Yb2O3, La2O3, or Gd2O3 to the Rh–Al2O3 catalyst enhanced the activity of the hydrogenation of CO to methane. There was the linear relationship between the carbon skeleton propagation of the hydrocarbons formed and the basicity of the rare earth oxides.

Infrared spectroscopic study of CO and CO2 adsorption on Rh–ZrO2, Rh–Al2O3 and Rh–MgO

The adsorption states of CO and CO2 on Rh catalysts supported on ZrO2, Al2O3 and MgO were studied using i.r. spectroscopy. Upon adsorption of CO on reduced Rh–ZrO2, the carbonate bands due to the reaction 2CO →C + CO2, together with the bands of twin, linear and bridge CO species were observed at moderate temperatures, whereas Rh–MgO gave no appreciable formation of CO2 even at higher temperatures (> 100 °C) and Rh–Al2O3 showed intermediate behaviour. On the adsorption of CO2, the linear CO band was formed at lower frequency than that on CO adsorption. The linear CO species formed from CO2 showed higher reactivity toward hydrogen compared with that from CO adsorption.