The influence of support on the geminal dicarbonyl species RhI(CO)2 on supported rhodium catalysts: an IR spectroscopic study

Mießner, H.; Gutschick, D.; Ewald, H.; Müller, Hansgeorg

doi:10.1016/0304-5102(86)85092-1

Cited by 36 publications

(41 citation statements)

References 55 publications

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“…The former are generally attributed to linear Rh-bonded CO vibrations and the latter to bridge Rh-coordinated CO. The presence of both types of species in Rh supported on macroporous materials 6,12,13,15-17,31,33,34,43-52 and zeolites 16,17,19,32,53 has been widely reported.…”

Section: Resultsmentioning

confidence: 99%

“…16,54 It results in two bands in the CO IR spectrum: one in-phase CO stretching vibration between 2118 and 2070 cm -1 and one out-of-phase stretching vibration between 2053 and 2007 cm -1 . 6,[12][13][14][15][16][17][18]30,31,[33][34][35][43][44][45][46][48][49][50][51][52][53][54][55][56] Next to these, linearly bonded CO adsorbed on Rh metallic particles has been reported to give rise to a band between 2075 and 2031 cm -1 , whereas CO linearly adsorbed on oxidized Rh 1+ or Rh 2+ crystallites is attended with a band between 2135 and 2110 cm -1 . 6,12,[15][16][17]19,[32][33][34][43][44][45][46][47][48][49][50][51]53 In order to unambiguously assign...…”

Section: Resultsmentioning

confidence: 99%

“…According to literature, the loading, dispersion, particle size, and coordination number of Rh, its precursor, the reduction temperature, and CO exposure pressure can affect the observed IR data, whereas sample pretreatment, CO exposure temperature, CO adsorption, and CO interaction with support cations may play a role as well. [12][13][14][15][16][17][18][19][20] To prevent erroneous assignments and conclusions, special attention has been paid to keep the experimental parameters and the instrumental settings as far as possible identical.…”

Section: Experimental Methodsmentioning

confidence: 99%

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Promotion Effects in the Oxidation of CO over Zeolite-Supported Rh Nanoparticles

et al. 2008

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Rh particles with an average diameter smaller than 1.5 nm have been supported on a series of zeolite Y samples. These zeolite materials contained different monovalent (H + , Na + , K + , Rb + , and Cs + ) and divalent (Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ ) cations and were used as model systems to investigate the effect of promoter elements in the oxidation of CO over supported Rh particles in excess of oxygen. Infrared (IR) spectroscopy was carried out to monitor the electronic changes in the local environment of Rh-adsorbed CO. It was found that the bands corresponding to two Rh gem-dicarbonyl species, Rh + (CO) 2 -(O z ) 2 and Rh + (CO) 2 -(O z )(H 2 O), shift to lower wavenumbers with increasing ionic radius/charge ratio of the cation. In addition, the relative intensity of the bridge bonded CO as compared to the total absorbance of Rh-bonded CO species decreases with increasing Lewis acidity, as expressed by the Kamlet-Taft parameter R of the cation. This trend could be directly correlated to the Rh CO oxidation activity, since low temperatures at 50% CO conversion corresponded with catalyst materials with a high contribution of bridge-bonded CO species and hence with small R values. A lower Lewis acidity causes an increased electron density on the framework oxygen atoms and thus an increased electron density on the zeolite-supported Rh particles. Comparable trends have been observed previously on a similar series of cation containing zeolite supported Pt catalyst materials.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Experimental Methodsmentioning

confidence: 99%

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Promotion Effects in the Oxidation of CO over Zeolite-Supported Rh Nanoparticles

et al. 2008

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“…At very low CO pressure (spectrum 1), a single band is observed at 2050 cm −1 , assigned to the stretching mode of linear monocarbonyl species on Rh metal particles, Rh 0 (CO) [14,15]. At increasing CO pressure, two shoulders appear above and below the band at 2050 cm −1 , due to, respectively, the symmetric and antisymmetric stretching modes of dicarbonyl species on oxidized Rh species, that is, Rh I (CO) 2 [16]. In same spectra, absorptions below 1800 cm −1 increase, with maxima discernible at 1680 cm [17][18][19].…”

Section: Resultsmentioning

confidence: 99%

“…The weak band discernible at 2096 cm −1 is due to the symmetric stretching mode of Rh I (CO)2 species. The twin antisymmetric mode, expected at around 2030 cm −1 [14][15][16], is most probably hidden in the tail of the main component at 2050 cm −1 , which indeed shows a low-frequency side asymmetry evidenced by the vertical broken line in the figure. In the same spectra, bands due to carbonate-, hydrogenocarbonate-, and formate-type species are also observed.…”

Section: Resultsmentioning

confidence: 99%

In Situ IR Characterization of CO Interacting with Rh Nanoparticles Obtained by Calcination and Reduction of Hydrotalcite‐Type Precursors

Basile

Bersani

Gallo

et al. 2011

International Journal of Spectroscopy

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Supported Rh nanoparticles obtained by reduction in hydrogen of severely calcined Rh/Mg/Al hydrotalcite-type (HT) phases have been characterized by FT-IR spectroscopy of adsorbed CO [both at room temperature (r.t.) and nominal liquid nitrogen temperature] and Transmission Electron Microscopy (TEM). The effect of reducing temperature has been investigated, showing that Rh crystal size increases from 1.4 nm to 1.8 nm when the reduction temperature increases from 750• C to 950 • C. The crystal growth favours the formation of bridged CO species and linear monocarbonyl species with respect to gem-dicarbonyl species; when CO adsorbs at r.t., CO disproportionation occurs on Rh and it accompanies the formation of Rh I (CO) 2 . The role of interlayer anions in the HT precursors to affect the properties of the final materials has been also investigated considering samples prepared from silicate-instead of carbonate-containing precursors. In this case, formation of Rh I (CO) 2 and CO disproportionation do not occur, and this evidence is discussed in terms of support effect.

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Supported rhodium catalysts. Support effects on state and dispersion of the rhodium

Zaki¹,

Tesche²,

Kraus³

et al. 1988

Surface & Interface Analysis

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Using SiO,, y-A120, and MgO as typical examples for acidic, amphoteric and basic oxides, the effect of the support nature on the behaviour of Rh was studied by temperature-programmed reduction, transmissioll electron microscopy and IR spectroscopy of adsorbed CO. Reduction is much easier on SiO, than on Al,O, and MgO. The highest metal dispersion is stabilized on Al,O, , while particle aggregation to particles with diameters of up to 6 nm occurs on SiO, during severe reduction and on MgO even under mild reduction conditions. The mobility of Rho atoms and the nucleation rates seem to be larger on MgO than on the other supports. In the presence of CO, the very small particles are disrupted with formation of Rh+(CO), complexes at temperatures below 300 K; at higher temperatures CO acts as a reducing agent and induces particle growth. It seems that particle disruption is favoured on the supports having the more acidic OH groups. Apart from the support nature, the nature of the precursor complex in solution and the solvent play a decisive role for the reducibility of rhodium.

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The influence of support on the geminal dicarbonyl species RhI(CO)2 on supported rhodium catalysts: an IR spectroscopic study

Cited by 36 publications

References 55 publications

Promotion Effects in the Oxidation of CO over Zeolite-Supported Rh Nanoparticles

Promotion Effects in the Oxidation of CO over Zeolite-Supported Rh Nanoparticles

In Situ IR Characterization of CO Interacting with Rh Nanoparticles Obtained by Calcination and Reduction of Hydrotalcite‐Type Precursors

Supported rhodium catalysts. Support effects on state and dispersion of the rhodium

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