Rhodium-carbon monoxide surface chemistry: the involvement of surface hydroxyl groups on alumina and silica supports

Abstract

Direct spectroscopic evidence has been obtained indicating that specific OH groups on A1203 and Si02 are consumed as CO interacts with supported Rh crystallites to produce atomically dispersed RhI(CO)2(a). The reaction (1 /x)Rh°* + OH(a) + 2CO(g) -* RhI(CO)2(a) + (l/2)H2(g) has been shown to involve isolated OH(a) groups rather than H-bonded associated OH(a) species. The process may also be reversed upon treatment of the chemisorbed CO layer with H2(g) at temperatures above ~200 K. With the H2 treatment, Rh*(CO)2(a) species are converted back to Rh°* species as judged by changes in the IR spectrum where terminal CO(a) species (on Rh°* sites) and isolated OH(a) groups are regenerated. Comparative kinetic studies of OH(a) and OD(a) species indicate that the rate controlling step in the production of Rh*(CO)2(a) does not exhibit a measurable kinetic isotope effect.

Attenuated total reflection infrared spectroscopy for studying adsorbates on planar model catalysts: CO adsorption on silica supported Rh nanoparticles

“…Linearly adsorbed CO is observed with diffuse reflection infrared Fourier transform spectroscopy for highly dispersed Rh on silica at 2058-2065 cm −1 at room temperature, and at 2028 cm −1 at 498 K, 27 and for silica supported Rh at 2048-2067 cm −1 . 26,40 The fact that the peak of linear adsorbed CO in our case is observed at a lower frequency may indicate a low CO coverage or the formation of rhodium carbonyl hydride ͑H-Rh-CO͒, of which the CO stretch vibration is observed at 2020-2039 cm −1 for alumina supported Rh. 28,29 Although the hydrogen may originate from the hydroxylated surface or any residual H 2 from the reduction step, no change in OH content of hydroxylated SiOH groups around 3700-3500 cm −1 is observed upon CO exposure.…”

In Situ-DRIFTS Study of Rh Promoted CuCo/Al2O3for Ethanol Synthesis via CO Hydrogenation

“…23 The characteristic bands due to the linear adsorption of CO at Rh 0 sites on the catalyst with 1 wt % Rh were observed at around 2054, 1857 cm −1 , which correspond to linear and bridged carbonyl species respectively. 24 The double bands around 2020 and 2010 cm −1 usually correspond to the gemdicarbonyl species on Rh + . 25 However, the band at 2020 cm −1 is absent on 1Rh-CuCo/Al 2 O 3 , suggesting that this species may overlap with linearly adsorbed CO species on Cu sites.…”

Rhodium Supported on Silica-Stabilized Alumina for Catalytic Decomposition of N2O

“…By comparing the TPR results of the catalysts with the catalytic activity, it is worthy of noting that the easily reduced rhodium oxide should be responsible for the enhanced activity of the Rh/Si 0.19 Al-T catalysts, again exemplified the assumption above. [22][23][24]. The band at 2069 cm -1 , ascribed to linear carbonyl species, and at 1881 cm -1 , due to bridging carbonyls, both adsorbed on metallic rhodium particles.…”