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Title: In Situ Structure-Function Studies of Oxide Supported Rhodium Catalysts by Combined Energy Dispersive XAFS and DRIFTS Spectroscopies

Abstract

The techniques of energy dispersive EXAFS (EDE), diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and mass spectrometry (MS) have been combined to study the structure and function of an oxide supported metal catalyst, namely 5 wt% Rh/Al2O3. Using a FreLoN camera as the EDE detector and a rapid-scanning IR spectrometer, experiments could be performed with a repetition rate of 50 ms. The results show that the nature of the rhodium centers is a function of the partial pressures of the reacting gases (CO and NO) and also temperature. This combination of gases oxidizes metallic rhodium particles to Rh(CO)2 at room temperature. The proportion of the rhodium adopting this site increases as the temperature is raised (up to 450 K). Above that temperature the dicarbonyl decomposes and the metal reclusters. Once this condition is met, catalysis ensues. Gas switching techniques show that at 573 K with NO in excess, the clusters can be oxidized rapidly to afford a linear nitrosyl complex; re-exposure to CO also promotes reclustering and the CO adopts terminal (atop) and bridging (2-fold) sites.

Authors:
 [1];  [2]; ;  [3];  [4]; ;  [1];  [5]
  1. School of Chemistry, University of Southampton, Southampton, SO17 1BJ (United Kingdom)
  2. (United Kingdom)
  3. Diamond Light Source, Chilton, Didcot, OX11 0DE (United Kingdom)
  4. CCLRC Daresbury Laboratory, Warrington, WA4 4AD (United Kingdom)
  5. ESRF, Grenoble, F-38043 (France)
Publication Date:
OSTI Identifier:
21054693
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 882; Journal Issue: 1; Conference: XAFS13: 13. international conference on X-ray absorption fine structure, Stanford, CA (United States), 9-14 Jul 2006; Other Information: DOI: 10.1063/1.2644606; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; ALUMINIUM OXIDES; CARBON MONOXIDE; CATALYSIS; CATALYSTS; FINE STRUCTURE; FOURIER TRANSFORM SPECTROMETERS; FOURIER TRANSFORMATION; GASES; INFRARED SPECTRA; INTERFACES; MASS SPECTROSCOPY; NITRIC OXIDE; OXIDATION; PARTIAL PRESSURE; RHODIUM; STRUCTURE FUNCTIONS; X-RAY SPECTROSCOPY

Citation Formats

Evans, John, Diamond Light Source, Chilton, Didcot, OX11 0DE, Dent, Andrew J., Diaz-Moreno, Sofia, Fiddy, Steven G., Jyoti, Bhrat, Tromp, Moniek, and Newton, Mark A. In Situ Structure-Function Studies of Oxide Supported Rhodium Catalysts by Combined Energy Dispersive XAFS and DRIFTS Spectroscopies. United States: N. p., 2007. Web. doi:10.1063/1.2644606.
Evans, John, Diamond Light Source, Chilton, Didcot, OX11 0DE, Dent, Andrew J., Diaz-Moreno, Sofia, Fiddy, Steven G., Jyoti, Bhrat, Tromp, Moniek, & Newton, Mark A. In Situ Structure-Function Studies of Oxide Supported Rhodium Catalysts by Combined Energy Dispersive XAFS and DRIFTS Spectroscopies. United States. doi:10.1063/1.2644606.
Evans, John, Diamond Light Source, Chilton, Didcot, OX11 0DE, Dent, Andrew J., Diaz-Moreno, Sofia, Fiddy, Steven G., Jyoti, Bhrat, Tromp, Moniek, and Newton, Mark A. Fri . "In Situ Structure-Function Studies of Oxide Supported Rhodium Catalysts by Combined Energy Dispersive XAFS and DRIFTS Spectroscopies". United States. doi:10.1063/1.2644606.
@article{osti_21054693,
title = {In Situ Structure-Function Studies of Oxide Supported Rhodium Catalysts by Combined Energy Dispersive XAFS and DRIFTS Spectroscopies},
author = {Evans, John and Diamond Light Source, Chilton, Didcot, OX11 0DE and Dent, Andrew J. and Diaz-Moreno, Sofia and Fiddy, Steven G. and Jyoti, Bhrat and Tromp, Moniek and Newton, Mark A.},
abstractNote = {The techniques of energy dispersive EXAFS (EDE), diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and mass spectrometry (MS) have been combined to study the structure and function of an oxide supported metal catalyst, namely 5 wt% Rh/Al2O3. Using a FreLoN camera as the EDE detector and a rapid-scanning IR spectrometer, experiments could be performed with a repetition rate of 50 ms. The results show that the nature of the rhodium centers is a function of the partial pressures of the reacting gases (CO and NO) and also temperature. This combination of gases oxidizes metallic rhodium particles to Rh(CO)2 at room temperature. The proportion of the rhodium adopting this site increases as the temperature is raised (up to 450 K). Above that temperature the dicarbonyl decomposes and the metal reclusters. Once this condition is met, catalysis ensues. Gas switching techniques show that at 573 K with NO in excess, the clusters can be oxidized rapidly to afford a linear nitrosyl complex; re-exposure to CO also promotes reclustering and the CO adopts terminal (atop) and bridging (2-fold) sites.},
doi = {10.1063/1.2644606},
journal = {AIP Conference Proceedings},
number = 1,
volume = 882,
place = {United States},
year = {Fri Feb 02 00:00:00 EST 2007},
month = {Fri Feb 02 00:00:00 EST 2007}
}
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  • Rhodium and platinum isocyanide complexes RhCl(CO)[CN(CH{sub 2}){sub 3}Si(OC{sub 2}H{sub 5}){sub 3}]{sub 2} (Rh-CNR{sub 2}), RhCl[CN(CH{sub 2}){sub 3}Si(OC{sub 2}H{sub 5}){sub 3}]{sub 3} (Rh-CNR{sub 3}), and PtCl{sub 2}[CN(CH{sub 2}){sub 3}Si(OC{sub 2}H{sub 5}){sub 3}]{sub 2} (Pt-CNR{sub 2}) were tethered to the silica-supported metal heterogeneous catalysts M-SiO{sub 2} (M = Pd, Pt, Ru) to give the TCSM (tethered complex on supported metal) catalysts Rh-CNR{sub 2}/Pd-SiO{sub 2}, Rh-CNR{sub 3}/M-SiO{sub 2} (M = Pd, Pt, Ru), and Pt-CNR{sub 2}/Pd-SiO{sub 2}. These TCSM catalysts were used to catalyze the hydrogenation of arenes (Rh-CNR{sub 2}/Pd-SiO{sub 2} and Rh-CNR{sub 3}/M-SiO{sub 2}) and cyclohexanone (Pt-CNR{sub 2}/Pd-SiO{sub 2}) under the mildmore » conditions of 40 C and 1 atm. They exhibit activities that are higher than those of the separate homogeneous rhodium (or platinum) isocyanide complex, the separate silica-supported metal heterogeneous catalyst, or the rhodium (or platinum) complex catalyst tethered on just SiO{sub 2}. The activities of the TCSM catalysts are strongly affected by the nature and loading of the supported metal in the catalyst. Among the three silica-supported metal M-SiO{sub 2} (M = Pd, Pt, Ru) catalysts, the rhodium complex Rh-CNR{sub 3} tethered on Pd-SiO{sub 2} exhibits the highest activity for the hydrogenation of toluene (TOF = 5.5 mol H{sub 2}/(mol Rh min) and TO = 2,420 mol H{sub 2}/mol Rh during 8.5 h). The Rh-CNR{sub 3}/Pd-SiO{sub 2} catalyst with 10 wt % Pd is more active than its counterparts with higher or lower palladium loadings. IR (DRIFT) spectral studies of the TCSM catalysts before and after being used for toluene hydrogenation show that the isocyanide ligands remain coordinated to the rhodium (or platinum) center even after extended use. Atomic emission spectroscopic analysis of hydrogenation solutions shows that there is no rhodium (or platinum) leaching into the solutions.« less