Rasband, PB
1993
Catalyst Characterization Using Quantitative FTIR: Co on Supported Rh
Rasband, P.B. and Hecker, W.C.
Journal of Catalysis, 139:55l, 1993. Funded by Brigham Young University.
Qualitative FTIR has been and continues to be one of the most utilized tools in the characterization of supported metal catalysts. Quantitative FTIR has the potential to allow catalysis researchers to determine the surface concentrations of active intermediates. However, its successful application depends upon an understanding of the factors affecting integrated absorption intensities (coefficients relating IR absorbance to surface concentration). This work addresses the effect of metal particle size and temperature on the absorption intensities for CO chemisorbed on Rh/SiO2. Absorption intensities for both linear and bridged CO surface species (a1 and Ab) were determined by combining peak area data from IR spectra with uptake measurements obtained in gravimetric experiments. This resulted in an A1 value of 13 (+/-2) and an Ab value of 42 (+/-6) cm/µmol. No statistically significant particle size effect has been observed for average spherical particle diameters ranging from 13 to 58 angstroms (100 to 22% dispersion). Also, integrated absorption intensities for linear and bridged CO were shown to vary little over the temperature range of 323 to 473 K. The discovery that absorption intensities determined for one temperature and metal dispersion may be used for other temperatures and dispersions is a welcome result that may broaden the application of quantitative FTIR. Rh dispersions were determined for Rh/SiO2 samples of 5 different weight loadings using the absorption intensities determined in this study. The variation of Rh dispersion with Rh loading was practically identical to that observed in nitrogen chemisorption experiments conducted on another series of Rh/SiO2 catalysts. Also, it was observed that the ratio of linear to bridges CO surface concentrations increased from 2 to 5 as Rh dispersion increased from 22 to 100%. These observations demonstrate the usefulness of a more fully developed quantitative FTIR technique.
1992
Catalyst Characterization Using Quantitative FTIR: CO on Supported Rh
Rasband, P.B. and Hecker, W.C.
Journal of Catalysis, 1992 (in press). Funded by Brigham Young University.
Qualitative FTIR has been and continues to be one of the most utilized tools in the characterization of supported metal catalysts. Quantitative FTIR has the potential to allow catalysis researchers to determine the surface concentrations of active intermediates. However, its successful application depends upon an understanding of the factors affecting integrated absorption intensities (coefficients relating IR absorbance to surface concentration). This work addresses the effect of metal particle size and temperature on the absorption intensities for CO chemisorbed on Rh/SiO2. Absorption intensities for both linear and bridged CO surface species (a1 and Ab) were determined by combining peak area data fro, IR spectra with uptake measurements obtained in gravimetric experiments. This resulted in an A1 value of 13 (± 2) and an Ab value of 42 (± 6) cm/µmol. No statistically significant particle size effect has been observed for average spherical particle diameters ranging from 13 to 58 angstroms (100 to 22% dispersion). Also, integrated absorption intensities for linear and bridged CO were shown to vary little over the temperature range of 323 to 473 K. The discovery that absorption intensities determined for one temperature and metal dispersion may be used for other temperatures and dispersions is a welcome result that may broaden the application of quantitative FTIR.
Rh dispersions were determined for Rh/SiO2 sample of 5 different weight loadings using the absorption intensities determined in this study. The variation of Rh dispersion with Rh loading was practically identical to that observed in hydrogen chemisorption experiments conducted on another series of Rh/SiO2 catalysts. Also, it was observed that the ratio of linear to bridges CO surface concentrations increased from 2 to 5 as Rh dispersion increased from 22 to 100%. These observations demonstrate the usefulness of a more fully developed quantitative FTIR technique.
Molybdena, Ceria, and Niobia Addition to Supported Rh Catalysts: Effects on NO Reduction by CO
Hecker, W.C.; Wardinsky, M.D.; Clemmer, P.G. and Rasband, P.B.
Proceedings of the Twelfth Canadian Symposium on Catalysis, 211-218, Alberta, Canada, May 1992. Funded by Brigham Young Unversity.
The kinetics of the reduction of NO by CO over Rh/molybdena/silica, Rh/ceria/silica, Rh/niobia/silica, and Rh/ceria/alumina catalysts have been studied. Catalysts have been characterized using H2 chemisorption and quantitative FTIR techniques for dispersion determination, and using in-situ and post reaction FTIR spectroscopy for site distribution study. The chief effect of molybdena, ceria, and niobia addition under the conditions of this study appears to be in the alteration of effective Rh particle size (dispersion) although Mo addition does seem to more directly affect catalyst activity. A plot of turnover does seem to more directly affect catalyst activity. A plot of turnover frequency versus Rh particle ize shows that all of the catalysts with the exception of the Rh/molybdena/silica exhibit a common structure sensitivity. This sensitivity has been explained qualitatively through mechanistic arguments.
1990
NO Reduction Activity and FTIR Characterization of Rhodium on Niobia-Modified SiO2
Rasband, P.B. and Hecker, W.C.
Catalysis Today, 8, 99-111, 1990. Funded by Brigham Young University.
Several 2% Rh/silica catalysts containing from 0 to 6% Nb205 were prepared by consecutive impregnations with aqueous solutions of niobium oxalate and rhodium trichloride. These catalysts were studied using Fourier Transform Infrared Spectroscopy (FTIR) to determine Rh oxidation state and dispersion. The addition of Nb205 to Rh/SiO2 resulted in a decrease in Rh(0) for relatively low niobia loadings (0 to 3% Nb2O5) and an increase in Rh(1) for higher niobia loadings (3 to 6% Nb205). These two effects combined to give a minimum Rh dispersion for a catalyst containing approximately 3% Nb2O5. For the reduction of NO by CO the niobia addition decreased the observed rate (per gram catalyst) but had little effect on activation energy or concentration dependencies. A combination of the observed rate and Rh dispersion data suggests that specific rate varies inversely with Rh dispersion for these catalysts and conditions.
Rasband, PB
1993
Catalyst Characterization Using Quantitative FTIR: Co on Supported Rh
Rasband, P.B. and Hecker, W.C.
Journal of Catalysis, 139:55l, 1993. Funded by Brigham Young University.
Qualitative FTIR has been and continues to be one of the most utilized tools in the characterization of supported metal catalysts. Quantitative FTIR has the potential to allow catalysis researchers to determine the surface concentrations of active intermediates. However, its successful application depends upon an understanding of the factors affecting integrated absorption intensities (coefficients relating IR absorbance to surface concentration). This work addresses the effect of metal particle size and temperature on the absorption intensities for CO chemisorbed on Rh/SiO2. Absorption intensities for both linear and bridged CO surface species (a1 and Ab) were determined by combining peak area data from IR spectra with uptake measurements obtained in gravimetric experiments. This resulted in an A1 value of 13 (+/-2) and an Ab value of 42 (+/-6) cm/µmol. No statistically significant particle size effect has been observed for average spherical particle diameters ranging from 13 to 58 angstroms (100 to 22% dispersion). Also, integrated absorption intensities for linear and bridged CO were shown to vary little over the temperature range of 323 to 473 K. The discovery that absorption intensities determined for one temperature and metal dispersion may be used for other temperatures and dispersions is a welcome result that may broaden the application of quantitative FTIR. Rh dispersions were determined for Rh/SiO2 samples of 5 different weight loadings using the absorption intensities determined in this study. The variation of Rh dispersion with Rh loading was practically identical to that observed in nitrogen chemisorption experiments conducted on another series of Rh/SiO2 catalysts. Also, it was observed that the ratio of linear to bridges CO surface concentrations increased from 2 to 5 as Rh dispersion increased from 22 to 100%. These observations demonstrate the usefulness of a more fully developed quantitative FTIR technique.
1992
Catalyst Characterization Using Quantitative FTIR: CO on Supported Rh
Rasband, P.B. and Hecker, W.C.
Journal of Catalysis, 1992 (in press). Funded by Brigham Young University.
Qualitative FTIR has been and continues to be one of the most utilized tools in the characterization of supported metal catalysts. Quantitative FTIR has the potential to allow catalysis researchers to determine the surface concentrations of active intermediates. However, its successful application depends upon an understanding of the factors affecting integrated absorption intensities (coefficients relating IR absorbance to surface concentration). This work addresses the effect of metal particle size and temperature on the absorption intensities for CO chemisorbed on Rh/SiO2. Absorption intensities for both linear and bridged CO surface species (a1 and Ab) were determined by combining peak area data fro, IR spectra with uptake measurements obtained in gravimetric experiments. This resulted in an A1 value of 13 (± 2) and an Ab value of 42 (± 6) cm/µmol. No statistically significant particle size effect has been observed for average spherical particle diameters ranging from 13 to 58 angstroms (100 to 22% dispersion). Also, integrated absorption intensities for linear and bridged CO were shown to vary little over the temperature range of 323 to 473 K. The discovery that absorption intensities determined for one temperature and metal dispersion may be used for other temperatures and dispersions is a welcome result that may broaden the application of quantitative FTIR.
Rh dispersions were determined for Rh/SiO2 sample of 5 different weight loadings using the absorption intensities determined in this study. The variation of Rh dispersion with Rh loading was practically identical to that observed in hydrogen chemisorption experiments conducted on another series of Rh/SiO2 catalysts. Also, it was observed that the ratio of linear to bridges CO surface concentrations increased from 2 to 5 as Rh dispersion increased from 22 to 100%. These observations demonstrate the usefulness of a more fully developed quantitative FTIR technique.
Molybdena, Ceria, and Niobia Addition to Supported Rh Catalysts: Effects on NO Reduction by CO
Hecker, W.C.; Wardinsky, M.D.; Clemmer, P.G. and Rasband, P.B.
Proceedings of the Twelfth Canadian Symposium on Catalysis, 211-218, Alberta, Canada, May 1992. Funded by Brigham Young Unversity.
The kinetics of the reduction of NO by CO over Rh/molybdena/silica, Rh/ceria/silica, Rh/niobia/silica, and Rh/ceria/alumina catalysts have been studied. Catalysts have been characterized using H2 chemisorption and quantitative FTIR techniques for dispersion determination, and using in-situ and post reaction FTIR spectroscopy for site distribution study. The chief effect of molybdena, ceria, and niobia addition under the conditions of this study appears to be in the alteration of effective Rh particle size (dispersion) although Mo addition does seem to more directly affect catalyst activity. A plot of turnover does seem to more directly affect catalyst activity. A plot of turnover frequency versus Rh particle ize shows that all of the catalysts with the exception of the Rh/molybdena/silica exhibit a common structure sensitivity. This sensitivity has been explained qualitatively through mechanistic arguments.
1990
NO Reduction Activity and FTIR Characterization of Rhodium on Niobia-Modified SiO2
Rasband, P.B. and Hecker, W.C.
Catalysis Today, 8, 99-111, 1990. Funded by Brigham Young University.
Several 2% Rh/silica catalysts containing from 0 to 6% Nb205 were prepared by consecutive impregnations with aqueous solutions of niobium oxalate and rhodium trichloride. These catalysts were studied using Fourier Transform Infrared Spectroscopy (FTIR) to determine Rh oxidation state and dispersion. The addition of Nb205 to Rh/SiO2 resulted in a decrease in Rh(0) for relatively low niobia loadings (0 to 3% Nb2O5) and an increase in Rh(1) for higher niobia loadings (3 to 6% Nb205). These two effects combined to give a minimum Rh dispersion for a catalyst containing approximately 3% Nb2O5. For the reduction of NO by CO the niobia addition decreased the observed rate (per gram catalyst) but had little effect on activation energy or concentration dependencies. A combination of the observed rate and Rh dispersion data suggests that specific rate varies inversely with Rh dispersion for these catalysts and conditions.