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Copper promoted cobalt and nickel catalysts supported on ceria−alumina mixed oxide / Benjaram M. Reddy in Industrial & engineering chemistry research, Vol. 48 N° 18 (Septembre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 18 (Septembre 2009) . - pp. 8478–8486 Titre : Copper promoted cobalt and nickel catalysts supported on ceria−alumina mixed oxide : structural characterization and CO oxidation activity Type de document : texte imprimé Auteurs : Benjaram M. Reddy, Auteur ; Komateedi N. Rao, Auteur ; Pankaj Bharali, Auteur Année de publication : 2010 Article en page(s) : pp. 8478–8486 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : CoO,  NiO,  CuO−CoO  CuO−NiO  nanocrystalline  Catalytic  activity Résumé : Catalytic activity of CoO, NiO, CuO−CoO, and CuO−NiO nanocrystalline mono- and bimetallic catalysts over a thermally stable and high surface area ceria−alumina mixed oxide support was evaluated for oxidation of carbon monoxide at normal atmospheric pressure and lower temperatures. The content of Co or Ni in the respective monometallic catalysts was 10 wt % and the Cu-promoted samples contained 5 wt % each. These catalysts were prepared by a wet impregnation procedure and the CeO2−Al2O3 support was obtained by a deposition precipitation method. The synthesized catalysts were characterized by BET surface area, X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDX), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. XRD patterns of 773 K calcined samples revealed the presence of metal oxide phases, namely, CeO2, CuO, NiO, and Co3O4 in the respective catalysts. However, after calcination at 1073 K, the XRD lines corresponding to CuO and NiO were absent. EDX results confirmed the actual amount of metal loadings in the respective catalysts. The H2-TPR results suggested that Cu-doping accelerates and decreases the onset reduction temperature of monometallic samples. Raman results of 773 K calcined samples showed a prominent broad peak at 461 cm−1 corresponding to the F2g Raman active mode of CeO2. The TEM studies confirmed the presence of nanosized composite oxides with narrow size distribution of metal oxide particles. The XPS results disclosed the presence of Cu1+ species along with Cu2+ and the promotional effect of Cu in Co-containing samples to suppress the formation of the CoAl2O4 phase. Among different catalysts, the copper promoted CuO−NiO/CeO2−Al2O3 sample exhibited better activity for CO oxidation at lower temperatures. The better activity of the catalyst is attributed to the formation of well-dispersed and highly reducible metal oxide species over the mixed oxide support. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900755b [article] Copper promoted cobalt and nickel catalysts supported on ceria−alumina mixed oxide : structural characterization and CO oxidation activity [texte imprimé] / Benjaram M. Reddy, Auteur ; Komateedi N. Rao, Auteur ; Pankaj Bharali, Auteur . - 2010 . - pp. 8478–8486. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 18 (Septembre 2009) . - pp. 8478–8486 Mots-clés : CoO,  NiO,  CuO−CoO  CuO−NiO  nanocrystalline  Catalytic  activity Résumé : Catalytic activity of CoO, NiO, CuO−CoO, and CuO−NiO nanocrystalline mono- and bimetallic catalysts over a thermally stable and high surface area ceria−alumina mixed oxide support was evaluated for oxidation of carbon monoxide at normal atmospheric pressure and lower temperatures. The content of Co or Ni in the respective monometallic catalysts was 10 wt % and the Cu-promoted samples contained 5 wt % each. These catalysts were prepared by a wet impregnation procedure and the CeO2−Al2O3 support was obtained by a deposition precipitation method. The synthesized catalysts were characterized by BET surface area, X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDX), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. XRD patterns of 773 K calcined samples revealed the presence of metal oxide phases, namely, CeO2, CuO, NiO, and Co3O4 in the respective catalysts. However, after calcination at 1073 K, the XRD lines corresponding to CuO and NiO were absent. EDX results confirmed the actual amount of metal loadings in the respective catalysts. The H2-TPR results suggested that Cu-doping accelerates and decreases the onset reduction temperature of monometallic samples. Raman results of 773 K calcined samples showed a prominent broad peak at 461 cm−1 corresponding to the F2g Raman active mode of CeO2. The TEM studies confirmed the presence of nanosized composite oxides with narrow size distribution of metal oxide particles. The XPS results disclosed the presence of Cu1+ species along with Cu2+ and the promotional effect of Cu in Co-containing samples to suppress the formation of the CoAl2O4 phase. Among different catalysts, the copper promoted CuO−NiO/CeO2−Al2O3 sample exhibited better activity for CO oxidation at lower temperatures. The better activity of the catalyst is attributed to the formation of well-dispersed and highly reducible metal oxide species over the mixed oxide support. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900755b

Thermal stability and dispersion behavior of nanostructured CexZr1-xO2 mixed oxides over anatase-TiO2 / Benjaram M. Reddy in Industrial & engineering chemistry research, Vol. 48 N°1 (Janvier 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N°1 (Janvier 2009) . - P. 453-462 Titre : Thermal stability and dispersion behavior of nanostructured CexZr1-xO2 mixed oxides over anatase-TiO2 : a combined study of CO oxidation and characterization by XRD, XPS, TPR, HREM, and UV-Vis DRS Type de document : texte imprimé Auteurs : Benjaram M. Reddy, Editeur scientifique ; Pankaj Bharali, Editeur scientifique ; Pranjal Saikia, Editeur scientifique Année de publication : 2009 Article en page(s) : P. 453-462 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Nanostructured  CexZr1−xO2  Thermal  stability  Oxides  Anatase-TiO2 Résumé : A study has been undertaken on the thermal stability and dispersion behavior of nanostructured CexZr1−xO2 mixed oxides over anatase-TiO2 support, synthesized by a deposition coprecipitation method and subjected to heat treatments at different temperatures. An unsupported CexZr1−xO2 mixed oxide was also synthesized by coprecipitation method for the purpose of comparison. The structural/morphological characterization was performed using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS), UV−visible diffuse reflectance spectroscopy (UV−vis DRS), and temperature-programmed reduction (TPR) techniques. XRD measurements revealed the presence of cubic Ce0.75Zr0.25O2 phase at 773 K and incorporation of more zirconium into the ceria lattice at higher temperatures. HREM analysis conformed highly dispersed Ce−Zr nano-oxides over anatase-TiO2 support having the sizes in the range of 3−5 nm at 773 K. At higher temperatures, a slight increase in the crystallite size (5−10 nm) has been observed. The XPS measurements revealed the stabilization of Ce3+ at higher temperatures and presence of Zr and Ti in 4+ oxidation states. UV−vis DRS studies showed that oxygen to metal (Ce4+/Ce3+) charge-transfer transitions occur at lower wavelengths in the case of CexZr1−xO2/TiO2 compared to pure CexZr1−xO2. TPR experiments revealed that the surface reduction of CexZr1−xO2/TiO2 takes place at lower temperatures, which facilitates better CO oxidation activity in comparison to the unsupported CexZr1−xO2. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8012677 [article] Thermal stability and dispersion behavior of nanostructured CexZr1-xO2 mixed oxides over anatase-TiO2 : a combined study of CO oxidation and characterization by XRD, XPS, TPR, HREM, and UV-Vis DRS [texte imprimé] / Benjaram M. Reddy, Editeur scientifique ; Pankaj Bharali, Editeur scientifique ; Pranjal Saikia, Editeur scientifique . - 2009 . - P. 453-462. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N°1 (Janvier 2009) . - P. 453-462 Mots-clés : Nanostructured  CexZr1−xO2  Thermal  stability  Oxides  Anatase-TiO2 Résumé : A study has been undertaken on the thermal stability and dispersion behavior of nanostructured CexZr1−xO2 mixed oxides over anatase-TiO2 support, synthesized by a deposition coprecipitation method and subjected to heat treatments at different temperatures. An unsupported CexZr1−xO2 mixed oxide was also synthesized by coprecipitation method for the purpose of comparison. The structural/morphological characterization was performed using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS), UV−visible diffuse reflectance spectroscopy (UV−vis DRS), and temperature-programmed reduction (TPR) techniques. XRD measurements revealed the presence of cubic Ce0.75Zr0.25O2 phase at 773 K and incorporation of more zirconium into the ceria lattice at higher temperatures. HREM analysis conformed highly dispersed Ce−Zr nano-oxides over anatase-TiO2 support having the sizes in the range of 3−5 nm at 773 K. At higher temperatures, a slight increase in the crystallite size (5−10 nm) has been observed. The XPS measurements revealed the stabilization of Ce3+ at higher temperatures and presence of Zr and Ti in 4+ oxidation states. UV−vis DRS studies showed that oxygen to metal (Ce4+/Ce3+) charge-transfer transitions occur at lower wavelengths in the case of CexZr1−xO2/TiO2 compared to pure CexZr1−xO2. TPR experiments revealed that the surface reduction of CexZr1−xO2/TiO2 takes place at lower temperatures, which facilitates better CO oxidation activity in comparison to the unsupported CexZr1−xO2. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8012677