Benjaram Reddy - Academia.edu (original) (raw)

Papers by Benjaram Reddy

Res Chem Intermediates, 1998

Langmuir, 2003

The evolution and physicochemical characteristics of CeO2-ZrO2 and V2O5/CeO2-ZrO2 samples under t... more The evolution and physicochemical characteristics of CeO2-ZrO2 and V2O5/CeO2-ZrO2 samples under the influence of thermal treatments from 773 to 1073 K were investigated using X-ray diffraction (XRD), BET surface area, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The CeO 2-ZrO2 mixed oxide was synthesized by a coprecipitation method, and a nominal 12 wt % V2O5 was deposited over the calcined support (773 K) by a wet impregnation technique. The X-ray powder diffraction analysis suggests formation of a Ce 0.75Zr0.25O2 cubic phase at 773 K. With increasing calcination temperature, better crystallization of this phase and incorporation of more zirconium into the ceria lattice were noted. The mean crystallite size and a cell parameter values obtained from XRD measurements strongly support this observation. The results further suggest that impregnation of vanadium oxide over the CeO2-ZrO2 surface accelerates the crystallization of Ce0.75Zr0.25O2 and incorporation of more zirconium into the ceria lattice, thereby facilitating appearance of zirconia-rich phases. A preferential formation of CeVO4 compound was also noted at higher calcination temperatures. The XRD and Raman results, in particular, provide direct evidence about the formation of CeVO 4. The XPS measurements reveal stabilization of Ce(III) at higher calcination temperatures and no significant changes in the oxidation states of Zr(IV) and V(V).

J Phys Chem B, 2004

The techniques of X-ray diffraction (XRD), Raman spectroscopy (RS), and X-ray photoelectron spect... more The techniques of X-ray diffraction (XRD), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS) were employed to investigate dispersion and structural characteristics of V 2 O 5 /CeO 2 -MO 2 (M ) Si 4+ , Ti 4+ , and Zr 4+ ) catalysts calcined at different temperatures from 773 to 1073 K. The CeO 2 -MO 2 (1:1 mole ratio) mixed oxides were obtained by soft chemical methods with ultrahigh-dilution solutions, and a nominal monolayer equivalent of V 2 O 5 was deposited over the calcined (773 K) supports. The XRD and RS results suggest that the CeO 2 -MO 2 carrier calcined at 773 K exhibits the presence of nanocrystalline cubic CeO 2 on the surface of SiO 2 in CeO 2 -SiO 2 , CeO 2 and TiO 2 (anatase) in CeO 2 -TiO 2 , and Ce 0.75 Zr 0.25 O 2 in CeO 2 -ZrO 2 samples. The impregnation of vanadia over CeO 2 -MO 2 and their subsequent calcination at higher temperatures leads to various modifications. The deposited V 2 O 5 is in a highly dispersed state when calcined at 773 K. In particular, no crystalline V 2 O 5 is observed at all calcination temperatures. The dispersed vanadia on the CeO 2 -MO 2 carrier induces better crystallization of various phases and a preferential formation of CeVO 4 in all samples. Incorporation of more zirconia into the Ce 0.75 Zr 0.25 O 2 cubic lattice leading to the manifestation of a Ce 0.16 Zr 0.84 O 2 tetragonal phase at higher calcination temperatures is noted in the case of CeO 2 -ZrO 2 samples. The RS measurements disclose the presence of oxygen vacancies/Ce 3+ in all samples in different proportions. The XPS results reveal that O 1s, Ce 3d, and V 2p core-level photoelectron peaks are sensitive to the calcination temperature and the nature of mixed-oxide system. The formation of CeVO 4 at various temperatures is established from all characterization results.

J Mol Catal a Chem, 2006

Influence of CaO on TiO2 (anatase) phase stabilization and dispersion behaviour of V2O5 over CaO–... more Influence of CaO on TiO2 (anatase) phase stabilization and dispersion behaviour of V2O5 over CaO–TiO2 mixed oxide support have been investigated using XRD, FTIR, Raman, XPS, and BET surface area techniques. The CaO–TiO2 binary oxide (1:1 molar ratio) was synthesized by a homogeneous co-precipitation method from ultrahigh dilute solutions of the corresponding chlorides and calcined at various temperatures from 723 to 1273 K. On the calcined CaO–TiO2 support (723 K) various amounts of V2O5 (2.5–10 wt.%) were deposited from ammonium metavanadate by a wet impregnation method and calcined at different temperatures. Conversion of cyclohexanol to cyclohexanone/cyclohexene was performed as a model reaction to assess the acid–base properties of the prepared catalysts. The CaO–TiO2 composite oxide exhibits reasonably high specific surface area and high thermal stability up to 1273 K retaining titania-anatase phase. The deposited V2O5 over CaO–TiO2 support is present mostly in a dispersed form. Further, a strong and preferential interaction between the basic CaO and the dispersed V2O5 leads to the formation of CaVO3 and the physicochemical properties of the prepared catalysts are clearly reflected in their catalytic activity.Influence of CaO on TiO2-anatase phase stabilization and dispersion of V2O5 over CaO–TiO2 have been investigated using different techniques. The CaO–TiO2 and V2O5/CaO–TiO2 exhibit more selectivity towards cyclohexanone and cyclohexene, respectively, reflecting their acid–base properties.

J Mol Catal a Chem, 2007

The influence of various alkaline earth metal oxides (CaO, SrO and BaO) on the acid–base properti... more The influence of various alkaline earth metal oxides (CaO, SrO and BaO) on the acid–base properties of TiO2 and the dispersion behaviour of V2O5 over MO−TiO2 (M = Ca, Sr and Ba) have been investigated systematically. The MO−TiO2 binary oxides (1:1 molar ratio) were synthesized by adopting a co-precipitation method from the corresponding chloride precursors by in situ hydrolysis with urea and calcined at various temperatures from 723 to 1073 K. A nominal 10 wt.% V2O5 was deposited over the calcined (773 K) MO−TiO2 supports by a wet impregnation method. The synthesized catalysts were characterized using X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), thermogravimetry–differential thermal analysis (TG–DTA) and BET surface area techniques. The MO−TiO2 composite oxides exhibited reasonably high-specific surface area and high-thermal stability retaining titania-anatase phase up to 1073 K treatment temperature. The impregnated V2O5 over MO−TiO2 binary oxides remained in a highly dispersed form. A preferential interaction between the basic MO and the dispersed V2O5 lead to the formation of MVO3 at higher calcination temperatures. The surface acid–base properties of the prepared samples were examined for the conversion of cyclohexanol to cyclohexanone/cyclohexene under normal atmospheric pressure. All the investigated samples were found to exhibit interesting catalytic properties.Influence of MO (M = Ca, Sr and Ba) on TiO2-anatase phase stabilization and dispersion of V2O5 over these have been investigated. The MO–TiO2 and V2O5/MO–TiO2 exhibit more selectivity towards cyclohexanone and cyclohexene respectively reflecting their acid–base properties.

Catalysis Letters, 2015

The development of noble-metal-free catalysts is currently a topic of paramount research investig... more The development of noble-metal-free catalysts is currently a topic of paramount research investigation in the chemical industry. In this work, a promising CeO 2 -MoO 3 /SiO 2 catalyst was synthesized for the oxidation of a wide variety of benzylamines with O 2 as the oxidant under solvent-free conditions. For comparison, the efficiency of CeO 2 and CeO 2 -MoO 3 catalysts were also studied for the oxidation of benzylamine under identical conditions. The physicochemical properties of the catalysts were thoroughly analysed using X-ray diffraction, Raman spectroscopy, Barrett-Joyner-Halenda pore size distribution, Brunauer-Emmet-Teller (BET) surface area, Fouriertransform infrared spectroscopy, ammonia-temperature programmed desorption (NH 3 -TPD), and X-ray photoelectron spectroscopy techniques. Characterization studies revealed that the CeO 2 -MoO 3 /SiO 2 catalyst shows favourable structural, textural and acidic properties, which are due to strong interaction between the Ce-Mo mixed oxide and the SiO 2 . In particular, the CeO 2 -MoO 3 /SiO 2 sample exhibits smaller crystallite size and highest BET surface area compared with the CeO 2 -MoO 3 and bare CeO 2 . Raman analysis revealed that the CeO 2 -MoO 3 /SiO 2 sample exhibits greater number of oxygen vacancy defects. The NH 3 -TPD studies indicated that the CeO 2 -MoO 3 /SiO 2 sample has large amount of acidic sites. Owing to the beneficial properties, the CeO 2 -MoO 3 /SiO 2 sample exhibited an outstanding catalytic performance for the aerobic oxidation of various benzylamines. The achieved benzylamine conversions are *16, 65 and 98 %, respectively, for CeO 2 , CeO 2 -MoO 3 and CeO 2 -MoO 3 /SiO 2 samples. Despite the nature of the catalyst used and the reaction conditions employed, almost *100 % selectivity for the dibenzylimine product was found in the present study. Remarkably, the CeO 2 -MoO 3 /SiO 2 catalyst can be repeatedly used up to 5 cycles without any considerable variation in the benzylamine conversion and imine product selectivity. Graphical Abstract The CeO 2 -MoO 3 /SiO 2 catalyst showed an outstanding efficiency in the oxidation of benzylamine, which is attributed to abundant acidic sites, large number of oxygen vacancies, and superior BET surface area.

The Journal of Physical Chemistry B, Sep 17, 2003

Microstructure evolution of ceria-based mixed oxides CeO 2 -MO 2 (M ) Si 4+ , Ti 4+ , and Zr 4+ )... more Microstructure evolution of ceria-based mixed oxides CeO 2 -MO 2 (M ) Si 4+ , Ti 4+ , and Zr 4+ ) after thermal treatments in the temperature range of 773-1073 K were investigated by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and other techniques. The CeO 2 -SiO 2 was synthesized by a deposition precipitation method, and a coprecipitation procedure was adopted to make CeO 2 -TiO 2 and CeO 2 -ZrO 2 binary oxides. The XRD measurements revealed the presence of crystalline cubic CeO 2 on the surface of SiO 2 in CeO 2 -SiO 2 , CeO 2 and TiO 2 (anatase) in CeO 2 -TiO 2 , and Ce 0.75 Zr 0.25 O 2 and Ce 0.6 Zr 0.4 O 2 phases in CeO 2 -ZrO 2 samples. The crystallinity of these phases increased as the calcination temperature increased. Estimations of the cell parameter a indicated an expansion of the CeO 2 lattice in the case of CeO 2 -TiO 2 samples, whereas a contraction was noted in the case of CeO 2 -ZrO 2 . Some incorporation of Si 4+ ions into the CeO 2 lattice was noted at higher calcination temperatures for the CeO 2 -SiO 2 samples. Raman measurements revealed the presence of oxygen vacancies, lattice defects, and the displacement of oxide ions from their normal lattice positions in the case of the CeO 2 -TiO 2 and CeO 2 -ZrO 2 samples. The XPS studies revealed the presence of silica, titania, and zirconia in their highest oxidation statessSi 4+ , Ti 4+ , and Zr 4+ sat the surface of the materials. Cerium is present in both Ce 4+ and Ce 3+ oxidation states, but in different proportions, depending on the mixed-oxide system and the calcination temperature used.

Res Chem Intermediates, 2001

The vapour phase selective oxidation of 4-methylanisole to anisaldehyde was investigated over dif... more The vapour phase selective oxidation of 4-methylanisole to anisaldehyde was investigated over different V 2 O 5 / MgO-Al 2 O 3 catalysts at 673 K and normal atmospheric pressure. Among various catalysts investigated the 16 wt% V 2 O 5 / MgO-Al 2 O 3 catalyst provided good conversion and product selectivity. The MgO-Al 2 O 3 mixed oxide was obtained by a co-precipitation method and V 2 O 5 was impregnated from ammonium metavanadate. The MgO-Al 2 O 3 support and various V 2 O 5 / MgO-Al 2 O 3 catalysts were characterized by means of X-ray diffraction, FT-infrared, electron spin resonance, scanning electron microscopy, ammonia and carbon dioxide chemisorption methods. The characterization results suggest that vanadia does not form layer structures on the support surface, instead interacts very strongly with the support, in particular with MgO, and forms amorphous compounds. The NH 3 and CO 2 uptake results provide an interesting information on the acid-base characteristics of these catalysts and correlate with their catalytic properties.

Catal. Sci. Technol., 2015

Doping ceria with heterocations is a commonly applied strategy to alter its structural and chemic... more Doping ceria with heterocations is a commonly applied strategy to alter its structural and chemical properties including its key feature oxygen storage capacity (OSC). Although a few papers have been published on the structural properties and chemical reactivity of Zn-doped ceria, one lacks a comprehensive investigation on the effect of zinc incorporation in the ceria lattice on its structural properties, and how it could be correlated to the changes in its chemical reactivity including OSC and catalytic activities.

The thermal stability of a nanosized Ce x Zr 1-x O 2 solid solution on a silica surface and the d... more The thermal stability of a nanosized Ce x Zr 1-x O 2 solid solution on a silica surface and the dispersion behavior of V 2 O 5 over Ce x Zr 1-x O 2 /SiO 2 have been investigated using XRD, Raman spectroscopy, XPS, HREM, and BET surface area techniques. Oxidative dehydrogenation of ethylbenzene to styrene was performed as a test reaction to assess the usefulness of the VO x /Ce x Zr 1-x O 2 /SiO 2 catalyst. Ce x Zr 1-x O 2 /SiO 2 (1:1:2 mol ratio based on oxides) was synthesized through a soft-chemical route from ultrahigh dilute solutions by adopting a deposition coprecipitation technique. A theoretical monolayer equivalent to 10 wt % V 2 O 5 was impregnated over the calcined Ce x Zr 1-x O 2 /SiO 2 sample (773 K) by an aqueous wet impregnation technique. The prepared V 2 O 5 /Ce x Zr 1-x O 2 /SiO 2 sample was subjected to thermal treatments from 773 to 1073 K. The XRD measurements indicate the presence of cubic Ce 0.75 Zr 0.25 O 2 in the case of Ce x Zr 1-x O 2 /SiO 2 , while cubic Ce 0.5 Zr 0.5 O 2 and tetragonal Ce 0.16 Zr 0.84 O 2 in the case of V 2 O 5 /Ce x Zr 1-x O 2 /SiO 2 when calcined at various temperatures. Dispersed vanadium oxide induces more incorporation of zirconium into the ceria lattice, thereby decreasing its lattice size and also accelerating the crystallization of Ce-Zr-O solid solutions at higher calcination temperatures. Further, it interacts selectively with the ceria portion of the composite oxide to form CeVO 4 . The RS measurements provide good evidence about the dispersed form of vanadium oxide and the CeVO 4 compound. The HREM studies show the presence of small Ce-Zr-oxide particles of ∼5 nm size over the surface of amorphous silica and corroborate with the results obtained from other techniques. The catalytic activity studies reveal the ability of vanadium oxide supported on Ce x Zr 1-x O 2 /SiO 2 to efficiently catalyze the ODH of ethylbenzene at normal atmospheric pressure. The remarkable ability of Ce x Zr 1-x O 2 to prevent the deactivation of supported vanadium oxide leading to stable activity in the time-on-stream experiments and high selectivity to styrene are other important observations.

ChemInform, 1999

Catalysts. -IR spectroscopy of CO adsorbed at low temp. (77 K) on Al 2 O 3 -TiO 2 samples suggest... more Catalysts. -IR spectroscopy of CO adsorbed at low temp. (77 K) on Al 2 O 3 -TiO 2 samples suggests an enrichment of TiO 2 on the surface. The IR spectrum of the calcined (at 773 K) 12 wt.% V 2 O 5 /Al 2 O 3 -TiO 2 catalyst shows the presence of two kinds of vanadium species, monomeric tetrahedral V V =O species and an amorphous VOx monolayer phase. CO adsorption on this sample results in the formation of CO→V IV carbonyl species. As reported in the literature no V V carbonyl species are detected. Reduction of the catalyst at 773 K leads to the formation of V III species which are stable towards reoxidation at low temp. (77 K) but can be reoxidized to V IV and V V at room temperature. -(CONCEPCION, P.; REDDY, B. M.; KNOEZINGER, H.; Phys. Chem. Chem. Phys. 1 (1999) 12, 3031-3037; Inst. Phys. Chem.,

Applied Surface Science, 2015

International Journal of Nanotechnology, 2010

Superior ceria-zirconia (Ce x Zr 1-x O 2 ; 1 : 1 mole ratio) solid solution was synthesised by em... more Superior ceria-zirconia (Ce x Zr 1-x O 2 ; 1 : 1 mole ratio) solid solution was synthesised by employing a poly-block copolymer surfactant combined with microwave treatment. For comparison purpose an identical composition ceria-zirconia solid solution was also prepared by a conventional coprecipitation method. The structural and textural characteristics of the synthesised samples were investigated using X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area, and BJH pore size distribution (PSD) methods. The catalytic activity was evaluated for CO oxidation at normal atmospheric pressure. The XRD measurements revealed the presence of cubic Ce 0.75 Zr 0.25 O 2 and Ce 0.6 Zr 0.4 O 2 phases in the conventional coprecipitation and surfactant-controlled microwave treated samples, respectively. The Ce x Zr 1-x O 2 solid solution prepared by surfactant-controlled microwave-assisted method exhibited a high specific surface area and mesoporosity. The SEM images suggested that all samples consist of typical spherical agglomerates with almost uniform size within the nanometer range. The TEM measurements revealed that the nanosized crystallites are in the narrow range between 4 nm and 8 nm and densely packed. Raman measurements revealed existence of more oxygen vacancies in the surfactant-controlled microwave treated sample. Interestingly, the Ce x Zr 1-x O 2 solid solution obtained by surfactant-controlled microwave treatment exhibited better CO oxidation activity than the conventional coprecipitated sample. Enhanced activity of the surfactant-controlled microwave treated sample is correlated with smaller crystallite size, mesoporosity, and more number of defects.

Catalysis Letters, 2015

Y-doped ceria-zirconia (Ce 0.8 Zr 0.12 Y 0.08 O 2-d , CZY) and ceria-lanthana (Ce 0.8 La 0.12 Y 0... more Y-doped ceria-zirconia (Ce 0.8 Zr 0.12 Y 0.08 O 2-d , CZY) and ceria-lanthana (Ce 0.8 La 0.12 Y 0.08 O 2-d , CLY) ternary oxide solid solutions were synthesized by a facile coprecipitation method. Structural, textural, redox, and morphological properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), inductively coupled plasma-optical emission spectroscopy (ICP-OES), Raman spectroscopy (RS), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction by hydrogen (H 2 -TPR), high resolution transmission electron microscopy (HRTEM), and Brunauer-Emmett-Teller surface area (BET SA) techniques. The formation of ternary oxide solid solutions was confirmed from XRD, RS, and UV-vis DRS results. ICP-OES analysis confirmed the elemental composition in the ternary oxide solid solutions. HRTEM images revealed irregular morphology of the samples. RS, UV-vis DRS, and XPS results indicated enhanced oxygen vacancies in the Y doped samples. H 2 -TPR profiles confirmed a facile reduction of CZY and CLY samples at lower temperatures. BET analysis revealed an enhanced surface area for CZY and CLY samples than the respective CZ and CL undoped mixed oxides. All these factors contributed to a better CO and soot oxidation performance of CZY and CLY samples. Particularly, the CLY sample exhibited highest catalytic activity among the various samples investigated. Graphical Abstract CZ CZY CL CLY 630 665 700 735 770 805 T 50 for CO Oxidation T 50 for Soot Oxidation Oxygen Vacancies (A V o /A F 2g Ratio) Catalysts T 50 (K) for CO/Soot Oxidation 0.1 0.2 0.3 0.4 Oxygen Vacancies (A V o /A F 2g Ratio)

Catalysis Today, 2015

The influence of dopant size and valence state on the reduction properties, oxygen defects, and l... more The influence of dopant size and valence state on the reduction properties, oxygen defects, and lattice strain in doped ceria has been studied fastidiously. This is of particular importance in environmental application, such as soot and CO oxidation. Herein, isovalent (Zr 4+ ) and aliovalent (La 3+ , Eu 3+ , and Sm 3+ ) metal ions doped ceria catalysts were synthesized by coprecipitation method with aqueous ammonia as the precipitant. The interplay of dopant size and valence in the ceria lattice is experimentally analysed in detail at the structural and electronic level by XRD, BET, TEM, Raman, TPR, and XPS techniques, and finally evaluated for soot and CO oxidation reactions. According to the analysis results, the size or the valence of the dopant or both together positively influence the ceria properties. The isovalent substituent (Zr 4+ ), which is different in size with respect to ceria, enhanced the ceria intrinsic activity by decreasing its reduction temperature and oxygen vacancy formation energy, thereby increased the activity. Whereas, aliovalent dopants (La 3+ , Eu 3+ , and Sm 3+ ) having different in size and valence compared to pure ceria further improved the structural and catalytic properties of bare ceria by inducing additional oxygen vacancies. The observed activity of doped materials towards soot and CO oxidation reactions is as follows: aliovalent doped ceria > isovalent doped ceria > ceria. The marked influence of isovalent and aliovalent dopants on the ceria properties are highlighted in this study. .in (B.M. Reddy).

Res Chem Intermediates, 1998

Langmuir, 2003

The evolution and physicochemical characteristics of CeO2-ZrO2 and V2O5/CeO2-ZrO2 samples under t... more The evolution and physicochemical characteristics of CeO2-ZrO2 and V2O5/CeO2-ZrO2 samples under the influence of thermal treatments from 773 to 1073 K were investigated using X-ray diffraction (XRD), BET surface area, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The CeO 2-ZrO2 mixed oxide was synthesized by a coprecipitation method, and a nominal 12 wt % V2O5 was deposited over the calcined support (773 K) by a wet impregnation technique. The X-ray powder diffraction analysis suggests formation of a Ce 0.75Zr0.25O2 cubic phase at 773 K. With increasing calcination temperature, better crystallization of this phase and incorporation of more zirconium into the ceria lattice were noted. The mean crystallite size and a cell parameter values obtained from XRD measurements strongly support this observation. The results further suggest that impregnation of vanadium oxide over the CeO2-ZrO2 surface accelerates the crystallization of Ce0.75Zr0.25O2 and incorporation of more zirconium into the ceria lattice, thereby facilitating appearance of zirconia-rich phases. A preferential formation of CeVO4 compound was also noted at higher calcination temperatures. The XRD and Raman results, in particular, provide direct evidence about the formation of CeVO 4. The XPS measurements reveal stabilization of Ce(III) at higher calcination temperatures and no significant changes in the oxidation states of Zr(IV) and V(V).

J Phys Chem B, 2004

The techniques of X-ray diffraction (XRD), Raman spectroscopy (RS), and X-ray photoelectron spect... more The techniques of X-ray diffraction (XRD), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS) were employed to investigate dispersion and structural characteristics of V 2 O 5 /CeO 2 -MO 2 (M ) Si 4+ , Ti 4+ , and Zr 4+ ) catalysts calcined at different temperatures from 773 to 1073 K. The CeO 2 -MO 2 (1:1 mole ratio) mixed oxides were obtained by soft chemical methods with ultrahigh-dilution solutions, and a nominal monolayer equivalent of V 2 O 5 was deposited over the calcined (773 K) supports. The XRD and RS results suggest that the CeO 2 -MO 2 carrier calcined at 773 K exhibits the presence of nanocrystalline cubic CeO 2 on the surface of SiO 2 in CeO 2 -SiO 2 , CeO 2 and TiO 2 (anatase) in CeO 2 -TiO 2 , and Ce 0.75 Zr 0.25 O 2 in CeO 2 -ZrO 2 samples. The impregnation of vanadia over CeO 2 -MO 2 and their subsequent calcination at higher temperatures leads to various modifications. The deposited V 2 O 5 is in a highly dispersed state when calcined at 773 K. In particular, no crystalline V 2 O 5 is observed at all calcination temperatures. The dispersed vanadia on the CeO 2 -MO 2 carrier induces better crystallization of various phases and a preferential formation of CeVO 4 in all samples. Incorporation of more zirconia into the Ce 0.75 Zr 0.25 O 2 cubic lattice leading to the manifestation of a Ce 0.16 Zr 0.84 O 2 tetragonal phase at higher calcination temperatures is noted in the case of CeO 2 -ZrO 2 samples. The RS measurements disclose the presence of oxygen vacancies/Ce 3+ in all samples in different proportions. The XPS results reveal that O 1s, Ce 3d, and V 2p core-level photoelectron peaks are sensitive to the calcination temperature and the nature of mixed-oxide system. The formation of CeVO 4 at various temperatures is established from all characterization results.

J Mol Catal a Chem, 2006

Influence of CaO on TiO2 (anatase) phase stabilization and dispersion behaviour of V2O5 over CaO–... more Influence of CaO on TiO2 (anatase) phase stabilization and dispersion behaviour of V2O5 over CaO–TiO2 mixed oxide support have been investigated using XRD, FTIR, Raman, XPS, and BET surface area techniques. The CaO–TiO2 binary oxide (1:1 molar ratio) was synthesized by a homogeneous co-precipitation method from ultrahigh dilute solutions of the corresponding chlorides and calcined at various temperatures from 723 to 1273 K. On the calcined CaO–TiO2 support (723 K) various amounts of V2O5 (2.5–10 wt.%) were deposited from ammonium metavanadate by a wet impregnation method and calcined at different temperatures. Conversion of cyclohexanol to cyclohexanone/cyclohexene was performed as a model reaction to assess the acid–base properties of the prepared catalysts. The CaO–TiO2 composite oxide exhibits reasonably high specific surface area and high thermal stability up to 1273 K retaining titania-anatase phase. The deposited V2O5 over CaO–TiO2 support is present mostly in a dispersed form. Further, a strong and preferential interaction between the basic CaO and the dispersed V2O5 leads to the formation of CaVO3 and the physicochemical properties of the prepared catalysts are clearly reflected in their catalytic activity.Influence of CaO on TiO2-anatase phase stabilization and dispersion of V2O5 over CaO–TiO2 have been investigated using different techniques. The CaO–TiO2 and V2O5/CaO–TiO2 exhibit more selectivity towards cyclohexanone and cyclohexene, respectively, reflecting their acid–base properties.

J Mol Catal a Chem, 2007

The influence of various alkaline earth metal oxides (CaO, SrO and BaO) on the acid–base properti... more The influence of various alkaline earth metal oxides (CaO, SrO and BaO) on the acid–base properties of TiO2 and the dispersion behaviour of V2O5 over MO−TiO2 (M = Ca, Sr and Ba) have been investigated systematically. The MO−TiO2 binary oxides (1:1 molar ratio) were synthesized by adopting a co-precipitation method from the corresponding chloride precursors by in situ hydrolysis with urea and calcined at various temperatures from 723 to 1073 K. A nominal 10 wt.% V2O5 was deposited over the calcined (773 K) MO−TiO2 supports by a wet impregnation method. The synthesized catalysts were characterized using X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), thermogravimetry–differential thermal analysis (TG–DTA) and BET surface area techniques. The MO−TiO2 composite oxides exhibited reasonably high-specific surface area and high-thermal stability retaining titania-anatase phase up to 1073 K treatment temperature. The impregnated V2O5 over MO−TiO2 binary oxides remained in a highly dispersed form. A preferential interaction between the basic MO and the dispersed V2O5 lead to the formation of MVO3 at higher calcination temperatures. The surface acid–base properties of the prepared samples were examined for the conversion of cyclohexanol to cyclohexanone/cyclohexene under normal atmospheric pressure. All the investigated samples were found to exhibit interesting catalytic properties.Influence of MO (M = Ca, Sr and Ba) on TiO2-anatase phase stabilization and dispersion of V2O5 over these have been investigated. The MO–TiO2 and V2O5/MO–TiO2 exhibit more selectivity towards cyclohexanone and cyclohexene respectively reflecting their acid–base properties.

Catalysis Letters, 2015

The development of noble-metal-free catalysts is currently a topic of paramount research investig... more The development of noble-metal-free catalysts is currently a topic of paramount research investigation in the chemical industry. In this work, a promising CeO 2 -MoO 3 /SiO 2 catalyst was synthesized for the oxidation of a wide variety of benzylamines with O 2 as the oxidant under solvent-free conditions. For comparison, the efficiency of CeO 2 and CeO 2 -MoO 3 catalysts were also studied for the oxidation of benzylamine under identical conditions. The physicochemical properties of the catalysts were thoroughly analysed using X-ray diffraction, Raman spectroscopy, Barrett-Joyner-Halenda pore size distribution, Brunauer-Emmet-Teller (BET) surface area, Fouriertransform infrared spectroscopy, ammonia-temperature programmed desorption (NH 3 -TPD), and X-ray photoelectron spectroscopy techniques. Characterization studies revealed that the CeO 2 -MoO 3 /SiO 2 catalyst shows favourable structural, textural and acidic properties, which are due to strong interaction between the Ce-Mo mixed oxide and the SiO 2 . In particular, the CeO 2 -MoO 3 /SiO 2 sample exhibits smaller crystallite size and highest BET surface area compared with the CeO 2 -MoO 3 and bare CeO 2 . Raman analysis revealed that the CeO 2 -MoO 3 /SiO 2 sample exhibits greater number of oxygen vacancy defects. The NH 3 -TPD studies indicated that the CeO 2 -MoO 3 /SiO 2 sample has large amount of acidic sites. Owing to the beneficial properties, the CeO 2 -MoO 3 /SiO 2 sample exhibited an outstanding catalytic performance for the aerobic oxidation of various benzylamines. The achieved benzylamine conversions are *16, 65 and 98 %, respectively, for CeO 2 , CeO 2 -MoO 3 and CeO 2 -MoO 3 /SiO 2 samples. Despite the nature of the catalyst used and the reaction conditions employed, almost *100 % selectivity for the dibenzylimine product was found in the present study. Remarkably, the CeO 2 -MoO 3 /SiO 2 catalyst can be repeatedly used up to 5 cycles without any considerable variation in the benzylamine conversion and imine product selectivity. Graphical Abstract The CeO 2 -MoO 3 /SiO 2 catalyst showed an outstanding efficiency in the oxidation of benzylamine, which is attributed to abundant acidic sites, large number of oxygen vacancies, and superior BET surface area.

The Journal of Physical Chemistry B, Sep 17, 2003

Microstructure evolution of ceria-based mixed oxides CeO 2 -MO 2 (M ) Si 4+ , Ti 4+ , and Zr 4+ )... more Microstructure evolution of ceria-based mixed oxides CeO 2 -MO 2 (M ) Si 4+ , Ti 4+ , and Zr 4+ ) after thermal treatments in the temperature range of 773-1073 K were investigated by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and other techniques. The CeO 2 -SiO 2 was synthesized by a deposition precipitation method, and a coprecipitation procedure was adopted to make CeO 2 -TiO 2 and CeO 2 -ZrO 2 binary oxides. The XRD measurements revealed the presence of crystalline cubic CeO 2 on the surface of SiO 2 in CeO 2 -SiO 2 , CeO 2 and TiO 2 (anatase) in CeO 2 -TiO 2 , and Ce 0.75 Zr 0.25 O 2 and Ce 0.6 Zr 0.4 O 2 phases in CeO 2 -ZrO 2 samples. The crystallinity of these phases increased as the calcination temperature increased. Estimations of the cell parameter a indicated an expansion of the CeO 2 lattice in the case of CeO 2 -TiO 2 samples, whereas a contraction was noted in the case of CeO 2 -ZrO 2 . Some incorporation of Si 4+ ions into the CeO 2 lattice was noted at higher calcination temperatures for the CeO 2 -SiO 2 samples. Raman measurements revealed the presence of oxygen vacancies, lattice defects, and the displacement of oxide ions from their normal lattice positions in the case of the CeO 2 -TiO 2 and CeO 2 -ZrO 2 samples. The XPS studies revealed the presence of silica, titania, and zirconia in their highest oxidation statessSi 4+ , Ti 4+ , and Zr 4+ sat the surface of the materials. Cerium is present in both Ce 4+ and Ce 3+ oxidation states, but in different proportions, depending on the mixed-oxide system and the calcination temperature used.

Res Chem Intermediates, 2001

The vapour phase selective oxidation of 4-methylanisole to anisaldehyde was investigated over dif... more The vapour phase selective oxidation of 4-methylanisole to anisaldehyde was investigated over different V 2 O 5 / MgO-Al 2 O 3 catalysts at 673 K and normal atmospheric pressure. Among various catalysts investigated the 16 wt% V 2 O 5 / MgO-Al 2 O 3 catalyst provided good conversion and product selectivity. The MgO-Al 2 O 3 mixed oxide was obtained by a co-precipitation method and V 2 O 5 was impregnated from ammonium metavanadate. The MgO-Al 2 O 3 support and various V 2 O 5 / MgO-Al 2 O 3 catalysts were characterized by means of X-ray diffraction, FT-infrared, electron spin resonance, scanning electron microscopy, ammonia and carbon dioxide chemisorption methods. The characterization results suggest that vanadia does not form layer structures on the support surface, instead interacts very strongly with the support, in particular with MgO, and forms amorphous compounds. The NH 3 and CO 2 uptake results provide an interesting information on the acid-base characteristics of these catalysts and correlate with their catalytic properties.

Catal. Sci. Technol., 2015

Doping ceria with heterocations is a commonly applied strategy to alter its structural and chemic... more Doping ceria with heterocations is a commonly applied strategy to alter its structural and chemical properties including its key feature oxygen storage capacity (OSC). Although a few papers have been published on the structural properties and chemical reactivity of Zn-doped ceria, one lacks a comprehensive investigation on the effect of zinc incorporation in the ceria lattice on its structural properties, and how it could be correlated to the changes in its chemical reactivity including OSC and catalytic activities.

The thermal stability of a nanosized Ce x Zr 1-x O 2 solid solution on a silica surface and the d... more The thermal stability of a nanosized Ce x Zr 1-x O 2 solid solution on a silica surface and the dispersion behavior of V 2 O 5 over Ce x Zr 1-x O 2 /SiO 2 have been investigated using XRD, Raman spectroscopy, XPS, HREM, and BET surface area techniques. Oxidative dehydrogenation of ethylbenzene to styrene was performed as a test reaction to assess the usefulness of the VO x /Ce x Zr 1-x O 2 /SiO 2 catalyst. Ce x Zr 1-x O 2 /SiO 2 (1:1:2 mol ratio based on oxides) was synthesized through a soft-chemical route from ultrahigh dilute solutions by adopting a deposition coprecipitation technique. A theoretical monolayer equivalent to 10 wt % V 2 O 5 was impregnated over the calcined Ce x Zr 1-x O 2 /SiO 2 sample (773 K) by an aqueous wet impregnation technique. The prepared V 2 O 5 /Ce x Zr 1-x O 2 /SiO 2 sample was subjected to thermal treatments from 773 to 1073 K. The XRD measurements indicate the presence of cubic Ce 0.75 Zr 0.25 O 2 in the case of Ce x Zr 1-x O 2 /SiO 2 , while cubic Ce 0.5 Zr 0.5 O 2 and tetragonal Ce 0.16 Zr 0.84 O 2 in the case of V 2 O 5 /Ce x Zr 1-x O 2 /SiO 2 when calcined at various temperatures. Dispersed vanadium oxide induces more incorporation of zirconium into the ceria lattice, thereby decreasing its lattice size and also accelerating the crystallization of Ce-Zr-O solid solutions at higher calcination temperatures. Further, it interacts selectively with the ceria portion of the composite oxide to form CeVO 4 . The RS measurements provide good evidence about the dispersed form of vanadium oxide and the CeVO 4 compound. The HREM studies show the presence of small Ce-Zr-oxide particles of ∼5 nm size over the surface of amorphous silica and corroborate with the results obtained from other techniques. The catalytic activity studies reveal the ability of vanadium oxide supported on Ce x Zr 1-x O 2 /SiO 2 to efficiently catalyze the ODH of ethylbenzene at normal atmospheric pressure. The remarkable ability of Ce x Zr 1-x O 2 to prevent the deactivation of supported vanadium oxide leading to stable activity in the time-on-stream experiments and high selectivity to styrene are other important observations.

ChemInform, 1999

Catalysts. -IR spectroscopy of CO adsorbed at low temp. (77 K) on Al 2 O 3 -TiO 2 samples suggest... more Catalysts. -IR spectroscopy of CO adsorbed at low temp. (77 K) on Al 2 O 3 -TiO 2 samples suggests an enrichment of TiO 2 on the surface. The IR spectrum of the calcined (at 773 K) 12 wt.% V 2 O 5 /Al 2 O 3 -TiO 2 catalyst shows the presence of two kinds of vanadium species, monomeric tetrahedral V V =O species and an amorphous VOx monolayer phase. CO adsorption on this sample results in the formation of CO→V IV carbonyl species. As reported in the literature no V V carbonyl species are detected. Reduction of the catalyst at 773 K leads to the formation of V III species which are stable towards reoxidation at low temp. (77 K) but can be reoxidized to V IV and V V at room temperature. -(CONCEPCION, P.; REDDY, B. M.; KNOEZINGER, H.; Phys. Chem. Chem. Phys. 1 (1999) 12, 3031-3037; Inst. Phys. Chem.,

Applied Surface Science, 2015

International Journal of Nanotechnology, 2010

Superior ceria-zirconia (Ce x Zr 1-x O 2 ; 1 : 1 mole ratio) solid solution was synthesised by em... more Superior ceria-zirconia (Ce x Zr 1-x O 2 ; 1 : 1 mole ratio) solid solution was synthesised by employing a poly-block copolymer surfactant combined with microwave treatment. For comparison purpose an identical composition ceria-zirconia solid solution was also prepared by a conventional coprecipitation method. The structural and textural characteristics of the synthesised samples were investigated using X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area, and BJH pore size distribution (PSD) methods. The catalytic activity was evaluated for CO oxidation at normal atmospheric pressure. The XRD measurements revealed the presence of cubic Ce 0.75 Zr 0.25 O 2 and Ce 0.6 Zr 0.4 O 2 phases in the conventional coprecipitation and surfactant-controlled microwave treated samples, respectively. The Ce x Zr 1-x O 2 solid solution prepared by surfactant-controlled microwave-assisted method exhibited a high specific surface area and mesoporosity. The SEM images suggested that all samples consist of typical spherical agglomerates with almost uniform size within the nanometer range. The TEM measurements revealed that the nanosized crystallites are in the narrow range between 4 nm and 8 nm and densely packed. Raman measurements revealed existence of more oxygen vacancies in the surfactant-controlled microwave treated sample. Interestingly, the Ce x Zr 1-x O 2 solid solution obtained by surfactant-controlled microwave treatment exhibited better CO oxidation activity than the conventional coprecipitated sample. Enhanced activity of the surfactant-controlled microwave treated sample is correlated with smaller crystallite size, mesoporosity, and more number of defects.

Catalysis Letters, 2015

Y-doped ceria-zirconia (Ce 0.8 Zr 0.12 Y 0.08 O 2-d , CZY) and ceria-lanthana (Ce 0.8 La 0.12 Y 0... more Y-doped ceria-zirconia (Ce 0.8 Zr 0.12 Y 0.08 O 2-d , CZY) and ceria-lanthana (Ce 0.8 La 0.12 Y 0.08 O 2-d , CLY) ternary oxide solid solutions were synthesized by a facile coprecipitation method. Structural, textural, redox, and morphological properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), inductively coupled plasma-optical emission spectroscopy (ICP-OES), Raman spectroscopy (RS), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction by hydrogen (H 2 -TPR), high resolution transmission electron microscopy (HRTEM), and Brunauer-Emmett-Teller surface area (BET SA) techniques. The formation of ternary oxide solid solutions was confirmed from XRD, RS, and UV-vis DRS results. ICP-OES analysis confirmed the elemental composition in the ternary oxide solid solutions. HRTEM images revealed irregular morphology of the samples. RS, UV-vis DRS, and XPS results indicated enhanced oxygen vacancies in the Y doped samples. H 2 -TPR profiles confirmed a facile reduction of CZY and CLY samples at lower temperatures. BET analysis revealed an enhanced surface area for CZY and CLY samples than the respective CZ and CL undoped mixed oxides. All these factors contributed to a better CO and soot oxidation performance of CZY and CLY samples. Particularly, the CLY sample exhibited highest catalytic activity among the various samples investigated. Graphical Abstract CZ CZY CL CLY 630 665 700 735 770 805 T 50 for CO Oxidation T 50 for Soot Oxidation Oxygen Vacancies (A V o /A F 2g Ratio) Catalysts T 50 (K) for CO/Soot Oxidation 0.1 0.2 0.3 0.4 Oxygen Vacancies (A V o /A F 2g Ratio)

Catalysis Today, 2015

The influence of dopant size and valence state on the reduction properties, oxygen defects, and l... more The influence of dopant size and valence state on the reduction properties, oxygen defects, and lattice strain in doped ceria has been studied fastidiously. This is of particular importance in environmental application, such as soot and CO oxidation. Herein, isovalent (Zr 4+ ) and aliovalent (La 3+ , Eu 3+ , and Sm 3+ ) metal ions doped ceria catalysts were synthesized by coprecipitation method with aqueous ammonia as the precipitant. The interplay of dopant size and valence in the ceria lattice is experimentally analysed in detail at the structural and electronic level by XRD, BET, TEM, Raman, TPR, and XPS techniques, and finally evaluated for soot and CO oxidation reactions. According to the analysis results, the size or the valence of the dopant or both together positively influence the ceria properties. The isovalent substituent (Zr 4+ ), which is different in size with respect to ceria, enhanced the ceria intrinsic activity by decreasing its reduction temperature and oxygen vacancy formation energy, thereby increased the activity. Whereas, aliovalent dopants (La 3+ , Eu 3+ , and Sm 3+ ) having different in size and valence compared to pure ceria further improved the structural and catalytic properties of bare ceria by inducing additional oxygen vacancies. The observed activity of doped materials towards soot and CO oxidation reactions is as follows: aliovalent doped ceria > isovalent doped ceria > ceria. The marked influence of isovalent and aliovalent dopants on the ceria properties are highlighted in this study. .in (B.M. Reddy).