Browsing by Author "Dasari, Hari Prasad"

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Ceria-Manganese Mixed Oxides as Catalyst for Soot and Co Oxidation Activity
(National Institute of Technology Karnataka, Surathkal, 2024) Atmuri, Shourya; Dasari, Hari Prasad
Automobile exhaust catalysts, like three-way catalytic converters are known to use Ceria coating for the fine dispersion of Platinum Group Metals (PGM). The Ceria coating acts as an active support. PGMs have certain shortcomings, such as, high prices, sintering at relatively low temperatures, and fouling due to SO2. Doping Ceria with other metals, like in the present work Manganese, boosts its catalytic properties while lessening or negating any determinantal effects. Manganese-doped Ceria catalysts have been widely studied as a catalyst for a variety of applications due to their attractive properties attained due to synergy achieved by favorable defects, physicochemical, and morphological features aiding in the oxidation processes. A systematic study has been carried out in the present work to study the effect of Manganese doping in Ceria and its soot oxidation activity from nanostructured powder to CO oxidation activity on structured catalysts, i.e., catalyst coated on to an Alumina wash-coated Cordierite honeycomb substrate. The EDTA-Citrate method was the choice of synthesis method for the powder catalyst. Since the variation in the atomic radius of both cations (Ce and Mn) is very large, phase difference and the existence of multiple oxidation states in Manganese, a complete solid solution is not feasible over the entire range of Manganese doping into the Ceria lattice. Consequently, two series of nanostructured powder catalysts were obtained, namely, Ceria-rich Ceria-Manganese and Manganese-rich Ceria-Manganese mixed oxides, with interesting morphological features attained due to the solubility limits. Ceria-Manganese mixed oxides (nanostructured powder catalysts) were examined by XRD, Raman spectroscopy, BET and BJH, FESEM, and TEM characterization techniques. A dip-coating technique was employed for coating of the Cordierite honeycomb substrate. The structured catalysts were utilized for CO oxidation. The adherence of the coating was tested by ultrasonication. XRD, Raman spectroscopy, and BET analysis probed the physicochemical parameters. Digital optical microscopy, and FESEM analysis analyzed the morphological features. Overall, the thesis concentrates on developing compositions of Ceria-Manganese oxides for soot and CO oxidation activity for a Catalyzed Diesel Particulate Filter (CDPF).
Ceria-samarium binary metal oxides: A comparative approach towards structural properties and soot oxidation activity
(2018) Anantharaman, A.P.; Geethu, J.; P, M.R.; Dasari, Hari Prasad; Lee, J.-H.; Bhaskar, Babu, G.U.; Dasari, H.
Binary metal oxides of CeO2-Sm2O3 (CSx, x varies from 10 to 90 mol%) along with pure CeO2 and Sm2O3 were synthesised successfully by the EDTA-Citrate method. From XRD, Raman spectroscopy and UV vis DRS results, the whole composition of metal oxides exist in three phases: (fluorite phase (F) (CS10-CS30), bi-phase (fluorite (F) + cubic (C)) (CS30-CS90) and cubic phase (C) (Sm2O3)). For CSx samples, the calculated band gap energy values obtained from the UV vis DRS results were in between 3.0 5.1 eV and fluorite phase samples (CS10 CS30) displayed lower band gap energy values (3.04 3.07 eV) than compared to the samples in other phases. Similarly, from XPS analysis, fluorite phase samples (CS10 CS30) showed higher surface oxygen vacancy concentration than compared to samples in other phases. Catalytic activity for soot oxidation is carried out on CSx samples, and the T50 temperature is in between 480 540 C. Fluorite phase samples (CS10 CS30) showed higher surface area, lower degree of agglomeration, lower band gap energy, higher oxygen vacancy concentration and better catalytic activity for soot oxidation. Among all the CSx samples, CS10 sample displayed highest surface area (38 m2/g), lowest degree of agglomeration (0.36), lowest band gap energy (3.04 eV), highest oxygen vacancy concentration (64%) and highest soot oxidation activity (T50 = 480 C). The order of the soot oxidation activity of CSx samples followed the same trend of band gap energy values. 2018 Elsevier B.V.
Dilatometer studies of praseodymium doped ceria: Effect of synthesis methods on sintering behaviour
(2020) Shajahan, I.; Dasari, Hari Prasad; Govardhan, P.
Praseodymium-doped ceria (Ce0.9Pr0.1O2, PDC), as an electrolyte material for IT-SOFCs, is investigated with respect to the effect of synthesis method and a detailed analysis was carried out to understand the effect on crystallite size, morphology, specific surface area and sintering behaviour. The various synthesis routes such as microwave assisted co-precipitation method, room temperature co-precipitation method and EDTA-citrate complexing method was adopted for the synthesis of praseodymium doped ceria-based nano-materials. XRD pattern confirms the fluorite-type crystal structure of ceria and Raman spectroscopy analysis confirms the structure with the presence of oxygen vacancies. PDC synthesised by microwave assisted co-precipitation method using isopropyl alcohol as solvent exhibited better sintering activity, reduced the sintering temperature and promoted the densification rate when compared to other synthesis methods with uni-model shrinkage behaviour with shrinkage maxima at 765 C. Based on two sintering models (CHR/Dorn method), the initial stage sintering mechanism was investigated in the present study and confirmed that the grain boundary diffusion (m = 2) as the dominant mechanism and the activation energy was found to be 116 kJ/mol (CHR model) and 176 kJ/mol (Dorn Method) for initial stages of sintering for PDC material synthesised by microwave assisted co-precipitation method using isopropyl alcohol as solvent. 2019 Elsevier B.V.
Effect of ionic radius on soot oxidation activity for ceria-based binary metal oxides
(2019) Anantharaman, A.P.; Dasari, Hari Prasad; Babu, G.U.B.; Dasari, H.
CeO2 (C) along with binary metal oxides of Ce0.9M0.1O2-? (M = Sn, Hf, Zr, Gd, Sm, and La; CT, CH, CZ CG, CS, and CL) are synthesized using the EDTA citrate method. Samples having an ionic radius smaller (CT, CH, and CZ) and larger (CG, CS, and CL) than Ce4+ are classified separately, and their soot oxidation activity is analyzed. The incorporation of dopant is confirmed from lattice constant variation in X-ray diffraction result. The critical descriptors for the activity are dopant nature (ionic radius and oxidation-state), single-phase solid solution, lattice strain, reactive (200) and (220) planes, Raman intensity ration (Iov/IF2g), optical bandgap, reducibility ratio, and surface oxygen vacancy. Smaller ionic radius, isovalent dopants (CH and CZ) create a defect site by lowering the optical bandgap along with improved surface oxygen vacancy concentration and thus enhanced soot oxidation activity. Aliovalent dopant with larger ionic radius shows the involvement of lattice oxygen in oxidation reaction by charge compensation mechanism. CL showed the highest activity amongst larger ionic radius samples. 2019 Curtin University and John Wiley & Sons, Ltd.
Effect of Nd-doping on soot oxidation activity of Ceria-based nanoparticles synthesized by Glycine Nitrate Process
(2019) Patil, S.S.; Dasari, Hari Prasad; Dasari, H.; Dasari, H.
Neodymium-doped Ceria (NDC, Nd = 0, 1, 3, 5, 10, 20 and 30 mol %) catalysts were successfully synthesized by Glycine-Nitrate-Process (GNP) and tested for soot oxidation activity. For all NDC catalysts, XRD and Raman spectroscopy analyses showed a fluorite structure of ceria having an F2gRaman active symmetric breathing mode (O-Ce-O). 1NDC catalyst displayed better T50 temperature (427?C) followed by 0NDC (435?C), and 30NDC showed the highest T50 temperature (460?C). From XPS analysis, 1NDC and 0NDC catalysts showed a high amount of Ce3+ concentration and the surface-active oxygen species than compared to other NDC catalysts and thus, resulted in better soot oxidation activity indicating that the surface Ce3+ concentration and surface-active oxygen species play a key descriptor role in tuning the soot oxidation activity of NDC catalysts. 2019 Elsevier B.V.
Effect of synthesis method on structural properties and soot oxidation activity of gadolinium-doped ceria
(2018) Anantharaman, A.P.; Gadiyar, H.J.; Surendran, M.; Rao, A.S.; Dasari, Hari Prasad; Babu, G.U.B.
Abstract: EDTA citrate complex and solvothermal methods were adopted for the synthesis of gadolinium-doped ceria (GDC) (Ce0.9Gd0.1O2) solid solution, and the obtained GDC sample is tested for soot oxidation activity. Based on XRD results, it was evident that the reactive facet planes of {100} and {110} were highly intense [intensity ratio (%) of (200)/(100) (34.2%) and (220)/(111) (51.2%)] for GDC prepared by the EDTA citrate method in comparison with the solvothermal method, and this highly intense reactive facet plane correlates to the lower energy for oxygen vacancy formation. Apart from the smaller crystallite size (10 nm) the GDC sample prepared by the EDTA citrate method displayed lower band gap energy (2.99 eV), higher ratio of reducibility (45.45%) and lower binding energy (528.8 eV) for surface-adsorbed oxygen. The GDC obtained by EDTA citrate method displayed a better soot oxidation activity (T50 = 468 C) than compared to the GDC obtained by solvothermal method (T50 = 500 C). The obtained results significantly show that the synthesis method plays a crucial role in controlling the structural properties and in enhancing the soot oxidation activity. 2018, Institute of Chemistry, Slovak Academy of Sciences.
Praseodymium doped ceria as electrolyte material for IT-SOFC applications
(2018) Shajahan, I.; Ahn, J.; Nair, P.; Medisetti, S.; Patil, S.; Niveditha, V.; Uday, Bhaskar, Babu, G.; Dasari, Hari Prasad; Lee, J.-H.
Praseodymium-doped ceria (PDC, Ce0.9Pr0.1O2) electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs) has been successfully synthesised by EDTA-citrate method. From X-Ray diffraction (XRD), fluorite structure along with a crystallite size of 5.4 nm is obtained for PDC nanopowder calcined at 350 C/24 h. Raman spectroscopy confirmed the structure, presence of oxygen vacancies with the manifestation of the main peak at 457 cm?1 and with a secondary peak at 550 cm?1. From Transmission Electron Microscopy (TEM) analysis, the average particle size is around 7 10 nm and selected area electron diffraction (SAED) patterns further confirmed the fluorite structure of PDC nanopowder. The PDC nanopowder displayed a BET surface area of 65 m2/g with a primary particle size of ?13 nm (calculated from BET surface area). Dilatometer studies revealed a multi-step shrinkage behaviour with the multiple peaks at 522, 1171 and 1461 C which may be originated due to the presence of multiple size hard agglomerates. The PDC electrolyte pellet sintered at 1500 C displayed an ionic conductivity of 1.213E-03 S cm?1 along with an activation energy of 1.28eV. Instead of a single fluorite structure, XRD of sintered PDC pellet showed multiple structures (Fluorite structure (CeO2) and cubic structure (PrO2). 2018 Elsevier B.V.
Record-low sintering-temperature (600 c) of solid-oxide fuel cell electrolyte
(2016) Dasari, Hari Prasad; Ahn, K.; Park, S.-Y.; Hong, J.; Kim, H.; Yoon, K.J.; Son, J.-W.; Kim, B.-K.; Lee, H.-W.; Lee, J.-H.
One of the major problems arising with Solid-Oxide Fuel Cell (SOFC) electrolyte is conventional sintering which requires a very high temperature (>1300 C) to fully densify the electrolyte material. In the present study, the sintering temperature of SOFC electrolyte is drastically decreased down to 600 C. Combinational effects of particle size reduction, liquid-phase sintering mechanism and microwave sintering resulted in achieving full density in such a record-low sintering temperature. Gadolinium doped Ceria (GDC) nano-particles are synthesized by co-precipitation method, Lithium (Li), as an additional dopant, is used as liquid-phase sintering aid. Microwave sintering of this electrolyte material resulted in decreasing the sintering temperature to 600 C. Micrographs obtained from Scanning/Transmission Electron Microscopy (SEM/TEM) clearly pointed a drastic growth in grain-size of Li-GDC sample (?150 nm) than compared to GDC sample (<30 nm) showing the significance of Li addition. The sintered Li-GDC samples displayed an ionic conductivity of ?1.00 10-2 S cm-1 at 600 C in air and from the conductivity plots the activation energy is found to be 0.53 eV. 2016 Elsevier B.V. All rights reserved.
Solubility Limits of Ceria-Zirconia-Lanthana Solid-Solutions
(2017) Abbas, Z.; Surendran, M.; Anjana, P.A.; Jidev, P.K.; Dasari, Hari Prasad; Sudhakar, Naidu, N.; Anandhan, S.; Bhat, K.U.; Bhaskar, Babu, G.U.; Prasad, Dasari, H.; Dasari, H.
We demonstrate, the solubility limits of Ceria-Zirconia-Lanthana (CZLa) solid-solutions with the increase in heat-treatment temperature from 600�C to 1300�C. CZLa nano-crystalline samples were successfully synthesized by EDTA-Citrate complex method and were characterized by Raman Spectroscopy (RS) and Transmission Electron Microscopy (TEM) analysis. With an increase in temperature, it is noticed that the solubility limit is decreased in CZLa system. At 600�C, a very good solubility is observed in CZLa system and is confirmed from RS analysis. At higher heat-treatment temperatures (1000 and 1300�C), with an increase in La content, Zr precipitated in the CZLa system and is confirmed from RS analysis. The reason for such kind of behavior in this CZLa system is clearly explained in this work. � 2017 Elsevier Ltd.
Soot Oxidation Activity of Redox and Non-Redox Metal Oxides Synthesised by EDTA Citrate Method
(2017) Anantharaman, A.P.; Dasari, Hari Prasad; Lee, J.-H.; Babu, G.U.B.; Dasari, H.
Abstract: In the present study, redox (CeO2, SnO2, Pr6O11 and Mn3O4) and non-redox (Gd2O3, La2O3 ZrO2 and HfO2) metal oxides were successfully synthesised using the EDTA citrate complexing method and tested for soot oxidation activity. The characterization of the metal oxides is carried out using FTIR, XRD, BET surface area, pore volume analyser, SEM and TEM. The redox nature and metal oxygen bond information of the metal oxides are obtained from XPS analysis. In redox metal oxides, three critical parameters [lattice oxygen binding energy, reduction temperature and ?r (ionic size difference of the corresponding metal oxide oxidation states)] govern the soot oxidation activity. Among the redox metal oxide samples, Mn3O4 and Pr6O11 samples showed lower binding energy for oxygen (O? 529.4, 528.9 eV respectively), lower reduction temperature (T? 317 and 512 C respectively) and have smaller ?r value (9 pm and 17 pm respectively). Thus, displayed a better soot oxidation activity (T50 = 484 and 482 C respectively) than compared to other redox metal oxides. Among the non-redox metal oxides, HfO2 sample displayed higher BET surface area (21.06 m2/g), lattice strain (0.0157), smaller ionic radius (58.2 pm) and higher relative surface oxygen ratio (58%) and thus resulted in a significantly better soot oxidation activity (T50 = 483 C) than compared to other non-redox metal oxides. Graphical Abstract: [Figure not available: see fulltext.]. 2017, Springer Science+Business Media, LLC.
Studies on the Solid Oxide Cell Perovskite Electrode Materials for Soot Oxidation Activity
(2019) Shenoy, C.S.; Patil, S.S.; Govardhan, P.; Shourya, A.; Dasari, Hari Prasad; Saidutta, M.B.; Dasari, H.
Solid oxide cell (SOC) perovskite electrode materials (BSCF (Ba0.5Sr0.5Co0.8Fe0.2O3-?), LSCF (La0.6Sr0.4Co0.2Fe0.8O3-?) and LSCM (La0.75Sr0.25Cr0.5Mn0.5O3-?)) were synthesised using microwave-assisted reverse-strike co-precipitation method and tested for soot oxidation activity. The calcined perovskite materials were characterized using FT-IR, XRD, SEM and BSE, BET and BJH and XPS analysis. The mean activation energy for soot oxidation was calculated from Ozawa plots at various heating rates (5, 10, 15 and 20 K/min) at different levels of soot conversions (T10 to T90) for BSCF, LSCM and LSCF perovskite materials and was around 133 11.5, 138 9.9 and 152 7.2 kJ/mol, respectively. Irrespective of the heating rates, BSCF material showed the lowest T50 temperature than compared to other samples, and it is correlated to the presence of Fe3O4 as a secondary phase. 2019, Springer Nature Switzerland AG.
A Study on Multi Doping Effect on Ceria Based Materials for Soot Oxidation Activity
(National Institute of Technology Karnataka, Surathkal, 2019) P. A, Anjana; Dasari, Hari Prasad
Ceria-based metal oxides are widely adopted as catalyst for various applications significantly due to its distinct features of cyclic redox properties, oxygen storage capacity, high metal solubility and thus, better solid solution formation. This work evaluates the impact of multi-dopants on ceria-based metal oxides for soot oxidation catalytic activity. An initial study on single metal oxides confirmed that the intrinsic nature of metal cation dictates the catalytic activity. Such that reducibility property controls the activity for redox metal oxides (CeO2, SnO2, Pr6O11, Mn3O4) and structural properties control for non-redox metal oxides (Gd2O3, La2O3, ZrO2, HfO2 and Sm2O3). Study on binary ceria-based metal oxide (CeO2-HfO2) confirms that the structural parameter (morphology and phase stability) controls the activity over whole composition range. With increase in dopant, phase separation occurs from fluorite phase, which in turn results in a morphological modification that reduces the catalytic activity. Ternary dopant (Mn) addition to the binary metal oxide (CeO2- HfO2 highest activity among binary metal oxide) at optimum composition enhances catalytic activity due to simultaneous reduction of Ce3+ and Mn4+ and improved oxygen vacancy. On further addition of dopant (Li, Ag, Ba and K) to CeO2-HfO2-Mn2O3 results in quaternary metal oxide that shows lowering of band gap, reactive planes and oxygen active sites that reduces active site and results in catalytic deactivation. Ternary doped sample along with binary metal oxides show the maximum activity due to its lower optical band gap, higher F2g content, higher reactive facet planes and higher reducibility ratio. Thus, it is not a single parameter that dictates the catalytic activity of ceria-based metal oxides. Intrinsic descriptors that control the activity are dopant nature, concentration and interference, apart from the extrinsic descriptor, that significantly modifies surface oxygen concentration. The thesis focuses the descriptors that actually controls the catalytic activity for multi doped ceria based metal oxides.
A Study on The Effect of Transition Metal Dopants In Ceria Praseodymium Catalyst for Soot Oxidation Activity and Its Kinetics
(National Institute of Technology Karnataka, Surathkal, 2023) Patil, Sunaina S; Dasari, Hari Prasad
The catalytic descriptors (lattice oxygen, metal-oxygen bond strength, host structure, redox capability, multi-functionality of active sites, site isolation, and phase cooperation) govern the heterogeneous oxidation reactions. The present study aims to explore the catalytic descriptors that govern the soot oxidation activity of transition metal doped Ceria-Praseodymium catalyst system and its kinetics thereof. The transition metal (0 to 20 mol %) doped Ceria-Praseodymium catalysts (Copper doped Ceria-Praseodymium, Cobalt doped Ceria-Praseodymium, Iron doped Ceria-Praseodymium, Manganese doped Ceria-Praseodymium and Chromium doped Ceria-Praseodymium) were successfully synthesized by Solution Combustion Method and characterized by X-Ray Diffraction, Raman Spectroscopy, Scanning Electron Microscopy, X-Ray Photoelectron Spectroscopy, BET & BJH surface area analysis, and tested for soot oxidation activity and its kinetic study using Thermo-gravimetric analysis. The 5 mol% Copper doped Ceria-Praseodymium catalyst system showed better soot oxidation activity which is attributed to the better reactive planes and chemisorbed oxygen species compared to other Copper-doped Ceria-Praseodymium catalyst system and Ceria-Praseodymium catalyst system. 5 mol% Cobalt doped Ceria-Praseodymium catalyst system showed better soot oxidation activity among the Co doped Ceria-Praseodymium catalysts, and the descriptors controlling the catalytic activity are phase cooperation (solid-solution formation) and better redox properties compared to Co-CP and CP catalyst systems. The descriptors controlling the soot oxidation activity of the Iron doped Ceria-Praseodymium catalyst system are (secondary phase formation and redox properties), and the 5 mol % Iron-doped Ceria-Praseodymium catalyst system showed better soot oxidation activity. In Manganese doped Ceria-Praseodymium catalyst system, the 5 mol% Manganese-doped Ceria-Praseodymium catalyst system showed better catalytic activity for the soot oxidation reaction. The descriptors controlling the soot oxidation activity are surface area, crystallite size, active surface adsorbed O- species, and Mn3+/Mn4+ surface concentration. The surface concentration of Cr3+ and Pr3+ played a significant descriptor role, and Chromium doped Ceria-Praseodymium catalyst system showed better soot oxidation activity than other Ceria-Praseodymium catalyst systems. As the Cr concentration increased, there was a decrease in the Cr3+ and Pr3+ concentrations in the Chromium-doped Ceria-Praseodymium catalyst system. Compared to all the transition metals doped Ceria-Praseodymium catalysts in the present study 5 mol % Cobalt doped Ceria-Praseodymium catalyst system showed better catalytic activity with lowest T50 of 349±1℃. ii In the transition metal (TM (5 mol%) = Cr, Mn, Fe, Co, and Cu) -doped Ceria-Praseodymium nanofiber catalysts 5 mol% Chromium doped Ceria-Praseodymium nanofiber showed better soot oxidation activity and is attributed to larger average pore size and pore volume and, the nano string diameter is smaller than all other nanofiber catalysts. The kinetic triplets namely activation energy, pre-exponential factor and the reaction models were evaluated.
Surface morphology and phase stability effect of Ceria-Hafnia (CHx) binary metal oxides on soot oxidation activity
(2018) Anantharaman, A.P.; Dasari, Hari Prasad; Babu, G.U.B.; Dasari, H.
CeO2-HfO2 (CHx) binary metal oxides over whole composition range (0 100%) are synthesised using the EDTA-Citrate method and calcined at 600 C/5 h. From XRD analysis, the sample series are classified as fluorite (F) phase for CH10-CH30, hybrid (F + M) phase for CH40-CH90 and monoclinic (M) phase for CH100 sample, respectively and the results were further confirmed using Raman spectroscopy. From SEM analysis, a clear surface morphology change is noticed for fluorite, hybrid and monoclinic phases of the CHx binary metal oxides. Further, Selected Area Electron Diffraction (SAED) analysis also confirmed the single and hybrid phases of CHx binary metal oxides. The soot oxidation for the CHx binary metal oxides displayed high catalytic activity for Fluorite phase (CH10 ? CH30) samples and a decrease in catalytic activity is noticed for the Hybrid phase (CH40 ? CH90) samples. The change in catalytic activity coincides with the change in the surface morphology and phase change for the CHx binary metal oxides. Among the Fluorite phase samples, CH10 sample displayed the highest catalytic activity (T50 = 430 C) with higher surface area (29 m2/g), lower particle size (26 nm), lower degree of agglomeration (? = 2.8) higher surface oxygen concentration (44%). Isothermal-Time-on-stream (ITOS) analysis also showed that the CH10 sample can achieve T50 in a shorter time than compared to other CHx binary metal oxides. Surface morphology and phase stability can also play as key descriptors in screening CHx binary metal oxides for soot oxidation activity. 2018 Elsevier B.V.
Synthesis of GDC electrolyte material for IT-SOFCs using glucose & fructose and its characterization
(2017) Medisetti, S.; Ahn, J.; Patil, S.; Goel, A.; Bangaru, Y.; Sabhahit, G.V.; Babu, G.U.B.; Lee, J.-H.; Dasari, Hari Prasad
Nano-powder of gadolinium-doped-ceria (GDC, Ce0.9Gd0.1O2) has been synthesized using a novel sol gel method with glucose and fructose as organic additives. The main objective of the present study is to find the suitability of this synthesis method in synthesizing ceria-based SOFC electrolyte materials and evaluate its performance. The average crystallite/particle size obtained from XRD, TEM, BET surface area was found to be 4 12 nm. The phase was found to be cubic fluorite from XRD and further the structure and the nature of oxygen vacancies was confirmed using Raman spectroscopy. Dilatometer studies illustrated two shrinkage maxima (450 C and 1450 C). The ionic conductivity measurements were done using DC four-probe method on the GDC electrolyte sintered at 1500 C. The sintered sample showed an ionic conductivity of 1.13E?02 Scm?1 at a temperature of 700 C in the air, and the activation energy is 1.02 eV. The present study reveals that this synthesis method can be adaptable for synthesizing SOFC electrolyte materials. 2017 Elsevier B.V.