Faculty Publications
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Item Soot Oxidation Activity of Redox and Non-Redox Metal Oxides Synthesised by EDTA–Citrate Method(Springer New York LLC barbara.b.bertram@gsk.com, 2017) Anjana, A.P.; Prasad Dasari, H.P.; Lee, J.-H.; Harshini, H.; Babu, G.U.B.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.Item Ceria-samarium binary metal oxides: A comparative approach towards structural properties and soot oxidation activity(Elsevier B.V., 2018) Anjana, A.P.; Geethu, J.; P, M.R.; Prasad Dasari, H.P.; Lee, J.-H.; Harshini, H.; Bhaskar Babu, G.U.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.Item Effect of ionic radius on soot oxidation activity for ceria-based binary metal oxides(John Wiley and Sons Ltd vgorayska@wiley.com Southern Gate Chichester, West Sussex PO19 8SQ, 2019) Anjana, A.P.; Prasad Dasari, H.P.; Harshini, H.; Babu, G.U.B.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.