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TEM observations of ceria sample (S3) synthesized using the precipitation method with 400 C calcination temperature and 1 : 2 Ce 3+ / chitosan weight ratio.
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Mesoporous, nano-structured ceria has been synthesized using a low-cost biopolymer chitosan as a template, and the same material has been studied for its COoxidation activity. The ceria thus prepared shows low crystallite size (6.5 nm), high surface area (BET-SA 144.2 m2 g−1) and mesopores (32.4 Å) without ordered structure. Different ceria samples...
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... could also be the most probable reason for the decrease of surface area for this sample. In Fig. 4, the TEM images display that sample S3 consists of sheets of mesoporous aggregates of cubic CeO 2 nanocrystals. Idiomorphic nanocrystals have well-developed crystal faces and size of about 8 nm (Fig. 4d). ...
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... in local- ized temperature during combustion. This could also be the most probable reason for the decrease of surface area for this sample. In Fig. 4, the TEM images display that sample S3 consists of sheets of mesoporous aggregates of cubic CeO 2 nanocrystals. Idiomorphic nanocrystals have well-developed crystal faces and size of about 8 nm (Fig. 4d). The size of the pores is observed to be equal to the size of the crystals. The honeycomb like pattern observed in Fig. 4b is an imprint of the template structure used during the synthesis. The electron diffraction pattern in Fig. 5 confirms the cubic CeO 2 structure (PDF ...
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... for this sample. In Fig. 4, the TEM images display that sample S3 consists of sheets of mesoporous aggregates of cubic CeO 2 nanocrystals. Idiomorphic nanocrystals have well-developed crystal faces and size of about 8 nm (Fig. 4d). The size of the pores is observed to be equal to the size of the crystals. The honeycomb like pattern observed in Fig. 4b is an imprint of the template structure used during the synthesis. The electron diffraction pattern in Fig. 5 confirms the cubic CeO 2 structure (PDF ...
Citations
... The four major IRspectral peaks at 3428, 1384, 1030, and 542 cm − 1 as well as a few weak peaks at 2922, 1612, and 846 cm − 1 in the frequency range 400-4000 cm − 1 , are observed for the investigated solid solutions. The main FTIR spectral bands for the as-synthesised B-doped CBO were observed at the wave frequency due to: (a) physically adsorbed water at 3422-3430 cm [39][40][41] and the Ce-O (III) bond's vibrational band [42,43]. When IR spectra are carefully examined, additional undersized satellite peaks can be seen as a result of (a) non-equivalent water molecules being stretched in phase at 2922 cm − 1 [44] [48], which indicated the B-atom's intercalation as well as the presence of the phosphate group in the solid solutions' lattice [49]. ...
A series of boron-doped cerium − bismuth oxide (CBO) solid solutions were fabricated by combustion method by using unimolecular mixture of nitrides of cerium and bismuth in presence of fuel i.e., urea at low temperature 300 • C. The combustion product possesses Bi 3+ ion and Ce 3+ and crystallized in a fluorite FCC phase. As-produced fine yellow powder crystallize in almost 13-32 nm size needle-shape particle, clustered in cotton-wool form. The photocatalytic water splitting activity was observed for the entire B-doped CBO series and the maximum hydrogen production was observed for 8 % B-doped CBO sample i.e. 332.43 µmol g − 1 h − 1 .
... With the widely accepted superiority of supported catalysts offering metal-support interactions over the conventional ones, CeO 2 has emerged as one of the most vital components of heterogeneously catalysed systems [1][2][3][4][5], in particular for reactions for clean energy and environment including the water-gas shift reaction [6][7][8][9][10], CO oxidation [11][12][13][14][15][16][17], automotive three-way catalysis [18,19], steam reforming [20][21][22][23][24][25], dry reforming [26][27][28][29][30] nitrogen reduction [31,32], and hydrogenation of alkynes [33][34][35]. Owing to this, there have been several experimental and theoretical investigations on CeO 2 supported transition metal systems as heterogeneous catalysts [13][14][15][36][37][38][39]. ...
Transition metals supported over CeO2 surfaces have attracted wide attention of materials researchers because of their vital applications in catalysis. CeO2 as a support is known to stabilise transition metal nanoparticles or clusters on its surface preventing the loss of their catalytic activities. To probe the reasons behind the stability of Pd3 and Pd4 clusters over CeO2 (111) and (110) surfaces with and without vacancy defects, we employed DFT calculations in this study. Our analysis revealed the effect of the vacancy defects to be marginal on the binding of the clusters over the studied surfaces. However, surface diffusion barriers were significantly altered by the presence of vacancies. Our investigation highlighted pristine CeO2(110) and sub-surface vacancy defected CeO2(111) surfaces as excellent materials providing good binding and high surface diffusion barriers for the localised binding of Pd3 and Pd4 clusters.
... The pore cerium oxide gives a particle size of 3.4 nm in agreement with the values between 3.24-3.89 nm earlier reported for ceria prepared via precipitation method [39]. Likewise, the pore volume obtained for all the samples is approximately constant despite increasing the Nb loading, suggesting the samples entail a narrow particle size distribution [40]. ...
... The pure cerium particles show cerium as fine and well dispersed, with uniform morphology and with the absence of any specific shape [24,41]. This fine structure suggests that CeO 2 is able to withstand the operational temperature employed during the calcination process [39]. The morphology of the pure Nb 2 O 5 discloses fine particles together with agglomerated and sponge shaped particles. ...
Catalytic capacity of ceria mainly stems from a facile switch in the Ce oxidation states from +4 to +4 − x . While various experimental and computational studies pinpoint the reduction chemistry of Ce atom through the creation of oxygen vacancies, the analogous process when ceria surface is decorated with cations remains poorly understood. Where such results are available, a synergy between experimental and first principle calculation is scarce. Niobium materials are evolving and their use in catalysis is being widely investigated due to their high surface acidity and thermal and chemical stability. This study aims to report structural and electronic properties of various configurations of mixed Ce–Nb oxides and elaborates on factors that underpin potential catalytic improvements. Evaluations of the samples through X-ray diffraction (XRD), Fourier transform infrared (FTIR), N 2 -adsorption–desorption, scanning electron microscope (SEM), energy dispersive spectroscope (EDS), and thermogravimetric (TGA) analyses are examined and discussed. First principles density functional theory (DFT) calculations provide structural features of the Ce–Nb solutions at low concentration of Nb via computing atomic charge distribution. Contraction in the lattice parameter after Nb doping was confirmed with both XRD and DFT results. SEM analysis reveals particle growth at the loading of 50 wt%. FTIR results established the Ce–Nb–O bond at 1,100 cm ⁻¹ and the TGA analysis confirms the thermal stability of Nb-doped ceria. Tetrahedral O atoms demonstrate an increase in electronegativity and this in turn facilitates catalytic propensity of the material because the O atoms will exhibit higher affinity for adsorbed reactants. Cerium oxide (CeO 2 ) after Nb doping displays a noticeable band gap narrowing, confirming the possible improvement in the catalytic behavior. The 4d states of the Niobium pentoxide (Nb 2 O 5 ) is found to fill up the 4f states of CeO 2 around the Fermi energy level promoting electrons excitation in the CeO 2 . Reported electronic, structural, and thermal characteristics herein indicate promising catalytic applications of niobium-promoted ceria.
... Four main FTIR spectral bands were observed for the solid solutions at wavenumbers (i) 3422-3430 cm À1 (physically adsorbed water on CeO 2 ), (ii) 1560-1601 cm À1 (interfacial water) belonging to the water stretching and bending vibration modes of physically adsorbed water (O-H) molecules, respectively, as illustrated in Fig. 4. 51 The intensive FTIR band at (iii) 1384 cm À1 could be due to the formation of a carbonate ion, a result of the synthesis process being carried out in an ambient atmosphere with urea and glucose. 52 (iv) One absorption band observed between the wavenumbers 530 cm À1 and 542 cm À1 belonged to the vibrations of Bi-O bands in the BiO 6 octahedral unit [53][54][55] and Ce-O(III) vibrations. 56 Besides the above main peaks a few very small-sized satellites peaks were also observed in the frequency ranges (i) 2922- 2962 cm À1 , (ii) 2852-2892 cm À1 , (iii) 1120 cm À1 and 1042-1068 cm À1 and (iv) 846 cm À1 . ...
A series of carbon-doped solid solutions of ceria bismuth oxide (CBO) were prepared by a solid solution method. Highly porous solid solutions crystallized in a fluorite phase and C-doped samples exhibited an enhanced band-gap and reduced lattice cell constants. Their photocatalytic activity was observed in terms of H2 and O2 production via water splitting. The maximum hydrogen production was observed for a 6% C-doped solid solution in methanolic solution, i.e. 5413.10 mmol H2 g-1 h-1 under 300 W Xe light irradiation. The 6% C-doped solid solution released maximum O2 (193.80 μmol O2 h-1 g-1) and H2 (323.00 μmol H2 h-1 g-1) from pure water under exposure to real sunlight due to the highly ordered atomic arrangement, high porosity, high crystallinity, low oxygen vacancies, and high OH-group concentration in the lattice.
... Therefore, it is evident that the hydrothermal reaction temperature affects the size and distribution of CeO 2 nanoparticles. It is important to note that CeO 2 shows size-dependent oxygen buffering capacity, which leads to changes in structural, chemical, and electronic properties [52,53]. An increment in particle size enables a larger active surface area for electron-hole pair generation and interaction with the electrolyte solution, in addition to the advantages of effective CeO 2 -TiO 2 heterojunction formation. ...
The search for a suitable photoelectrode material remains the most challenging problem in photoelectrochemical applications. Metal oxides are favorable for their chemical stability under an aqueous environment. This work presents size and distribution controlled CeO2 nanoparticles on TiO2 nanorod arrays achieved through a systematic variation of the hydrothermal process temperature. In a two-step hydrothermal process, single crystalline TiO2 nanorods are first grown on fluorine doped tin oxide (FTO) coated glass substrate using titanium (IV) butoxide precursor followed by a treatment with cerium nitrate to obtain CeO2 nanoparticles over TiO2. Variation of the hydrothermal process temperature in the second step from 80 ˚C to 150 ˚C results in CeO2 nanoparticles with a systematic variation of size and distribution over TiO2 nanorods. We demonstrate that an effective heterojunction between the CeO2 nanoparticles and TiO2 nanorod forms at a process temperature of 120 ˚C, which is manifested by improved photoelectrochemical performance. The CeO2-TiO2 heterojunction photoanode shows a photocurrent density of 3.77 mA/cm² (at 1.23 V vs. RHE) in 1 M KOH solution under one Sun (100 mW/cm²) illumination, which is approximately three times higher than that of bare TiO2 nanorod arrays. Further, Applied Bias Photon-to-current Efficiency (ABPE) is estimated to be 2.01 %. Diffuse Reflectance Spectra (DRS) shows a redshift of ∼ 0.1 eV in CeO2-TiO2 heterojunction that signifies the contribution of CeO2 towards visible light absorption. The Electrochemical Impedance Spectroscopy (EIS) shows a lower value for charge transfer resistance in samples processed at 120 ˚C. The superior photoelectrochemical performance of CeO2-TiO2 heterojunction is attributed to the collective contributions of visible light absorption and efficient charge transfer at the CeO2-TiO2 interface.
... Carbon monoxide (CO) is a kind of gas that is formed as a product of incomplete carbon combustion reaction, which is a common process found in the environment [1]. Despite the common happening of this gas, the presence of this compound is extremely increasing since the age of industrial revolution, contributing to the high level of this gas in the atmosphere beyond the tolerated limit in some regions. ...
... Although these catalysts are considered as good enough, the exploration for catalyst of this process is still widely done, to meet the better conversion and efficiency. Another improvement aspects searched are the activity in lower temperature, selectivity, stability, and also the economic aspect on making those catalyst [1]. ...
The use of some base metal oxide already widely studied for having beneficial properties in CO oxidation catalytic system. The properties of these base metals such as lower working temperature, high CO affinity, and economically cheaper would be beneficial for this solid system catalyst. The study of various base metal oxides shown these kinds of characteristics, but there still a few analyses of comparison among the various base oxide metals used as the support system for the oxidation reaction catalytic system. This study would give a comparison in the difference of the adsorption energy of various base oxide metals. This adsorption energy is one factor that promoting the activity of the catalytic system due to its affinity to the reactant on their surfaces. The DFT ab initio calculation for this comparison shows that NiO is the base metal oxide that having the highest CO adsorption energy. This oxide could be a potential support system combined with potential solid oxidative catalytic system.
... Strain is a chemically benign method of property tuning. 191 As a catalyst, nanoceria has been utilized as regenerative catalyst for hydrocarbon conversion reactions, [192][193][194][195][196][197][198][199] selective oxidation of alcohols, 196,200 used as a fuel additive, [201][202][203][204][205][206][207][208] water splitting and water gas shift reactions. [209][210][211][212][213][214][215] 4.3.1 Hydrocarbon conversion reactions. ...
... [209][210][211][212][213][214][215] 4.3.1 Hydrocarbon conversion reactions. Nanoceria and ceria-metal hetronano-structures have been used for the synthesis or conversion reaction of various hydrocarbon compounds useful in organic synthesis, biological applications and pharmaceutical industry such as N-substituted pyrrole, aryl ethers, N-arylated compounds, benzimidazoles, lactic acid, benzaldehydes etc. [192][193][194][195][196][197][198][199] Mechanisms for these reactions are often complex but the role of ceria as catalyst is common. ...
... Ceria has size dependent oxygen buffering capacity: decrease in size leads to change in structural, chemical and electronic properties. 192,197,198 Decrease in size of ceria nanoparticles below 5 nm dramatically increases reducible oxygen. 197 4.3.2 ...
Nanocrystalline cerium oxide (nanoceria) is a rare earth oxide with a complex surface chemistry. This material has seen substantial investigation in the recent years in both fundamental and applied studies due largely to more precise characterization of the unique surface structures, which mediate its pronounced redox activity. In particular, oxygen storage/buffering capacities have been thoroughly correlated with synthesis and processing condition effects on other material features such as surface (micro-) faceting, reconstruction, and (extent of) hydration. Key material features such as these modulate nanoceria redox performance by changing the crystal microenvironment. In this review, we present nanoengineering methods, which have produced increased nanoceria performance in biomedical, energy, and catalysis applications. The impact of combined/cooperative theoretical and experimental studies are highlighted throughout.
... Valechha et al. previously showed that the catalytic activity of CO oxidation was linearly proportional to the surface area of CeO 2 catalysts synthesized by the combustion method. 47 Singhania also synthesized RE (La, Pr, Nd, and Pm)-doped CeO 2 catalyst using the citric acidaided sol−gel method which was different from our synthesis method. Especially, it was reported that the large surface area was one of the reasons that La dopant had the higher CO oxidation activity than the other dopants. ...
Rare earth (RE) metals have often been used as dopants to improve the catalytic activity of ceria. However, their exact role in the activity of ceria catalyst has not been clearly identified. Combining experimental and theoretical approaches, we extensively investigate CO oxidation as a model reaction on RE-doped ceria (REC). The apparent activity is linearly proportional to the specific surface area (AS), which is enlarged by RE dopants as a consequence of surface stabilization. To decouple the effect of each RE dopant on the surface inherent activity, we set AS of REC to be almost constant by adjusting the pH during synthesis. In this case, however, pure ceria shows higher activity than any REC. We therefore conclude that although the RE dopants have lower intrinsic activity than that of Ce, they have an important effect of increasing AS to a level that pure ceria can never attain synthetically, thereby increasing their catalytic activity.
... [2][3][4] CO oxidation is considered as a reference reaction to explore heterogeneous catalysis in the past decades. [5][6][7] Earlier studies investigated that the CO oxidation on noble metal catalysts such as Pt, [8][9][10] Au, [11][12][13] Pd [14][15][16][17] or Rh-based [18] nanoparticles or alloys. To improve the stability and reactivity of supported catalysts, previous studies reported that the noble metal clusters anchored on metal oxides (e. g., MgO, [19] FeO x , [20] CeO 2 , [21][22][23] ZnO, [24] TiO 2 [25] ) can show a highly catalytic activity for CO oxidation at low temperature. ...
Based on density functional theory (DFT) calculations, the formation geometries, stability and catalytic properties of single‐atom iron anchored on xN‐doped graphene (xN‐graphene‐Fe, x=1, 2, 3) sheet are systemically investigated. It is found that the different kinds and numbers of gas reactants can effectively regulate the electronic structure and magnetic properties of the 3 N‐graphene‐Fe system. For NO and CO oxidation reactions, the coadsorption configurations of NO/O2 and CO/O2 molecules on a reactive substrate as the initial state are comparably analyzed. The NO oxidation reactions through the Langmuir–Hinshelwood (LH) and Eley‐Rideal (ER) mechanisms have relatively smaller energy barriers than those of the CO oxidation processes. In comparison, the preadsorbed 2NO reacting with 2CO molecules (2NO+2CO→2CO2+N2) through ER reactions (<0.4 eV) are energetically more favorable processes. These results can provide beneficial references for theoretical studies on NO and CO oxidation and designing graphene‐based catalyst for toxic gas removal.
... Only peaks attributed to this structure are available with no other parallel existing phase. But in Fig. 4b, excess Ce atoms form their native oxides (Valechha et al., 2011) along with anticipated perovskite formula and further confirmed by the presence of peaks at 28.6 (111), 33.5 (200) got matched with JCPDS file #655923. At last, the XRD diffractogram in Fig. 4a contains several peaks specified multiple phase formations. ...
Barium cerate, a novel solid base catalyst was employed in transesterification reaction for biodiesel production. The catalyst was characterized by Thermogravimetric analyses, powder X-ray Diffraction, Scanning Electron Microscopy attached with energy dispersive unit, Fourier Transform Infrared Spectroscopy. Karanja oil was used as non-edible feedstock for biodiesel production. The fatty acid profile of feedstock was analyzed by Gas Chromatography-Mass Spectrometry. In the present study, calcination temperature was optimized for synthesis of perovskite barium cerate with highest phase purity. Additionally, various Ba/Ce stoichiometric ratios were also checked to evaluate the active metal phase of catalyst. Ultimately, perovskite structure with 1:1 Ba/Ce was found to be most efficient one to catalyze the transesterification. This owed to the higher basicity value as well as compact and well-arranged perovskite crystal system which facilitate the catalysis on its surface. It produced the karanja oil methyl ester with 98.4% conversion at following experimental conditions: catalyst dose (1.2 wt %), oil to methanol molar ratio (1:19), reaction temperature (65 °C), reaction time (100min), and agitation speed (600 rpm). The pseudo-first order kinetic model was also successfully established for transesterification reaction. Green chemistry metrics (E-factor) and turn over frequency were also evaluated for methanolysis reaction. Barium cerate exhibited sixth cycle reusability with 81% methyl ester conversion. Therefore the prepared catalyst was ascertained as a sustainable heterogeneous catalyst for transesterification reaction. The physicochemical properties of the synthesized karanja oil methyl ester were measured according to ASTM D 6751 and were found to be within the permissible range. It ensured the compatibility of produced biodiesel with existing CI engines without any further modification.
