Catalytic Activity Of CeO2 Research Articles

Enhancing the Electrical, Dielectric, and Structural Properties of CeO2-ZrO2 Nanocomposites

For enhancing the breakdown strength and increase the capacity of high voltage power supply with high oxidation stability and good electric properties, Ceramic nanomaterials like zirconia (ZrO2) and Ceria (CeO2) preferred due to their strong insulating property and high relative permittivity. In this article, we have reported the synthesis of CeO2/ZrO2 nanocomposite by chemical method. The use of surfactants during synthesis have an adverse effect on the catalytic activity of CeO2 with different morphologies like nanorods, nanocubes, and nano-octahedra. In addition, zirconia can be synthesized via a variety of techniques, including sol-gel, hydrothermal, and precipitation procedures, and combined with other metal oxide nanoparticles. The synthesized nanocomposites were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM). The crystalline nature and mixed phase of CeO2/ZrO2 nanoparticles have been confirmed by the findings of XRD and SEM analysis. At various frequencies and temperatures, the dielectric constant and dielectric loss of the synthesized nanoparticles were determined. The conductivity and dielectric characteristics of the synthesized samples exhibited temperature and frequency dependency, indicating that the dopant concentration had a significant impact. As frequency increased, the nanoparticles' tangent loss and dielectric constant dropped sharply. These nano-composites can be used as a metal oxide semiconductor for memory devices as well as fuel cells.

Sponge-inspired MXene@CeO2 detector for ultra-sensitive detection of glucose

Non-invasive sweat detectors can monitor the glucose level of diabetes in a painless way. However, most detectors need to collect enough sweat through external exercise or active stimulation, which increases the inconvenience of the user and reduces the applicable population. In this study, we propose an ultra-sensitive biomimetic glucose detector to detect the sweat produced by thermoregulation without additional exercise and stimulation. Inspired by the predator process of sponge in the sea, the sensing material of MXene (Ti3C2Tx) @CeO2 hydrogels employed the “laminae-trestle-laminae” (L-T-L) structure of sponge to adsorb and transport glucose molecules in sweat. CeO2 grafted onto the MXene surface can detect glucose by the catalytic activity of CeO2. The glucose detector with an ultra-low limit of detection (LOD = 0.004 μM), excellent sensitivity (801.27 μA⋅μM−1⋅cm−2), and a broad linear detection range (LDR = 0.01–2.5 μM) can satisfy detection requirements in human sweat after dilution. In real applications, the detector can detect glucose in the sweat of diabetic patients for five consecutive days and detect the glucose content in the daily drinks of patients. Our findings demonstrate the high potential of sponge-inspired MXene@CeO2 glucose detector for routine medical testing.

Influence of Y Doping on Catalytic Activity of CeO2, MnOx, and CeMnOx Catalysts for Selective Catalytic Reduction of NO by NH3

Novel yttrium-doped CeO2, MnOx, and CeMnOx composites are investigated as catalysts for low-temperature NH3-SCR. The study involves the preparation of unmodified oxide supports using a citrate method followed by modification with Y (2 wt.%) using two approaches, including the one-pot citrate method and incipient wetness impregnation of undoped oxides. The NH3-SCR reaction is studied in a fixed-bed quartz reactor to test the ability of the prepared catalysts in NO reduction. The gas reaction mixture consists of 800 ppm NO, 800 ppm NH3, 10 vol.% O2, and He as a balance gas at a WHSV of 25,000 mL g−1 h−1. The results indicate that undoped CeMnOx mixed oxide exhibits significantly higher deNOx performance compared with undoped and Y-doped MnOx and CeO2 catalysts. Indeed, yttrium presence in CeMnOx promotes the competitive NH3-SCO reaction, reducing the amount of NH3 available for NO reduction and lowering the catalyst activity. Furthermore, the physical-chemical properties of the prepared catalysts are studied using nitrogen adsorption/desorption, XRD, Raman spectroscopy, temperature-programmed reduction with hydrogen, and temperature-programmed desorption of ammonia. This study presents a promising approach to enhancing the performance of NH3-SCR catalysts at low temperatures that can have significant implications for reducing NO emissions.

Hydrothermal aging mechanism of K/CeO2 catalyst in soot catalytic combustion based on the Ostwald ripening mechanism

The thermogravimetric analysis (TGA) experiment of CeO2 and K/CeO2 catalysts prepared with the incipient wetness impregnation method was carried out for the soot catalytic combustion at different K loadings before and after hydrothermal aging. The structure, morphology, and catalytic activity of CeO2 and K/CeO2 catalysts were thoroughly investigated with the means of N2 adsorption/desorption, XRD, XPS, and H2-TPR. The density functional theory (DFT) operation was applied to explain the mechanism of the decrease in catalytic activity of CeO2 and K/CeO2 catalysts after hydrothermal aging. TGA showed that the Tmax of the hydrothermal aging K/CeO2 catalyst was 505 °C, which was higher than CeO2 at 473 °C. After hydrothermal aging, CeO2 catalysts were less agglomerated than K/CeO2, and the ratio of Ce3+/Ce4+ decreases, but the mobile oxygen OII/OI ratio in the lattice were increased compared to CeO2 catalysts. DFT calculations showed that K doping significantly increases the surface energy and decreases the oxygen vacancy formation energy of (1 1 1), (2 0 0), (2 2 0), and (3 1 1) crystal planes, leading to enhanced catalytic combustion performance of the K/CeO2 catalyst soot based on the Mars-Van Krevelen mechanism. Furthermore, K doping decreased the adsorption energy of H2O and the energy barrier of K atoms diffusing near the surface of K/CeO2 catalyst crystals from 5.92 eV to 2.46 eV, which resulted in the loss of the active center number because of migration and coalescence (sintering) caused by crystal plane instability based on the Ostwald ripening mechanism.

CeO2 QDs anchored on MnO2 nanoflowers with multiple synergistic effects for amplified tumour therapy

Chemodynamic therapy (CDT) is an emerging tumour-specific therapeutic technology. However, the relatively insufficient catalytic activity of CDT agents in the tumour microenvironment (TME) limits their biomedical application. In addition, severe hypoxia and glutathione (GSH) overexpression in the TME greatly limit the antitumour efficiency of monotherapy. Herein, a cancer cell membrane-camouflaged and ultrasmall CeO2-decorated MnO2 (mMC) composite is developed for amplified CDT, photodynamic therapy (PDT) and photothermal therapy (PTT). Due to the homotypic targeting ability of cancer cell membranes, mMC nanoparticles preferentially accumulate in tumour tissue. In the TME, CeO2 acts as a highly efficient CDT agent to convert endogenous H2O2 to toxic reactive oxygen species (ROS) for killing cancer cells. Meanwhile, MnO2 irradiated with near-infrared (NIR) light displays prominent hyperthermia and ROS generation performance to perform PTT and PDT. Moreover, MnO2 can produce oxygen to ameliorate hypoxia and deplete GSH to relieve the antioxidant capability of tumours, which is beneficial to the simultaneous augmentation of PDT and CDT. Most importantly, the catalytic activity of CeO2 was greatly improved by hyperthermia. Consequently, a significantly enhanced therapeutic efficiency was obtained by the above multiple synergistic effects. This work provides a proof of concept for amplified tumour therapy by synchronously self-supplying oxygen, consuming GSH, and enhancing catalytic activity.

Porous CeO2 nanorods loaded with indocyanine green for enhanced tumor-specific therapy

Recently, catalytic therapy on the basis of Fenton reaction represents a very promising paradigm for potential cancer therapy, which has inspired great research interest and got fast progress. Nevertheless, it remains challenging to fabricate nanocatalytic systems that can precisely perform catalytic activity in tumor tissues without causing toxicity to adjacent normal tissues. Herein, we designed and fabricated a porous CeO2 nanorods that can selectively perform therapeutic activity in the weakly acidic tumor microenvironment via converting H2O2 into •OH to kill cancer cells, meanwhile, the normal tissues are protected by decomposing H2O2 into O2 in the physiological environment. Specifically, benefiting from the porous structure, such CeO2 nanorods could be loaded with Indocyanine green (ICG) that could both contribute itself to generate singlet oxygen (1O2) and convert near-infrared (NIR) light to hyperthermia. Once exposed to NIR light, on the one hand, the catalytic activity of CeO2 was significantly enhanced by photothermal effect of ICG for highly efficient tumor catalytic therapy; on the other hand, the generated hyperthermia and 1O2 by ICG can further synergistically enhance the therapy efficiency via directing killing cancer cells. The current study provides a proof-of-concept demonstration of tumor-specific therapy with minimal non-targeted toxicity.

Morphological Effect of CeO2 Catalysts on Their Catalytic Performance in Lean Methane Combustion

Sheaf-like and layered CeO2 with micro/nanocomposite structure were synthesized by a simple and friendly hydrothermal method and used in lean methane combustion. The relationship between the CeO2 structure and catalytic performance in lean methane combustion has been studied by the means of XRD, SEM, TEM&HRTEM, H2-TPR, BET and XPS. According to the H2-TPR results, the reducibility of sheaf-like CeO2 is higher compared with layered CeO2. XPS results reveal that oxygen vacancies are more easily formed on the surface of sheaf-like CeO2 than that on layered CeO2 surface. The catalytic activity of CeO2 in lean methane combustion is strongly related to its morphology; the obtained sheaf-like CeO2 with better reducibility and larger content of Ce3+ exhibits much higher catalytic activity in lean methane combustion compared with the layered CeO2.

Enhanced core–shell CeO2:Er,Yb@W18O49 heterojunction H2 generation by multiband emissions of Er ions

The core–shell CeO2:Er,Yb@W18O49 heterojunction is successfully synthesized via the facile solvothermal method. The octahedral CeO2:Er,Yb nanocrystal’s core exhibits green (2H11/2, 4S3/2 → 4I15/2), red (4F9/2 → 4I15/2) and NIR (4I11/2 → 4I15/2 and 4I13/2 → 4I15/2) emission under 980 nm laser diode excitation, and the multiband emissions are absorbed by the W18O49 nanowire’s shell, re-exciting its higher energy localized surface plasmon resonances (LSPR). With the excitation of 980 nm, the photocatalytic property of CeO2:Er,Yb@W18O49 for hydrogen (H2) evolution from ammonia borane (BH3NH3), a three-fold increase compared to W18O49, is researched. The application of natural sunlight for the production of H2 is studied, and an obvious H2 production enhancement compared to the use of W18O49 (two-fold) is also observed. This remarkable enhancement in the catalytic activity of CeO2:Er,Yb@W18O49 heterostructures is ascribed to the re-excitation of LSPR by multiband emissions of CeO2:Er,Yb.

Theoretical investigation of dephosphorylation of phosphate monoesters on CeO2(111)

The dephosphorylation of neutral model phosphate monoesters on CeO2(111), including para-nitrophenyl phosphate and methyl phosphate, has been studied theoretically using self-consistent, periodic density functional theory calculations at the GGA+U-PW91 level. These phosphate monoesters interact strongly with CeO2(111) by forming a bond between the P atom and a surface lattice O atom. A surface-assisted hydrolysis mechanism is proposed for the catalytic dephosphorylation of the phosphate monoesters on CeO2(111), which involves P-O ester bond scission followed by phosphate hydration and product desorption. The energies of the transition states for the P-O ester bond scission are found to follow a linear scaling relation with respect to the energies of the dissociated fragments reasonably well. A nearly spontaneous transfer of one of the H atoms on the phosphate group to the alkoxide group produces the corresponding alcohol. The hydration of the remaining HPO3 group has a maximum activation energy of ca. 1.1 eV in vacuo. Thus although the nature of the alkoxide group affects the activation of the P-O ester bond, it should not affect the overall catalytic activity of CeO2(111) for dephosphorylation because the hydration of the phosphate group is rate-limiting.

Effect of Gd infiltration on NiO-CeO 2 anode substrates for intermediate-temperature solid oxide fuel cells

Abstract In this study, solid oxide fuel cells (SOFCs) were fabricated using cerium oxide in the anode support layer (ASL) instead of gadolinium-doped ceria (GDC). To compensate for the deficiency in ionic conductivity and catalytic activity of CeO2, a gadolinium nitrate solution was infiltrated in the ASL before sintering at 1450 °C. The ohmic and polarization resistance of the cell were reduced upon Gd-nitrate infiltration, which also increased the sinterability of the ASL. However, excessive infiltration was found to degrade the electrochemical properties of the cell. Therefore, the conditions for infiltration were optimized in this study. The peak power density of the cell after Gd-nitrate infiltration was 0.662 W, 68% higher than that of the reference cell without Gd-nitrate infiltration.

Investigations on the Antimony Promotional Effect on CeO2–WO3/TiO2 for Selective Catalytic Reduction of NOx with NH3

AbstractAntimony‐doped CeO2–WO3/TiO2 catalysts were prepared by a conventional ultrasonic‐assisted impregnation method and employed for selective catalytic reduction of NOx with NH3 at low temperature. Both experimental work and theoretical studies were employed to elucidate the effect of the antimony on promoting the CeO2–WO3/TiO2 catalyst. The catalytic activity of CeO2–WO3/TiO2 was largely improved after the addition of antimony oxide. It was found that antimony doping reduced the crystal size and strengthened the synergistic effect between the metal cations, which resulted in a favorable catalyst surface status with abundant active surface oxygen, Brønsted acid sites, and effective electron transfer. Both in situ diffuse reflectance infrared Fourier transform analysis and DFT calculation results revealed that the ammonia and NOx desorption behavior over the catalyst surface were considerably different. For the ammonia species, rather large amounts of the active NH4+ and NH3 species anchored on the surface of the Sb‐doped CeO2–WO3/TiO2. In view of the NOx species, the amount of nonactive bidentate nitrate species was largely reduced and the amount of active gaseous NO2 species was clearly enhanced, which lowered the activation energy of the catalytic process and gave rise to the elevated low‐temperature NH3 selective catalytic reduction activity. All these preferable properties resulted in the elevated de‐NOx activity of the Sb‐doped CeO2–WO3/TiO2 catalyst.

Cerium dioxide catalyzed synthesis of methyl N-phenylcarbamate from carbon dioxide, aniline and methanol in the presence of n-butyllithium

Direct synthesis of methyl N-phenylcarbamate (MPC) from carbon dioxide (CO2), aniline and methanol catalyzed by cerium dioxide (CeO2) in the presence of n-butyllithium (BuLi) was developed. The catalytic activity of CeO2 was significantly improved by the addition of BuLi. The conversion of aniline and the yield of MPC were dependent on the amount of CeO2 and BuLi, reaction conditions including the pressure of CO2, reaction time and temperature, and 9.4% yield of MPC was obtained under the optimized conditions. The formation pathway of MPC was also investigated in detail by varying reactants based on previously reported investigations, and phenyl isocyanate (PI) was believed to be the intermediate for the synthesis of MPC. A possible reaction pathway for the direct synthesis of MPC from CO2, aniline and methanol was proposed.

Synthesis, characterisation and photo-catalytic activity of CeO<SUB align="right">2/Fe<SUB align="right">2O<SUB align="right">3 nano-composite

Preparation of nano-composite mixed oxides has a great current interest because it can improve the behaviour of the two metal oxides and enhance formation of new stable compounds which have different chemical and physical properties. Nano-composite CeO2-Fe2O3 samples with different molar ratios of the two oxides have been synthesised by co-precipitation method to study the effect of Fe2O3 doping on the magnetic properties and catalytic activity of CeO2. The prepared nano-sized catalysts are characterised by XRD, TEM and SEM. Magnetic properties were measured to evaluate the proposed nano-composite samples. From magnetic measurements it was established that the saturation magnetisation in all doped samples is higher than in pure ceria. A great application of the prepared nano-composites, with a vital role in our daily life, is the purification of the polluted waters from some toxic dyes. Complete photo-catalytic degradation of toxic Bromopyrogallol red dye (BPR) is achieved revealing that all doped samples have higher catalytic activities than those of pure catalysts (CeO2 and Fe2O3).

Comparison of preparation methods for ceria catalyst and the effect of surface and bulk sulfates on its activity toward NH3-SCR

A series of CeO2 catalysts prepared with sulfate (S) and nitrate (N) precursors by hydrothermal (H) and precipitation (P) methods were investigated in selective catalytic reduction of NOx by NH3 (NH3-SCR). The catalytic activity of CeO2 was significantly affected by the preparation methods and the precursor type. CeO2-SH, which was prepared by hydrothermal method with cerium (IV) sulfate as a precursor, showed excellent SCR activity and high N2 selectivity in the temperature range of 230–450°C. Based on the results obtained by temperature-programmed reduction (H2-TPR), transmission infrared spectra (IR) and thermal gravimetric analysis (TGA), the excellent performance of CeO2-SH was correlated with the surface sulfate species formed in the hydrothermal reaction. These results indicated that sulfate species bind with Ce4+ on the CeO2-SH catalyst, and the specific sulfate species, such as Ce(SO4)2 or CeOSO4, were formed. The adsorption of NH3 was promoted by these sulfate species, and the probability of immediate oxidation of NH3 to N2O on Ce4+ was reduced. Accordingly, the selective oxidation of NH3 was enhanced, which contributed to the high N2 selectivity in the SCR reaction. However, the location of sulfate on the CeO2-SP catalyst was different. Plenty of sulfate species were likely deposited on CeO2-SP surface, covering the active sites for NO oxidation, which resulted in poor SCR activity in the test temperature range. Moreover, the resistance to alkali metals, such as Na and K, was improved over the CeO2-SH catalyst.

Influence of CeO2 morphology on the catalytic activity of CeO2–Pt hybrids for CO oxidation

Ceria, because of its excellent redox behavior and oxygen storage capacity, is used as a catalyst for several technologically important reactions. In the present study, different morphologies of nano-CeO2 (rods, cubes, octahedra) were synthesized using the hydrothermal route. An ultrafast microwave-assisted method was used to efficiently attach Pt particles to the CeO2 polyhedra. These nanohybrids were tested as catalysts for the CO oxidation reaction. The CeO2/Pt catalyst with nanorods as the support was found to be the most active catalyst. XPS and IR spectroscopy measurements were carried out in order to obtain a mechanistic understanding and it was observed that the adsorbed carbonates with lower stability on the reactive planes of nanorods and cubes are the major contributor to this enhanced catalytic activity.

Hydrothermal Synthesis of CeO2 Nanoparticles on Activated Carbon with Enhanced Desulfurization Activity

Nanosized CeO2 particles with a diameter of ∼200 nm were successfully loaded on activated carbon (AC) via a single-step hydrothermal process. The synthetic parameters, including hydrothermal temperature, precursor concentration, and reaction time, were regulated to control the size of the as-prepared CeO2 nanoparticles. The catalytic activity of CeO2 nanoparticles/AC was investigated by dynamic adsorption of SO2 from simulated flue gas, and the results exhibited remarkably enhanced SO2 adsorption capacity. The reaction mechanism of adsorbing and trapping SO2 by CeO2 nanoparticles/AC was discussed by laser Raman spectroscopy, X-ray powder diffraction, and thermodynamic calculations, which demonstrated that, in the presence of SO2 and O2, the generation of sulfate, accompanied by partial reduction of Ce4+ to Ce3+, was the key process during SO2 removal in our desulfurization experiments.

Mn-Cu and Mn-Ce Composite Oxides for Decolouration of Acid Red 186 Solutions by CWO

Decolouration by catalytic oxidation of Acid Red 186 dye solutions was investigated using several manganese-based heterogeneous catalysts, namely MnOx (manganese oxides), Mn-Cu and Mn-Ce composite oxides. Also, catalytic activity of CeO2 and CuOx (copper oxides) were tested. Catalysts were used in slurry conditions, at 130ºC and oxygen partial pressure of 15 bar. Additional uncatalysed run and thermolysis (no catalyst, no oxygen) were studied. The results revealed that MnOx and Mn-Cu were the most active catalysts concerning the reduction of colour. MnCu5 and CuOx led to the highest TOC decreases. From the overall process (colour and TOC reductions) and having in consideration catalyst stability, MnCu5 was considered suitable to AR186 oxidation.

Structure evolution of nanocrystalline CeO2 and CeLnOx mixed oxides (Ln = Pr, Tb, Lu) in O2 and H2 atmosphere and their catalytic activity in soot combustion

This paper reports results of studies on structure and activity in soot combustion of nanocrystalline CeO2 and CeLnOx mixed oxides (Ln=Pr, Tb, Lu, Ce/Ln atomic ratios 5/1). Nano-sized (4–5nm) oxides with narrow size distribution were prepared by a microemulsion method W/O. Microstructure, morphology and reductivity of the oxides annealed up to 950°C in O2 and H2 were analyzed by HRTEM, XRD, FT-IR, Raman spectroscopy and H2-TPR. Obtained mixed oxides had fluorite structure of CeO2 and all exhibited improved resistance against crystal growth in O2, but only CeLuOx behaved better than CeO2 in hydrogen.The catalytic activity of CeO2, CeLnOx and physical mixtures of CeO2+Ln2O3 in a model soot oxidation by air was studied in “tight contact” mode by using thermogravimetry. Half oxidation temperature T1/2 for soot oxidation catalysed by nano-sized CeO2 and CeLnOx was similar and ca. 100°C lower than non-catalysed oxidation. However, the mixed oxides were much more active during successive catalytic cycles, due to better resistance to sintering. Physical mixtures of nanooxides (CeO2+Ln2O3) showed exceptionally high initial activity in soot oxidation (decrease in T1/2 by ca. 200°C) but degraded strongly in successive oxidation cycles. The high initial activity was due to the synergetic effect of nitrate groups present in highly disordered surface of nanocrystalline Ln2O3 and enhanced reductivity of nanocrystalline CeO2.

Preparation and photochemical properties of nanoparticles of ceria doped with zinc oxide

AbstractNanoparticles of CeO2 doped with ZnO were syn thesised via soft solution chemical processes at 40°C and a final pH of 6. The particle size of CeO 2decreased markedly after doping with ZnO. The solubility limit of ZnO in Ce1-xZnxO2-x was determined to be x = 0·561. The oxidation catalytic activity of CeO2 was effectively decreased by doping with ZnO. For the oxidation of phenol, the photocatalytic activity of ZnO doped CeO2 was much lower than that of fine titania particles. ZnO doped CeO2 showed excellent UV absorption and transparency in the visible region, in a similar manner to undoped CeO2.

Catalytic activity of CeO2 and Pr2O3 for the liquid-phase benzylation of o-xylene to 3,4 – dimethyldiphenylmethane

The liquid phase benzylation of o-xylene with benzyl chloride over rare earth oxide catalysts like CeO2 and Pr2O3 was studied in a batch reactor at atmospheric pressure and 363 K. Surface area, pore volume, DTA, acid strength distribution on the catalyst surface and optimum temperature of the catalyst are reported.