Cerium Hydroxycarbonate Research Articles

Novel Ce(OH)CO3/carbon nanotubes hybrid material towards a highly sensitive electrochemical dopamine determination in real urine samples

Cerium hydroxycarbonate and multiwalled carbon nanotubes (Ce(OH)CO3/CNT), drop-casted onto a glassy carbon (GC) electrode and electrochemically treated (tCe(OH)CO3/CNT) has been obtained as a new hybrid material. tCe(OH)CO3/CNT was characterized through SEM, FT-IR, UV–Vis, and electrochemical techniques such as cyclic voltammetry (CV) with different redox couples as Fe2+/3+, Fe(CN)63-/4− or Ru(NH3)62+/3+and electrochemical impedance spectroscopy (EIS) measurements with Fe(CN)63-/4−. The charge transfer resistance (RCT) value of tCe(OH)CO3/CNT was up to two orders of magnitude lower than the RCT of bare GC electrodes and these results were confirmed by the effective heterogeneous electron transfer rate constant values (k°eff, 2.4 10−3 vs 7.0 10−4, respectively). The calibration curve of DA exhibits a linear response within the range of 0.1 and 70 μmol L−1 with a correlation coefficient (R2) of 0.987 (n = 3) and a limit of detection of 0.003 μmol L−1. Inorganic and organic interferents do not alter significatively the selectivity. The electrochemical treatment of Ce(OH)CO3 and CNT generates a modified electrode which successfully combines the selectivity of Ce towards catechol with the high conductivity of CNT presenting an ideal performance for the electrochemical DA determination in 5 real urine samples (1.94 μmol L−1 in a 1:20 dilution) using differential pulse voltammetry (DPV) with an RSD < 6.1 %.

A comparison of Cu/CeO2 catalysts prepared via different precipitants/digestion methods for single stage water gas shift reactions

CeO2 supports have been synthesized through a different precipitation/digestion method with various cerium precursors (cerium hydroxide (CH), cerium hydroxy carbonate (CHC), cerium carbonate (CC)). Nano-sized CeO2 supports with a high BET surface area were prepared through the pre-calcination of cerium precursors. 20 wt.% of Cu was loaded onto the prepared CeO2 supports through an incipient wetness impregnation method. Among the prepared catalysts, Cu/CeO2-CHC yielded the highest CO conversion between the temperature range from 200 to 360 °C. This result was primarily due to possessing the highest Cu dispersion and a high oxygen storage capacity (OSC). In addition, the 20 wt.% Cu/CeO2 catalyst exhibited 100 % CO2 selectivity.

Deactivation of Ceria Supported Palladium through C–C Scission during Transfer Hydrogenation of Phenol with Alcohols

The stability of palladium supported on ceria (Pd/CeO2) was studied during liquid flow transfer hydrogenation using primary and secondary alcohols as hydrogen donors. For primary alcohols, the ceria support was reduced to cerium hydroxy carbonate within 14 h and was a contributing factor toward catalyst deactivation. For secondary alcohols, cerium hydroxy carbonate was not observed during the same time period and the catalyst was stable upon prolonged reaction. Regeneration through oxidation/reduction does not restore initial activity likely due to irreversible catalyst restructuring. A deactivation mechanism involving C–C scission of acyl and carboxylate intermediates is proposed.

Nanostructured Materials Prepared by Surface-Assisted Reduction: New Catalysts for Methane Oxidation.

Cerium formate hollow spheres and cerium hydroxycarbonate nanorods with residual formate groups are effective for reducing palladium(II) salts onto their surfaces. Calcination of the new materials obtained by this surface-assisted reduction method gives highly active PdO/CeO2 nanostructures with Pd well dispersed on the substrate. Temperature-programmed oxidation experiments showed that these nanomaterials are good catalysts for the low-temperature oxidation of methane, with 50% conversion temperatures (T(50%)) at ∼300 °C.

Optimization of a highly active nano-sized Pt/CeO2 catalyst via Ce(OH)CO3 for the water-gas shift reaction

Crystalline cerium hydroxy carbonate (CHC: Ce(OH)CO3) was prepared by a novel precipitation/digestion method at room temperature in air. The nano-sized CeO2 supports were obtained by the thermal decomposition of CHC and the Pt/CeO2 catalysts were prepared by an incipient wetness impregnation method. The pre-calcination temperature and aging time were optimized to obtain a highly active Pt/CeO2 catalyst for the water gas shift reaction (WGS). The Pt/CeO2 catalyst exhibited the highest CO conversion (82%) and the lowest activation energy (55 kJ/mol) at a very high gas hourly space velocity (GHSV) of 45,515 h−1 when the optimized synthesis parameter (pre-calcined temperature = 400 °C and aging time = 4 h) was used in the synthesis of CeO2. This is mainly due to the high BET surface area, nano-sized CeO2, and intimate interaction between Pt and CeO2.

Synthesis of Highly Active Nano-Sized Pt/CeO2 Catalyst via a Cerium Hydroxy Carbonate Precursor for Water Gas Shift Reaction

A novel precipitation/digestion route has been developed to synthesize crystalline cerium hydroxy carbonate (CHC: Ce(OH)CO3) by using an equimolar quantity of cerium nitrate (Ce(NO3)3·6H2O) and mixed precipitants (KOH + K2CO3) at room temperature. Nano-sized CeO2 supports could be prepared by the pre-calcination of CHC at 400 °C for 4 h. A highly active water gas shift (WGS) catalyst, 1 wt.% Pt/CeO2 catalyst showed almost equilibrium CO conversion with 100% CO2 selectivity at 320 °C even at the gas hourly space velocity (GHSV) of 45,625 h−1. A novel precipitation/digestion route has been developed to synthesize crystalline cerium hydroxy carbonate (CHC: Ce(OH)CO3) by using an equimolar quantity of cerium nitrate (Ce(NO3)3·6H2O) and mixed precipitants (KOH + K2CO3) at room temperature. Nano-sized CeO2 supports could be prepared by the pre-calcination of CHC at 400 °C for 4 h. A highly active water gas shift (WGS) catalyst, 1 wt.% Pt/CeO2 catalyst showed almost equilibrium CO conversion with 100% CO2 selectivity at 320 °C even at the gas hourly space velocity (GHSV) of 45,625 h−1.

Biomolecule-assisted synthesis of rare earth hydroxycarbonates

A biomolecule-assisted synthetic route has been developed for the preparation of orthorhombic lanthanide hydroxycarbonate crystals with interesting assembly features, using various amino acids as capping ligands for the synthesis. Reaction mechanism to the materials is proposed. The biomolecule additives played an important role in modifying the microstructures, and the morphology of crystals could be spindly, spherical, and dumbbell-like. Thermal analysis indicated that the as-prepared cerium hydroxycarbonate was stable below 240 °C, and NdOHCO 3 was stable below 400 °C. The CeOHCO 3 sample showed intensive broad band emission centered at 370 nm, which may be used as a next-generation black-light material to control pests. Fluorescence of the materials is dependent on the structure. Therefore, simply alternating reaction parameters would vary microstructures and tune the optical properties of the materials.

Self-assembly of cerium compound nanopetals via a hydrothermal process: Synthesis, formation mechanism and properties

Nanopetals of cerium hydroxycarbonate have been synthesized via a controlled hydrothermal process in a mixed water–ethanol medium. Electron microscopy indicates that each microsized flower consists of tens to hundreds of cerium hydroxycarbonate nanopetals. These nanopetals have a very large aspect ratio: a width as large as 10 μm, with a thickness as thin as 10 nm. The formation of the cerium compound depends strongly on the composition of the precursors, and is attributed to the favored ethanol oxidation by Ce(IV) ions over Ce(IV) hydrolysis process. Raman studies showed that microflower CeO 2 preferentially stabilizes O 2 as a peroxide species on its surface for CO oxidation.

Shape control of CeO2 nanostructure materials in microemulsion systems

Two morphological structure nanomaterials of Cerium oxide (CeO2), such as comet-like and prism-like, were prepared by thermal decomposition of cerium hydroxycarbonate precursors. The precursors were synthesized in microemulsion system under solvothermal condition at different reaction temperatures. In the microemulsion systems, ethoxylated nonylphenol (TX-10) and 1-butanol were acted as surfactant and cosurfactant, respectively.

Activity and stability of low-content gold–cerium oxide catalysts for the water–gas shift reaction

We report here on the high activity and stability of low-content gold–cerium oxide catalysts for the water–gas shift reaction (WGS). These catalysts are reversible in cyclic reduction–oxidation treatment up to 400°C, are non-pyrophoric, and are thus potential candidates for application to hydrogen generation for fuel cell power production. Low-content (0.2–0.9at.%) gold–ceria samples were prepared by single-pot synthesis by the urea gelation/coprecipitation method; and by sodium cyanide leaching of high-content (2–8at.%) gold–ceria materials prepared by various techniques. The low-content gold–ceria catalysts are free of metallic gold nanoparticles. Gold is present in oxidized form, as verified by a variety of analytical techniques. However, these materials display the same WGS activity as the high-content gold ones, and remain free of gold nanoparticles after use in a reaction gas stream composed of 11% CO–26% H2O–26% H2–7% CO2–balance He up to 300°C. We show that the determining factor for the retention of active gold in ceria is the surface properties of the latter. Measurements of lattice constant expansion indicate gold ion substitution in the ceria lattice. The turnover frequency of WGS under the assumption of fully dispersed gold is the same for a variety of low-content gold–ceria preparations. The stability of gold–ceria in various gas compositions and temperatures was good. The most serious stability issue is formation of cerium hydroxycarbonate in shutdown operation.

Hydrothermal deposition of cerium hydroxycarbonate thin films on glass

The first success in the preparation of rare earth hydroxycarbonate thin films has been achieved. Cerium hydroxycarbonate films were prepared by a hydrothermal deposition method, the sample of a single orthorhombic phase was deposited at a lower temperature while those of orthorhombic and hexagonal phases were obtained at higher temperatures. The crystals in the films could be ellipsoidal, prismatic, or rhombic, depending on the deposition conditions applied. The thin films could be candidates for developing novel optical materials and for advanced ceramics processing.

Preparation of cerium hydroxycarbonate by a surfactant-assisted route

Cerium hydroxycarbonate (CeOHCO 3) with shuttle-like morphology has been conveniently synthesized at 90 °C from aqueous solution in the presence of polyvinylpyrrolidone (PVP). The products were characterized by X-ray diffraction, transmission electron microscopy and photoluminescent (PL) techniques. The as-prepared CeOHCO 3 was found to have a PL emission at about 347 nm. Experimental conditions as well as the role of PVP played in the reaction were also explored.

Synthesis of cerium hydroxycarbonate powders via a hydrothermal technique

CeOHCO 3 powders have been directly synthesized using a hydrothermal process at temperatures as low as 160°C. The well-dispersed powders are obtained in a short period of reaction time during hydrothermal reaction via the hydrolysis of urea. For synthesizing CeOHCO 3, the concentration of urea is found to be a crucial determinant, which has significant effects on the morphology of the derived powders. When low urea concentrations are provided, the formed particles are rhomboidal platelets. On the other hand, the high urea concentrations cause the shape of the powders to become prismatic. Increasing the concentration of urea tends to increase the particle size as well as the aspect ratio of CeOHCO 3 powders. After further heating at 500°C, a phase transformation from orthorhombic CeOHCO 3 to cubic CeO 2 takes place. The crystallinity and size of CeO 2 strongly depend on the particle size of CeOHCO 3.

Hydrothermal evolution of the thiourea-cerium(III) nitrate system: formation of cerium hydroxycarbonate and hydroxysulfate.

Through the examination of solutions by Raman spectroscopy and the characterization of solid products by XRD, XPS, and FT-IR spectroscopy, the hydrothermal evolution of the thiourea−cerium nitrate system was investigated. Thiourea decomposes before the formation of orthorhombic CeOHCO3. Monoclinic CeOHSO4 is produced after SO42- is derived from NO3- and HS- in the solution at higher temperatures. PL spectra show that the new phase has a photoluminescence intensity that is about 400 times that of CeOHCO3.

Preparation of Yttrium, Lanthanum, Cerium, and Neodymium Basic Carbonate Particles by Homogeneous Precipitation

Uniform yttrium, lanthanum, cerium, and neodymium basic carbonate particles were prepared by homogeneous precipitation. Powders were characterized with respect to size, shape, crystal structure, and thermal decomposition behavior. Yttria precursor particles were spherical, monosized (0.4 {mu}m), and amorphous; whereas lanthana, neodymia, and ceria precursors were prismatic (ranging from 1 to 6 {mu}m in size) and crystalline. Crystal structure was found to be ancylite-type orthorhombic symmetry in all three cases. Upon heating in air, yttrium, lanthanum, and neodymium precursors underwent two-step decomposition to first form oxycarbonate and then oxide. Cerium hydroxycarbonate decomposed in a single step to form the oxide.