A new approach to deep desulfurization of gasoline by electrochemically catalytic oxidation and extraction

In order to further reduce the sulfur content in gasoline, a new desulfurization process for gasoline was obtained by means of electrochemically catalytic oxidation and extraction with an electrochemical fluidized-bed reactor. The particle group anode was activated carbon-supported lead dioxide (β-PbO₂/C). The electrolyte was aqueous NaOH solution, and copper pillar was cathode in the electrochemical reactions. The β-PbO₂/C particle group anodes can remarkably accelerate the electrochemical reaction rate and promote the electrochemical catalysis performance for the electrochemical desulfurization reaction. Also, gasoline desulfurization rule was investigated in an alkali solution. The experimental results indicated that the optimal desulfurization conditions were as follows: the cell voltage, the pH value of the electrolyte, feed volume flow rate and the β-PbO₂ percentage by weight were 3.2 V, pH value 13.1, 300 ml min^{− 1} and 5.0 wt.%, respectively. Under these conditions the concentration of sulfur in gasoline was reduced from 310 to 40 μg g^{− 1}, and the main properties of the product were not significantly affected. Based on these experimental results, a mechanism of indirect electrochemical oxidation was proposed.     

Synthesis of a highly active carbon-supported Ir–V/C catalyst for the hydrogen oxidation reaction in PEMFC

The active, carbon-supported Ir and Ir–V nanoclusters with well-controlled particle size, dispersity, and composition uniformity, have been synthesized via an ethylene glycol method using IrCl₃ and NH₄VO₃ as the Ir and V precursors. The nanostructured catalysts were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The catalytic activities of these carbon-supported nanoclusters were screened by applying on-line cyclic voltammetry and electrochemical impedance spectroscopy techniques, which were used to characterize the electrochemical properties of fuel cells using several anode Ir/C and Ir–V/C catalysts. It was found that Ir/C and Ir–V/C catalysts affect the performance of electrocatalysts significantly based on the discharge characteristics of the fuel cell. The catalyst Ir–V/C at 40 wt.% displayed the highest catalytic activity to hydrogen oxidation reaction and, therefore, high cell performance is achieved which results in a maximum power density of 563 mW cm⁻² at 0.512 V and 70 °C in a real H₂/air fuel cell. This performance is 20% higher as compared to the commercial available Pt/C catalyst. Fuel cell life test at a constant current density of 1000 mA cm⁻² in a H₂/O₂ condition shows good stability of anode Ir–V/C after 100 h of continuous operation.     

Study of cerium species in molten Li2CO3–Na2CO3 in the conditions used in molten carbonate fuel cells. Part I: Thermodynamic, chemical and surface properties

The chemical and surface behaviour of cerium oxide, a candidate material for MCFC applications is analysed in Li₂CO₃–Na₂CO₃ carbonate eutectic in reducing (H₂:CO₂:H₂O:CO) and oxidizing (O₂:CO₂) atmospheres. The electrochemical stability domains of cerium species are established at different temperature on the basis of thermochemical calculations. CeO₂ is the stable species whatever the acidity level in both the anode and cathode conditions; nevertheless, a partial solubility of Ce₂O₃ in CeO₂ can be predicted. The solubility of cerium and cerium oxide samples, determined by absorption spectrophotometry, is about 5 × 10^–4 mol kg^–1 in cathodic conditions and 3 × 10^–4 mol kg^–1 in anodic conditions. X-ray diffraction (XRD) confirmed the presence of CeO₂ at the surface of the samples. Incorporation of sodium species in the CeO₂ lattice is likely; the presence of Ce(III) in long endurance tests was detected by X-ray photoelectron spectroscopy (XPS).     

Preferential CO oxidation in H2-rich gas mixtures over Au/doped ceria catalysts

Nanosized gold catalysts supported on doped ceria were prepared by deposition–precipitation method. A deep characterization study by HRTEM/EDS, XRD, FT-Raman, TPR and FTIR was undergone in order to investigate the effect of ceria modification by various cations (Sm³⁺, La³⁺ and Zn²⁺) on structural and redox properties of gold catalysts. Doping of ceria affected in different way catalytic activity towards purification of H₂ via preferential CO oxidation. The following activity order was observed: Au/Zn–CeO₂ > Au/Sm–CeO₂ > Au/CeO₂ > Au/La–CeO₂. The differences in CO oxidation rates were ascribed to different concentration of metallic gold particles on the surface of Au catalysts (as confirmed by the intensity of the band at 2103 cm⁻¹ in the FTIR spectra collected during CO–O₂ interaction). Gold catalysts on modified ceria showed improved tolerance towards the presence of CO₂ and H₂O in the PROX feed. The spectroscopic experiments evidence enhanced reactivity when PROX is performed in the presence of H₂O already at 90 K.     

Investigation of palladium interaction with cerium oxide and its state in catalysts for low-temperature CO oxidation

Palladium catalysts supported on nanosized CeO₂ supports were synthesized by different methods. The catalysts showed high low-temperature activity (LTA) in CO oxidation. The synthesized palladium–ceria catalysts for low-temperature CO oxidation were investigated by a complex of physicochemical methods, and their catalytic performance was determined in the light-off regime. It was shown using high-resolution transmission electron microscopy (HRTEM) and EDX microanalysis that the catalysts with high LTA are characterized by exceptionally high dispersity of palladium on the surface of the supports. Two different states of palladium were observed by XPS. They correspond to the surface interaction phases (SIPs) as Pd_xCeO_2−δ and small metal clusters (<10 Å). According to diffraction images obtained by HRTEM, the latter have flattened shape due to epitaxial binding between (1 1 1) facets of palladium and CeO₂. Two types of CO adsorption sites (Pd²⁺ and Pd⁰) were distinguished by FTIR. They can be attributed to SIP (Pd²⁺) and palladium in flat metal clusters (Pd^δ+ and Pd⁰). The drop of LTA in CO oxidation is related to the loss of the palladium chemical interaction with the surface of the support and palladium sintering to form PdO nanoparticles. The formation of PdO particles is stimulated by crystallization of CeO₂ particle surface due to the calcination of support at temperatures above 600 °C. The XPS, HRTEM and FTIR data give reliable evidence that PdO particles are not responsible for LTA in CO oxidation.In this work, the structure of the active sites consisting of two phases: atomically dispersed palladium within the SIP and palladium metal nanoclusters is proposed. The catalyst pretreatment in hydrogen was found to improve significantly its catalytic (LTA) properties. The effect of the hydrogen pretreatment was supposed to be related to the formation of hydroxyl groups and their effect on the electronic and geometrical state of the surface active sites and their possible direct participation in CO oxidation.     

CHARACTERIZATION OF CERIUM OXIDE AND CARBON SUPPORTED Ag-Cu ELECTRO-CATALYSTS FOR ANODE ELECTRODE IN DIRECT ETHANOL FUEL CELLS

In this study, electrochemical and spectroscopic characterization of home-made CeO₂, activated carbon-based Ag-Cu electro-catalysts, and preliminary anode polarization results in a direct ethanol fuel cell test system were presented. Ag-Cu transition metal couples were impregnated onto carbon and cerium oxide supports by wet impregnation, ion exchange, and co-precipitation techniques. Wet impregnation technique was selected for further spectroscopic analysis and fuel cell testing due to its easy metal loading advantage and highest peak currents in ethanol-containing electrolyte environment. When Ag and Cu were loaded 37.5 and 12.5 wt.% onto carbon and cerium oxide by wet impregnation technique, XPS analysis indicated an appreciable amount of Ag and Ag₂O and a high amount of CuO. In cerium oxide-based samples atomic percentage of oxygen fits well with the stoichiometry of CuO/CeO₂. Preliminary results show that BET surface area and the current peaks exhibit a close resemblance (highest BET surface area indicates highest anodic dissolution current), which is thought to be due to the high accessibility of copper layers impregnated onto cerium oxide and activated carbon in H₂SO₄ electrolyte environment. Hydrogen reduction of CeO₂-based samples prepared by wet impregnation at 750°C greatly improved anode polarization and onset oxidation potential.     

Electrochemical behavior of a platinum anode for reduction of uranium oxide in a LiCl molten salt

The electrochemical behavior of a platinum anode has been investigated during the electrolysis of uranium oxide in a LiCl molten salt. Pt is oxidized to Pt²⁺ at 2.6 V (vs. Li–Pb reference electrode) in the absence of O²⁻ ion. The platinum dissolution takes place at a more anodic potential with an increase of O²⁻ ion. Although the main anodic process in the electrolysis is the oxygen evolution by oxidation of O²⁻ ion at a higher concentration of Li₂O, a thin film due to the formation of Li₂PtO₃ was coated on the anode surface. The platinum dissolution proceeds with an intergranular corrosion-like behavior at a low concentration of Li₂O.     

Preferential oxidation of CO in excess hydrogen over a nanostructured CuO–CeO2 catalyst with high surface areas

CuO–CeO₂ is prepared by coprecipitation and ethanol washing and characterized using BET, HR-TEM, XRD and TPR techniques. The results show that CuO–CeO₂ is nanosized (r_TEM = 6.5 nm) and possesses high surface area (S_BET = 138 m² g⁻¹). Furthermore, some lattice defects in the surface of CuO–CeO₂ are found, which are beneficial to enhance catalytic performance of CuO–CeO₂ in preferential oxidation of CO in excess hydrogen (PROX). Consequently, the nanostructured CuO–CeO₂ exhibits perfect catalytic performance in PROX. Namely, CO content can be lowered to less than 100 ppm at 150 °C with 100% selectivity of O₂ in the presence of 8% CO₂ and 20% H₂O at .     

Oxidation of silicon nitride hot pressed with CeO2 and SiO2 additions

(CeO₂ + SiO₂)-doped hot pressed silicon nitride shows parabolic oxidation kinetics in dry flowing air at T = 773 to 1673 K. Possible oxidation mechanisms have been proposed. The apparent activation energy for oxidation ( 350 kJmol⁻¹) suggests migration of impurity cations through the grain boundary phase to the silicon nitride/oxide reaction interface as the probable rate-limiting step. The very low solubility of cerium in silicate melts appears to be an important factor for oxidation. Cristobalite and ceria were the main crystalline oxidation products, the genesis and morphology of CeO₂ crystals being strictly related to oxidation temperature and cooling rate. A previously unknown hexagonal high-temperature form of ceria crystallized in samples subjected to very fast quenching.     

A mechano- and electrochemically controlled SnSb/C nanocomposite for rechargeable Li-ion batteries

At present, graphite (LiC₆: 372 mAh g⁻¹, 840 mAh cm⁻³) is used as the anode material for lithium-ion batteries. However, methods to enhance the energy density, cyclability, initial Coulombic efficiency, and rate capability of lithium-ion batteries are still actively being researched. Here, we report a simple, fast, and novel method for transforming micron-sized Sn and Sb powders into ca. 10 nm- and 2–3 nm-sized SnSb crystallites by mechanochemical synthesis and electrochemical reactions, respectively. These nanocrystallites are uniformly distributed in an amorphous carbon matrix, resulting in a SnSb/C nanocomposite structure. The fabricated SnSb/C nanocomposite showed excellent electrochemical properties, such as a high energy density (1st charge: 706 mAh g⁻¹), long cyclability (ca. 550 mAh g⁻¹ over 300 cycles), good initial Coulombic efficiency (ca. 81%), and a fast rate capability (1C: 590 mAh g⁻¹, 2C: 550 mAh g⁻¹).     

Synthesis of CeO2 nanoparticles by rapid thermal decomposition using microwave heating

Abstract

This article describes the synthesis of a CeO₂ fine powder by thermal decomposition of cerium oxalate and cerium nitrate powders using a microwave furnace. Plate-like crystalline CeO₂ particles were obtained using the cerium oxalate precursor powder. Using the cerium nitrate powder as a precursor, spherical crystalline CeO₂ particles were obtained with a primary particle diameter of 30?nm and secondary particle size of 550?nm.     

Plant-based synthesis of cerium oxide nanoparticles as a drug delivery system in improving the anticancer effects of free temozolomide in glioblastoma (U87) cells

Nowadays, nanocarriers were proven to contain the potential of improving cancer treatments and are utilized to carry anticancer medications to tumors. In this study, cerium oxide nanoparticles (CeO₂-NPs) were synthesized by using Caccinia macranthera leaf extract as the stabilizer and reducer agent, as well as cerium nitrate salt as the supplier source of cerium. The synthesized CeO₂-NPs were analyzed through different procedures such as UV–Vis, FTIR, FESEM/EDX/PSA, XRD, XPS, and TGA/DTA. The outcomes of XRD and FTIR analyses con?rmed the synthesis of pure and crystalline structures of CeO₂-NPs. The average size and zeta potential of our nanoparticles were about 30 nm and ?18.5 mV, respectively. According to the results of XPS analysis, the percentage of Ce⁴⁺ was more than that of the Ce³⁺ oxidation state in synthesized NPs. The CeO₂-NPs were loaded with Temozolomide (TMZ) as an anti-cancer drug through electrostatic interaction and the produced nano-drug (CeO₂-TMZ) was delivered to glioblastoma multiforme (GBM) tumor cells. In conformity to the observations, the drug loading content (DLC) and drug loading efficiency (DLE) of CeO₂-TMZ were about 89.10 and 20.29, respectively. In comparison to the TMZ drug, the in vitro assay exhibited the exertion of higher antiproliferative activities, cell cycle arrest, apoptosis, and expression of p53 by CeO₂-TMZ, which proves the promising capability of this drug as a remedial factor for cancer treatment.     

Effect of sintering on the catalytic activity of a Pt based catalyst for CO oxidation: Experiments and modeling

The goal of this paper was to make the link between sintering of a 1.6% Pt/Al₂O₃ catalyst and its activity for CO oxidation reaction. Thermal aging of this catalyst for different durations ranging from 15 min to 16 h, at 600 and 700 °C, under 7% O₂, led to a shift of the platinum particle size distributions towards larger diameters, due to sintering. These distributions were studied by transmission electron microscopy. The number and the surface average diameters of platinum particles increase from 1.3 to 8.9 nm and 2.1 to 12.8 nm, respectively, after 16 h aging at 600 °C. The catalytic activity for CO oxidation under different CO and O₂ inlet concentrations decreases after aging the catalyst. The light-off temperature increased by 48 °C when the catalyst was aged for 16 h at 600 °C. The CO oxidation reaction is structure sensitive with a catalytic activity increasing with the platinum particle size. To account for this size effect, two intrinsic kinetic constants, related either to platinum atoms on planar faces or atoms on edges and corners were defined. A platinum site located on a planar face was found to be 2.5 more active than a platinum site on edges or corners, whatever the temperature. The global kinetic law {r (mol m⁻² s⁻¹) = 103 × exp(−64,500/RT)[O₂]^0.74[CO]^−0.5)} related to a reaction occurring on a platinum atom located on planar faces allows a simulation of the CO conversion curves during a temperature ramp. Modeling of the catalytic CO conversion during a temperature ramp, using the different aged catalysts, allows prediction of the CO conversion curves over a wide range of experimental conditions.     

Electrodeposited PtCo and PtMn electrocatalysts for methanol and ethanol electrooxidation of direct alcohol fuel cells

PtCo and PtMn electrocatalyst particles were successfully synthesized on Ti substrate by the electrodepostion method. PtCo particles deposited are star-shaped particles with size of 100–200 nm and very porous with many slices of 10 nm. On the other hand, PtMn particles are spherical and have no obvious conglomeration, and the particle is in the range of 100–200 nm. The results reveal that the effect of the incorporation of Co and Mn on the electrochemical active surface area of Pt nanoaprticles is very small. However, incorporation of trace Co and Mn in Pt (e.g., Pt₁₀₀₀Co and Pt₁₀₀₀Mn) has dramatic effect on the electrochemical oxidation reaction of alcohol. The mass specific peak current for the methanol oxidation in alkaline media is 49 mA cm⁻² and 39 mA cm⁻² on Pt₁₀₀₀₀Mn and Pt₁₀₀₀Co, which is three and two times higher, respectively, than that on pure Pt electrocatalyst nanoparticles. PtMn and PtCo electrocatalysts also show significant enhanced stability for methanol oxidation. However, the electrocatalytic enhancement of Co or Mn to Pt is relatively small for the electrooxidation reactions of ethanol in alkaline media.     

Electrochemical regeneration of ceric sulphate in an undivided cell

Ceric sulphate (0–0.5 m) was generated electrochemically from cerous sulphate slurries (0.5–0.8 m total cerium) in 1.61 m sulphuric acid, at 50 °C, using a bench scale differential area undivided electrochemical cell with an anode to cathode ratio of eleven. A cell current efficiency for Ce(IV) of 90% was obtained at an anode current density of 0.25 A cm^–2. An empirical model illustrates an increase in overall current efficiency for Ce(IV) with an increase in electrolyte velocity, an increase in total cerium concentration, and a decrease in the cell current. From separate kinetic studies on rotating electrodes, both, anode and cathode kinetics were found to be affected by cerium sulphate adsorption processes. Anode adsorption of cerous sulphate species leads to inhibited mass transfer and negatively affected current efficiencies for Ce(IV). Cathode adsorption of cerium sulphate is thought to be responsible for high cathode current efficiencies for hydrogen (93–100%). The dissolved cerous sulphate concentration increased with increasing ceric sulphate and total cerium sulphate concentrations resulting in slurries with a stable dissolved cerous sulphate concentration of as high as 0.851 m in 1.6 m H₂SO₄ at room temperature.     

Fast catalytic degradation of organic dye with air and MoO3:Ce nanofibers under room condition

One-dimensional Ce doped MoO₃ nanofibers with different Ce doping amount have been synthesized by a combination method of sol–gel process and electrospinning technique. X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) were used to characterize the resulting samples. These fibers are interesting for a number of catalytic applications. The best catalytic activity was obtained over 11.86 wt.% CeO₂-doped MoO₃ with 98% degradation effect of 0.3 g L⁻¹ Safranin-T by air under room condition towards complete degradation products such as HCO₃⁻ and NO₃⁻ within 20 min. The leaching test showed that this MoO₃:Ce nanofiber catalyst has an excellent stability and can be used as a rapid heterogeneous catalyst for about ten times by simply treatment.     

Electro-catalytic degradation of methylene blue wastewater assisted by Fe2O3-modified kaolin

The electrochemical oxidation of methylene blue (MB) wastewater assisted by Fe₂O₃-modified kaolin in a 200 mL electrolytic batch reactor with graphite plate as electrodes was investigated. The catalyst was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of pH, current density and introduction of NaCl on the efficiency of the electrochemical degradation process were also studied. It was found that Fe₂O₃-modified kaolin has higher catalytic activity in the electrochemical degradation of MB wastewater. 96.47% chemical oxygen demand (COD) removal was obtained in 40 min of electrochemical treatment of MB wastewater at pH 3, current density was equal to 69.23 mA cm⁻².     

Hydrogen Production Via CH4 and CO Assisted Steam Electrolysis

Porous composite anodes consisting of a yttria-stabilized zirconia (YSZ) backbone that was impregnated with CeO₂ and various amounts of metallic components including Cu, Co and Pd were fabricated. The performance of these anodes was then tested in a solid oxide water electrolysis cell under conditions where the anode was exposed to the reducing gasses H₂, CH₄ and CO. The reducing gasses were used to decrease the electrochemical potential of the cell and increase overall efficiency. The results of this study show that Cu–CeO₂–YSZ anodes have low catalytic activity for the oxidation of CO and CH₄ and are not very effective in lowering the cell potential while operating in the reducing gas assisted mode. The addition of Co to the Cu–CeO₂–YSZ anode resulted in a modest increase in the catalytic activity and enhanced the thermal stability of the anode. A Pd–C–CeO₂–YSZ anode was found to have the highest catalytic activity of those tested and gave the largest reductions in the operating potential of the solid oxide electrolysis cell.     

Utilization of carbon dioxide as soft oxidant for oxydehydrogenation of ethylbenzene to styrene over V2O5–CeO2/TiO2–ZrO2 catalyst

Vanadium oxide and cerium oxide doped titania–zirconia mixed oxides were explored for oxidative dehydrogenation of ethylbenzene to styrene utilizing carbon dioxide as a soft oxidant. The investigated TiO₂–ZrO₂ mixed oxide support with high specific surface area (207 m² g⁻¹) was synthesized by a coprecipitation method. Over the calcined support (550 °C), a monolayer equivalent (15 wt.%) of V₂O₅, CeO₂ or a combination of both were deposited by using wet-impregnation or co-impregnation methods to make the V₂O₅/TiO₂–ZrO₂, CeO₂/TiO₂–ZrO₂ and V₂O₅–CeO₂/TiO₂–ZrO₂ combination catalysts, respectively. These catalysts were characterized using X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature preprogrammed reduction (TPR), CO₂ temperature preprogrammed desorption (TPD) and BET surface area methods. All characterization studies revealed that the deposited promoter oxides are in a highly dispersed form over the support, and the combined acid–base and redox properties of the catalysts play a major role in this reaction. The V₂O₅–CeO₂/TiO₂–ZrO₂ catalyst exhibited a better conversion and product selectivity than other combinations. In particular, the addition of CeO₂ to V₂O₅/TiO₂–ZrO₂ prevented catalyst deactivation and helped to maintain a high and stable catalytic activity.     

Study of LiNi0.5Mn1.5O4 synthesized via a chloride-ammonia co-precipitation method: Electrochemical performance, diffusion coefficient and capacity loss mechanism

LiNi_0.5Mn_1.5O₄ powders are prepared via a new co-precipitation method. In this method, chloride salts are used as precursors and ammonia as a precipitator. The impurity of chlorine can be removed via a thermal decomposition of NH₄Cl in the subsequent calcination. X-ray diffraction pattern reveals that the final product is a pure spinel phase of LiNi_0.5Mn_1.5O₄. Scanning electron microscopy shows that the powders have an octahedron shape with a particle size of about 2 μm. Electrochemical test shows that the LiNi_0.5Mn_1.5O₄ powders exhibit an excellent cycling performance and after 300 cycles, the capacity retention is 83%. The lithium diffusion coefficient is measured to be 5.94 × 10⁻¹¹ cm² s⁻¹ at 4.1 V, 4.35 × 10⁻¹⁰ cm² s⁻¹ at 4.75 V and 7.0 × 10⁻¹⁰ cm² s⁻¹ at 4.86 V. The mechanism of capacity loss is also explored. After 300 cycles, the cell parameter ‘a’ decreases by 0.54% for the quenched sample (LiNi_0.5Mn_1.5O_4−δ) and by 0.42% for the annealed sample (LiNi_0.5Mn_1.5O₄). Besides, it is the first time to identify experimentally that the Ni and Mn ions dissolved in the electrolyte can be further deposited on the surface of anode.