Citric Complex Method Research Articles

Impact of preparation methods on the performance of Cu/Ni/Zr catalysts for methanol decomposition

Utilizing waste heat from engine exhausts to decompose methanol into a hydrogen (H2) and carbon monoxide (CO) mixture, subsequently reintroduced into the engine, offers a significant potential to enhance engine efficiency and reduce emissions. The efficacy of the catalyst is crucial, as it directly influences the composition of the decomposition gases, thereby impacting energy conservation and emissions reduction. This study investigates the impact of various preparation methods for the self-developed Cu/Ni/Zr catalyst for methanol hydrogenation decomposition. These techniques include the co-precipitation method, co-impregnation method, and citrate complexation method, evaluated within a temperature spectrum of 220 °C–320 °C. Employing analytical methods such as x-ray Photoelectron Spectroscopy (XPS), x-ray Diffraction (XRD), Thermogravimetric Analysis-Differential Scanning Calorimetry (TGA-DSC), Brunauer–Emmett–Teller (BET), Temperature-Programmed Reduction (TPR), and Scanning Electron Microscopy (SEM) analysis, the study elucidates the mechanism of methanol decomposition catalyzed by Cu/Ni/Zr. The findings indicate that the catalyst’s activity, in terms of decomposition rate and hydrogen content, ranks in descending order from the co-impregnation method, followed by the citrate complexation method, to the co-precipitation method.

The Effect of Different Polyol Precursors on Disordered Spinel ZnAl2O4 Structure Prepared by the Polymeric Citrate Complex Method and the Corresponding Catalytic Behavior in the Glycerolysis of Urea

ZnAl2O4 is a cubic close‐packed oxide with tetrahedral and octahedral sites in the lattice structure. The catalytic activity of ZnAl2O4 is strongly connected with the surface properties caused by the partially inverse spinel ZnAl2O4 structure. In this research, ZnAl2O4 catalysts are prepared for the glycerolysis of urea via the polymeric citrate complex method using polymeric templates made of citric acid with a different polyol precursor. Depending on the polyol precursor, the partial inversion parameters representing the disordered bulk ZnAl2O4 structure are controlled, which results in different surface AlO4/AlO6 ratios and surface acidity. The specific surface areas of the prepared ZnAl2O4 catalysts are proportional to the molecular weight of the polyol precursor. The s–ZnAl2O4 (polyol precursor = sorbitol) prepared via two pathways from citrate complex and polymeric citrate complex shows the highest inversion parameter and surface acidity, leading to the highest glycerol carbonate (GC) yield and glycerol conversion in the glycerolysis of urea. A relationship between the GC yield and the surface properties, such as the acidity and inversion parameters, is established.

Ce–Zr-based mixed oxide catalyst for oxidative depolymerization of kenaf stalk (biomass) into vanillin

Since petroleum became depleted, rapid attention has been devoted to renewable energy sources such as lignocellulosic biomass to produce useful chemicals for industry (for instance vanillin). Three primary components of lignocellulose are lignin, cellulose, and hemicellulose. This paper uses microwave-assisted technology to oxidize the kenaf stalk (lignocellulosic biomass) and extract lignin to produce vanillin. Catalysts with variable acid–base and redox properties are essential for the mentioned effective conversion, for this reason, CeO2–CA, ZrO2–CA, and CeZrO2–CA catalysts were synthesized. The citrate complexation method was used for the catalyst synthesis and the physicochemical characteristics were analyzed by XRD, FTIR, FE–SEM, TEM, BET, and TPO. The characterization results demonstrated that CeZrO2–CA shows the smallest sized crystallites with a large specific surface area among the other chosen catalysts. For vanillin production, the effect of reaction temperature, reaction time, and catalyst loading was studied. It was observed that compared to other catalysts, CeZrO2–CA produced the highest vanillin yield of 9.90% for kenaf stalk for 5 wt% of CeZrO2–CA at 160 °C for 30 min. Furthermore, vanillin production using extracted lignin is studied keeping CeZrO2–CA as a catalyst and with the same operating parameters, which yielded 14.3% of vanillin. Afterward, the change in yield with respect to pH is also presented. Finally, the recyclability of catalyst is also studied, which showed that it has a strong metal support and greater stability which may give industrial applications a significant boost.Graphical

Effect of Calcination Temperatures on Surface Properties of Spinel ZnAl2O4 Prepared via the Polymeric Citrate Complex Method-Catalytic Performance in Glycerolysis of Urea.

In this study, we investigated urea glycerolysis over ZnAl2O4 catalysts that were prepared by using a citrate complex method and the influence of calcination temperatures on the surface properties of the prepared catalysts by varying the calcination temperature from 550 °C to 850 °C. As the reciprocal substitution between Al3+ and Zn2+ cations led to the formation of a disordered bulk ZnAl2O4 phase, different calcination temperatures strongly influenced the surface properties of the ZnAl2O4 catalysts, including oxygen vacancy. The increase in the calcination temperature from 550 °C to 650 °C decreased the inversion parameter of the ZnAl2O4 structure (from 0.365 to 0.222 for AlO4 and 0.409 to 0.358 for ZnO6). The disordered ZnAl2O4 structure led to a decrease in the surface acidity. The ZnAl2O4-550 catalyst had a large specific surface area, along with highly disordered surface sites, which increased surface acidity, resulting in a stronger interaction of the Zn NCO complex on its surface and an improvement in catalytic performance. Fourier transform infrared and thermogravimetric analysis results of the spent catalysts demonstrated the formation of a greater amount of a solid Zn NCO complex over ZnAl2O4-550 than ZnAl2O4-650. Consequently, the ZnAl2O4-550 catalyst outperformed the ZnAl2O4-650 catalyst in terms of glycerol conversion (72%), glycerol carbonate yield (33%), and byproduct formation.

Bimetallic Ni-Co Alloy Derived from Perovskite as Precursor on SiO2 as Catalysts for CO Methanation

The supported bimetallic Ni-Co alloy catalysts modified with La2O3 were prepared by using the perovskite composite oxide of LaNi[Formula: see text]Co[Formula: see text]O3/SiO2 as the precursor, which were obtained by the impregnation method combined with the citrate complex method. The samples were characterized through using XRD, BET, H2-TPR, CO-TPD, TG and XPS, and the catalytic performances for CO methanation was investigated. The component among the bimetallic (Ni-Co) alloy-La2O3/SiO2 catalyst would be mutually diluted, consequently exhibiting pretty good resistance to metal sintering. The carbon deposition on the catalyst surface mainly depends on the adsorption form of CO, the doping of Co changed the adsorption form and adsorption strength of Co, thereby, the bimetallic Ni-Co catalyst showed strong resistance to carbon deposition. Comparing with the mono-metallic nickel catalyst, the supported bimetallic Ni-Co alloy catalysts exhibited good catalytic activity, selectivity and stability for CO methanation, especially excellent resistance to carbon deposition and metal sintering.

Dimethyl Ether Oxidation over Copper Ferrite Catalysts

The depletion of fossil energy sources and the legislation regarding emission control demand the use of alternative fuels and rapid progression of aftertreatment technologies. The study of dimethyl ether (DME) catalytic oxidation is important in this respect, as DME is a promising clean fuel and at the same time a VOC pollutant present in the tail gases of industrial processes. In the present work, copper ferrite catalysts synthesized via the citrate complexation method have been evaluated in DME oxidation. N2-physisorption, XRD, H2-TPR, and XPS were employed for the characterization of the mixed oxide catalysts. The copper ferrite spinel phase was detected in all samples accompanied by a gradual decrease in the bulk CuO phase upon increase in iron content, with the latter never vanishing completely. The Fe0.67Cu0.33 catalyst exhibited the highest catalytic activity in DME oxidation, attaining approximately a 4-fold higher oxidation rate compared to the respective pure copper and iron oxides. The enhanced catalytic performance was attributed to the higher specific surface area of the catalyst and its enhanced redox properties. Highly dispersed copper species were developed owing to the formation of the spinel phase. DME-TPD/TPSR experiments showed that the surface lattice oxygen of the Fe0.67Cu0.33 catalyst can oxidize preadsorbed DME at a lower temperature than all other catalysts which is in agreement with the H2-TPR findings.

Effect of morphology and oxidation state of nickel on diesel soot oxidation activity

NiO sample is synthesized using the EDTA citrate complex method and calcined at 600 °C/5 h. Ni sample was acquired by reducing NiO to Ni at 600 °C in 4% H2/N2 atmosphere. Its physicochemical properties were obtained by XRD and Raman spectroscopy analysis, where it confirmed the complete reduction of NiO to Ni. SEM and TEM micrographs revealed a drastic particle growth for the Ni, indicating NiO sintering during the reduction process and a considerable surface morphology change. Ozawa and KAS methods were used to calculate the mean activation energy (Ea) value. NiO displayed lower Ea than Ni. Hence, NiO showed better catalytic activity than Ni.

CO2‐resistant SDC‐SSAF oxygen selective dual‐phase hollow fiber membranes

AbstractCe0.85Sm0.15O1.925–Sm0.6Sr0.4Al0.3Fe0.7O3‐δ (SDC‐SSAF) hollow fiber membranes aimed for oxyfuel application are fabricated via a phase inversion‐sintering technique using powders synthesized from EDTA–citrate complex method. Oxygen ions transport is revealed to be the limiting step that determines the overall oxygen transport rate in SDC‐SSAF. SDC‐SSAF hollow fiber membrane attained a maximum flux of 2.6 ml min−1 cm−2 at 950°C under an oxygen partial pressure difference of 1/0.02 atm (feed/permeate). Variation in oxygen partial pressure on the permeate side exerts larger influence on the oxygen permeation flux relative to the change on the feed side. Stability tests over 100 h demonstrate stable oxygen permeation flux under both He and CO2 sweep conditions.

Methane catalytic combustion over CeO2-ZrO2-Sc2O3 mixed oxides

In this work nanostructured CeO2-ZrO2-Sc2O3 mixed oxides prepared by citrate complexation method are studied. The effects of the co-substitution of ZrO2 and Sc2O3 in the CeO2 lattice are assessed in terms of the reducibility of the samples and their catalytic activity towards oxidation of methane. In situ X-ray absorption near edge structure (XANES) and X-ray powder diffraction (XPD) experiments with synchrotron light were performed to study the oxygen exchange capacity of these ternary oxides in reaction conditions and their structure stability. Catalytic experiments for complete methane combustion indicated a superior performance of samples containing Sc2O3 compared to the CeO2-ZrO2 one in terms of reaction onset temperature, conversion values and activation energy. Samples with 4 at% and 6 at% Sc doping exhibited a stable behavior at 800 °C during 7.5 h on-stream experiments. Structural stability was confirmed by in-situ XPD experiments with no secondary phase segregation or carbon deposition in reaction conditions.

Enhancement of CO2 Methanation over La-Modified Ni/SBA-15 Catalysts Prepared by Different Doping Methods

A new, highly active Ni-La2O3/SBA-15(C) catalyst for CO2 methanation was prepared using a citrate complex method, where the formed LaNiO3 with perovskite structure was a key precursor. The physicoc...

Disordered structure of ZnAl2O4 phase and the formation of a Zn NCO complex in ZnAl mixed oxide catalysts for glycerol carbonylation with urea

The effect of a disordered ZnAl2O4 spinel structure on glycerol carbonylation with urea was investigated with pure ZnAl2O4 (c-ZnAl2O4) and ZnAl mixed oxide (c-ZnAlO) prepared by a citrate complex method, and ZnAl physically-mixed oxide (p-ZnAlO). During catalysts preparation, a disordered bulk ZnAl2O4 phase generated disordered sites on the surface: the Al3+ cations substituting for Zn2+ cations at the tetrahedral sites, and the surface oxygen vacancy corresponding to the Zn2+ cations substituting for Al3+ cations at the octahedral sites. The disordered surface sites increased in order of p-ZnAlO < c-ZnAlO < c-ZnAl2O4, which was proportional to the surface acidity. c-ZnAlO exhibited the best reaction performance due to the existence of a solid zinc isocyanate (Zn NCO) complex on the disordered sites. Here, we proposed that the solid Zn NCO complex preferentially generated glycerol carbonate (GC), while the liquid Zn NCO complex produced both GC and zinc glycerolate.

Highly -sensitive near infrared luminescent nanothermometers based on binary mixture

We propose a simple strategy to obtain a luminescence intensity ratio nanothermometer operating in the near infrared range (1000–1700 nm) by use of binary mixtures of lanthanide doped Y2O3 selected as 1%Ho - Y2O3 + 1%Er - Y2O3 and 1%Ho - Y2O3 + 1%Nd - Y2O3. All nanoparticles were synthetized by citrate complexation method and thermally annealed at 800 °C. The temperature evolution of the emission properties was monitored in the range of 297–472 K and analyzed in terms of emission shape, intensity, dynamics, excitation wavelength, acquisition mode and weight ratio of the binary mixture. A maximum relative sensitivity of 1%K−1 at 297 K was recorded for the 3/1 weight ratio Ho – Y2O3 + Er – Y2O3 binary mixture upon excitation at 536.8 nm. For the more appropriate excitation wavelength for bioimaging applications at 649.7 nm, a relative sensitivity of 0.55–0.6% K−1 was recorded in the relevant physiological temperature range (300–320 K) for the 3/1 weight ratio Ho – Y2O3 + Er – Y2O3 binary mixture. To the best of our knowledge, our study also represents a first report on the near -infrared luminescence (around 1200 nm) lifetime thermometry for a Ho doped nanoparticle. Comparison with the literature demonstrates that our system represents a promising near-infrared thermometer, with a non-sophisticated and reproducible configuration that is open to multiple optimization routes.

Preparation and Evaluation of Copper–Manganese Oxide as a High-Efficiency Catalyst for CO Oxidation and NO Reduction by CO

In this work, highly efficient Cux–Mn composite catalysts (0 ≤ x ≤ 0.20) were synthesized by an improved hydrothermal–citrate complex method and tested in the catalytic total oxidation of CO and the removal of NO by CO. The influence of Cu on manganese oxide materials was characterized by several techniques, including FESEM, HRTEM, XRD, BET analysis, H2 TPR, O2 TPD, XPS, and DRIFTS. Possible reaction mechanisms for the NO + CO model reaction and CO oxidation were also tentatively proposed. The Cu-modified manganese oxide materials showed higher catalytic activity in CO oxidation and the selective catalytic reduction (SCR) of NO with CO than pure MnOx materials. The improved catalytic activity in CO oxidation observed for the copper–manganese oxide catalyst was associated with a greater amount of adsorbed oxygen species and high lattice oxygen mobility due to the formation of a Cu1.5Mn1.5O4 spinel active phase (Cux2+–Mnx3+–[O(y–z)⊙z] species). Furthermore, in terms of the CO-SCR model reaction, the surface...

Effect of Zn substitution to a LaNiO3−δ perovskite structured catalyst in ethanol steam reforming

A LaNi1−xZnxO3−δ perovskite structured oxide catalyst is prepared with a one-step citrate complex method and applied as the precursor of the catalyst in ethanol steam reforming (ESR) reaction. The Zn substitution makes the perovskite-oxide difficult to be reduced due to the strong bond of La–O–Zn, which favors the formation of small Ni particle size thus moderates the sintering of nickel. The doping of Zn also effectively suppresses coking in the reaction. The spillover of oxygen and the electron donation effect of Zn species to the surface of metallic nickel is confirmed with an XPS technique. The doping amount shows an optimum value and a LaNi0.85Zn0.15O3−δ sample exhibits the highest H2 product yield and best stability at 700 °C.

Catalytic conversion of syngas to higher alcohols over mesoporous perovskite catalysts

Two types of mesoporous perovskite-type oxides (Meso-PTOs) were synthesized by combining a templated synthesis and a citrate complex method. The Meso-PTO catalysts exhibited superior catalytic activity in the higher alcohols synthesis from syngas compared to the bulk-PTO, likely due to the increased dispersion of active sites on the high surface of the Meso-PTOs. Moreover, the Meso-PTOs show higher productivity for C3 and C4 alcohols as well as C2+ oxygenates. Among the two Meso-PTOs developed here, the mesoporous LaFe0.7Cu0.3O3 catalyst was capable of significant suppression of the methanation reaction and better selectivity to higher alcohols compared to the mesoporous LaCo0.7Cu0.3O3 catalyst.

Rare Earth Ion Doped Ceria As Electrolytes For Solid Oxide Fuel Cell

We report the nature of rare earth ion doped ceria (REC), Ce0.8Ln0.2O2−δ, (Ln = Y 3+ , Gd 3+ , Sm 3+ , Nd 3+ and La 3+ ) as oxide ion conductors for their plausible application as electrolytes in intermediate temperature solid oxide fuel cell (SOFC). The samples were prepared by citrate-complexation method and characterized by XRD, SEM/ EDX and UV-Visible spectra. The cubic fluorite-type crystal structure is confirmed from XRD patterns, and the observed lattice parameters are in agreement with calculated values. The UV-Vis spectra of the particles dispersed in aqueous medium showed absorption in the UV region which is ascribed to charge-transfer transition. The dc conductivities at 673 K are in the order of Ce0.8Sm0.2O2−δ > Ce0.8Gd0.2O2−δ > Ce0.8Y0.2O2−δ > Ce0.8Nd0.2O2−δ > Ce0.8La0.2O2−δ and their corresponding activation energies are 0.85, 0.87, 0.87, 0.88 and 0.95 eV. Based on ionic and electronic transference numbers, electrical conductivity obtained here is purely ionic, i.e., oxide ion conductors. Copyright © 2016 VBRI Press.

Screening of Er3+/Yb3+Codoped RE–Ta–O and RE–Nb–O (RE = Y, La, or Gd) Upconversion Phosphors

Upconversion (UC) phosphors comprising Er3+/Yb3+ codoped rare-earth complex oxides, RExTayOz and RExNbyOz (RE = Y, La, or Gd), were synthesized via the gelable citrate complex method, and their UC emission properties were compared. This led to the discovery of an intense green-emitting UC phosphor, YTa7O19:Er3+/Yb3+, which is the first example of a YTa7O19 UC phosphor host material. Green UC emission obtained using optimum Er3+ and Yb3+ content was 20 times stronger than that obtained using a Y2O3 host.

Synthesis and application of rare-earth elements (Gd, Sm, and Nd) doped ceria-based solid solutions for methyl mercaptan catalytic decomposition

A series of rare earth elements with different ionic radii (RE=Gd, Sm and Nd) doped ceria solid solutions and pure ceria catalyst were rapidly prepared by citrate-complexation method. These catalysts were evaluated for catalytic decomposition of methyl mercaptan as a model odorous sulfur containing pollutant. According to the XRD, Raman, XPS, H2-TPR, OSC, FT-IR and CO2-TPD characterization results, the radius of RE cation played an important role in determining the structural and surface characteristics of RE doped ceria catalysts, which could affect the catalytic stability for CH3SH decomposition. Thereinto, Ce0.75Gd0.25O2-δ, with a moderate increase in the alkalinity, possessed more oxygen vacancies. More of structural defects and active sites could be provided, which should be in favor of improving catalytic stability. But for Ce0.75Nd0.25O2-δ, with too many basic sites, more of active sites would be occupied and plenty of cerium sulfide species (Ce2S3) would be accumulated on the catalyst during the reaction processes. The accumulation of Ce2S3 mainly caused the deactivation of catalyst. The catalytic stability of Ce0.75Sm0.25O2-δ was comparable to that of CeO2, which might be resulted from the combined effect of the increased oxygen vacancies and basic sites.

Citrate complexation microwave-assisted synthesis of Ce0.8Zr0.2O2 nanocatalyst over Al2O3 used in CO oxidation for hydrogen purification: influence of composite loading and synthesis method

Nanostructured Ce0.8Zr0.2O2/Al2O3 composite catalyst was synthesized by modified citrate complexation method. Utilizing microwave combustion endowed the sample with more uniform and homogenous pattern leading to better CO oxidation.

Effect of Crystallite Size and Crystallinity on Photoluminescence Properties and Energy Transfer of Y6MoO12:Eu

The phosphors Y6MoO12:Eu3+ have been synthesized via citrate complexation method at different calcination temperatures. The evolutions of the crystal structure and the photoluminescence (PL) properties were characterized by means of powder X‐ray diffraction (XRD), Raman and PL spectra, respectively. It was revealed that a red emission could be obtained via three excitation channels, namely f–f transition of Eu3+ ions, charge‐transfer transition from O2 to Eu3+, and interband transition (IBT) of MoO6 groups. The PL spectra and their temporal decay character of Eu3+ ions depended on both crystal structure and excitation channel. The emission reduced with the crystallite size when Eu3+ ions were excited directly, but the emission evolved in a different model with the host lattices were excited. The effect of grain boundary and other lattice defect on the energy transfer and dissipation within the phosphors were discussed.