Homogeneous Deposition Precipitation Method Research Articles

Improved photoluminescence property by homogeneous deposition-precipitation method for Eu2+ doping in Si–N–O frameworks

The highly dispersed Eu2+ activators with improved photoluminescence property have been successfully achieved by a homogeneous deposition-precipitation (DP) process and the followed heat treatment using SrSi2O2N2 lattice as the typical Si–N–O frameworks. The phase composition, photoluminescence properties and surface states were investigated by XRD, fluorescence spectrophotometer, FESEM and XPS. Compared with the sample prepared by traditional solid state reaction (SSR) method, the luminescence intensity of the SrSi2O2N2: Eu2+ phosphor prepared by DP method exhibits an enhanced luminescence intensity with 1.4 times for green emission peak at 529 nm under excitation of 370 nm. The homogeneous DP process facilitates the uniform distribution of Eu2+ activators in the Si–N–O frameworks and results in a slower decreasing tendency between emission intensity and Eu2+ concentration. The results of FESEM and decay times indicated that the phosphors prepared by DP and SSR method exhibit the characteristic folded platelet-like morphology and similar fluorescence lifetime (918.4 ns and 914.4 ns, respectively). The XPS results revealed that the amount of Sr–O bands in the phosphor prepared by DP method is much higher than that in the sample prepared by SSR method. Interestingly, the SrSi2O2N2: Eu2+ phosphor can be obtained through this DP method even at a low heat treatment temperature (800 °C) under a strongly reducing atmosphere. It is suggested that the deposition-precipitation process will be an efficient synthetic strategy to construct uniform Eu2+ distribution in Si–N–O frameworks and further to enhance the luminescence intensity of the SrSi2O2N2: Eu2+ phosphor.

Heterogeneous catalytic reduction of anthropogenic pollutant, 4-nitrophenol by Au/AC nanocatalysts

Activated carbon-supported gold nanocatalysts (Au/AC) were synthesized by the homogeneous deposition–precipitation (HDP) method by adding drop-wise of NaBH4 into the aqueous solution of HAuCl4. Catalytic activity of these nanocatalysts was investigated for the reduction of the anthropogenic pollutant, 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The physico-chemical properties of the nanocatalysts were characterized by XRD, TEM, BET surface area, pore size distribution, XPS and UV–Vis spectroscopy techniques. Gold nanoparticles (Au NPs) with high percentage of dispersion on a high surface area activated carbon (AC) support, show excellent catalytic performance in terms of activity and selectivity for 4-NP reduction. The reaction rate was measured to be pseudo-first-order with respect to 4-NP. The pseudo-first-order rate constant and the activation energy were estimated to be 1.2–4.2 × 10−3 s−1 at 25 °C and 26.38 kJ mol−1, respectively. Moreover, the catalytic activity was found to increase with increase in Au content of the catalyst. The reusability of the nanocatalyst showed a better reduction of 4-NP to 4-AP even after 5 successive re-cycles. The foregoing study clearly suggests that synthesis of Au/AC nanocatalysts by HDP method is efficient towards the development of a newer and a novel catalyst.

Synthesis and Evaluation of Copper-Supported Titanium Oxide Nanotubes as Electrocatalyst for the Electrochemical Reduction of Carbon Oxide to Organics

Carbon dioxide (CO2) is considered as the prime reason for the global warming effect and one of the useful ways to transform it into an array of valuable products is through electrochemical reduction of CO2 (ERC). This process requires an efficient electrocatalyst with high faradaic efficiency at low overpotential and enhanced reaction rate. Herein, we report an innovative way of reducing CO2 using copper-metal supported on titanium oxide nanotubes (TNT) electrocatalysts. The TNT support material was synthesized using alkaline hydrothermal process with Degussa (P-25) as a starting material. Copper nanoparticles were anchored on the TNT by homogeneous deposition-precipitation method (HDP) with urea as precipitating agent. The prepared catalysts were tested in a home-made H-cell with 0.5 M NaHCO3 aqueous solution in order to examine their activity for ERC and the optimum copper loading. Continuous gas-phase ERC was carried out in a solid polymer electrolyte (SPE) reactor. The 10% Cu/TNT catalysts were employed in the gas diffusion layer (GDL) on the cathode side with Pt-Ru/C on the anode side. Faradaic efficiencies for the three major products namely methanol, methane, and CO were found to be 4%, 3%, and 10%, respectively at −2.5 V with an overall current density of 120 mA/cm2. The addition of TNT significantly increased the catalytic activity of electrocatalyst for ERC. It is mainly attributed to their better stability towards oxidation, increased CO2 adsorption capacity and stabilization of the reaction intermediate, layered titanates, and larger surface area (400 m2/g) as compared with other support materials. Considering the low cost of TNT, it is anticipated that TNT support electrocatalyst for ECR will gain popularity.

Effect of alkali metals on the performance of CoCu/TiO2 catalysts for CO2 hydrogenation to long-chain hydrocarbons

CoCu/TiO2 catalysts promoted using alkali metals (Li, Na, K, Rb, and Cs) were prepared by the homogeneous deposition-precipitation method followed by the incipient wetness impregnation method. The influences of the alkali metals on the physicochemical properties of the CoCu/TiO2 catalysts and the catalytic performance for CO2 hydrogenation to long-chain hydrocarbons (C5+) were investigated in this work. According to the characterization of the catalysts based on X-ray photoelectron spectroscopy, X-ray diffraction, CO2 temperature-programmed desorption (TPD), and H2-TPD, the introduction of alkali metals could increase the CO2 adsorption and decrease the H2 chemisorption, which could suppress the formation of CH4, enhance the production of C5+, and decrease the hydrogenation activity. Among all the promoters, the Na-modified CoCu/TiO2 catalyst provided the maximum C5+ yield of 5.4%, with a CO2 conversion of 18.4% and C5+ selectivity of 42.1%, because it showed the strongest basicity and a slight decrease in the amount of H2 desorption; it also exhibited excellent catalytic stability of more than 200 h.

Nanoparticles based on copper deposited on carbon spheres. Preparation, characterization and application for CO2 photo-electrochemical reduction

In this study, we have examined the performance of copper nanoparticles deposited on carbon spheres with a mass weigh of 10wt% (labeled 10Cu-CSs) via photo-electrochemical reduction of carbon dioxide (CO2). The carbon spheres (CSs) were prepared by a chemical vapor deposition method and 10Cu-CSs was made via a homogeneous deposition precipitation method. The materials were characterized by different physico-chemical techniques such as X-ray diffraction (XRD), Raman, Fourier transform infrared (FTIR) and diffuse reflectance (DR) spectroscopy, electrical conductivity and photo-electrochemical studies. The 10Cu-CSs material was studied for the photo-electrochemical reduction of CO2 under visible light illumination. The synthesized material exhibited a single phase monoclinic structure of CuO deposited on CSs as confirmed by XRD, Raman and FTIR spectroscopies results. The semi-conductor property was established by electrical conductivity, and the activation energy obtained was ca. 0.04eV. The UV–visible absorption spectrum showed a direct band gap transition with gap energy of 1.22eV. The material synthesized was a cathode semi-conductor with p-type conductivity. The deposition of copper nanoparticles enhanced the CO2 photo-conversion to formic acid under the reaction conditions. In particular, 10Cu-CSs demonstrated gave formic acid, which was at a higher potential than standard redox potentials of copper. Furthermore, the photo-electrochemical characterization showed that the deposition of the copper onto CSs used as electrode effectively generated photo-induced electron/hole pairs under visible light irradiation leading an enhancement of photo-reduction under visible light in a NaHCO3 electrolyte.

Possible roles of uterine PGRMC1 in the implantation and decidualization

In this study, we have examined the performance of copper nanoparticles deposited on carbon spheres with a mass weigh of 10 wt% (labeled 10Cu-CSs) via photo-electrochemical reduction of carbon dioxide (CO2). The carbon spheres (CSs) were prepared by a chemical vapor deposition method and 10Cu-CSs was made via a homogeneous deposition precipitation method. The materials were characterized by different physico-chemical techniques such as X-ray diffraction (XRD), Raman, Fourier transform infrared (FTIR) and diffuse reflectance (DR) spectroscopy, electrical conductivity and photo-electrochemical studies. The 10Cu-CSs material was studied for the photo-electrochemical reduction of CO2 under visible light illumination. The synthesized material exhibited a single phase monoclinic structure of CuO deposited on CSs as confirmed by XRD, Raman and FTIR spectroscopies results. The semi-conductor property was established by electrical conductivity, and the activation energy obtained was ca. 0.04 eV. The UV–visible absorption spectrum showed a direct band gap transition with gap energy of 1.22 eV. The material synthesized was a cathode semi-conductor with p-type conductivity. The deposition of copper nanoparticles enhanced the CO2 photo-conversion to formic acid under the reaction conditions. In particular, 10Cu-CSs demonstrated gave formic acid, which was at a higher potential than standard redox potentials of copper. Furthermore, the photo-electrochemical characterization showed that the deposition of the copper onto CSs used as electrode effectively generated photo-induced electron/hole pairs under visible light irradiation leading an enhancement of photo-reduction under visible light in a NaHCO3 electrolyte.

Water gas shift activity of Au–Re catalyst over microstructured cordierite monolith wash-coated by ceria

Water-gas shift (WGS) activity of 1.4 wt.% Au–0.2 wt.% Re/CeO2 catalyst was investigated over microchannel cordierite monolith as a low pressure drop and easy to miniaturize reactor structure for small size applications like fuel processors. The catalyst was prepared by wash-coating the colloidal ceria, which is believed to be one of the best support for WGS, over the wall of cordierite monolith followed by depositing Au and Re using homogeneous deposition–precipitation (HDP) method; then the WGS activity of the catalyst was tested in a microflow reactor. The SEM-EDS and ICP characterization tests were also performed. Initially, the monolithic Au/CeO2 had lower performance than the particulate catalyst but its activity improved significantly by adding Re as promoter and making some modifications in HDP method. Then 10% CO2 and 25% H2 was introduced to the feed (both separately and together) to simulate a realistic feed from a fuel processor, and both equilibrium and actual CO conversions were decreased as expected; however, the performance of monolithic Au–Re/CeO2 was still satisfactory indicating that this structure could have a potential for small scale medium temperature WGS applications.

Vapor Phase Oxidation of Benzyl Alcohol over Nano Au/SBA-15 Catalysts: Effect of Preparation Methods

Au/SBA-15 nano catalysts were synthesized from four different methods, viz., homogeneous deposition–precipitation, micro-emulsion, impregnation and polyol, and their catalytic activities were investigated for the vapor phase oxidation of benzyl alcohol to benzaldehyde. The physico-chemical properties of the catalysts were characterised by XRD, TEM, BET surface area, pore size distribution, CO-chemisorption and XPS techniques. The structural data of the catalysts along with their catalytic studies indicate that the presence of very small metallic Au0 species with particle size of 7–8 nm, was responsible for the higher activity observed in the vapor phase oxidation of benzyl alcohol reaction. The title reaction, though industrially important, was used as a test reaction to investigate firstly, the influence of different preparation methods on the uniform dispersion of gold particles on the support SBA-15 and to understand the metal-support interaction in Au/SBA-15 catalysts, and secondly, to study the catalytic performance of the catalyst (Au/SBA-15) in terms of activity, selectivity and stability over a period of reaction time. The conversion of benzyl alcohol was found to increase with decrease in the size of gold particles. Smaller gold particles with higher percentage of dispersion on the support SBA-15 had a beneficial effect on the catalytic activity. Among the four methods used for the preparation of gold on SBA-15 support, the catalyst prepared by homogeneous deposition–precipitation method showed the best performance in terms of conversion, selectivity for benzaldehyde and longer catalyst life. Vapor phase oxidation of benzyl alcohol over nano Au/SBA-15 catalysts.

Bimetallic synergistic Au/CuO-hydroxyapatite catalyst for aerobic oxidation of alcohols

A catalyst consisting of Au supported on copper oxide-modified hydroxyapatite (Au/CuO-HAP) was prepared using a homogeneous deposition-precipitation method. The catalyst was characterized using atomic absorption spectrometry, N2 adsorption-desorption, powder X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic performance in liquid-phase aerobic oxidation of alcohols was investigated. The catalytic activity and benzaldehyde selectivity in benzyl alcohol oxidation with the bimetallic Au/CuO-HAP catalyst were significantly better than those with monometallic Au/HAP and CuO-HAP catalysts. The conversion of benzyl alcohol and selectivity for benzaldehyde at 120 °C for 1.5 h under aerobic oxidation conditions were 99.7% and 98.4%, respectively. Various aromatic alcohols were selectively converted to their corresponding aldehydes or ketones over Au/CuO-HAP. The Au/CuO-HAP catalyst could be reused at least four times without loss of activity.

Preparation Method for Ruthenium Catalysts Supported by Carbon‐Coated Aluminum Foams

AbstractA preparation method is proposed for coating aluminum and aluminum alloy foams with a porous carbon layer for application as a catalyst support. The polymerization of furfuryl alcohol with diluted oxalic acid was used as precursor for the carbon layer. The polymer layer was distributed by applying centrifugal forces via spinning foam substrates during the polymerization process to prevent clogging and for homogeneous growth of the polymer layer. A homogeneous deposition precipitation method was applied for incorporation of ruthenium on carbon‐coated foam substrates. The carbon coating was characterized by X‐ray tomography to measure the thickness distribution. The specific surface and pore volume distribution were determined by gas adsorption (BET) and mercury porosimetry. The prepared Ru/C foam catalysts were adopted as a stirrer in a rotating foam reactor for hydrogenation of glucose, a simple biomass model substance.

Vapor Phase Oxidation of Benzyl Alcohol Over Gold Nanoparticles Supported on Mesoporous TiO2

The vapor phase oxidation of benzyl alcohol was investigated over gold nanoparticles supported on mesoporous titanium dioxide (anatase) catalysts under aerobic conditions. The catalysts were prepared by homogeneous deposition–precipitation method using urea as the precipitating agent. The physico-chemical properties of the synthesized catalysts were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), pore size distribution (PSD), CO-chemisorption and X-ray photoelectron spectroscopy (XPS) techniques. The crystallite size of gold in Au/TiO2 catalysts was measured from XRD. The mesoporosity of TiO2 support and Au/TiO2 catalysts were confirmed by PSD analysis. TEM results suggest that gold nanoparticles are well dispersed over mesoporous TiO2. The catalytic functionality is well substantiated with particle size measured from TEM. XPS results reveal the formation of Au(0) after chemical reduction by NaBH4. The vapor phase benzyl alcohol oxidation was used as a test reaction to investigate the influence of the metal, nature of the support, and of metal-support interactions in Au/TiO2 catalysts and also the catalytic activity and stability of the Au/TiO2 catalysts. The conversion of benzyl alcohol was found to increase with decrease in the size of gold particles. Smaller gold particles and a higher amount of small gold particles had a beneficial effect on the catalytic activity. The catalytic activity in the presence of oxygen is believed to be associated with the transport of electrons through the catalyst to the adsorbed oxygen on the surface. .

Preparation of halloysite nanotube-supported gold nanocomposite for solvent-free oxidation of benzyl alcohol.

Gold nanoparticles supported on halloysite nanotubes (Au/HNTs) were prepared by a homogeneous deposition-precipitation method. The specific characteristics of the catalyst were characterized in detail, in relation to their performance for solvent-free oxidation of benzyl alcohol. The particular structure of the catalyst resulted in high catalytic activity and stability compared with other supported gold catalysts. The enhanced catalytic activity of the Au/HNTs catalyst was mainly attributed to the presence of a higher amount of oxidized gold species and the tubular structure of the HNTs.

Effect of the Cu/SBA-15 catalyst preparation method on methyl acetate hydrogenation for ethanol production

Methyl acetate (MA) hydrogenation to ethanol was investigated over SBA-15 supported copper (Cu/SBA-15) catalysts prepared by different methods, including impregnation, deposition precipitation, and homogeneous deposition precipitation. The catalysts were characterized by means of the Brunauer–Emmett–Teller method, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction and X-ray photoelectron spectroscopy. Of the three catalysts, it was found that the Cu/SBA-15 catalyst prepared by the homogeneous deposition precipitation method has the smallest particle size, and the appropriate Cu+/(Cu+ + Cu0) molar ratio of 53.5%. The high dispersion of the active components, and the synergetic effect between Cu0 and Cu+ contributed to the high activity of Cu/SBA-15 prepared via the homogeneous deposition precipitation method. A MA conversion of 93.6% with an ethanol selectivity of 98.5% was obtained for MA hydrogenation in methanol solution under mild reaction conditions. Both of these values were much higher than those obtained over catalysts prepared by the other two methods. The catalyst still maintained good performance in the co-hydrogenation of acetic acid and MA in methanol solution. A high MA conversion of 99.5% and an ethanol selectivity of 99.5% were obtained for pure MA hydrogenation over the best catalyst. It was found that methanol solution inhibited the conversion of MA, and suppressed the side reaction of MA trans-esterification with the product ethanol at higher LHSV.

Electrochemical Reduction of Carbon Dioxide over CNT-Supported Nanoscale Copper Electrocatalysts

This paper presents the experimental investigation of copper loaded carbon nanotubes (CNTs) electrocatalysts for the electrochemical reduction of carbon dioxide. The electrocatalysts were synthesized by homogeneous deposition precipitation method (HDP) using urea as precipitating agent. The prepared catalysts were characterized by TEM, SEM, XRD, XPS, BET, and FTIR for their morphology and structure. Characterization results confirm the deposition of Cu nanoparticles (3–60 nm) on CNTs. Linear sweep voltammetry (LSV) and chronoamperometry (CA) were used to investigate the activity of the as-prepared catalysts for the electrochemical reduction of carbon dioxide. The electrocatalysts reduced CO2with high current density in the potential range 0~−3 V versus SCE (standard calomel electrode). Among all catalysts tested, 20 wt. % copper loaded CNTs showed maximum activity. Gas chromatograph with TCD was used to analyze liquid phase composition. The faradaic efficiency for methanol formation was estimated to be 38.5%.

Epoxidation of styrene by t-butyl hydroperoxide over gold nanoparticles supported on Yb2O3: Effect of gold deposition method, gold loading, and calcination temperature of the catalyst on its surface properties and catalytic performance

Surface properties and epoxidation performance of Au/Yb2O3 catalyst are influenced by the method of gold deposition [viz. deposition–precipitation (DP), homogeneous deposition–precipitation (HDP) or impregnation], gold loading (0.9–6.6wt%), and the catalyst calcination temperature (400–900°C)]. The catalyst showed the best epoxidation performance when it was prepared by the HDP method and calcined at 500°C. The Au/Yb2O3 catalyst even after calcination at 900°C showed good activity and epoxide selectivity. Both Au0 and Au3+ surface species were found in the catalyst calcined at 800°C, but only Au0 species were observed at the lower calcination temperatures (<600°C). The selectivity for styrene oxide increased continuously with the reaction temperature (from 75°C to 97°C) and time (1–5h), indicating that styrene oxide did not undergo secondary reactions under these conditions.

Studies on the removal of 2-propanol by Ag@Fe2O3 core–shell structured catalyst

A series of Ag@Fe2O3 core–shell structured catalysts were prepared in this study. The Fe-compound shell was first grown using a homogeneous deposition precipitation method in which urea was added to assist ferrihydrite formation on the surface of the silver core and to inhibit individual particle formation in the solution. Following 5h calcination at 400°C, the ferrihydrite shell was transformed into the rice-shaped and porous Fe2O3 shell. These catalysts were then characterized and tested for the catalytic removal of 2-propanol at different temperatures. The core–shell particles exhibited higher oxidation activities than that of either of pure Ag and Fe2O3. Our results also indicated the existence of an optimal amount of Fe2O3 shell, suggesting the importance of mass transfer in this oxidation reaction.

Influence of active metal loading and oxygen mobility on coke-free dry reforming of Ni–Co bimetallic catalysts

Two different techniques (precipitation with ammonia and hydrothermal synthesis with ethylene glycol, both followed by autoclave aging) were employed for the synthesis of CeO2–ZrO2 mixed oxides on a 80–20wt.% basis. Aging parameters, such as time and temperature, were systematically investigated in order to determine the optimal conditions to maintain high surface area and oxygen mobility of the prepared solids. Different loadings of nickel and cobalt (3, 6, 12 and 18wt.%) were subsequently deposited via homogeneous deposition precipitation method. Calcined bimetallic catalysts were characterized by N2 adsorption–desorption, XRD, H2-TPR, TPO-TGA and FE-SEM methods, and tested for activity, selectivity and stability in the reforming of equimolar CH4–CO2 gas streams. During temperature programmed methane reforming tests, syngas with a H2/CO ratio between 0.3 and 0.79 was produced. Growth of carbon nanofilaments over the catalyst does not lead to deactivation, but can cause reactor plugging. Two conditions are vital and must be fulfilled simultaneously to avoid excessive carbon deposition: strong interaction between the NiCo bimetallic particles and CeZr support, which exists only at NiCo loadings up to 6wt.%, as well as high oxygen mobility within the highly defective CeO2–ZrO2 crystalline lattice for timely carbon oxidation.

Highly Sensitive Methane Sensors Based on Pd/HMS and Pd/SBA-15 Composite Prepared by Homogeneous Deposition-Precipitation Method

Highly Sensitive Methane Sensors Based on Pd/HMS and Pd/SBA-15 Composite Prepared by Homogeneous Deposition-Precipitation Method

Carbon nanofiber growth on carbon paper for proton exchange membrane fuel cells

Homogeneous deposition precipitation (HDP) of nickel has been investigated for the growth of carbon nanofibers (CNFs) on carbon paper for use in proton exchange membrane fuel cells as a gas diffusion layer. Selective CNF growth on only one side of carbon paper is required to transfer the generated protons on platinum catalyst fast enough to avoid any proton mass transfer losses. For this purpose, a mask deposition holder was designed to deposit the nickel hydroxide which is reduced to nickel with hydrogen before catalyzing the CNF growth. The deposition time effect on the catalyst loading and the effect of the catalyst loading variation on the yield of CNF growth on carbon paper were investigated. Both effects had linear dependence in the region of interest. The HDP of nickel on the carbon paper ensured strong attachment of nickel crystals on the carbon paper fibers keeping the porosity at a promising level with an acceptable BET area of CNFs. The HDP method provides fine-tuning in the CNF layer thickness only on one side of the carbon paper with good reproducibility in the deposition of nickel.

Copper–manganese oxide catalysts supported on alumina: Physicochemical features and catalytic performances in the aerobic oxidation of benzyl alcohol

We report the facile synthesis of alumina supported copper–manganese mixed oxide catalysts by a homogeneous deposition–precipitation method and the catalytic applications of these catalysts in the oxidation of benzyl alcohol using molecular oxygen. Benzyl alcohol conversion of ca. 90.9% was achieved with benzaldehyde as the main product. The catalyst can be recycled consecutively up to seven runs without appreciable loss of its activity and selectivity. Characterizations with X-ray diffraction, transmission electron microscopy, Raman, X-ray absorption spectroscopy, and hydrogen temperature-programmed reduction suggested the formation of a mixed oxide (Mn 1.5Cu 1.5O 4) microcrystalline phase after adding copper to the manganese supported on alumina. Such formation would account for the high catalytic performance. Calcination under high temperature decomposed this mixed oxide phase, resulting in a poor catalytic activity.