Deposition Precipitation Method Research Articles

Synthesis of Gold Nanoparticles over CoAl Mixed Oxide for Ethanol Oxidation Reaction.

Catalytic total oxidation is an effective technique for the treatment of industrial VOCs principally resulting from industrial processes using solvents and usually containing mono-aromatics (BTEX) and oxygenated compounds (acetone, ethanol, butanone). The aim of this work is to deposit gold nanoparticles on CoAl mixed oxide issued from layered double hydroxide (LDH) precursor by using the deposition precipitation (DP) method, which is applied with two modifications, labeled method (A) and method (B), in order to enhance the interaction of the HAuCl4 precursor with the support. Method (A) involves the hydrolysis of the HAuCl4 precursor after addition of the support, while in method (B), the gold precursor is hydrolyzed before adding the support. The two methods were applied using as support the CoAl mixed oxide and the LDH precursor. Samples were characterized by several physical chemical techniques and evaluated for ethanol total oxidation. Method (B) allowed the ethanol oxidation activity to be enhanced for the resulting Au/CoAlOx catalysts thanks to the high surface concentration of Co2+ and improved reducibility at low temperature. The presence of gold permits to minimize the formation of by-products, notably, methanol, allowed for a total oxidation of ethanol at lower temperature than the corresponding support.

Au Nanoparticles Supported on Hydrotalcite-Based MMgAlOx (M=Cu, Ni, and Co) Composite: Influence of Dopants on the Catalytic Activity for Semi-Hydrogenation of C2H2

Semi-hydrogenation of acetylene to ethylene over metal oxide-supported Au nanoparticles is an interesting topic. Here, a hydrotalcite-based MMgAlOx (M=Cu, Ni, and Co) composite oxide was exploited by introducing different Cu, Ni, and Co dopants with unique properties, and then used as support to obtain Au/MMgAlOx catalysts via a modified deposition–precipitation method. XRD, BET, ICP-OES, TEM, Raman, XPS, and TPD were employed to investigate their physic-chemical properties and catalytic performances for the semi-hydrogenation of acetylene to ethylene. Generally, the catalytic activity of the Cu-modified Au/CuMgAlOx catalyst was higher than that of the other modified catalysts. The TOR for Au/CuMgAlOx was 0.0598 h−1, which was 30 times higher than that of Au/MgAl2O4. The SEM and XRD results showed no significant difference in structure or morphology after introducing the dopants. These dopants had an unfavorable effect on the Au particle size, as confirmed by the TEM studies. Accordingly, the effects on catalytic performance of the M dopant of the obtained Au/MMgAlOx catalyst were improved. Results of Raman, NH3-TPD, and CO2-TPD confirmed that the Au/CuMgAlOx catalyst had more basic sites, which is beneficial for less coking on the catalyst surface after the reaction. XPS analysis showed that gold nanoparticles exhibited a partially oxidized state at the edges and surfaces of CuMgAlOx. Besides an increased proportion of basic sites on Au/CuMgAlOx catalysts, the charge transfer from nanogold to the Cu-doped matrix support probably played a positive role in the selective hydrogenation of acetylene. The stability and deactivation of Au/CuMgAlOx catalysts were also discussed and a possible reaction mechanism was proposed.

Bimetallic Ni-Co catalyst for improving selectivity in transfer hydrogenation of phenolic compounds

The study investigated the transfer hydrogenation of guaiacol, anisole, phenol, and positional isomers of dimethoxybenezene using 2-PrOH as the H-donor over Ni, Co, and Ni-Co catalysts. The catalysts, which contained 5 wt% metal, were prepared by the deposition-precipitation method. The results showed that the catalysts had developed a pore structure and fine metal particles. The Ni and Ni-Co catalysts demonstrated exceptional activity in the transfer hydrogenation of phenolic compounds with a substrate to metal molar ratio of 100 to 1. Furthermore, the addition of Co to Ni significantly impacted the selectivity of transfer hydrogenation promoting hydrodeoxygenation of anisole and guaiacol.

Preparation of Hydrophobic Au Catalyst and Application in One-Step Oxidative Esterification of Methacrolein to Methyl Methacrylate.

The water produced during the oxidative esterification reaction occupies the active sites and reduces the activity of the catalyst. In order to reduce the influence of water on the reaction system, a hydrophobic catalyst was prepared for the one-step oxidative esterification of methylacrolein (MAL) and methanol. The catalyst was synthesized by loading the active component Au onto ZnO using the deposition-precipitation method, followed by constructing the silicon shell on Au/ZnO using tetraethoxysilane (TEOS) to introduce hydrophobic groups. Trimethylchlorosilane (TMCS) was used as a hydrophobic modification reagent to prepare hydrophobic catalysts, which exhibited a water droplet contact angle of 111.2°. At a temperature of 80 °C, the hydrophobic catalyst achieved a high MMA selectivity of over 95%. The samples were characterized using XRD, N2 adsorption, ICP, SEM, TEM, UV-vis, FT-IR, XPS, and water droplet contact angle measurements. Kinetic analysis revealed an activation energy of 22.44 kJ/mol for the hydrophobic catalyst.

Fine-tuning the electronic properties of Au toward two-dimensional clusters with higher activity for ethanol conversion

Efficient Au/m-ZrO2 catalysts for the conversion of ethanol to acetaldehyde and ethyl acetate were obtained by the deposition precipitation method. The present work investigates the impact of the electronic properties of Au supports on m-ZrO2 catalysts on ethanol dehydrogenation. The Au4f7/2 binding energy (BE) and the average Au-Au nearest-neighbor distances (RAu-Au) were associated with surface defects characterized by CO adsorption. The BE and RAu-Au properties are correlated among themselves, changing by Au loading and pretreatments in an inert atmosphere at different temperatures. Although the RAu-Au unveils a boost of the reaction rates for shorter distances, the coupling of Au and m-ZrO2 produced a bifunctional catalyst. Theoretical studies indicate that molecular ethanol adsorption and formation of the ethoxy intermediate represented a feasible pathway for the activation of ethanol on the Au-ZrO2 interface. The RAu-Au toward of 2D clusters conferred high catalytic activity and low apparent activation energy for ethanol dehydrogenation.

Selective hydrogenation of acetylene over Pd/In2O3@SiO2: The effect of the catalyst reduction temperature

Tuning the hydrogenation activity of Pd is an effective method to achieve selective hydrogenation of acetylene. The previous study shows that Pd has a strong interaction with In2O3, causing a significant change in the electronic structure of the palladium catalyst. Herein, Pd/In2O3@SiO2 was prepared by a deposition-precipitation method for selective hydrogenation of acetylene. After the reduction by flowing hydrogen, Pd-In intermetallic compounds can be formed. The concentration of the formed intermetallic compounds is closely associated with the reduction temperature. The Pd-In intermetallic compounds suppress the hydrogen activation ability of Pd and significantly weaken the adsorption of ethylene. Especially, a weak adsorption of di-σ-bonded ethylene is observed, which facilitates the desorption of ethylene and promotes the ethylene selectivity in the semi-hydrogenation of acetylene. The experimental study confirms that there exists an optimum reduction temperature (250 °C) for the formation of the Pd-In intermetallic compounds, with which ∼ 80 % ethylene selectivity and 100 % acetylene conversion have been achieved at 140 °C.

Synthesis of novel Ag/AgBr/K0.4Y0.7Sb2O6.25 nanocomposite with enhanced photocatalytic properties

Devoloping efficient wastewater treatment photocatalysts capable of improving water quality is undoubtedly one of the main problems of present society. In recent years, novel plasmonic photocatalysts have shown new possible applications in photocatalytic wastewater treatment due to their unique properties. In this work, a novel Ag/AgBr/K0.4Y0.7Sb2O6.25 composite was successfully fabricated by photo-reduction using the pre-prepared AgBr/K0.4Y0.7Sb2O6.25 and K0.4Y0.7Sb2O6.25 (KYSbO). The AgBr/KYSbO and KYSbO were synthesized by deposition-precipitation and precipitation-heating methods. The visible-light photocatalytic performance of parent KYSbO and Ag/AgBr/KYSbO composite was evaluated using methylene blue (MB) as a model organic pollutant. The effects of catalyst dosage, pH and the initial concentration of the MB dye solution on the photocatalytic activity were also investigated in this study. Remarkably, the Ag/AgBr/KYSbO composite exhibited superior visible-light photocatalytic activity for the degradation of MB than that of parent KYSbO. MB was degraded to 91.6% in the presence of parent KYSbO after visible irradiation of 180 min, while 93.2% degraded in merely 30 min in the case of Ag/AgBr/KYSbO composite. The superior improvement in the photocatalytic activity of the Ag/AgBr/KYSbO composite can be credited to the efficient separation of photoinduced electron-hole pairs and the extended visible-light response range. Superoxide radicals are crucial for MB photocatalytic degradation in the Ag/AgBr/KYSbO composite. The possible photocatalytic mechanism was proposed.

C–C bond coupling differences between β-O-4 and 4-O-5 ether bonds over hydrophobic mesoporous Ru/MY-O catalysts: from lignin model compounds to polycyclic alkanes

MY zeolites with mesopores were prepared by hydrothermal method using functionalized SiO2 (F-SiO2) as a silica source, and hydrophobic bifunctional Ru/MY-O catalysts were obtained by deposition precipitation method and silylation treatment. This work aims at obtaining polycyclic alkane (PCA) based high-density hydrocarbon fuels (HDHFs). We focused on the catalytic hydroconversion (CHC) of 2-phenoxy-1-phenylethanol (PP-ol) and oxydibenzene (ODB), two typical lignin-related model compounds (LRMCs), over Ru/MY-O. The effects of different reaction conditions and catalysts on the product distribution in PP-ol and ODB were investigated. The partial hydrogenation of ODB was found to be a necessary step before achieving C-O ether bond cleavage and C-C bond coupling. The balance of metal/acidic sites is critical for maximizing PCA yields. Changes in the metal/acid ratio had a greater effect on PCA yield in PP-ol than in ODB. Poor stability of cycloalkyl cations and partial hydrogenation of ODB hinder the generation of C-C coupling products. The incorporation of mesopores and hydrophobic treatment were found to weaken the negative effects of C-C bond coupling products and water on the catalyst. The conversion of Ru3/MY-O was improved by nearly 10% compared to Ru3/Y in the fifth cycle reaction. This work provided a theoretical basis for the generation of HDHFs from lignin.

Hydrogen Production from Hydrous Hydrazine Decomposition Using Ir Catalysts: Effect of the Preparation Method and the Support

Herein, Ir/CeO2 catalysts were prepared using the deposition–precipitation method with NaOH or urea as the precipitating agent or using sol immobilization with tetrakis(hydroxymethyl)phosphonium chloride (THPC) as the protective and reducing agent. The effect of the preparation method on Ir catalyst activity was evaluated in the liquid-phase catalytic decomposition of hydrous hydrazine to hydrogen. Ir/CeO2 prepared using sol immobilization and DP NaOH showed the best activity (1740 h−1 and 1541 h−1, respectively) and yield of hydrogen (36.6 and 38.9%). Additionally, the effect of the support was considered, using TiO2 and NiO in addition to CeO2. For this purpose, the sol immobilization of preformed nanoparticles technique was considered because it allows the same morphology of the immobilized particles to be maintained, regardless of the support. Ir deposited on NiO resulted in the most selective catalyst with a H2 yield of 83.9%, showing good stability during recycling tests. The catalysts were characterized using different techniques: X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with an X-ray detector (EDX) and inductively coupled plasma–mass spectroscopy (ICP-MS).

CO2 hydrogenation to methanol over the copper promoted In2O3 catalyst

The metal promoted In2O3 catalysts for CO2 hydrogenation to methanol have attracted wide attention because of their high activity with high methanol selectivity. However, there was still no experimental confirmation if copper could be a good promoter for In2O3. Herein, the Cu promoted In2O3 catalyst was prepared using a deposition-precipitation method. Such prepared Cu/In2O3 catalyst shows significantly higher CO2 conversion and space time yield (STY) of methanol, compared to the un-promoted In2O3 catalyst. The loading of Cu facilitates the activation of both H2 and CO2 with the interface between the Cu cluster and defective In2O3 as the active site. The Cu/In2O3 catalyst takes the CO hydrogenation pathway for methanol synthesis from CO2 hydrogenation. It exhibits a unique size effect on the CO adsorption. At temperatures below 250 °C, CO adsorption on Cu/In2O3 is stronger than that on In2O3, causing higher methanol selectivity. With increasing temperatures, the Cu catalyst aggregates, which leads to the formation of weak CO adsorption site and causes a decrease in the methanol selectivity. Compared with other metal promoted In2O3 catalysts, it can be concluded that the catalyst with stronger CO adsorption possesses higher methanol selectivity.

Engineering the CuO/MnO2 interface with multivalent conversion for low-temperature and efficient CO oxidation

A novel interface of MnO2 with CuO with multivalent conversion is fabricated by the deposition-precipitation method for low-temperature and efficient CO oxidation. It is found that the temperature for CO thermal-catalytic oxidation to reach a complete conversion significantly decreases to 105 °C for the CuO/MnO2. A combination of experimental and theoretical studies demonstrates the successful formation of the CuO/MnO2 interface, inducing a pronounced effect that promotes CO oxidation. The CuO/MnO2 interface leads to the formation of Cu-O-Mn, a superior redox system with multivalent conversion (Cu+ + Mn4+ ↔ Cu2+ + Mn3+, Cu+ + Mn3+ ↔ Cu2+ + Mn2+), abundant active sites, excellent ability to activate O2, the rapid oxygen transfer, and more suitable adsorption energy for O2, CO, and CO2. These characteristics are advantageous to CuxO-MnxOy for achieving a 100 % removal of CO at a lower temperature. Furthermore, the computational study reveals that the CO oxidation process follows two mechanistic pathways (Eley-Rideal (E-R) and Mars-van Krevelen (M-K)), indicating that there is no competitive adsorption of CO and O2 on the CuO/MnO2. This study shows that the interface created between suitable metal oxides can improve the catalytic performance and provides new perspective for catalyst design and performance enhancement mechanisms.

Comprehensive investigation of the mutual effect of Ce and W species in the NH3-SCR catalyst

CeO2–WO3 catalysts were synthesized using the coprecipitation method (CW-C), mixing method (CW-M) and deposition–precipitation method (CW-DP).

Uncalcined TS-1 supported Au catalyst via NaBH4 reduction method for propylene epoxidation: Insights into the H2 pretreatment effect on catalytic performance

Stable and efficient Au-supported titanium silicalite-1 (TS-1) catalysts are essential for the direct epoxidation of propylene (DEP) using O2 and H2. But the deposition-precipitation method for Au/TS-1 contains low Au capture efficiency and rapid deactivation rate. Herein, Au/TS-1-B (uncalcined TS-1) catalysts were synthesized through a NaBH4 reduction method. The impact of H2-thermal-pretreatment on DEP activities was studied. H2-pretreatment can enhance propylene oxide selectivity, shorten activation time and reduce deactivation rate of catalyst. Organic-templates on the surface of TS-1-B and stabilizers coated on Au-nanoparticles can be partially removed under H2-treatment, thus exposing more active sites for Au and Ti and facilitating their interactions. Furthermore, more porous structures with reduced acid sites and enhanced surface hydrophobicity of pretreated catalyst can promote DEP reaction. Solid stability in TS-1-B, high Au utilization resulting from the reduction method, and favorable modifications through H2-thermal treatment contribute to the exploration of more robust DEP catalyst performance.

One-step Mo-doped praseodymium oxide construction of oxygen vacancies for efficient photothermal co-catalytic Suzuki coupling reaction

The photothermal synergistic catalytic Suzuki coupling reaction is a sustainable approach to generate biphenyl compounds using clean and renewable solar energy. The one-step Mo doping engineering resulted in more oxygen vacancies and surface free electrons on the PrxOy surface of hollow porous nanotube morphology. Subsequently, energy-efficient and environmentally friendly catalysts (PdO/PrxOy−Moz) with higher catalytic activity were successfully prepared by deposition precipitation method. The concave and convex surfaces of the carriers could better capture visible light. Mo doping greatly extends the visible absorption range of PrxOy. More OVs defects in the PrxOy−Moz carrier inhibit the complexation of photogenerated electron-hole pairs and induce the transfer of free and photogenerated electrons to Pd. The electron-rich Pd accelerated the oxidative addition step of aryl halides to aryl phenylboronic acids, which greatly improved the catalytic performance of PdO/PrxOy−Moz in the photothermal co-catalytic Suzuki coupling reaction.

Bi-doped CuCeO2−x nanorod catalysts for photothermal CO-PROX in H2-rich streams: Enhanced oxygen vacancy and light absorption capacity

The wide band gap of ceria limited the light absorption and photothermal conversion of copper-ceria catalyst for photothermal preferential oxidation of CO (CO-PROX). In the present work, doping Bi element was adopted to regulate the energy band and catalytic performance of CuCeO2−x nanorod catalysts for photothermal CO-PROX. Bi/CuCeO2−x nanorods were synthesized by co-precipitation hydrothermal and deposition precipitation method. The Bi/CuCeO2−x catalyst with the molar ratio of Bi/Ce 2.5% exhibited the best catalytic performance and the CO conversion reached 90% under 2.5 suns with a surface temperature of 120 °C. The doped Bi species were incorporated into the CeO2 lattice and promoted the formation of oxygen vacancy sites and the strong Cu-Ce interaction, as revealed by XRD, XPS, Raman and H2-TPR results. In addition, doping Bi reduced the band gap of ceria nanorod from 2.77 to 2.47 eV and remarkably enhanced the UV–vis light response and photogenerated carrier separation of Bi/CuCeO2−x-2.5.

Facile construction of 2D Ni2P/Bi12O17Cl2 composite to reinforce photocatalytic degradation performance of antibiotics in water

Utilizing highly efficient and stable photocatalysts to remove residual organic pollutants in wastewater has been deemed to be a promising and green technique for environmental management. Herein, novel 2D Ni2P/Bi12O17Cl2 composites have been prepared by a facile deposition-precipitation method, and the structure, morphology, optical, photo-electrochemical and photoluminescence properties were characterized particularly. Oxytetracycline (OTC), phenol and methyl orange (MO) were selected as target pollutants to evaluate the photocatalytic performance of the Ni2P/Bi12O17Cl2. Under visible light illumination (λ > 420 nm), the Ni2P/Bi12O17Cl2 photocatalyst possesses outstanding photocatalytic properties for the degradation of OTC, phenol and MO than those of Bi12O17Cl2. The enhanced photocatalytic activity of the Ni2P/Bi12O17Cl2 is attributed to Ni2P acting as photogenerated electrons trappers to reinforce photoinduced charges separation. Furthermore, the Ni2P/Bi12O17Cl2 photocatalyst owns outstanding stability. This study might shed light on the enhanced photocatalytic capacities of bismuth oxyhalide by means of embellishing transition metal phosphides in environment remediation fields.

Plasma-assisted deposition of Mn and Fe phases on CeO2 biomorphic fibers for soot combustion and CO oxidation

In the present work, the gliding arc (glidarc) plasma technique is for the first time explored as a novel precipitation-deposition method to generate fibrous catalysts. Precisely, Mn and Fe oxides were plasma-precipitated on a fibrous ceria support and evaluated in two reactions of environmental interest, (1) soot combustion and (2) CO oxidation. Pure CeO2 fibers (Fib Ce) were obtained via a biotemplate route with the idea of starting from a support already active in oxidation reactions, and then further improving its activity by supporting on its surface Fe and Mn oxides. The precipitates were identified by XRD, FTIR and LRS, and their loadings and distributions assessed by ICP and EDX respectively. α-Fe2O3 and Mn3O4 phases were detected. XPS confirmed the presence of Mn and Fe on the surface of Fib Ce and revealed that the deposition of Fe logically gave a superficial Fe/Ce ratio much higher than the bulk one and provoked an increase in Ce3+/Ce4+ and Oads/Ce ratios. On the contrary, Mn-supported samples did not affect considerably the Ce3+/Ce4+ and Oads/Ce ratios and presented a Mn/Ce ratio closer to that of the bulk. The latter suggests that Mn has integrated the ceria structure. For reaction (1), the deposition of Fe by plasma drastically degraded the performance of the bare support, whereas Mn deposition greatly increased the activity of Fib Ce. The same activity order was observed for reaction (2): Mn-Fib Ce > Fib Ce > Fe-Fib Ce.

Magnet-responsive choline carbomer ionogels as a versatile and recyclable catalyst for one-pot synthesis of benzopyran in water

Ionogels are gaining popularity as a potential replacement for volatile organic solvents in various processes, such as catalysts, electrochemistry, spectroscopy, and medicinal chemistry, due to their low toxicity, high thermal stability, and good solubility. Magnet-responsive ion gels with high magnetic susceptibility are promising and can be used as catalysts, sensors, and MRI contrast agents. Herein, we fabricated simple and novel magnet choline carbomer ionogels using a precipitation-deposition method with carbomers and choline hydroxide. The morphology and structure of the resulting ionogels were analyzed using various characterization techniques, including FTIR, EDX, TGA, and SEM spectroscopy. These magnet ionogels were effective catalysts for a one-pot, three-component synthesis of benzopyran derivatives, providing mild reaction conditions, environmental friendliness, and good to excellent (78–96%) yields within a short reaction time (1–2 h). Additionally, the magnet ionogels were easily recyclable, and they could be reused up to five times without catalytic deactivation.

ИЗУЧЕНИЕ ПРОЦЕССА ГИДРИРОВАНИЯ КАРБОНИЛЬНЫХ СОЕДИНЕНИЙ В ПРИСУТСТВИИ НАНОСТРУКТУРИРОВАННЫХ НИКЕЛЕВЫХ КАТАЛИЗАТОРОВ

The influence of the catalyst preparation method on the process of hydrogenation of carbonyl compounds in the presence of nickel catalysts obtained by the deposition-precipitation method using urea as a precipitant was studied. It has been shown that an increase in the content of nickel and modifiers helps to increase the substrate conversion using the example of the methyl isobutyl ketone (MIBK) hydrogenation reaction.

Effect of HCl Treatment on Acidity of Pd/TiO2 for Furfural Hydrogenation

The acidity of supports can have a positive effect on their catalytic behaviors. Herein, the effects of HCl treatment of TiO2 on its acidic properties and catalytic activity were investigated. TiO2 was treated with various molar concentrations of HCl. Subsequently, Pd was deposited on the treated TiO2 via the deposition–precipitation method; here, the catalysts were denoted as Pd/xH-T, where X is the molar concentration of HCl. Evidently, the amount of strong acid in TiO2 increased with HCl treatment, whereas that in TiO2 treated with a high concentration (5 M) of HCl decreased. After Pd was supported, the amount of acid slightly decreased compared with that on the TiO2 support; however, the order of the acid amounts was similar. The strong acid density increased such that Pd/2H-T had the highest acid content, whereas Pd/5H-T had the lowest. The Pd/2H-T catalyst exhibited the highest selectivity for THFA (95.4%), thus confirming that the selectivity for THFA is correlated with the amount of strong acid. Thus, THFA selectivity is affected by the number of strongly acid sites.