Studies on cobalt catalyst supported on silica with different pore size for Fischer–Tropsch synthesis

The adsorption and surface reactions of acetonitrile and acetonitrile-oxygen gas mixture were studied on TiO₂-supported Au catalysts at 300–673 K. FTIR spectra show different kinds of molecularly adsorbed CH₃CN:acetonitrile can be bonded to weak Lewis acid sites (2295 cm⁻¹), to strong Lewis acid sites (2337 cm⁻¹) of titania; it can be coordinated linearly through the lone electron pair of the N atom on Au sites and η² (C,N) CH₃CN species can be formed on Au particles. CH₃CN dissociates on Au sites, the resulting CN_(a) can be oxidized in small extent by lattice oxygen and in a greater extent by gaseous oxygen into NCO surface species. The formation of other products (CH₃NH₂, H₂, CO₂, CH₄, C₂H₄ and CO) was demonstrated and discussed.     

A novel SiO2 supported Pd metal catalyst for the Heck reaction

A ligand-free heterogeneous metal catalyst system (represented as Pd/SiO₂ (O)) derived by calcination of Pd(acac)₂/SiO₂ in air and its catalytic properties toward the Heck coupling of bromobenzene (PhBr) and styrene have been studied. X-ray photoelectron spectroscopy (XPS) and catalytic results demonstrate that most of Pd²⁺ is reduced to Pd⁰ on SiO₂ by N,N-dimethylacetamide (DMA) during the Heck reaction and that the resulting Pd⁰/SiO₂ is highly active for the Heck reaction, the remaining Pd²⁺/SiO₂ is not responsible for the high activity. Pd/SiO₂ (O) possesses incomparable advantages over a heterogeneous homolog (represented as Pd/SiO₂ (H)) prepared by reduction of Pd(acac)₂/SiO₂ in H₂ as a pre-catalyst in both activity and catalyst recycling. The activity over Pd/SiO₂ (O) is comparable to that over a homogeneous Pd system. Transmission electron microscopy (TEM) analysis illustrates that the high activity over Pd/SiO₂ (O) consists in the small size of supported Pd particles generated in-situ with gentle reducing agents at a mild temperature.     

Preparation of poly (acrylic acid) containing core‐shell type resin for removal of basic dyes

BACKGROUND: A core‐shell type carboxylic acid modified resin was prepared and dye sorption characteristics of the resin were investigated. The resulting grafted resin material has been shown to be an efficient sorbent for removal of basic dyes from water as a result of the carboxylic acid group's affinity towards basic dye molecules. RESULTS: The resin was characterized using Fourier transform infrared spectroscopy (FT‐IR) and titrimetric methods. The basic dyes (methylene blue and crystal violet) were removed by contacting the swollen resin with aqueous dye solutions at room temperature. The adsorption capacities of resin were determined by colorimetric analysis of the residual dye content in the adsorption medium, which gave capacities for methylene blue and crystal violet of 300 and 250 mg g^?1 resin, respectively. The prepared resin is also able to remove basic dyes completely from dilute aqueous dye solutions. Batch kinetic sorption experiments determined that a pseudo‐second‐order rate kinetic model was applicable. CONCLUSION: Flexibility of the polymer side chains is expected to provide pseudo‐homogeneous reaction conditions and easy accessibility of the functional groups involved. The adsorbents are expected to have the advantage of mobility of the grafted chains in the removal of basic dyes from aqueous mixtures. The resin has potential as an adsorbent for removal of basic dyes for use over a wide pH range. Copyright © 2011 Society of Chemical Industry     

Comparison of ion-exchange resins for efficient cobalt(II) removal from acidic streams

The ion-exchange method was applied for cobalt(II) removal from acidic streams using Lewatit MonoPlus TP 220, Purolite A 830, Lewatit SR 7, Purolite S 984, Purolite A 400 TL, Lewatit AF 5, Dowex PSR 2, and Dowex PSR 3. The effects of phase contact time, acid concentration, initial Co(II) concentration, and temperature were evaluated. The cobalt(II) desorption, ion exchanger reuse, and attenuated total reflection with the Fourier transform infrared spectroscopy, column studies were also performed. Lewatit MonoPlus TP 220 exhibits the highest sorption capacities and sorption follows the pseudo-second-order kinetics. The Freundlich model fitted the experimental data adequately. Desorption of cobalt(II) loaded is not quantitative. Sorption capacity reduction after three cycles of sorption–desorption (static method) was not observed.     

Nano-Mg(OH)2 platelets coated flexible polyurethane foam for fast and environment-friendly removal of Cu2+ from aqueous solution

In this study, flexible polyurethane foam (FPUF) was successfully coated with nano-Mg(OH)₂ platelets. Due to the strong interaction between chitosan and nano-Mg(OH)₂, it was possible to yield modified foam with a weight-gain of up to 15 wt% by depositing one chitosan layer and one nano-Mg(OH)₂ layer. Meanwhile, the adsorption isotherms of Cu²⁺ on FPUF covered with 10 wt% coating (FPUF-10) shows the Langmuir behavior. It was found that for the FPUF-10, the removal % for Cu²⁺ after 30 min and 50 min treatment were 86% and 90%, respectively. Moreover, the maximum removal % could reach up to 95%.     

Preparation of Silica-PAN Functionalized Nanoextractants for the Extraction of Ferbam from Various Samples

1-(2-pyridylazo)-2-naphthol modified SiO₂ nanoparticles were synthesized and evaluated as a nanoadsorbent for removing Ferbam from various environmental sources and fortified grain and vegetables samples. The 1-(2-pyridylazo)-2-naphthol modified SiO₂ nanoparticles were prepared by the sol-gel method. Nanoparticles were characterized by SEM and FT-IR. The adsorption of Ferbam was examined by the batch equilibrium technique. Conditions of the analysis such as preconcentration factor, effect of pH, sample volume, shaking time, elution conditions, and effects of interfering ions for the recovery of analyte were investigated. The equilibrium data analyzed by using the Langmuir isotherm, and the Freundlich and Temkin isotherm models, showed better agreement with the former model. The adsorption capacity of nanometer SiO₂-1-(2-pyridylazo)-2-naphthol was found to be 50.70 μmol/g at optimum pH and the detection limit (3σ) was 0.40 μg/L. The extractant showed rapid kinetic sorption. The adsorption equilibrium of Ferbam on nanometer SiO₂-1-(2-pyridylazo)-2-naphthol was achieved in 10 mins. Adsorbed Ferbam was easily eluted with 6 mL of 6 M hydrochloric acid. The maximum preconcentration factor was 58.33. The method was applied for the determination of trace amounts of Ferbam in various water samples and fortified samples.     

Effect of the metal oxide loading on the activity of silica supported MoO3 and V2O5 catalysts in the selective partial oxidation of methane

Precipitated silica catalysts loaded with either MoO₃ (0.2–4.0 wt%) or V₂O₅ (0.2–5.3 wt%) have been studied in the selective partial oxidation of methane to formaldehyde with molecular oxygen at 520 °C. The functionality of the SiO₂ surface towards the formation of HCHO is significantly promoted by V₂O₅, while it is depressed by the MoO₃.     

Effects of poly (vinyl alcohol) (PVA) content on preparation of novel thiol-functionalized mesoporous PVA/SiO2 composite nanofiber membranes and their application for adsorption of heavy metal ions from aqueous solution

Thiol-functionalized mesoporous poly (vinyl alcohol)/SiO₂ composite nanofiber membranes and pure PVA nanofiber membranes were synthesized by electrospinning. The results of Fourier transform infrared (FTIR) indicated that the PVA/SiO₂ composite nanofibers were functionalized by mercapto groups via the hydrolysis polycondensation. The surface areas of the PVA/SiO₂ composite nanofiber membranes were >290 m²/g. The surface areas, pore diameters and pore volumes of PVA/SiO₂ composite nanofibers decreased as the PVA content increased. The adsorption capacities of the thiol-functionalized mesoporous PVA/SiO₂ composite nanofiber membranes were greater than the pure PVA nanofiber membranes. The largest adsorption capacity was 489.12 mg/g at 303 K. The mesoporous PVA/SiO₂ composite nanofiber membranes exhibited higher Cu²⁺ ion adsorption capacity than other reported nanofiber membranes. Furthermore, the adsorption capacity of the PVA/SiO₂ composite nanofiber membranes was maintained through six recycling processes. Consequently, these membranes can be promising materials for removing, and recovering, heavy metal ions in water.     

壳聚糖基大孔炭质整体材料的制备及其对痕量二氧化硫的吸附性能

以壳聚糖为碳源,综合采用冰模板技术和低温热解炭化技术,制备出具有蜂窝状孔结构特征的大孔炭质整体材料,研究了此类新材料对痕量二氧化硫的吸附性能及再生能力。结果表明,大孔炭质整体材料蜂窝状孔结构的形成及其规整程度与冰模板过程的冷冻时间等因素密切相关;200℃下低温热处理可得到具有丰富表面含氮官能团的大孔炭质整体材料;经氨水溶液中的离子交换功能化处理后,该大孔炭质整体材料对低浓度SO₂的吸附容量显著提高,可达到57 mg·g^-1;吸附饱和后,经空气简单吹扫处理,大孔炭质整体材料即可大部分再生,少数不可再生部分是由于质子化的氨基与亚硫酸根和硫酸根在吸附过程中形成了不可逆化学吸附产物季铵盐所致。壳聚糖基大孔炭质整体吸附剂材料有望在污染空气的脱硫净化,特别是在质子交换膜燃料电池的阴极空气脱硫净化方面发挥重要作用。     

Novel porous organic triazine‐based polyimide with high nitrogen levels for highly efficient removal of Ni(II) from aqueous solution

In this study, a porous organic triazine‐based polyimide (PPI network) was prepared from 2,4,6‐tris(hydrazino)‐s‐triazine and 3,4,9,10‐perylenetetracarboxylic dianhydride. TGA, Fourier transform infrared spectroscopy, field emission SEM, XRD and a nitrogen sorption study confirmed the PPI network structure. Then, the synthesized PPI network was used to evaluate Ni²⁺ ion removal from aqueous solution and the effective parameters on adsorption functions of Ni²⁺ ions such as initial concentration, contact time and pH of the solution in batch adsorption experiments was studied. The results showed that the maximum adsorption capacity (q_m) of Ni²⁺ ions was 36.1 mg g^?1 in only 30 min with a pH of 7. The kinetics and adsorption isotherm were identified to be better fitted by the pseudo‐second‐order model and the Langmuir model, respectively. Based on the results, the proposed adsorbent has good potential for removing Ni²⁺ ions from aqueous solutions. © 2019 Society of Chemical Industry     

Cloud-point measurement of the biodegradable poly(d,l-lactide-co-glycolide) solution in supercritical fluid solvents

Experimental data of high pressure phase behavior between 35 °C and 105 °C and pressures up to 2,200 bar is presented for poly(d,l-lactic acid)(d,l-PLA) and poly(lactide-co-glycolide)₁₅ (PLGA₁₅), PLGA₂₅, and PLGA₅₀ in supercritical carbon dioxide, trifluoromethane (CHF₃), chlorodifluoromethane (CHClF₂), dichloromethane (CH₂Cl₂), and chloroform (CHCl₃). d,l-PLA dissolves in carbon dioxide at pressures of 1,250 bar, in CHF₃ at pressures of 500 to 750 bar, and in CHClF₂ at pressures of 30–145 bar. As glycolic acid (glycolide) is added to the backbone of PLGA, the cloud point pressure increases by 36 bar/(mol GA) in carbon dioxide, 27 bar/(mol GA) in CHF₃, and by only 3.9 bar/(mol GA) in CHClF₂. PLGA₅₀ does not dissolve in carbon dioxide at pressures of 2,800 bar, whereas it is readily soluble in CHClF₂ at pressures as low as 95 bar at 40 °C. Cloud point behavior of d,l-PLA, PLGA₁₅, and PLGA₂₅ in supercritical carbon dioxide shows the effect of glycolide content between 35 °C and 108 °C. Also, the phase behavior for poly(lactic acid) — carbon dioxide-CHClF₂ mixture shows the changes of pressure-temperature slope, and with CHClF₂ concentration of 6 wt%, 19 wt%, 36 wt% and 65 wt%. The cloud-point behavior shows the impact of glycolide content on the phase behavior of PLA, PLGA₁₅, PLGA₂₅ and PLGA₅₀ in supercritical CHClF₂. A comparison was made between the phase behaviors of d,l-PLA and poly(l-lactide)(l-PLA) in supercritical CHF₃. The phase behavior of CHF₃ as a cosolvent for 5 wt% d,l-PLA-supercritical carbon dioxide system is presented for the effect being added 10 wt% and 29 wt% to CHF₃ content.     

Oxidation of CH4 over Pd supported on TiO2-doped SiO2: Effect of Ti(IV) loading and influence of SO2

Titania-modified silicas with different weight% of TiO₂ were prepared by sol–gel method and used as supports for Pd (1 wt%) catalysts. The obtained materials were tested in the oxidation of methane under lean conditions in absence and in presence of SO₂. Test reactions were consecutively performed in order to evaluate the thermal stability and poisoning reversibility. Increasing amounts of TiO₂ improved the catalytic activity, with an optimum of the performance for 10 wt% TiO₂ loading. Moreover, the titania-containing catalysts exhibited a superior tolerance towards SO₂ by either adding it to the reactants or feeding it as a pure pretreatment atmosphere at 350 °C. Catalysts were characterized by XPS, XRD, FT-IR and BET measurements. According to the structural and surface analyses, the mixed oxides contained Si–O–Ti linkages which were interpreted as being responsible for the enhanced intrinsic activity of supported PdO with respect to PdO on either pure SiO₂ or pure TiO₂. Moreover, the preferential interaction of the sulfur molecule with TiO₂ and the easy SO_x desorption from high surface area silica were the determining factors for the superior SO₂ tolerance of the TiO₂-doped catalysts.     

Three-dimensional g-C3N4/MgO composites as a high-performance adsorbent for removal of Pb(II) from aqueous solution

ABSTRACT

A novel, three-dimensional material of g-C₃N₄/MgO was prepared by pyrolysis method. The adsorption behavior for Pb(II) onto g-C₃N₄/MgO was systematically investigated. The adsorption experiments confirmed that the g-C₃N₄/MgO exhibited remarkable adsorption performance owing to its rough morphology and abundant active sites on the surface. The maximum adsorption capacities for Pb(II) reached to 220.3, 226.2 and 235.1 mg/g at 308 K, 318 K and 328 K, respectively. The optimum adsorbent dosage was 1.0 g/L. The adsorption kinetics and isotherm could be well described by the pseudo-second-order model and Langmuir isotherm model, respectively. The adsorption process was spontaneous and endothermic.     

Preparation and barrier property of poly(vinyl alcohol)/SiO<Subscript>2</Subscript> hybrid coating films

Using sol-gel method, poly(vinyl alcohol)/SiO₂ hybrid coating materials with an improved gas barrier property could be produced. Phase compatibility between organic PVA segments and inorganic silicate network in the hybrid was evaluated by analyzing FT-IR spectra and investigating the crystallization behavior in terms of X-ray diffraction patterns for the hybrid gels. For the preparation of coating film with barrier property, the biaxially oriented polypropylene (BOPP) substrate was coated with the hybrid sols by a spin coating method. Morphological analysis for the fractured surface of the hybrid gel and the surface of the coated film was performed not only to examine the microstructure of the hybrid, but also to propose evidence for the oxygen permeation behavior through the coated film. It was revealed that an optimum amount of inorganic silicate precursor, TEOS, should be used to obtain high barrier PVA/SiO₂ hybrid coating materials with enhanced micro-phase morphology and optical transparency. This homogeneous morphology densified with nano-structured silicate, obtained at optimal conditions, was found to result in a significant increase in the oxygen barrier property of film coated with PVA/SiO₂ hybrid by about 50 times relative to the pure BOPP substrate. In addition, the effect of pretreatments of the BOPP substrate surface on the barrier property was also examined.     

Monomer concentration effect on the phase behavior of poly(propyl acrylate) and poly(propyl methacrylate) with supercritical CO2 and C2H4

Experimental cloud-point data to temperature of 186 °C and pressure of ~2,500 bar are presented for ternary mixtures of poly(propyl acrylate)(PPA)-CO₂-propyl acrylate (PA) PPA-C₂H₄-PA and poly(propyl methacrylate) (PPMA)-CO₂-propyl methacrylate (PMA) systems. Cloud-point pressures of PPA-CO₂-PA system were measured in the temperature range of 32 °C to 175 dgC and to pressures as high as 2,070 bar with PA concentrations of 0.0, 5.0, 11.7 and 30.4 wt%. Adding 34.1 wt% PA to the PPA-CO₂ mixture significantly changes the phase behavior. This system changes the pressure-temperature slope of the phase behavior curves from U-LCST region to LCST region as the PA concentration increases. Cloud-point data to 170 °C and 1,400 bar are presented for PPA-C₂H₄-PA mixtures and with PA concentration of 0.0, 5.7, 15.5 and 22.2 wt%. The cloud-point curve of PPA-C₂H₄ system shows relatively flat at 730 bar for temperatures between 41 and 150 °C. With 15.5 and 22.2 wt% PA the cloud-point curve exhibits a positive slope that extends to 35 °C and ~180 bar. Also, the ternary PPMA-CO2-PMA system was measured below 186 °C and 2,484 bar, and with cosolvent of 5.2-20.1 wt%. PPMA does not dissolve in pure CO₂ to 233 °C and 2,500 bar. Also, when 41.5 wt% PMA is added to the PPMA-CO₂ solution, the cloud-point curve shows the typical appearance of a lower critical solution temperature (LCST) boundary.     

Synthesis of poly-(BA-co-MMA) latexes filled with SiO2 for coating in construction applications

The synthesis of acrylic latexes filled with silica nanoparticles have been developed in the present work. Moreover, a exhaustive study of the influence of the synthesis conditions on the latex characteristics has been performed. The latex particles morphology has been observed using transmission electron microscopy (TEM) showing a raspberry morphology. Completely transparent coatings have been synthesized using these latexes and a high dispersion degree of the nanosize SiO₂ into the polymer matrix has been achieved. These characteristics of these latexes make especially suitable for construction applications (i.e., to protect natural stone). Nanoindentation tests have been carried out in order to measure the mechanical properties of the coating. These tests showed an increment of the elastic modulus and hardness, improving mechanical properties when SiO₂ is added to the polymer matrix.     

Study of the Supported K2MoO4 Catalyst for Methanethiol Synthesis by One Step from High H2S-Containing Syngas

ESR and XPS are used to study the Mo-based catalysts MoO₃/K₂CO₃/SiO₂ and K₂MoO₄/SiO₂ prepared with two kinds of precursors, (NH₄)₆Mo₇O₂₄4H₂O and K₂MoO₄. The catalytic properties of the catalysts for methanethiol synthesis from high H₂S-containing syngas are explored. The activity assay shows that the two catalysts have much the same activity for the reaction. By the ESR characterization of both functioning catalysts, the resonant signals of oxo-Mo(V) (g=1.93), thio-Mo(V) (g=1.98) and S (g=2.01 or 2.04) can be detected. In the catalyst MoO₃/SiO₂ modified with K₂CO₃, as increasing amounts of K₂CO₃ are added, the content of oxo-Mo(V) increases, but thio-Mo(V) decreases. The XPS characterization indicates that Mo has mixed valence states of Mo⁴⁺, Mo⁵⁺ and Mo⁶⁺, and that S includes three kinds of species: S^2– (161.5 eV), [S–S]^2– (162.5 eV) and S⁶⁺ (168.5 eV). Adding K₂CO₃ promoter to the catalysts, the Mo species of high valence state is easily sulphided and reduced to Mo₂S and oxo-M(V), and the derivation of [S–S]^2– and S^2– species from S is promoted simultaneously. The methanethiol synthesis is favored if the mole ratio of (Mo⁶⁺ + Mo⁵⁺)/Mo⁴⁺ 0.8 and S^2–/[S–S]^2– is kept at a value of about 1.     

A highly active silica(silicon)-supported vanadia catalyst for C1 oxygenates and hydrocarbon production from partial oxidation of methane

A very low surface area silica-silicon substrate has been used as a support for vanadium oxide and has been tested in the partial oxidation of methane. Use of a reactor with variable dead volume ahead of the bed of the catalyst allows determining the relevance of gas phase reactions in initiating methane conversion. Experimental evidence supports that at atmospheric pressure C₁ oxygenates are essentially produced on the catalyst surface rather than in the gas phase. Comparison with a high surface area silica-supported vanadium oxide catalyst clearly highlights the double role of surface area in promoting catalytic activity, but also in promoting non-selective further oxidation of reaction products. It is shown that a reaction system combining dead volume upstream the bed of the catalyst and a very low surface area is very promising to activate methane conversion to C₁ oxygenates and C₂₊ hydrocarbons at remarkable TOF number preventing further non-selective oxidation. In addition, production of C₂₊ hydrocarbons is observed at temperatures as low as 750 K.     

Removal of Ni(II), Cd(II), and Pb(II) from a ternary aqueous solution by amino functionalized mesoporous and nano mesoporous silica

In the present study, the application for the removal of Ni(II), Cd(II) and Pb(II) ions from aqueous solution by using mesoporous silica materials, namely, MCM-41, nanoparticle of MCM-41, NH₂-MCM-41 (amino functionalized MCM-41) and nano NH₂-MCM-41 was investigated. Suitable adsorbents preparation techniques were developed in the laboratory. The effects of the solution pH, metal ion concentrations, adsorbent dosages, and contact time were studied. It was found that NH₂-MCM-41 showed the highest uptake for metal ions in aqueous solution. The results indicated that the adsorption of Ni(II), Cd(II) and Pb(II) ions on the surface of the adsorbent was increased with increasing solution pH. The experimental data were analyzed using the Langmuir and Freundlich equations. Correlation coefficients were determined by analyzing each isotherm. It was found that the Langmuir equation showed better correlation with the experimental data than the Freundlich. According to the parameters of the Langmuir isotherm, the maximum adsorption capacity of NH₂-MCM-41 for Ni(II), Cd(II) and Pb(II) was found to be 12.36, 18.25 and 57.74 mg/g, respectively. The kinetic data of adsorption reactions and the evaluation of adsorption equilibrium parameters were described by pseudo-first-order and pseudo-second-order equations. The synthesized solid sorbents were characterized by Fourier transform infrared (FT-IR) spectrometry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen sorption measurements.     

Response surface methodology approach for the optimization of tartrazine removal by heterogeneous photo-Fenton process using mesostructured Fe2O3-suppoted ZSM-5 prepared by chitin-templating

A statistical optimization of tartrazine dye removal process from aqueous solution by heterogeneous photo–Fenton process using Fe₂O₃-supported ZSM-5 catalyst was performed. ZSM-5 support was prepared by chitin-templating technique to obtain a mesoporous structure. Thereafter, Fe₂O₃ was supported on ZSM-5 through wet impregnation method. This material was characterized by different techniques and posteriorly evaluated as a catalyst for the removal of tartrazine from aqueous solution. A central composite rotational design coupled with response surface methodology approach was used to evaluate the influence of different reaction conditions on the decolorization of a solution containing tartrazine and to obtain the optimum conditions. Under the optimum experimental conditions of dye decolorization, a mineralization experiment was conducted through analysis of total organic carbon. In these conditions, 95% of decolorization was achieved at 30?min of reaction and a significant mineralization of 80% was observed at 180?min. Therefore, the photo-Fenton process using Fe₂O₃-supported ZSM-5 prepared by chitin-templating was proved to be feasible for both the decolorization and mineralization of tartrazine in aqueous solution.