Effect Of Preparation Procedure Research Articles

Similarities and Differences of the Active Sites in Basic and Advanced MgCl2‐Supported Ziegler‐Natta Propylene Polymerization Catalysts

AbstractThough preparation procedures of heterogeneous Ziegler‐Natta catalysts for propylene polymerization are sophisticated, it is uncertain whether the nature of the active sites is similar or different for different preparation procedures. In this study, the effects of preparation procedures on the nature of the active sites were investigated by stopped‐flow polymerization in combination with microstructure analysis of polymers. Both basic and advanced types of catalysts showed the same two kinds of isospecific active site, which indicated little influence of the preparation method on the active site structure. On the contrary, the ratios of the two kinds of isospecific sites were not the same, resulting in variation of average polymer properties.magnified image

Effect of preparation procedure on the properties of CeO2

The effect of preparation procedure on the physicochemical and catalytic properties of CeO2 was studied. Differences in the electronic and structural characteristics of CeO2 depending on preparation procedure and treatment temperature were found using X-ray diffraction analysis, transmission electron microscopy, UV-visible electronic spectroscopy, and X-ray photoelectron spectroscopy. With the use of the temperature-programmed reaction with CO, it was demonstrated that CeO2 samples with a high concentration of point defects—oxygen vacancies caused by the presence of Ce3+—were characterized by an increased mobility of bulk oxygen. The samples of CeO2 with a high concentration of structural defects—micropores of size 1–2 nm and stepwise vicinal faces in crystallites—exhibited a high catalytic activity in the reaction of CO oxidation.

Effects of preparation procedure in sol–gel method on performance of MoO3/SiO2 catalyst for liquid phase epoxidation of propylene with cumene hydroperoxide

The 15% MoO3/SiO2 catalysts were synthesized by a modified base-catalyzed sol–gel method and characterized by Raman, XRD, FT-IR, UV–vis, NH3-TPD and ICP. The catalytic performance of MoO3/SiO2 for the liquid phase epoxidation of propylene with cumene hydroperoxide (CHP) and the effects of preparation procedure on its physicochemical and catalytic properties were studied. The results show that, in the processes of preparing catalyst, the solvent of ammonium heptamolybdate and the sequence of feeding would affect the existing states of molybdenum species on silica support significantly. When 1,2-propanediol was used as the solvent and an appropriate sequence of feeding was adopted, the β-MoO3 species and monomeric molybdenum species can form on silica to make for the promotion of MoO3/SiO2 catalyst. Without any depressor in the reaction system, at 80°C and 2.2MPa for 4h, the conversion of CHP is above 99% and the selectivity to PO reaches 85.3%.

Effect of preparation procedure on the structure, morphology, and optical properties of nanocomposites of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] with gold nanoparticles

Morphology, spectroscopic properties and molecular structure defects are characterized and compared for two types of poly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene]vinylene} (MEH-PPV) – Au nanoparticles (NPs) nanocomposites prepared by different procedures known for nanocomposites with other polymers: (a) nanocomposites M, prepared by mixing a dichloromethane (DCM) solution of MEH-PPV with Au nanoparticle organosol in DCM, and (b) nanocomposites R, prepared by the in situ interfacial reduction of Au 3+ salt with NaBH 4 in the presence of polymer. In nanocomposite M the molecular weight (MW) distribution as well as molecular structure of parent MEH-PPV remains practically intact and the polymer forms a matrix in which, at higher polymer concentrations, Au NPs are almost uniformly distributed and preserve the particle-size distribution found for the parent sol. The aggregation of Au NPs is observed as the polymer concentration in the nanocomposite M is decreased. For nanocomposites R: (i) a broad particle-size distribution and formation of Au aggregates, (ii) a slight decrease in molecular weight of MEH-PPV with respect to the parent polymer, and (iii) a decrease in the extent of conjugation of MEH-PPV chains fairly exceeding that observed for MEH-PPV chains degraded to the same MW values in air at ambient light were observed. These features of nanocomposites R are shown to be a consequence of side reactions of MEH-PPV with H[AuCl 4]/TOAB complex in the reaction mixture prior to the addition of the reducing agent. Unlike the case of nanocomposites M, the higher the polymer concentration, the larger is the mean size of Au NPs that tend to form larger aggregates in nanocomposites R.

Effect of preparation procedure on redox states of iron in soda-lime silicate glass

The redox state of iron in soda-lime silicate glass was determined by analysis of the optical absorption bands due to Fe 2+ and Fe 3+ states. When raw materials containing Fe 2O 3 were heated gradually to 1400 °C, the total-Fe content of the glass was 9.4% Fe 2+, but rapid heating at 1400 °C increased the Fe 2+ content to 11.7%. The oxygen activity (aO 2) in the corresponding melts was measured using zirconia and Pt electrodes. The value increased with increasing temperature in the gradually heated sample and reached log(aO 2) = 0.03 at 1400 °C, but was about 2.5 times lower in the rapidly heated sample at log(aO 2) = −0.37. After SnO addition to the raw material, oxygen activity depended strongly on heating speed: log(aO 2) at 1400 °C fell as low as −1.8 with rapid temperature increase but was about −0.2 or higher with gradual heating. The Fe 2+ content of the cooled glass was consistent with the oxygen activity of the melts. The effect of heating speed was attributed to the formation of a melt layer on the surface of the raw material.

Effects of Preparation Procedures and Structure of IrO2-Ta2O5 Coated Insoluble Anodes on Durability

The IrO2-Ta2O5 anodes for copper foil production were studied. As the thermal decomposition temperature of the catalytic layers becomes lower such as 613 K, no PbO2 deposits from the sulfuric solution containing lead ions. The short lifetime of these anodes can be improved by inserting the IrO2-Ta2O5 interlayer prepared at 743 K, because the adhesiveness between the catalytic layer and the titanium substrate becomes stronger. Another method to improve the lifetime is the etching process of the titanium substrate. New etching method in sulfuric acid also provides longer lifetime of the catalytic layer prepared at 613 K, on which no PbO2 deposits.

Structural, mechanical and electrical characterization of epoxy-amine/carbon black nanonocomposites

This work presents an insight into the effect of preparation procedure and the filler content on both electrical and mechanical properties of a nanocomposite system. For the preparation of the nanocomposites diglycidyl ether of bisphenol A (DGEBA) was used with triethylenetetramine (TETA) as a curing agent. As fillers carbon black (CB) nanoparticles with size from 25 to 75 nm were used. The characterization was done using Dynamic Mechanical Analysis (DMA), Dielectric Relaxation Spectroscopy (DRS), Differential Scanning Calorimetry (DSC), Wide Angle X-ray Diffraction (WAXD) and electrical conductivity measurements. The dependence of the dynamic mechanical and dielectric parameters (E', E, tanδ, e', e, σ and Tg) is associated with the filler content and is controlled by the employed curing conditions. An increase in electrical conductivity, which is observed at about 1% w/w of carbon black, indicates the creation of conducting paths and is associated with the Maxwell Wagner Sillars (MWS) relaxation, probably due to the formation of aggregated microstruc- tures in the bulk composite.

Effects of Preparation Procedures and Structure of IrO2-Ta2O5 Coated Insoluble Anodes on Durability

not Available.

The effect of preparation procedure and composition of water-ethanol suspensions of amorphous silica on their aggregative stability and kinetics of coagulation

The method of flow ultramicroscopy is employed to study the effect of the composition and preparation procedure of dilute water-ethanol suspensions of two samples of amorphous silica (fractionated fused quartz and monodisperse amorphous silica) on the kinetics of their coagulation. It is revealed that all suspensions prepared by the addition of silica powders to water-ethanol mixtures with ethanol contents of 96 and 40 vol % are stable with respect to aggregation, as the suspensions prepared by the addition of aliquots of concentrated dispersions of the aforementioned silica samples in 96% ethanol aged for different time periods to water-ethanol mixtures containing 96 vol % ethanol. At a 40-vol % content of ethanol in the mixture, the coagulation whose character (including “superfast” coagulation) substantially depends on the time of aging of initial concentrated silica dispersions occurs. Furthermore, kinetic studies are performed for the coagulation of dilute silica suspensions prepared by the addition of silica powders to water-ethanol solutions containing 40 vol % of ethanol and traces (<1 ppm) of poly(ethoxysilane), poly(acrylic acid), and a supernatant prepared by the centrifugation of concentrated silica dispersion in 96% ethanol aged for more than 3 months. It is found that the addition of aliquots of the aforementioned ethanol solutions to silica suspensions in 40% ethanol, which are initially stable with respect to aggregation, causes their superfast coagulation.

Capillary electrophoresis monitors enhancement in subcellular reactive oxygen species production upon treatment with doxorubicin.

This study investigated the role of doxorubicin (DOX) accumulation in reactive oxygen species (ROS) production detected in individually electrophoresed organelles, including mitochondria, acidic organelles, and peroxisomes. While bulk measurements of ROS production in cells and organelles are not capable of discriminating between the effects of preparative procedures on measured ROS production, capillary electrophoresis with dual laser-induced detection of individual organelles demonstrated a difference in the measured ROS production as a result of various preparative procedures. Using this technique, the three different types of detected organelles (i) produce ROS and do not have detectable levels of DOX, (ii) contain detectable DOX but do not produce ROS, or (iii) produce ROS and accumulate DOX. The third type displays two subpopulations of organelles, one of which demonstrated a direct relationship between DOX uptake and subsequent ROS production, corresponding most likely to mitochondria, and a second one with low DOX uptake but large variation in ROS production, corresponding most likely to acidic organelles.

Carbon-supported cobalt catalyst for ammonia synthesis: Effect of preparation procedure

Supported cobalt catalysts were synthesised, characterised (by H 2 TPD, XRD, TEM), and tested in ammonia synthesis at 9.0 MPa (400–470 °C; H 2:N 2 = 3:1). Partly graphitised carbon of high surface area (840 m 2/g), cobalt nitrate, and barium nitrate were used as a support, a precursor of the active phase, and a promoter precursor, respectively. Both cobalt dispersion in the Ba-doped catalyst and, to a greater extent, catalytic properties of the promoted Co surfaces (TOF) proved to be dependent on the unpromoted material pretreatment (reduction in H 2, subsequent calcination in air). The kinetic studies of NH 3 synthesis have shown explicitly that Ba-promoted cobalt on carbon is very active and less inhibited by the ammonia product than the commercial magnetite-based material.

Effect of preparation procedure of Iro2–Nb2o5 anodes on surface and electrocatalytic properties

The influence of the electrode manufacturing procedure on surface and electrocatalytic properties for oxygen and ozone evolution at electrodes of nominal composition Ti/[IrO2–Nb2O5] (45:55 mol%) was investigated. Thermal decomposition at 450 °C (1 h, air stream) was adopted as standard procedure. Metal support pretreatment, solvent mixture, method of applying the precursor mixture and calcination procedure were all investigated. X-ray diffraction, scanning electronic microscopy, voltammetric and differential capacity analysis show the use of HCl 1:1 as solvent and applying the mixture by brush led to fragile rugged/porous oxide coatings. However, for the same conditions, but controlled calcination (heating/cooling rates), the coating becomes more compact. Using isopropanol as solvent results in a more homogeneous coating, presenting the lowest morphology factor. Kinetic investigation shows the rugged/porous coating presents the lowest Tafel slopes and the highest global electrocatalytic activity for OER. The more compact the coating the lower the electrochemically active surface area and the global OER activity. Ozone efficiency depends on the electrochemically active area while support pretreatment strongly influences the lifetime of the electrode. Application of a Pt interlayer between the oxide and Ti base improves the service life.

EFFECTS OF PREPARATION PROCEDURE AND ELECTRIC FIELD FREQUENCY ON THE DIELECTRIC CONSTANTS AND ELECTRORHEOLOGY OF A ZEOLITE/SILICONE OIL SUSPENSION

Determined were the effects of preparation procedure and electric field frequency f = dc to 105 Hz on the dielectric constants and ER response (shear rate [Formula: see text]) of a suspension in silicone oil of 23 wt.% zeolite particles originally containing 19 wt.% H 2 O . Heating the oil and the zeolite particles at 110°C both prior to, and following, mixing decreased the conductivity of the suspension more than simply heating the suspension following mixing. The double heating procedure reduced the complex dielectric constant [Formula: see text] of the particles and the complex mismatch parameter β*. The ER shear stress τ E was proportional to [Formula: see text] for the single heating and [Formula: see text] for the double heating, where [Formula: see text] is the complex dielectric constant of the silicone oil. The lower exponent corresponds to a higher water content and in turn higher conductivity of the suspension. Erratic ER response occurred for f =10 Hz in tests with [Formula: see text], but not in tests with [Formula: see text].

Microwave-assisted hydrothermal synthesis of hydroxy-sodalite zeolite membrane

A high quality pure hydroxy-sodalite zeolite membrane was successfully synthesized on an α-Al 2O 3 support by a novel microwave-assisted hydrothermal synthesis (MAHS) method. Influence of synthesis conditions, such as synthesis time, synthesis procedure, etc., on the formation of hydroxy-sodalite zeolite membrane by MAHS method was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas permeation measurements. The synthesis of hydroxy-sodalite zeolite membrane by MAHS method only needed 45 min and synthesis was more than 8 times faster than by the conventional hydrothermal synthesis (CHS) method. A pure hydroxy-sodalite zeolite membrane was easily synthesized by MAHS method, while a zeolite membrane, which consisted of NaX zeolite, NaA zeolite and hydroxy-sodalite zeolite, was usually synthesized by CHS method. The effect of preparation procedures had a dramatic impact on the formation of hydroxy-sodalite zeolite membrane and a single-stage synthesis procedure produced a pure hydroxy-sodalite zeolite membrane. The pure hydroxy-sodalite zeolite membrane synthesized by MAHS method was found to be well inter-grown and the thickness of the membrane was 6–7 μm. Gas permeation results showed that the hydrogen/ n-butane permselectivity of the hydroxy-sodalite zeolite membrane was larger than 1000.

A new approach of selective Ge deposition for RhGe/Al 2O 3 catalysts: characterization and testing in 2,2,3-trimethylbutane hydrogenolysis

A series of Rh monometallic and RhGe/Al 2O 3 catalysts was prepared in a dynamic reactor by anchoring Ge( n-C 4H 9) 4 on Rh surface, containing preadsorbed hydrogen and by subsequent hydrogenolysis of the surface organometallic complexes. Different amounts of organometallic Ge compound were introduced, corresponding nominally to 1/20, 1/2, 2 Ge monolayers. The samples were characterized by FTIR of CO, transmission electron microscopy (TEM), hydrogen chemisorption and hydrogenolysis of 2,2,3-trimethylbutane (223TMB) as a test reaction. Hydrogen chemisorption and TEM results are consistent with (i) the effect of preparation procedure on the morphology of the monometallic sample, (ii) the surface deposition of Ge on Rh particles. Concerning the effect of preparation, the grafting procedure led for blank experiments (Ge-free catalysts) to a slight sintering which can be avoided by Ge anchoring. On the other hand, we used the relative normalized intensities of linear and bridged CO species of FTIR measurements to identify the location of Ge deposits. The amount of the Ge compound introduced had a pronounced effect on the final landing position of Ge. Excess Ge( n-C 4H 9) 4 resulted in a statistical deposition on the surface of Rh or a slight diffusion in Rh lattice, while low-Miller-index microfacets were preferentially occupied when the amount of tetra- n-butylgermanium was markedly lower than that for monolayer coverage. The presence of quaternary carbon atom in the reactant molecule (223TMB) induced changes in the chemisorption geometry deduced from the shift of maximum activity towards lower p(H 2). In the wide negative hydrogen order region breaking of CC bonds can be the slowest step. Low-Miller-index microfacets of Rh particles may be active in multiple CC bond cleavage during one residence time of the reactant molecule.

The effect of preparation procedures on the morphology of melanin from the ink sac of Sepia officinalis.

The structure of melanin extracted from the ink sac of the cuttlefish Sepia officinalis was examined for different methods of isolation and purification of the pigment. Scanning electron microscopy (SEM) images of Sepia eumelanin prepared by different procedures establish that multi-microm-sized aggregates reported by previous workers are generated by their sample preparation, and that the dominant constituents of Sepia melanin are approximately 150 nm spherical granules. Brunauer-Emmett-Teller (BET) measurements reveal that Sepia eumelanin from Sigma (prepared by spray drying the pigment) has a surface area of 14.3 m2/g. Pigment extracted directly from the fresh ink sac and then freeze-dried has a surface area of 21.5 m2/g, while CO2-supercritically dried has a surface area of 37.5 m2/g. This is consistent with SEM images showing that the process of freeze-drying produces aggregates, but to a lesser extent than spray drying. Supercritical drying of the sample produces suspensions of the individual approximately 150 nm granule, which is more reflective of the natural pigment. Brunauer-Emmett-Teller surface area analysis and Barrett-Joyner-Halenda (BJH) pore volume analysis indicate that the surface of the granules is not smooth and the interior of the granules is not porous, but rather the aggregates of granules are porous. Ultra-high resolution SEM and atomic force microscopy (AFM) images show the granules are easily deformed and are comprised of smaller constituents. De-aggregation of the granules by sonication and ultra-filtration reveal a range of structures depending on the pore size of the membrane used. The implications of these results on quantifying photochemical properties and kinetic reaction rate constants of melanin are discussed.

Effects of preparation procedures on ascorbic acid retention in pickled hot peppers

The effect of preparation procedures (with and without sugar and chickpea) on ascorbic acid in pickled (acidification with vinegar) green hot peppers during pickling and the storage period (8 weeks) was studied. Ascorbic acid values in fresh pepper rapidly decreased after pickled processing (first 3 weeks) and then did not significantly (P=0.05) change through the storage time (8 weeks), but sugar and chickpea added together in pickling pepper processing resulted in greater ascorbic acid retention. The retention was 48.2% and 40.9% for 3 and 8 weeks, respectively.

NOx Reduction by Potassium-Containing Coal Briquettes. Effect of Preparation Procedure and Potassium Content

The activity of potassium-containing bituminous coal briquettes for NOx reduction in an oxygen-rich environment has been investigated at temperatures of 300 and 350 °C. Two different procedures hav...

Effect of preparation procedures on the activity of supported palladium/lanthanum methanol decomposition catalysts

A series of palladium catalysts promoted with lanthanum were prepared on a silica support and the activities of these catalysts examined for the decomposition of methanol into CO and H 2. The preparation procedure and the La 2O 3/Pd weight ratio of these Pd/La 2O 3/SiO 2 catalysts (5 wt.% Pd) was found to be important for high catalytic activities. If Pd is deposited after La 2O 3 using a precipitation procedure, the methanol decomposition activity increases up to a La 2O 3/Pd weight ratio of 1.0. The optimized weight ratio for the methods of co-precipitation and co-impregnation were found to be 0.8 and 0.5, respectively. Relatively low activities are obtained if a sequential procedure with La 2O 3 deposition in the final step is applied. The effect of the preparation procedure and La 2O 3/Pd weight ratio on activity of the resulting catalysts can be explained by: (i) the amount of Pd particles in contact with La 2O 3 moieties, positively affecting the activity, and (ii) the extent of coverage of Pd particles by La 2O 3 patches, negatively affecting the activity.

Alkali-Free ZSM-5 Membranes: Preparation Conditions and Separation Performance

Alkali-free, H−ZSM-5 membranes were synthesized by in-situ crystallization on porous α-alumina, γ-alumina, and stainless steel tubular supports. Membranes prepared from different Si sources were characterized by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. Membranes prepared under different conditions were also characterized by single-gas permeances of H2, N2, n-C4H10, i-C4H10, and SF6 and by separation selectivities of n-C4H10/i-C4H10 mixtures from 300 to 473 K. The effects of preparation procedure, crystallization time and temperature, number of synthesis layers, gel dilution, Si source, and type of support were studied. The permeation and separation properties of the membranes depend strongly on the preparation procedure. Permeating synthesis solution into the pores of the support before hydrothermal treatment allows zeolites crystal growth within those pores. Increasing the crystallization time and temperature increases the n-C4H10/i-C4H10 separation selectivities...