High Initial Activity Research Articles

Deactivation mechanism of Pd supported on ordered and non-ordered mesoporous silica in the direct H 2O 2 synthesis using CO 2-expanded methanol

The deactivation mechanism of Pd supported on silica and mesoporous silica (SBA-15) using CO 2-expanded methanol as solvent was studied in the direct synthesis of H 2O 2 in batch and semi-continuous batch reactor tests as well as its hydrogenolysis. Fresh and used catalysts were characterized by TPR and CO chemisorption. The results evidence the presence of deactivation, which can be correlated to the loss of accessible active metal surface area due to sintering of Pd, but there is also an effect of the presence of the ordered mesoporous structure and of the reaction conditions. The higher concentration of H 2 in solution in semi-continuous batch reactor tests with respect to batch reactor tests leads to a more relevant deactivation in Pd-SiO 2 with respect to Pd-SBA-15, but a higher initial activity, due to the fact that H 2 accelerates the reduction of the Pd species which are less reducible in Pd-SiO 2 than in Pd-SBA-15. Pd-SBA-15 shows a higher H 2O 2 selectivity and productivity with respect to Pd-SiO 2 in batch reactor tests, related to the presence of easier reducible Pd species. Another difference is related to the different mechanism of sintering. On the SBA-15 support, due to the presence of the ordered mesoporosity, the Pd particles migrate into the SBA-15 channels forming elongated 1D-type particles. In Pd-SiO 2 catalyst, instead, the sintering of the Pd particles leads to large aggregates of Pd particles in the range of 20–25 nm.

Sorption and catalytic effects upon the dehydration of methanol on perfluorinated copolymer-containing sulfo groups

The peculiarities of methanol transformation on the surface of perfluorinated copolymer, fluoroplastic, containing sulfo groups were studied. At temperatures of 70–120°C, the polymer was established to have high initial activity during the conversion of methanol into dimethyl ether; this reaction was, however, accompanied by strong water sorption that leads to a rapid drop in the activity. The sorption/desorption processes were characterized by temperature effects such as heating during sorption and cooling during desorption. The structure of the polymer in the salt (sodium cations) and acid (hydrolyzed polymer) forms was studied by IR spectroscopy. H3O+SO3− ionic pairs were found to be present in the acid form.

Imaging of activated macrophages in experimental osteoarthritis using folate-targeted animal single-photon-emission computed tomography/computed tomography

Evaluation of macrophage activation may provide essential information about the etiology and progression rate of osteoarthritis (OA). Activated macrophages abundantly express folate receptor β (FRβ), which can be targeted using radioactive-labeled folic acid. This study was undertaken to investigate whether macrophage activation can be monitored in small animal models of OA using a folate radiotracer and to determine whether macrophage activation differs in different models of OA with different OA progression. Two rat models of OA were used: the mono-iodoacetate (MIA) model, which is a fast-progressing biochemically induced model, and the anterior cruciate ligament transection (ACLT) model, which induces OA at a slower pace. Images were obtained using high-resolution small animal single-photon-emission computed tomography/computed tomography. The specificity of the technique was tested by eradicating macrophages using clodronate-laden liposomes and blockade of FRβ by cold folic acid. The MIA model had high initial macrophage activation, with a peak after 2 weeks which disappeared after 8 weeks. The ACLT model showed less activation but was still active 12 weeks after induction. The technique allowed monitoring of the disease process over time, in which late stages of the disease showed less macrophage activation than early stages, especially in the fast-progressing MIA model of OA. Our findings indicate that macrophage activation in experimental OA can clearly be demonstrated and monitored by the folate radiotracer. The high resolution, high sensitivity, and high specificity of the technique allow clear localization of macrophage activity in a disease model that is not known for abundant macrophage involvement.

Studies on Substituted Aromatic Diselenides as Catalysts for Selective Alcohol Oxidation Using tert‐Butyl Hydroperoxide

AbstractWe have investigated the Ph2Se2‐catalysed oxidation of alcohols with tert‐butyl hydroperoxide (TBHP) by using a variety of spectroscopic techniques and reaction calorimetry. We showed that the active oxidant is benzeneseleninic anhydride (BSA), formed by reaction of Ph2Se2 with TBHP. The influence of aromatic substituents on the activity of a selection of nine aromatic diselenides involved in alcohol oxidations was studied. Calorimetric experiments showed that compounds that are activated more rapidly have higher initial activity in the catalytic oxidation of benzyl alcohol. An exception to this rule was observed when the diselenide contained a dimethylamino group in the ortho position, which can apparently compensate for its slow pre‐activation by a special ortho effect. An aliphatic alcohol, 1‐decanol was also used as a substrate. Besides diphenyl diselenide only three of the substituted diaryl diselenides studied showed reasonable activity after pre‐activation with TBHP. Dimesityl diselenide displayed the highest activity and selectivity for the oxidation of 1‐decanol. Specificity for a given aldehyde could be achieved by using an oxidant and substrate feed protocol.

Etherification of Biodiesel-Based Glycerol with Bioethanol over Tungstophosphoric Acid To Synthesize Glyceryl Ethers

Etherification of biodiesel-based glycerol with bioethanol was investigated over a series of catalysts. The etherification of glycerol performed on acid catalysts, such as H-ZSM5, H-β, tungstophosphoric acid (HPW), FeCl3, AlCl3, and H2SO4, was found. Basic catalysts (such as alkaline earth oxides, MgO) are inactive for the reaction. Bulk HPW and SiO2-supported HPW catalysts exhibited the highest activity among the tested catalysts, with a 97.1% conversion of glycerol. Over the HPW catalyst, the etherification reactions were carried out at different temperatures, varied ratios between ethanol and glycerol, different catalyst amounts, and different reaction times. The SiO2-supported HPW catalyst has a high initial activity, but it deactivated gradually because of the leaching of HPW.

Hierarchically structured Fe/ZSM-5 as catalysts for the oxidation of benzene to phenol

Different synthetic routes including carbon black and organosilane, templating and desilication were successfully employed to synthesize hierarchical Fe/ZSM-5 zeolites with improved catalytic performance in benzene oxidation to phenol with nitrous oxide. All these mesoporous zeolites show similar crystallinity, which is lower as compared to a conventional Fe/ZSM-5 catalyst. Hierarchical Fe/ZSM-5 catalysts exhibit superior catalytic performance, especially in terms of stability, in the selective oxidation of benzene to phenol with nitrous oxide. The best performance is obtained for the organosilane templated zeolites. The high initial activity and stability are related to the high interconnectivity of the micropores and mesopores, thus limiting the zeolite domain size. This results in enhanced mass transport and prevents fast blocking of the micropore space by carbonaceous byproducts.

To grow up with Crohn’s disease

To assess the characteristics and course of childhood-onset Crohn's disease among Hungarian patients. Records of 81 patients admitted between 1984 and 2006 and treated at least for one year until the 18th year of age were reviewed. There was a 62% male dominance and a rate of 12.5% of familial cases. The diagnostic lag was 11.36 (1-96) months. The mean age was 13.6 years (4-17), the activity index was 37.88 (5-80) at diagnosis and the initial frequencies were as follows: ileal affection 87%, stricturing and penetrating forms 27%, perianal manifestation 26%, giant cells or granuloma formation 47%, malnutrition 23,5%, growth failure 11%. Steroid therapy and azathioprin treatment were given in 84% and 62% of the patients, respectively. Biologic treatment was not possible during the study period. 31% of the patients underwent surgery (abdominal surgery 20%, perianal surgery 11%). When patients reached the 18th year of age the mean activity index decreased to 6.63 (0-35), the rate of malnutrition to 9.9% and that of growth failure to 2.5%. All these changes were statistically significant. Characteristics of childhood-onset Crohn's disease in Hungary are similar to those obtained in other European countries. The prolonged diagnostic lag, the high initial activity index, the granuloma formation and the stricturing/penetrating behavior may predict subsequent complications and need for surgery, and, therefore, justify intense initial therapy. The early introduction of immunomodulatory therapy affects favorably the course of illness.

Initial salivary α-amylase activity predicts malignant ventricular arrhythmias and short-term prognosis after ST-segment elevation myocardial infarction

BackgroundVentricular arrhythmias (VA), including ventricular tachycardia and ventricular fibrillation, are the most common remediable cause of death in patients with acute myocardial infarction. Augmented sympathetic neural activity to the heart...

The catalytic stability of Mo/HZSM-5 in methane dehydroaromatization at severe and periodic CH 4–H 2 switch operating conditions

The very rapid deactivation behavior of Mo/HZSM-5 catalyst in the non-oxidative CH 4 dehydroaromatization at severe conditions requests its cyclic or continuous regeneration in a practical system. While oxidation of active Mo 2C to MoO 3 followed by its sublimation at temperature >773 K under oxidative atmospheres excludes the possibility of using any oxygen-containing gases to regenerate Mo/HZSM-5 catalyst, it has been demonstrated that its high initial activity can be maintained via its continuous regeneration in H 2 in a two-bed circulating fluidized bed system at 1073 K. The key to design such a system is determination and optimization of the mean residence times of Mo/HZSM-5 in its CH 4 converter and regenerator. Presently, a series of deactivation (reaction)–regeneration cycle tests were designed and carried out over a well-characterized 5 wt%Mo/HZSM-5 at practically required severe conditions (1073 K and 21,080 and 40,000 mL/g/h) to clarify the effect of CH 4 and H 2 exposure durations on the activity stability. Simultaneously, TPO analyses of the samples deactivated in CH 4 for different durations at 1073 K and measurements of the H 2-regeneration kinetics of the same coked samples at the same temperature were conducted to gain a better understanding of the kinetic characteristics of coke formation and removal. Furthermore, measurements of the dynamic variations of the outlet benzene concentration in the CH 4 exposures in different cycles of a typical cycle test and numerical analysis of the resultant concentration–time curves were performed to determine the minimum and maximum mean residence times of the catalyst in a fluidized bed CH 4 converter. At last, a triple-bed circulating fluidized reactor system based on a large degree of deactivation–long time regeneration cycle test was proposed to realize an effectively continuous regeneration of Mo/HZSM-5 and therefore an efficiently continuous conversion of CH 4 to benzene.

Mesoporous Ti-MCM-41 materials as photodegradation catalysts of 2,4,6-trichlorophenol in water

Titanium-modified MCM-41 type mesoporous silica materials were prepared by hydrothermal [Ti-MCM-41(HT)], sol–gel [Ti-MCM-41(SG)] and post-synthesis impregnation [TiO2/MCM-41] methods. The materials were characterized and tested as photocatalysts in the oxidative degradation reaction of 2,4,6-trichlorophenol (2,4,6-TCP) in water. The catalysts showed high initial activity. The produced acetate and chloride ions were found to inhibit the degradation reaction. The Ti-MCM-41(HT) sample showed higher overall activity than the Ti-MCM-41(SG) catalyst. One of the probable reasons for this is the difference in the distribution of the active sites that determines the rates of electron (e−)–hole (h+) recombination within the photoactive species. The HT preparation was found to contain silica-bound titania in higher dispersion, while the SG preparation contained also polymerized species with Ti–O–Ti bonds.

α-Pinene isomerisation over heteropoly acid catalysts in the gas-phase

The isomerisation of α-pinene was studied in the gas phase over solid heteropoly acid (HPA) catalysts in a fixed-bed continuous flow reactor at 200 °C and ambient pressure. The catalysts included bulk and SiO 2-supported H 3PW 12O 40 and bulk Cs 2.5H 0.5PW 12O 40 possessing strong Brønsted acid sites, as well as composites prepared by supporting 15 wt% H 3PW 12O 40 on Nb 2O 5, ZrO 2 and TiO 2 possessing both Brønsted and Lewis acid sites of moderate strength. The reaction yielded camphene as the main product in a mixture with monoterpene by-products such as limonene, terpinolenes, terpinenes, β-pinene, p-cymene and others. The HPA catalysts with strong Brønsted acid sites exhibited high initial activities, but suffered from catalyst deactivation, resulting in low camphene yields. Conversely, the HPA catalysts supported on Nb 2O 5, ZrO 2 and TiO 2, although weaker acids, showed more stable performance in α-pinene isomerisation. The HPA catalyst supported on TiO 2 gave a camphene yield of 51% and a total camphene and limonene yield of 58%.

EFFECTS OF CONFINEMENT IN CARBON NANOTUBES ON THE PERFORMANCE AND LIFETIME OF FISCHER-TROPSCH IRON NANO CATALYSTS

The effects of confinement in carbon nanotubes on Fischer-Tropsch (FT) activity, selectivity and lifetime of Carbon NanoTubes (CNTs) supported iron catalysts are reported. A method was developed to control the position of the catalytic sites on either inner or outer surface of carbon nanotubes. TEM analyses revealed that more than 80% of iron oxide particles can be controlled to be positioned at inner or outer surface of the nanotubes. Deposition of iron oxide inside the nanotube pores decreased the average size of the iron oxide particles from 14 to 7 nm and shifted the reduction peak temperature of iron oxide species to lower temperatures (from 389 to 371 o C , 428 to 413 o C and 580 to 530 o C) and improved the reducibility of the catalyst by 25%. Catalytic performances of the catalysts in terms of FT experiment were tested in a fixed-bed micro reactor; the catalyst with catalytic sites inside the pores showed 23% higher initial activity than the catalyst with catalytic sites outside the pores. Also, the catalyst with catalytic sites inside the pores exhibited higher selectivity to heavier hydrocarbons (40.5% vs. 32.9% C5 + selectivity). In addition, deposition of catalytic sites on interior surface of the nanotubes resulted in a more stable catalyst, while its counterpart experienced 46.4% deactivation within a period of 720 h due to catalytic sites sintering. It is concluded that encapsulation of the catalytic nanoparticles inside the nanotubes prevents the catalytic site agglomeration.

Self-ignition combustion synthesis of LaNi 5 utilizing hydrogenation heat of metallic calcium

This paper describes self-ignition combustion synthesis (SICS) of LaNi 5 in a pressurized hydrogen atmosphere using metallic calcium as both the reducing agent and the heat source. In this study, the effects of hydrogen on the ignition temperature and the hydrogenation properties of the products were mainly examined. In the experiments, La 2O 3, Ni, and Ca were dry-mixed in the molar ratio of 1:10:6 and then heated up at a hydrogen pressure of 1.0 MPa until the ignition due to the hydrogenation of calcium. For the sake of comparison, the same experiments were performed in a normal argon atmosphere. The results showed that the ignition temperature was drastically lowered by hydrogen; it was only 600 K in the case of hydrogen as compared to 1100 K in the case of argon. The products also exhibited high initial activity and hydrogen storage capacity of 1.54 mass%. The proposed method offers many benefits for using cost-effective rare-earth oxide, saving productive time and energy, improving initial activity of the product and applying to any AB 5-type hydrogen storage alloy.

Computer simulation of time-dependent magma ascent processes involving bubbly and gassy flows

Time-dependent magma ascent processes were analyzed using a computer simulation of bubbly and gassy (gas-particle dispersion) magma flows in a vertical conduit connected at its bottom to a magma chamber having finite capacity. Volatile elements in the bubbly flow were assumed to escape from the magma through lateral permeable gas flow driven by the pressure gradient originating from viscous resistance to the ascent velocity-dependent expansion of bubbles. The bubbly flow was assumed to fragment and to transform into a gassy flow when its gas volume fraction exceeded a critical value. Based on the simulation, an eruption is predicted to be explosive or effusive when a dimensionless degassing factor, which is proportional to the permeability and viscosity of the magma, is smaller or greater than a critical value, respectively. The state of gassy flow was calculated from the mass and momentum conservations that are met quasi-statically with continuities of mass flux and pressure at the interface with the underlying bubbly flow. The inertia force and an effective wall friction were considered as resistive forces working on the gassy flow. Some of the results of the simulation are shown to be consistent with observations of some recent eruptions. An effusive or explosive eruption is predicted to have relatively high activity with large exit velocities at its initial stage. The initial high activity is particularly significant for explosive eruptions that involve the rapid growth of a gassy flow zone. Explosive eruptions are shown to involve more efficient magma transport with higher mass flow rates than effusive eruptions, as has been predicted by some previous analyses of stationary magma flow. The efficient magma transport of explosive eruptions is associated with a peculiar pressure distribution consisting of gentler and steeper pressure gradients in the gassy and bubbly flow zones, respectively. At the interface between bubbly and gassy flows, the pressure scaled by that at the conduit bottom was found to be nearly constant through time. This peculiar pressure distribution allows explosive eruptions to be fed with more magma than has been stored in excess of the lithostatic balance. This mechanism can produce such anomalously low pressure in the chamber that significant surface subsidence and caldera formation may result.

Side reactions of 4-acetamido-TEMPO as the catalyst in cellulose oxidation systems

Abstract TEMPO/hypochlorite oxidation of cellulosics are frequently used to obtain water-soluble polyglucuronates or nano-disperse materials. The reaction under neutral conditions offers a big advantage over hitherto applied alkaline systems as base-induce β-elimination reactions causing severe cellulose degradation are suppressed. Although 4-acetamido-TEMPO seems to offer high initial activities in cellulose oxidation, the TEMPO derivative is irreversibly converted into species with much lower reactivity. The degradation pathways and the chemical structure of the 4-acetamido-TEMPO-derived (by)products have been clarified. Degradation is strongly dependent on the pH value of the reaction mixture. In acidic conditions (pH<5), 4-oxo-TEMPO is formed by an oxidative deamination process, the 4-oxo-derivative still being capable of performing cellulose oxidation. In alkaline media, a similar process proceeds, but is immediately followed by a Favorskij rearrangement to a pyrrolidine-3-carboxylic acid (PROXYL) derivative. In both cases, the released acetamido moiety is slowly converted into methylamine by a decarboxylative rearrangement (Hofmann degradation). The results suggest that the instability and the chemical fate of 4-acetamido-TEMPO needs to be considered when cellulose oxidations and their kinetics are addressed: the recyclability of the 4-acetamido-TEMPO catalyst is rather limited.

The kinetic evidence for the formation of multiple active species in a bis(phenoxy-imine) zirconium dichloride/MAO catalyst during ethylene polymerization

The effects of polymerization time and temperature on the molecular weight and molecular weight distribution of polyethylene, produced over homogeneous catalyst bis[N-(3-tert-butyl salicylidene)anilinato]zirconium(IV) dichloride tBu-L2ZrCl2/MAO have been studied. The data on the number of active centers (CP) and propagation rate constants (kP) at different polymerization time have been obtained as well. It was found that at a short polymerization time two types of active centers, producing low molecular weight PE (Mw = (4–10) × 103 g mol−1) are formed. The number of these centers was estimated to be 11% of total zirconium complex and their reactivity is very high (the kP value was found to be 54 × 103 L mol−1 s−1 at 35 °C). High initial activity of the catalyst fell with the increase in polymerization time, whereas the polydispersity values of the resulting PE increase due to formation of new centers, producing high molecular weight PE (Mw = (30–1300) × 103 g mol−1). It was found that the decrease in activity is caused by reducing the initial active centers number and lower reactivity of the new-formed centers (kP = 17 × 103 L mol−1 s−1).

Hydroconversion of sunflower oil on Pd/SAPO-31 catalyst

This work presents results from the hydroconversion of sunflower oil on the bifunctional Pd/SAPO-31 catalyst as a perspective technological way for single-stage production of hydrocarbons in the diesel fuel range that have improved low-temperature properties. Transformation of sunflower oil was performed at temperatures of 310–360 °C and WHSV = 0.9–1.6 h −1, under a pressure of 2.0 MPa in a laboratory flow reactor. Gaseous and liquid reaction products were analyzed by GC using an internal standard method as well as by 1H and 13C NMR spectroscopy. At temperatures 320–350 °C, liquid reaction product contained only hydrocarbons, the main components were identified as C 17 and C 18 n-alkanes and i-alkanes. Pd/SAPO-31 catalyst demonstrated high initial activity for the hydroconversion of the feed and good isomerizating properties, but its deactivation was followed after several hours of operation. Physico-chemical properties of both fresh and spent catalysts were compared. The influence of reaction conditions on the composition of the reaction products is also discussed.

Study on Au/Al 2O 3 catalysts for low-temperature CO oxidation in situ FT-IR

Au/Al 2O 3 catalyst was prepared by a modified anion impregnation method and investigated with respect to its initial activity and stability for low-temperature CO oxidation. The activity changes of the catalyst were examined after separate treatment in CO+O 2 or CO 2+O 2. Furthermore, in situ FT-IR studies were performed to investigate the species on the surface when CO or CO+O 2 or CO 2+O 2 was selected separately as adsorption gas. The results showed that Au/Al 2O 3 catalyst exhibited very high initial activity, but the catalytic activity was found to decrease gradually during CO oxidation with time on stream. And also, the activity of the catalyst declined after treatment in CO+O 2 or CO 2+O 2. The formation and accumulation of carbonate-like species during CO oxidation or treatment in CO+O 2 or CO 2+O 2 might be mainly responsible for the activity decrease, which was reversible.

Growth and Interface Evolution of HfO2 Films on GaAs(100) Surfaces

The initial film growth (2–100 cycles) and the interface evolution of thin films on GaAs surfaces were investigated for an atomic layer deposition chemistry that utilizes tetrakis(ethylmethyl) amino hafnium and at . Starting surfaces include native oxide and HF or -etched substrates. X-ray photoelectron spectroscopy shows that deposition on native oxide GaAs surfaces results in the gradual consumption of the arsenic and gallium oxides. Arsenic oxides are easier to remove, leaving some metallic arsenic–arsenic suboxide at the interface. The removal of the gallium oxides is slower, and some residual and are detected after 100 process cycles. High resolution transmission electron microscopy confirms the presence of an almost sharp interface for the 100 cycle (12 nm) film and indicates that the as-deposited film is polycrystalline. The depositions on either HF or -etched substrates result in a sharp interface with very little residual gallium oxide and arsenic suboxide present. Rutherford backscattering spectroscopy shows that steady-state growth comparable to that achieved on is reached after ALD cycles for all GaAs surfaces; however, high initial surface activity is detected for the etched surfaces.

Catalytic characterization of pure SnO 2 and GeO 2 in methanol steam reforming

Structural changes of a variety of different SnO, SnO 2 and GeO 2 catalysts upon reduction in hydrogen were correlated with associated catalytic changes in methanol steam reforming. Studied systems include SnO, SnO 2 and GeO 2 thin film model catalysts prepared by vapour phase deposition and growth on polycrystalline NaCl surfaces and, for comparison, the corresponding pure oxide powder catalysts. Reduction of both the SnO 2 thin film and powder at around 673 K in 1 bar hydrogen leads to a substantial reduction of the bulk structure and yields a mixture of SnO 2 and metallic β-Sn. On the powder catalyst this transformation is fully reversible upon oxidation in 1 bar O 2 at 673 K. Strongly reduced thin films, however, can only be re-transformed to SnO 2 if the reduction temperature did not exceed 573 K. For GeO 2, the situation is more complex due to its polymorphism. Whereas the tetragonal phase is structurally stable during reduction, oxidation or catalytic reaction, a small part of the hexagonal phase is always transformed into the tetragonal at 673 K independent of the gas phase used. SnO 2 is highly active and CO 2 selective in methanol steam reforming, but the initial high activity drops considerably upon reduction between 373 and 573 K and almost complete catalyst deactivation is observed after reduction at 673 K, which is associated with the parallel formation of β-Sn. In close correlation to the structural results, the catalytic activity and selectivity can be restored upon an oxidative catalyst regeneration at 673 K. Tetragonal GeO 2 exhibits only a small activity and no pronounced selectivity to either CO or CO 2, at least after reduction. In its fully oxidized state release of surface/lattice oxygen results in a non-catalytic formation of CO 2 by oxidation of CO originating from catalytic dehydrogenation.