Positive Catalytic Effect Research Articles

Theoretical studies on atmospheric reactions of CH2FO2 with HO2 and HO2⋅H2O complex

The formations of CHFO, 1O2, O3 and 3O2 in CH2FO2+HO2 and CH2FO2+HO2⋅H2O reaction are studied by employing the quantum chemical calculations with B3LYP and CCSD(T) theoretical methods, canonical variational transition (CVT) state theory with small curvature tunneling (SCT) correction. The calculated results show that the formations of CHFO and 3O2 are main products in the naked reaction of CH2FO2+HO2. When water is added, the formations of CHFO and O3 are main products in CH2FO2+HO2⋅H2O reaction. Moreover, the calculated rate constants for the title reaction without and with a water molecule show that, although the single water molecule plays a positive catalytic effect on enhancing the rate for CHFO and O3 formation, in humid conditions the effective rate of CH2FO2+HO2 reaction will changes little with respect to dry conditions.

Catalytic activity and surface characteristics of layered Zn–Al–Si materials supported platinum

The present work aims at the preparation and characterization of novel catalysts based on layered double hydroxide structures (LDHs) containing Zn 2+, Al 3+ and Si 4+ cations in host layers and platinum species supported over the surface of these structures. LDHs with different Zn/Al/Si ratios were prepared via a co-precipitation method. Characterization of Zn–Al–Si layered double hydroxides was carried out using energy-dispersive X-ray spectrometry, X-ray powder diffraction, infrared spectra, thermal analyses and scanning electron microscopy. Experimental results revealed the presence of only crystalline phases of layered double hydroxides containing about 20–40 mol% of aluminum and silicon. These novel materials are commonly used as supports for platinum catalysts. Layered double hydroxide supported platinum samples were characterized through nitrogen adsorption–desorption, X-ray powder diffraction, infrared spectra and thermal analyses. The activity of the prepared platinum catalysts was tested through cyclohexane dehydrogenation and n-hexane cracking using a pulse flow system. Our results suggested that the Zn–Al–Si layered double hydroxides have a positive catalytic effect towards dehydrogenation.

Synthesis and photocatalytic properties of nano-MoS 2/kaolin composite

A nano-MoS 2/kaolin composite was synthesized by calcining a MoS 3/kaolin precursor in H 2, which was obtained via a quick deposition of MoS 3 on kaolin under a strong acidic condition. The obtained nano-MoS 2/kaolin composite was characterized using X-ray diffraction spectroscopy, Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy, high-resolution transmission electron microscopy, thermal analysis, ultraviolet–visible spectroscopy, and Fourier transform infrared spectroscopy. The results show that the composite had a 16 m 2/g BET surface area. MoS 2 in the composite was composed of layered structures with thickness of ∼5 nm and length of ∼10 nm. The composite contained an intensive absorption at 380–500 nm, which is in the visible light region, and presented a positive catalytic effect on removing methyl orange from the aqueous solution. The catalytic activity of the composite was influenced by the initial concentration of methyl orange, the amount of the catalyst, the pH value, and the degradation temperature. In addition, the composite catalyst could be regenerated and repeatedly used via filtration. The deactivating catalyst could be reactivated after catalytic reaction by heating at 450 °C for 30 min in H 2. The kaolin can decrease the sizes of nano-MoS 2 and improve the photo absorption of the composite. Thus, the composite shows excellent catalytic properties. Moreover, the kaolin mineral is very cheap and the using of the composite is very low-cost and practical.

The effect of morphology and size on the photocatalytic properties of MoS2

The photocatalytic properties of MoS2 samples including nano-ball, nano-slice and bulk 2H-MoS2 were evaluated and compared with that of the anatase TiO2 using the degradation reaction of methyl orange under visible light. The catalytic behaviors of the samples were also characterized using transmission electron microscopy, Brunauer-Emmett-Teller (BET) surface area, ultraviolet-visible spectroscopy, and FTIR spectroscopy. The results show that the bulk MoS2 and the anatase TiO2 were almost inactive under visible light. The nano-slice presented the most positive catalytic effect because it has a wide absorption at 400–700 nm and a high BET surface area. Though the BET surface area of the nano-ball was lower than that of the nano-slice, it has an active curved basal surface and presented a catalytic activity close to that of the nano-slice. Moreover, the MoS2 nano-slice catalyst could be conveniently regenerated after filtration and drying.

Synthesis of nano-MoS2/TiO2 composite and its catalytic degradation effect on methyl orange

A nano-MoS2/TiO2 composite was synthesized in H2 atmosphere by calcining a MoS3/TiO2 precursor, which was obtained via a quick deposition of MoS3 on anatase nano-TiO2 under a strong acidic condition. The obtained nano-MoS2/TiO2 composite was characterized by X-ray diffraction spectroscopy, Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive spectrometry, ultraviolet–visible spectroscopy, and Fourier transform infrared spectroscopy. The results show that the composite had a high BET surface area because of its small size and irregularly layered structure. MoS2 in the composite was composed of typical layered structures with thicknesses of 2–8 nm and lengths of 10–40 nm. The composite contained a wide and intensive absorption at 400–700 nm, which is in the visible light region, and presented a positive catalytic effect on removing methyl orange from the aqueous solution. The catalytic activity of the composite was influenced by the initial concentration of methyl orange, the amount of the catalyst, the pH value, and the degradation temperature. In addition, the composite catalyst could be regenerated and repeatedly used via filtration three times. The deactivating catalyst could be reactivated after catalytic reaction by heating at 450 °C for 30 min in H2.

Influence on hydrogen production of the minor components of natural gas during its decomposition using carbonaceous catalysts

In this work, the catalytic decomposition of the minor hydrocarbons present in natural gas, such as ethane and propane, over a commercial carbon black (BP2000) is studied. The influence of the reaction temperature on the product gas distribution was investigated. Increasing reaction temperatures were found to increase both hydrocarbon conversion and hydrogen selectivity. Carbon produced by ethane and propane was predominantly deposited as long filaments formed by spherical aggregates with diameters on the order of nanometres. Furthermore, the influence of ethane and propane on methane decomposition over BP2000 was also investigated, showing enrichment in hydrogen concentration with the addition of small amounts of these hydrocarbons in the feed. Additionally, the positive catalytic effect of H 2S on methane decomposition over BP2000 is addressed.

Positive and negative catalytic effects of a nickel mesh catalyst for the partial oxidation of ethane

The catalytic reactions between O 2 and hydrocarbons are an important class of reactions in energy and chemical industries. This study aims to investigate the complicated reactions involving reactive radicals on the catalyst surface and in the gas phase during the partial oxidation/combustion of light alkanes. In order to avoid intra-particle transport constraints associated with the traditional porous catalysts, a non-porous nickel mesh catalyst has been used in this study for the partial oxidation of ethane with O 2 at 625 °C at atmospheric pressure. The catalytic effects of the nickel mesh strongly depended on the flow rate of gas reactants passing through the mesh. At a low gas flow rate, the nickel mesh catalyst showed negative effects for the oxidation of ethane. At a high gas flow rate, the same catalyst showed positive catalytic effects. Our results can be explained by considering the selective/preferential adsorption and desorption of different radicals onto and from the catalyst surface. It is believed that the desorption of some surface generated radicals (e.g. OH radicals) may be greatly affected by the thickness of the mass transfer gas film around the mesh wires, which in turn is affected by the gas flow rate passing through the mesh.

Effective Electrocatalytic Oxidation of Glucose at Platinum Nanoparticle-based Carbon Electrodes

Abstract The effective direct electrocatalytic oxidation of glucose in alkaline solution at electrochemically deposited Pt nanoparticle-modified glassy carbon electrode is reported, for the first time. Catalytic oxidation of glucose was observed and comparison to a previously reported system based on gold nanoparticles showed a significant positive catalytic effect of the prepared electrodes in the current study: a considerable shift of the oxidation peak potential by ca. 280 mV was found. I–t measurements revealed that only a very minute Pt loading as small as ca. 9.2×10−3 mg cm−2 is required to obtain comparable current densities with those at Au nanoparticles.

Two-State Model Based on Electron-Transfer Reactivity Changes to Quantify the Noncovalent Interaction between Co(NH3)5Cl2+ and 18-Crown-6 Ether: The Effect of Second-Sphere Coordination on Electron-Transfer Processes

The electron-transfer reaction between [Fe(CN)6]4- and [CoCl(NH3)5]2+ was studied in the presence of 18-crown-6 ether (18C6) in different reaction media constituted by water and acetonitrile as organic cosolvent at 298.2 K. The results corresponding to this reaction show a clear influence of 18C6 on the kinetics: a positive catalytic effect. Trends in the observed reactivity are explained by a change in the degree of association of one of the reactants (the cobalt complex) with the 18C6. This association is governed by an equilibrium constant that depends on the dielectric constant of the medium. The results show an increase of the rate constants for the electron-transfer process as the 18-crown-ether concentration increases and an increase of the binding free energy of the cobalt complex to the 18C6 when the electrostatic field of the medium becomes weaker. An analysis of the experimental data allows not only the reactivity changes associated with adducts formation processes for an electron-transfer reaction but also information on the binding free energy of the cobalt complex to the 18C6 to be obtained, which can be quantified by using a two-state model. We have found a good correlation between the energy of binding and the Kosower's Z-value. The influence of the 18C6 in the intramolecular electron transfer in the binuclear complex [Fe(CN)5pzCo(NH3)5] has been also investigated.

Influence of salts on the dehydration of several biomass-derived polyols in sub- and supercritical water

We investigated the dehydration of several biomass-derived polyols in sub- and supercritical water, in particular m-erythritol, 1,2-propanediol and 1,3-propandiol. The resulting main products were 1,4-anhydroerythritol and propionaldehyde. The additives tested for their catalytic performance were among others zinc, nickel, copper, magnesium and sodium sulfate as well as sulfuric acid. A positive catalytic effect of bivalent transition metal salts was found. Initial educt and ZnSO 4 concentration variations were carried out in order to determine the reaction orders. Further, activation energies and activation volumes were measured for zinc catalysed dehydrations of the above-mentioned polyols. Finally, a possible explanation for the reaction enhancing or inhibiting effect of different salts is given and discussed.

Effect of metal ad-layers on Au(1 1 1) electrodes on electrocatalytic reduction of oxygen in an alkaline solution

Oxygen reduction reaction was investigated in an O 2-saturated 0.1 M NaOH solution at Au(1 1 1) single crystal electrodes modified with various ad-metals (Cu, Ag and Bi) by underpotential deposition (upd). An increase in the catalytic activity was observed upon deposition of metal ad-atoms submonolayer for all prepared electrodes: Cu ad-layer was found, for the first time, to show a very interesting positive catalytic effect in contrast with reported data in acidic media, i.e., an apparent four-electron reduction process due to considerable enhancement of the disproportionation of hydrogen peroxide on the 1/3 monolayer (ML) Cu-modified Au(1 1 1) electrode. An interesting catalytic activity was also obtained at the 1/3 ML Ag ad-atoms modified Au(1 1 1) electrode, where a significant increase in reduction current was shown to suggest a four-electron reduction of oxygen to water. The Bi ad-atoms modified Au(1 1 1) electrode, Bi(2 × 2)–Au(1 1 1), showed positive catalytic activity by a limiting current of twice higher than at a bare Au(1 1 1) electrode with peak potential at ca. −0.38 V vs. Ag|AgCl|KCl(sat).

Determination of nickel(II) by its influence on the oxidation of 3,3’,5,5’-tetramethylbenzidine with periodate

The negative catalytic action of nickel(II) in the oxidation of 3,3’,5,5’-tetramethylbenzidine with periodate and its positive catalytic effect in the same reaction in the presence of an activator (dimethylglyoxime) have been applied to the development of analytical procedures for the determination of this metal ion, which proved to be more sensitive in the case of a positive catalytic effect (the detection limit of nickel is 103 times lower).

Electrocatalytic oxidation of sugars on silver-UPD single crystal gold electrodes in alkaline solutions

A highly catalytic system for sugar oxidation in alkaline media is presented, for the first time, in which glucose oxidation takes place at ca. −0.44 V (vs. Ag|AgCl). Modification of Au(1 1 1) single crystal surface by under potential deposition (UPD) was carried out for a variety of metals and catalytic effect for sugar oxidation has been studied in 0.1 M NaOH. UPD of Ag ad-atoms on Au electrodes were of the best catalytic activity compared to other metals (Cu, Co, Ru, Cd, Ir, and Pt, etc.). For aldose type monosaccharide studied (glucose, mannose and xylose) as well as for aldose-containing disaccharides (maltose and lactose), one significant oxidation peak was obtained, however, no significant oxidation current was observed for disaccharides like sucrose. Gluconolactone and mannolactone gave no oxidation current at negative potentials at which glucose was oxidized, indicating no more than two-electron oxidation took place. With Ag ad-atoms coverage of ca. 0.3 monolayer leads to a positive catalytic effect expressed through a negative shift of ca. 0.14 V (glucose case) on the oxidation potential and a slight increase in peak current. At the Au(1 0 0) surface similar results to those at an Au(1 1 1) electrode were also observed.

Preparation and Characterization of Electrolessly Deposited Platimum and Palladium Nanoparticles on Pyrolyzed Photoresist Films on Silicon Substrates

The effects of metal depositions on pyrolyzed photoresist films (PPF) grown on silicon substrates were investigated. A silicon chip, spin-coated with a positive photoresist was pyrolyzed through heating to form a PPF, or a conductive carbon film. For increasing periods of time, nanometersized metal particles of platinum and palladium were spontaneously deposited on conductive carbon films by immersion in solutions of 0.049% HF containing 100 ppm, 200 ppm, and 500 ppm concentrations of metal ions Pt2+ or Pd2+. Following each hour of deposition, the electrochemical behavior of the metal-deposited carbon films were investigated by cyclic voltammetry, utilizing a 0.1 M H2SO4 electrolyte system. The electron-transfer rates and characteristics of hydrogen evolution exhibited positive catalytic effects when the platinum and palladium nanoparticles were deposited on the carbon films. Scanning electron microscopy and energy-dispersive x-ray analysis were employed to characterize the surface morphology and distribution of metal nanoparticles on the PPF surface based on metal ion concentration and deposition time. The depositions of metal nanoparticles accelerate the electron transfer process, which could improve the efficiency and performance of PPF electrodes in the production of hydrogen fuel.

Effect on Liquefaction of Pulverizing Coal and Catalyst to Fine Particles

The effect on liquefaction of the pulverization of coal and catalyst to ultrafine particles with the recently developed slurry jet mill was examined. Experiments were conducted in a 200-mL stainless steel autoclave with stirrer at 420, 440, and 450 °C under 8.5 MPa of initial hydrogen pressure for 60 min. The conversion calculated from the amount of THFI (THF-insoluble fraction) for thermal liquefaction without catalyst at 440 °C were almost the same (90 wt %) for 100 mesh coal (average particle diameter: 80 μm) and finely pulverized coal (average particle diameter: 8 μm). However, the gas yield was low and the HS (n-hexane-soluble fraction) yield was high at 32.6 wt % for finely pulverized coal. In catalytic liquefaction, the HS yield was 2 to 5 wt % higher and the THFS (THF-soluble fraction) yield was 3 to 5 wt % lower for finely pulverized coal compared with the yields for 100 mesh coal. The HS yield reached 45.1 wt % for finely pulverized coal when 4.4 wt % of finely pulverized iron oxide−sulfur catalyst was used. This indicates that the diffusion of the radicals, produced from bond dissociation, to solvent at the first-stage cracking and the rapid hydrogen transfer from solvent to the radicals during the second-stage reaction are enhanced by the larger active surface of the finely pulverized coal. A similar increase in the HS yield to 52.4 wt % by the addition of 0.5 wt % cationic surfactant to the finely pulverized coal slurry was observed, while an HS yield of 45.1 wt % was obtained without surfactant. We conducted additional experiments on liquefaction of a coal−used tire mixture. HS yields were enhanced by the addition of tires, and a positive catalytic effect on coal liquefaction of zinc/carbon black from the used tires was indicated.

Decomposition of t-Butanol in Water by γ-Irradiation Combined with Ozone; Cupric Ion Effect

Abstract When t-butanol in aqueous system was decomposed by simultaneous application of γ-rays and ozone treatment, the addition of the cupric ion (Cu2+) drastically improved the efficiency of the removal of organic substances from water. The major reason for the remarkable decrement of total organic substances is the positive catalytic effect of Cu2+ on the oxidation of carboxylic acids.

Effect of 2-hydroxypropyl-β-cyclodextrin on the stability of prostaglandin E 2 in solution

The potential use of 2-hydroxypropyl-β-cyclodextrin (HP-β-CyD) in the stabilization of prostaglandin E 2 (PGE 2) was investigated. Inclusion complexation of PGE 2 with HP-β-CyD was estimated by circular dichroism spectroscopy. The effect of HP-β-CyD on the dehydration rate of PGE 2 and the isomerization rate of PGA 2 was examined by comparing the rate constant of PGE 2 alone with that of the inclusion complex of PGE 2 with HP-β-CyD in each buffered solution. The dehydration rate of PGE 2 and the isomerization rate of PGA 2 under acidic conditions were decreased by HP-β-CyD, while the rates under basic conditions were increased, probably due to positive catalytic effects on the reactions. The retardation of the dehydration and isomerization rates at low pH might be the effect of inclusion complexation with HP-β-CyD.

Catalytic effects of silver in the microbiological leaching of finely ground chalcopyrite-containing ore materials in shake flasks

The microbiological leaching of copper ores was evaluated with samples that contained chalcopyrite (CuFeS 2), pyrite (FeS 2), pyrrhotite (Fe 1− x S), and sphalerite (ZnS) in varying proportions as the main sulfide minerals. The solubilization of copper from chalcopyrite was slow in contrast to the rapid solubilization of zinc. The addition of up to 30 mg/l silver, either as a sulfate or nitrate salt, enhanced the bacterial leaching of copper from chalcopyrite. The positive catalytic effect was related to the concentration of the silver added. The enhancement of the copper leaching due to the silver addition was negligible in the absence of bacteria. Only trace concentrations of silver were detected in leach solution samples. The leaching of iron and zinc was inhibited by silver addition and a transient period of depressed Eh was typically associated with this phase. The addition of silver also enhanced the bacterial leaching of a purified chalcopyrite sample. Increased solubilization of copper and iron was obtained concurrently with the formation of sulfate. Mass balance studies and stoichiometric calculations indicated elemental sulfur formation and the precipitation of iron and sulfate during the leaching. Potassium jarosite [KFe 3(SO 4) 2(OH) 6] was identified by X-ray diffraction in Fe(III)-containing precipitates.

The electrocatalytic influence of underpotential heavy metal adsorbates on the electrochemical behaviour of ammonia and hydroxylamine on platinum

The influence of the underpotential deposition of Pb, Tl and Bi on the oxidation of ammonia and on the reduction and oxidation processes of hydroxylamine on platinum has been studied in alkaline solutions. Pronounced inhibition effects caused by underpotential metal adsorbates have been detected for either the oxidation of ammonia or the reduction of hydroxylamine. On the other hand, the same metal adsorbates markedly increase the electrocatalytic activity of the Pt electrode for hydroxylamine oxidation. The observed negative and positive catalytic effects have been interpreted in terms of the electronic and adsorption properties of the Pt substrate, which are strongly modified by the underpotential metal adsorbates.

Oxygen reduction electrocatalysis by underpotential deposited metal atoms at different single crystal faces of gold and silver

Electrocatalytic effects of underpotential lead and bismuth adsorbates on the cathodic reduction of O 2 and H 2O 2 in perchloric acid solution obtained on rotating disc Au and Ag single crystal surfaces of (111), (100) and (110) crystallographic orientation are discussed. On the clean Ag substrates the complete 4-electron reduction of O 2 to H 2O takes place whereas on Au the incomplete 2-electron reduction to H 2O 2 predominantly occurs, exhibiting pronounced structural effects. The underpotential deposition of Pb on Ag surfaces leads to a partial inhibition of the O 2 reduction whereas on Au (111) and (100) surfaces positive catalytic effects are observed. Measurements of H 2O 2 reduction indicate that an important part of the catalytisis on Ag and Au can be attributed to a decrease or increase of the rate of further reduction of H 2O 2 to H 2O. The results are discussed in terms of different adsorption models for the O 2 molecule.