Catalytic Effect Of Metal Ions Research Articles

DL‐malic acid for inhibiting the re‐ignition of long‐flame coal and its micro‐reaction mechanism

AbstractTo study the metal ion chelating agent (DL‐malic acid) inhibiting oxidation characteristics of residual coal in goaf, the microscopic thermal transformation characteristics of the treated coal samples were obtained using apparent morphology, infrared spectroscopy, free radical testing, and thermal analysis. The results demonstrate that after the addition of malic acid, the sphericity and roundness of the coal samples decrease, and the small fractured particles accumulate in the pores of the oxidized coal samples and, thereby, reduce the number of coal–oxygen contact sites. The addition of 10% malic acid promotes the conversion of functional groups (FG) and free radicals in pre‐oxidized coal, inhibits the catalytic effect of metal ions, generates more active sites, and increases the total heat release during the combustion process. There are strong endothermic points in the malic acid‐treated coal samples, and the free water evaporation blocked by small particles in the holes delays the initial heat release temperature of the coal samples. Pre‐oxidation can promote changes in the valence state of metal ions in coal, increase the adhesion between broken pre‐oxidized coal particles via malic acid chelation, and lose the catalytic effect of metal ions; this inhibits the process of oxidative re‐ignition of coal samples.

Experimental Study of New Antioxidant to Inhibit Spontaneous Combustion of Coal

ABSTRACT Free radicals and metal ions are key factors causing coal spontaneous combustion. In order to effectively suppress coal spontaneous combustion, experiments were conducted using luteolin as an inhibitor, luteolin is abbreviated as LUT. The influence of different concentrations of LUT on the spontaneous combustion heat characteristics of coal was tested using a C600 high-precision microcalorimeter, and the inhibition mechanism was inferred by FTIR. The experimental results show that LUT is an effective coal oxygen inhibitor, under the same action conditions, different concentrations of LUT can absorb heat to different degrees, delay the initial exothermic temperature of coal, prolong the heat absorption phase of coal. Compared with raw coal, 6 wt% LUT absorbs the most heat, the starting exothermic temperature is delayed by 46°C, and the activation energy is increased by 47.89 kJ/mol, the functional group -OH content decreased by 43.4%, -CH3 decreased by 32.1%, -CH2-decreased by 37.76%. Based on this, the mechanism of inhibition is inferred, LUT not only removes free radicals (ROO•) during the chain initiation stage and captures free radicals (•OH) in the reaction chain but also chelates metal ions to inhibit the catalytic effect of metal ions during the free radical reaction, which can play a dual role in preventing free radical generation and interrupting the free radical chain reaction. The results of the study can provide a novel, environmentally friendly and effective way to prevent the spontaneous combustion of coal.

Determination of elemental impurities in lomefloxacin hydrochloride ear drops by ICP-MS Using Oxygen Reaction Mode and study of their catalytic effect on photodegradation reaction.

According to the requirements of ICH Q3D, a method for simultaneous determination of 12 element impurities in lomefloxacin hydrochloride ear drops by inductively coupled plasma mass spectrometry (ICP-MS) was established. However, this product contains high concentrations of organic compounds such as glycerol and ethanol, and there will be interference of soluble carbon when it is determined by direct injection method. Therefore, we applied ICP-MS using oxygen reaction mode to reduce the effect of high organic matter on plasma body. The catalytic effect of trace metal ions on the photodegradation of lomefloxacin hydrochloride was also investigated. The sample was dissolved, diluted and directly determined by direct injection using oxygen reaction mode of ICP-MS with 45 Sc, 73 Ge and 115 In as the internal standards. The direct injection using oxygen reaction mode was equipped with argon-oxygen mixer. To investigate the catalytic effect of metal ions on photodegradation, a series of combinations of lomefloxacin hydrochloride mixed with different metal ions were designed. After being irradiated under ultraviolet light for 10 days, the photodegradation impurities in combinations were determined by HPLC. The linear relationships in the corresponding concentration range for 12 element impurities were good (r>0.9993). Limits of detection were between 0.002~1.294 ng·mL-1 . The average recoveries were 93.7%-108.2%, and the precision RSD were 0.04% ~ 0.55% (n=6). The experimental results showed that metal ions had a certain catalytic effect on photodegradation of lomefloxacin when EDTA, Mg2+ and Cu2+ coexisted. The ICP-MS using oxygen reaction mode is suitable to direct determination of the sample rich in organic matter without digestion, can effectively eliminate the interference of high organic matter in this product. The established method was rapid, sensitive, accurate, and can be used for the quality control of elemental impurities in lomefloxacin hydrochloride ear drops.

Research on chemical resistance characteristics of water-immersed coal with different metamorphic degrees

In order to reduce the risk of spontaneous combustion of coal left after long-term flooding in the goaf of the mine, in this paper, the inhibitory properties of different inhibitors on two kinds of water-immersed coals with different metamorphic degrees were studied in depth. The experiment selected Pingzhuang brown coal and Shaqu coking coal as research objects. The raw coal and water-immersed coal samples were compared and analyzed by thermogravimetric experiment method and Fourier transform infrared spectroscopy experiment method. The study showed that the activation temperature of brown coal and coking coal decreased by 7.91 and 2.25 °C respectively, and the activation energy decreased by 43.18 kJ/mol and 20.58 kJ/mol respectively. The natural tendency of coal was enhanced after water immersion, and water immersion had a greater impact on low-metamorphic brown coal. After adding four kinds of inhibitors, MgCl2, TEMPO, TPPI and PA to the two water-immersed coals, it was found that TPPI could significantly reduce the heat release rate of water-immersed brown coal, and the reduction value was 10.49 W/mg. The dry cracking temperature of water-immersed brown coal increased by 11.75 °C, and PA greatly increased the combustion activation energy of water-immersed coking coal by 25.77 kJ/mol. Meanwhile, it was found from the microscopic active groups that TTPI increased the content of water-immersed brown coal ether bonds by 4.84%. The absorption peak intensity of oxygen-containing functional groups such as C=O was significantly weakened. Similarly, PA also produced a large number of stable ethers in water-immersed coking coal, whose content increased by 5.21%, and the hydroxyl content decreased most significantly. The decomposition of TPPI into phosphoric acid after heating can inhibit the growth of active groups such as a large number of oxygen-containing functional groups in the water-immersed brown coal, thereby reducing the risk of spontaneous combustion. As a metal chelator, PA can reduce the catalytic effect of metal ions in water-immersed coking coal with fewer active groups, and inhibit coal spontaneous combustion by generating stable metal complexes to increase activation energy. This indicated that TTPI had the best inhibitory effect on water-immersed brown coal, while PA was more suitable for water-immersed coking coal.

Metabolic engineering of Bacillus subtilis with an endopolygalacturonase gene isolated from Pectobacterium. carotovorum; a plant pathogenic bacterial strain.

Pectinolytic enzymes or pectinases are synthesized naturally by numerous microbes and plants. These enzymes degrade various kinds of pectin which exist as the major component of the cell wall in plants. A pectinase gene encoding endo-polygalacturonase (endo-PGase) enzyme was isolated from Pectobacterium carotovorum a plant pathogenic strain of bacteria and successfully cloned into a secretion vector pHT43 having σA-dependent promoter for heterologous expression in Bacillus subtilis (WB800N).The desired PCR product was 1209bp which encoded an open reading frame of 402 amino acids. Recombinant proteins showed an estimated molecular weight of 48 kDa confirmed by sodium dodecyl sulphate–polyacrylamide-gel electrophoresis. Transformed B. subtilis competent cells harbouring the engineered pHT43 vector with the foreign endo-PGase gene were cultured in 2X-yeast extract tryptone medium and subsequently screened for enzyme activity at various temperatures and pH ranges. Optimal activity of recombinant endo-PGase was found at 40°C and pH 5.0. To assay the catalytic effect of metal ions, the recombinant enzyme was incubated with 1 mM concentration of various metal ions. Potassium chloride increased the enzyme activity while EDTA, Zn++ and Ca++, strongly inhibited the activity. The chromatographic analysis of enzymatic hydrolysates of polygalacturonic acid (PGA) and pectin substrates using HPLC and TLC revealed tri and tetra-galacturonates as the end products of recombinant endo-PGase hydrolysis. Conclusively, endo-PGase gene from the plant pathogenic strain was successfully expressed in Bacillus subtilis for the first time using pHT43 expression vector and could be assessed for enzyme production using a very simple medium with IPTG induction. These findings proposed that the Bacillus expression system might be safer to escape endotoxins for commercial enzyme production as compared to yeast and fungi. Additionally, the hydrolysis products generated by the recombinant endo-PGase activity offer their useful applications in food and beverage industry for quality products.

Study on the characteristics and mechanism of DL-malic acid in inhibiting spontaneous combustion of lignite and bituminous coal

Inhibitors play an important role in preventing and controlling coal spontaneous combustion (CSC). In this study, the effect of DL-malic acid, an environment-friendly inhibitor, on the CSC characteristics of lignite and bituminous coal was studied. A contrastive analysis was conducted on the inhibitory effects of malic acid solution with different concentrations on CSC. Moreover, the inhibition characteristics of malic acid on coal samples with different soaking times were analyzed. In so doing, the inhibition mechanism of malic acid on CSC was revealed. It was found that malic acid can obviously inhibit CSC of lignite and bituminous coal. After the treatment of malic acid, the concentrations of CO released by coal samples during oxidation fall, and the crossing-point temperatures increase. Compared with the raw coal, the acid-treated coal corresponds to lower concentrations of free radicals and functional groups –CH2- and –CH3 and boasts better thermal stability before 150 °C. A contrastive analysis on the inhibitory effects on coal samples with different soaking times disclose that the water-soaked coal sample is inhibited better in CSC by malic acid than the unsoaked coal sample. The malic acid solution can effectively weaken the catalytic effect of metal ions in coal and inhibit the generation of free radicals, thus inhibiting CSC well.

Demonstrating solvent management technologies for an aqueous AMP/PZ solvent

Within the transatlantic project LAUNCH, solvent management strategies are validated by test campaigns at four capture plants with an adequate plant size and in an industrial environment (3 pilot facilities with a capture capacity of up to 0.4 tCO2/h and a commercial plant with 12 tCO2/h). At the capture pilot plant at Niederaussem, which separates in 24/7 mode the CO2 from the flue gas of the adjacent 1,000 MW lignite-fired block of the power plant, three degradation control technologies with different effect mechanisms are investigated in testing campaigns with the so-called CESAR1 solvent (>14,000 testing hours with an aqueous solution of 3.0 molar (~26.74 wt.-%) 2-amino-2-methylpropan-1-ol (AMP) and 1.5 molar (~12.92 wt.-%) piperazine (PZ): adsorptive removal of trace elements from the solvent by active carbon, removal of ionic trace elements from the solvent by ion exchange and removal of NO2 from the flue gas by thiosulfate/sulfite dosing. Activation of carbon and particle filters after 5,184 and 6,048 hours testing time resulted in a removal of coloring agents, iron and nickel from the solvent. Additionally, the increase of Cl-, SO42- and NO3- concentrations could be reduced, but no clear effect on the solvent degradation rate was observed. Anionic degradation products and trace components can be effectively removed from the aged solvent by ion exchange with an anionic exchange resin. Laboratory tests with the anionic resin and three cationic resins provide promising results to remove metal ions from the solvent. As iron can be removed from the solvent using the anionic resin, but not nickel, this is a strong indication that iron is dissolved in the solvent in the form of an anionic complex, which highlights the importance of the solvent matrix when investigating the catalytic effect of metal ions on amine degradation. Despite a concentration of 175 mmol/kg thiosulfate and 32 mmol/kg sulfite and a pH value of >8.5 of a scrubbing solution in a pre-treatment scrubber, it was not possible to remove NO2 from the flue gas. Laboratory tests confirmed the effect of the pre-treatment concept. Either the mass transfer is not sufficient in the scrubber or new NO2 is formed after the pre-treatment from NO in the flue gas. This will be

Efeitos dos Íons Fe3+, Fe2+, Co2+ e Cr3+ na Estabilidade Oxidativa e Cinética da Reação de Oxidação do Biodiesel com e sem a Adição de Extrato de Alecrim

Since biodiesel has unsaturated esters in its composition, it is susceptible to oxidation reaction. Studies have shown that small traces of transition metals are able to promote biodiesel oxidation. Biodiesel samples containing Cr3+, Co2+, Fe2+ and Fe3+ ions, in the presence and absence of rosemary extract, were submitted to the Rancimat test at 110 oC to verify the biodiesel oxidative stability against the catalytic action of these ions. The results were compared with control samples without and with rosemary extract. The control without extract presented induction period of 8.29 hours and the control with extract 11.42 hours. Regarding the catalytic effect of metal ions on biodiesel, in the absence of extract the sample containing Fe3+ showed induction period at 0.25 hours, indicating total degradation of the biofuel. For the samples containing the other cations, in the absence of the extract the catalytic effect followed the order Fe2+>Cr3+>Co2+. In the presence of extract the order presented was Fe3+>Fe2+>Co2+>Cr3+.

Experimental study on the inhibitory effect of ethylenediaminetetraacetic acid (EDTA) on coal spontaneous combustion

The inorganic salts in coal contain a certain number of metal ions, among which transition metal ions can exert a certain catalytic effect on coal spontaneous combustion by reducing the activation energy of coal oxygen reaction. Therefore, the addition of metal chelating agent in coal will definitely reduce the catalytic effect of metal ions, so as to inhibit coal spontaneous combustion. In this paper, the inhibitory effect of a common metal chelating agent ethylenediaminetetraacetic acid (EDTA) on coal spontaneous combustion was studied. Four coal samples were selected in this study. First, basic data such as the types and contents of transition metal elements in coal samples were measured via X-ray fluorescence (XRF). Then, thermal analyses, infrared spectrum experiments, low-temperature oxidation experiments and crossing point temperature experiments were performed on WL coal samples before and after EDTA treatment. The experimental results show that there is no mass gain caused by oxygen adsorption in the EDTA-treated coal sample throughout the heating process. In addition, the treated coal sample exhibit a great reduction in its content of oxygen functional groups, a decrease in the concentration of gas products and a rise of the crossing point temperature, indicating that EDTA has a strong inhibitory effect on coal. The calculation of the apparent activation energy reveals that the activation energies of the inhibited coal sample were 51.18 kJ/mol and 43.42 kJ/mol in the temperature ranges of 30–70 °C and 80–180 °C, respectively, which are 7.94 kJ/mol and 8.28 kJ/mol higher than those of the raw coal. This proves that the metal chelating agent EDTA is able to inhibit coal spontaneous combustion by chelating transition metal ions to increase the activation energy. Finally, experiments were carried out to study the inhibitory effects of EDTA on different coal samples, which suggests that EDTA can exert good inhibitory effects on different coal samples.

Study on the Volatiles and Kinetic of in-Situ Catalytic Pyrolysis of Swelling Low-Rank Coal

A new method combined solvent swelling with an in-situ catalytic effect of metal ions was developed and introduced in coal pyrolysis to increase the coal conversion and the tar yield as well as to improve the quality of the tar products. Low-rank coal of Shendong coal from China was used to investigate the effect of demineralization, swelling, and in-situ catalysis on pyrolysis reactivity and kinetic characteristics, yield distribution of products, and the tar composition. The experiments were performed using a thermogravimetric analyzer/Fourier transform infrared spectrometer (TG-FTIR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and a fixed-bed reactor to examine the pyrolysis behavior of raw coal, demineralized coal, methanol swelling demineralized coal, and methanol swelling with metal ions (Ca2+, Cu2+, and Co2+) in-situ-impregnated coal, respectively. The results showed that coal conversion could be promoted by pretreatment of solvent swelling and in-situ-impregnated Cu2+ and Co2+ ions...

Catalyst metal ions and luminol bifunctionalized gold nanoparticles: Unique chemiluminescence property for Cu(II) monitoring

Abstract In this work, catalyst metal complexes and luminol bifunctionalized AuNPs by virtue of cysteine as bridge molecule (M/cysteine-luminol-AuNPs), and catalyst metal ions and luminol directly bifunctionalized AuNPs (MI-luminol-AuNPs) by virtue of 3-aminophthalate anion as in situ chelators were prepared for the first time. Particularly, MI-luminol-AuNPs prepared with Co(II) and Cu(II) exhibited highly enhanced chemiluminescence (CL) activities. The greatly enhanced CL activities were attributed to the synergetic catalytic effect of metal ions and AuNPs on luminol-H2O2 CL reaction. Interestingly, special two peak CL emission was observed with Cu(II) and luminol directly bifunctionalized AuNPs (Cu(II)-luminol-AuNPs) reacted with H2O2. Thus, a simple CL sensing strategy was developed for Cu(II) monitoring by virtue of Cu(II) regulated on-site assembly of Cu(II)-luminol-AuNPs. The linear detection range was from 20 to 800 μM, and the limit of detection was 5.0 μM. Finally, the proposed detection method was successfully applied to the determination of Cu(II) ions in real spiked water samples.

The Catalytic Effect of Metal Ions on the Degradation of 4-Chlorophenol Induced by an Aqueous Pulsed Discharge Plasma

The influence of metal ions, such as Fe2+, Fe3+, Cu2+ and Mn2+, on 4-CP degradation was investigated in an aqueous pulsed discharge plasma system with or without the addition of a TiO2 photo-catalyst. From an analysis of the pseudo first-order rate constant (kCP) and energy efficiency (G50%) for 4-CP degradation, the experimental results show that the degradation of 4-CP is much enhanced in the presence of ferrous ions at the optimal concentration of 0.2∼0.8 mmol/L or 0.2 mmol/L in an aqueous pulsed discharge plasma without or with the TiO2 system, respectively, and the enhancement is ascribed to plasma induced Fenton and photo-Fenton reactions. Meanwhile, the rank of such metal ions for catalytic effect on 4-CP degradation was Fe2+> Fe3+ > Cu2+ > Mn2+ and Fe2+ > Fe3+ > Mn2+ > Cu2+ for the former and the latter systems, respectively, and the reasons behind this were discussed through the analysis of active species, especially hydrogen peroxide.

Pre-evaluation of metal ions as a catalyst on chemiluminometric sequential injection analysis with luminol–H 2O 2 system

Catalytic effect of metal ions on luminol chemiluminescence (CL) was investigated by sequential injection analysis (SIA). The SIA system was set up with two solenoid micropumps, an eight-port selection valve, and a photosensor module with a fountain-type chemiluminescence cell. The SIA system was controlled and the CL signals were collected by a LabVIEW program. Aqueous solutions of luminol, H 2O 2, and a sample solution containing metal ion were sequentially aspirated to the holding coil, and the zones were immediately propelled to the detection cell. After optimizing the parameters using 1 × 10 −5 M Fe 3+ solution, catalytic effect of some metal species was compared. Among 16 metal species examined, relatively strong CL responses were obtained with Fe 3+, Fe 2+, VO 2+, VO 3 −, MnO 4 −, Co 2+, and Cu 2+. The limits of detection by the present SIA system were comparable to FIA systems. Permanganate ion showed the highest CL sensitivity among the metal species examined; the calibration graph for MnO 4 − was linear at the concentration level of 10 −8 M and the limit of detection for MnO 4 − was 4.0 × 10 −10 M (S/N = 3).

Effects of coexisting metal ions on the redox potential dependence of chalcopyrite leaching in sulfuric acid solutions

The leaching rate of chalcopyrite (CuFeS 2) in H 2SO 4 solutions depends on the redox potential determined by the concentration ratio of Fe 3+ to Fe 2+, and the rate is higher at redox potentials below a critical value (critical potential). In actual leaching systems, different metal ions are released from coexisting minerals to the aqueous phase. The present study investigated the effects of coexisting metal ions on the critical potential of chalcopyrite leaching. Shaking-flask leaching experiments were carried out with 0.1 g of ground chalcopyrite and 10 cm 3 of 0.1 kmol m − 3 H 2SO 4 containing 0.1 kmol m − 3 Fe 2+ and 0.001 kmol m − 3 of the metal ions at 298 K in air. The initial redox potential was adjusted by adding Fe 3+, and the amount of Cu extracted after 24 h was investigated as a function of the potential. The results indicate that the critical potential increases by the addition of Ag + or Bi 3+ but is not affected by Pd 2+, Hg 2+, Cd 2+, Zn 2+, Ni 2+, Co 2+, or Mn 2+. The results were interpreted by a reaction model assuming the formation of intermediate Cu 2S due to the reduction of chalcopyrite and subsequent oxidation of the Cu 2S at potentials below the critical potential. Catalytic effects of metal ions on chalcopyrite leaching are also discussed based on the experimental results and the proposed model.

Interaction between ozone and the chloride ion in sulfuric acid solutions up to 6-M concentration

The effect of sulfuric acid concentration on Cl2 evolution in the reaction between O3 and Cl− has been investigated. The catalytic effects of metal ions in this reaction have been studied as a function of solution acidity. The chlorine evolution rate increases markedly with increasing acid concentration. At acid concentrations below 4 mol/l, the most effective catalyst is Co2+. The catalytic activities of Fe3+ and Cu2+ peak at \(C_{H_2 SO_4 } \) = 4.8 mol/l. In passing to highly acidic solutions (\(C_{H_2 SO_4 } \) > 5 mol/l), the catalytic activity of the metal ions decreases, but the chlorine evolution rate remains high owing to the high acidity. Kinetics of VO2+ oxidation with ozone in acid media have been studied, and the ozone solubility in aqueous sulfuric acid has been measured.

Metal ion-catalyzed Diels-Alder and hydride transfer reactions. Catalysis of metal ions in the electron-transfer step.

Rates of Diels-Alder cycloaddition of anthracenes with p-benzoquinone and its derivatives as well as rates of hydride-transfer reactions from 10-methyl-9,10-dihydroacridine to the same series of p-benzoquinones are accelerated significantly in the presence of metal ions in acetonitrile. An extensive comparison of the catalytic effects of metal ions in electron transfer from one-electron reductants (cobalt tetraphenylporphyrin and decamethylferrocene) to p-benzoquinones with those in the Diels-Alder reactions of the quinones as well as the hydride-transfer reactions has revealed that the catalysis of metal ions in each case is ascribed to the 1:1 and 1:2 complexes formed between the corresponding semiquinone radical anions and metal ions. The transient absorption and ESR spectra of the semiquinone radical anion-metal ion complexes are detected directly in the electron-transfer reduction of p-benzoquinone derivatives in the presence of metal ions. The catalytic reactivities of a variety of metal ions in each reaction are well correlated with the energy splitting values of pi(g) levels because of the complex formation between O(2)(.-) and M(n+), which are derived from the g(zz) values of the ESR spectra of the O(2)(.-)-M(n+) complex.

Synergistic Catalysis of Dimetilan Hydrolysis by Metal Ions and Organic Ligands

Hydrolysis of the insecticide dimetilan, which possesses a N,N-dimethylcarbamate moiety and a N,N-disubstituted urea moiety, has been used to explore metal ion-organic ligand synergistic effects on the degradation of agrochemicals. Dimetilan hydrolysis is strongly catalyzed by +II transition metal ions exhibiting strong affinities for nitrogen- and oxygen-donor ligands (NiII, CuII, and ZnII) but not PbII, which exhibits only a weak affinity. Comparisons among these four metal ions strongly suggest that metal ion coordination of dimetilan is necessary for catalysis to occur. A combined mechanism of metal ion coordination of dimetilan and the generation of a MeOH+ nucleophile is most plausible for the metal-catalyzed hydrolysis. In the absence of metal ions, citric acid (CIT), ethylenediamine (EN), and N-(2-hydroxyethyl)ethylenediamine (HEEN) ligands alone do not affect dimetilan hydrolysis. However, addition of these ligands significantly changes the catalytic effect of metal ions. CIT and EN reduce the ca...

Oxidation of sulfur (IV) by oxygen in aqueous solution: role of some metal ions

Catalytic effect of metal ions: Cr(VI), Cr(III), Cd(II), V(V) and chloride anion, on the oxidation of S(IV) in aqueous solution, at concentrations of metal ions and S(IV) usually found in urban atmospheres, were studied under controlled experimental conditions (pH (2.1 - 4,5), T (25.0 - 35.0 °C), air flow rate, concentration of reactants, etc...). The kinetic constant determined at 25.0 °C and pH range (2.1 - 4.5), using ultra pure water was 8.0 ± 0.5 x 10-4 s-1. This value was considered as a reference for the oxidation reaction rate. The kinetic constants determined in the presence of Cr(VI) revealed that the oxidation reaction of S(IV) is quite influenced by the acidity. At pH = 2.1 (K = 2.3 x 10-2 mg-1 L s-1) the reaction is carried out with a rate five times greater when compared to pH = 2.6 (K = 4.3 x 10-3 mg-1 L s-1) and thirty times greater when compared to pH = 3.4 (K= 8.0 x 10 -4 mg-1 L s-1). The following rate expression was obtained at pH = 2.6: -r(S(IV) =K [Cr(VI)] [S(IV)] and the activation energy found was: Ea =70.3KJ/mol. No catalytic effects were observed for Cd(II) or chloride ion, while inhibitory effects were observed for Cr(III) and V(V) ions.

Catalytic effects of metal ions on the electrochemical reduction of nitrate ions at mercury electrode.

Two kinds of catalytic effects of metal ions on the electrochemical reduction of nitrate ions at mercury electrodes are discussed. For the first group (Group A), consisting of metal ions, such as alkaline-earth, zirconium, etc., the nitrate is reduced at a more positive potential than the reduction potential of the above metal ions. For the second group (Group B) containing as molybdenum, uranium, etc., the nitrate is reduced at the reduction potential of metal ions, and is accompanied by the so-called catalytic enhancement of the reduction current of metal ions. In general, one of the chemical properties of Group A ions in aqueous solution is that they are proton producing when they polymerize with OH bridging while Group B ions consume protons to polymerize with oxygen bridging. It is suggested that, in both group ions, species having the hydroxyl group could play a very important role for the reduction of nitrate.

Aqueous S(IV) oxidation—I. Catalytic effects of some metal ions

Abstract Catalytic effect of metal ions [Fe(III), Mn(II), Cu(II), Pb(II) and Zn(II)] on the oxidation of S(IV) in aqueous solution at concentrations of metal ions and S(IV) as found in an urban atmosphere were studied under controlled experimental conditions (T, pH air flow rate, mixing, concentration of reactant, etc.). The following rate expressions were obtained: −rS(IV) = k [Fe(III)] [S(IV)], −rS(IV) = k [Mn(II)] [S(IV)]0.65, −rS(IV) = k [Cu(II)] [S(IV)]2. The activation energy equals 104 kJ mol−1 for Fe(III), 63.3 kJ mol−1 for Mn(II), and 116.8 kJ mol−1 for Cu(II) catalysed S(IV) oxidation.