Chemisorbed oxygen can be determined quantitatively by the measurement of gaseous N2/N2O liberated by treatment with hydrazine sulphate/hydroxylamine hydrochloride. The amount of chemisorbed oxygen depends on the degree of dispersion during irradiation and also the -dose. The chemisorption is enhanced in the presence of moisture. The partial reduction of the transition metal ion favours the formation of chemisorbed oxygen. 相似文献
The interference by dissolved oxygen is an obstacle in electrochemical immunoassays. The authors are reporting here on a method that employs a working potential that is below the reduction potential for oxygen and hence is not interfered by oxygen/air. Ternary Pt-Co-Cu nanodendrites were prepared by a one-pot reaction. They were placed on a glassy carbon electrode (GCE) modified with gold nanoparticles (AuNPs) where they showed excellent catalytic activity toward the reduction of hydrogen peroxide at a reduction potential of ?0.015 V (vs. SCE). Dissolved oxygen, in contrast, is not reduced at this potential. In order to obtain a sandwich-type of voltammetric immunosensor, antibody against insulin (Ab1) immobilized on the AuNPs on the GCE. The secondary antibody (Ab2) was labeled with Pt-Co-Cu nanodendrites as signal marker for signal amplification. After adding hydrogen peroxide, its catalytic oxidation by the immunosensor depends on its loading with insulin. Hence, insulin can be quantified due to the positive correlation that exists between current and the concentration of ternary Pt-Co-Cu nanodendrites on the electrode. The sensor has a linear response in the 0.2 pM to 2 nM insulin concentration range, with a 0.08 pM detection limit. The assay is well reproducible, acceptably selective, and the sensor is fairly stable over time.
ESR spectra are reported for O2, H2SO2, and N2O adsorbed at low temperatures on n-type rutile after reduction with hydrogen at 700–1000C (<1% reduction). The gases alter the conductivity and produce ESR signals at liquid-nitrogen temperature (i. e., are chemisorbed), but the binding is very weak, being reversible for O2, H2, and He at that temperature. It is considered that the high polarizability of the lattices causes very shallow surface acceptor levels to arise by physical adsorption; these localize the conduction electrons at lattice ions adjacent to the adsorbed molecules. 相似文献
Manganese–copper bimetal oxide catalysts supported on ZSM5 and acid-treated multi-walled carbon nanotubes (MWCNTs) were produced by incipient wetness impregnation for selective catalytic reduction of NO with dielectric barrier discharge plasma. Plasma can activate molecules even at ambient temperature, generating active oxygen species such as O, O3, and HO2 radicals, which can oxidize NO to NO2 effectively. The SCR activity of Mn–Cu/MWCNTs was studied and compared to that of the Mn–Cu/ZSM5. The obtained samples were characterized by XRD, SEM, TEM, ICP, H2-TPR, Raman spectroscopy, and XPS. The results show that Mn–Cu/MWCNTs catalyst possesses NO removal activity superior to that of the Mn–Cu/ZSM5 catalyst. MWCNTs-based catalyst attains NO removal efficiency of 88% at 480 J/L, while the ZSM5-supported catalyst achieves NO removal efficiency of 82% at the same energy density. The oxygen content increased from 3.33 to 19.07% on the nanotube surface after introducing Mn and Cu, which almost remained unchanged on ZSM5. The oxygen-containing functionalities are important for NOx adsorption and removal. Moreover, the characterization revealed that CuO is the main phase of copper oxide, but copper dispersion decreases on Mn–Cu/ZSM5 surface because of the formation of copper dimer species. The manganese is well-dispersed on the catalysts, MnO2 and Mn2O3 contents of Mn–Cu/MWCNTs are larger than that of Mn–Cu/ZSM5, MnO2 is the predominant phase of manganese oxide. 相似文献
Catalysis of mixed oxide LaMnO3 was studied for the decomposition of hydrogen peroxide (H2O2). The catalyst was -irradiated in open petri dishes, vacuum, dry oxygen and moist oxygen. LaMnO3 irradiated in moist oxygen showed highest catalytic activity. X-ray photoelectron spectroscopic (XPS) studies were carried out to investigate the surface modifications occurred during -irradiaiton of LaMnO3. No significant change in the surface was noticed in LaMnO3 irradiated in vacuum and dry oxygen. However, LaMnO3 irradiated in moist oxygen and in open petri dishes showed the reduction of transition metal (MN3+ to Mn2+) which in turn leads to the formation of chemisorbed superoxide ions (O
2–
) and surface carbonate species (CO
32–
). The latter processes decreases the electrical conductivity by trapping the charge carriers. The hydrated electron generated by the radiolysis of moisture reduces the transition metal. A qualitative molecular orbital model has been proposed for the chemisorption of O
2–
on the reduced transition metal centers (Mn2+). 相似文献
The specific features of the catalytic reduction of methylviologen by dihydrogen in water in the presence of platinum colloids synthesized by various methods are studied. The colloids prepared by the radiation-chemical reduction of PtCl42– in the presence of polyacrylate or polyphosphate as stabilizers and colloids prepared by the reduction with dihydrogen efficiently catalyze the reaction. The citrate colloids synthesized by the reduction of PtCl62– with citric acid are characterized by a prolonged induction period after which these colloids also gain the catalytic activity. We assume that the citrate platinum colloids are giant clusters with the close-packed metal core containing the magic number of platinum atoms (Pt561), which are coordinated by the ligand molecules blocking the surface of the metal particle. In the presence of H2, the ligand molecules are decomposed or removed from the surface, which is accompanied by the appearance of the catalytic activity. 相似文献
The active state of palladium for NO reduction with methane (CH4-SCR) was investigated by comparing the catalytic activity of Pd/H-ZSM-5 with that of PdO/SiO2. High catalytic activity for CH4-SCR was given by Pd/H-ZSM-5 in the temperature range of 300–500 °C. PdO/SiO2 catalyzed the reaction between NO2 and CH4 in the absence of oxygen, which retarded the reaction by consuming CH4 in combustion. CH4 combustion occurred on either zeolite-supported or silica-supported catalyst, while NO preferentially retarded the combustion
on Pd/H-ZSM-5. NO was found to be chemisorbed on the palladium sites in zeolite, while it was hardly chemisorbed on PdO/SiO2. NaCl titration showed that the palladium species in zeolite are Pd2+ cations content, on which NO is strongly chemisorbed resulting in high selectivity for CH4-SCR. 相似文献
A series of CeO2/Al2O3 catalysts was modified with praseodymium oxide using an extrusion method. The catalytic activities of the obtained catalysts were measured for the selective catalytic reduction of NO with NH3 to screen suitable addition of praseodymium oxide. These samples were characterized by XRD, N2‐BET, NH3‐TPD, NO‐TPD, Py‐IR, H2‐TPR, Raman spectra and XPS, respectively. Results showed the optimal catalyst with the Pr/Ce molar ratio of 0.10 exhibited more than 90% NO conversion in a wide temperature range of 290–425°C under GHSV of 5000 h?1. The number of Lewis acid sites and the chemisorbed oxygen concentration of the catalysts would increase with the Pr incorporation, which was favorable for the excellent catalytic performance. In addition, the Pr incorporation inhibited growth of the Al2O3 crystal particles and led to the lattice expansion of CeO2, which increased catalytic activity. The results implied that the higher chemisorbed oxygen concentrations and the more Lewis acid sites were conductive to obtain the excellent SCR activity. 相似文献
The transport properties and morphological characteristics of perfluorinated membranes after deposition of the layer of platinum dispersion on the surface are studied. The significant effect of preliminary modification of perfluorinated membraned with polyaniline on the diffusion permittivity of the composite and the morphology of the layer of platinum dispersion is determined. Testing the composites as proton conductors with a catalytic layer on the surface in an air–hydrogen fuel cell has shown the effect of the asymmetry of the electrochemical characteristics of the membrane–electrode assembly at various orientations of the layer of platinum dispersion towards hydrogen and air flows. A higher catalytic activity of the composite membranes in the oxygen reduction reaction is determined in the case platinum dispersion is deposited onto the membrane preliminarily modified with polyaniline.
Uniform iron nanoparticles dispersed on polyaniline have been used as catalysts for the direct conversion of synthesis gas into lower olefins. As compared to active carbon and N-doped active carbon, polyaniline as a support of Fe catalysts showed higher selectivity of lower olefins(C_(2–4)=). The C_(2–4)=selectivity reached ~50% at a CO conversion of 79% over a 10 wt% Fe/polyaniline catalyst without any promoters.The XRD, H_2-TPR, TEM and HRTEM studies revealed that the presence of nitrogen-containing groups in polyaniline structure could promote the dispersion and reduction of iron oxides, forming higher fraction of iron carbides with smaller mean sizes and narrower size distributions. The propylene-TPD result indicates that the use of polyaniline support facilitates the desorption of lower olefins, thus suppressing the consecutive hydrogenation to form undesirable lower paraffins. 相似文献
The voltammetry method with a linear potential scan is used for investigating the effect the electrode material (Ni, Co, electrodes on the basis of cobalt oxides modified with carbon) exerts on the reduction of gaseous oxygen at interfaces solid fluoride-conducting electrode LaF3:Eu2+/electrode, O2, and conjugated processes. Properties of the modified electrodes are characterized by the impedance spectroscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy methods. The oxygen reaction is irreversible at the LaF3:Eu2+|Ni (or Co) interfaces. At the interface of LaF3:Eu2+ with modified electrodes Co (C n at %), where n = 5 and 9, mobile forms of oxygen are reversible and the reduction of gaseous and chemisorbed oxygen is controlled by diffusion with different effective kinetic parameters. 相似文献
We report on a modified glassy carbon electrode (GCE) for sensing hydrogen peroxide (H2O2). It was constructed by consecutive electrochemical deposition of poly(anthranilic acid) and poly(diphenylamine sulfonate) on the GCE, followed by the deposition of copper oxide (CuO). The morphology and electrochemistry of the modified electrode was characterized by atomic force microscopy, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. The catalytic performance of the sensor was studied with the use of differential pulse voltammetry under optimized conditions. This sensor displayed significantly better electrocatalytic activity for the reduction of H2O2 in comparison to a GCE without or with modification with CuO or polymer films alone. The response to H2O2 is linear in the range between 0.005 to ~11 mM, and the detection limit is 0.18 μM (at an S/N of 3).
A new bio-mimetic sensor, CuO/PANA@PSDS/GCE, was prepared, it exhibited a better electrocatalytic activity toward the reduction of the H2O2 compared with that of the CuO/GCE, PANA@PSDS/GCE, and GCE. Its increased catalytic response was due to the polyaniline doped (PANA@PSDS) film, which enlarges the specific surface area of the electrode, and increases the loading of the CuO nano-particles. 相似文献
Iridium nanoparticles (IrNPs) with intrinsic oxidase-like activity were synthesized by using sodium citrate as the stabilizer and NaBH4 as the reducing agent. The IrNPs have an average diameter of 2.5 ± 0.5 nm and exhibit excellent oxidase-like property. Under the catalytic action of the IrNPs, 3,3′,5,5′-tetramethylbenzidine (TMB) is oxidized by dissolved oxygen (DO) to form a blue product with an absorption maximum at 652 nm. The catalytic activity is ascribed to the production of superoxide anion radical (O2ˉ?). The chromogenic reaction is exploited for the determination of DO. The method exhibits a wide calibration range from 12.5 to 257.5 μM of DO and a limit of detection as low as 4.7 μM. Compared to other methods, this method presented here shows improved precision and faster response time.
The influence of hydrogen-containing molybdenum and tungsten bronzes on the catalytic activity of palladium composite catalysts for the oxidation of H2, CO, and CH4 was studied. It was found that the composite catalysts containing HxMO3 phases (M = W or Mo), which were formed by the reduction of MoO3 and WO3 oxides with hydrogen in the presence of deposited Pd, showed higher catalytic activity in the oxidation of small molecules (H2, CO, and CH4) with excess oxygen than the traditional Pd/Al2O3 deposited catalyst with the same content of the deposited metal. It was shown that the thermal stability of the HxMO3 phases was the limiting factor influencing the activity of these composite catalysts. 相似文献
A fluorescence assay is described for the fluorometric determination of dopamine (DA). It based on the use of silica-coated CdTe quantum dots (QD@SiO2). These were fabricated through a hydrothermal process. When DA is added to a solution of the QD@SiO2 and then oxidized by oxygen under catalytic action of tyrosinase to form dopamine quinone, the fluorescence of QD@SiO2 (acquired at excitation/emission wavelengths of 310/525 nm) decreases due to an electron transfer quenching processes. The assay has a linear calibration plot in the 0.05 to 30 μM DA concentration range and a 12.5 nM detection limit (at an S/N ratio of 3). The method was applied to the determination of DA in spiked human serum samples.
Selective catalytic reduction of NO by propene has been investigated over noble metal (Pt, Pd, Rh)-based ZSM-5 catalysts. These samples were tested in a gas mixture system in the presence of excess oxygen, simulating lean-burn exhaust gases. The sequence in activity for NO reduction was Pt > Rh Pd. Regarding the selectivity of the reaction to N2, an opposite trend was observed: Rh > Pd Pt. The catalytic systems have presented stable operation under isothermal conditions during time-on-stream experiments. 相似文献
The active phase surface of a series of -Al2O3-supported vanadium oxide catalysts has been determined by a kinetic method. A correlation is found between the size of the active surface and the catalytic activity of the samples during NO reduction with NH3. The results from the differential determination of the active phase surface can be used for predicting the catalytic activity of the catalysts investigated. 相似文献
A layer-by-layer (LbL) composition comprising ultrathin anionic layers of silicododecamolybdate and cationic layers of poly(allyl ammonium) is synthesized. The synthesis is realized by means of successive immersion of a glassy-carbon rod into aqueous sulfuric acid solutions of silicododecamolybdic acid and poly(allyl ammonium) hydrochloride. Cyclic voltammetry shows that the silicododecamolybdate anion in the composition undergoes three steps of reversible reduction with formal potentials of 0.34, 0.22, and 0.02 V (SCE). It is established that in the course of synthesis one can obtain a sixfold increase in the currents of redox conversions as compared with currents of a monolayer of the anion chemisorbed on glassy carbon. The LbL composition exhibits catalytic activity during electrochemical reduction of NO2?: the cathodic current of the third redox transition considerably increases and the peak in the reverse run of a cyclic voltammogram disappears. The calculated Michaelis constant of 5 × 10?2 M speaks of a high catalytic activity of the electrode. 相似文献