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1.
Impedance measurements, over a wide range of frequencies, of a platinum electrode immersed in a solution of Br2/Br− (HClO4, aq.), allow us to obtain the values of the exchange current jo, it being also possible to study its variation with the experimental conditions. The results thus obtained depend on the surface state of the electrode. With activated electrodes, the Randles circuit explains well enough the electrochemical behaviour of this system. With poisoned electrodes the circuit is inadequate, but it can be shown that the exchange current is decreased by the poisoning effect. Decrease of the exchange current with increase of surface oxidation of the electrode has also been observed.
As a first approximation the poisoning effects can be explained by a diminution of the effective area concerned with electron transfer, but the inadequacy of the Randles circuit indicates that adsorption processes have to be taken into account. 相似文献
2.
P. Kormali T. Triantis D. Dimotikali A. Hiskia E. Papaconstantinou 《Applied catalysis. B, Environmental》2006,68(3-4):139-146
Parallel experiments under similar conditions, using various substrates (atrazine, fenitrothion, 4-chlorophenol and 2,4-D) and OH radical scavengers (Br−, isopropyl alcohol, tertiary butyl alcohol and acetone), have shown that the photooxidizing mode of PW12O403− and TiO2, i.e., OH radicals and/or holes (h+), depends on the nature of substrate and the mode of investigation. This provides an explanation for the controversial results reported in the literature. Atrazine shows that both PW12O403− and TiO2 operate, mainly, via OH radicals and to a lesser extent with holes (h+), whereas, fenitrothion suggests that both systems operate almost exclusively, via OH radicals. Differences in the action of the catalysts are encountered in the photodegradation of 4-chlorophenol (4-ClPh) and 2,4-dichlorophenoxyacetic acid (2,4-D). PW12O403− appears to operate essentially via OH radicals, whereas, h+ appear to be the major oxidant with TiO2. Overall, though, the action of OH radicals relative to h+ appears to be more pronounced with PW12O403− than TiO2. 相似文献
3.
The effect of different chemical parameters on photocatalytic inactivation of E. coli K12 is discussed. Illumination was produced by a solar lamp and suspended TiO2 P-25 Degussa was used as catalyst. Modifications of initial pH between 4.0 and 9.0 do not affect the inactivation rate in the absence or presence of the catalyst. Addition of H2O2 affects positively the E. coli inactivation rate of both photolytic (only light) and photocatalytic (light plus TiO2) disinfection processes. Addition of some inorganic ions (0.2 mmol/l) like HCO3−, HPO42−, Cl−, NO3− and SO42− to the suspension affects the sensitivity of bacteria to sunlight in the presence and in absence of TiO2. Addition of HCO3− and HPO42− resulted in a meaningful decrease in photocatalytic bactericidal effect while it was noted a weak influence of Cl−, SO42− and NO3−. The effect of counter ion (Na+ and K+) is not negligible and can modify the photocatalytic process as the anions. Bacteria inactivation was affected even at low concentrations (0.2 mmol/l) of SO42− and HCO3−, but the same concentration does not affect the resorcinol photodegradation, suggesting that disinfection is more sensitive to the presence of natural anions than photocatalytic degradation of organic compounds. The presence of organic substances naturally present in water like dihydroxybenzenes isomers shows a negative effect on photocatalytic disinfection. The effect of a mixture of chemical substances on photocatalytic disinfection was also studied by adding to the bacterial suspension nutrient broth, phosphate buffer and tap water. 相似文献
4.
With an aim to improve the 5 V capacity and cyclability of the LiMn1.5Ni0.5O4 spinel oxide, three series of Cr substitutions have been pursued with y ≤ 0.2: LiMn1.5Ni0.5−yCryO4, LiMn1.5−0.5yNi0.5−0.5yCryO4, and LiMn1.5−0.33yLi0.33yNi0.5−yCryO4. While the first series involves an increase in the Mn3+ content, the second and third series are designed to maintain charge neutrality (Mn4+, Ni2+, Cr3+, and Li+) without introducing Mn3+ ions. The LiMn1.5Ni0.5−yCryO4 series experiences a widening of the 4 V plateau and a decrease in the 5 V capacity compared to LiMn1.5Ni0.5O4 due to an increase in the Mn3+ content. On the other hand, the LiMn1.5−0.5yNi0.5−0.5yCryO4 series shows a suppression of the 4 V plateau and an increase in the 5 V capacity due to the elimination of the Mn3+ions. The LiMn1.5−0.33yLi0.33yNi0.5−yCryO4 series shows a suppression of the 4 V plateau at low Cr contents, but an increase in the 4 V plateau as the Cr content increases above 0.1. Among the various compositions investigated, LiMn1.45Ni0.45Cr0.1O4 exhibits the best combination of high 5 V capacity (128 mAh/g at 5–4.2 V) and excellent capacity retention (98% in 50 cycles) compared to 118 mAh/g and 92% for LiMn1.5Ni0.5O4. 相似文献
5.
Jianrong Niu Jiguang Deng Wei Liu Lei Zhang Guozhi Wang Hongxing Dai Hong He Xuehong Zi 《Catalysis Today》2007,126(3-4):420-429
Nanometer perovskite-type oxides La1−xSrxMO3−δ (M = Co, Mn; x = 0, 0.4) have been prepared using the citric acid complexing-hydrothermal-coupled method and characterized by means of techniques, such as X-ray diffraction (XRD), BET, high-resolution scanning electron microscopy (HRSEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and temperature-programmed reduction (TPR). The catalytic performance of these nanoperovskites in the combustion of ethylacetate (EA) has also been evaluated. The XRD results indicate that all the samples possessed single-phase rhombohedral crystal structures. The surface areas of these nanomaterials ranged from 20 to 33 m2 g−1, the achievement of such high surface areas are due to the uniform morphology with the typical particle size of 40–80 nm (as can be clearly seen in their HRSEM images) that were derived with the citric acid complexing-hydrothermally coupled strategy. The XPS results demonstrate the presence of Mn4+ and Mn3+ in La1−xSrxMnO3−δ and Co3+ and Co2+ in La1−xSrxCoO3−δ, Sr substitution induced the rises in Mn4+ and Co3+ concentrations; adsorbed oxygen species (O−, O2−, or O22−) were detected on the catalyst surfaces. The O2-TPD profiles indicate that Sr doping increased desorption of the adsorbed oxygen and lattice oxygen species at low temperatures. The H2-TPR results reveal that the nanoperovskite catalysts could be reduced at much lower temperatures (<240 °C) after Sr doping. It is observed that under the conditions of EA concentration = 1000 ppm, EA/oxygen molar ratio = 1/400, and space velocity = 20,000 h−1, the catalytic activity (as reflected by the temperature (T100%) for EA complete conversion) increased in the order of LaCoO2.91 (T100% = 230 °C) ≈ LaMnO3.12 (T100% = 235 °C) < La0.6Sr0.4MnO3.02 (T100% = 190 °C) < La0.6Sr0.4CoO2.78 (T100% = 175 °C); furthermore, there were no formation of partially oxidized by-products over these catalysts. Based on the above results, we conclude that the excellent catalytic performance is associated with the high surface areas, good redox properties (derived from higher Mn4+/Mn3+ and Co3+/Co2+ ratios), and rich lattice defects of the nanostructured La1−xSrxMO3−δ materials. 相似文献
6.
Yunwen Liao Dingquan Xiao Dunmin Lin Jianguo Zhu Ping Yu Lang Wu Xiaoping Wang 《Ceramics International》2007,33(8):1445-1448
Bi0.5(Na1−x−yKxAgy)0.5TiO3 piezoelectric ceramics were prepared by conventional ceramic processes. X-ray diffraction patterns show a pure perovskite structure, indicating that the K+ and Ag+ ions substitute for the Na+ ions in Bi0.5Na0.5TiO3. The temperature dependence of the dielectric constant and dissipation factor shows all ceramics to experience two phase transitions: from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric. The transition temperature from ferroelectric to anti-ferroelectric and the temperature at which the dielectric constant reaches its maximum value decrease with the increase of K+ amount. At room temperature, the ceramics containing 17.5–20 mol% K+ and 2 mol% Ag+ exhibit high piezoelectric constant (d33 = 180 pC/N) and high electromechanical coupling factor (kp = 35%). 相似文献
7.
Toshihiro Daimon Tsutomu Hirakawa Masahiro Kitazawa Junya Suetake Yoshio Nosaka 《Applied Catalysis A: General》2008,340(2):169-175
The production and decay of singlet molecular oxygen (1O2) in TiO2 photocatalysis were investigated by monitoring its phosphorescence under various reaction conditions. First, the effects of additives such as KBr, KSCN, KI, H2O2, and ethanol on the amount of 1O2 produced by photo excitation of P25 TiO2 were measured. The same additives were employed to investigate the effect on the amount of O2− produced. Comparison between the effects on 1O2 and O2− suggested that 1O2 is formed by the electron transfer mechanism, the reduction of molecular oxygens to O2− by photogenerated electrons and the subsequent oxidation of O2− to 1O2 by photogenerated holes. The formation of 1O2 decreased at pH < 5 and pH > 11, indicating that the intermediate O2− is stabilized at the terminal OH site of the TiO2 surface in the pH range of 5 < pH < 11. Eighteen commercially available TiO2 photocatalysts were compared on the formation of 1O2 and O2− in an aqueous suspension system. The formation of 1O2 was increased with decreasing size of TiO2 particles, indicating that a large specific surface area causes a higher possibility of reduction producing O2− and then a large amount of 1O2 is formed. The difference in the crystal phase (rutile and anatase) did not affect the formation of 1O2. 相似文献
8.
Mohammed A. Amin Sayed S. Abd El Rehim S.O. Moussa Abdallah S. Ellithy 《Electrochimica acta》2008,53(18):5644-5652
The influence of various concentrations of NaClO4, as a pitting corrosion agent, on the corrosion behaviour of pure Al, and two Al–Cu alloys, namely (Al + 2.5 wt% Cu) and (Al + 7 wt% Cu) alloys in 1.0 M Na2SO4 solution was investigated by potentiodynamic polarization and potentiostatic techniques at 25 °C. Measurements were conducted under the influence of various experimental conditions, complemented by ex situ energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) examinations of the electrode surface. In free perchlorate sulphate solutions, for the three Al samples, the anodic polarization exhibits an active/passive transition. The active dissolution region involves an anodic peak (peak A) which is assigned to the formation of Al2O3 passive film on the electrode surface. The passive region extends up to 1500 mV with almost constant current density (jpass) without exhibiting a critical breakdown potential or showing any evidence of pitting attack. For the three Al samples, addition of ClO4− ions to the sulphate solution stimulates their active anodic dissolution and tends to induce pitting corrosion within the oxide passive region. Pitting corrosion was confirmed by SEM examination of the electrode surface. The pitting potential decreases with increasing ClO4− ion concentration indicating a decrease in pitting corrosion resistance. The susceptibility of the three Al samples towards pitting corrosion decreases in the order: Al > (Al + 2.5 wt% Cu) alloy > (Al + 7 wt% Cu) alloy. Potentiostatic measurements showed that the rate of pitting initiation increases with increasing ClO4− ion concentration and applied step anodic potential, while it decreases with increasing %Cu in the Al samples. The inhibitive effect of SO42− ions was also discussed. 相似文献
9.
Non-stoichiometric V6O13±0.2 (VOy) prepared by thermal decomposition of NH4VO3 in N2 atmosphere is investigated cathode material for Li batteries. The maximum lithium composition is found to be Li2y-3VOy. The emf vs composition relationship of Li/LixVO2.144 is determined in the interval 0 < x < 1.3, yielding a theoretical energy density of 890 Wh kg−1. The kinetics and reversibility of the VOy electrode is investigated by cyclic voltammetry and cycling of test cells. The lithium diffusion coefficient and the electronic conductivity of the oxide is found to decrease with increasing lithium content. The cyclability of very thin electrodes is found to be excellent, but inferior results are obtained with practical cells, presumably due to degradation of electrode structure. 相似文献
10.
The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C3H6 over CuO/γ-Al2O3 has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu0/Cu+ to Cu2+ by NO and O2, (ii) the co-adsorption of NO/NO2/O2 to produce Cu2+(NO3−)2, and (iii) the reaction of Cu2+(NO3−)2 with C3H6 to produce N2, CO2, and H2O. Increasing the O2/NO ratio from 25.0 to 83.4 promotes the formation of NO2 from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO2/O2. This reactant mixture allows the formation of Cu2+(NO3−)2 and its reaction with the C3H6 to occur at a higher rate with a higher selectivity toward N2 than the low O2/NO flow. Both the high and low O2/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C3H7---NO2, C3H7---ONO, CH3COO−, Cu0---CN, and Cu+---NCO intermediates toward N2, CO2, and H2O products. High O2 concentration in the high O2/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O2/NO SCR at 523–698 K. High O2 concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O2 concentration at temperatures above 723 K. 相似文献
11.
P. Ciambelli S. Cimino S. De Rossi L. Lisi G. Minelli P. Porta G. Russo 《Applied catalysis. B, Environmental》2001,29(4):232-250
Catalytic methane combustion and CO oxidation were investigated over AFeO3 (A=La, Nd, Sm) and LaFe1−xMgxO3 (x=0.1, 0.2, 0.3, 0.4, 0.5) perovskites prepared by citrate method and calcined at 1073 K. The catalysts were characterized by X-ray diffraction (XRD). Redox properties and the content of Fe4+ were derived from temperature programmed reduction (TPR). Specific surface areas (SA) of perovskites were in 2.3–9.7 m2 g−1 range. XRD analysis showed that LaFeO3, NdFeO3, SmFeO3 and LaFe1−xMgxO3 (x·0.3) are single phase perovskite-type oxides. Traces of La2O3, in addition to the perovskite phase, were detected in the LaFe1−xMgxO3 catalysts with x=0.4 and 0.5. TPR gave evidence of the presence in AFeO3 of a very small fraction of Fe4+ which reduces to Fe3+. The fraction of Fe4+ in the LaFe1−xMgxO3 samples increased with increasing magnesium content up to x=0.2, then it remained nearly constant. Catalytic activity tests showed that all samples gave methane and CO complete conversion with 100% selectivity to CO2 below 973 and 773 K, respectively. For the AFeO3 materials the order of activity towards methane combustion is La>Nd>Sm, whereas the activity, per unit SA, of the LaFe1−xMgxO3 catalysts decreases with the amount of Mg at least for the catalysts showing a single perovskite phase (x=0.3). Concerning the CO oxidation, the order of activity for the AFeO3 materials is Nd>La>Sm, while the activity (per unit SA) of the LaFe1−xMgxO3 catalysts decreases at high magnesium content. 相似文献
12.
Yi Feng Wang Kyu Hyoung Lee Hiromichi Ohta Kunihito Koumoto 《Ceramics International》2008,34(4):849-852
To clarify the effect of substitutional electron doping on the thermoelectric figure of merit (ZT = S2σTκ−1) of Ruddlesden–Popper phase SrO(SrTiO3)n (or Srn+1TinO3n+1), measurements were conducted for several thermoelectric parameters, e.g. electrical conductivity (σ), Seebeck coefficient (S) and thermal conductivity (κ), of (Sr1−xREx)n+1TinO3n+1 (n = 1 or 2, RE (rare earth): La or Nd, x = 0.05 and 0.1) dense ceramics prepared by a conventional solid-state reaction and hot-pressing technique. Crystal structures of the resultant ceramics were represented as (Sr1−xREx)n+1 TinO3n+1 evaluated by powder X-ray diffraction followed by the Rietveld analysis. All the ceramics exhibited electrical conductivity and the σ values simply depended on the dopant concentration, indicating that both La3+ and Nd3+ ions act as electron donors. The |S| values increased with temperature due to decrease in the chemical potential. Significant reduction of the κ values was observed as compared to cubic-perovskite SrTiO3. The ZT value increased with temperature and reached 0.15 at 1000 K for (Sr0.95La0.05)3Ti2O7. 相似文献
13.
V. C. Belessi C. N. Costa T. V. Bakas T. Anastasiadou P. J. Pomonis A. M. Efstathiou 《Catalysis Today》2000,59(3-4):347-363
Mixed oxides of the general formula La0.5SrxCeyFeOz were prepared by using the nitrate method and characterized by XRD and Mössbauer techniques. The crystal phases detected were perovskites LaFeO3 and SrFeO3−x and oxides -Fe2O3 and CeO2 depending on x and y values. The low surface area ceramic materials have been tested for the NO+CO and NO+CH4+O2 (“lean-NOx”) reactions in the temperature range 250–550°C. A noticeable enhancement in NO conversion was achieved by the substitution of La3+ cation at A-site with divalent Sr+2 and tetravalent Ce+4 cations. Comparison of the activity of the present and other perovskite-type materials has pointed out that the ability of the La0.5SrxCeyFeOz materials to reduce NO by CO or by CH4 under “lean-NOx” conditions is very satisfying. In particular, for the NO+CO reaction estimation of turnover frequencies (TOFs, s−1) at 300°C (based on NO chemisorption) revealed values comparable to Rh/-Al2O3 catalyst. This is an important result considering the current tendency for replacing the very active but expensive Rh and Pt metals. It was found that there is a direct correlation between the percentage of crystal phases containing iron in La0.5SrxCeyFeOz solids and their catalytic activity. O2 TPD (temperature-programmed desorption) and NO TPD studies confirmed that the catalytic activity for both tested reactions is related to the defect positions in the lattice of the catalysts (e.g., oxygen vacancies, cationic defects). Additionally, a remarkable oscillatory behavior during O2 TPD studies was observed for the La0.5Sr0.2Ce0.3FeOz and La0.5Sr0.5FeOz solids. 相似文献
14.
Anatolii G. Belous Oleg V. Ovchar Marjeta Macek-Krzmanc Matjaz Valant 《Journal of the European Ceramic Society》2006,26(16):3733-3739
Ceramics with a composition close to BaZn2Ti4O11 were synthesized according to various substitutional mechanisms in order to verify an existence of a homogeneity range in the vicinity of this composition. Structural and microstructural investigations showed that the crystal structure of BaZn2Ti4O11 was formed in the homogeneity range corresponding to the formula BaZn2 − xTi4O11 − x (0 < x < 0.1). Densely sintered BaZn2 − xTi4O11 − x (0 < x < 0.1) ceramics exhibited a dielectric constant around 30, τf = −30 ppm/K and high Q × f values, which increased from 68,000 GHz at x = 0 to 83,000 GHz at x = 0.05. Structurally, the deficiency of Zn in BaZn2 − xTi4O11 − x (0 < x < 0.1) resulted in a slight decrease in the unit-cell volume. The influence of secondary phases in the BaZn2Ti4O11-based materials on the microwave dielectric properties was also investigated. A presence of small amounts of ZnO, BaTiO3, hollandite-type solid solutions (BaxZnxTi8 − xO16) and BaTi4O9 caused a decrease in Q × f values. 相似文献
15.
We have obtained mass spectra of negative ions produced by rays in artificial air at atmospheric pressure (N2: 80%, O2: 20%, H2O: 20–1500 ppm, CO2: 0.2–300 ppm, NO, NO2 0.02 ppm). We observed two main categories: hydrates built on simple ions (O2−, O3−, OH−, CO3−, CO4−, HCO3−, NO2−, NO3−), hydrates built on complex ions (NOx−, HNOγ, HCO3−HNOx, x = 2,3; Y = 2, 3). For high values of hygrometry, CO2 content and ageing time (5 msec) we observe the disappearance of O2−, O3−, OH− hydrates whereas the major part of the spectrum consists of complex ions. 相似文献
16.
Preparations and physico-chemical characterizations of NASICON-type compounds in the system Li1+xAlxA2−xIV(PO4)3 (AIV=Ti or Ge) are described. Ceramics have been fabricated by sol-gel and co-grinding processes for use as ionosensitive membrane for Li+ selective electrodes. The structural and electrical characteristics of the pellets have been examined. Solid solutions are obtained with Al/Ti and Al/Ge substitutions in the range 0≤x≤0·6. A minimum of the rhombohedral c parameter appears for x about 0·1 for both solutions. The grain ionic conductivity has been characterized only in the case of Ge-based compounds. It is related to the carrier concentration and the structural properties of the NASICON covalent skeleton. The results confirm that the Ti-based framework is more calibrated to Li+ migration than the Ge-based one. A grain conductivity of 10−3 S cm−1 is obtained at 25°C in the case of Li1·3Al0·3Ti1·7(PO4)3. A total conductivity of about 6×10−5 S cm−1 is measured on sintered pellets because of grain boundary effects. The use of such ceramics in ISE devices has shown that the most confined unit cell (i.e. in Ge-based materials) is more appropriate for selectivity effect, although it is less conductive.© 相似文献
17.
Catalytic oxidation of p-xylene (PX) to terephthalic acid (TA) was studied with catalysts containing cobalt acetate, manganese acetate, CoBr2 and MnBr2. The catalysts contain neither highly corrosive hydrogen bromide nor other metal ions, and have the advantage of easy catalyst recovery. The effects of Br/Co atomic ratio, reaction time and temperature, PX concentration, oxygen pressure, and catalyst concentration on PX conversion and product/intermediate yields were investigated. The catalyst system had a suitable reaction temperature of 100 °C, which was much lower than the commercial process temperature (175–225 °C). The maximum product (TA) yield was 93.5%, obtained at a Br/Co atomic ratio of three. Higher Br concentration resulted in the lower TA yield, which was ascribed to the benzylic bromide formation. The synthesis of TA could be adequately described as four reaction steps in series (PX → p-tolualdehyde → p-toluic acid → 4-carboxybenzaldehyde → TA), with a pseudo-first-order rate equation for each step, and the third step was rate-limiting. The rate constant ratios (kj/k3, j = 1 → 4) obtained at 100 °C were similar to the kj/k3 values reported earlier for cobalt acetate/manganese acetate/HBr catalysts in a range of 185–191 °C. 相似文献
18.
The swelling features of gelatine gels in water (good solvent) were studied as a function of thermodynamic conditions of sol—gel transition and ripening. It is shown that the degree of equilibrium swelling Qe varies with the volume fraction of the polymer in a casting solution φo in accordance with the prediction of the classic theory: Qe φo−0.4. Qc, as a function of the gelation temperature Tg, the ripening time tr and φo, can be rescaled and described by the single empirical equation: Qe Tg−x tr−yφo−0.4, where x = 0.1, y = 0.15 for wet gels and X = −0.5, y = 0.04 for dried gels. The kinetics of macroscopic swelling is described by the equation of Peters and Candau, with values of collective diffusion coefficients being in good agreement with values obtained by other workers via photon correlation spectroscopy. 相似文献
19.
Microwave dielectric properties of (Zn1/3Nb2/3)0.40(Ti1−xSnx)0.60O2 ceramics were investigated as a function of SnO2 content (0.15 ≤ x ≤ 0.30). A single phase with tetragonal rutile structure was obtained through the entire composition. The unit-cell volume of the specimens was increased with SnO2 content, due to the larger ionic radius of Sn4+ (0.69 Å) than that of Ti4+ (0.605 Å) for octahedral site. Dielectric constant (K) of the sintered specimens was affected by the dielectric polarizability. Quality factor (Qf) was dependent on the degree of reduction of Ti4+ ion. With an increase of SnO2 content, the temperature coefficient of resonant frequency (TCF) of the specimens decreased due to the decrease of the octahedral distortion of rutile structure. 相似文献
20.
S. Cimino L. Lisi S. De Rossi M. Faticanti P. Porta 《Applied catalysis. B, Environmental》2003,43(4):397-406
Structural, redox and catalytic deep oxidation properties of LaAl1−xMnxO3 (x=0.0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0) solid solutions prepared by the citrate method and calcined at 1073 K were investigated. XRD analysis showed that all the LaAl1−xMnxO3 samples are single phase perovskite-type solid solutions. Particle sizes and surface areas (SA) are in the 280–1180 Å and 4–33 m2 g−1 ranges, respectively. Redox properties and the content of Mn4+ were derived from temperature programmed reduction (TPR) with H2. Two reduction steps are observed by TPR for pure LaMnO3, the first attributed to the reduction of Mn4+ to Mn3+ and the second due to complete reduction of Mn3+ to Mn2+. The presence of Al in the LaAl1−xMnxO3 solid solutions produces a strong promoting effect on the Mn4+→Mn3+ reducibility and inhibits the further reduction to Mn2+. Both for methane combustion and CO oxidation all Mn-containing perovskites are much more active than LaAlO3, so pointing to the essential role of the transition metal ion in developing highly active catalysts. Partial dilution with Al appears to enhance the specific activity of Mn sites for methane combustion. 相似文献