A series of palladium-substituted La2CuO4, corresponding to the formula La2Cu1 −xPdxO4 (x = 0−0.2) were prepared by metal nitrate decomposition in a polyacrylamide gel. This method allows an easy incorporation of palladium in the mixed-oxides, which are formed at moderate temperature with rather high specific areas (13–17 m2/g). The partial substitution of copper for palladium allows a strong improvement of the three-way catalytic activity, in particular for NO reduction. The light-off temperatures for the conversions of CO, NO and C3H6 decreased markedly when increasing the palladium content, the activity of catalysts La2Cu0.9Pd0.1O4 and La2Cu0.8Pd0.2O4 being comparable to that of a Pt-Rh/CeO2–Al2O3 catalyst for NO reduction, and higher for CO and C3H6 oxidation.

All the La2Cu1 − x PdxO4 catalysts are activated under reacting conditions. This activation corresponds to the destruction of the mixed-oxide structure, with formation of reduced Pd0 ions atomically dispersed, surrounded by Cu+ and Cu2+ species on a lanthanum oxycarbonate matrix. This high dispersion state of the two transition metals in various oxidation states is supposed to originate from the initial La2Cu1 −xPdxO4 structure.

Palladium-substituted lanthanum cuprates: application to automotive exhaust purification

Tuning the photoluminescence of Eu 2+ and Eu 3+ co-doped SrSO 4 through post annealing technique

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 γ-dose. The chemisorption is enhanced in the presence of moisture. The partial reduction of the transition metal ion favours the formation of chemisorbed oxygen.

The gamma-ray induced chemisorption of oxygen on perovskite type catalysts: determination by reduction with hydrazine sulphate/hydroxylamine hydrochloride

Electronspin resonance (ESR) studies of γ-irradiated LaNiO3 revealed the formation of chemisorbed superoxide ion (O2−) and F centers (electrons trapped in anion vacancies). X-ray photoelectron spectroscopy (XPS) showed that the γ-irradiation of LaNiO3 in the presence of moisture leads to the reduction of the transition metal (Ni3+ to Ni2+) which in turn facilitates the formation of O2− and surface carbonate species (CO32−). A qualitative molecular orbital model has been proposed for the chemisorption of O2− on the reduced transition metal centers (Ni2+). The hydrated electron generated by the radiolysis of moisture reduces the transition metal. Gamma-irradiated LaNiO3 shows enhanced catalytic activity for the decomposition of hydrogen peroxide (H2O2) and the increase in catalytic activity is attributed to the reduced metal content. The formation of chemisorbed oxygen decreases the electrical conductivity by trapping the charge carriers.

Physico-chemical and catalytic properties of gamma-irradiated lanthanum nickelate (LaNiO3)

Catalysis of mixed oxide LaMnO3 was studied for the decomposition of hydrogen peroxide (H2O2). The catalyst was γ-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 γ-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 3 2− ). 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+).

XPS characterization of gamma-ray induced chemisorption of oxygen in lanthanum manganate (LaMnO3)

The effect of60Co γ-radiation on La2CuO4 solid catalyst prepared by the ceramic method has been studied. Gamma irradiation of La2CuO4 samples has been found to increase the Cu+ content, electrical conductivities and decrease the magnetic susceptibilities of the catalyst. The results have been interpreted on the basis of the crystal field model of the structure of La2CuO4.

Effect of60Co gamma radiation on La2CuO4

The catalytic activity of La2CuO4 for the decomposition of H2O2 was studied in detail. La2CuO4 was prepared by the ceramic method in four different ways. Gamma irradiation of the La2CuO4 samples increased their catalytic activity irrespective of the method of preparation. The enhanced catalytic activity is attributed to irradiation generated Cu+ centres on the surface of the catalyst.

Influence of60Co gamma radiation on La2CuO4 catalyst for the decomposition of hydrogen peroxide

A new method for the continuous determination of H2O2 is described based on the catalytic decomposition of H2O2 by LaCoO3. Oxygen liberated is measured by a gas meauuring burette. γ-irradiated catalyst enhances the catalytic activity and decreases the time required for complete decomposition. The procedure is suitable for microdetermination of H2O2 in various food products.

J. C. Kuriacose

Papers

The gamma-ray induced chemisorption of oxygen on perovskite type catalysts: determination by reduction with hydrazine sulphate/hydroxylamine hydrochloride

Effect of60Co gamma radiation on La2CuO4

Influence of60Co gamma radiation on La2CuO4 catalyst for the decomposition of hydrogen peroxide

A simple method for the determination of residual amount of H2O2 a preservative present in the milk