Influence of MgO loading on the structure and catalytic performance of Pd/γ-Al2O3, I. Effect of interaction between MgO and γ-Al2O3

The influence of MgO dispersed on -Al₂O₃ in different amounts on the structure and performances of Pd/-Al₂O₃ catalysts has been studied by means of XRD, H₂–O₂ titration, BET and catalytic activity test for CO oxidation. It was found that introduction of MgO enhanced greatly the CO oxidation activity of catalyst. It seems that the enhanced activity stems from the stronger interaction between MgO and -Al₂O₃ at a given temperature (e.g. 450 °C).     

Studies on the liquid-liquid extraction and precipitate flotation of the second kind of Co(II) using 8-hydroxy quinoline

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 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⁺).     

Fuel Combustion Reactions and Catalysts: XXI. Synthesis and Characterization of Modified Mn–Al–O Catalysts for High-Temperature Oxidation

The phase composition of supported Mn–Al–O catalysts and their activity in the reaction of methane oxidation were studied depending on the composition of aluminum oxide supports (-Al₂O₃ with different -Al₂O₃ contents modified with individual Mg, La, and Ce oxides or Mg + La and Mg + Ce oxide mixtures) and calcination temperatures (500, 900, and 1300°C). It was found that the Mn–Al–O catalysts based on -alumina containing -Al₂O₃ and modified with Mg, La, or Ce additives are more active and thermally stable (up to 1300°C) than the samples based on pure -Al₂O₃. A conclusion was drawn that a higher degree of disorder of the structure of -Al₂O₃, compared to that of -Al₂O₃, is favorable for a deeper interaction of manganese and modifying additives with the support at the early stages of the synthesis and for the formation of Mn–Al compounds with complex composition (solid solutions and/or hexaaluminates) at 1300°C. These compounds are responsible for the stability and high activity of the catalysts in methane oxidation.     

Radiation-Induced Transformations of Iron(II) Formate

The solid-phase decomposition of the iron formate crystal hydrate Fe(HCOO)₂ · 2H₂O under exposure to ⁶⁰Co -rays or 3.5-MeV electrons was studied. It was found that the irradiation of this salt to absorbed doses of 0.1–2 MGy resulted in the radiolysis of water of crystallization and the HCOO^– anion and in the reduction or oxidation of the Fe²⁺ cation. The composition of the solid-phase (-Fe, -Fe, FeO, -Fe -Fe₂O₃, Fe₃O₄, and FeCO₃) and gaseous (H₂O, CO, CO₂, HCOOH, and CH₄) radiolysis products of the substance was determined.     

Oxidation of methane, butane and carbon monoxide on Al?Fe oxide catalysts

The activity of the catalysts obtained by supporting Fe³⁺ oxalate complexes on -and -Al₂O₃ in oxidation of CH₄, C₄H₁₀ and CO has been studied. The composition of the impregnating solution and the temperature of catalyst thermal treatment were varied. The most active catalysts were prepared by impregnation of -Al₂O₃ with (NH₄)₃[Fe(C₂O₄)₃] solutions at pH=2.0–3.5. Their activity appears to be close to that of Al-Mg-Cr catalysts in butane oxidation and even exceeds this in CO oxidation.     

Effect of gamma-irradiation on the catalytic activity and selectivity of gamma-alumina

Methanol conversion reaction was carried out in contact with a poorly crystalline -alumina pre-irradiated with different doses of -rays. The reaction was conducted at 140–440°C using a flow technique under atmospheric pressure. The results obtained revealed that -irradiation of Al₂O₃ resulted in drastic modifications of its activity and selectivity in methanol conversion reaction. The dose of 15 Mrad was sufficient to suppress completely the formation of dimethyl ether (DME) and stimulated the formation of methane, which started at 200°C instead of 300°C in the case of the unirradiated alumina specimen. However, the rate of CH₄ formation was found to decrease as a function of the dose employed. When the dose reached 140 Mrad, DME was reproduced with a rate comparable to that measured for the unirradiated catalyst sample. These results permitted us to conclude that DME is produced on the weak acidic sites (Brönsted acidity of Al₂O₃) and is not necessarily an intermediate compound for methane formation that takes place directly from methanol on strong acidic sites (Lewis acidity). The doses of 15–75 Mrad expelled completely the Brönsted acidic sites from Al₂O₃ surface, and the doses above this limit brought about a transformation of Lewis acidic sites into Brönsted acidity that is responsible for dimethyl ether formation. This transformation occurs by the action of liberated water from the dehydration of methyl alcohol.     

Study of the influence of alkali element compounds on the activity of aluminopalladium catalysts for oxidation of carbon monoxide

A discussion is presented of a discovery that the anionic part of sodium salts introduced into the catalyst by impregnation of -Al₂O₃ after deposition of palladium salts and their reduction in that catalyst affects the activity and dynamic properties of the catalysts in the oxidation reaction of CO into CO₂ at stoichiometric ratios of CO/O₂ = 2.Scientific-Production Association Gos. In-t Prikl. Khim., Leningrad. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 5, pp. 591–595, September–October, 1991. Original article submitted July 17, 1991.     

Thermal characterisation of chemically reduced electrolytic manganese dioxide

Summary Samples of electrolytic manganese dioxide (EMD) were chemically reduced using 2-propanol under reflux (82°C) for 1, 2, 3, 6 and 24 h intervals. XRD analysis showed that the -MnO₂ structure was preserved although the lattice dimensions were observed to increase with increasing degree of reduction to accommodate the intercalation of protons. The exception was the 24 h reduced sample which contained two phases; -MnO₂ and -MnOOH. Three regions of decomposition in the range of 50 to 1000°C were observed using thermogravimetric analysis coupled with mass spectrometry (TG-MS) and were accounted for as water removal below 390°C, reduction of MnO₂ to Mn₂O₃ between 400 and 600°C, and Mn₂O₃ to Mn₃O₄ between 600 and 1000°C. Again the exception proved to be the 24 h reduced sample which was observed to decompose predominantly in one step between 400 and 600°C directly to Mn₃O₄.