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Substituted and non-stoichiometic perovskite catalysts for destruction of chlorinated volatile organic compounds
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Development of perovskite catalysts for destruction of waste gases containing chlorinated compounds
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Solid state equilibria in the system Al2O3-La2O3-Cr2O3: Reactivity catalyst/support LaCrO3/Al2O3
No full textThe zone of the ternary system Al2O3-La2O3-Cr2O3 delimited by LaCrO3, LaAlO3, Al2O3 and Cr2O3 has been examined. The existence of an extended field of mixed crystals with rhombohedral symmetry LaAl1-xCrxO3 (0≤x≤0·85) has been verified. On the other hand, for x>0·85, the solids show XR diffraction spectrograms typical of the orthorhombic phase LaCrO3. It has been found a small isomorphous substitution of Al3+ by Cr3+ in the β-alumina type phase, leading to the formation of the LaAl11-x CrxO18 series (0≤x≤0·75); moreover, the existence of Al2-xCrxO3 (0≤x≤2) mixed crystals field has been confirmed. Finally it has been experimentally verified that catalytic systems formed by mechanical mixtures of LaCrO3 and Al2O3 prepared anyhow (LaCrO3 dispersed or supported on Al2O3) result thermodynamically unstable whatever the composition
Co, Ni, Cu aluminates supported on mullite precursors via a solid state reaction
No full textFinely dispersed Me-aluminates (Me=Ni, Co, Cu), stable up to 1000-1100°C, are obtained by diffusion and reaction with mullite precursors. The Me-aluminates are ‘reaction supported', indeed these phases are synthesized in form of finely dispersed cristalline region in a supporting inert material, this latter providing high surface area together with thermal and mechanical stability. Two different preparative routes are exploited, the reactivity of Co, Ni is higher with route A, in which these metals diffuse and react with pre-formed γ-Al2O3 nanoparticles to form the corresponding aluminates. Cu reacts in different way, promoting the formation of mullite, without being incorporated into its structure. For this reason the preparative route which employs impregnation of 400°C mullite amorphous precursor (route B) yields complete reaction of CuO with alumina to form Cu-aluminate, dispersed on a mullite substrate at the final temperature of 980°C. This material shows remarkable catalytic activity in CH4 oxidation
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