Masakuni Ozawa

Thermal stability and characterization of γ-Al2O3 modified with rare earths

Rare earth modification was effective for improving the thermal stability of γ-Al2O3. It inhibited the grain growth of transition Al2O3 and the formation of α-Al2O3. The surface area was 12 m2 g−1 for pure Al2O3, 40 m2 g−1 for ceriummodified Al2O3 and 51–59 m2 g−1 for Al2O3 modified with lanthanum and others, heated at 1200°C for 5 h. The activation energy of α transformation, evaluated by differential thermal analysis, was 581–583 kJ mol−1 for pure and cerium-modified Al2O3 and 635–655 kJ mol−1 for Al2O3 modified with lanthanum, samarium and ytterbium. Lanthanum inserted into the crystal lattice of Al2O3 with spinel structure, whereas cerium existed on the Al2O3 surface as a form of CeO2. The difference in states between La3+ and Ce4+ can explain that the modification of lanthanum is more effective than that of cerium for improving the thermal resistance of γ-Al2O3.

Preparation and characterization of zirconium dioxide catalyst supports modified with rare earth elements

Abstract ZrO2 catalyst supports modified with rare earth elements were prepared by coprecipitation from an aqueous solution of zirconium oxychloride and rare earth chlorides. The crystallization of amorphous hydrous ZrO2 was inhibited by doping with rare earths; the crystallization temperature was elevated as the amount and ionic radius of the rare earth modifiers was increased. Only modification using cerium had no effect on the crystallization process. The behavior of cerium was different from that of other rare earth elements with valency + 3. A metastable cubic phase was formed for ZrO2 modified with 10 mol.% lanthanum, neodymium and samarium by heating at 600°C. X-ray diffraction and Raman data indicated that the metastable phase had large microstrain and short-range ordering similar to tetragonal symmetry. Rare earth modified ZrO2 showed a large surface area and good thermal stability as a catalyst support. The carbon monoxide oxidation activity of iron was enhanced by modification with neodymium of ZrO2 supports. The results suggest the effectiveness of rare earth modified ZrO2 as catalyst supports.

SOLID-STATE THERMAL BEHAVIOR OF COPPER-MODIFIED ALUMINA TOWARD LEAN-BURN EXHAUST NO REMOVAL CATALYST

Abstract Solid-state thermal behavior and catalytic activity of copper-modified alumina were studied in view of the possible use as automotive lean-bum NOx removal catalysts. The solid-state reaction of copper impregnated on an alumina support at elevated temperatures was examined by X-ray diffraction (XRD) and electron spin resonance (ESR), and the NO removal performance was evaluated under lean-bum conditions. The Cu-impregnated alumina subjected to heat-treatment at 900°C in air showed a NO removal efficiency of 20% at A/F= 18 and space velocity = 100000 h−1. Novel Cu-modified A1203 was observed at the temperature range of 830–950°C, which was characterized by XRD peaks appearing at d = 0.2-0.195, 0.241, and 0.268 nm, besides minute amounts of δ- and γ-type A12O3 were confirmed to be present. Structural stability of this modified alumina having de-NOx active Cu species was limited below temperatures of 930°C. The authors propose the concept of bulk-state structural modification of alumina with Cu for the improvement of thermal durability of lean-burn de-NOx catalysts.

Reduction reaction of lanthanum-added cerium dioxide with carbon monoxide

The reaction of lanthanum-added cerium dioxide with carbon monoxide was examined by using a CO pulse reaction method and high-temperature X-ray diffraction (XRD). The lanthanum addition enhanced the activity of cerium dioxide for oxidizing carbon monoxide under moderately reducing conditions. Isothermal XRD observation at 500 and 700 °C indicated that the reduction reaction of CeO2 and La-added CeO2 with CO progressed in CO-N2 flowing gas. The kinetics of the reaction CeO2 + x/2CO → Cex1−x/4+Cex3+O2−x/2 + x/2CO2 + x/2V0 was analysed by Janders model: [1−(1−x)1/3]2=kt.

Neutron and Raman scattering studies of surface adsorbed molecular vibrations and bulk phonons in ZrO2 nanoparticles

Abstract Inelastic neutron-scattering method (neutron spectroscopy) was applied to the study of the phonon densities of states of zirconia nanoparticles, the OH stretch vibrations of physisorbed water molecules and chemisorbed hydroxyl groups on the surface. Raman scattering was also used to measure the zone-center phonon modes. The observed distinct phonon frequencies and band widths at 10–120 meV reflect the different crystalline symmetries and compositional fluctuations in the small grain and interfacial regions of monoclinic ZrO 2 , tetragonal or mixed cubic and tetragonal rare-earth-modified zirconia. The observed neutron spectra for pure ZrO 2 , Ce 0.1 Zr 0.9 O 2 and Nd 0.1 Zr 0.9 O 1.95 display a band consisting of peaks at 25, 30, and meV and a broad band extending from 50 to 100 meV. The OH bonds in surface hydroxyl groups and water on these zirconias result in the different frequencies of the OH stretch vibrations at 400–600 meV.

Development of Thermal Resistant Three-Way Catalysts

Automotive catalysts with a good thermal durability have been developed by modifying the composition of additives. On the basis of the experimental results, the authors have designed optimal Pt/Rh/Ce three-way catalysts, which have showed significantly improved thermal durability and performance

Influence of heat treatment with nitrogen in positive-temperature-coefficient-type BaTiO3

Abstracts are not published in this journal

Crystal structure and short range oxygen defects in La- and Nd-modified ZrO2

Abstract The crystal structure of rare earth modified zirconia and the associated oxygen defects were studied by neutron diffraction. A Rietveld analysis of the neutron powder patterns of heat-treated samples of La- and Nd—10 mol% ZrO2 revealed the composition of a major tetragonal phase (space group P42/nmc) and a minor cubic phase (space group Fm3m). The short-range oxygen defects structure was examined by a Fourier filtering technique. A real-space correlation function, obtained from a Fourier transform of the filtered residual diffuse scattering, showed evidence of static, oxygen vacancy-induced atomic displacements along the 〈1 1 1〉 and other directions of the pseudocubic cell.

Structural and ESR characterization of heat-stable manganese-alumina lean NO removal catalyst

Abstract Manganese (Mn) oxides supported by gamma aluminas were studied toward heat-stable automotive lean-burn NOx removal catalysts. The solid-state reaction and structural transformation at 600–1100°C were examined by X-ray diffraction and electron spin resonance (ESR). Mn-alumina catalysts subjected to heat treatment at 1000°C in air retained the NO removal conversion efficiency of 22% at 350–400°C for a model exhaust with S.V. = 100,000 h−1. The ESR suggested that a part of the dispersed Mn2+ changed to ESR-silent Mn3+ and formed clusters or disordered oxide of Mn at 1000°C.

Solid-state reaction examination of copper oxide impregnated on pure and La-modified gamma alumina

Transition metal oxides dispersed in support oxides have been studied as catalysts for various chemical processes and the removal of environmental pollution. Recently, copper-exchanged zeolites including ZSM-5 have been extensively studied for high potential use as exhaust de-NOx catalysts in automobile engines and factory generator systems [1]. However, the aluminosilicates decompose under thermally hard conditions above 900 °C and following solid-state reactions lead to a large degredation of catalytic activity to remove NOx species. The study of the thermal behaviour and stability of catalytic compositions gives important information for the materials design of new catalysts and the improvement of their thermal durability. Copper oxide impregnated on gamma alumina (7-A1203) has been traditionally examined for oxidation reactions at low temperatures, however, the thermal behaviour at temperatures above 900 °C has rarely been reported. Highly dispersed copper on an alumina support is considered as a potential alternative material for a de-NOx catalyst if its stability can be improved at elevated temperatures. In this letter, we describe the solid-state reaction of highly dispersed copper on pure and La-modified y-A1203. The difference in thermal behaviour of copper oxide between pure and La-modified y-A1203 support and the phase evolution of these systems should be emphasized for the purpose of proposing basic data to develop improved catalysts. La-modified y-A1203 powders with 0 to 10 mol % LaOl.s were prepared by an impregnation procedure, as reported in a previous paper [2]. Powdered alumina with surface area of 100 m2/g was impregnated using an aqueous solution of lanthanum nitrate, and then dried at 110 °C for 10 h and heated at 600 °C for 3 h in air. The impregnation of 5 to 20 mol % Cu to alumina supports was performed by aqueous copper nitrate, and then dried at 110 °C for 10 h and heated at 500 °C for 3 h in air. The samples were heated at temperatures of 800 °C to 1100 °C for 3 h in air. The evolution phases were examined by an X-ray diffraction (XRD) technique. Here we described the case of catalysts having 10 mol % Cu which are supported by pure and 10 mol% Laadded y-Al203 in order to examine the typical effect of La-modification on an alumina support. Fig. 1 shows the XRD patterns of 10mol% Cu-impregnated pure y-A1203 followed by heat treatment temperatures of 800 to 1000 °C for 3 h in air. Pure y-type alumina transforms to 0-type at the temperature range of 800 °C to 1000 °C and changes to 0:-type above 1050 °C. However, the data in Fig. 1 indicate that Cu-impregnated 7-A1203 transforms not to 0-type but to y-type modified with Cu at a temperature range of 800 °C to 900 °C. The characteristics of this Cu-modified y-phase were shown by diffraction peaks at 0.268 and 0.196 nm (20 = 33.4 ° and 46.3 ° in Fig. 1) in addition to the usual y-type pattern [3]. The data are believed to characterize the