Coarsening of Mesoporous α-Al2 3 Ceramics

Until recently, the processing of high surface area alumina ceramics has been restricted to transitional phases such as , , and . In this study, a nanocrystalline -Al_{2 3} powder (100 m²/g) was processed into mesoporous -Al_{2 3} ceramics with surface areas in the range 20 to 80 m²/g. Hence, the opportunity exists to study the effect of thermal treatment on the pore structure of a high surface area -Al_{2 3} ceramic in the temperature range 600°C to 1000°C. The reduction in surface area was characterized as pure coarsening by surface diffusion. Examination of the pore structure showed both intraparticle pores and interparticle pores in the temperature range 600°C to 800°C and only interparticle pores above 800°C. The powder particles were dense and polycrystalline. However, much of their internal structure is lost in heat treatments above 1000°C.     

Catalytic Performance of B2O3/TiO2–ZrO2 for Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime: The Effect of Boria Loading

A series of boria catalysts supported on titania–zirconia mixed oxide (B₂O₃/TiO₂–ZrO₂) with different boria loadings (8–20 wt%) were prepared and characterized by X-ray diffraction, adsorption of nitrogen, ¹¹B magic angle spinning (MAS) NMR measurements and temperature-programmed desorption (TPD) of ammonia. The catalytic performance of B₂O₃/TiO₂–ZrO₂ for vapor-phase Beckmann rearrangement of cyclohexanone oxime to -caprolactam was studied at 300°C. It was found that the lactam selectivity increased with increasing of boria loading, whereas a maximum oxime conversion was obtained at the boria loading of 12 wt%. The acid sites of medium strength on the surface of the catalyst play an important role in the selective formation of lactam.     

Active-oxygen species on non-reducible rare-earth-oxide-based catalysts in oxidative coupling of methane

From supplementary in situ Raman spectroscopic studies of active-oxygen species on non-reducible rare-earth-oxide-based catalysts in the oxidative coupling of methane (OCM) and structural adaptability considerations, further support has been obtained for our proposal that there may be an active and elusive precursor (of O₂ ^– and O₂ ^2– adspecies), most probably O₃ ^2– formed from reversible redox coupling of an O₂ adspecies at an anionic vacancy with a neighboring O^2– in the surface lattice. This active precursor may initiate H abstraction from CH₄ and be itself converted to OH^–+O₂ ^–, or it may abstract an electron from the oxide lattice and be converted to O₂ ^2–+O^–. The prospect of developing this type of OCM catalysts is discussed.     

Thermally stable alumina–gallia aerogel as a catalyst for NO reduction with C3H6 in the presence of excess oxygen

In order to improve thermal stability, an alumina–gallia aerogel was prepared and the catalyst performance for NO reduction with C₃H₆ was compared with that of an alumina–gallia xerogel. Basically, both were prepared by a sol–gel method with supercritical drying for the former, while with oven drying for the latter. Upon heating at 800, 900, and 1000°C, the aerogel exhibited higher NO conversion than the xerogel at reaction temperature <400°C, while NO conversion was lower on the former than on the latter at >500°C. At 450°C, NO conversion was almost the same for these two catalysts. A marked difference was observed upon heating them at 1100°C: the aerogel still maintained quite a high activity, while the xerogel greatly lost it. After heating the aerogel at 1100°C, -phase alumina remained untransformed with its surface area of 80 m²/g, while the xerogel was completely transformed to -alumina with its surface area of 6 m²/g. The high activity remaining on the aerogel heated at 1100°C was ascribed to its large surface area.     

Heterogeneous asymmetric reactions. 23. Enantioselective hydrogenation of ethyl pyruvate over cinchonine- and α-isocinchonine-modified platinum catalysts

The enantioselective hydrogenation of ethyl pyruvate to (S)-ethyl lactate over cinchonine- and -isocinchonine-modified Pt/Al₂O₃ catalysts was studied as a function of modifier concentration and reaction temperature. The maximum enantioselectivities obtained under the applied mild conditions were 89% ee using cinchonine (0.014 mmoldm^–3, 1 bar H₂, 23°C, 6% AcOH in toluene), and 76% ee in the case of -isocinchonine (0.14 mmoldm^–3, 1 bar H₂, –10°C, 6% AcOH in toluene). Since -isocinchonine of rigid structure exists only in anti-open conformation these data provide additional experimental evidence to support the former suggestion concerning the dominating role of anti-open conformation in these cinchona-modified enantioselective hydrogenations.     

Adsorption Isotherm and Pore Characteristics of Nano Alumina Derived from Sol-Gel Boehmite

This paper deals with a systematic investigation on the synthesis of aluminium oxide starting from mono hydroxy aluminium oxide (boehmite, (AlOOH)) which in turn is synthesized from aluminium nitrate. Boehmite on heating forms , transitional alumina and -alumina phases in the temperature range 400–600, 800–1050 and 1050–1100°C respectively. Calculation from XRD, using Scherer equation shows that -alumina has crystallite size in the range 5–10 nm, while and -alumina are in the range 10–20 nm and -alumina is about 33 nm. The textural features of aqueous sol-gel boehmite samples calcined at various temperatures were analyzed by specific surface area measurements and adsorption isotherm features. Maximum specific surface area of 266 m²/g is observed for the precursor calcined at 400°C and a minimum of 5 m²/g at 1100°C. Total pore volume is maximum for the precursor calcined at 600°C (0.2653 cm³/g). Average pore size ranges from 3 nm (400°C) to 11 nm (1100°C). The adsorption isotherms also show a change from Type IV to Type II with increase in temperature showing difference in surface properties. The information from t-plots, pore size distribution and cumulative pore volume data also indicates differences in porosity features of boehmite on calcination. The adsorption isotherm and pore size distribution analysis show maximum microporosity at 400°C, while maximum mesoporosity is observed at 600°C. At higher temperatures, porosity decreases, even though small fraction of pores in the mesopore range is still retained. At 1100°C, there is structural transformation from transitional to -alumina, with very low specific surface area 5 m²/g and pores in the size range of 11 nm. The various data presented in this study will be useful in the synthesis of alumina with tailor made properties.     

Synthesis, Characterization and Optimum Reaction Conditions of Oligo-N, N′-bis (2-hydroxy-1-naphthalidene) Thiosemicarbazone

The oxidative polycondenzation reaction conditions of N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone (HNTSC) using air oxygen, H₂O₂ and NaOCl were studied in an aqueous alkaline medium between 50–90°C. Oligo-N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone was characterized by ¹H-NMR, FT-IR, UV-Vis, size exclusion chromatography (SEC) and elemental analysis techniques. Solubility testing of oligomer was investigated using organic solvents such as DMF, THF, DMSO, methanol, ethanol, CHCl₃, CCl₄, toluene acetonitrile, ethyl acetate, concentrated H₂SO₄ and an aqueous alkaline solution. Using NaOCl, H₂O₂ and air O₂ oxidants, conversion to oligo-N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone (OHNTSC) of N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone was found to be 85, 80 and 76%, respectively, in an aqueous alkaline medium. According to the SEC analyses, the number-average molecular weight, weight-average molecular weight and polydispersity index values of OHNTSC synthesized were found to be 1050 gmol^–1 1715 gmol^–1 and 1.63, using NaOCl, and 2137, 2957 gmol^–1 and 1.38, using air O₂ and 2155 gmol^–1 4164 gmol^–1 and 1.93, using air H₂O₂, respectively. Also, TG analysis was shown to be unstable of oligo-N, N-bis (2-hydroxy-1-naphthalidene) thiosemicarbazone against thermo-oxidative decomposition. The weight loss of OHNTSC was found to be 97.29% at 900°C.     

Origin of rate bistability in Mn–O/Al2O3 catalysts for carbon monoxide oxidation: role of the Jahn–Teller effect

Peculiarities in catalytic activity in carbon monoxide oxidation as well as some structure, electronic and magnetic properties of the three oxide catalysts, Mn³⁺–O/Al₂O₃ (1), Mn³⁺–O–Fe/Al₂O₃ (Mn-substituted spinel, 2) and -Fe₂O₃/Al₂O₃ (3), were studied by kinetic measurements and by Mössbauer spectroscopy. The catalysts 1 and 2 showed a kinetic bistability with a sharp transition towards more reactive state at 200°C (ignition point). In contrast, for catalyst 3, at 200–250°C, the behavior of reaction rate against temperature did not display noticeable hysteresis. On cooling the catalysts 1 and 2, extinction was observed at about 170 and 120°C, respectively, i.e., at 30–80°C lower than the corresponding ignition points. Proximity of activation energy for the high and low activity (15–19 kJ/mol) for both Mn-containing catalysts suggests an increase in the number of active sites at high temperature with no changes in the reaction mechanism. The considerable difference between Mn-containing catalysts 1, 2 and Fe-containing catalyst 3 may be caused by Jahn–Teller (JT) type distortions of the oxygen polyhedron around Mn³⁺. A significant spontaneous axial bond stretching within the local polyhedron seems to diminish Mn–O binding energy, facilitate the participation of surface oxygen species, O_S, in the oxidation of CO by a redox mechanism and promote oxygen vacancies at the surface that would cause considerable effect on the activity. An increase in the width of the counterclockwise hysteresis loop for the catalyst 2 compared to the catalyst 1 indicates that clusters of mixed spinel provide more active sites and more labile O_S species than clusters of the binary Mn oxide.     

Porous Properties of γ-Alumina/Potassium Aluminosilicate Gel Composites Prepared by Selective Leaching and Precipitation Method

Composites of mesoporous -alumina and potassium aluminosilicate (KAS) gel were prepared by selective leaching of calcined kaolinite using KOH solution followed by neutralization of the solution at pH 5.5 with nitric acid. The porous properties of the composites were characterized by N₂ gas adsorption and their microtextures were observed by electron microscope. The resultant composites have specific surface areas of about 290 m²/g, pore sizes of about 1.85 nm in radius and pore volumes of about 0.5 ml/g. The porous properties of the composites are compared with those of -alumina and KAS gel.     

High‐activity catalyst of SO 4 2− /ZrO2 supported on γ‐Al2O3 for n‐butane isomerization

A series of Al₂O₃supported SO ₄ ^2– /ZrO₂ superacid catalysts (named SZ/Al₂O₃) were prepared by a precipitation method and their catalytic behavior for nbutane isomerization at low temperature in the absence of H₂ and at high temperature in the presence of H₂ was studied in this paper. The catalytic activities of some of these catalysts were enhanced significantly at both low and high temperatures. At 250°C after 6 h on stream, the steady activity of the most active sample, 60%SZ/Al₂O₃, is about two times higher than that of conventional SZ. The texture properties of catalysts were studied by the methods of XRD and the adsorption of N₂. Experimental evidence of IR of adsorbed pyridine indicates that the significant activity enhancements of SZ/Al₂O₃ catalysts are caused by the increasing of the amount of strong acid sites.     

Studies on the redox behaviour of La1.867Th0.100CuO4 and its catalytic performance for NO decomposition

La_1.867Th_0.100CuO₄ was prepared by means of the citric acid complexing method. The reduction–oxidation (redox) properties of this composite oxide have been investigated by using the XRD, TGA, EPR, TPD, and SEM methods. The fresh (non-reduced) La_1.867Th_0.100CuO₄ catalyst is single phase with tetragonal K₂NiF₄-type structure. There were three reduction steps observed over La_1.867Th_0.100CuO₄ in the temperature ranges of 25–100, 100–300, and 300–500 °C, respectively. After reduction at 300 °C, the material still retained its original single phase but there were oxygen vacancies generated in the lattice. After reduction at 500 °C, it decomposed to a mixture of oxides. In the course of reduction, trapped electrons were generated. During the oxidation of the reduced sample, O ₂ ^– was detected. Apparently, oxygen vacancies are able to stabilise O ₂ ^– on the surface of the -1ptcatalyst. NO adsorption on both the fresh and reduced La_1.867Th_0.100CuO₄ samples generated NO radicals and O ₂ ^– species. On a La_1.867Th_0.100CuO₄ sample reduced at 300 °C, [O₂NO₂]^2– was generated in NO adsorption and decomposed to N₂ and O^2– at ca. 730 °C. After reduction, the O ₂ ^– inside the La_1.867Th_0.100CuO₄ lattice became more mobile and participated in the decomposition of [O₂NO₂]^2–. The fresh (non-reduced) La_1.867Th_0.100CuO₄ sample with cation defects in its lattice shows higher NO decomposition activity than the fresh La₂CuO₄ sample in which there are no cation defects. The 300 °C-reduced La_1.867Th_0.100CuO₄ with cation defects and oxygen vacancies is more active than the fresh one for NO decomposition. The redox action between Cu⁺ and Cu²⁺ is an essential process for NO decomposition.     

Effect of topaz on the synthesis of mullite in mixtures of kaolinite and alumina

The synthesis of mullite in mixtures of kaolinite and alumina in the presence of small amounts of topaz is studied. Topaz is shown to activate the synthesis of both the primary (from kaolinite) and secondary mullite (through binding silica produced by thermal degradation of kaolinite), decrease the temperature of synthesis by 100°C, and increase the total yield of mullite. Products of the thermal degradation of topaz — mullite and gaseous chemically active fluoride compounds — are shown to play the role of mineralizing agents.Translated from Novye Ogneupory, No. 8, pp. 49 – 53, August, 2004.For previous communication, see Novye Ogneupory, No. 7, 41 – 46 (2004).     

First In Situ Raman Study of Vanadium Oxide Based SO2 Oxidation Supported Molten Salt Catalysts

In situ Raman spectroscopy at temperatures up to 500°C is used for the first time to identify vanadium species on the surface of a vanadium oxide based supported molten salt catalyst during SO₂ oxidation. Vanadia/silica catalysts impregnated with Cs₂SO₄ were exposed to various SO₂/O₂/SO₃ atmospheres and in situ Raman spectra were obtained and compared to Raman spectra of unsupported model V₂O₅–Cs₂SO₄ and V₂O₅–Cs₂S₂O₇ molten salts. The data indicate that (1) the V^V complex V^VO₂(SO₄)₂ ^3– (with characteristic bands at 1034 cm^–1 due to (V=O) and 940 cm^–1 due to sulfate) and Cs₂SO₄ dominate the catalyst surface after calcination; (2) upon admission of SO₃/O₂ the excess sulfate is converted to pyrosulfate and the V^V dimer (V^VO)₂O(SO₄)₄ ^4– (with characteristic bands at 1046 cm^–1 due to (V=O), 830 cm^–1 due to bridging S–O along S–O–V and 770 cm^–1 due to V–O–V) is formed and (3) admission of SO₂ causes reduction of V^V to V^IV (with the (V=O) shifting to 1024 cm^–1) and to V^IV precipitation below 420°C.     

Synthesis of Titania Pillared Saponite in Aqueous Solution of Acetic Acid

The preparation of TiO₂-pillared saponite was carried out in a CH₃COOH aqueous solution. Titanium ion species to intercalate into the interlayer of saponite were obtained by an addition of Ti(C₃H₇O)₄ to an aqueous solution of CH₃COOH and by subsequent aging of the solution for a prescribed time. Ti⁴⁺-intercalated saponite including organic materials was obtained by ion exchange. After the sample was calcined at 500°C in air, TiO₂-pillared saponite was obtained. The resulting TiO₂-pillared saponite (Ti-Sapo) possessed surface areas in the range 300–400 m²/g and a sharp pore size distribution with the pore radius of 1.2 nm. The basal spacing of the product heated at temperature >250°C was about 2.45 nm. The pillar height of TiO₂ in the Ti-Sapo was estimated to be 1.5 nm.     

Isotopic assessment of CO<Subscript>2</Subscript> production through soil organic matter decomposition in the tropics

Values of ¹³C and ¹⁵N of soil organic matter (SOM) under different land cover in Pasir Mayang, Jambi Province, Sumatra Island, Indonesia were examined to apply them as indicators of SOM dynamics and related CO₂ production. The ¹³C and ¹⁵N values of SOM increased with depth in the 0–30 cm layer in the preserved forest, reflecting ¹³C and ¹⁵N richment in SOM through mineralization and immobilization. The degree of vertical enrichment, difference between 0–5 cm and 10–15 cm SOM, was more pronounced in ¹⁵N than in ¹³C at all sites in Pasir Mayang. The ¹³C -SOM profiles fluctuated through clear-cutting the forest and subsequent burning, which was due to input of biomass with higher C/N molar ratio and lower ¹³C value than the original SOM. However, the ¹⁵N-SOM profiles before and after such a drastic event did not change appreciably. The ¹⁵N-SOM became higher as the C/N ratio decreased and as soil sugar content decreased. These observations suggest that ¹⁵N-SOM is a variable that changes with the amount of easily decomposable organic matter (EDOM) in soil. Soil incubation experiments demonstrated a correlation between CO₂ production rate and degree of vertical ¹⁵N-enrichment in SOM, which was applied to field data to estimate CO₂ production through SOM decomposition. A similar analysis was performed with the soils collected at 27 locations in other districts in Jambi Province than Pasir Mayang. In five locations covered by oil palm plantation, CO₂ production through SOM decomposition controlled 70 of variation in CO₂ emission among the locations. In the remaining 22 locations, however, the CO₂ emission was neither related to CO₂ production from SOM nor to ground litter amount. This observation indicated that mechanisms other than dead organic matter decomposition such as root respiration were dominant sources for CO₂ emission in these sites.     

Synthesis of nano-crystalline Ce0.9Gd0.1O1.95 electrolyte by novel sol–gel thermolysis process for IT-SOFCs

In the present work, nano-crystalline Ce_0.9Gd_0.1O_1.95 (GDC) powder has been successfully prepared by a novel sol–gel thermolysis method using a unique combination of urea and PVA. The gel precursor obtained during the process was calcined at 400 and 600 °C for 2 h. A range of analyzing techniques including XRD, TGA, BET, SEM, EDS and TEM were employed to characterize the physical and chemical properties of obtained powders. GDC gel precursors calcined at 400 and 600 °C were found to have an average crystallite size of 10 and 19 nm, respectively. From the result of XRD patterns, we found that well-crystalline cubic fluorite structure GDC was obtained by calcining the precursor gel at 400 and 600 °C. It has been also found that the sintered samples with lower temperature calcined powder showed better sinterability as well as higher ionic conductivity of 2.21 × 10⁻² S cm⁻¹ at 700 °C in air.     

Dielectric properties and microstructures of CaSiO3 ceramics with B2O3 addition

The effects of B₂O₃ additives on the sintering behavior, microstructure and dielectric properties of CaSiO₃ ceramics have been investigated. The B₂O₃ addition resulted in the emergence of CaO–B₂O₃–SiO₂ glass phase, which was advantageous to lower the synthesis temperature of CaSiO₃ crystal phase, and could effectively lower the densification temperature of CaSiO₃ ceramic to as low as 1100 °C. The 6 wt% B₂O₃-doped CaSiO₃ ceramic sintered at 1100 °C possessed good dielectric properties: _r = 6.84 and tan δ = 6.9 × 10⁻⁴ (1 MHz).     

Reductive Activation of Dioxygen in Catalytic Systems Including Platinum and Heteropoly Compounds: Oxidation of Cyclohexane

Thermal activation of clayzic catalyst has been thoroughly investigated by calcining anhydrous ZnCl₂ impregnated on Mont-K10 with different ZnCl₂ loadings (0.5-2.0 mmol g^-1) under static or flowing air at 270 °C and also under N₂ flow at different temperatures (150-400 °C). Depending upon the ZnCl₂ loading and calcination temperatures, an appreciable amount of HCl is evolved in the thermal activation, indicating an occurrence of reaction between the ZnCl₂ and the surface hydroxyl groups of the clay (- OH + ZnCl₂ - O - Zn - Cl + HCl), leading to formation of new Lewis acid sites (- O - Zn -Cl). The Cl/Zn ratio, surface area and catalytic activity (in the benzene benzylation by benzyl chloride at 80 °C) of the clayzic formed in the thermal activation are influenced markedly by the ZnCl₂ loading and calcination conditions (temperature and gas atmosphere). The maximum catalytic activity for the clayzic is observed at the optimum ZnCl₂ loading (about 1.0 mmol g^-1) and calcination temperature (about 270 °C). The thermal activation at 270 °C under flowing N₂ led to a most active clayzic catalyst for the benzene benzylation. A temperature-programmed evolution of HCl in the calcination of ZnCl₂/Mont-K10 with different ZnCl₂ loadings from 25 to 400 °C at a linear heating rate of 2 °C min^-1 has also been investigated.     

The influence of thermal pretreatment of Re/γ-alumina catalysts in hydrogen on their activity for hydrogenation and hydrogenolysis of benzene

The specific activity of Re/-alumina catalysts (10.4 and 1.04 wt% Re) preheated in hydrogen at 550–800°C for benzene hydrogenation and hydrogenolysis at 80–300°C has been found to not change or to increase with increasing pretreatment temperature, respectively. The results are discussed in relation to the metal dispersion.