Preparation,characterization and hydrotreating performances of ZrO2–Al2O3-supported NiMo catalysts

A series of Al₂O₃–ZrO₂ composite supported NiMo catalysts with various ZrO₂ contents were prepared. Several techniques including XRD, SEM, N₂ physisorption, H₂-TPR, and UV–vis DRS were used for typical physico-chemical properties characterization of the ZrO₂–Al₂O₃ composite supports and their NiMo/ZrO₂–Al₂O₃ catalysts. The test results showed that the composite supports prepared by the chemical precipitation method existed as amorphous phase in the samples with insufficient contents of ZrO₂, and the incorporation of ZrO₂ into supports provided a better dispersion of NiMo species, which made their reductions become easier. The pyridine-adsorbed FT-IR results indicated that the Lewis acid sites of catalysts increased significantly by the introduction of ZrO₂ into the supports. The activities of these catalysts for diesel oil hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) were evaluated in a high pressure micro-reactor system. The results showed that the ZrO₂–Al₂O₃-supported NiMo catalysts with suitable ZrO₂ contents exhibited much higher catalytic activities than that of Al₂O₃-supported one, and when the ZrO₂ contents were 15% and 5%, the NiMo/Al₂O₃–ZrO₂ catalysts presented the highest HDS and HDN activities, respectively.     

Surface and bulk crystallization in Nd2O3–Al2O3–SiO2–TiO2 glasses

Neodymium aluminosilicate (Nd₂O₃–Al₂O₃–SiO₂; NdAS) glasses have been investigated for the effect of concentration of TiO₂ on the crystallization mechanism and for the effect of surface condition on crystal growth. NdAS glasses with 0–10 wt.% TiO₂ were heat-treated for nucleation and crystal growth and were examined for phase separation and morphology of surface crystals as well as for crystal growth rate. All the glasses exhibit surface crystallization, however, the glass having 8 wt.% TiO₂ also exhibits internal crystallization after a two-stage heat treatment. Surface crystallization was dependent on the condition of the glass surface and the amount of TiO₂. The crystal growth on the cut surface was faster than on the fractured surface and the growth rate in surface increased with increasing TiO₂. The phase separation found in NdAS glasses containing above 8 wt.% TiO₂, was confirmed to be an important factor controlling the internal crystallization process in Nd₂O₃–Al₂O₃–SiO₂–TiO₂ glasses.     

Synthesis,Characterization and Application of Co–MgO Mixed Oxides in Oxidation of Carbon Monoxide

The present work deals with the synthesis of nanostructured Co–MgO mixed oxides with different weight ratios of cobalt by a facile co-precipitation method as a catalyst for low-temperature CO oxidation. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption/desorption (BET), Fourier transform infrared spectroscopy (FTIR), and transmission and scanning electron microscopies (TEM and SEM) techniques. The results revealed that inexpensive cobalt–magnesium mixed metal oxide nanoparticles have a high potential as catalyst in low-temperature CO oxidation. The Co–MgO mixed oxide with 30 wt.% cobalt had the highest activity. The results showed that the catalysts pretreated under O₂-containing atmosphere possessed higher activity compared to the catalyst pretreated under H₂ atmosphere. Co–MgO catalyst showed a good repeatability in reaction condition. The stability test exhibited that the Co–MgO mixed oxides were highly stable for CO oxidation over a 30 h time on stream in the feed gas containing a high amount of moisture and CO₂.     

Synthesis and Characterization of Titania Nanoparticles on the Surface of Microporous Perlite Using Sol–Gel Method: Influence of Titania Precursor on Characteristics

Titania colloidal nanoparticles have been successfully fabricated by a very simple and inexpensive sol–gel spin-coating method on the surface perlite granules. This was achieved by adjustment of the sol–gel parameters such as the precursors, spin-coating time and heating processes. Five samples were prepared using different titania e.g. Millennium, Degussa P25, titania nanoparticle, sol–gel derived titania and rutile nanoparticles precursors. Titania nanoparticles were grown on perlite granules by the controlled immobilization of titania. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were employed to investigate the growth and morphology of the titania coating on perlite granules. The results showed surface modification of perlite granules with uniform coating of titania on supports and confirmed that the coatings are composed of aggregated crystallites of 11–61 nm in diameter, good compositional uniformity and good adherence of the fabricated titania layer on perlite granules. The synthesis of adsorptive supports for immobilization of powdery photocatalysts would show significant improvements in both practical use and degradation efficiency of photocatalysis in environmental protection.     

Characterization and sintering of gels in the system MgO–Al2O3–SiO2

Cordierite aerogels, made by supercritical drying, and xerogels, formed by ambient pressure drying, have been prepared by combining two different recipes. The chemical composition of the gels varied from stoichiometric cordierite 2MgO·Al₂O₃·5SiO₂ to 0·5MgO·1·4Al₂O₃·5SiO₂ due to different procedures for washing of the gels. The crystallization of nearly stoichiometric cordierite gels was shown to be relatively complex involving the formation of several metastable phases such as μ-cordierite (Mg₂Al₄Si₅O₁₈), spinel (Al₆Si₂O₁₃) and sapphirine (Mg₄Al₈Si₂O₂₀) before the equilibrium phase composition was obtained at around 1350°C. On the other hand, during crystallization of gels with stoichiometry close to 0·5MgO·1·4Al₂O₃·5SiO₂ the equilibrium phases mullite, cristobalite and α-cordierite were the major phases formed during heat treatment. A lower densification rate was observed for aerogels compared to xerogels due to a larger pore size. A lower crystallization temperature in aerogels probably due to heterogeneous nucleation reduced the densification. For gels with a composition near 0·5MgO·1·4Al₂O₃·5SiO₂ nucleation and densification occur simultaneously and large differences in the densification behavior was observed. ©     

Phase diagram study and thermodynamic modeling of the Na2O–Al2O3–ZrO2 system

The phase diagram of the Na₂O–Al₂O₃–ZrO₂ system was experimentally studied at 1500°C–1650°C by a classical equilibration/quenching method and differential thermal analysis followed by X-ray diffraction phase analysis and electron probe micro-analysis. A sealed Pt crucible was utilized to prevent the volatile loss of Na₂O during high-temperature phase equilibrium experiments and the hydration upon quenching. The phase diagram of the Na₂O–Al₂O₃–ZrO₂ system was revealed for the first time. Based on the present experimental data and available binary modeling results in literature, the thermodynamic modeling of the ternary system was performed using the Calculation of Phase Diagram method and the phase diagram of the entire the Na₂O–Al₂O₃–ZrO₂ system was constructed and the optimized thermodynamic properties for all solids and liquid phase within the ternary system were obtained.     

Fabrication and microstructure of Al2O3–ZrO2(3Y)–SiC nanocomposites

Al₂O₃–ZrO₂(3Y)–SiC composite powder was prepared by the heterogeneous precipitation method. Calcinating temperature of the powder was important to obtain dense sintered body. The nanocomposites were got by hot-pressing, and addition of ZrO₂ did not raise the sintering temperature. Some Al₂O₃ grain shape was elongated, and Al₂O₃ grain size was about μm. Nano SiC particles were observed uniformly distributing throughout the composites, and most of them were located within the matrix grains. Because SiC particles located within ZrO₂ grains influenced the phase transformation of ZrO₂, the sintering of nanocomposites, which controlled grain size and transformable ZrO₂ amount, become important to get high performance. The strength of 80 wt% Al₂O₃–15 wt% ZrO₂–5 wt% SiC nanocomposites was 555 MPa, and toughness was 3·8 MPa m^1/2, which were higher than those of monolithic Al₂O₃ ceramics. ©     

Relationship Between the Synthesis and Structure of Ceramic Precursors of the TiO2–CeO2–ZrO2 System

Refractories and Industrial Ceramics - Tetragonal solid solutions based on the TiO2–CeO2–ZrO2 system stable up to 1,350°C were obtained. A method of pH titration of the initial...     

Synthesis of Camphene by α-Pinene Isomerization Using W2O3–Al2O3 Catalysts

W₂O₃–Al₂O₃ catalysts prepared by “sol–gel” and impregnation methods were characterised by XRD, FTIR and nitrogen adsorption. Both catalysts were tested in the isomerization of α-pinene in a batch reactor at atmospheric pressure and 150 °C. Conversion of α-pinene and selectivity to camphene was superior for the “sol–gel” catalyst than that observed for the impregnated catalyst.     

Mechanical and functional properties of Al2O3–ZrO2–MWCNTs nanocomposites

Multi-walled carbon nanotubes (MWCNTs) are often reported as additives improving mechanical and functional properties of ceramic composites. However, despite tremendous efforts in the field in the past 20 years, the results are still inconclusive. This paper studies room temperature properties of the composites with polycrystalline alumina matrix reinforced with 0.5–2 vol.% MWCNTs (composites AC) and zirconia toughened alumina with 5 vol.% of yttria partially stabilised zirconia (3Y-PSZ) containing 0.5–2 vol.% of MWCNTs (composites AZC). Dense composites were prepared through wet mixing of the respective powders with functionalised MWCNTs, followed by freeze granulation, and hot-pressing of granulated powders. Room temperature bending strength, Young's modulus, indentation fracture toughness, thermal and electrical conductivity of the composites were studied, and related to their composition and microstructure. Slight increase of Young's modulus, indentation fracture toughness, bending strength, and thermal conductivity was observed at the MWCNTs contents ≤1 vol.%. At higher MWCNTs contents the properties were impaired by agglomeration of the MWCNTs. The DC electrical conductivity increased with increasing volume fraction of the MWCNTs.     

Ultrasound Synthesis of Polyindole–TiO2 Nanocomposite and Evaluation of Antibacterial Activity

The present work reports the synthesis and evaluation of antimicrobial activity of polyindole–TiO₂ nanocomposite. Polyindole–TiO₂ nanocomposite was synthesized by aqueous in situ chemical polymerization of indole using ammonium persulfate as an oxidant under ultrasonic condition. The synthesized polyindole and polyindole–TiO₂ nanocomposites were characterized by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscope, thermogravimetric analysis, and X-ray diffraction techniques. A sharp peak at ～1,402?cm^?1 is due to the stretching vibrations of O?Ti?O bond in polyindole–TiO₂ nanocomposite. The X-ray diffraction pattern shows the major diffraction peaks at 25°C and 48°C, indicating TiO₂ in anatase form. Polyindole–TiO₂ shows maximum activity against gram-positive Staphylococcus aureus and Bacillus subtilis as compared to gram-negative Escherichia coli.     

Effects of KF Loading on Mg–Al Mixed Oxides for the Selective Synthesis of Trimethylolpropane Triesters

A series of Mg–Al hydrotalcites (HTCs) calcined at different temperatures were evaluated for their suitability as solid base catalysts for the selective synthesis of trimethylolpropane triesters (TMPTEs) via transesterification of trimethylolpropane (TMP) with a mixture of C₈–C₁₀ fatty acid methyl esters (FAMEs). The effect of potassium fluoride (KF) loading of the calcined HTCs on the physicochemical and catalytic properties of the materials attained was ascertained. Using a 5?wt% catalyst loading and a FAME:TMP molar ratio of 3.5:1 at 170°C for 8?h, the Mg–Al mixed oxide obtained by calcining HTC at 500°C (HTC-500) gave the highest TMPTE selectivity and FAME conversion. Impregnating HTC-500 with 10?wt% KF (KF/HTC-500) generated strongly basic KMgF₃, KOH, K₂O, and coordinatively unsaturated F^? sites. The FAME conversion and TMPTE yield obtained over different HTC and KF/HTC-500 catalysts depended on their total basicity, where a basic strength of 15?H_{_}?3, a common homogeneous base for the polyol ester production.     

Citrate-Nitrate Synthesis and the Electrophysical Properties of Ceramics in the K2O–TiO2–Fe2O3 System

Glass Physics and Chemistry - This paper presents a study of the electrically conductive properties of ceramics based on phases crystallizing in the K2O–Fe2O3–TiO2 system, when using...     

Heat-Insulating Properties of High-Alumina Materials Filament-Reinforced with Glass Fiber of the Al2O3–SiO2 and Al2O3–SiO2–ZrO2 Systems

Refractories and Industrial Ceramics - Refractory heat-insulating materials produced in Russia are characterized. The thermal stability of high-alumina heat-insulating materials filament-reinforced...     

Mechanism of the hydrodenitrogenation of o-toluidine and methylcyclohexylamine over NiMo/γ-Al2O3

The hydrodenitrogenation (HDN) of o-toluidine and its reaction intermediates was studied over a NiMo/γ-Al₂O₃ catalyst. The kinetics of the HDN of methylcyclohexylamine and of the hydrogenation of cyclohexene were also studied. Hydrogenation of o-toluidine alone produces methylcyclohexene and methylcyclohexane. When a sufficient quantity of cyclohexene is added during the HDN of toluidine, methylcyclohexylamine, the first intermediate in the hydrogenation of toluidine, becomes detectable. Because of its strong adsorption constant and high rate constant for reacting further to methylcyclohexene and methylcyclohexane, methylcyclohexylamine is not observed in the HDN of toluidine. Adding cyclohexene decreases the adsorption of methylcyclohexylamine, thus enabling its detection. The rate and adsorption constants of methylcyclohexylamine and cyclohexene in the HDN of methylcyclohexylamine were calculated by fitting the kinetic data to a Langmuir–Hinshelwood equation. A two-site model was used to describe the surface reactions, with one site for the methylcyclohexylamine reactions and the other for the cyclohexene reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal shock resistance of Cr2O3–Al2O3–ZrO2 bricks with the microstructure of Cr2O3 aggregates coated by ZrO2

Zirconia-coated Cr₂O₃ aggregates synthesized by mixing ZrO₂ powders and Cr₂O₃ aggregates with a phenolic resin binder followed by thermosetting treatment were employed as modified Cr₂O₃ aggregates to obtain Cr₂O₃–Al₂O₃–ZrO₂ bricks (high-chromia bricks). The elastic modulus (E) and cold modulus of rupture (CMOR) of these high-chromia bricks before and after thermal shock cycles were systematically investigated, and the residual ratios of CMOR and E were calculated. The thermal shock resistance of the high-chromia bricks was significantly improved by the factor of modification of Cr₂O₃ aggregates. The mechanism of the improved thermal shock resistance of these high-chromia bricks was studied via microstructure analysis, and the crack propagation behavior was analyzed by scanning electron microscopy (SEM). The fracture work (γ_WOF), thermal shock damage factor (R′′′′), and thermal stress crack stability parameter (R_st) were measured and calculated using the wedge splitting test (WST). The results indicate that the porous ZrO₂ coating layer wrapped the Cr₂O₃ aggregates, forming modified Cr₂O₃ aggregates that can increase crack deflection, free path of crack propagation, and fracture work, thus improving the thermal shock resistance of high-chromia bricks. The thermal shock resistance of the fabricated high-chromia bricks was highly correlated with the thickness of the ZrO₂ coating layer surrounding the Cr₂O₃ aggregates. The variation trend of R_st is well consistent with the experimental results, which is suitable to evaluate the thermal shock resistance of high-chromia bricks.     

Initial catalyst deactivation in the hydrotreatment of coal liquid over NiMo and CoMoγAl2O3 catalysts

The Australian brown coal-derived oil mixed with a hydrogenated creosote oil was hydrotreated over NiMo and CoMoγAl₂O₃ catalysts. The initial catalytic activities varied with the reaction for each catalyst: converting of the hexane-insolubles to the hexane-soluble oils(HDHI) > hydrodesulfurization(HDS) > hydrodenitrogenation(HDN) > hydroconverting of the 623 K⁺ residues to the 623 K⁻ oils(HDC). A NiMo catalyst showed higher activities than a CoMo catalyst did. The initial catalyst deactivation was significant in the order of HDC > HDN > HDS > HDHI for each catalyst. The degrees of the deactivation were larger for a CoMo catalyst. The analyses of the spent catalysts showed that the pore volumes and the surface areas were decreased markedly by the carbonaceous deposits, in which higher amounts of the N- and O-containing compounds accumulated. The XPS and elemental analyses of the spent catalysts indicated that the decreases in the amounts of sulfur during the course of run were linked with the decreases in the sulfidic states of molybdenum(Mo⁴⁺ species) and the promoters. These carbonaceous deposits and the changes in chemical states of the supported metals were interpreted as the main reasons for the initial catalyst deactivation.