IR study on migration of 18OCH3 species on ZrO2

The migration of methoxy groups on ZrO₂ was studied by using ¹⁸O-labelling and IR spectroscopy. The C-O bond of the methoxy group was found to remain intact during the migration of the bridged species to the vacant terminal sites on ZrO₂. This revised version was published online in July 2006 with corrections to the Cover Date.     

聚甲醛/共聚酰胺共混物的结晶形态及力学性能

研究了共聚酰胺含量对聚甲醛/共聚酰胺(POM/COPA)共混物结晶形态及力学性能的影响。结果表明:POM/COPA共混物中存在氢键相互作用;结晶温度对POM的结晶形态有较大影响,温度较高时POM结晶较完善,球晶尺寸较大;同时,COPA的加入使共混物的球晶细化,极大地改善了POM的韧性。当COPA含量为4%时,共混物缺口冲击强度达到最大值,拉伸强度几乎不变,POM/COPA具有较理想的综合力学性能。     

纳米SiO2／双马来酰亚胺复合材料的性能研究

采用浇铸成型法制备了纳米SiO2粒子填充双马来酰亚胺(BMI-BA)复合材料，研究了纳米SiO2的填充量对复合材料滑动磨损性能的影响。在磨损机上测试该复合材料的摩擦和磨损性能，利用扫描电镜(SEM)观察了复合材料的磨损表面和对磨环的表面形貌。结果表明，纳米SiO2能够有效地提高复合材料的力学性能和摩擦学性能。当纳米SiO2粒子的添加量为0．75％(质量含量，下同)时，复合材料的综合力学性能最好；当纳米SiO2粒子的的添加量为1．0％时，复合材料的耐磨性能最好。SEM显示复合材料主要是黏着磨损，能在对磨环上形成薄而连续的均匀转移膜，而BMI-BA树脂主要发生的是疲劳磨损，并伴有塑性变形。     

Low-temperature Oxidation of Carbon Monoxide on Co/ZrO2

A 10%Co/ZrO₂ catalyst prepared by impregnation was tested for its activity for the oxidation of CO to CO₂ in excess oxygen. Activity tests showed that conversion could be obtained at temperatures as low as 20 °C. Time-on-stream studies showed no loss of activity in these experiments, indicating that this catalyst is stable in the experimental oxidizing conditions. The activation energy for the CO to CO₂ oxidation reaction was calculated as E_a = 54 kJ/mol over this catalyst. Characterization of the material by thermogravimetric analysis, temperature-programmed techniques, X-ray photoelectron spectroscopy, and laser Raman spectroscopy indicate that Co₃O₄ is present on monoclinic ZrO₂ after the calcination of the catalyst.     

SELECTIVE CARBON MONOXIDE OXIDATION IN H2-RICH GAS STREAM OVER Co3O4/CeO2/ZrO2, Ag/CeO2/ZrO2, AND MnO2/CeO2/ZrO2 CATALYSTS

Activity and selectivity of selective CO oxidation in an H₂-rich gas stream over Co₃O₄/CeO₂/ZrO₂, Ag/CeO₂/ZrO₂, and MnO₂/CeO₂/ZrO₂ catalysts were studied. Effects of the metaloxide types and metaloxide molar ratios were investigated. XRD, SEM, and N₂ physisorption techniques were used to characterize the catalysts. All catalysts showed mesoporous structure. The best activity was obtained from 80/10/10 Co₃O₄/CeO₂/ZrO₂ catalyst, which resulted in 90% CO conversion at 200°C and selectivity greater than 80% at 125°C. Activity of the Co₃O₄/CeO₂/ZrO₂ catalyst increased with increase in Co₃O₄ molar ratio.     

Improvement of Pt/ZrO2 by CeO2 for high pressure CH4/CO2 reforming

CH₄/CO₂ reforming over Pt/ZrO₂, Pt/CeO₂ and Pt/ZrO₂ with CeO₂ was investigated at 2 MPa. Pt/ZrO₂, which shows stable activity under 0.1 MPa, and Pt/CeO₂ showed gradual deactivation with time at the high pressure. The deactivation was suppressed drastically on Pt/ZrO₂ with CeO₂ prepared by different impregnation order (co-impregnation of Pt and CeO₂ on ZrO₂, and consecutive impregnation of Pt and CeO₂ on ZrO₂). The amount of coke deposition was found insignificant and similar among all the catalysts (including Pt/ZrO₂ and Pt/CeO₂). Catalytic activity after the reaction for 24 h was in agreement with Pt particle size after the reaction for same period, indicating that the difference of the catalytic stability is mainly dependent on the extent of Pt aggregation through catalyst preparation, H₂ reduction, and the CH₄/CO₂ reforming. Pt aggregation and the amount of coke deposition were least pronounced on (Pt–Ce)/ZrO₂ prepared by impregnation of CeO₂ on Pt/ZrO₂ and the catalyst showed highest stability.     

Infrared studies of ethene hydrogenation over ZrO2

Hydrogenation of adsorbed ethene over ZrO₂ at low temperature was observed by in situ infrared transmission spectroscopy. It was found that di-hydrogen was directly activated on the site where ethene was already adsorbed, which was confirmed by the comparison of adsorbed species produced during the reaction and adsorbed ethane species.     

Matrix–filler interactions in polysilazane-derived ceramics with Al2O3 and ZrO2 fillers

Interactions between a poly(vinyl)silazane and Al₂O₃ or Y₂O₃-stabilised ZrO₂ fillers were studied during the fabrication of polysilazane-derived bulk ceramics in order to investigate the influence of oxide fillers on resulting properties. Specimens were produced by coating of the filler powders with the polysilazane, warm-pressing of the resulting composite powders, and pyrolytic conversion in flowing N₂ at various temperatures between 1000 °C and 1400 °C. Significant differences in densification were observed, depending on the filler used. Reactions between the polysilazane-derived matrix and Al₂O₃ or ZrO₂ at temperatures ≥1300 °C resulted in the formation of Si₅AlON₇ or ZrSiO₄, respectively. Reactivity in the polysilazane-derived component was a result of SiO₂ contamination caused primarily by adsorbed species on the filler particle surface. Knowledge of polysilazane/filler interface processes is found to be decisive for the prediction of properties such as shrinkage and porosity, which heavily influence performance of a material.     

Infrared and carbon dioxide chemisorption study of Mo/ZrO2 catalysts

The interaction of Mo with zirconia has been investigated by infrared spectroscopy (IR) and carbon dioxide chemisorption. Quantitative analysis of the IR results indicated that Mo interacts preferentially with the most basic hydroxyl group (high frequency band at 3775 cm^–1). An approximately 79% decrease in the 3775 cm^–1 band is observed vs. 21% for the low frequency band at 3673 cm^–1, with increasing the Mo loading up to 1 wt%. The relative decrease of the IR band at 3775 cm^–1 was identical to that measured for the CO₂ uptake. The Mo cross-sections estimated from CO₂ chemisorption results were much higher than those typically reported for the Mo system. It was concluded that, as previously reported for the Mo/Al₂o₃ system, CO₂ chemisorption overestimates the surface coverage of Mo/ZrO₂ catalysts.     

Characterization of Supported NiSO4 and Effect of TiO2–ZrO2 Composition on Catalytic Activity for Acid Catalysis

A series of catalysts, NiSO₄/TiO₂–ZrO₂ having different TiO₂–ZrO₂ composition, for acid catalysis was prepared by the impregnation method using an aqueous solution of nickel sulfate. The addition of TiO₂ to ZrO₂ improved the surface area of the catalyst and enhanced its acidity remarkably because of the formation of new acid sites through the charge imbalance of Ti–O–Zr bonding. The binary oxide, TiO₂–ZrO₂ calcined above 600 °C resulted in the formation of crystalline orthorhombic phase of ZrTiO₄. Therefore, NiSO₄/TiO₂–ZrO₂ calcined at 500 °C exhibited a maximum catalytic activity for acid catalysis, and then the catalytic activity decreased with the calcination temperature. The correlation between catalytic activity and acidity held for both reaction, 2-propanol dehydration and cumene dealkylation. NiSO₄ supported on 50TiO₂–50ZrO₂ (TiO₂/ZrO₂ ratio = 1) among TiO₂–ZrO₂ binary oxides exhibited the highest catalytic activity for acid catalysis.     

Catalytic Performance of Pt/ZrO2 and Pt/Ce-ZrO2 Catalysts on CO2 Reforming of CH4 Coupled with Steam Reforming or Under High Pressure

CO₂ reforming of methane was performed on Pt/ZrO₂ and Pt/Ce-ZrO₂ catalysts at 1073K under different reactions conditions: (i) atmospheric pressure and CH₄:CO₂ ratio of 1:1 and 2:1; (ii) in the presence of water and CH₄:CO₂ ratio of 2:1; (iii) under pressure (105 and 190 psig) and CH₄:CO₂ ratio of 2:1. The Pt supported on ceria-promoted ZrO₂ catalyst was more stable than the Pt/ZrO₂ catalyst under all reaction conditions. We ascribe this higher stability to the higher density of oxygen vacancies on the promoted support, which favors the cleaning mechanism of the metal particle. The increase of either the CH₄:CO₂ ratio or total pressure causes a decrease in activity for both catalysts, because under either case the rate of methane decomposition becomes higher than the rate of oxygen transfer. The Pt/Ce-ZrO₂ catalyst was always more stable than the Pt/ZrO₂ catalyst, demonstrating the important role of the support on this reaction.     

Oxidation of o-Xylene to Phthalic Anhydride on Sb-V/ZrO2 Catalysts

Zirconia-supported and bulk-mixed vanadiumantimonium oxide catalysts were used for the oxidation of o-xylene to phthalic anhydride. X-ray diffraction, Raman spectroscopy and photoelectron spectroscopy were used for characterization. It was found that vanadium promotes the transition of tetragonal to monoclinic zirconia. The simultaneous presence of Sb and V on zirconia at low coverage led to a preferential interaction of individual V and Sb oxides with the zirconia surface rather than the formation of a binary Sb-V oxide, while at higher Sb-V contents the formation of SbVO₄ took place. Sb-V/ZrO₂ catalysts showed high activity for o-xylene conversion and better selectivity to phthalic anhydride as compared to V/ZrO₂ catalysts. However, their selectivity to phthalic anhydride was poor in comparison to a V/TiO₂ commercial catalyst. The improved selectivity of the Sb-containing catalysts is attributed to the blocking of non-effective surface sites of ZrO₂, the decrease of the total amount of acid sites and the formation of surface V-O-Sb-O-V structures.     

Fabrication of Polyimide-Modified UHMWPE Composites and Enhancement Effect on Tribological Properties

Polyimide-modified ultrahigh molecular weight polyethylene (UHMWPE) composites were fabricated by hot-press molding process. Mesoscopic morphologies of polyimide/UHMWPE blending systems show high compatibility between the phases of polyimide and UHMWPE when the weight ratio of polyimide is no more than 50?wt%. Investigation of the tribological properties with a reciprocating ball-on-flat contact tribometer shows that the polyimide filler has important effects on the friction and wear behavior of UHMWPE composites. Compared to pure UHMWPE, the composite with 50?wt% polyimide improved tribological properties best and exhibited 43.1% reduction in friction coefficient and 66.7% reduction in wear volume loss.     

Synthesis of porous Al2O3/ZrO2 nanocomposites by chemical vapour deposition

Al₂O₃/ZrO₂ one-dimensional nanocomposite structures were synthesised by chemical vapour deposition using Al₂O₃ nanowires and a ZrCl₄ powder source at a temperature of 800?°C and a pressure of 130?Pa. The samples were characterised using X-ray diffraction, the scanning electron microscopy, the transmission electron microscopy, and N₂ adsorption–desorption. The results revealed that Al₂O₃/ZrO₂ composite nanowires coated with surface-embedded ZrO₂ nanocrystals were formed and that the ZrO₂ macroporous and mesoporous structures changed as the ZrO₂ deposition time increased. The pore structure and surface area were also elucidated from the N₂ adsorption–desorption measurements.     

Evaluation of oxygen storage profile on CeO2–ZrO2 mixed oxides by periodic injections of O2 pulse and their reduction behavior

Oxygen storage profile on CeO₂–ZrO₂ mixed oxide (CZ) has been observed by periodic injections of O₂ pulse. The reduction behavior of oxygen after the O₂ pulse injection was also investigated using Temperature Programmed Reduction (TPR) method. The oxygen storage profiles of the CZ catalyst with κ-CeZrO₄ phase indicate that the solid solution phase facilitates to diffuse oxygen into the bulk, and TPR profiles suggest that oxygen is preferentially stored by the reaction with Ce³⁺ species derived from CeO₂ phase compared with those from the κ-CeZrO₄ phase, especially at low temperatures.     

Effect of Sizes of Nano Ca3(PO4)2 on Mechanical and Thermal Properties of Polyurethane Foam Composites

Particular sizes of nano inorganic filler, Ca₃(PO₄)₂ were prepared by following the matrix mediated growth technique. Composite foams were prepared on addition of different concentration (0.5–2.5 wt.%) of nano size filler in a single–phase polyurethane matrix. The differential Scanning Calorimetry (DSC) for composite as well as pure polyurethane was done to ascertain the degree of interaction of filler with the structure of the matrix as active sites. The degree of cell formation increases on increase in amount of reduced size nano filler in the composites where as decrease in case of larger size filler in composites. The increment in specific gravity from 0.17–0.25 for reduced nano size filler and 0.17–0.18 in case of larger size filler makes a strong support for the increment of cell numbers. The significant enhancement 250% in compressive strength, and the reduction of cell sizes shown in optical photographs satisfies the reasons of increment in heat of fusion (ΔH) in DSC. The decrement in (ΔH) cal/g in case of larger size filler for curing shows the conduction of heat is more due formation of cells less in numbers results in reduction of rate of heating more. Thermal gravimetric analysis (TGA) was done to know the degradation behavior. The TGA results, shows increment in onset temperature and mid temperature of the first step degradation in case of larger size nano filler. Decrement of flammability from 0.47–13.14 sec/mm for reduced nano size filler and 0.47–8.23 sec/mm in case of larger size filler, show that the incorporation of nano particles not only improves the mechanical properties but also retards the flammability.     

Biomimetic Catalysts Based on Au@TiO2-MoS2-CeO2 Composites for the Production of Hydrogen by Water Splitting

The photocatalytic hydrogen evolution reaction (HER) by water splitting has been studied, using catalysts based on crystalline TiO₂ nanowires (TiO₂NWs), which were synthesized by a hydrothermal procedure. This nanomaterial was subsequently modified by incorporating different loadings (1%, 3% and 5%) of gold nanoparticles (AuNPs) on the surface, previously exfoliated MoS₂ nanosheets, and CeO₂ nanoparticles (CeO₂NPs). These nanomaterials, as well as the different synthesized catalysts, were characterized by electron microscopy (HR-SEM and HR-TEM), XPS, XRD, Raman, Reflectance and BET surface area. HER studies were performed in aqueous solution, under irradiation at different wavelengths (UV-visible), which were selected through the appropriate use of optical filters. The results obtained show that there is a synergistic effect between the different nanomaterials of the catalysts. The specific area of the catalyst, and especially the increased loading of MoS₂ and CeO₂NPs in the catalyst substantially improved the H₂ production, with values of ca. 1114 μm/hg for the catalyst that had the best efficiency. Recyclability studies showed only a decrease in activity of approx. 7% after 15 cycles of use, possibly due to partial leaching of gold nanoparticles during catalyst use cycles. The results obtained in this research are certainly relevant and open many possibilities regarding the potential use and scaling of these heterostructures in the photocatalytic production of H₂ from water.     

Catalytic behaviour of Cu/ZrO2 and Cu/ZrO2(SO 4 2− ) in the reduction of nitric oxide by decane in oxygen-rich atmosphere

The selective catalytic reduction (SCR) of NO by decane under an oxidising atmosphere has been carried out on Cu/ZrO₂ and Cu/ZrO₂(SO ₄ ^2– ). Zirconia-supported Cu catalysts were prepared by ligand exchange with Cu acetylacetonate followed by calcination at 773 K. The solids obtained were characterised by temperature programmed reduction (TPR) by hydrogen and temperature programmed desorption (TPD) of NO. Cu/ZrO₂ is active and selective in the reduction of NO by decane at low temperature (< 600 K) but oxidises NO to NO₂ between 640 and 770 K. By contrast, whatever the temperature, a total selectivity to nitrogen is obtained with Cu/ZrO₂(SO ₄ ^2– ). About 40% NO conversion to N₂ is observed with GHSV of 70 000 h^–1. The promoting effect of sulfate is attributed to the large increase of acidity and the strong interaction between copper and sulfur species which is evidenced by TPD of NO and TPR by H₂.     

The friction and wear properties of nanometer ZrO2-filled polyetheretherketone

Nanometer ZrO₂ filled polyetheretherketone (PEEK) composite blocks with different filler proportions were prepared by compression molding. Their friction and wear properties were investigated on a block-on-ring machine by running a plain carbon steel (AISI 1045 steel) ring against the composite block. The morphologies of the wear traces were observed by scanning electron microscopy (SEM). Results indicated that nanometer ZrO₂-filled PEEK exhibited lower friction coefficient and wear rate in comparison with pure PEEK. The lowest wear rate was obtained with the composite containing 7.5 wt % ZrO₂. The SEM pictures of the wear traces indicated that the plucked and ploughed marks appeared on the wear scar of pure PEEK, while the scuffing on the wear scar of 7.5 wt % nanometer ZrO₂-filled PEEK was obviously abated. Thus, it was inferred that the improvement in the tribological behavior of nanometer ZrO₂-filled PEEK composite was closely related to the improved characteristics of the worn surfaces. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 135–141, 1998     

The obtaining of high-density specimens and analysis of mechanical strength characteristics of a composite based on ZrO2-WC nanopowders

The structures, processes of shrinkage, and phase composition of the compact system ZrO₂-WC, obtained by hot pressing with the transmission of high current, are considered in the article. We found that as a result of compaction, the ZrO₂-WC-ceramics have uniform density distribution, with the following optimal mode consolidation values T = 1,350°C, P = 30 MPa and t = 2 min. These conditions allow us to achieve the best combination of ceramic properties by criteria density and strength.