Michael addition of nitromethane to 3-buten-2-one catalyzed by potassium fluoride supported on Al2O3, ZnO, SnO2, sepiolite, AlPO4, AlPO4?Al2O3 and AlPO4?ZnO

The Michael addition of nitromethane to 3-buten-2-one has been carried out in the absence of solvent, using potassium fluoride supported on Al₂O₃, ZnO, SnO₂, sepiolite, AlPO₄, AlPO₄–Al₂O₃ and AlPO₄–ZnO catalysts. We found that KF/ZnO easily performed the Michael addition and thus, ZnO is a better support for the basic reagent than Al₂O₃. Besides, the Michael addition was not successful with AlPO₄ or AlPO₄-metal oxide acidic supports.

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3--2- , , Al₂O₃, ZnO, SnO₂, , AlPO₄, AlPO₄–Al₂O₃ AlPO₄–ZnO. , KF/ZnO .. ZnO, , , Al₂O₃. , , AlPO₄ AlPO₄- .

     

Vapor-phase synthesis of isoprene from formaldehyde and isobutylene over CuSO4?MOx/SiO2 catalysts

Vapor-phase synthesis of isoprene from formaldehyde and isobutylene over CuSO₄–MO_x/SiO₂ catalysts has been studied. The results show that CuSO₄–MO_x/SiO₂ catalysts exhibit a good catalytic activity; especially when the metal oxides have appropriate basicity, is isoprene yield greatly enhanced. The results of product analysis indicate that there are side-reactions during isoprene production, which are isoprene hydrogenation, polymerization of isobutylene, copolymerization of isobutylene and isoprene, and reaction of C₅ aldehyde and ketone formed during isoprene production. In addition, catalytic behavior of the catalysts and probable mechanism of side-reactions are discussed.

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CuSO₄–MO_x/SiO₂. ; , . , , , , , , C₅ , . .

     

Kinetic simulation of oxidative dehydrogenation of n-butenes over SnO2?Sb2O4 catalysts

A previously suggested reaction mechanism was utilized to evaluate a kinetic model for the oxidation of n-butenes over ShSb=31 mixed oxide catalyst. With this model, kinetic curves measured at 673 K were simulated, illustrating the changes of amounts of undetectable surface components, too.

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- SnSb=31 . , 673 K, .

     

Understanding the intrinsic synergistic mechanism between Pt–O–Ti interface sites and TiO2 surface sites of Pt/TiO2 catalysts in Fenton-like reaction

Identifying the active site of oxide-supported metal catalysts and revealing the intrinsic synergistic mechanism between metal and oxide support remain a large challenge.Herein,we report the identification and separation of the Pt–O–Ti interface and TiO₂ surface in Pt–TiO₂ -based catalysts by depositing different thickness of TiO₂ shell with ～0.4-nm micropores onto the surface of Pt/TiO₂ catalyst through atomic layer deposition(ALD).In the oxidation of...     

Estimation of kinetic parameters in oxidative dehydrogenation of n-butenes over SnO2?Sb2O4 catalysts

Kinetic curves measured in the oxidation of n-butenes over a SnSb=31 mixed oxide catalyst were fitted by the kinetic model put forward in a previous paper. The goodness of fitting shows that the kinetic behavior of this complex reaction system can be described by a mechanism involving acidic and redox sites on the catalyst surface.

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- SnSb=31 , . , , - .

     

Study of acid-base properties of a SiO2?AlPO4 (80∶20 W/W) catalyst

2-Methyl-3-butyn-2-ol (MBOH) transformation was used as a test reaction in order to determine the acid-base properties of a SiO₂/AlPO₄ (80∶20 w/w) catalyst. Experiments were carried out in a microcatalytic pulse reactor and in a continuous-flow reactorvia Temperature Programmed Surface Reactions-Mass Spectrometry (TPSR-MS). Results are compared to acid-base properties calculated by other instrumental techniques.     

Acid-base properties of the surface of the α-Al2O3 suspension

The distribution of the acid-base centers on the surface of α-Al₂O₃ suspension particles was studied by potentiometric titration, and the corresponding pK spectra were constructed. It was inferred that the double electric layer created by the supporting electrolyte substantially affected the screening of the acid-base centers on the particle surface of the suspension.     

Physicochemical properties and hds activity of CoMo?P?Al2O3 catalysts

Porous structure, acidity and hds activity of the CoMo–P–Al₂O₃ catalysts have been studied. Phosphorus was introduced jointly with molybdenum. This method of phosphorus incorporation gave substantial diminution of surface area, moderate changes of acidity and decrease in hds activity for the catalysts with P₂O₅ content higher than 5 wt.%.

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, CoMo–P–Al₂O₃. . , P₂O₅ 5 .%.

     

Effect of preparation methods on Co/ZrO2 catalysts in Fischer–Tropsch synthesis

Cobalt was incorporated into the zirconia support by different methods. The reducibility and activity of the catalysts was directly related to the preparation methods. Impregnated Co/ZrO₂ catalyst showed the highest reduction degree and the highest CO hydrogenation activity.     

ZrO2前体的制备方法对WOX-/ZrO2

考察了ZrO2前体的制备方法对WOX-/ZrO2的性质及其正庚烷临氢异构化反应性能的影响,同时采用BET、XRD、Py-IR等手段对其进行了表征.结果表明,ZrO2前体的制备方法会明显影响ZrO2前体的比表面积及WOX-/ZrO2催化剂中四方ZrO2和单斜ZrO2晶型的比例,同时WO3的分散程度也有差异.单斜ZrO2太多及WO3晶型的出现会降低正庚烷临氢异构化反应活性;而ZrO2全部为四方晶型时,虽然有利于提高低温反应活性,但缺点是裂解选择性太高;而当单斜ZrO2和四方ZrO2共存,但以四方ZrO2为主,且没有WO3晶型出现时,既可保持较高的反应活性,同时又具有极高的异构化选择性.     

Influence of preparation on the structure and co conversion of γ-Bi2MoO6 catalysts

The effect of treatment conditions during preparation and activation of γ-Bi₂MoO₆ catalysts was investigated. Catalytic evaluation shows that CO conversion is much higher for catalysts obtained under vapor controlled evaporation conditions (CE) than for standard evaporation catalysts (SE). Characterization results show that preparation under SE conditions induces segregation of Bi₂O₃ on the surface of Bi₂MoO₆ catalysts decreasing their catalytic activity. Catalysts treatment under hydrogen reactivates the catalytic properties of SE samples.     

Solid state synthesis of CuFe2O4 from Cu(OH)2?·?CuCO3–4FeC2O4?·?2H2O mixtures: mechanism of reaction and thermal characterization of CuFe2O4

Copper Ferrite has been prepared by solid state synthesis of milled mixtures of copper basic carbonate [Cu(OH)₂ · CuCO₃] and iron (II) oxalate dihydrate [FeC₂O₄ · 2H₂O]. The reaction mechanism has been studied by simultaneous TG/DSC analysis: the different steps of the mass loss process have been individuated along with the relevant enthalpy terms starting from both physical and mechanically activated mixtures. CuFe₂O₄ has been synthesized by annealing the mechanically activated mixture at 750–800 °C while no pure CuFe₂O₄ is obtained by annealing the physical mixture at temperatures as high as 1100 °C. CuFe₂O₄ has been characterized as concerns the molar het capacity, the tetragonal–cubic transition enthalpy and the Curie point.     

A Raman spectroscopic study of the XeOF4/XeF2 system and the X-ray crystal structure of α-XeOF4·XeF2

The mixed oxidation state complexes, α-XeOF₄·XeF₂ and β-XeOF₄·XeF₂, result from the interaction of XeF₂ with excess XeOF₄. The X-ray crystal structure of the more stable α-phase shows that the XeF₂ molecules are symmetrically coordinated through their fluorine ligands to the Xe(VI) atoms of the XeOF₄ molecules which are, in turn, coordinated to four XeF₂ molecules. The high-temperature phase, β-XeOF₄·XeF₂, was identified by low-temperature Raman spectroscopy in admixture with α-XeOF₄·XeF₂; however, the instability of the β-phase precluded its isolation and characterization by single-crystal X-ray diffraction. The Raman spectrum of β-XeOF₄·XeF₂ indicates that the oxygen atom of XeOF₄ interacts less strongly with the XeF₂ molecules in its crystal lattice than in α-XeOF₄·XeF₂. The ¹⁹F and ¹²⁹Xe NMR spectra of XeF₂ in liquid XeOF₄ at −35 °C indicate that any intermolecular interactions that exist between XeF₂ and XeOF₄ are weak and labile on the NMR time scale. Quantum-chemical calculations at the B3LYP and PBE1PBE levels of theory were used to obtain the gas-phase geometries and vibrational frequencies as well as the NBO bond orders, valencies, and NPA charges for the model compounds, 2XeOF₄·XeF₂, and XeOF₄·4XeF₂, which provide approximations of the local XeF₂ and XeOF₄ environments in the crystal structure of α-XeOF₄·XeF₂. The assignments of the Raman spectra (−150 °C) of α- and β-XeOF₄·XeF₂ have been aided by the calculated vibrational frequencies for the model compounds. The fluorine bridge interactions in α- and β-XeOF₄·XeF₂ are among the weakest for known compounds in which XeF₂ functions as a ligand, whereas such fluorine bridge interactions are considerably weaker in β-XeOF₄·XeF₂.     

有机体系中纳米TiO2 / ZrO2修饰电极的制备及电催化活性

The complexes Ti(OCH₂CH₂O)₂ and Zr(OCH₂CH₂O)₂ were directly synthesized by using HOCH₂CH₂OH dissolution in 50 mL flask. The nano-ZrO₂ / TiO₂ powders were prepared by a direct sol-gel synthesis using the above solution and followed by drying at 400 ℃ for 2 h. The complexes were characterized by FTIR and ¹H NMR. XRD and TEM were used to investigate the structure of nano-ZrO₂ / TiO₂. The results show that the complexes containing ^-OCH₂CH₂O^- group could prevent the precursor from agglomeration and sintering during the hydrolysis and calcination process. The ZrO₂ / TiO₂ powders of 20～35 nm was thus obtained in a high purity. The highly active nano-ZrO₂ / TiO₂ modified electrode was prepared by using daubing and calcination. The electro-catalytic activities of this electrode in (COOH)₂ were investigated. The discharge current of nano-ZrO₂ / TiO₂ electrode increased obviously. In preparative electrolysis under optimal conditions, the average yield and current efficiency for HOOC-CHO were 84.7% and 91.6 %, respectively.     

Role of support nature （γ-Al2O3 and SiO2-Al2O3） on the performances of rhenium oxide catalysts in the metathesis of ethylene and 2-pentene

The metathesis of ethylene and 2-pentene was studied as an alternative route for propylene production over Re2O7/γ-Al2O3 and Re2O7/SiO2-Al2O3 catalysts. Both NH3 temperature-programmed desorption (NH3-TPD) and H2 temperature-programmed reduction (H2-TPR) results showed that Re2O7/SiO2-Al2O3 exhibited stronger acidity and weaker metal-support interaction than Re2O7/γ-Al2O3. At 35 60℃, isomerization free metathesis was observed only over Re2O7/γ-Al2O3, suggesting that the formation of metal-carbene metathesis active sites required only weak acidity. Our results suggest that on the Re2O7/SiO2-Al2O3, hydrido-rhenium species ([Re]-H) were formed in addition to the metathesis active sites, resulting in the isomerization of the initial 1-butene product into 2-butenes. A subsequent secondary metathesis reaction between these 2-butenes and the excess ethylene could explain the enhanced yields of propylene observed. The results demonstrate the potential for high yield of propylene from alternative feedstocks.     

Effect of some parasite surface reactions on the variation of electrical conductance in the H2?Pt/Al2O3 system

The charge transfer at the interface H₂-0.5% Pt/Al₂O₃ was studied by using the transient response of the AC electrical conductance. The transient response for water and oxygen contaminated surface was of the overshoot-type.     

Study of the selectivity of a V2O5?ZrO2 catalyst for partial oxidation ofo-xylene at high temperatures

It has been established that at high temperatures (above 450°C) the V₂O₅−ZrO₂ catalyst exhibits a higher selectivity in the oxidation ofo-xylene to phthalic anhydride than does the conventional V₂O₅−TiO₂(a) catalyst. The catalyst selectivity is found to increase with respect to partial oxidation ofo-xylene, the valuable by-product maleic anhydride being obtained. Studies by different physicochemical methods have shown that V₂O₅−ZrO₂ undergoes no significant phase and structural changes under high-temperature conditions.     

Growth mechanism of palladium clusters on rutile TiO2 （110） surface

Oxide-supported transition metal systems have been the subject of enormous interest due to the improvement of catalytic properties relative to the separate metal.Thus in this paper,we embark on a systematic study for Pd n (n=1-5) clusters adsorbed on TiO2 (110) surface based on DFT-GGA calculations utilizing periodic supercell models.A single Pd adatom on the defect-free surface prefers to adsorb at a hollow site bridging a protruded oxygen and a five-fold titanium atom along the [110] direction,while Pd dimer is located on the channels with the Pd-Pd bond parallel to the surface.According to the transition states (TSs) search,the adsorbed Pd trimer tends to triangular growth mode,rather than linear mode,while the Pd4 and Pd5 clusters prefer three-dimensional (3D) models.However,the oxygen vacancy has almost no influence on the promotion of Pd n cluster nucleation.Additionally,of particular significance is that the Pd-TiO2 interaction is the main driving force at the beginning of Pd nucleation,whereas the Pd-Pd interaction gets down to control the growth process of Pd cluster as the cluster gets larger.It is hoped that our theoretical study would shed light on further designing high-performance TiO2 supported Pd-based catalysts.     

TiO2/蒙脱石纳米复合物中TiO2的结构相变

以钛酸丁酯和季铵盐改性有机蒙脱石为原料,采用原位水解法和原位脱羟法制备了TiO2/蒙脱石纳米复合物。采用X射线衍射(XRD)、拉曼光谱(Raman)表征了不同焙烧温度下TiO2/蒙脱石纳米复合物中TiO2的结构相变,并与不同焙烧温度下纯TiO2的结构相变进行对比。结果发现TiO2/蒙脱石纳米复合物中TiO2从锐钛矿相开始转变为金红石的最低温度要比纯TiO2从锐钛矿开始相转变为金红石的最低温度高200℃,且在焙烧温度1 200℃时还存在锐钛矿相,而纯TiO2在焙烧温度800℃时就全部转换为金红石相。TiO2/蒙脱石纳米复合物中TiO2和纯TiO2的平均晶粒度都随焙烧温度升高而增大,但TiO2/蒙脱石纳米复合物中TiO2的平均晶粒度要小于相同温度下焙烧纯TiO2的平均晶粒度。表明蒙脱石结构层的硅氧结构抑制了TiO2晶型由锐钛矿相向金红石相的转变,进而使相变温度升高,同时阻碍了晶体的生长。