Exoemission and catalytic activity of oxides with perovskite and spinel structures in the oxidation of CO and hydrocarbons

Low-temperature (20—400 °C) exoemission of negative charges from mixed oxides having the perovskite structure M¹M²O₃ (M¹ = La; M² = Co, Mn, Ni) or the spinel structure M¹M² ₂O₄ (M¹ = Cu; M² = Fe, Co, Cr) was studied. The relationship between the catalytic activity in CO, ethylbenzene, and propylene oxidation and the emissivity of the oxides was elucidated. The role of weakly bound oxygen and variable-valence ions in the exoemission and redox catalysis by mixed oxides is discussed.     

Nonoxidative methane conversion into aromatic hydrocarbons on tungsten-containing pentasils

The effects of the tungsten concentration and of the method of tungsten introduction into ZSM-5 pentails with different SiO₂/Al₂O₃ molar ratios on the acidity and the activity of the resulting catalysis in nonoxidative methane conversion into aromatic hydrocarbons are considered. The catalysts obtained from the SiO₂/Al₂O₃ = 40 pentasil and a nanosized tungsten powder are the most active and the most stable. The maximum methane conversion and the highest yield of aromatic hydrocarbons are achieved on the zeolite containing 8.0 wt % tungsten nanopowder.     

The synthesis of mesoporous zeolite beta aggregates without the use of second template and additive

Zeolite Beta Aggregates have been synthesized by the self-assembly of Beta nanoparticles without the use of second template or additive, where the large zeolitic aggregates avoided the filtration difficulties and the presence of mesopore reduced the diffusion limitation. The samples were characterized by XRD, N₂-sorption, SEM, TEM, thermogravimetric analysis, IR spectroscopy and temperature programmed desorption of ammonia. The results showed that the SiO₂/Al₂O₃ ratio played a key role on the particle size, mesopore volume and particle–particle aggregation process of zeolite Beta. The sample with SiO₂/Al₂O₃ ratio below 60 had improved textual and acidic properties and exhibited the best catalytic activity to the alkylation of phenol with tert-butanol.     

Exoemission accompanying the decomposition of methanol on zinc oxide

The electronic phenomena accompanying the adsorption and dehydrogenation of methanol on zinc oxide were studied using the method of exoemission of negative charges. Postemission excited from ZnO by an electron beam was found to be suppressed by the adsorption of methanol vapor, which exhibited electron acceptor properties. Subsequent heating to temperatures close to the temperature of the beginning of methanol decomposition increased the intensity of exoemission, which was evidence of the participation of emission centers (O^δ?) in dehydrogenation. A possible mechanism of methanol decomposition with the participation of surface V _s hole centers (O^δ?) of zinc oxide was suggested.     

Al (110) surface oxide thermal stability in ultrahigh vacuum

This research characterizes the stability of the Al₂O₃ surface oxide on Al (110) as a function of temperature and within an ultrahigh vacuum environment (p < 5 × 10^?12 Torr). Auger electron spectroscopy and temperature desorption spectroscopy were used to correlate the change in oxygen and carbon surface concentration. The surface oxide was observed to remain stable up to 350–400 °C. Above this temperature, the oxide began to dissociate resulting in a CO desorption peak at 425 °C followed by extensive dissolution of the C and O into the Al bulk. A second and much smaller CO desorption peak was observed at 590 °C in concert with complete oxide breakdown and the virtual disappearance of surface carbon and oxygen. Extrapolation of the Auger electron spectral ratios of C_KLL and O_KLL peaks to the sum of the Al⁰_LVV and Al³⁺_LVV peak suggests that the surface concentration of each approaches zero at ~640 °C. The predominant mechanism for reduction of the surface oxide occurs by dissolution into the bulk instead of desorption. Copyright © 2013 John Wiley & Sons, Ltd.     

系列硅铝比纳米薄层ZSM-5分子筛的合成和表征

以自制不对称双子季铵盐表面活性剂为模板, 在水热合成体系中控制合成系列硅铝比纳米薄层ZSM-5分子筛.采用X射线衍射(XRD)、N₂吸附-脱附、X射线荧光光谱(XRF)、扫描电镜(SEM)和²⁷Al魔角旋转核磁共振(²⁷Al MAS-NMR)对合成的样品进行了表征. 详细研究了晶化温度、晶化时间、结构导向剂(SDA)用量、碱度等对合成的影响和纳米薄层ZSM-5分子筛的形成过程. 结果表明: 分子筛硅铝比越高, 结构导向剂用量越大, 所需的晶化时间越短; 晶化温度越高, 晶化时间越短; 且不同硅铝比纳米薄层ZSM-5分子筛的形貌规整度、比表面积和介孔/微孔孔容比例随着硅铝比而变化.     

Preparation of highly active and reusable heterogeneous Al2O3–Pd catalysts by the sol–gel method using bayberry tannin as stabilizer

A novel heterogeneous Al₂O₃–Pd catalyst has been prepared by the sol–gel method; bayberry tannin (BT) was used as stabilizer to prevent the migration and aggregation of Pd species during calcination. According to N₂ adsorption/desorption determination, Al₂O₃–Pd has a mesoporous structure and its specific area is as high as 336.5 m²/g. Transmission electron microscopy observation indicated that the size of the Pd particles was greatly reduced by the presence of BT. On the basis of X-ray photoelectron spectra analysis, it was found that the most of Pd nanoparticles were dispersed in the pores, implying that BT can prevent migration of Pd particles from the pores to the outer surface of Al₂O₃ during calcination. For comparison, Al₂O₃–Pd^* was prepared by the sol–gel method but without use of BT. In the hydrogenation of acrylic acid, Al₂O₃–Pd had high catalytic activity and excellent reusability compared with commercial and traditionally prepared heterogeneous Pd catalysts. The turnover number of Al₂O₃–Pd is as high as 11,328.0 mol/mol after recycling seven times, which is much higher than that of a commercial Pd–C catalyst (8048.0 mol/mol).     

Weakly bound oxygen in the catalytic CO oxidation and exoemission from complex oxides having a spinel structure

The catalytic activity of complex oxides M^IM^II ₂O₄ (M^I=Cu, Ni, Co, Zn, or Mg; M^II=Mn or Cr) with a spinel structure in the oxidation of CO and the low-temperature (20–400°C) exoemission of negative charges from their surface were investigated. A relationship between the catalytic activity and the emissivity of the systems under study was found. The role of the charged species of weakly bound oxygen in exoemission and oxidative catalysis by the complex oxides is discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1618–1621, September, 1997.     

Effect of Support of СоМоS Catalysts on Hydrodeoxygenation of Guaiacol as a Model Compound of Biopetroleum

СоМоS/Sup catalysts were prepared from 12-molybdophosphoric heteropoly acid and cobalt citrate, with Al₂O₃, SiO₂, TiO₂, and ZrO₂ used as supports (Sup). The synthesized catalysts were studied by low-temperature nitrogen adsorption, X-ray diffraction, temperature-programmed ammonia desorption, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The catalytic properties of the catalysts were studied in a flow-through installation at 260 and 340°С, pressure of 3.0 MPa, feed space velocity of 80 h^–1, and Н2/feed ratio of 500 L_n.c. L^–1. The guaiacol hydrodeoxygenation rate increases with a decrease in the mean length of the active phase particles, irrespective of the kind of the oxide support. As for the support effect, the catalyst activity decreases in the order SiO₂ > Al₂O₃ > ZrO₂ ~ TiO₂. On the other hand, the catalysts supported on ZrO₂ and Al₂O₃ exhibit the highest stability. The causes of the observed trends and the possible relationships between the characteristics of the catalysts and active phase nanoparticles are discussed.     

Effect of pretreatment temperature on the acidity and aniline alkylation activity over HZSM-5

HZSM-5 zeolites with SiO₂/Al₂O₃ ratios of 30–280 are pretreated at 773 K and 1173 K. The effect of pretreatment temperature on acidity measured by ammonia desorption and aniline alkylation activity over these zeolites in the entire SiO₂/Al₂O₃ ratio range studied is discussed.IICT Communication No.: 3399     

Key Role of a-Top CO on Terrace Sites of Metallic Pd Clusters for CO Oxidation

Pd-based catalysts are the most widely used for CO oxidation because of their outstanding catalytic activity and thermal stability. However, fundamental understanding of the detailed catalytic processes occurring on Pd-based catalysts under realistic conditions is still lacking. In this study, we investigated CO oxidation on metallic Pd clusters supported on Al₂O₃ and SiO₂. High-angle annular dark-field scanning transmission electron microscopy revealed the formation of similar-sized Pd clusters on Al₂O₃ and SiO₂. In contrast, CO chemisorption analysis indicated a gradual change in the dispersion of Pd (from 0.79 to 0.2) on Pd/Al₂O₃ and a marginal change in the dispersion (from 0.4 to 0.24) on Pd/SiO₂ as the Pd loading increased from 0.27 to 5.5 wt %; these changes were attributed to differences in the metal-support interactions. Diffuse reflectance infrared Fourier-transform spectroscopy revealed that fewer a-top CO species were present in Pd supported on Al₂O₃ than those in Pd supported on SiO₂, which is related to the morphological differences in the metallic Pd clusters on these two supports. Despite the different dispersion profiles and surface characteristics of Pd, O₂ titration demonstrated that linearly bound CO (with an infrared signal at 2090 cm⁻¹) reacted first with oxygen in the case of CO-saturated Pd on Al₂O₃ and SiO₂, which suggests that a-top CO on the terrace site plays an important role in CO oxidation. The experimental observations were corroborated by periodic density functional calculations, which confirmed that CO oxidation on the (111) terrace sites is most plausible, both kinetically and thermodynamically, compared to that on the edge or corner sites. This study will deepen the fundamental understanding of the effect of Pd clusters on CO oxidation under reaction conditions.     

Preparation of superhydrophobic PET fabric from Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> hybrid: geometrical approach to create high contact angle surface from low contact angle materials

In this work we prepare high contact Poly Ethylene Terephthalate (PET) fabric surface from low contact angle materials. Superhydrophobic PET fabric is prepared by coating the fabric with hybrid Al₂O₃–SiO₂ sol. In this case, the high contact angle Al₂O₃–SiO₂ hybrid is created from low contact angle Al₂O₃ and SiO₂ precursors. PET treated with hybrid Al₂O₃–SiO₂ exhibit Water Contact Angle (WCA) as 150°, while PET treated with individual Al₂O₃ sol or SiO₂ sol exhibits lower WCA, (Al₂O₃ WCA = 137°; SiO₂ WCA = 141°). FESEM and AFM investigations show that the hybrid Al₂O₃–SiO₂ sol and individual Al₂O₃ or SiO₂ sol imparted different roughness geometry on the PET fabric surface. We observe surface structure of fish fin-like, particle-like and hybrid fin-particle for treated PET fabric with; Al₂O₃, SiO₂ and hybrid Al₂O₃–SiO₂ sol, under FESEM and AFM observations.AFM observations show the evolution of roughness (Ra) dimension of different surface structures with the order of: SiO₂ < Al₂O₃ < Al₂O₃–SiO₂ (Ra = 31, 63 and 273 nm). We believe that the disparity of the surface geometries lead into different surface WCA. FTIR spectra of Hybrid Al₂O₃–SiO₂ shows additional peak at 902, 850, 557, and 408 cm⁻¹ which can be ascribed to the hybridization structure.     

Electronically excited oxygen atoms,O(21D2). A time-resolved study of the collisional quenching by the gases H2, D2, CH4, NO,NO2, N2O,and C3O2 using atomic absorption spectroscopy in the vacuum ultraviolet

Time-resolved atomic absorption spectroscopy in the vacuum ultraviolet has been employed to monitor electronically excited oxygen atoms, O(2¹D₂), following their genera-tion by the flash photolysis of ozone in the Hartley band region. We report the first values for the absolute second-order rate constants describing the removal of the excited atom on collision with the molecules H₂, D₂, CH₄, NO, NO₂, N₂O, and C₃O₂. Where possible, these data are considered within the context of restrictions arising from spin and orbital symmetry and are further discussed in tems of previously reported relative rate data derived from indirect measurements. Consideration is given to the importance of these rate con-stants in discussing processes taking place in the earth's atmosphere and in systems giving rise to chemical laser action.     

Preparation of ZSM‐5 Coated on Monolithic Interconnected Macroporous Al2O3 Using Cheap n‐Butylamine as Template

Using cheap n‐butylamine as template, ZSM‐5 zeolites have been successfully synthesized and coated on monolithic interconnected macroporous Al₂O₃ by the secondary growth method. The use of cheap n‐butylamine could significantly reduce the synthesis cost. Hierarchical monolithic ZSM‐5 zeolites were prepared from synthetic mixtures with different H₂O/Na₂O or SiO₂/Al₂O₃ ratio. The synthesized samples were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR) and N₂ adsorption‐desorption. The results show that the hierarchical monolithic zeolites were obtained with cheap n‐butylamine template as template. During the hydrothermal reaction process, the morphology of the micrometer‐sized support was well maintained. The irregular crystals were formed in a wide range of the H₂O/Na₂O or SiO₂/Al₂O₃ ratio of synthetic mixtures and coated on monolithic Al₂O₃. The relative crystallinity of the zeolites was highest at H₂O/Na₂O=250 or SiO₂/Al₂O₃=160. This type of composites exhibited hierarchical porous structures and relatively high specific surface areas.     

Supported Gold Nanoparticles for Efficient α‐Oxygenation of Secondary and Tertiary Amines into Amides

Although the α‐oxygenation of amines is a highly attractive method for the synthesis of amides, efficient catalysts suited to a wide range of secondary and tertiary alkyl amines using O₂ as the terminal oxidant have no precedent. This report describes a novel, green α‐oxygenation of a wide range of linear and cyclic secondary and tertiary amines mediated by gold nanoparticles supported on alumina (Au/Al₂O₃). The observed catalysis was truly heterogeneous, and the catalyst could be reused. The present α‐oxygenation utilizes O₂ as the terminal oxidant and water as the oxygen atom source of amides. The method generates water as the only theoretical by‐product, which highlights the environmentally benign nature of the present reaction. Additionally, the present α‐oxygenation provides a convenient method for the synthesis of ¹⁸O‐labeled amides using H₂¹⁸O as the oxygen source.     

Defects and characteristics of the structure and properties of aluminum oxides

Based on IR spectroscopy data, it was established that nonstoichiometry defects in the structure of aluminum oxides were components of the Wannier-Mott exciton states and included the Al-O, Al-Al, O₂, O ₂ ⁺ , O ₂ ^? , O ₂ ^2? , O₃, and O_2n isolated oscillators in the ground and electronically excited states. It was shown that their presence manifested itself by thermoemission of molecular oxygen singlet forms, excess heat capacity, and anomalous diamagnetism at elevated temperatures.     

Chemiluminescence from eukaryotic and prokaryotic cells: reducing potential and oxygen requirements.

Abstract— The postphagocytic microbicidal activity of polymorphonuclear leukocytes (PMNL), the effector phagocytes of the acute inflammatory response, is metabolically characterized by increased glucose oxidation via the hexose monophosphate shunt and by increased non-mitochondrial oxygen consumption. These metabolic alterations result from the phagocytic activation of a membrane-associated NADPH:O, oxidoreductase. The products of univalent reduction of O₂ by this enzyme, O^-₂ and H ⁺, may further react to yield potential microbicidal oxidants such as H₂O₂, OC1^--, OH, and ¹A_gO₂. The microbicidal activity of PMNL is associated with the generation of luminescence. This chemiluminescence correlates with the metabolic generation of reducing potential and O₂ consumption, and is proposed to originate from the relaxation of the electronically excited products of microbicidal oxidation. The importance of O₂ in microbicidal metabolism will be considered, and data demonstrating the O₂-dependence of PMNL-chemiluminescence are presented. The phenomenon of chemiluminescence from non-bioluminescent bacteria is also described, and preliminary data from luminescence studies of Streptococcus faecalis are presented. The relationship of light emission to bacterial metabolism and O₂ toxicity is considered. Evidence for the bacterial generation of O^-₂ is presented, and the role of O^-2 and H₂O₂ in oxidative reactions productive of electronic excited molecular products is discussed.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. XVI. Reduktionsverhalten amorpher NiO?Al2O3/SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XVI. Reduction Behaviour of Amorphous NiO? Al₂O₃/SiO₂ Catalysts The reduction behaviour of NiO? Al₂O₃/SiO₂ catalysts prepared by precipitationdeposition is influenced by the phase composition (amorphous nickel layersilicates and nickel alumino layersilicates, nickel spinels, nickel oxide) and the differences of the composition between surface and bulk. TPR measurements, determinations of the reduction degree, and the nickel particle sizes by static magnetic measurements showed that the reducibility of the NiO? Al₂O₃/SiO₂ catalysts is enhanced and the nickel dispersity is decreased at low Al₂O₃ contents. The decrease of the reducibility at Al₂O₃ contents >5 mole% is caused by the formation of nickel spinels and the decrease of the Ni^II ion surface concentration.     

Fabricating hierarchical ZSM-5 to induct long chain antioxidant coenzyme Q10 for biomedical application

The study investigates the hydrophobic antioxidant Coenzyme Q10 (CoQ10) adsorption over industrially relevant hierarchical ZSM-5 for potential therapeutic applications. The designing of hierarchical nanocomposites was optimized with two different NaOH/CTAB ratios (0.18 and 0.62) over ZSM-5 (SiO₂/Al₂O₃ = 22–27) of different crystal sizes (0.5 µm, 2.0 µm and 3.0 µm) and different SiO₂/Al₂O₃ ratios (23, 80, 280 and 1500) through top-down approach. Hydrothermal stability of samples was studied using 100% water steam at 700 °C and 750 °C for 2 h, respectively. Reassembling nano ZSM-5 into hierarchical composite was found to exhibit ordered/disordered hexagonal mesophase depending on alkaline treated ZSM-5 crystal sizes and silica to alumina ratios. The phase changes were analyzed using different textural characterizations such as X-ray diffraction, BET surface area, ammonia desorption technique, ²⁷Al MAS NMR, thermogravimetric analysis and transmission electron microscope. 21 different nanoformulations were screened for CoQ10 adsorption and subsequently selected samples were applied for curcumin and ascorbic acid adsorption. Hierarchical ZSM-5 with SiO₂/Al₂O₃ ratio 80 (ZSM-5-80 (0.62)) was found to be steam stable and optimum with highest Q10 adsorption (55%). The adsorption influence over different crystal size and silica to alumina ratios, clearly showed the dependency over synergistic action of textural characteristics such as external surface area, pore volume, and weak acidity. The structured nanosupports with pore sizes between 3 and 4.0 nm were found to exhibit highest CoQ10 adsorption.