Mehri Sanati

Gas sensors in Synthesis, Properties and Applications of Oxide Nanomaterials

Current oxide nanomaterials knowledge to draw from and build on Synthesis, Properties, and Applications of Oxide Nanomaterials summarizes the existing knowledge in oxide-based materials research. It gives researchers one comprehensive resource that consolidates general theoretical knowledge alongside practical applications. Organized by topic for easy access, this reference: Covers the fundamental science, synthesis, characterization, physicochemical properties, and applications of oxide nanomaterials Explains the fundamental aspects (quantum-mechanical and thermodynamic) that determine the behavior and growth mode of nanostructured oxides Examines synthetic procedures using top-down and bottom-up fabrication technologies involving liquid-solid or gas-solid transformations Discusses the sophisticated experimental techniques and state-of-the-art theory used to characterize the structural and electronic properties of nanostructured oxides Describes applications such as sorbents, sensors, ceramic materials, electrochemical and photochemical devices, and catalysts for reducing environmental pollution, transforming hydrocarbons, and producing hydrogen With its combination of theory and real-world applications plus extensive bibliographic references, Synthesis, Properties, and Applications of Oxide Nanomaterials consolidates a wealth of current, complex information in one volume for practicing chemists, physicists, and materials scientists, and for engineers and researchers in government, industry, and academia. Its also an outstanding reference for graduate students in chemistry, chemical engineering, physics, and materials science.

Ammoxidation of Toluene over TiO2(B)-Supported Vanadium Oxide Catalysts

TiO2(B) was used as a support for vanadium oxide with loadings in the range 1/4 to 10 theoretical layers. The vanadium could be separated into two parts, which were soluble and insoluble in NH3(aq), respectively. Insoluble vanadium, in an amount corresponding to a complete monolayer at high loadings, was present as V4+ in freshly prepared catalysts. Diffuse reflectance FTIR spectroscopy was used to characterize the catalysts. The bands assigned to stretching vibrations of hydroxyl groups on TiO2(B) were found to decrease in intensity with increasing vanadium loading. Spectra in the V=O and V-O-V vibration region revealed a rather complex growth pattern. For a catalyst covered with a complete monolayer, vanadium strongly interacting with the support is present as interconnected tetrahedral V4+ units. When the loading is increased, several additional layers of V5+ in tetrahedral coordination can exist on top of the monolayer. At higher loadings, there is an abrupt change in structure, resulting in the formation of an amorphous phase built up from distorted VO6 octahedra. Also, crystalline V2O5 is formed. The catalysts were used in the ammoxidation of toluene to benzonitrile. Multilayer catalysts showed better catalytic performance in comparison with crystalline V2O5 and catalysts exposing monolayer species. (Less)

Characteristics of aerosol particles formed during grate combustion of moist forest residue

The characteristics of aerosol particles formed during combustion of moist forest residue were studied as a function of load in a I MW moving grate boiler and at almost full load in a similar larger 6 MW boiler. The coarse (1 mum 12) were K, S and Cl in the fine mode and Ca, K and S in the coarse mode. The dominant ions in the fine mode were K+, SO42- and CO32-. The fine mode particles had hygroscopic growth factors of around 1.65 at RH=90%, with a deliquescence point at a relative humidity between 30% and 60%. It was assessed that K2CO3 is responsible for the low deliquescence point. Fine mode particles of a given dry diameter had similar chemical composition

Surface characterization and reactivity in ammoxidation reactions of vanadium antimonate catalysts

Unsupported vanadium antimonate catalysts with Sb/V ratios of 1 and 5 and samples with the latter ratio supported on alumina were studied in toluene and propane ammoxidation to benzonitrile and acrylonitrile, respectively, and were characterized by X-ray photoelectron spectroscopy (XPS) analysis before and after catalytic tests. Activity data for toluene ammoxidation suggest that excess antimony with respect to the stoichiometric amount required for forming the VSbO4 rutile phase affects the dispersion of the latter phase giving smaller particles. Vanadium sites are involved both in the activation of toluene and in the insertion of nitrogen in this reaction, whereas antimony does not play a specific role in the reaction mechanism. In propane ammoxidation, on the other hand, due to a higher reaction temperature with respect to toluene (500°C vs. 370°C), free vanadia on the surface of the catalyst has a negative influence on the selectivity because it promotes the conversion of ammonia to nitrogen, decreasing the surface nitrogenous species required for the selective formation of acrylonitrile. Excess antimony is thus necessary for completing the reaction between antimony and vanadium oxides, but antimony also participates in the reaction mechanism. In propane ammoxidation, in fact, XPS data show that both vanadium and antimony sites are reduced. Tentatively, vanadium sites are involved in the activation of propane, while antimony sites insert nitrogen. The differences between the toluene and propane ammoxidation mechanisms are interpreted to be primarily related to the different reaction temperatures.

Comparison of high-solids to liquid anaerobic co-digestion of food waste and green waste.

Co-digestion of food waste and green waste was conducted with six feedstock mixing ratios to evaluate biogas production. Increasing the food waste percentage in the feedstock resulted in an increased methane yield, while shorter retention time was achieved by increasing the green waste percentage. Food waste/green waste ratio of 40:60 was determined as preferred ratio for optimal biogas production. About 90% of methane yield was obtained after 24.5 days of digestion, with total methane yield of 272.1 mL/g VS. Based the preferred ratio, effect of total solids (TS) content on co-digestion of food waste and green waste was evaluated over a TS range of 5-25%. Results showed that methane yields from high-solids anaerobic digestion (15-20% TS) were higher than the output of liquid anaerobic digestion (5-10% TS), while methanogenesis was inhibited by further increasing the TS content to 25%. The inhibition may be caused by organic overloading and excess ammonia.

Vanadia Catalysts on Anatase, Rutile, and TiO2(B) for the Ammoxidation of Toluene: An ESR and High-Resolution Electron Microscopy Characterization

Three titania polymorphs, anatase, rutile, and TiO2(B), were used as supports for vanadia. Catalysts with nominal loadings corresponding to 1.5 and 5 theoretical layers were prepared. True monolayer samples were obtained by NH3(aq)-treatment of the samples with 5 nominal vanadia layers. Prepared catalysts were characterized by chemical analysis, ESR, and high-resolution electron microscopy. It was observed that an almost complete monolayer of vanadia can be formed on anatase and TiO2(B). The monolayer on TiO2(B) consists of V4+ species. A magnetic species attributable to tetrahedral states of vanadium was found to dominate the ESR resonance. Chemical analysis of the monolayer on anatase showed the presence of both V4+ and V4+ species. The ESR spectrum indicated a high degree of V4+-V4+ interaction. From the characterizations of rutile-supported samples it seems that the support interface is a solid solution of V4+. On all supports, vanadium on top of the monolayer is present as V5+. High-resolution micrographs of the samples with the highest loading revealed the formation of amorphous vanadia on both anatase and rutile. On TiO2(B), vanadia was found to grow coherently at the titania interface. The catalysts were used in the oxidation and ammoxidation of toluene to benzaldehyde and benzonitrile, respectively. Considering both activity and selectivity, multilayers of vanadia supported on TiO2(B) show a good performance for both reactions.

Zirconia-supported vanadium oxide catalysts for ammoxidation and oxidation of toluene : a characterization and activity study

A series of samples of vanadia supported on monoclinic zirconia were prepared with nominal loadings from a half up to sixteen theoretical vanadia layers. The samples were characterized with X-ray diffraction, scanning electron microscopy combined with energy dispersive X-ray analysis, high-resolution electron microscopy, Raman and diffuse reflectance infrared spectroscopy, and were used in the oxidation and the ammoxidation of toluene. At loadings in the monolayer range, Raman and infrared bands from decavanadate-like and dehydrated tetrahedral vanadia species were at ca. 990 and ca. 1025 cm−1, respectively. Raman bands at 821 and 880 cm−1 were present only at the lowest loading and are characteristic of orthovanadate and pyrovanadate species, respectively. X-ray diffraction, Raman and infrared spectroscopic results revealed formation of some crystalline V2O5 and ZrV2O7 at loadings exceeding a theoretical monolayer. In this case, consideration of Raman intensity variations allowed the conclusion that additional non-crystalline vanadia must be present. According to high-resolution electron micrographs, this vanadia consists of an amorphous overlayer, 4–8 atomic layers thick. In toluene oxidation zirconia-supported vanadia compared with crystalline V2O5 was found less selective for benzaldehyde formation. In toluene ammoxidation, on the other hand, vanadia on zirconia was found to possess good activity and selectivity for benzonitrile formation. Amorphous vanadia was the most active structure on zirconia, while the selectivities for nitrile and aldehyde formations were almost independent of the loading for one theoretical layer and above.

Effective Density Characterization of Soot Agglomerates from Various Sources and Comparison to Aggregation Theory

Soot particle (black carbon) morphology is of dual interest, both from a health perspective and due to the influence of soot on the global climate. In this study, the mass-mobility relationships, and thus effective densities, of soot agglomerates from three types of soot emitting sources were determined in situ by combining a differential mobility analyzer (DMA) and an aerosol particle mass analyzer (APM). High-resolution transmission electron microscopy was also used. The soot sources were diesel engines, diffusion flame soot generators, and tapered candles, operated under varying conditions. The soot microstructure was found to be similar for all sources and settings tested, with a distance between the graphene layers of 3.7–3.8 Å. The particle specific surface area was found to vary from 100 to 260 m2/g. The particle mass-mobility relationship could be described by a power law function with an average exponent of 2.3 (±0.1) for sources with a volatile mass fraction <10% and primary particle sizes of 11–29 nm. The diesel exhaust from a heavy duty engine at idling had a substantially higher volatile mass fraction and a higher mass-mobility exponent of 2.6. The mass-mobility exponent was essentially independent of the number of primary particles in the range covered (Npp = 10–1000). Despite the similar exponents, the effective density varied substantially from source to source. Two parameters were found to alter the effective density: primary particle size and coating mass fraction. A correlation was found between primary particle size and mass-mobility relationship/effective density and an empirical expression relating these parameters is presented. The effects on the DMA-APM results of doubly charged particles and DMA agglomerate alignment were investigated and quantified. Finally, the dataset was compared to three theoretical approaches describing agglomerate particles’ mass-mobility relationship. Copyright 2013 American Association for Aerosol Research

Hygroscopic Behavior of Aerosol Particles Emitted from Biomass Fired Grate Boilers

This study focuses on the hygroscopic properties of submicrometer aerosol particles emitted from two small-scale district heating combustion plants (1 and 1.5 MW) burning two types of biomass fuels (moist forest residue and pellets). The hygroscopic particle diameter growth factor (Gf) was measured when taken from a dehydrated to a humidified state for particle diameters between 30–350 nm (dry size) using a Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA). Particles of a certain dry size all showed similar diameter growth and the Gf at RH = 90% for 110/100 nm particles was 1.68 in the 1 MW boiler, and 1.5 in the 1.5 MW boiler. These growth factors are considerably higher in comparison to other combustion aerosol particles such as diesel exhaust, and are the result of the efficient combustion and the high concentration of alkali species in the fuel. The observed water uptake could be explained using the Zdanovski-Stokes-Robinson (ZSR) mixing rule and a chemical composition of potassium salts only, taken from ion chromatography analysis of filter and impactor samples (KCl, K2SO4, and K2CO3). Agglomerated particles collapsed and became more spherical when initially exposed to a moderately high relative humidity. When diluted with hot particle-free air, the fractal-like structures remained intact until humidified in the H-TDMA. A method to estimate the fractal dimension of the agglomerated combustion aerosol and to convert the measured mobility diameter hygroscopic growth to the more useful property volume diameter growth is presented. The fractal dimension was estimated to be ∼ 2.5.

DRIFT study of the oxidation and the ammoxidation of toluene over a TiO2(B)-supported vanadia catalyst

A DRIFT study of the adsorption and the (amm) oxidation of toluene was carried out at 150–300°C on a TiO2(B)-supported vanadia catalyst with a loading corresponding to 1.9 Mg V2O5 per m2 of the support surface area. In the absence of NH3 and gaseous oxygen, the adsorption of toluene at 150°C produces benzyl and benzoate intermediates. After one hour at the same temperature, further conversion of benzyl species, probably benzyloxy, into benzoate species is observed. Upon introduction of NH3 into the reaction cell, some benzonitrile is formed together with intermediates which possibly are (C6H5)CH(NH2)O- and (C6H5)C(NH2)(O-)2 species. Subsequent heat treatment at 300°C causes an increase in the amounts of benzonitrile and CO2 formed and the simultaneous disappearance of the precursor intermediates. On the basis of identified intermediates and observed transformations, a mechanism for the partial (amm)oxidation of toluene is proposed. The formation of CO2 is believed to pass over intermediates, which are identified as benzoquinone and butenolide species.