Catalytic conversion of wastes from the bioethanol production into carbon nanomaterials

This work addressed the production of carbon nanomaterials (CNMs) by catalytic conversion of wastes from the bioethanol industry, in the form of either sugarcane bagasse or corn-derived distillers dried grains with solubles (DDGS). Both bagasse and DDGS were pyrolysed at temperatures in the range of 600-1000 degrees C. The pyrolyzate gases were then used as CNM growth agents by chemical vapor deposition on stainless steel meshes, serving as both catalysts and substrates. CNM synthesis temperatures of 750-1000 degrees C were explored, and it was determined that their growth was most pronounced at 1000 degrees C. The nanomaterials produced from pyrolysis of bagasse were in the form of long, straight, multi-wall nanotubes with smooth walls and axially uniform diameters. Typical lengths were circa 50 mu m and diameters were in the range of 20-80 nm. The nanomaterials produced from pyrolysis of DDGS were in the form of long, entangled, rope-like structures with rugged walls, and axially non-uniform diameters. Typical diameters were in the range of 100-300 nm and their lengths were in the tens of microns. This process also produces a bio-syngas byproduct that is enriched in hydrogen. (C) 2011 Elsevier B.V. All rights reserved.

Catalytic conversion to N2O to N2 over potassium catalyst supported on activated carbon

Catalytic conversion of N2O to N-2 With potassium catalysts supported on activated carbon (K/AC) was investigated. Potassium proves to be much more active and stable than either copper or cobalt because potassium possesses strong abilities both for N2O chemisorption and oxygen transfer. Potassium redispersion is found to play a critical role in influencing the catalyst stability. A detailed study of the reaction mechanism was conducted based upon three different catalyst loadings. It was found that during temperature-programmed reaction (TPR), the negative oxygen balance at low temperatures (< 50 degrees C) is due to the oxidation of the external surface of potassium oxide particles, while the bulk oxidation accounts for the oxygen accumulation at higher temperatures (below ca. 270 degrees C). N2O is beneficial for the removal of carbon-oxygen complexes because of the formation of CO2 instead of CO and because of its role in making the chemisorption of produced CO2 on potassium oxide particles less stable. A conceptual three-zone model was proposed to clarify the reaction mechanism over K/AC catalysts. CO2 chemisorption at 250 degrees C proves to be an effective measurement of potassium dispersion. (C) 1999 Academic Press.

Basic properties of potassium oxide supported on zeolite y studied by pyrrole-tpd and catalytic conversion of methylbutynol

ABSTRACT We report on the basic properties of zeolite NaY and potassium supported on NaY (K/NaY) assessed by pyrrole-TPD and MBOH transformation. Pyrrole-TPD revealed that impregnation of zeolite NaY with potassium promoted additional adsorption sites for pyrrole compared to parent zeolite. For zeolite with various potassium loadings, pyrrole adsorbed on K/NaY decreased with increased potassium loading. Reduction in pyrrole adsorption could be due to potassium hindering intrinsic basic sites (lattice oxygen), to oxide of potassium occluding in zeolite cavities restricting access for pyrrole, or to K2O reacting with pyrrole to form nondesorbed pyrrolate anions. On MBOH transformation, potassium almost completely suppressed NaY acid sites while K/NaY basicity increased with potassium loading.

Catalytic conversion of solvent refined coal to liquid products /

"LBL-6807."

Montmorillonite/carbon nanocomposites prepared from sucrose for catalytic applications

Sucrose was used to prepare montmorillonite/carbon nanocomposites by calcination in a reduced atmosphere. The aim was to investigate the changes derived from varying the clay and sucrose content in the resulting material and to change the adsorption properties to evaluate its potential to be used in catalytic applications. X-ray diffraction patterns revealed the formation of an intercalated nanostructure composed of carbon-filled clay mineral layers, which was confirmed by the Fourier transform infrared spectra and thermogravimetry curves. Differences in composition and texture surface were detected by scanning electron microscopy images and were supported by viscosity measurements. These measurements were helpful in understanding why the sample prepared with the highest sucrose content presented the lowest gasoline and methylene blue adsorption results and why the highest adsorption properties were attributed to the sample with the highest clay content. Moreover, BET and BJH studies allowed understanding oleic acid catalytic conversion. Finally, a water flux simulation test was performed to determine the mechanical resistance in comparison to an activated carbon. It was found that the nanocomposites were more resistant, supporting their use in catalytic applications for a longer period of time. (C) 2011 Elsevier B.V. All rights reserved.

A comparative study of N2O conversion to N-2 over Co/AC and Cu/AC catalysts

Catalytic conversion of N2O to N-2 over Cu- and Co-impregnated activated carbon catalysts (Cu/AC and Co/AC) was investigated. Catalytic activity measurements were carried out in a fixed-bed flow reactor at atmospheric pressure. The catalysts were characterized by N-2 adsorption, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). This study aimed to provide insights into the following aspects: the metal dispersion, changes in pore structure, influence of catalyst loading on reaction, and reaction mechanism. Increasing loading of Co or Cu led to decreasing dispersion, but 20 wt % loading was an upper limit for optimal activities in both cases, with too high loading causing sintering of metal. Co exhibited a relatively better dispersion than Cu. Impregnation of metal led to a large decrease in surface area and pore volume, especially for 30 wt % of loading. 20 wt % of loading has proved to be the optimum for both Cu and Co, which shows the highest activity. Both N2O-Co/AC and -Cu/AC reactions are based upon a redox mechanism, but the former is limited by the oxygen transfer from catalysts to carbon, while N2O chemisorption on the surface of Cu catalyst controls the latter. The removal of oxygen from cobalt promotes the activity of Co/AC, but it is beneficial for Cu/AC to keep plenty of oxygen to maintain the intermediate oxidation of copper-Cu1+. The different nature of the two catalysts and their catalytic reaction mechanisms are closely related to their different electronegativities.

Hydroisomerization of n-decane over SAPO-11 catalysts synthesized with methylamine as co-template

The present work deals with preliminary studies concerning a new synthesis approach to prepare SAPO materials with AEL structure and evaluate their catalytic behavior in the hydroisomerization of long paraffins. The new SAPO-11 catalysts were synthesized with the help of a small amine (methylamine, MA) added during the preparation of the initial gel. As MA incorporates into the structure of the final materials, it contributes, together with DPA (dipropylamine), to an increase in Si incorporation as isolated species, which results in Bronsted acid sites. Thus, this new and original synthesis strategy allows to obtain materials with enhanced Bronsted acidity when compared with free MA materials. The catalysts were tested in n-decane hydroisomerization (n-decane was used as a model molecule) and confirmed the effect of MA on the acidic properties of the catalysts. The samples synthesized with MA present a higher number of acid sites that increase the catalytic conversion but have a negative effect in the isomerization selectivity, i.e. a more significant amount of cracking products is formed.

Nanosized Nb-TiO2 gas sensors derived from alkoxides hydrolization

Nanocrystalline TiO2 modified with Nb has been produced through the sol-gel technique. Nanopowders have been obtained by means of the hydrolysis of pure alkoxides with deionized water and peptization of the resulting hydrolysate with diluted acid nitric at 100 C. The addition of Nb stabilizes the anatase phase to higher temperatures. XRD spectra of the undoped and the Nb-doped samples show that the undoped sample has been almost totally converted to rutile at 600 C, meanwhile the doped samples present still a low percentage of rutile phase. Nanocrystalline powders stabilized at 600 C with grain sizes of about 17 nm have successfully been synthesized by the addition of Nb with a concentration of 2% at., which appears to be an adequate additive concentration to improve the gas sensor performances, such as it is suggested by the catalytic conversion efficiency experiments performed from FTIR measurements. FTIR absorbance spectra show that catalytic conversion of CO occurs at lower temperatures when niobium is introduced. The electrical response of the films to different concentrations of CO and ethanol has been monitored in dry and wet environments in order to test the influence of humidity in the sensor response. The addition of Nb decreases the working temperature and increases the stability of the layers. Also, large enhancement of the response time is obtained even with lower working temperatures. Moreover, humidity effects on the gas sensor response toward CO and ethanol are less important in Nb-doped samples than in the undoped ones.

Nanosized Nb-TiO2 gas sensors derived from alkoxides hydrolization

Nanocrystalline TiO2 modified with Nb has been produced through the sol-gel technique. Nanopowders have been obtained by means of the hydrolysis of pure alkoxides with deionized water and peptization of the resulting hydrolysate with diluted acid nitric at 100 C. The addition of Nb stabilizes the anatase phase to higher temperatures. XRD spectra of the undoped and the Nb-doped samples show that the undoped sample has been almost totally converted to rutile at 600 C, meanwhile the doped samples present still a low percentage of rutile phase. Nanocrystalline powders stabilized at 600 C with grain sizes of about 17 nm have successfully been synthesized by the addition of Nb with a concentration of 2% at., which appears to be an adequate additive concentration to improve the gas sensor performances, such as it is suggested by the catalytic conversion efficiency experiments performed from FTIR measurements. FTIR absorbance spectra show that catalytic conversion of CO occurs at lower temperatures when niobium is introduced. The electrical response of the films to different concentrations of CO and ethanol has been monitored in dry and wet environments in order to test the influence of humidity in the sensor response. The addition of Nb decreases the working temperature and increases the stability of the layers. Also, large enhancement of the response time is obtained even with lower working temperatures. Moreover, humidity effects on the gas sensor response toward CO and ethanol are less important in Nb-doped samples than in the undoped ones.

Catalysis by gold for biomass transformations

The development of new technologies to supplement fossil resources has led to a growing interest in the utilization of alternative routes. Biomass is a rich renewable feedstock for producing fine chemicals, polymers, and a variety of commodities replacing petroleumderived chemicals. Transformation of biomass into diverse valuable chemicals is the key concept of a biorefinery. Catalytic conversion of biomass, which reduces the use of toxic chemicals is one of the important approaches to improve the profitability of biorefineries. Utilization of gold catalysts allows conducting reactions under environmentally-friendly conditions, with a high catalytic activity and selectivity. Gold-catalyzed valorization of several biomass-derived compounds as an alternative approach to the existing technologies was studied in this work. Isomerization of linoleic acid via double bond migration towards biologically active conjugated linoleic acid isomers (CLA) was investigated. The activity and selectivity of various gold catalysts towards cis-9,trans-11-CLA and trans-10,cis-12-CLA were investigated in a semi-batch reactor, showing that the yield of the desired products varied, depending on the catalyst support. The structure sensitivity in the selective oxidation of arabinose was demonstrated using a series of gold catalysts with different Au cluster sizes in a shaker reactor operating in a semibatch mode. The gas-phase selective oxidation of ethanol was studied and the influence of the catalyst support on the catalytic performance was investigated. The selective oxidation of the lignan hydroxymatairesinol (HMR), extracted from the Norway spruce (Picea abies) knots, to the lignan oxomatairesinol (oxoMAT) was extensively investigated. The influence of the reaction conditions and catalyst properties on the yield of oxoMAT was evaluated. In particular, the structure sensitivity of the reaction was demonstrated. The catalyst deactivation and regeneration procedures were studied. The reaction kinetics and mechanism were advanced.

Synthesis, Characterization and Applications of Modified TiO2 Systems

This thesis is divided in to 9 chapters and deals with the modification of TiO2 for various applications include photocatalysis, thermal reaction, photovoltaics and non-linear optics. Chapter 1 involves a brief introduction of the topic of study. An introduction to the applications of modified titania systems in various fields are discussed concisely. Scope and objectives of the present work are also discussed in this chapter. Chapter 2 explains the strategy adopted for the synthesis of metal, nonmetal co-doped TiO2 systems. Hydrothermal technique was employed for the preparation of the co-doped TiO2 system, where Ti[OCH(CH3)2]4, urea and metal nitrates were used as the sources for TiO2, N and metals respectively. In all the co-doped systems, urea to Ti[OCH(CH3)2]4 was taken in a 1:1 molar ratio and varied the concentration of metals. Five different co-doped catalytic systems and for each catalysts, three versions were prepared by varying the concentration of metals. A brief explanation of physico-chemical techniques used for the characterization of the material was also presented in this chapter. This includes X-ray Diffraction (XRD), Raman Spectroscopy, FTIR analysis, Thermo Gravimetric Analysis, Energy Dispersive X-ray Analysis (EDX), Scanning Electron Microscopy(SEM), UV-Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS), Transmission Electron Microscopy (TEM), BET Surface Area Measurements and X-ray Photoelectron Spectroscopy (XPS). Chapter 3 contains the results and discussion of characterization techniques used for analyzing the prepared systems. Characterization is an inevitable part of materials research. Determination of physico-chemical properties of the prepared materials using suitable characterization techniques is very crucial to find its exact field of application. It is clear from the XRD pattern that photocatalytically active anatase phase dominates in the calcined samples with peaks at 2θ values around 25.4°, 38°, 48.1°, 55.2° and 62.7° corresponding to (101), (004), (200), (211) and (204) crystal planes (JCPDS 21-1272) respectively. But in the case of Pr-N-Ti sample, a new peak was observed at 2θ = 30.8° corresponding to the (121) plane of the polymorph brookite. There are no visible peaks corresponding to dopants, which may be due to their low concentration or it is an indication of the better dispersion of impurities in the TiO2. Crystallite size of the sample was calculated from Scherrer equation byusing full width at half maximum (FWHM) of the (101) peak of the anatase phase. Crystallite size of all the co-doped TiO2 was found to be lower than that of bare TiO2 which indicates that the doping of metal ions having higher ionic radius into the lattice of TiO2 causes some lattice distortion which suppress the growth of TiO2 nanoparticles. The structural identity of the prepared system obtained from XRD pattern is further confirmed by Raman spectra measurements. Anatase has six Raman active modes. Band gap of the co-doped system was calculated using Kubelka-Munk equation and that was found to be lower than pure TiO2. Stability of the prepared systems was understood from thermo gravimetric analysis. FT-IR was performed to understand the functional groups as well as to study the surface changes occurred during modification. EDX was used to determine the impurities present in the system. The EDX spectra of all the co-doped samples show signals directly related to the dopants. Spectra of all the co-doped systems contain O and Ti as the main components with low concentrations of doped elements. Morphologies of the prepared systems were obtained from SEM and TEM analysis. Average particle size of the systems was drawn from histogram data. Electronic structures of the samples were identified perfectly from XPS measurements. Chapter 4 describes the photocatalytic degradation of herbicides Atrazine and Metolachlor using metal, non-metal co-doped titania systems. The percentage of degradation was analyzed by HPLC technique. Parameters such as effect of different catalysts, effect of time, effect of catalysts amount and reusability studies were discussed. Chapter 5 deals with the photo-oxidation of some anthracene derivatives by co-doped catalytic systems. These anthracene derivatives come underthe category of polycyclic aromatic hydrocarbons (PAH). Due to the presence of stable benzene rings, most of the PAH show strong inhibition towards biological degradation and the common methods employed for their removal. According to environmental protection agency, most of the PAH are highly toxic in nature. TiO2 photochemistry has been extensively investigated as a method for the catalytic conversion of such organic compounds, highlighting the potential of thereof in the green chemistry. There are actually two methods for the removal of pollutants from the ecosystem. Complete mineralization is the one way to remove pollutants. Conversion of toxic compounds to another compound having toxicity less than the initial starting compound is the second way. Here in this chapter, we are concentrating on the second aspect. The catalysts used were Gd(1wt%)-N-Ti, Pd(1wt%)-N-Ti and Ag(1wt%)-N-Ti. Here we were very successfully converted all the PAH to anthraquinone, a compound having diverse applications in industrial as well as medical fields. Substitution of 10th position of desired PAH by phenyl ring reduces the feasibility of photo reaction and produced 9-hydroxy 9-phenyl anthrone (9H9PA) as an intermediate species. The products were separated and purified by column chromatography using 70:30 hexane/DCM mixtures as the mobile phase and the resultant products were characterized thoroughly by 1H NMR, IR spectroscopy and GCMS analysis. Chapter 6 elucidates the heterogeneous Suzuki coupling reaction by Cu/Pd bimetallic supported on TiO2. Sol-Gel followed by impregnation method was adopted for the synthesis of Cu/Pd-TiO2. The prepared system was characterized by XRD, TG-DTG, SEM, EDX, BET Surface area and XPS. The product was separated and purified by column chromatography using hexane as the mobile phase. Maximum isolated yield of biphenyl of around72% was obtained in DMF using Cu(2wt%)-Pd(4wt%)-Ti as the catalyst. In this reaction, effective solvent, base and catalyst were found to be DMF, K2CO3 and Cu(2wt%)-Pd(4wt%)-Ti respectively. Chapter 7 gives an idea about the photovoltaic (PV) applications of TiO2 based thin films. Due to energy crisis, the whole world is looking for a new sustainable energy source. Harnessing solar energy is one of the most promising ways to tackle this issue. The present dominant photovoltaic (PV) technologies are based on inorganic materials. But the high material, low power conversion efficiency and manufacturing cost limits its popularization. A lot of research has been conducted towards the development of low-cost PV technologies, of which organic photovoltaic (OPV) devices are one of the promising. Here two TiO2 thin films having different thickness were prepared by spin coating technique. The prepared films were characterized by XRD, AFM and conductivity measurements. The thickness of the films was measured by Stylus Profiler. This chapter mainly concentrated on the fabrication of an inverted hetero junction solar cell using conducting polymer MEH-PPV as photo active layer. Here TiO2 was used as the electron transport layer. Thin films of MEH-PPV were also prepared using spin coating technique. Two fullerene derivatives such as PCBM and ICBA were introduced into the device in order to improve the power conversion efficiency. Effective charge transfer between the conducting polymer and ICBA were understood from fluorescence quenching studies. The fabricated Inverted hetero junction exhibited maximum power conversion efficiency of 0.22% with ICBA as the acceptor molecule. Chapter 8 narrates the third order order nonlinear optical properties of bare and noble metal modified TiO2 thin films. Thin films were fabricatedby spray pyrolysis technique. Sol-Gel derived Ti[OCH(CH3)2]4 in CH3CH2OH/CH3COOH was used as the precursor for TiO2. The precursors used for Au, Ag and Pd were the aqueous solutions of HAuCl4, AgNO3 and Pd(NO3)2 respectively. The prepared films were characterized by XRD, SEM and EDX. The nonlinear optical properties of the prepared materials were investigated by Z-Scan technique comprising of Nd-YAG laser (532 nm,7 ns and10 Hz). The non-linear coefficients were obtained by fitting the experimental Z-Scan plot with the theoretical plots. Nonlinear absorption is a phenomenon defined as a nonlinear change (increase or decrease) in absorption with increasing of intensity. This can be mainly divided into two types: saturable absorption (SA) and reverse saturable absorption (RSA). Depending on the pump intensity and on the absorption cross- section at the excitation wavelength, most molecules show non- linear absorption. With increasing intensity, if the excited states show saturation owing to their long lifetimes, the transmission will show SA characteristics. Here absorption decreases with increase of intensity. If, however, the excited state has strong absorption compared with that of the ground state, the transmission will show RSA characteristics. Here in our work most of the materials show SA behavior and some materials exhibited RSA behavior. Both these properties purely depend on the nature of the materials and alignment of energy states within them. Both these SA and RSA have got immense applications in electronic devices. The important results obtained from various studies are presented in chapter 9.

[M(CO)4(2,2′-bipyridine)] (M = Cr, Mo, W) as efficient catalysts for electrochemical reduction of CO2 to CO at a gold electrode

Group 6 complexes of the type [M(CO)4(bpy)] (M=Cr, Mo, W) are capable of behaving as electrochemical catalysts for the reduction of CO2 at potentials less negative than those for the reduction of the radical anions [M(CO)4(bpy)].−. Cyclic voltammetric, chronoamperometric and UV/Vis/IR spectro-electrochemical data reveal that five-coordinate [M(CO)3(bpy)]2− are the active catalysts. The catalytic conversion is significantly more efficient in N-methyl-2-pyrrolidone (NMP) compared to tetrahydrofuran, which may reflect easier CO dissociation from 1e−-reduced [M(CO)4(bpy)].− in the former solvent, followed by second electron transfer. The catalytic cycle may also involve [M(CO)4(H-bpy)]− formed by protonation of [M(CO)3(bpy)]2−, especially in NMP. The strongly enhanced catalysis using an Au working electrode is remarkable, suggesting that surface interactions may play an important role, too.

Enzyme immobilization on Ag nanoparticles/polyaniline nanocomposites

We show a simple strategy to obtain all efficient enzymatic broelectrochemical device, in which urease was immobilized oil electroactive nanostructured membranes (ENMs) made with polyaniline and silver nanoparticles (AgNP) stabilized in polyvinyl alcohol (PAni/PVA-AgNP). Fabrication of the modified electrodes comprised the chemical deposition of polyaniline followed by drop-coating of PVA-AgNP and urease, resulting in a final ITO/PAni/PVA-AgNP/urease electrode Configuration. For comparison. the electrochemical performance of ITO/PAni/urease electrodes (without Ag nanoparticles) was also studied. The performance of the modified electrodes toward Urea hydrolysis was investigated via amperometric measurements, revealing a fast increase in cathodic current with a well-defined peak upon addition of urea to the electrolytic solution. The cathodic currents for the ITO/PAni/PVA-AgNP urease electrodes were significantly higher than for the ITO/PAni/urease electrodes. The friendly environment provided by the ITO/PAni/PVA-AgNP electrode to the immobilized enzyme promoted efficient catalytic conversion of urea into ammonium and bicarbonate tons. Using the Michaelis-Menten kinetics equation, a K(M)(aPP) of 2.7 mmol L(-1) was obtained. indicating that the electrode architecture employed may be advantageous for fabrication of enzymatic devices with improved biocatalytic properties. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.