1,720,959 research outputs found
Metal oxides catalysts for the synthesis of value-added chemicals from 2nd generation sugars and sugar derivatives
No full textThe present Ph.D. thesis provides some examples of innovative 2nd generation catalytic processes for the conversion of renewable raw materials into green value-added chemicals. In particular, D-glucose and some its derivatives, all ideally representing waste materials of dedicated biomasses, agricultural residues, or solid organic urban waste exploitation in the biorefinery plant, were converted into useful chemical building-blocks.
After a brief introduction to the topic and the description of the experimental method, each chapter of the work is based on one or more scientific articles either published or submitted. Among the possible catalytic reactions, the hydrogenation, oxidation and hydrodeoxygenation were investigated: for this purpose, several novel catalysts were synthetized, tested and characterized. The catalysts were made from precursor solutions with the incipient wet impregnation method or with the solution combustion synthesis, depending by the catalyst type. The conversion of glucose and some glucose-derivatives was typically performed under gentle operative conditions and in aqueous mean.
Pt-based catalysts were tested for glucose conversion to adipic acid in a two-step process carried out in water solution without any pH control by investigating the effect of a series of supporting materials (active carbon, alumina, silica and ceria). The process consisted in the D-saccharic acid (SacA) production by D-glucose catalytic wet air oxidation followed by a hydrodeoxygenation treatment of SacA to adipic acid (AA) with the same catalyst. The main limit of using Pt for D-glucose oxidation is represented by the catalyst inhibition operated by the first product of the reaction, the gluconic acid (GluA), which prevents the consecutive reaction of SacA formation, but a deeper investigation of the reaction scheme allowed us to assess that over Pt/alumina the consecutive oxidation of gluconic acid to SacA is slightly favored under uncontrolled pH too.We have demonstrated that a 5.2 wt.% Pt on γ-alumina sample, the catalysts presenting the larger amount of strong Brønsted acid sites, was the best material for obtaining SacA (with a molar yield of about 13.5%); afterward, by performing the halogen-promoted hydrodeoxygenation of the resulting solution, the SacA was quantitatively converted into AA (and thus the overall adipic acid molar yield from glucose was about 13.0%).
Effectively, The efficient conversion of common biomass derivatives, as D-glucose, into value-added chemicals has received a great deal of attention in the last few years. Several heterogeneous catalytic systems, characterized by noble metals, have already been investigated for the Catalytic Wet Air Oxidation (CWAO) of derived biomass. Nevertheless, the redox effect of such catalysts on biobased compounds has not been described in detail. In the present thesis, some perovskite type oxides (Fe, Co, Mn) that present high redox properties and stability under hydrothermal conditions have been tested to establish their ability to convert D-glucose into C6 aldaric acid, lactic acid (LacA) and levulinic acid (LevA). The influence of the reaction temperature, and the affinity of the catalysts to hydrogen and oxygen on the distribution of the liquid products have been investigated. In the best conditions, 50.3 mol.% and 69.5 mol.% of lactic and levulinic acid have been obtained by employing LaCoO3 and LaMnO3, respectively. Apart from the oxidative effect, which has led to several oxidation products, a high reductive effect of the catalysts has enabled the conversion of some key intermediates, such as pyruvic acid (PyrA) and hydroxymethylfurfural (HMF), into the desired products. LaMnO3, which has resulted to be the most oxidizable/reducible catalyst over a low temperature range, has shown the best performance of the studied perovskite type oxides; it has been found to promote the conversion of hydroxymethylfurfural to levulinic acid and to give the highest overall molar yield.
Moreover, performing catalysts have been synthetized through incipient wet impregnation and tested for cis,cis-muconic acid (ccMA) hydrogenation to adipic acid.
Before the hydrogenation, the investigation on the solubility of ccMA dissolution in different polar solvents has been carried out by characterizing and modelling the dissolution as a function of temperature. Water, ethanol, 2-propanol and acetic acid have been investigated as solvents in the range temperatures from a 298.15 to 348.15 K. Owing to the absence of ccMA solubility data, the reliability of the adopted experimental set-up was validated comparing published and experimental solubility data of a similar compound, that is, AA. From the results, it has emerged that the employed system is appropriate for the determination of molar fractions of an organic compound dissolved in polar solvents. The molar fraction and temperature were correlated using the Apelblat equation model, which is applied for the mathematic fitting of experimental data.
A total relative average deviation of 3.54% was obtained for the experimental results and the solubility data obtained with the model, thus attesting the adequacy for this study. The use of Apelblat equation also allowed to determine the apparent molar enthalpy and molar entropy of dissolution. The dissolution of ccMA in water, ethanol, 2-propanol and acetic acid, over temperatures ranging from 298.15 to 348.15 K, has been shown to be endothermic.
The activity of Pt-based catalysts has been compared with a Ni-based catalyst at a gentle condition. A supported 14.2 wt.% Ni on γ-alumina converted 100% of muconic acid, yielding 99.4 mol.% of AA.
Finally, the oxidative cracking of 5-keto-L-aldonic acids to tartaric acid (TarA) was successfully performed at room temperature and atmospheric pressure in a carbonate buffer (pH = 10.34), by employing various V-based catalysts. The performance of the novel heterogeneous V-based catalysts was compared with the one of a conventional homogeneous system.
The effect of the catalysts was obvious and 2%VOx/ZrO2 was found to be the best catalyst for the 5-keto-aldonic acids conversion to tartaric acid. The tartaric acid selectivity was equal to 74.5% and 44.3% starting from the 5-keto-D-gluconic acid (5kGl) and 5-keto-L-galactonic acid (5kGa), respectively. The best performances in terms of tartaric acid selectivity were obtained at the beginning of reaction, and about one fourth of the carbon moles were converted into tartaric acid after 24 h of reaction. The substrate was entirely converted after 24 h indicating that several by-products were also produced during the reaction. So, an overall reaction pathway was supposed and the effect of the vanadium structure to the catalytic activity was hypothesized. Moreover, the reaction mechanism of the 5-keto-aldonic acids conversion to tartaric acid promoted by the anchoring VOx-support bond was described
A novel pH uncontrolled route for the synthesis of adipic acid from glucose over Pt/alumina catalyst
No full text
Thermodynamics of cis,cis-muconic acid solubility in various polar solvents at low temperature range
No full textSolubility of Cis, Cis-muconic acid in various polar solvents from 298.15 K to 348.15 K
No full textThe present work concerns with an investigation on the solubility of cis,cis-muconic acid dissolution in different polar solvents by characterizing and modeling the dissolution as a function of temperature. Water, ethanol, 2-propanol and acetic acid have been investigated as solvents in the range temperatures from a 298.15 to 348.15 K. Owing to the absence of cis,cis-muconic acid solubility data, the molar fraction and temperature were correlated using the modified Apelblat equation model, which is applied for the mathematic fitting of experimental data. A total relative average deviation of 3.54% was obtained for the experimental results and the solubility data obtained with the model, thus attesting the adequacy for this study. The use of modified Apelblat equation also allowed to determine the molar enthalpy and molar entropy of dissolution. The dissolution of cis,cis-muconic acid in water, ethanol, 2-propanol and acetic acid, over temperatures ranging from 298.15 to 348.15 K, has been shown to be exothermi
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
