Hydrothermal stability of Ru/SiO2-C: A promising catalyst for biomass processing through liquid-phase reactions

In this work, structural and morphological properties of SiO2-C composite material to be used as support for catalysts in the conversion of biomass-derived oxygenated hydrocarbons, such as glycerol, were investigated in liquid water under various temperatures conditions. The results show that this material does not lose surface area, and the hot liquid water does not generate changes in the structure. Neither change in relative concentrations of oxygen functional groups nor in Si/C ratio due to hydrothermal treatment was revealed by X-ray photoelectron spectroscopy (XPS) analysis. Raman analysis showed that the material is made of a disordered graphitic structure in an amorphous silica matrix, which remains stable after hydrothermal treatment. Results of the hydrogenolysis of glycerol using a Ru/SiO2-C catalyst indicate that the support gives more stability to the active phase than a Ru/SiO2 consisting of commercial silica

The Role of Acid Sites in the Catalytic Performance of Tungsten Oxide during the Dehydration of Isopropyl and Methyl Alcohols

Abstract WO 3 catalyst was prepared by thermal decomposition of ammonium metatungstate (AMT) in a static air atmosphere for 3h at 450, 550, 650 and 750 o C. The techniques employed for characterization of the catalyst were TG, DTA, XRD, FTIR, N 2 -sorption measurements. The surface acidity of the catalyst was investigated by adsorption of pyridine and 2, 6-dimethyl pyridine. The catalytic properties of the catalyst were carried out for the dehydration of isopropyl and methyl alcohols. The results revealed that WO 3 is more active toward isopropanol dehydration than methanol dehydration. Also reflect that the reaction mechanism and the yield of propene and dimethyl ether produced from dehydration of isopropyl and methyl alcohols are controlled by the strength of acid sites

Stable hydrosols for TiO2 coatings

The optimum processing parameters required to synthesize, by hydrolysis of titanium isopropoxide (TIP), highly stable hydrosols composed of nanoparticles of the smallest possible size, are deduced both from data available in literature and from our own experiments. The colloids prepared in these conditions are composed of aggregates of anatase (*90%) and brookite crystallites (5–6 nm). They are suitable for coatings and have longterm stability (more than one year) in terms of polymorphic composition, crystallite and agglomerate size. Stable sols composed solely of anatase crystallites (4 nm) can be prepared by partially complexing the TIP by acetylacetone before hydrolysis. It is not possible to produce porous films with these colloids because they are stabilized by electrostatic repulsion which causes the particles to organize themselves, during the drying step, to form materials with a close packed structure. However, coatings with controlled porosity can be prepared from these stable sols through the post addition of polymers, like PEG or block copolymers

Synthesis and Modification of Polymer Membranes for Pervaporation and Gas Separation

Trimesoyl chloride (TMC) crosslinked poly(vinyl alcohol) (PVA) / chitosan (CS) membranes and synthetic polyimide membranes were prepared for pervaporation dehydration of isopropanol and gas separation. PVA membranes were interfacially crosslinked with different amounts of TMC/hexane, and the degree of crosslinking was characterized by Fourier Transform Infrared Spectroscopy - Attenuated Total Reflectance Spectroscopy (FTIR-ATR) and water uptake. The asymmetric structure of the PVA-TMC membranes was revealed by FTIR-ATR. Thermal analysis was performed to understand the pyrolysis mechanism, which was supposed to be a combination of elimination of water and/or trimesic acid followed by breakage of the main chain. Water permeation and pervaporation dehydration of isopropanol were conducted, and the results showed that PVA-3TMC had the best overall pervaporation properties among the four PVA-TMC membranes studied. Sorption properties and pervaporation behavior of the PVA-3TMC membrane were investigated. The effects of water/isopropanol on the polymer matrix and the possible change of the degree of crystallinity induced by the sorbed water were believed to account for the sorption properties. For water permeation and pervaporation dehydration of isopropanol in a heating-cooling cycle, the permeation flux did not change significantly, and the selectivity was improved by the formation of crystallites during the heating run. For pervaporation in the diluting and concentrating runs at 60 °C, there was no change in the membrane permeability. Chitosan membranes were interfacially crosslinked in TMC/hexane with different crosslinking time. The membrane with a higher degree of crosslinking showed a higher degree of swelling in water at room temperature. A two-stage thermal decomposition mechanism was proposed based on thermal analyses. Pure gas permeation was performed with CO2 and N2 at room temperature, and CS-TMC-2 showed the best performance, with a CO2 permeability of ~163 Barrer and a CO2/N2 permeability ratio of ~42. Pervaporation was carried out for dehydration of isopropanol with the unconditioned and conditioned membranes, and the CS-TMC-3 membrane showed the best pervaporation performance. Pervaporation and gas separation properties were affected by the crosslinking-induced relaxation and the mobility/packing properties of the CS-TMC matrices. 4,4'-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA)-based and 2,2-bis[4-(3,4-dicarboxyphenoxy) phenyl]propane dianhydride (BPADA)-based copolyimides were synthesized from one-step high-temperature polymerization in m-cresol. Polymers were characterized with Gel Permeation Chromatography (GPC), FTIR, Nuclear Magnetic Resonance Spectroscopy (NMR), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Surface free energies and interfacial free energies were calculated from contact angles to characterize hydrophilicity of the polyimide membranes. Gas permeation properties of 6FDA-based copolyimide membranes were studied with N2, O2, H2, He and CO2, and pervaporation dehydration of isopropanol was performed with 6FDA-based and BPADA-based membranes. An empirical linear moiety contribution approach was proposed, and the moiety contribution factors were used to illustrate the effects of dianhydrides and diamines on permselectivities of the copolyimide membranes. Bulky side groups, flexibility of polymer main chains, structures of monomer moieties, and interactions between gas molecules and polymer chains were shown to affect gas permselectivities, while in pervaporation, both sorption and diffusion properties were affected by the interactions between penetrants and polymer matrices as well as the steric effects of monomer moieties

Intrinsic kinetics of lower alcohols: C2, C3 dehydration over Lewis acidic ordered mesoporous silicate: Zr-KIT-6

KIT-6 materials are large pore cubic Ia3d mesoporous silicate, with tunable pore size (4-12 nm) and pore wall thickness (4-6 nm). The three-dimensional structure of KIT-6 provides more mass transfer channels within the pore structure and also reduces the propensity for pore blockage. With the incorporation of zirconium into KIT-6 structure, the materials displayed mild Lewis acidity exclusively. These characteristics allow Zr-KIT-6 to be a promising catalyst for alcohol dehydration to olefins. Therefore, the emerging biomass-based renewable chemicals industry will particularly benefit from the availability of such catalysts for dehydration of long-chain alcohols from biomass based feedstock. In this study, the dehydration of short-chain alcohols, including isopropanol (IPA) and ethanol (EtOH), were carried out over three Zr-MIT-6 samples with different Si/Zr ratios ranging from 20 to 100. In the temperature range of 180-300 °C, the Zr-KIT-6 materials were shown to be highly active for of IPA dehydration to propylene (selectivity 98.5%). While, ethylene formed with the selectivity of 70%-80% when dehydrating EtOH at 300-380 °C range. 30 h continuous run revealed slight catalyst deactivation for IPA dehydration; and the catalyst started to deactivate after 60 h for EtOH dehydration. Kinetic models were established for both of these two reactions. The activation energy for IPA and EtOH dehydration, estimated from intrinsic rate constants normalized with respect to the Lewis acid sites, were approximately 48.9 ± 0.5 kJ/mol and 79.5 ± 0.7 kJ/mol, respectively, which are found to be lower than or comparative with most other Brønsted or Lewis acidic heterogeneous catalysts reported in the literature for such reactions. This clearly shows that the Zr-KIT-6 materials are a superior and promising class of highly active, selective and durable alcohol dehydration catalysts. Although, IPA and EtOH are short-chain alcohols, establishing such activity is key to their potential use as solid acid catalysts for even bulkier substrates

Reactions of Alcohols and Organophosphonates on Tungsten Trioxide Epitaxial Films

The adsorption, diffusion, reactions, and desorption of water, alcohols, ethers, and an organophosphonate were studied using calibrated thermal desorption spectroscopy (CTDS) on thin film WO3(OOl) surfaces grown epitaxially on a single crystal α- Al2O3(li02) (sapphire) substrate. The studies were conducted on oxidized and reduced surfaces, which were characterized by x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The desorption spectra for molecular desorption of all of these molecules shifted to lower temperature with increasing coverage, and had overlapping tails on the high temperature side. Monte Carlo simulations show that this typical desorption shape can be characterized by first-order or pseudo-first-order desorption kinetics in which rapid diffusion allows the molecules to find and desorb from the most strongly bound sites of a heterogeneous surface. For methanol, UPS revealed molecular adsorption on the oxidized surface and dissociative adsorption on the reduced surface, but only molecular desorption of methanol was detected. For ethanol and isopropanol, competition between molecular desorption and dehydroxylation at lower temperature controls the alkoxy coverage remaining and consequently, the selectivity toward alkenes. The selectivity was coverage dependent, but was not significantly different on the oxidized and reduced WO3(001) surfaces. The rate limiting step in the dehydration of the alkoxy species to ethylene or propylene was identified as C-0 bond scission. Dimethoxymethane showed some decomposition to methanol on both surfaces, while only molecular desorption was found for dimethyl ether. Dimethyl methyl phosphonate (DMMP) decomposed on both the reduced and oxidized surfaces through loss of methoxy groups. Methanol and dimethyl ether were detected on the oxidized surface, while only dimethyl ether was observed on the reduced surface. Comparison of the dimethyl ether production with spectra following adsorption of dimethyl ether suggests that the rate limiting step is a surface catalyzed, intramolecular coupling reaction between methoxy groups. The C1s and P2p XPS features were consistent with a methyl phosphate-like species remaining after DMMP decomposition

Crosslinked nanocomposite sodium alginate-based membranes with titanium dioxide for the dehydration of isopropanol by pervaporation

The work of H.G. Premakshi and M.Y. Kariduraganavar was supported by the Department of Science & Technology, New Delhi, through the DST-PURSE-Phase-II program (Grant No. SR/PURSE PHASE-2/13 (G)). The work of GRM is supported by the Fundação para a Ciência e a Tecnologia (FCT) and Centro2020 through the project references: UID/Multi/04044/2019; PAMI-ROTEIRO/0328/2013 (No. 022158).Sodium alginate (NaAlg) based membranes were prepared using a solution technique, crosslinked with poly(styrene sulfonic acid-co-maleic acid) (PSSA-co-MA). Subsequently, the membranes were modified by the incorporation of 0, 10, 20, 30 and 40% w/w of titanium dioxide with respect to sodium alginate. The membranes thus obtained were designated as M, M-1, M-2, M-3 and M-4, respectively. An equilibrium swelling experiment was performed using dfferent compositions of the water and isopropanol mixtures. Subsequently, we used a pervaporation cell fitted with each membrane in order to evaluate the extent of the pervaporation dehydration of isopropanol. Among the membranes studied, the membranes containing 40 mass% of titanium dioxide exhibited the highest separation factor() of 24,092, with a flux(J) of 18.61x10-² kg/m².h at 30ºC for 10 mass%w/w of water in the feed. The total flux and the flux of water were found to overlap with each other, indicating that these membranes can be e ectively used to break the azeotropic point of water–isopropanol mixtures. The results clearly indicate that these nanocomposite membranes exhibit an excellent performance in the dehydration of isopropanol. The activation energy values obtained for the water permeation were significantly lower than those of the isopropanol permeation, underlining that these membranes have a high separation ability for the water isopropanol system. The estimated activation energies for total permeation (EP) and total di usion (ED) values ranged between 10.60 kJ.mol-¹ and 3.96 kJ.mol­-¹, and 10.76 kJ.mol-¹ and 4.29 kJ.mol-¹, respectively. The negative change in the enthalpy values for all the membranes indicates that sorption was mainly dominated by Langmuir’s mode of sorption.info:eu-repo/semantics/publishedVersio