Informace o publikaci
NON-HYDROLYTIC SOL-GEL SYNTHESIS OF HYBRID METALLOSILICATES FOR ETHANOL DEHYDRATION
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| Rok publikování | 2018 |
| Druh | Konferenční abstrakty |
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| Popis | Metallosilicates are particularly useful in heterogeneous catalysis, since their acido-basic properties can be tuned by the amount, nature and dispersion of the metals incorporated in the silica matrix, by synthesis conditions, by post-treatments, etc.1 Metallosilicates are used as catalysts in epoxidation of alkenes, cracking, isomerization reactions, etc. Nowadays they are applied in the biomass and biofuel sector, where they catalyze the dehydration of bioalcohols, (trans)esterification and hydrolysis in oleochemistry, biopolymer hydrolysis, condensation reactions, etc.2 However for this modern purpose the performance of metallosilicates is not fully satisfactory, mainly due to their low stability in the presence of water.3 To tackle these challenges we propose to introduce hydrophobic organic groups into metallosilicate materials. As a synthetic route, non-hydrolytic sol-gel preparation is used. It allows for the synthesis of highly porous and amorphous metallosilicates with homogeneous distribution of active metal sites within the silicate matrix.4,5 The introduction of organic groups (R) takes place during the polycondensation reactions (eq. 1 and 2), no additional treatment is necessary and therefore the whole procedure is completed within one single step. ?(R-)Si-Cl + R´-O-M? › ?(R-)Si-O-M? + R´Cl (1) ?(R-)Si-OAc + R´2N-M? › ?(R-)Si-O-M? + R´2NAc (2) Influence of several parametres on hydrothermal stability, porosity, acidity, and activity in ethanol dehydration is studied. These are particularly (i) the synthetic route chosen (alkyl halide vs. acetamide elimination, eq. 1 and 2, respectively), (ii) the metal (M) introduced (Al vs Nb, both are known to produce acid materials however their strength is different), and (iii) the nature of organic groups (R) incorporated within the silicate matrix (terminal vs bridging, aryl- vs alkyl-). Prepared materials are characterized by a wide array of physico-chemical techniques. The presence of hydrophobic organic groups in the gels is revealed by IR spectroscopy. Their influence is established by hydrothermal stability tests (flow in water-saturated air, fixed bed). Textural characterization is done by N2-physisorption. Acidic properties of the catalysts are followed by thermally programmed desorption of NH3. FTIR coupled with pyridine adsorption reveals the nature of the acidic sites. Catalyst surface is analyzed by X-ray photoelectron spectroscopy (XPS). Thermal analysis (TGA) is used to study the stability of organic groups. Finally solid-state NMR allows us estimate homogeneity and structural motifs present in the materials. Catalytic performance in the dehydration of ethanol is evaluated in a dedicated fully-automated gas-phase fixed-bed micro-reactor with online analytical facilities (GC). Catalytic behaviour (activity, selectivity, stability) is correlated with the parameters of the preparation parameters. Well–known acidic catalysts (ß-zeolite and commercial silica-alumina) are used as benchmarks. References (1) Ciriminna, R.; Cara, P. D.; Sciortino, M.; Pagliaro, M. Catalysis with Doped Sol-Gel Silicates. Adv. Synth. Catal. 2011, 353 (5), 677–687. (2) Behrens, M.; Datye, A. K. Catalysis for the Conversion of Biomass and Its Derivatives, Edition Op.; 2013. (3) Zapata, P. A.; Faria, J.; Ruiz, M. P.; Jentoft, R. E.; Resasco, D. E. Hydrophobic Zeolites for Biofuel Upgrading Reactions at the Liquid–Liquid Interface in Water/Oil Emulsions. J. Am. Chem. Soc. 2012, 134 (20), 8570–8578. (4) Debecker, D. P.; Mutin, P. H. Non-Hydrolytic Sol-Gel Routes to Heterogeneous Catalysts. Chem. Soc. Rev. 2012, 41 (9), 3624–3650. (5) Styskalik, A.; Skoda, D.; Barnes, C.; Pinkas, J. The Power of Non-Hydrolytic Sol-Gel Chemistry: A Review. Catalysts 2017, 7 (6), 168. |