N-butyraldehyde/N-valeraldehyde Self-Condensation Catalyzed By MIL-100（Fe） And MIL-100（Fe）-encapsulated H₄SiW₁₂O₄₀

The self-condensations of n-butyraldehyde and n-valeraldehyde are key steps of carbon chain growth for commercial production of 2-ethylhexanal（2EHO）and 2-propylheptanol（2-PH）.Research on the reactions and their catalysts are of importance in academia and application.Because there exist Lewis acidity of unsaturated metal sites in mental organic framework materials MIL accompanying with high specific surface area and porosity,MIL-100（Fe）and MIL-100（Fe）-encapsulated silicotungstic acid(H₄SiW₁₂O₄₀)were successively prepared,and their catalytic performance for n-butyraldehyde and n-valeraldehyde self-condensation reaction was separately investigated.First of all,MIL-100（Fe）catalyst was successfully prepared and the catalytic performance for n-valeraldehyde self-condensation to 2-propyl-2-heptenal（2P2H）was evaluated.The suitable reaction conditions for n-valeraldehyde self-condensation reaction were obtained as follows:a weight percentage of MIL-100（Fe）=15wt.%,reaction temperature of 130℃,and reaction time of 8h.Under the above conditions,the conversation of n-valeraldehyde and the yield of 2P2H were 73.5%and 63.2%,respectively.The components existing in the reaction system were identified by GC-MS analysis and then a possible reaction network of n-valeraldehyde self-condensation to 2P2H catalyzed by MIL-100（Fe）was established based on speculation of the side-reactions.The MIL-100（Fe）catalyst could be reused for four times without a significant loss in its catalytic performance.Secondly,a novel heterogeneous H₄SiW₁₂O₄₀@MIL-100（Fe）catalyst was successfully prepared by encapsulation of H₄SiW₁₂O₄₀ into the mental organic framework MIL-100（Fe）.Then the catalytic performance of H₄SiW₁₂O₄₀@MIL-100（Fe）and the effect of reaction conditions on n-butyraldehyde self-condensation to 2-ethyl-2-hexenal（2E2H）were investigated.The suitable reaction conditions for n-butyraldehyde self-condensation reaction were obtained as follows:H₄SiW₁₂O₄₀ loading=13.7%,a weight percentage of H₄SiW₁₂O₄₀@MIL-100（Fe）=15wt.%,reaction temperature of 120℃,and reaction time of6h.Under the above conditions,the conversation of n-butyraldehyde was 72.9%and the yield of 2E2H was 60.9%.The reaction components formed over the H₄SiW₁₂O₄₀@MIL-100（Fe）catalyst were identified by GC-MS analysis and then some side-reactions were speculated and a possible reaction network for n-butyraldehyde self-condensation to 2E2H catalyzed by H₄SiW₁₂O₄₀@MIL-100（Fe）was proposed.Furthermore,the reason for the catalyst deactivation and the method of its regeneration were explored.The results of ICP-AES,BET and FT-IR analyses showed that the deactivation of H₄SiW₁₂O₄₀@MIL-100（Fe）was due to the pore blockage from the adsorption of some organic compounds onto the surface of H4SiW12O40@MIL-100（Fe）.The deactivated H4SiW12O40@MIL-100（Fe）could be regenerated by the treatment with absolute ethanol at 80℃to remove the organic compounds and then could be reused four times with a tolerable loss of its catalytic activity.The H4SiW12O40 was encapsulated into MIL-100（Fe）mesoporous cages to overcome the problem that heteropolyacid was difficult to be separated and reused due to its dissolution in the self-condensation reaction of n-butyraldehyde.