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23-P-22 - The design of zeolites catalysts for the synthesis of organe blossom and apple fragrances
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23-P-21 - Novel delaminated zeolites are more active acid catalysts than conventional zeolites and mesoporous AI/MCM-41 for the synthesis of fine chemicals M.J. Climent, A. Corma,* V. Forn6s, H. Garcia, S. Iborra, J. Miralles and I. Rodriguez
ITQ-CSIC-UPC, Universidad Polit6cnica de Valencia, Valencia, Spain. Fax 34 96 3877807. ITQ-2 zeolite prepared by delamination of MCM-22 precursor, is formed by disordered individual sheets of crystalline zeolitic layers in where the Bronsted acid sites are of zeolitic nature and the vast majority of them accessible to large molecules. The delaminated zeolite combines the acid characteristic of microporous zeolites with accessibility of the sites of mesoporous A1/MCM-41 and amorphous silica-alumina. The superior catalytic performance of delaminated zeolites compared to conventional zeolites and A1/MCM-41 is examplified for reactions involving large reactant molecules, namely: the preparation of dimethyl acetals, the Beckmann rearrangement of bulky cycloalkanone oximes and hydroxylation of aromatics.
23-P-22 - The design of zeolites catalysts for the synthesis of orange blossom and apple fragrances M.J. Climent, A. Corma and A. Velty
Instituto de Tecnologia Quimica (UP v-csIc). Universidad Polit6cnica de Valencia. Avenida de los Naranjos s/n, 46022, Valencia, Spain. The synthesis of propylene glycol acetal of methylnaphthyl ketone and ethylene glycol acetal of ethyl acetoacetate, which are flavouring materials with orange blossom and apple scent respectively, have been obtained successfully in presence of different zeolites. It has been found that a higher concentration of acid sites in the catalyst does not guarantee a better catalytic performance and for acetalization reaction the hydrophobic properties of catalyst are as important as the concentration of active sites. This work presents the crucial role that the control of the textural and adsorption properties play in optimizing a zeolite catalyst for the production of these two fragrances.
23-P-23 - Catalytic in-situ infrared spectroscopic study of n-butyraldehyde aldol condensation U. Rymsa, M. Hunger and J. Weitkamp
Institute of Chemical Technology, University of Stuttgart, D-70550 Stuttgart, Germany Aldol condensation of n-butyraldehyde on cesium-exchanged zeolites X and Y, mesoporous MCM-41 and silica gel impregnated with cesium salt yield initially 2-ethylhexenal with 100 % selectivity at a high conversion. The active catalysts suffer from fast deactivation, which is probably caused by a Tishchenko side reaction leading to the formation of butyric acid. A carboxylate ion strongly adsorbed on the catalyst surface is detected by in-situ infrared spectroscopy. It probably poisons the active sites and furthermore blocks the pores of microand mesoporous catalysts. Carboxylate formation cannot be suppressed by carrying out the reaction in hydrogen or by adding water to the feed. However, complete catalyst regeneration can be achieved by heating in nitrogen at around 350 to 400 ~
23-P-21 - Novel delaminated zeolites are more active acid catalysts than conventional zeolites and mesoporous AI/MCM-41 for the synthesis of fine chemicals M.J. Climent, A. Corma,* V. Forn6s, H. Garcia, S. Iborra, J. Miralles and I. Rodriguez
ITQ-CSIC-UPC, Universidad Polit6cnica de Valencia, Valencia, Spain. Fax 34 96 3877807. ITQ-2 zeolite prepared by delamination of MCM-22 precursor, is formed by disordered individual sheets of crystalline zeolitic layers in where the Bronsted acid sites are of zeolitic nature and the vast majority of them accessible to large molecules. The delaminated zeolite combines the acid characteristic of microporous zeolites with accessibility of the sites of mesoporous A1/MCM-41 and amorphous silica-alumina. The superior catalytic performance of delaminated zeolites compared to conventional zeolites and A1/MCM-41 is examplified for reactions involving large reactant molecules, namely: the preparation of dimethyl acetals, the Beckmann rearrangement of bulky cycloalkanone oximes and hydroxylation of aromatics.
23-P-22 - The design of zeolites catalysts for the synthesis of orange blossom and apple fragrances M.J. Climent, A. Corma and A. Velty
Instituto de Tecnologia Quimica (UP v-csIc). Universidad Polit6cnica de Valencia. Avenida de los Naranjos s/n, 46022, Valencia, Spain. The synthesis of propylene glycol acetal of methylnaphthyl ketone and ethylene glycol acetal of ethyl acetoacetate, which are flavouring materials with orange blossom and apple scent respectively, have been obtained successfully in presence of different zeolites. It has been found that a higher concentration of acid sites in the catalyst does not guarantee a better catalytic performance and for acetalization reaction the hydrophobic properties of catalyst are as important as the concentration of active sites. This work presents the crucial role that the control of the textural and adsorption properties play in optimizing a zeolite catalyst for the production of these two fragrances.
23-P-23 - Catalytic in-situ infrared spectroscopic study of n-butyraldehyde aldol condensation U. Rymsa, M. Hunger and J. Weitkamp
Institute of Chemical Technology, University of Stuttgart, D-70550 Stuttgart, Germany Aldol condensation of n-butyraldehyde on cesium-exchanged zeolites X and Y, mesoporous MCM-41 and silica gel impregnated with cesium salt yield initially 2-ethylhexenal with 100 % selectivity at a high conversion. The active catalysts suffer from fast deactivation, which is probably caused by a Tishchenko side reaction leading to the formation of butyric acid. A carboxylate ion strongly adsorbed on the catalyst surface is detected by in-situ infrared spectroscopy. It probably poisons the active sites and furthermore blocks the pores of microand mesoporous catalysts. Carboxylate formation cannot be suppressed by carrying out the reaction in hydrogen or by adding water to the feed. However, complete catalyst regeneration can be achieved by heating in nitrogen at around 350 to 400 ~