The effect of activation treatments of K-free and K-MoVSbO bronzes on either their physico-chemic... more The effect of activation treatments of K-free and K-MoVSbO bronzes on either their physico-chemical characteristics or catalytic properties for propane partial oxidation have been studied. The as-synthesized materials, hydrothermally prepared and presenting (SbO)(2)M20O56 type structure (the so called M1-phase), were activated by different heat-treatments, characterized (XRD, SEM-EDS, HRTEM, V K-edge, Sb L-1- and K-edges XANES, EPR, XPS, NH3-TPD) and tested in propane partial oxidation. In general, the selectivity to acrylic acid (the most valuable product) was higher in K-containing MoVSbO catalysts. In addition, different trend in the catalytic behavior was found between K-free and K-containing MoVSbO series, mostly related to different changes in crystalline phases distribution and catalysts surface characteristics (composition and acid properties) induced by the several activation treatments which also modified the average Sb oxidation state.
In the last years, 'in situ&a... more In the last years, 'in situ' solid-state NMR has been applied to investigate the Beckmann rearrangement of oximes into amides using zeolites and mesoporous materials of different structure containing Brønsted acids or silanol groups as active sites. DFT methods have been applied to model the geometry of the complexes resulting from adsorption of reactants, reaction intermediates and products on clusters representing the zeolite centers, and their (15)N and (13)C NMR chemical shift calculated theoretically. This article reviews the results reported in the bibliography on the Beckmann rearrangement of various oximes (acetophenone oxime, cyclohexanone oxime and cyclododecanone oxime) mainly using 'in situ'(15)N NMR spectroscopy and theoretical calculations, and are compared with those obtained by 'in situ' infrared spectroscopy. The combination of experiment and theory has been shown to be very useful for the interpretation of the NMR spectra and the identification of the species present at different reaction temperatures.
... Direct Synthesis and Characterization of Hydrophobic Aluminum-Free Ti−Beta Zeolite. ... Abstr... more ... Direct Synthesis and Characterization of Hydrophobic Aluminum-Free Ti−Beta Zeolite. ... Abstract. Incorporation of Ti into the framework of aluminium-free zeolite Beta has been achieved in F - medium and has produced hydrophobic selective oxidation catalysts. ...
Page 1. Magic angle spinning NMR investigations on amorphous aluminophosphate oxynitrides Teresa ... more Page 1. Magic angle spinning NMR investigations on amorphous aluminophosphate oxynitrides Teresa Blasco, Avelino Corma,* Lorenzo FernaŤndez, Vicente ForneŤs and Rut Guil-LoŤpez Instituto de (Universidad de V alenciaČCSIC), Avda. ...
Theoretical calculations and in situ solid state NMR spectroscopy have been combined to get insig... more Theoretical calculations and in situ solid state NMR spectroscopy have been combined to get insight on the nature of the active sites for the Beckmann rearrangement reaction in borosilicate zeolites. The interaction of a B site in zeolite Beta with a series of probe molecules (ammonia, pyridine, acetone and water) has been modelled and the (15)N and (11)B NMR isotropic chemical shift of the resulting complexes calculated and compared with experimental in situ NMR results. This approach has allowed validation of the methodology to model the adsorption on a zeolite boron site of molecules of varying basicity which are either protonated or non-protonated. The limitation is that theoretical calculations overestimate the effect of molecular adsorption through hydrogen bonds on the calculated isotropic (11)B NMR chemical shift.Theoretical and experimental results on the adsorption of acetophenone and cyclohexanone oximes on zeolite B-Beta indicate that Brønsted acid sites protonate the oximes, changing the boron coordination from trigonal to tetrahedral. Comparison of theoretical and experimental (15)N NMR chemical shifts of the adsorbed amides (acetanilide and epsilon-caprolactam) indicates that they are non-protonated, and the (11)B NMR spectra show that, as expected, boron remains in trigonal coordination with an isotropic delta(11)B(exp) which differs from the calculated value delta(11)B(calc).
The Beckmann rearrangement of acetophenone oxime using zeolite H-beta and silicalite-N as catalys... more The Beckmann rearrangement of acetophenone oxime using zeolite H-beta and silicalite-N as catalysts has been investigated by means of (15)N and (13)C solid state NMR spectroscopy in combination with theoretical calculations. The results obtained show that the oxime is N-protonated at room temperature on the acid sites of zeolite H-beta. At reaction temperatures of 423 K or above, the two isomeric amides, acetanilide and N-methyl benzamide (NMB) are formed, and interact with the Brønsted acid sites of zeolite H-beta through hydrogen bonds. The presence of residual water hydrolyzes the two amides, while larger amounts inhibit the formation of NMB and cause the total hydrolysis of the acetanilide. Over siliceous zeolite silicalite-N, containing silanol nests as active sites, the oxime is adsorbed through hydrogen bonds and only acetanilide is formed at reaction temperatures of 423 K or above. In the presence of water, the reaction starts at 473 K, still being very selective up to 573 K, and the amide is partially hydrolyzed only above this temperature .
ABSTRACT Copper and cerium bi-component modifications of KIT-6 were prepared by wetness impregnat... more ABSTRACT Copper and cerium bi-component modifications of KIT-6 were prepared by wetness impregnation technique from the corresponding nitrate precursors. Nitrogen physisorption, XRD, FTIR of adsorbed CO, UV-Vis, XPS and TPR were used for their characterization. The catalytic activity of the obtained materials was tested in ethyl acetate oxidation and compared to those achieved over SBA-15-supported catalysts. It was established that the interaction between copper and ceria species results in the formation of finely dispersed CuO nanoparticles on the ceria ones, which are stabilized by an interface layer of penetrated into the ceria lattice copper ions in different oxidative state. This process seems to be facilitated in the more opened 3D-structure of KIT-6, which provides better catalytic activity even at high Cu/Ce ratio than those observed for the SBA-15 modifications.
Collection of Czechoslovak Chemical Communications, 1998
Page 1. OXIDATIVE DEHYDROGENATION OF ETHANE ON VANADIUM-CONTAINING ALUMINOPHOSPHATES WITH AFI STR... more Page 1. OXIDATIVE DEHYDROGENATION OF ETHANE ON VANADIUM-CONTAINING ALUMINOPHOSPHATES WITH AFI STRUCTURE Teresa BLASCO a1, Patricia CONCEPCION a, Jose M. LOPEZ NIETO a2,* and Arturo ...
ABSTRACT Finding the culprits: In situ NMR spectroscopy combined with theoretical calculations sh... more ABSTRACT Finding the culprits: In situ NMR spectroscopy combined with theoretical calculations show the formation of acetyl species covalently bound to framework oxygen atoms in acid zeolites. These species, and not the usually assumed acylium cations, are the reactive intermediates in Friedel-Crafts acylation and Koch carbonylation reactions on zeolites.
The effect of activation treatments of K-free and K-MoVSbO bronzes on either their physico-chemic... more The effect of activation treatments of K-free and K-MoVSbO bronzes on either their physico-chemical characteristics or catalytic properties for propane partial oxidation have been studied. The as-synthesized materials, hydrothermally prepared and presenting (SbO)(2)M20O56 type structure (the so called M1-phase), were activated by different heat-treatments, characterized (XRD, SEM-EDS, HRTEM, V K-edge, Sb L-1- and K-edges XANES, EPR, XPS, NH3-TPD) and tested in propane partial oxidation. In general, the selectivity to acrylic acid (the most valuable product) was higher in K-containing MoVSbO catalysts. In addition, different trend in the catalytic behavior was found between K-free and K-containing MoVSbO series, mostly related to different changes in crystalline phases distribution and catalysts surface characteristics (composition and acid properties) induced by the several activation treatments which also modified the average Sb oxidation state.
In the last years, 'in situ&a... more In the last years, 'in situ' solid-state NMR has been applied to investigate the Beckmann rearrangement of oximes into amides using zeolites and mesoporous materials of different structure containing Brønsted acids or silanol groups as active sites. DFT methods have been applied to model the geometry of the complexes resulting from adsorption of reactants, reaction intermediates and products on clusters representing the zeolite centers, and their (15)N and (13)C NMR chemical shift calculated theoretically. This article reviews the results reported in the bibliography on the Beckmann rearrangement of various oximes (acetophenone oxime, cyclohexanone oxime and cyclododecanone oxime) mainly using 'in situ'(15)N NMR spectroscopy and theoretical calculations, and are compared with those obtained by 'in situ' infrared spectroscopy. The combination of experiment and theory has been shown to be very useful for the interpretation of the NMR spectra and the identification of the species present at different reaction temperatures.
... Direct Synthesis and Characterization of Hydrophobic Aluminum-Free Ti−Beta Zeolite. ... Abstr... more ... Direct Synthesis and Characterization of Hydrophobic Aluminum-Free Ti−Beta Zeolite. ... Abstract. Incorporation of Ti into the framework of aluminium-free zeolite Beta has been achieved in F - medium and has produced hydrophobic selective oxidation catalysts. ...
Page 1. Magic angle spinning NMR investigations on amorphous aluminophosphate oxynitrides Teresa ... more Page 1. Magic angle spinning NMR investigations on amorphous aluminophosphate oxynitrides Teresa Blasco, Avelino Corma,* Lorenzo FernaŤndez, Vicente ForneŤs and Rut Guil-LoŤpez Instituto de (Universidad de V alenciaČCSIC), Avda. ...
Theoretical calculations and in situ solid state NMR spectroscopy have been combined to get insig... more Theoretical calculations and in situ solid state NMR spectroscopy have been combined to get insight on the nature of the active sites for the Beckmann rearrangement reaction in borosilicate zeolites. The interaction of a B site in zeolite Beta with a series of probe molecules (ammonia, pyridine, acetone and water) has been modelled and the (15)N and (11)B NMR isotropic chemical shift of the resulting complexes calculated and compared with experimental in situ NMR results. This approach has allowed validation of the methodology to model the adsorption on a zeolite boron site of molecules of varying basicity which are either protonated or non-protonated. The limitation is that theoretical calculations overestimate the effect of molecular adsorption through hydrogen bonds on the calculated isotropic (11)B NMR chemical shift.Theoretical and experimental results on the adsorption of acetophenone and cyclohexanone oximes on zeolite B-Beta indicate that Brønsted acid sites protonate the oximes, changing the boron coordination from trigonal to tetrahedral. Comparison of theoretical and experimental (15)N NMR chemical shifts of the adsorbed amides (acetanilide and epsilon-caprolactam) indicates that they are non-protonated, and the (11)B NMR spectra show that, as expected, boron remains in trigonal coordination with an isotropic delta(11)B(exp) which differs from the calculated value delta(11)B(calc).
The Beckmann rearrangement of acetophenone oxime using zeolite H-beta and silicalite-N as catalys... more The Beckmann rearrangement of acetophenone oxime using zeolite H-beta and silicalite-N as catalysts has been investigated by means of (15)N and (13)C solid state NMR spectroscopy in combination with theoretical calculations. The results obtained show that the oxime is N-protonated at room temperature on the acid sites of zeolite H-beta. At reaction temperatures of 423 K or above, the two isomeric amides, acetanilide and N-methyl benzamide (NMB) are formed, and interact with the Brønsted acid sites of zeolite H-beta through hydrogen bonds. The presence of residual water hydrolyzes the two amides, while larger amounts inhibit the formation of NMB and cause the total hydrolysis of the acetanilide. Over siliceous zeolite silicalite-N, containing silanol nests as active sites, the oxime is adsorbed through hydrogen bonds and only acetanilide is formed at reaction temperatures of 423 K or above. In the presence of water, the reaction starts at 473 K, still being very selective up to 573 K, and the amide is partially hydrolyzed only above this temperature .
ABSTRACT Copper and cerium bi-component modifications of KIT-6 were prepared by wetness impregnat... more ABSTRACT Copper and cerium bi-component modifications of KIT-6 were prepared by wetness impregnation technique from the corresponding nitrate precursors. Nitrogen physisorption, XRD, FTIR of adsorbed CO, UV-Vis, XPS and TPR were used for their characterization. The catalytic activity of the obtained materials was tested in ethyl acetate oxidation and compared to those achieved over SBA-15-supported catalysts. It was established that the interaction between copper and ceria species results in the formation of finely dispersed CuO nanoparticles on the ceria ones, which are stabilized by an interface layer of penetrated into the ceria lattice copper ions in different oxidative state. This process seems to be facilitated in the more opened 3D-structure of KIT-6, which provides better catalytic activity even at high Cu/Ce ratio than those observed for the SBA-15 modifications.
Collection of Czechoslovak Chemical Communications, 1998
Page 1. OXIDATIVE DEHYDROGENATION OF ETHANE ON VANADIUM-CONTAINING ALUMINOPHOSPHATES WITH AFI STR... more Page 1. OXIDATIVE DEHYDROGENATION OF ETHANE ON VANADIUM-CONTAINING ALUMINOPHOSPHATES WITH AFI STRUCTURE Teresa BLASCO a1, Patricia CONCEPCION a, Jose M. LOPEZ NIETO a2,* and Arturo ...
ABSTRACT Finding the culprits: In situ NMR spectroscopy combined with theoretical calculations sh... more ABSTRACT Finding the culprits: In situ NMR spectroscopy combined with theoretical calculations show the formation of acetyl species covalently bound to framework oxygen atoms in acid zeolites. These species, and not the usually assumed acylium cations, are the reactive intermediates in Friedel-Crafts acylation and Koch carbonylation reactions on zeolites.
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