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Anabela A. Valente - One of the best experts on this subject based on the ideXlab platform.

  • olefin oligomerisation over nanocrystalline mfi based micro mesoporous Zeotypes synthesised via bottom up approaches
    Renewable Energy, 2019
    Co-Authors: Andreia F. Silva, Auguste Fernandes, Margarida M. Antunes, Maria Filipa Ribeiro, Carlos M. Silva, Anabela A. Valente
    Abstract:

    Abstract The oligomerisation of 1-butene was studied under high-pressure continuous-flow conditions (200–250 °C, 30–40 bar), in the presence of micro/mesoporous Zeotypes based on the MFI topology, which were prepared via different non-destructive bottom-up strategies: crystallization of silanized protozeolitic units; co-templating with a dual function (polymeric) template; and using a sole structure directing agent (non-surfactant and non-polymeric) to generate mesoporosity. The synthesis method influenced the material properties and consequently the catalytic performance. In targeting hydrocarbons with boiling point ranges characteristics of diesel, the Zeotypes benefited from regular morphology, reduced crystallite size, mesoporosity and enhanced molar ratio of Lewis (L) to Bronsted (B) acid sites (L/B). In general, the Zeotypes outperformed commercial zeolite ZSM-5. The best-performing zeotype was prepared according to the Serrano strategy based on the crystallization of silanized zeolitic seeds, and led to 97% conversion and an average space-time yield of liquid products of 1077 mg gcat−1 h−1, at 250 °C, 40 bar. The Zeotypes seemed more stable than the commercial zeolite, based on molecular level characterization studies of the used/regenerated catalysts, with some differences in catalytic activity.

  • Olefin oligomerisation over nanocrystalline MFI-based micro/mesoporous Zeotypes synthesised via bottom-up approaches
    Renewable Energy, 2019
    Co-Authors: Andreia F. Silva, Auguste Fernandes, Margarida M. Antunes, Maria Filipa Ribeiro, Carlos M. Silva, Anabela A. Valente
    Abstract:

    Abstract The oligomerisation of 1-butene was studied under high-pressure continuous-flow conditions (200–250 °C, 30–40 bar), in the presence of micro/mesoporous Zeotypes based on the MFI topology, which were prepared via different non-destructive bottom-up strategies: crystallization of silanized protozeolitic units; co-templating with a dual function (polymeric) template; and using a sole structure directing agent (non-surfactant and non-polymeric) to generate mesoporosity. The synthesis method influenced the material properties and consequently the catalytic performance. In targeting hydrocarbons with boiling point ranges characteristics of diesel, the Zeotypes benefited from regular morphology, reduced crystallite size, mesoporosity and enhanced molar ratio of Lewis (L) to Bronsted (B) acid sites (L/B). In general, the Zeotypes outperformed commercial zeolite ZSM-5. The best-performing zeotype was prepared according to the Serrano strategy based on the crystallization of silanized zeolitic seeds, and led to 97% conversion and an average space-time yield of liquid products of 1077 mg gcat−1 h−1, at 250 °C, 40 bar. The Zeotypes seemed more stable than the commercial zeolite, based on molecular level characterization studies of the used/regenerated catalysts, with some differences in catalytic activity.

Magnus Skoglundh - One of the best experts on this subject based on the ideXlab platform.

  • Methoxy ad-species in MFI Zeotypes during methane exposure and methanol desorption followed by in situ IR spectroscopy
    Catalysis Today, 2020
    Co-Authors: Simone Creci, Xueting Wang, Per-anders Carlsson, Anna Martinelli, Magnus Skoglundh
    Abstract:

    Abstract The formation and evolution of methoxy ad-species in MFI Zeotypes after CH4 exposure, and during temperature programmed desorption of CH3OH have been investigated in situ with diffuse reflectance Fourier transform infrared spectroscopy. Fe and/or Al atoms have been incorporated in framework position prior to crystallization and the influence of the resulting acidity on CH4 activation and CH3OH desorption has been examined. The results show that the presence of Fe promotes CH4 activation and that methanol is more strongly bound to the zeotype in the presence of Al. Because CH4 activation and CH3OH extraction are two of the key steps in the direct conversion of methane to methanol, our results indicate that Al-free Zeotypes containing Fe atoms pinpoint important catalyst design parameters needed for this reaction.

  • tuned acidity for catalytic reactions synthesis and characterization of fe and al mfi Zeotypes
    Topics in Catalysis, 2019
    Co-Authors: Simone Creci, Xueting Wang, Per-anders Carlsson, Magnus Skoglundh
    Abstract:

    The addition of elements other than Al in the framework structures of zeotype materials gives the opportunity to tune the acidity of the zeotype and thus might expand the possibilities in the field of acid-catalyzed reactions. Here, we have synthesized silicalite (MFI) with and without Fe and/or Al in the framework structure. To understand the mechanism of the removal of the structure directing agent (SDA) from the as synthesized samples we combine X-ray diffraction, nitrogen sorption and in situ IR spectroscopy experiments. IR spectroscopy is also used to examine the acid species with and without NH3 as probe molecule. Furthermore, NO adsorption is performed to characterize the different metal species. The results of the IR experiments during calcination of the SDA suggest that the SDA first loses contact with the internal surface of the zeotype and then at higher temperature is oxidized to CO2. The IR spectra of the zeotype samples in the H+-form show that the sample containing both Fe and Al shows a broader and less intense peak at 3620 cm−1 indicating the presence of two distinct Bronsted acid sites, one associated to Fe and one to Al. The IR experiments after NH3 adsorption confirm these results and thus the following series of increasing acidity could be outlined: 0 = pure silicalite < Fe-silicalite < Fe/Al-silicalite < Al-silicalite. Finally, the IR experiments after NO adsorption shows the presence of nitrates in the Fe-containing samples suggesting the formation of extra framework Fe species.

  • Tuned Acidity for Catalytic Reactions: Synthesis and Characterization of Fe- and Al-MFI Zeotypes
    Topics in Catalysis, 2019
    Co-Authors: Simone Creci, Xueting Wang, Per-anders Carlsson, Magnus Skoglundh
    Abstract:

    The addition of elements other than Al in the framework structures of zeotype materials gives the opportunity to tune the acidity of the zeotype and thus might expand the possibilities in the field of acid-catalyzed reactions. Here, we have synthesized silicalite (MFI) with and without Fe and/or Al in the framework structure. To understand the mechanism of the removal of the structure directing agent (SDA) from the as synthesized samples we combine X-ray diffraction, nitrogen sorption and in situ IR spectroscopy experiments. IR spectroscopy is also used to examine the acid species with and without NH3 as probe molecule. Furthermore, NO adsorption is performed to characterize the different metal species. The results of the IR experiments during calcination of the SDA suggest that the SDA first loses contact with the internal surface of the zeotype and then at higher temperature is oxidized to CO2. The IR spectra of the zeotype samples in the H+-form show that the sample containing both Fe and Al shows a broader and less intense peak at 3620 cm−1 indicating the presence of two distinct Bronsted acid sites, one associated to Fe and one to Al. The IR experiments after NH3 adsorption confirm these results and thus the following series of increasing acidity could be outlined: 0 = pure silicalite 

Andreia F. Silva - One of the best experts on this subject based on the ideXlab platform.

  • olefin oligomerisation over nanocrystalline mfi based micro mesoporous Zeotypes synthesised via bottom up approaches
    Renewable Energy, 2019
    Co-Authors: Andreia F. Silva, Auguste Fernandes, Margarida M. Antunes, Maria Filipa Ribeiro, Carlos M. Silva, Anabela A. Valente
    Abstract:

    Abstract The oligomerisation of 1-butene was studied under high-pressure continuous-flow conditions (200–250 °C, 30–40 bar), in the presence of micro/mesoporous Zeotypes based on the MFI topology, which were prepared via different non-destructive bottom-up strategies: crystallization of silanized protozeolitic units; co-templating with a dual function (polymeric) template; and using a sole structure directing agent (non-surfactant and non-polymeric) to generate mesoporosity. The synthesis method influenced the material properties and consequently the catalytic performance. In targeting hydrocarbons with boiling point ranges characteristics of diesel, the Zeotypes benefited from regular morphology, reduced crystallite size, mesoporosity and enhanced molar ratio of Lewis (L) to Bronsted (B) acid sites (L/B). In general, the Zeotypes outperformed commercial zeolite ZSM-5. The best-performing zeotype was prepared according to the Serrano strategy based on the crystallization of silanized zeolitic seeds, and led to 97% conversion and an average space-time yield of liquid products of 1077 mg gcat−1 h−1, at 250 °C, 40 bar. The Zeotypes seemed more stable than the commercial zeolite, based on molecular level characterization studies of the used/regenerated catalysts, with some differences in catalytic activity.

  • Olefin oligomerisation over nanocrystalline MFI-based micro/mesoporous Zeotypes synthesised via bottom-up approaches
    Renewable Energy, 2019
    Co-Authors: Andreia F. Silva, Auguste Fernandes, Margarida M. Antunes, Maria Filipa Ribeiro, Carlos M. Silva, Anabela A. Valente
    Abstract:

    Abstract The oligomerisation of 1-butene was studied under high-pressure continuous-flow conditions (200–250 °C, 30–40 bar), in the presence of micro/mesoporous Zeotypes based on the MFI topology, which were prepared via different non-destructive bottom-up strategies: crystallization of silanized protozeolitic units; co-templating with a dual function (polymeric) template; and using a sole structure directing agent (non-surfactant and non-polymeric) to generate mesoporosity. The synthesis method influenced the material properties and consequently the catalytic performance. In targeting hydrocarbons with boiling point ranges characteristics of diesel, the Zeotypes benefited from regular morphology, reduced crystallite size, mesoporosity and enhanced molar ratio of Lewis (L) to Bronsted (B) acid sites (L/B). In general, the Zeotypes outperformed commercial zeolite ZSM-5. The best-performing zeotype was prepared according to the Serrano strategy based on the crystallization of silanized zeolitic seeds, and led to 97% conversion and an average space-time yield of liquid products of 1077 mg gcat−1 h−1, at 250 °C, 40 bar. The Zeotypes seemed more stable than the commercial zeolite, based on molecular level characterization studies of the used/regenerated catalysts, with some differences in catalytic activity.

Michael Fischer - One of the best experts on this subject based on the ideXlab platform.

  • Computational evaluation of aluminophosphate Zeotypes for CO2/N2 separation.
    Physical chemistry chemical physics : PCCP, 2017
    Co-Authors: Michael Fischer
    Abstract:

    Zeolites and structurally related materials (Zeotypes) have received considerable attention as potential adsorbents for selective carbon dioxide adsorption. Within this group, Zeotypes with aluminophosphate composition (AlPOs) could be an interesting alternative to the more frequently studied aluminosilicate zeolites. So far, however, only a few AlPOs have been characterised experimentally in terms of their CO2 adsorption properties. In this study, force-field based grand-canonical Monte Carlo (GCMC) simulations were used to evaluate the potential of AlPOs for CO2/N2 separation, a binary mixture that constitutes a suitable model system for the removal of carbon dioxide from flue gases. A total of 51 frameworks were considered, all of which have been reported either as pure AlPOs or as heteroatom-containing AlPO derivatives. Prior to the GCMC simulations, all structures were optimised using dispersion-corrected density-functional theory calculations. The potential of these 51 systems for CO2/N2 separation was assessed in preliminary calculations (Henry constants and CO2 uptake at selected pressures). On the basis of these calculations, 21 AlPOs of particular interest were selected, for which 15 : 85 CO2/N2 mixture adsorption isotherms were calculated up to 10 bar. For adsorption-based separations using an adsorption pressure of 1 bar (vacuum-swing adsorption), AlPOs with GIS, ATN, ATT, and SIV topologies were predicted to be most attractive, as they combine high CO2/N2 selectivities (75 to 140) and reasonable CO2 working capacities (1 to 1.7 mmol g−1). Under pressure-swing adsorption conditions, there is a tradeoff between selectivity and working capacity: while highly selective AlPOs like GIS reach only moderate working capacities, the frameworks with the highest working capacities above 2 mmol g−1, AFY, KFI, and SAV, have lower selectivities between 25 and 35. To gain atomic-level insights into the host–guest interactions, interaction energy maps were computed for selected AlPOs. The computational assessment presented here can guide future experimental efforts in the development and optimisation of AlPO-based adsorbents for selective CO2 adsorption.

  • computational evaluation of aluminophosphate Zeotypes for co2 n2 separation
    Physical Chemistry Chemical Physics, 2017
    Co-Authors: Michael Fischer
    Abstract:

    Zeolites and structurally related materials (Zeotypes) have received considerable attention as potential adsorbents for selective carbon dioxide adsorption. Within this group, Zeotypes with aluminophosphate composition (AlPOs) could be an interesting alternative to the more frequently studied aluminosilicate zeolites. So far, however, only a few AlPOs have been characterised experimentally in terms of their CO2 adsorption properties. In this study, force-field based grand-canonical Monte Carlo (GCMC) simulations were used to evaluate the potential of AlPOs for CO2/N2 separation, a binary mixture that constitutes a suitable model system for the removal of carbon dioxide from flue gases. A total of 51 frameworks were considered, all of which have been reported either as pure AlPOs or as heteroatom-containing AlPO derivatives. Prior to the GCMC simulations, all structures were optimised using dispersion-corrected density-functional theory calculations. The potential of these 51 systems for CO2/N2 separation was assessed in preliminary calculations (Henry constants and CO2 uptake at selected pressures). On the basis of these calculations, 21 AlPOs of particular interest were selected, for which 15 : 85 CO2/N2 mixture adsorption isotherms were calculated up to 10 bar. For adsorption-based separations using an adsorption pressure of 1 bar (vacuum-swing adsorption), AlPOs with GIS, ATN, ATT, and SIV topologies were predicted to be most attractive, as they combine high CO2/N2 selectivities (75 to 140) and reasonable CO2 working capacities (1 to 1.7 mmol g−1). Under pressure-swing adsorption conditions, there is a tradeoff between selectivity and working capacity: while highly selective AlPOs like GIS reach only moderate working capacities, the frameworks with the highest working capacities above 2 mmol g−1, AFY, KFI, and SAV, have lower selectivities between 25 and 35. To gain atomic-level insights into the host–guest interactions, interaction energy maps were computed for selected AlPOs. The computational assessment presented here can guide future experimental efforts in the development and optimisation of AlPO-based adsorbents for selective CO2 adsorption.

  • Accurate structures and energetics of neutral-framework Zeotypes from dispersion-corrected DFT calculations.
    The Journal of chemical physics, 2017
    Co-Authors: Michael Fischer, Ross J. Angel
    Abstract:

    Density-functional theory (DFT) calculations incorporating a pairwise dispersion correction were employed to optimize the structures of various neutral-framework compounds with zeolite topologies. The calculations used the PBE functional for solids (PBEsol) in combination with two different dispersion correction schemes, the D2 correction devised by Grimme and the TS correction of Tkatchenko and Scheffler. In the first part of the study, a benchmarking of the DFT-optimized structures against experimental crystal structure data was carried out, considering a total of 14 structures (8 all-silica zeolites, 4 aluminophosphate Zeotypes, and 2 dense phases). Both PBEsol-D2 and PBEsol-TS showed an excellent performance, improving significantly over the best-performing approach identified in a previous study (PBE-TS). The temperature dependence of lattice parameters and bond lengths was assessed for those Zeotypes where the available experimental data permitted such an analysis. In most instances, the agreement between DFT and experiment improved when the experimental data were corrected for the effects of thermal motion and when low-temperature structure data rather than room-temperature structure data were used as a reference. In the second part, a benchmarking against experimental enthalpies of transition (with respect to α-quartz) was carried out for 16 all-silica zeolites. Excellent agreement was obtained with the PBEsol-D2 functional, with the overall error being in the same range as the experimental uncertainty. Altogether, PBEsol-D2 can be recommended as a computationally efficient DFT approach that simultaneously delivers accurate structures and energetics of neutral-framework Zeotypes.

  • Benchmarking DFT-GGA calculations for the structure optimisation of neutral-framework Zeotypes
    Theoretical Chemistry Accounts, 2016
    Co-Authors: Michael Fischer, Felix O. Evers, Filip Formalik, Adam Olejniczak
    Abstract:

    Structure optimisations in the framework of plane-wave density functional theory (DFT) were performed for a set of reference structures of neutral-framework Zeotypes and related compounds. The reference set comprised eight all-silica zeolites, four aluminophosphate Zeotypes, and two dense polymorphs of SiO_2 (α-quartz) and AlPO_4 (α-berlinite). The optimisations considered a total of five GGA-type exchange–correlation functionals (GGA = generalised gradient approximation). Along with the very popular PBE functional, which is well-known to overestimate the lattice dimensions, two GGA functionals designed for solids (WC and PBEsol) and two variants of PBE including a pairwise dispersion correction (PBE-D2 and PBE-TS) were included. A detailed analysis of the agreement between DFT-optimised structures and experimental crystal structure data (obtained for calcined systems) showed that the inclusion of a dispersion correction greatly improves the prediction of the lattice parameters, with PBE-TS performing particularly well. On the other hand, WC and PBEsol give T–O bond lengths (T = tetrahedral sites) that are in better agreement with experimental data. The accurate reproduction of the T–O–T angles was found to be particularly challenging, as functionals without dispersion correction tend to overestimate these angles, whereas dispersion-corrected variants underestimate them. For all-silica zeolites, the present results were compared to those of a previous DFT study using the hybrid B3LYP-D2 functional and to results of molecular mechanics calculations employing two popular force fields, with none of these methods performing better than PBE-TS or PBE-D2. In order to better understand some of the shortcomings of the functionals considered, additional results for two outliers that were removed from the set of reference structures were analysed. Finally, the ability to reproduce the relative stability was assessed for those SiO_2 frameworks for which experimental enthalpies of transition are available. Here, PBE-D2 outperformed PBE-TS, which showed a systematic tendency to overestimate the energy difference (relative to α-quartz). On the basis of the present work, PBE-TS can be recommended as a reasonable default choice for structure optimisations of neutral-framework Zeotypes. While future benchmarking work could address a wider range of functionals and dispersion correction schemes, it needs to be considered that the limited availability of low-temperature crystal structure data limits the accuracy with which the deviations between computation and experiment can be assessed for this group of materials.

Simone Creci - One of the best experts on this subject based on the ideXlab platform.

  • Methoxy ad-species in MFI Zeotypes during methane exposure and methanol desorption followed by in situ IR spectroscopy
    Catalysis Today, 2020
    Co-Authors: Simone Creci, Xueting Wang, Per-anders Carlsson, Anna Martinelli, Magnus Skoglundh
    Abstract:

    Abstract The formation and evolution of methoxy ad-species in MFI Zeotypes after CH4 exposure, and during temperature programmed desorption of CH3OH have been investigated in situ with diffuse reflectance Fourier transform infrared spectroscopy. Fe and/or Al atoms have been incorporated in framework position prior to crystallization and the influence of the resulting acidity on CH4 activation and CH3OH desorption has been examined. The results show that the presence of Fe promotes CH4 activation and that methanol is more strongly bound to the zeotype in the presence of Al. Because CH4 activation and CH3OH extraction are two of the key steps in the direct conversion of methane to methanol, our results indicate that Al-free Zeotypes containing Fe atoms pinpoint important catalyst design parameters needed for this reaction.

  • tuned acidity for catalytic reactions synthesis and characterization of fe and al mfi Zeotypes
    Topics in Catalysis, 2019
    Co-Authors: Simone Creci, Xueting Wang, Per-anders Carlsson, Magnus Skoglundh
    Abstract:

    The addition of elements other than Al in the framework structures of zeotype materials gives the opportunity to tune the acidity of the zeotype and thus might expand the possibilities in the field of acid-catalyzed reactions. Here, we have synthesized silicalite (MFI) with and without Fe and/or Al in the framework structure. To understand the mechanism of the removal of the structure directing agent (SDA) from the as synthesized samples we combine X-ray diffraction, nitrogen sorption and in situ IR spectroscopy experiments. IR spectroscopy is also used to examine the acid species with and without NH3 as probe molecule. Furthermore, NO adsorption is performed to characterize the different metal species. The results of the IR experiments during calcination of the SDA suggest that the SDA first loses contact with the internal surface of the zeotype and then at higher temperature is oxidized to CO2. The IR spectra of the zeotype samples in the H+-form show that the sample containing both Fe and Al shows a broader and less intense peak at 3620 cm−1 indicating the presence of two distinct Bronsted acid sites, one associated to Fe and one to Al. The IR experiments after NH3 adsorption confirm these results and thus the following series of increasing acidity could be outlined: 0 = pure silicalite < Fe-silicalite < Fe/Al-silicalite < Al-silicalite. Finally, the IR experiments after NO adsorption shows the presence of nitrates in the Fe-containing samples suggesting the formation of extra framework Fe species.

  • Tuned Acidity for Catalytic Reactions: Synthesis and Characterization of Fe- and Al-MFI Zeotypes
    Topics in Catalysis, 2019
    Co-Authors: Simone Creci, Xueting Wang, Per-anders Carlsson, Magnus Skoglundh
    Abstract:

    The addition of elements other than Al in the framework structures of zeotype materials gives the opportunity to tune the acidity of the zeotype and thus might expand the possibilities in the field of acid-catalyzed reactions. Here, we have synthesized silicalite (MFI) with and without Fe and/or Al in the framework structure. To understand the mechanism of the removal of the structure directing agent (SDA) from the as synthesized samples we combine X-ray diffraction, nitrogen sorption and in situ IR spectroscopy experiments. IR spectroscopy is also used to examine the acid species with and without NH3 as probe molecule. Furthermore, NO adsorption is performed to characterize the different metal species. The results of the IR experiments during calcination of the SDA suggest that the SDA first loses contact with the internal surface of the zeotype and then at higher temperature is oxidized to CO2. The IR spectra of the zeotype samples in the H+-form show that the sample containing both Fe and Al shows a broader and less intense peak at 3620 cm−1 indicating the presence of two distinct Bronsted acid sites, one associated to Fe and one to Al. The IR experiments after NH3 adsorption confirm these results and thus the following series of increasing acidity could be outlined: 0 = pure silicalite