Marton Kollar | Chemical Research Center of Hungarian Academy of Sciences (original) (raw)
Papers by Marton Kollar
Phase-pure [Al]BEA and [Al,B]BEA zeolites, prepared by solid-state recrystallization of synthetic... more Phase-pure [Al]BEA and [Al,B]BEA zeolites, prepared by solid-state recrystallization of synthetic aluminum-containing magadiites and conventionally synthesized [B]BEA, were tested, after ion exchange with nickel, as bifunctional catalysts for hydroconversion of n-heptane. The reducibility of nickel ions incorporated into BEA zeolites by ion exchange was investigated by temperature-programmed reduction (TPR). The acidity of the samples was characterized with strong (pyridine (Py) and ammonia (NH3)) and weak (nitrogen) bases. The adsorbed bases were studied by transmission FT-IR (Py), diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy (N2), and temperature-programmed ammonia evolution (TPAE, NH3). Over Ni/H-[B]BEA the reactants were completely converted via fast hydrogenolysis, whereas this reaction pathway plays only a negligible role in the hydroconversion over Ni/H-[Al]BEA and Ni/H-[Al,B]BEA zeolites. Boron-containing BEA zeolites were less active catalysts than the boron-free catalyst in the principal unimolecular hydroconversion reactions. However, incorporation of boron into the framework of BEA zeolite results in a considerable selectivity shift toward isomerization. Results suggest that the acid strength of bridged hydroxyls, probed with weak (N2) and strong basis (pyridine), was found to be similar in the boron-free and boron-containing BEA samples. The decrease in the isomerization rate and the increase of the apparent activation energy upon incorporation of boron may be attributed to the decrease in the heat of n-heptane adsorption.► [Al]-, [B]- and [Al,B]BEA zeolites were prepared by recrystallization of magadiite. ► Ni/H-[Al,B]BEA showed high activity (60%) and selectivity (92%) in C7 conversion. ► Incorporation of B into BEA results in a selectivity shift toward isomerization. ► n-Heptane hydroconversion rate decreased over boron-containing Ni/H-BEA catalysts. ► Acid sites of BEA can be tuned by insertion of boron and by ion exchange with Na.
Microporous and Mesoporous Materials, Jan 1, 2008
Aluminum-free MCM-22 type ferrisilicate, [Fe]MCM-22 (Si/Fe = 19.2) and, for comparison, MCM-22 al... more Aluminum-free MCM-22 type ferrisilicate, [Fe]MCM-22 (Si/Fe = 19.2) and, for comparison, MCM-22 aluminosilicate, [Al]MCM-22 (Si/Al = 13.1), were synthesized. The materials and their precursors were characterized by X-ray diffractometry (XRD), thermogravimetry (TG), transmission and diffuse reflectance Fourier-transform infrared spectroscopy (FT-IR and DRIFTS), temperature-programmed ammonia evolution (TPAE), in situ Mössbauer spectroscopy and temperature-programmed reduction with hydrogen (H2-TPR). The presence of Fe3+ T atoms (FeFW) were indicated by the appearance of a νOH IR-band at 3634 cm−1. The red shift of the νOH band, induced by the H-bonding of bridged hydroxyls and N2, was smaller for the [Fe]MCM-22 (64 cm−1) than for the [Al]MCM-22 (86 cm−1). The smaller shift evidences sites of weaker intrinsic acid strength. The rate and temperature of the TG-release of hexamethyleneimine template showed relation with the acidity of the sample. The amount of Fe3+ species, present in highly distorted tetrahedral coordination state, was in good correspondence with the concentration of the Brønsted acid sites. After reduction with H2 or CO, Fe2+ appeared in a novel coordination state. Results suggest that these Fe2+ species are bound to the framework via oxygen atoms. Reducibility of the framework iron is related to the high concentration of hydroxyl nests generated in both the wide (12-MR) and the narrow (10-MR) channels of [Fe]MCM-22 during the synthesis and/or template removal.
Studies in Surface Science and Catalysis, Jan 1, 2010
MCM-22/MCM-41 composite, having hierarchical micro/mesoporous pore structure, was prepared using ... more MCM-22/MCM-41 composite, having hierarchical micro/mesoporous pore structure, was prepared using two-step synthesis method. Accordingly, mesoporous MCM-41 silica was synthesized in the presence of a delaminated MCM-22 zeolite precursor (dl-MCM-22). The structure, texture, and the acidity of the composite were compared to the corresponding properties of the MCM-22 zeolite. The hydroconversion of n-heptane was studied over the Ni,H-forms of these preparations at 240 °C and 5 bar total pressure. At equal space times, regardless of the Ni-loading (Ni/H+ = ~0.25 or 0.5), the rate of cracking was significantly lower over the composite than over the zeolite catalysts. The lower cracking activity was attributed to the faster transport of the reactants and products within the composite particles. At similar conversions similar selectivities were obtained over the compared catalysts.
Applied Catalysis A-general, Jan 1, 2011
Small (S)- and large (L)-crystalline zeolite MCM-22 precursors with the same Si/AlF ratio of 17, ... more Small (S)- and large (L)-crystalline zeolite MCM-22 precursors with the same Si/AlF ratio of 17, were synthesized and either converted to zeolites MCM-22(S/L) or delaminated. From the delaminated zeolite MCM-22 precursors delaminated zeolites MCM-22 (dl-MCM-22(S/L)) were prepared. Delaminated zeolite precursors were admixed to the synthesis mixture of mesoporous silica MCM-41 to obtain the respective dl-MCM-22/MCM-41(S/L) composite materials. The preparations were characterized by XRD, N2 adsorption measurements, scanning electron microscopy. FT-IR spectroscopic studies of pyridine (Py) and 2,4-dimethylquinoline (2,4-DMQ) adsorption were used for determination of total (Brønsted and Lewis acidity) and external Brønsted acidity, respectively. It was found that the crystallite size of the MCM-22 precursors strongly influenced the structural, acidic and catalytic properties of the delaminated and composite materials. The effectiveness of the delamination procedure for the zeolite MCM-22(S) precursor having smaller and thinner particles is higher. At same synthesis gel compositions, the amount of mesoporous fraction in the composite materials was different. In dl-MCM-22/MCM-41(S) composite the formation of the mesoporous component was suppressed. Moreover, delamination resulted, for both delaminated and composite materials, in a similar decrease in the Brønsted acidity.The reduction in toluene disproportionation activity confirmed the above structural and acidity changes. 2,4-DMQ adsorption results proved that both the dl-MCM-22 samples and the composites possess higher amount of external Brønsted acid sites than zeolite MCM-22. The enhanced external acidity and accessibility of the active sites of these preparations appeared favorable when more basic and bulkier reactant, such as 1,2,4-trimethylbenzene was transformed..▶ The crystallite size of zeolite MCM-22 precursor is crucial for the effectiveness of its delamination and insertion in a composite with MCM-41. ▶ The lamellae structuring defines the acidity and catalytic performance of the delaminated and composite materials. ▶ Delamination and preparation of composites consisting of zeolite MCM-22 and MCM-41 silicate are beneficial for catalytic transformations of more basic and bulkier alkylaromatic reactants.
![Research paper thumbnail of Comparative catalytic studies on alkylaromatics transformations over [Al]MCM-22 and boron-substituted [Al, B]MCM-22](https://attachments.academia-assets.com/20992771/thumbnails/1.jpg)
](… and Mesoporous Materials, Jan 1, 2009
The catalytic performance of [Al]MCM-22 and boron-containing [Al, B]MCM-22 was compared in the co... more The catalytic performance of [Al]MCM-22 and boron-containing [Al, B]MCM-22 was compared in the conversion of four alkyl aromatic hydrocarbons in view of the impact of their cage/channel pore structure. The contribution of the pore geometry to the observed molecular-sieve effects is discussed on the basis of the XRD, thermal analysis (TGA) of template and coke removal, N 2 adsorption, 11 B-MAS NMR and the catalytic test reactions. It was found that the reaction products distribution is thermodynamically or selectively controlled, depending on the type of the pores to which the different feed molecules and reaction intermediates have an access, and on the presence or absence of boron in the framework. The geometric constraints caused by the introduction of framework boron and the framework Al-and B-atoms positioning regulate the product selectivity in these transformations.
Reaction Kinetics and Catalysis Letters, Jan 1, 2007
Microporous and Mesoporous Materials, Jan 1, 2007
Micro/mesoporous aluminosilicate composites were prepared applying a two-step hydrothermal synthe... more Micro/mesoporous aluminosilicate composites were prepared applying a two-step hydrothermal synthesis procedure. In the first step a zeolitic component, i.e., the precursor of zeolite MCM-22 was synthesized and its swollen and partially delaminated derivatives were prepared. In the second step mesoporous MCM-41 silicate was synthesized in a slurry of the above MCM-22 type precursor from additional silicate source and using hexadecyltrimethylammonium bromide (CTMABr) template. The structure, morphology and the acidic properties of the obtained composite materials were characterized by X-ray diffraction, infrared spectroscopy, N2 adsorption isotherms, and electron microscopy (SEM and TEM). The results suggest that the composite materials were built from nanosize, randomly orientated stacks of thin layers of MCM-22 type zeolite and of mesoporous silicate MCM-41 material. The catalytic activity of the composite material was compared to that of the zeolite MCM-22 in the hydroconversion of heptane.
Journal of Molecular …, Jan 1, 2010
Fischer-Tropsch mechanism 15%Co,0.5%Pt/␥-alumina Co 2+ -alumina-pillared clays Operando DRIFTS a ... more Fischer-Tropsch mechanism 15%Co,0.5%Pt/␥-alumina Co 2+ -alumina-pillared clays Operando DRIFTS a b s t r a c t Natural gas and coal are converted to fuels by the Fischer-Tropsch reaction, i.e., by reacting CO with H 2 , the currently accepted mechanism involving surface carbide formation. We have monitored the adsorbed species and their evolution during Fischer-Tropsch reaction on the commercial catalyst Pt,Co/␥-Al 2 O 3 (as a standard), on Co/alumina-pillared montmorillonite (Co,Al-EFW) and its beidellite analogue (both are tri-octahedral smectite clays, but beidellite possesses tetrahedrally coordinated Al in the sheets) via optical diffuse reflectance (DRS 1 ) and variable temperature in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS 2 ). We show that in this case over Pt/Co-␥-Al 2 O 3 , under model conditions, H 2 reacts with CO forming H-C O bridges over [Co-O 2 -Co] units; this transition state moiety also involves adjacent matrix Al-O-CO units. Subsequent stages provide differing oxygenate species via concerted acid-base reactions. The early stages of the Fischer-Tropsch synthesis thus do not involve surface carbide species and surface oxygenates are generated via concerted reaction of support surface Al-OH with the above HCO-bridging binuclear Co 2+ unit. (J. Valyon). 1 Optical diffuse reflectance spectroscopy. 2 Diffuse reflectance infrared Fourier transformation spectroscopy.
Phase-pure [Al]BEA and [Al,B]BEA zeolites, prepared by solid-state recrystallization of synthetic... more Phase-pure [Al]BEA and [Al,B]BEA zeolites, prepared by solid-state recrystallization of synthetic aluminum-containing magadiites and conventionally synthesized [B]BEA, were tested, after ion exchange with nickel, as bifunctional catalysts for hydroconversion of n-heptane. The reducibility of nickel ions incorporated into BEA zeolites by ion exchange was investigated by temperature-programmed reduction (TPR). The acidity of the samples was characterized with strong (pyridine (Py) and ammonia (NH3)) and weak (nitrogen) bases. The adsorbed bases were studied by transmission FT-IR (Py), diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy (N2), and temperature-programmed ammonia evolution (TPAE, NH3). Over Ni/H-[B]BEA the reactants were completely converted via fast hydrogenolysis, whereas this reaction pathway plays only a negligible role in the hydroconversion over Ni/H-[Al]BEA and Ni/H-[Al,B]BEA zeolites. Boron-containing BEA zeolites were less active catalysts than the boron-free catalyst in the principal unimolecular hydroconversion reactions. However, incorporation of boron into the framework of BEA zeolite results in a considerable selectivity shift toward isomerization. Results suggest that the acid strength of bridged hydroxyls, probed with weak (N2) and strong basis (pyridine), was found to be similar in the boron-free and boron-containing BEA samples. The decrease in the isomerization rate and the increase of the apparent activation energy upon incorporation of boron may be attributed to the decrease in the heat of n-heptane adsorption.► [Al]-, [B]- and [Al,B]BEA zeolites were prepared by recrystallization of magadiite. ► Ni/H-[Al,B]BEA showed high activity (60%) and selectivity (92%) in C7 conversion. ► Incorporation of B into BEA results in a selectivity shift toward isomerization. ► n-Heptane hydroconversion rate decreased over boron-containing Ni/H-BEA catalysts. ► Acid sites of BEA can be tuned by insertion of boron and by ion exchange with Na.
Microporous and Mesoporous Materials, Jan 1, 2008
Aluminum-free MCM-22 type ferrisilicate, [Fe]MCM-22 (Si/Fe = 19.2) and, for comparison, MCM-22 al... more Aluminum-free MCM-22 type ferrisilicate, [Fe]MCM-22 (Si/Fe = 19.2) and, for comparison, MCM-22 aluminosilicate, [Al]MCM-22 (Si/Al = 13.1), were synthesized. The materials and their precursors were characterized by X-ray diffractometry (XRD), thermogravimetry (TG), transmission and diffuse reflectance Fourier-transform infrared spectroscopy (FT-IR and DRIFTS), temperature-programmed ammonia evolution (TPAE), in situ Mössbauer spectroscopy and temperature-programmed reduction with hydrogen (H2-TPR). The presence of Fe3+ T atoms (FeFW) were indicated by the appearance of a νOH IR-band at 3634 cm−1. The red shift of the νOH band, induced by the H-bonding of bridged hydroxyls and N2, was smaller for the [Fe]MCM-22 (64 cm−1) than for the [Al]MCM-22 (86 cm−1). The smaller shift evidences sites of weaker intrinsic acid strength. The rate and temperature of the TG-release of hexamethyleneimine template showed relation with the acidity of the sample. The amount of Fe3+ species, present in highly distorted tetrahedral coordination state, was in good correspondence with the concentration of the Brønsted acid sites. After reduction with H2 or CO, Fe2+ appeared in a novel coordination state. Results suggest that these Fe2+ species are bound to the framework via oxygen atoms. Reducibility of the framework iron is related to the high concentration of hydroxyl nests generated in both the wide (12-MR) and the narrow (10-MR) channels of [Fe]MCM-22 during the synthesis and/or template removal.
Studies in Surface Science and Catalysis, Jan 1, 2010
MCM-22/MCM-41 composite, having hierarchical micro/mesoporous pore structure, was prepared using ... more MCM-22/MCM-41 composite, having hierarchical micro/mesoporous pore structure, was prepared using two-step synthesis method. Accordingly, mesoporous MCM-41 silica was synthesized in the presence of a delaminated MCM-22 zeolite precursor (dl-MCM-22). The structure, texture, and the acidity of the composite were compared to the corresponding properties of the MCM-22 zeolite. The hydroconversion of n-heptane was studied over the Ni,H-forms of these preparations at 240 °C and 5 bar total pressure. At equal space times, regardless of the Ni-loading (Ni/H+ = ~0.25 or 0.5), the rate of cracking was significantly lower over the composite than over the zeolite catalysts. The lower cracking activity was attributed to the faster transport of the reactants and products within the composite particles. At similar conversions similar selectivities were obtained over the compared catalysts.
Applied Catalysis A-general, Jan 1, 2011
Small (S)- and large (L)-crystalline zeolite MCM-22 precursors with the same Si/AlF ratio of 17, ... more Small (S)- and large (L)-crystalline zeolite MCM-22 precursors with the same Si/AlF ratio of 17, were synthesized and either converted to zeolites MCM-22(S/L) or delaminated. From the delaminated zeolite MCM-22 precursors delaminated zeolites MCM-22 (dl-MCM-22(S/L)) were prepared. Delaminated zeolite precursors were admixed to the synthesis mixture of mesoporous silica MCM-41 to obtain the respective dl-MCM-22/MCM-41(S/L) composite materials. The preparations were characterized by XRD, N2 adsorption measurements, scanning electron microscopy. FT-IR spectroscopic studies of pyridine (Py) and 2,4-dimethylquinoline (2,4-DMQ) adsorption were used for determination of total (Brønsted and Lewis acidity) and external Brønsted acidity, respectively. It was found that the crystallite size of the MCM-22 precursors strongly influenced the structural, acidic and catalytic properties of the delaminated and composite materials. The effectiveness of the delamination procedure for the zeolite MCM-22(S) precursor having smaller and thinner particles is higher. At same synthesis gel compositions, the amount of mesoporous fraction in the composite materials was different. In dl-MCM-22/MCM-41(S) composite the formation of the mesoporous component was suppressed. Moreover, delamination resulted, for both delaminated and composite materials, in a similar decrease in the Brønsted acidity.The reduction in toluene disproportionation activity confirmed the above structural and acidity changes. 2,4-DMQ adsorption results proved that both the dl-MCM-22 samples and the composites possess higher amount of external Brønsted acid sites than zeolite MCM-22. The enhanced external acidity and accessibility of the active sites of these preparations appeared favorable when more basic and bulkier reactant, such as 1,2,4-trimethylbenzene was transformed..▶ The crystallite size of zeolite MCM-22 precursor is crucial for the effectiveness of its delamination and insertion in a composite with MCM-41. ▶ The lamellae structuring defines the acidity and catalytic performance of the delaminated and composite materials. ▶ Delamination and preparation of composites consisting of zeolite MCM-22 and MCM-41 silicate are beneficial for catalytic transformations of more basic and bulkier alkylaromatic reactants.
… and Mesoporous Materials, Jan 1, 2009
The catalytic performance of [Al]MCM-22 and boron-containing [Al, B]MCM-22 was compared in the co... more The catalytic performance of [Al]MCM-22 and boron-containing [Al, B]MCM-22 was compared in the conversion of four alkyl aromatic hydrocarbons in view of the impact of their cage/channel pore structure. The contribution of the pore geometry to the observed molecular-sieve effects is discussed on the basis of the XRD, thermal analysis (TGA) of template and coke removal, N 2 adsorption, 11 B-MAS NMR and the catalytic test reactions. It was found that the reaction products distribution is thermodynamically or selectively controlled, depending on the type of the pores to which the different feed molecules and reaction intermediates have an access, and on the presence or absence of boron in the framework. The geometric constraints caused by the introduction of framework boron and the framework Al-and B-atoms positioning regulate the product selectivity in these transformations.
Reaction Kinetics and Catalysis Letters, Jan 1, 2007
Microporous and Mesoporous Materials, Jan 1, 2007
Micro/mesoporous aluminosilicate composites were prepared applying a two-step hydrothermal synthe... more Micro/mesoporous aluminosilicate composites were prepared applying a two-step hydrothermal synthesis procedure. In the first step a zeolitic component, i.e., the precursor of zeolite MCM-22 was synthesized and its swollen and partially delaminated derivatives were prepared. In the second step mesoporous MCM-41 silicate was synthesized in a slurry of the above MCM-22 type precursor from additional silicate source and using hexadecyltrimethylammonium bromide (CTMABr) template. The structure, morphology and the acidic properties of the obtained composite materials were characterized by X-ray diffraction, infrared spectroscopy, N2 adsorption isotherms, and electron microscopy (SEM and TEM). The results suggest that the composite materials were built from nanosize, randomly orientated stacks of thin layers of MCM-22 type zeolite and of mesoporous silicate MCM-41 material. The catalytic activity of the composite material was compared to that of the zeolite MCM-22 in the hydroconversion of heptane.
Journal of Molecular …, Jan 1, 2010
Fischer-Tropsch mechanism 15%Co,0.5%Pt/␥-alumina Co 2+ -alumina-pillared clays Operando DRIFTS a ... more Fischer-Tropsch mechanism 15%Co,0.5%Pt/␥-alumina Co 2+ -alumina-pillared clays Operando DRIFTS a b s t r a c t Natural gas and coal are converted to fuels by the Fischer-Tropsch reaction, i.e., by reacting CO with H 2 , the currently accepted mechanism involving surface carbide formation. We have monitored the adsorbed species and their evolution during Fischer-Tropsch reaction on the commercial catalyst Pt,Co/␥-Al 2 O 3 (as a standard), on Co/alumina-pillared montmorillonite (Co,Al-EFW) and its beidellite analogue (both are tri-octahedral smectite clays, but beidellite possesses tetrahedrally coordinated Al in the sheets) via optical diffuse reflectance (DRS 1 ) and variable temperature in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS 2 ). We show that in this case over Pt/Co-␥-Al 2 O 3 , under model conditions, H 2 reacts with CO forming H-C O bridges over [Co-O 2 -Co] units; this transition state moiety also involves adjacent matrix Al-O-CO units. Subsequent stages provide differing oxygenate species via concerted acid-base reactions. The early stages of the Fischer-Tropsch synthesis thus do not involve surface carbide species and surface oxygenates are generated via concerted reaction of support surface Al-OH with the above HCO-bridging binuclear Co 2+ unit. (J. Valyon). 1 Optical diffuse reflectance spectroscopy. 2 Diffuse reflectance infrared Fourier transformation spectroscopy.