P. Sazama - Academia.edu (original) (raw)

Papers by P. Sazama

Topics in Catalysis, 2018

Reduction of NO by NH 3 over metal-promoted zeolites represents the principal reaction in the sel... more Reduction of NO by NH 3 over metal-promoted zeolites represents the principal reaction in the selective catalytic reduction (SCR) technology for NOx removal from Diesel engine exhausts. It has been established that addition of ammonium nitrate (AN) to the reaction mixture substantially enhances the rate of this reaction, decreasing the temperature necessary for an efficient deNOx process. Nevertheless, the nature of this effect has not been completely elucidated. To investigate the NO + AN reaction mechanism, we have used individual reactants labeled with either 15 N or 18 O (or both isotopes), thus obtaining an experimental background for proposing the route of the SCR accelerated by AN addition. For this study, we have used as the catalysts H-BEA and Fe/H-BEA zeolites with various Si/Al ratios and various amounts and states of the iron species. Keywords Ammonium nitrate decomposition • NH 3-SCR mechanism • Fe-zeolites • 15 N and 18 O isotopic labeling Electronic supplementary material The online version of this article (

The Journal of Physical Chemistry C, 2011

We present a multistep method combining multispectroscopic experiments with DFT calculations to d... more We present a multistep method combining multispectroscopic experiments with DFT calculations to determine the complete Al distribution in silicon-rich zeolites, independent of the presence of AlÀOÀ(SiÀO) n ÀAl (n = 1, 2) sequences in their frameworks. 29 Si MAS NMR spectroscopy is employed to confirm the absence of AlÀOÀSiÀOÀAl in the framework of silicon-rich zeolites while 27 Al 3Q MAS NMR spectroscopy and DFT computations of 27 Al isotropic chemical shifts serve to determine the locations of isolated Al atoms. The maximum ion-exchange capacity of zeolites for [Co 2þ (H 2 O) 6 ] 2þ reveals the presence of close Al atoms (i.e., those Al atoms which are able to balance [Co 2þ (H 2 O) 6 ] 2þ ions). Then visible spectroscopy of the bare Co(II) ion in the dehydrated zeolite of the samples with close Al is utilized to identify the locations of the corresponding AlÀOÀ(SiÀO) 2 ÀAl pairs in a ring. Subsequently, their 27 Al isotropic chemical shifts are evaluated at DFT and the complete Al distribution is determined. The complete Al siting in three ferrierite samples with only isolated framework Al atoms and two ferrierites with AlÀOÀ(SiÀO) 2 ÀAl sequences was determined. Our results reveal that the Al siting in the former samples varies with the conditions of the zeolite synthesis; Al is present in three or four sites (T1b, T2, T3, and T4) depending on the sample while T1a is never occupied by Al and the concentrations of Al atoms in various T sites are very diverse. For ferrierites with both isolated and close Al atoms, isolated Al atoms occupy the T2, T3, and T4 sites and the close Al atoms are arranged in Al(T1a)ÀOÀ(SiÀO) 2 ÀAl(T1a) and Al(T2)ÀOÀ(SiÀO) 2 ÀAl(T2) sequences forming the R and β À 2 cationic sites, respectively. Isolated Al atoms do not occupy the T1b site and close Al atoms do not form Al(T4)ÀOÀ(SiÀO) 2 À Al(T4) sequences of the β À 1 site. The differences between the concentrations of Al in T sites are not as pronounced as those for the ferrierite samples with only isolated framework Al atoms. In addition, our results reveal that the Al siting in ferrierite is not random and depends on the conditions of the zeolite synthesis.

The Journal of Physical Chemistry C, 2013

Periodic DFT molecular dynamics and FTIR spectroscopy were used to investigate the cationic sites... more Periodic DFT molecular dynamics and FTIR spectroscopy were used to investigate the cationic sites of ferrierite exchanged with Co(II) and Cu(II) and their complexes with NO. Particular attention was paid to the effect of the Al siting in sixmembered rings forming the cationic sites on the structure of these sites and the corresponding binding energies of Me(II) (Me = Co and Cu). Our calculations show that both the cations upon binding to cationic sites induce a rearrangement of the local structure of the zeolite framework. The rearrangement is significant for the α and β-2 sites while it is minor for the β-1 site. Comparison of the observed and theoretical NO stretching frequencies of ferrierite Co(II) and Cu(II) complexes with a NO molecule permitted the assignment of IR bands to the individual types of cationic sites. For NO-Coferrierite, the IR bands found at 1956, 1941, and 1935 cm −1 can be assigned to NO-Co complexes with Co(II) located in the α, β-1, and β-2 sites, respectively. Similarly for NO-Cu-ferrierite, the frequencies of 1864, 1912, 1904, and 1892 cm −1 belong to NO-Cu complexes having Cu(II) accommodated in the α, β-1, β-2 (conformer 1), and β-2 (conformer 2) sites, respectively. The calculated adsorption energies are systematically higher for Co(II) than for Cu(II) for all the three sites and are in the order α > β-2 > β-1 for both the cations. Our computational results further reveal that upon binding Me(II) both the local structure of the zeolite framework as well as the binding energies of Me(II) strongly depend on the Al siting in the rings forming the cationic sites. The calculated relative binding energies of Me(II) are in the order β-1 > β-2 > α for both the cations. The general tendency of Me(II) accommodated in a cationic site to react is inversely proportional to the corresponding binding energies. We also showed that FTIR spectroscopy of complexes of NO and Me(II)-exchanged ferrierite can serve to identify the Al siting in the sixmembered rings forming cationic sites.

Microporous and Mesoporous Materials, 2011

A series of micro-and micro-mesoporous H-ZSM-5 zeolites with highly regular and, on the other sid... more A series of micro-and micro-mesoporous H-ZSM-5 zeolites with highly regular and, on the other side, a defective framework were prepared by synthesis and post-synthesis treatment, and their activity was investigated in transformation of methanol to low olefins, aromatics and paraffins. 27 Al MAS NMR and FTIR spectroscopy of OH groups and C"N groups of adsorbed d 3-acetonitrile were used for analysis of the population of framework Al-and Si-related defective sites. Beside framework Al atoms in regular Td coordination, perturbed Td coordinated Al atoms and partly extra-framework Al species, and the internal Si-OH groups as Si-related defects were identified. The increase in the concentration of framework Aland Si-defective sites in microporous H-ZSM-5 was manifested in methanol transformation in the increased yields of aromatics and paraffins, while highly regular framework preferred formation of low C 2 and C 3 olefins. The non-defective micro-mesoporous H-ZSM-5 prepared by alkaline and subsequent oxalic acid leaching of the zeolite with silanols typical for external crystal surface gave substantially longer catalyst lifetime. The micro-mesoporous H-ZSM-5 (synthesized by using carbon particles) exhibited high content of defective sites, i.e., inner silanols, interacting OH groups, perturbed framework Al atoms and Al-Lewis sites, provided a slight increase in the yield of paraffins and C þ 6 aromatics, and particularly much lower catalyst lifetime compared to the sample of similar composition and synthesis procedure carried out without carbon presence. These findings point out on the importance of highly regular framework of H-ZSM-5 for methanol to olefin transformation, and on the way of preparation of micro-mesoporous H-ZSM-5 by desilication with alkaline solution followed by acid leaching of electron acceptor sites, resulting in the high lifetime of the catalyst.

Microporous and Mesoporous Materials, 2011

Two parent ferrierites with similar Si/Al ratio (8.5 and 10.5), a commercial and a laboratory spe... more Two parent ferrierites with similar Si/Al ratio (8.5 and 10.5), a commercial and a laboratory specimen with different distribution of Al atoms in the framework, were used for the preparation of model Fe-ferrierite catalysts for N2O decomposition. As proven by UV–Vis analysis of the fully exchanged Co(II)-ferrierites, the two ferrierites differ in the distribution of framework Al between Al–O–(Si–O)2–Al sequences

Journal of Physics: Condensed Matter, 2009

The crystal structure, optical absorption, and photoluminescence of chromium impurity centers wer... more The crystal structure, optical absorption, and photoluminescence of chromium impurity centers were studied in nanocrystalline SrTiO(3):Cr (0.1 mol%) powders with average particle size within the range 13-100 nm prepared by the Pechini-type polymeric sol-gel method. Only the presence of a cubic perovskite phase of O(h)(1) symmetry was proved for the powders at room temperature, by means of x-ray diffraction. The lattice constant a = 3.910 Å, larger than that of bulk SrTiO(3) crystals (a = 3.905 Å), was found for nanoparticles with the size about 20 nm. The optical absorption edge and the zero-phonon R-line ([Formula: see text]) of luminescence of the octahedral Cr(3+) centers shifted to higher energies with decreasing nanoparticle size. These size effects were regarded as intrinsic to SrTiO(3). An unusual and large temperature shift of the R-line position very similar to the 'dielectric related' one of the bulk crystals was observed for all powders, evidencing their quantum paraelectric behavior. However, the powders with the average particle size about 13 and 20 nm did not reveal completely reproducible behavior of the R-line position at low temperatures. This instability was considered a possible manifestation of a low-temperature phase transition in small enough SrTiO(3) nanoparticles.

Journal of Catalysis, 2008

The effect of the distribution of Al atoms in the framework of H-ZSM-5, controlled by zeolite syn... more The effect of the distribution of Al atoms in the framework of H-ZSM-5, controlled by zeolite synthesis, on the product yields in 1-butene conversion to low olefins, aromatics and paraffins has been investigated for a series of zeolites, both synthesized and commercial, with Si/Al ranging from 12.6 to 43.6. The 27 Al and 29 Si MAS NMR of the corresponding Na-ZSM-5 and their exchange capacities for Co(II) ions and quantitative analysis of d-d transitions of bare Co(II) ions in the dehydrated CoNa-ZSM-5 were used for determination of the population of the [Al-O-(Si-O) n-Al] sequences in the framework. The Si-Al sequences with n = 1 were not present in the synthesized or commercial samples. The exchange capacity of Co(II) ions corresponded to the concentration of "close" framework Al atoms present mostly in the six-membered framework rings (n = 2) of the cationic sites. The concentration of "single" Al atoms was calculated from the difference between the total concentration of Al and twice the concentration of the exchanged Co(II) ions. The enhanced formation of aromatics in 1-butene conversion for H-ZSM-5 with similar Si/Al ratio, but higher concentration of "close" Al atoms in the framework is accounted for enhancing the rate of hydrogen transfer reactions, in contrast to samples with higher concentration of "single" Al atoms, where olefin cracking is preferred. As low-temperature (20 K) IR analysis of adsorbed hydrogen showed that the acid strength of the protonic sites in the H-ZSM-5 samples is very similar, the differences in the selectivity of 1-butene cracking and aromatization are thought to be caused by different distribution of framework Al atoms and thus also of the protonic sites. This finding opens a new potential for advanced tailoring of zeolite catalyst selectivity.

Journal of Catalysis, 2005

The effect of hydrogen and carbon monoxide on the selective catalytic reduction of NO x with deca... more The effect of hydrogen and carbon monoxide on the selective catalytic reduction of NO x with decane over a 2 wt% Ag/Al 2 O 3 catalyst was investigated. Hydrogen promoted NO x conversion during the SCR reaction, in contrast to carbon monoxide, which had a slightly detrimental effect on catalyst activity. However, in situ UV-vis spectroscopy showed that both carbon monoxide and hydrogen promoted the formation of Ag clusters during the reaction. This, coupled with previous EXAFS experiments and UV-vis data on the rate of change of cluster formation, demonstrate that the enhanced activity from the addition of hydrogen to the NO x-SCR mix cannot be attributed exclusively to the formation of Ag clusters. It is proposed that hydrogen itself participates directly in the reaction mechanism.

Journal of Catalysis, 2005

Decane-SCR-NO x , oxidation of NO and decane by molecular oxygen, and these reactions enhanced by... more Decane-SCR-NO x , oxidation of NO and decane by molecular oxygen, and these reactions enhanced by hydrogen over Ag/alumina were investigated by monitoring of gaseous product composition, surface intermediates (in situ FTIR), and the state of silver (in situ UV-vis) under realistic reaction conditions in the steady-state and transient modes. It has been shown that oxidation of NO or decane by oxygen is greatly affected by the presence of decane or NO. Monodentate nitrates are formed preferentially and are more reactive compared with the bidentate species. Oxidation of decane mostly yields surface acetates, and the presence of NO x favors the formation of formates (acrylates). The reaction steps most enhanced by the addition of hydrogen to the SCR-NO x reaction are the transformations of the intermediate-CN species into-NCO and oxidation of the hydrocarbon to formates (acrylates). Although NO-NO 2 oxidation is also enhanced by hydrogen, this effect does not contribute to the increased rate of the SCR-NO x reaction. A small part of very reactive Ag + (estimated to be < 5%) is reduced to metallic charged Ag n δ+ clusters (n 8) during both the decane-and H 2 /decane-SCR-NO x reactions. The number of Ag n δ+ clusters formed depends mainly on the level of NO conversion to nitrogen, regardless of whether the conversion level is attained by the addition of hydrogen or by an increased concentration of decane or oxygen in the feed. The time-resolved responses of NO x-N 2 conversion and of the number of Ag n δ+ clusters to the addition/removal of hydrogen from the reactants indicate that the Ag n δ+ clusters are mainly formed because of the reducing effect of adsorbed CH x O-containing reaction intermediates. The active sites are suggested to be single Ag + ions or small Ag 2 O species. Hydrogen itself takes part in the SCR-NO x reaction. It is supposed that it dissociates, forms Ag-hydride, and enhances SCR-NO x by initiation radical reactions.

Journal of Catalysis, 2010

The role of the distribution of aluminium in the framework of beta zeolites in the formation of v... more The role of the distribution of aluminium in the framework of beta zeolites in the formation of various types of counter Co species of different activity in C 3 H 8-SCR-NO in the absence/presence of 10% water vapour was investigated. Different concentrations of Al atoms in the Al-O-(Si-O) 2-Al sequences in one ring (Al pairs) and isolated Al atoms in Al-O-(Si-O) n>2-Al sequences located in two framework rings of parent BEA* zeolites were obtained by variation of the zeolite synthesis and by post-synthesis dealumination. Al atoms in the framework and their distribution were characterized by the combination of 29 Si MAS NMR of the parent BEA* zeolites and UV-Vis spectroscopy of the maximum-Co(II)-loaded BEA*. The concentration of Al pairs corresponded to the concentration of bare Co(II) ions in dehydrated maximum exchanged-Co(II)-BEA* calculated from the Vis spectra. Co-BEA* zeolites prepared by ion exchange from Co nitrate solution contained bare Co(II) ions balanced by Al pairs, which were formed preferentially, and ''monovalent" Co-oxo species balanced by the isolated Al atoms. The relative concentration of bare Co(II) ions and Co-oxo species depends on the degree of Co(II) ion exchange and the concentration of Al pairs and isolated Al atoms in the zeolite framework. Superior activity was found with the counter Co-oxo species balancing isolated Al atoms, surviving even in wet (10% H 2 O) NO x streams. The bare Co(II) ions were active in dry NO x streams, but their activity was negligible in wet NO x streams. A highly active catalyst (more than twice than the other Co-BEA*) can be prepared by using a BEA zeolite containing a predominant concentration of isolated Al atoms in the framework.

Journal of Catalysis, 2014

The heterogeneity and redox behavior of Fe-cationic species in Fe-ZSM-5 catalysts for N 2 O decom... more The heterogeneity and redox behavior of Fe-cationic species in Fe-ZSM-5 catalysts for N 2 O decomposition and NH 3-SCR-NO x were analyzed by Mössbauer and UV-Vis spectroscopy, TPR-H 2 , and reaction kinetic measurements. Iron was introduced into ZSM-5 zeolites of similar Si/Al but with different populations of close (Al-Si-Si-Al sequences in one ring-Al pairs) and far distant (single Al in different rings) Al atoms in the zeolite framework. It has been found that Al pairs in 6MRs of the framework greatly stabilize divalence of bare Fe(II) ions and [Fe(II)-O-Fe(II)] 2+ complexes even in oxidizing atmosphere. These species were completely oxidized only with N 2 O and recognized as the most active sites in N 2 O decomposition. On the contrary, the prevailing concentration of single Al atoms resulted at comparable conditions in high population of Fe(III)-oxo species. Fe(III)-oxo species of low nuclearity with partially compensated positive charge by the zeolite framework facilitate the formation of highly active oxygen species in an O 2-containing atmosphere and are the most active sites in NH 3-SCR-NO x. These findings show that manipulation of the structure of Fe-cationic species can be achieved by the synthesis of zeolites with different distributions of Al atoms between Al pairs and single Al atoms in the framework. This represents a potential for tailoring of catalytic properties of Fe-zeolite based catalysts for abatement of nitrogen oxides.

Applied Catalysis B: Environmental, 2007

The kinetic model of the reduction of NO to N2 with decane, developed based on the experimental d... more The kinetic model of the reduction of NO to N2 with decane, developed based on the experimental data over Fe-MFI catalyst, has been applied for the oxidation of NO to NO2 and reduction of NO2 to N2 with decane over Cu-MFI catalyst. The model fits well the experimental data of oxidation of NO as well as reduction of NO to

Applied Catalysis A: General, 2005

The cracking of 2-methyl-2-butene was carried out as a model reaction of C 4 + olefins cracking b... more The cracking of 2-methyl-2-butene was carried out as a model reaction of C 4 + olefins cracking by using of various zeolite and zeotype catalysts to obtain light olefins, such as ethylene and propylene. Only ZSM-5 and ZSM-11 zeolites with 10-MRP with intersecting channels and acid sites concentration ranging between 0.03 and 0.1 mmol/g exhibit high and stable selectivity to C 2-C 4 olefins at high conversion level. Active and selective catalysts were prepared by three different methods: direct synthesis of H-ZSM-5 with high Si/Al ratio, steaming of H-ZSM-5 and ''partial'' ammonium ion exchange of Na-ZSM-5. Neither H-(Al)ZSM-5 with high concentration of acid sites nor H-(Fe)ZSM-5 are suitable catalysts as they catalyze hydrogen-transfer reactions yielding paraffins and aromatics, showing the importance of low concentration and high strength of acid sites for cracking activity-selectivity. High yield of butenes in the reaction products indicates that pentenes cracking in 10-MRP proceeds via formation of voluminous carbenium ion intermediates demanding sufficient space inside of zeolites channel. Therefore, the presence of intersection of 10-MRP is very important. While in ZSM-5 and ZSM-11 zeolites the low amount of active sites mainly situated in the pores intersection is sufficient to achieve high activity-selectivity in the case of mono-dimensional 12-MRP zeolites such as mordenite and ZSM-12 and also with 10-MRP ferrierite much higher total acid concentration is necessary, as vast of the acid sites, situated out of the main channel do not take part in the reaction. AlPO-11 materials with narrow mono-dimensional channel exhibit low conversion with majority of b-scission cracking mechanism independently on the acid sites concentration.

Applied Catalysis A: General, 2011

The structure, properties and activity of the counter Co, Cu and Fe ion species depending on the ... more The structure, properties and activity of the counter Co, Cu and Fe ion species depending on the distribution of aluminium atoms in the framework between Al pairs of Al–O–(Si–O)2–Al sequences in one ring and isolated Al atoms (Al–O–(Si–O)n&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;2–Al sequences) in two rings are analyzed. The effect of the Al distribution on the activity of metal ion species is investigated for

Angewandte Chemie International Edition, 2013

Catalysis Today, 2011

Iron ferrierites with low iron content (Fe/Al between 0.018 and 0.072) were used as model catalys... more Iron ferrierites with low iron content (Fe/Al between 0.018 and 0.072) were used as model catalysts to evaluate the participation of individual iron species, with special interest in the role of iron in ␤ cationic sites, for formation of active sites for N 2 O decomposition. Despite low iron content, the catalysts with prevailing iron located in ␤ sites of two types exhibited high conversions of N 2 O and activity increase with increase of iron loading. These results indicate formation of the active iron species already at very low concentrations, while at higher concentration level would part of the iron enter also into less active positions. Semi-quantitative analysis of the TOF values of individual iron centers was done using the recently established Mössbauer parameters of the Fe(II) parameters for individual iron cationic species, i.e. ␤ (␤-1 and ␤-2) and ␣ sites [1]. The evaluation of the TOF presents a new support for the role of iron in ␤ sites in N 2 O decomposition and further indicates similar role of both ␤-1 and ␤-2 sites in formation of the Fe• • •Fe active site.

Materials Science and Technology, 2009

Journal of Physics: Condensed Matter, 2009

Microporous and Mesoporous Materials, 2011

A series of micro- and micro-mesoporous H-ZSM-5 zeolites with highly regular and, on the other si... more A series of micro- and micro-mesoporous H-ZSM-5 zeolites with highly regular and, on the other side, a defective framework were prepared by synthesis and post-synthesis treatment, and their activity was investigated in transformation of methanol to low olefins, aromatics and paraffins. 27Al MAS NMR and FTIR spectroscopy of OH groups and CN groups of adsorbed d3-acetonitrile were used for analysis

Microporous and Mesoporous Materials, 2011

Topics in Catalysis, 2018

The Journal of Physical Chemistry C, 2011

The Journal of Physical Chemistry C, 2013

Microporous and Mesoporous Materials, 2011

Journal of Physics: Condensed Matter, 2009

Journal of Catalysis, 2008

Journal of Catalysis, 2005

Journal of Catalysis, 2010

Journal of Catalysis, 2014

Applied Catalysis B: Environmental, 2007

Applied Catalysis A: General, 2005

Applied Catalysis A: General, 2011

Angewandte Chemie International Edition, 2013

Catalysis Today, 2011

Materials Science and Technology, 2009

Journal of Physics: Condensed Matter, 2009

Microporous and Mesoporous Materials, 2011