Dynamics of nanocrystal structure induced by surface chemistry

Research group no. 16

Dynamics of nanocrystal structure induced by surface chemistry

Group leader

dr hab. Zbigniew Kaszkur

Research topics

Our research focuses on structure of nanocrystalline materials (mostly metals and alloys) and on dynamics of its change during chemisorption, chemical reaction and transport phenomena. We study atomic scale structure via diffraction and large scale atomistic simulations, developing tools of powder nanocrystallography, also of quasicrystalline nonperiodic systems. Most catalytic systems fall within the scope of our interest.

Members

  • dr inż. Wojciech Juszczyk
  • dr hab. Beata Lesiak-Orłowska
  • dr Dmytro Lisovytskiy 
  • dr Bogusław Mierzwa 
  • mgr Neha Rangam 
  • mgr Ilia Smirnov 
  • dr inż. Maciej Zieliński

Research

Presentation of dr Maciej Zieliński at Joint Polish-German Crystallographic Meeting (2020)

Metal-Support Interactions in Gold Quasicrystals Deposited on CeO2 Catalyst Revealed by In-Operando Powder X-Ray Diffraction Coupled with Mass Spectrometry - Presentation of dr Maciej Zieliński at Joint Polish-German Crystallographic Meeting (Wrocław, 2020). Due to limits imposed onto file size that can be uploaded to this website, the presentation has lowered resolution and was divided into three parts. The final MSword document contains comments that are supposed to guide a viewer through the slides.

Diffusion and segregation kinetics in immiscible metallic nanoalloys Au-Pt (Ilia Smirnov, presentation at JPGCM-2020)

The attached pdf document is a presentation of MSc Ilia Smirnov at the Joint Polish-German Crystallographic Meeting, Wroclaw 2020. Due to a limited size of the attached files the presentation was divided onto 3 parts and is in low resolution resulting in the shown atomistic models being blurred.

PhD Thesis of Maciej Zieliński brilliantly defended on Sept. 25th 2019

Structure dynamics of heterogeneous catalysts based on nanocrystalline gold in oxidation-reduction (REDOX) reactions. by Maciej Zieliński, MSc. Eng.
Supervisor: Zbigniew Kaszkur, PhD., DSc., Assoc. Prof. IPC PAS

The main scope of this research was to study the dynamic structure changes of the surface of heterogeneous catalysts containing supported nanocrystalline gold as their active component. Two model reactions were selected: stoichiometric oxidation of carbon monoxide (CO) by the molecular oxygen (O2) (abbrev. sCOOX) and preferential oxidation of CO in the presence of H2 (abbrev. PROX). Gold catalysts themselves are promising materials e.g. in the fuel cell industry for purification of hydrogen stream from CO, which contaminates the components of cells and decreases their efficiency.

The primary experimental technique used was the in-operando Nanocrystalline X-Ray Diffraction (NXRD) which was based on Powder X-Ray Diffraction (PXRD) coupled with Mass Spectrometry (MS) and a customised measurement strategy was applied. Furthermore, the in-operando Transmission Electron Microscopy (TEM) was also employed as a complementary technique. In this way, the research was focused specifically on investigation of crystal structures evolution under working conditions of the catalysts. Both experimental approaches were the world’s newest methods able to address the question of the role of the heterogeneous catalyst surface in the chemical reaction mechanism.

Catalysts facilitate chemical reactions to run under milder conditions or favour desired products if competing ones can be formed. It is the surface of the heterogenous solid catalyst that takes part in the reaction with gaseous reagents, so the gas molecules need first to adsorb on this surface. The assumed hypothesis suggested that the interaction with adsorbents results in immediate perturbation of the initially relaxed structure of the surface. PXRD and TEM are particularly suitable for detection of even little changes of the crystal lattice. The surface needs to adapt to the new electronic and energetic circumstances in order to dissipate the emerging energy excess. After the final products have been formed, these products desorb and the catalyst surface recovers its pristine configuration. The whole path is cyclically repeated, but the catalyst does not deteriorate in time.

In the case of nanocrystals, the surface constitutes a large fraction of the whole particle structure. Consequently, any change occurring at the surface affects the bulk part of the particle as well. Hence, tracking of the surface structure evolution was equally possible at the atomic level and through the averaged phenomena of X-Ray and electron diffraction.

Three catalysts containing gold nanoparticles (AuNPs) deposited on different supports: cerium (IV) oxide (ceria, 9.4%wt. Au/CeO2), silica (7.16%wt. Au/SiO2) and carbon (20% wt. Au/C), were selected as the objects of interest for this research. The most remarkable results were obtained for ceria decorated with AuNPs. It was the most efficient catalyst reaching over 80% conversion of CO to CO2 with high selectivity against water (H2O) production (in PROX reaction). It was concluded that ceria provided its extended surface for adsorption of CO and storage of activated oxygen moieties. AuNPs, or their perimeter at the interphase with ceria, were crucial for the CO2 production as pure CeO2 remained inactive under the same reaction conditions. Moreover, gold facilitated adsorption of reductive molecules (e.g. hydrogen, H2) on ceria and, thus, induced the redistribution of oxygen vacancies inside the ceria nanocrystals. Bare CeO2 was unaffected by the hydrogen atmosphere at ~150°C, while in the presence of gold the structure of ceria slightly expanded. It corresponded to the appearance of higher number of Ce3+ ions in the CeO 2-x particle core.

The Au/SiO2 and Au/C catalysts were observed to be much less active in the sCOOX and PROX reactions. The reactivity of the silica-supported one strongly depended on the content of water vapour in the gas atmosphere. The comparison of the metal-support interactions (MSI) between the reducible semiconducting CeO2 and non-reducible insulating SiO2 inspired conclusions on the reaction mechanism. The Au/C catalyst served as the reference of the catalytic activity of the bare gold nanocrystals.

The electron microscopy studies strongly implied that, although the imaging conditions were carefully chosen and did not influence the chemical activity results, the electron beam altered the irradiated sample electronic structure – additional part of Ce4+ ions in ceria were most probably reduced temporarily to Ce3+. This phenomenon has to be considered in detail in the future.

The Thesis is available at http://rcin.org.pl/dlibra/docmetadata?id=81875   or from Z.Kaszkur webpage kaszkur.net.pl.

The real background and peak asymmetry in diffraction on nanocrystalline metals.

The publication by by Zbigniew Kaszkur, Maciej Zieliński, Wojciech Juszczyk J. Appl. Cryst. (2017). 50, 585-593.

The paper deals with two fundamental problems in powder diffraction on nanocrystalline solids- finding the real background of a diffraction peak and the peak asymmetry.

The 'background problem' is at the basis of PXRD analysis. All material estimates deeply depend on it. If microstrain plays no important role in the diffraction pattern, the proposed analysis is the objective approach.
The paper explains why the diffraction peaks from nanometals are usually asymmetric and how one can extract from the peak shape the lattice constant - size dependency and the column size distribution. The asymmetry arises from a common phenomenon for nanocrystalline solids- size dependency of the measured lattice constant. For nanocrystalline metals this can be modified by adsorption from a gas atmosphere.

A fundamental problem in interpretation of diffraction from a multi-phase material is to separate peaks originating from only one phase from the background intensity. To this end our Team made a spectacular step - we have developed method to calculate the 'true background' of the peak, based on exact physical criteria. We proposed fitting the peaks to the Voigt shape function and application of condition given by Balzar (Balzar, D. (1993). J. Res. Natl Inst. Stand. Technol. 98, 321–353). The Voigt function as a convolution of Cauchy and Gauss functions is a particularly suitable expression for the peak shape owing to its simple Fourier properties. They enable simple, direct calculation of atom Column Length Distribution (CLD). Using the above mentioned criterion one can optimize the fit in respect to the background parameters.

The method is applicable if so called microstrains are not important factors in the peak broadening - the situation often met in catalytic studies. Currently the method was tested on supported metal nanocrystals.
The developed method enables in depth insight into the structure of nanocrystals and their surface. Monitoring the structural evolution during physico-chemical process- e.g. catalytic reaction at the surface of metal catalyst, may provide evidence of reversible elongations of nanocrystals along some directions. They result from a stronger bonding of some crystal faces with the adsorbing reagents. The crystallite responds by increasing surface of that faces, changing its shape and minimizing the energy. Such changes we have observed e.g. for nanocrystalline gold.

The proposed approach is especially 'strong' when applied to pattern evolution during in situ treatment of metal nanocrystals.
The developed method paves the way to understand why nanocrystalline gold makes a good catalyst in oxidation of carbon monoxide - the principal poison in the fuel cell technology.

Diffusion in metals.

Elementary mechanisms of diffusion in metals are studied on the example of PdAg nanoalloy. A uniform nanoalloy has been obtained with reversible and repeatable surface segregation (Pd or Ag) during heating at 400 deg.C in changing atmosphere (He or CO) (Kaszkur, Juszczyk, Łomot, Phys. Chem. Chem. Phys., 2015, 17, 28250).

The phenomenon of strong adsorption of CO onto Pd can be employed to generate uniform PdAg alloys. If sintering can be avoided, the nanoalloy can be subjected to repeatable processes of segregation of Pd and then Ag to the surface. The rate of both diffusion phenomena differs substantially. An atomistic understanding of them suggests a quite different mechanism for both as Pd diffusion to the surface runs in an environment depleted of vacancies. This recalls an old discussion concerning the diffusion basics before discovery of the Kirkendall effect. We observed that diffusion transport is slower than the bulk diffusion reported in the literature.
Evidently the macroscopic diffusion involves different mechanisms with diffusion along grain boundaries, dislocations and the effect of impurities. A study of segregation phenomena in nanocrystals can allow an insight into more elementary lattice transport. Switching off the dominating vacancy mechanism of diffusion allows us to study other subtle transport phenomena in alloys.

Anomalous diffusion in nanocrystalline metals

Poster presented on ICP microsymposium (based on Kaszkur et al.  Phys. Chem. Chem. Phys., 2015, 17, 28250--28255 )

Powder nanocrystallography (principles)

During the last century developements of powder diffraction were based on the theory of crystallography but constructed as a phenomenological methods using several approximate formulae. They describe temperature effects, microstrain, crystal size etc.
Theoretical principles of powder diffraction can be derived from the Debye summation formula. Computational power of contemporary computers makes now possible testing of the widely used approximate methods via construction of a complex atomistic structural model and direct calculation of its diffraction pattern. The model can involve strain, defects and its time evolution can be monitored via molecular dynamics. Such tests [1,2,3] prove that even fundamental laws (e.g. Bragg Law, Debye-Waller (D-W) effect) become less accurate and applicable when decreasing crystal size. E.g. Rietveld refinement method, even if well convergent, is not suitable for trustworthy description of nanocrystal structure.

For small size nanocrystals (D<10-20 nm) the observed lattice parameter usually depends on the size (as proven for nanometals), the peak position does not correspond to the real interplanar distance and different peaks point to different lattice parameters. Microstrain has different than in bulk character and is mostly linked to the crystal surface, size induced polimorphic transitions may occur and atom thermal oscillations at the surface may seriously modify classic form of the D-W effect. Along with that we can observe surface reconstruction, concentration gradient of elements e.g. in surface segregation, partial amorphisation etc.

This is why powder diffraction of small nanocrystals requires new, different than classic methodologies, and atomistic simulations are well posed for their fundamental test.

Such tests suggest that the structural effects although complex, can be effectively studied during evolution of several experimental parameters like temperature or gas composition. The latter is especially important as nanocrystals having large surface to bulk atom ratio have their structure very sensitive to the gas atmosphere. This is why the suggested experimental methods are in situ ones. Analysis of a single diffraction pattern and derivation of material parameters have to account for all possible diffractometric errors and the results have often limited accuracy. On the other hand the study of evolution and measurements of differences are much more precise- most of diffractometric errors is repeatable and cancel out in difference. The overall precission is then mostly due to measuring statistics.
 The method proposed by my group focuses on adapting the measurement strategy to address the most interesting structural motifs in chemistry- structure of the surface. Often it is the only part of the material that is modified. It already enabled analysis of surface reconstruction of Pt nanocrystals during hydrogen desorption [4] and NO chemisorption [5] explaining the discovered phenomenon of a low temperature Pt coallescence. We have proposed general method for detection of the surface reconstruction phenomenon on metal nanocrystals [6]. In studies of nanoalloys we have achieved control of elements segregation in PdAg enabling repeatable and reversible segregation and its atomistic model interpretation. The study allowed insight into elementary diffusion phenomena running in the nanocrystal and their mechanism - different than vacancy driven [7].

The proposed tools of nanocrystallography can be applied within the so called pressure and material gaps- conditions not often accesible for other experimental techniques.

References:

  • [1]. Kaszkur Z., J.Appl.Crystall., 33 (2000) 87.
  • [2]. Kaszkur Z., Mierzwa B., Pielaszek J., J.Appl.Crystall., 38 (2005) 266 .
  • [3]. Kaszkur Z., Zeitschrift für Kristallographie, 23 (2006) 147.
  • [4]. Rzeszotarski P., Kaszkur Z., Phys.Chem.Chem.Phys., 11 (2009) 5416.
  • [5]. Kaszkur Z., Rzeszotarski P., Juszczyk W., J.Appl.Crystallogr., 47 (2014) 2069.
  • [6]. Kaszkur Z., Mierzwa B., Juszczyk W., Rzeszotarski P., Łomot D., RSC Adv., 4 (2014) 14758.
  • [7]. Kaszkur Z., Juszczyk W., Łomot D., Phys.Chem.Chem.Phys.,17 (2015)  28250.

Development of nanocrystallography

Powder diffraction has been developed as a phenomenological science based on perfect crystallography but with a lot of formal assumptions that could not be verified on a precise atomistic model due to complexity involved. This applies to analysis of diffraction peak broadening i.e. Scherrer formula, Williamson-Hall analysis, Debye-Waller effect etc. Approaching  small nanostructures the atomistic models become now possible and all the PXRD methodology can be verified ab initio using basic for diffraction Debye formula and even not assuming Bragg's law. This ab initio analysis reveals that Bragg's law for small nanocrystals is no longer precisely obeyed and that peak position no longer points to the real interatomic distance. This was proved and pointed to in a series of our papers since 2001.
However the atomistic models are not often used nor the Debye summation formula for diffraction pattern calculation. Most papers, interesting on the obtained material side, discuss structure of even small nanoparticles with no proper account on their natural feature - violating Bragg's law causing small shifts of peak positions even for perfect lattice with no strain. The Debye formula calculated patterns for a simple fragments of perfect lattice can easily reveal that various peaks point to different lattice parameter and that Bragg's law points to interlayer distance different than assumed for the model fragment. For larger particles (>10nm) this effect may be difficult to notice. This is why diffraction studies of nanoparticles has to be divided between larger nanoparticles (D> 10-20 nm) and smaller ones. To the first class most of the classic powder diffraction techniques applies including Rietveld refinement with all the phenomenological treatment of strain, texture, Debye-Waller effect, vacancies etc.

For the second class of materials its lattice parameter often depends on size, the Bragg's law is inaccurate, the strain may have significant surface oriented component, the polymorphism may be size driven, the thermal effect may be more complex due to surface atoms oscillation, there may be noticeable effects of surface reconstruction, larger thermal fluctuations leading to partial amorphisation, concentration gradients caused by segregation etc. These interesting phenomena can be tackled by diffraction but e.g. Rietveld method is here of limited use. Most published papers shows no creativity in this respect but stubbornly applies the textbook methodology and tries to apply classic polycrystalline methods without checking on the models.

The research method of our choice to address the above mentioned structural problems is in situ powder diffraction focused on analysis of dynamics of a very small changes in diffraction peaks position, intensity and width. This way one can follow subtle transitions of metal nanocrystals surface ocuring in response to a chemical process at the surface (e.g. adsorption or reaction).
Due to systematic errors the measurment accuracy is as a rule much lower than the precission and repeatability. Analysing evolution one deals with differences of quantities for which most of experimental errors is the same so they vanish on subtraction. Accuracy of the evolution is thus much better than that of a single measurement and nearly equal to experimental precission.

This allows detection of a subtle changes interpreted by atomistic simulations in terms of a nanocrystal surface changes.
The proposed methods and tools are mostly new to crystallography but address the most sensitive questions of nanocrystallography.
A popular definition of nanocrystallography is - a branch of science applying methods of crystallography to nanocrystals. This definition  already does not apply to novel methods of electron nanocrystallography or femtosecond nanocrystallography that address studies of atomic and molecular arrangements in a scale of nanometers but using methods and tools not used previously. It becomes now apparent that structural studies of small nanocrystals of size below 10 nm rise specific questions and require specific methods. With measurable effects of surface relaxation and reconstruction that can be chemically induced the classic tools like Bragg's law, Rietveld refinement, strain analysis etc. are not well applicable. Developed by us for in situ powder diffraction a method to monitor and interpret changes to nanocrystal surface structure allows detection of a chemically induced surface reconstruction as well as observations of surface induced symmetry violations and nanocrystal reshaping. As most of crystallographic rules for small nanocrystals is no longer strictly obeyed, the proposed method builds up new tools of 'true nanocrystallography' basing on atomistic simulations.

After our successful first observation of dynamics of Pt surface reconstruction [1] on hydrogen desorption we were able to measure a degree of surface relaxation (affecting the overall interplanar spacing) on adsorption and relate it to the adsorption energy and the coverage. The observation of changing on adsorption interplanar spacing much exceeding the change expected from adsorption energy and coverage, is indicative of a lateral surface reconstruction phenomenon [2]. Such a tool allowed us to propose an explanation of the observed quick coalescence of Pt in NO atmosphere at 80 deg.C, in terms of a turbulence caused by a self-canceling cyclic surface reconstruction, the reconstruction being detected by our method [3]. The cyclic phenomenon would be caused by a changing on reconstruction number of the atoms exposed to the adsorbate. The caused surface turbulence forms a likely driving force for a nanocluster transport and merger.

The developed tools allows also e.g. explanation and control of the reversible surface segregation phenomena in PdAg nanoalloy giving insight into elementary diffusion mechanisms [4].

This novel nanocrystallography can be well applied to nanocrystals under pressure overcoming known in catalysis so called pressure gap and material gap.

  • 1. Rzeszotarski P., Kaszkur Z., Phys.Chem.Chem.Phys., 11, 5416 – 5421 (2009).
  • 2. Kaszkur Z., Rzeszotarski P., Juszczyk W., J.Appl.Crystallogr.,  (2014), 47, 2069-2077.
  • 3. Kaszkur Z., Mierzwa B., Juszczyk W., Rzeszotarski P., Łomot D., RSC Adv., 4 (28), 14758 – 14765 (2014) .
  • 4. Kaszkur Z., Juszczyk W., Łomot D., Phys.Chem.Chem.Phys., (2015), under review.

NANOKRYSTALOGRAFIA IN SITU (in Polish)

Dyfrakcja proszkowa rozwija sie od stulecia jako nauka fenomenologiczna oparta na teorii krystalografii ale uzupełniona o szereg przybliżonych formuł opisujących efekty temperaturowe, mikronaprężeń, rozmiaru krystalitów itp. Jej podstawy teoretyczne można oprzeć na fundamentalnej dla dyfrakcji proszkowej formule sumacyjnej Deby'e. Obecne możliwości obliczeniowe komputerów umożliwiają sprawdzenie części stosowanych przybliżonych formuł przez obliczenie dyfraktogramu wprost ze złożonego modelu atomowego, w którym można symulować naprężenia i defekty sieci. Takie testy [1,2,3] prowadzą do wniosku, że podstawowe prawa dyfrakcji (np.prawo Bragga, opis efektu Debye-Wallera D-W) są coraz mniej dokładnie spełniane przy zmniejszaniu rozmiarów krystalitów i np. metoda Rietvelda, choć często zbieżna, nie nadaje się do wiarygodnego opisu struktury małych nanokryształów. Dla nanokryształów o małych rozmiarach (D<10-20nm) obserwowana stała sieci zależy zwykle od rozmiaru, położenie refleksu nie wyznacza rzeczywistej odległości międzypłaszczyznowej a różne refleksy wskazują na inne stałe sieci. Mikronaprężenia mają inny charakter niż w fazie litej i związane są głównie z powierzchnią krystalitów, występuje indukowany rozmiarem polimorfizm a drgania termiczne na powierzchni mogą zmieniać postać efektu D-W. Obserwowane są efekty rekonstrukcji powierzchni, gradientów koncentracji pierwiastków np. w segregacji powierzchniowej, częściowej amorfizacji itp.

Dlatego też dyfrakcja proszkowa małych nanokryształów wymaga opracowania nowych różnych od klasycznych podejść metodycznych a symulacje atomistyczne wraz z formułą Deby'e stanowią ich fundamentalny test.

Testy takie sugerują, że badane efekty są wielowymiarowe i ich efektywne badanie możliwe jest w trakcie ewolucji szeregu parametrów doświadczalnych jak temperatura czy skład gazowej atmosfery. Jest to tym bardziej istotne, że nanokryształy, mając znacznie większy stosunek powierzchni do objętości mają strukturę silnie zależną od składu atmosfery i sugerowanymi metodami badawczymi są metody in situ. O ile analiza pojedynczych dyfraktogramów musi uwzględniać czasem znaczące błędy dyfraktometryczne i ma małą dokładność o tyle badanie ewolucji dyfraktogramów może się oprzeć na analizie różnic, które mierzone są z wysoką precyzją (zależną głównie od statystyki pomiarowej) gdyż błędy dyfraktometryczne odejmują się.

Proponowana przez mój zespół metoda badawcza umożliwia interpretację w/w zjawisk i umożliwiła np. analizę rekonstrukcji powierzchni nanokryształów Pt przy desorpcji wodoru [4] oraz chemisorpcji NO [5] wyjaśniając nowoodkryte zjawisko niskotemperaturowej koalescencji Pt. Zaproponowaliśmy ogólną metodę detekcji rekonstrukcji powierzchni nanokryształów [6]. W badaniach nanokrystalicznych stopów udało się uzyskać kontrolę nad stopniem segregacji składników (stop PdAg) umożliwiającą powtarzalną i odwracalną segregację oraz jej interpretację modelową. Umożliwiły one wgląd w elementarne zjawiska dyfuzji biegnące w nanokrysztale stopu i w ich mechanizm- różniący się od mechanizmu wakancyjnego [7].

Proponowane, nowe narzędzia nanokrystalografii in situ można stosować w obszarze tzw. przerwy ciśnieniowej i materiałowej- rzadko dostępnej do badań innymi technikami.

Literatura

  • [1]. Kaszkur Z., J.Appl.Crystall., 33 (2000) 87.
  • [2]. Kaszkur Z., Mierzwa B., Pielaszek J., J.Appl.Crystall., 38 (2005) 266 .
  • [3]. Kaszkur Z., Zeitschrift für Kristallographie, 23 (2006) 147.
  • [4]. Rzeszotarski P., Kaszkur Z., Phys.Chem.Chem.Phys., 11 (2009) 5416.
  • [5]. Kaszkur Z., Rzeszotarski P., Juszczyk W., J.Appl.Crystallogr., 47 (2014) 2069.
  • [6]. Kaszkur Z., Mierzwa B., Juszczyk W., Rzeszotarski P., Łomot D., RSC Adv., 4 (2014) 14758.
  • [7]. Kaszkur Z., Juszczyk W., Łomot D., Phys.Chem.Chem.Phys., (2015), DOI: 10.1039/C5CP00312A

Research overview 2013

Laboratory of X-ray Powder Diffraction and Spectrometry has a long standing experience in in situ powder diffraction as well as EXAFS (Extended X-ray Absorption Fine Structure) studies [eg. 1,2]. For in situ diffraction the employed equipment includes a range of 'in lab' constructed environmental cameras (J.Zieliński) as well as position sensitive detector INEL CPS120 (fig.1). The group undertook also successful combined XRD- Impedance Spectroscopy studies with a specially constructed in situ XRD cell [3].

Since 1997 the laboratory began research leading to development of a new powder diffraction in situ technique allowing surface science studies of nanocrystals in a chemical reaction conditions. The recent proof-of-concept work [4] shows in situ monitoring of a surface reconstruction of Pt nanocrystal surface (fig.2). On the development path the laboratory has showed deviations from Bragg law due to nanocrystallinity- pure size effect and a surface relaxation effect. The first diffraction experimental observation of surface relaxation of Pd nanocrystals has been published in 2000 [5] parallely with development of molecular simulation tools to interpret the observed diffraction phenomena [6]. The developed tools are available as program CLUSTER (Kaszkur, Mierzwa) - simulation package including graphical interface (fig.3).

The developed tools were applied to interpret phenomena of surface segregation in nanocrystalline bimetallic alloys [7,8] including reversal of the concentration profile in changing gaseous environment. Also interpretation of changing diffraction profiles on exposition of nanocrystalline Pd to hydrogen, proving existence of non-forming hydride phase icosahedral Pd clusters, was possible with the developed software.

List of principal methodology publications

  • Kaszkur Z., Zieliński M., Juszczyk Z., The real background and peak asymmetry in diffraction on nanocrystalline metals. J. Appl. Cryst. (2017), 50, 585-593.
  • Kaszkur Z., Juszczyk W., Łomot D., Self-diffusion in nanocrystalline alloys, Phys. Chem. Chem. Phys., 2015, 17, 28250-28255.
  • Kaszkur Z., Rzeszotarski P., Juszczyk W., Powder Diffraction in studies of nanocrystal surfaces - chemisorption on Pt. J.Appl.Cryst., 47, 2069-2077(2014)
  • Kaszkur Z., Mierzwa B., Juszczyk W.,Rzeszotarski P., Łomot D., Quick low temperature coalescence of Pt nanocrystals on silica exposed to NO- the case of reconstruction driven growth? RSC Adv ., 4(28), 14758 – 14765 (2014).
  • Rzeszotarski P., Kaszkur Z., "Surface reconstruction of Pt nanocrystals interacting with gas atmosphere. Bridging the pressure gap with in situ diffraction". Phys.Chem.Chem.Phys., 11, 5416 - 5421(2009)
  • Kaszkur Z., "Test of applicability of some powder diffraction tools to nanocrystals". Z. Krist. 23, 147-154 (2006).
  • Kaszkur Z., Mierzwa B., Pielaszek J., "Ab initio test of the Warren-Averbach analysis on model palladium nanocrystals". J. Appl. Cryst. 38, 266-273 (2005).
  • Kaszkur Z., "Direct observation of chemisorption induced changes in concentration profile in Pd-Au alloy nanosystems via in situ X-ray powder diffraction". Phys. Chem. Chem. Phys. 6, 193-199(2004).
  • Kaszkur Z., "Nanopowder diffraction analysis beyond the Bragg law applied to Palladium". J. Appl. Cryst. 33, 87-94(2000).
  • Kaszkur Z., "Powder Diffraction beyond the Bragg law: study of palladium nanocrystals". J. Appl. Cryst. 33, 1262-1270(2000).
  • Kaszkur Z.A., Mierzwa B., Segregation in model palladium-cobalt clusters, Phil. Mag. A 77, 781-800(1998).
  • Kaszkur Z., General Approach to the Radial Distribution Function Analysis of Solid Carbons,.Fuel , 69, 834-839 (1990).
  • Kaszkur Z., Convolutional Approach to the Normalisation of Intensity Scattered by Polycrystalline Substances, J.Appl.Cryst., 23 ,180-185 (1990).
  • Kaszkur Z., The Influence of the Texture on Radial Distribution Function of Solid Carbons, J.Appl.Cryst. , 22 (3),205(1989).
  • Kaszkur Z., Stachurski J., Pielaszek J., X-Ray Diffraction Study of the Palladium-Carbon System, J.Phys.Chem.Solids , 47 ,795(1986).

Direct Formic Acid Fuel Cell (DFAFC) - XRD camera for operando studies during cell operation

The attached poster presents construction of a transmission XRD camera fro DFAFC in operando studies.

Publications

2021

Giannakoudakis, D. A., Vikrant, K., LaGrow, A. P., Lisovitskiy, D., Kim, K.-H., Bandosz, T. J., & Colmenares, J. C.
Scrolled titanate nanosheet composites with reduced graphite oxide for photocatalytic and adsorptive removal of toxic vapors.
Chemical Engineering Journal, https://doi.org/10.1016/J.CEJ.2021.128907

Patkowski, W., Kowalik, P., Antoniak-Jurak, K., Zybert, M., Ronduda, H., Mierzwa, B., Próchniak, W., & Raróg-Pilecka, W.
On the Effect of Flash Calcination Method on the Characteristics of Cobalt Catalysts for Ammonia Synthesis Process.
European Journal of Inorganic Chemistry, https://doi.org/10.1002/ejic.202100117

Kowalewski, E., Krawczyk, M., Słowik, G., Kocik, J., Pieta, I. S., Chernyayeva, O., Lisovytskiy, D., Matus, K., & Śrębowata, A.
Continuous-flow hydrogenation of nitrocyclohexane toward value-added products with CuZnAl hydrotalcite derived materials.
Applied Catalysis A: General, https://doi.org/10.1016/j.apcata.2021.118134

Fernández-Ropero, A. J., Zawadzki, B., Kowalewski, E., Pieta, I. S., Krawczyk, M., Matus, K., Lisovytskiy, D., & Śrębowata, A.
Continuous 2-Methyl-3-Butyn-2-ol Selective Hydrogenation on Pd/γ-Al2O3 as a Green Pathway of Vitamin A Precursor Synthesis.
Catalysts, https://doi.org/10.3390/catal11040501

Cooperation

Sheridan College, Ontario, Canada

The aim of the collaboration is to investigate ceria-based catalysts doped with alkali metal ions, namely the influence of those ions on the planes exhibited by ceria and its lattice parameter under different atmospheres (E. Iwanek).

Fritz Haber Institute of the Max-Planck-Society

The cooperation aiming at merger of the in situ Transmission Electron Microscopy with the developed by us XRD technique of nanopowder diffraction. Peeping at atomistic mechanisms of chemical reactions in heterogenous catalysis requires in situ insight into microscopic and nanoscopic structure, its dynamics and linking the nanoscopic properties with the net outcome of the reaction. TEM meets then fundamental requirement to visualize the atomic environment that is representative for the catalyst. Our diffraction technique may monitor the reaction in a long run detecting occuring phenomena of surface reconstruction, subtle phase transitions, changes in average crystal morphology, surface segregation etc. The results can be a valuable hint for in situ TEM as to physico-chemical conditions to be employed in attempt to visualize the most interesting phenomena in atomic scale.

On the German side the cooperation involves dr. Thomas Lunkenbein of Department of Inorganic Chemistry (head) and dr. Marc Georg Willinger (former head), Electron Microscopy Group.

Currently our PhD student MSc Eng Maciej Zieliński is visiting the FHI group in the frame of DAAD scholarship (2 months) being trained in in situ TEM techniques.

Institute of Catalysis Bulgarian Academy of Science

Collaboration aiming at ex situ structural characterization of Au catalysts supported on ceria (modified) used in PROX and WGS reactions. The Bulgarian team is a well known group specializing in catalytical characterization (including temperature programmed techniques) of catalysts and in particular in catalysis on gold.

From the Bulgarian side the collaboration partners are profs. Tatyana Tabakova and Lyuba Ilieva.

Laboratoire Matériaux et Phénomènes Quantiques (CNRS - UMR 7162) Université Paris 7

Collaboration aiming at combining in situ TEM with our technique of nanopowder diffraction. The collaborating laboratory is headed by prof. Christian Ricolleau.

Institute of Physical Chemistry - research groups

  • ZB 02 - Group of molecular films research (W. Kutner)
  • ZB 09 - Coordination complexes and functional materials (J.Lewiński)
  • ZB15 - Modern Heterogenous Catalysis (J.Sa)
  • ZB 19 - Characterization of processes in first atomic layers of a solid surface (A.Jablonski)
  • ZB 23 - Modified electrodes for potential application in sensors and cells (M.Opallo)
  • ZB 28 - Catalysis for sustainable energy production and environmental protection, CatSEE (J. C. Colmenares)

Other Polish institutions

  • Faculty of Chemical and Process Engineering  Warsaw University of Technology (W. Raróg-Pilecka, M.Gliński)
  • Faculty of Chemistry, Warsaw University (M.Skompska)

Financing

17.08.2010- 31.12.2014

International project non-cofunded : "Segregation dynamics and three-stage melting process of nanocrystalline bimetallic alloys- structure in-situ study and atomistic simulations" 17.08.2010- 31.12.2014, granted by Ministry of Science and Higher Education, decision No 753/N-COST/2010/0, principal investigator.Z.Kaszkur.

Contribution:

Determination of a Pd-Ag mobility rates in nanoalloy and establishing controll over its segregation state, promoting Pd segregation via CO adsorption. Discovery of a method to uniformize non-uniform Pd-Ag alloy.

20.08.2010-19.12.2013

Research Project N N204097839 :"Structure evolution of metal-catalyst during surface chemical reaction" granted by Ministry of Science and Higher Education, dates 20.08.2010-19.12.2013, principal investigator Z.Kaszkur.

Contribution:

Developement and application of a new method of XRD structural studies in situ of nanometals and of dynamics of their surface. Developement of a method enabling detection of surface reconstruction effects versus surface relaxation. Discovery and insight into a new process of quick Pt nanocrystal coallescence rationalized via self-lifting reconstruction mechanism.

20.02.2015-19.08.2017

Research Project 2014/13/B/ST4/04619 :"Structure dynamics of nanocrystalline gold during WGS and PROX reactions- new approachto the reaction mechanism", 20.02.2015- , granted by National Science Center of Poland, principal investigator Z.Kaszkur.

01.03.2019 - 28.02.2022

Research project 2018/29/B/ST4/00710 "Diffusion in bimetallic nanoalloys" granted by National Science Center (NCN) of Poland. Principal investigator Z.Kaszkur.

01.02.2019 - 31.12.2020

Research project 2018/29/N/ST4/01465 granted by National Science Centre of Poland

"Structure dynamics of surface of catalytic systems based on nanocrystalline gold loaded on oxide supports in chemoselective Reduction of (Volatile) α,β-Unsaturated Carbonyl compounds (R-(V)ABUC)"

Principal Investigator: Maciej Zieliński, PhD Eng.

The main idea of this project was inspired by curiosity to answer the question how supported heterogeneous gold (Au) catalysts work. They are going to be tested in reaction of Reduction of (Volatile) α,β–Unsaturated Carbonyl compounds (R-(V)ABUC) with gaseous hydrogen. Among possible outcomes of this reaction, production of unsaturated alcohol (allylic alcohol) is the most challenging. The main aim concentrates on explaining why gold catalysts can be efficiently applied to production of derivatives of unsaturated carbonyl compounds.

As bulk gold does not interact readily with surroundings even if its surface was modified and developed, a hypothesis was formulated that the whole gold particle structure reconstruction is necessary in order that gold becomes a chemically active species. In contrast to bulk, in which any distortion created on the surface can be dissipated and compensated in the volume of the (poly)crystal, surface of a nanocrystal is a significant and, thus, important part of its structure. Following this concept, any disturbance of the equilibrium state of the surface should also affect deeper parts of the particle structure as a result of the attempt to compensate the influence of external stimulus.

One of the best techniques to track cyclic structural changes happening under reaction conditions is in operando Nanocrystalline X-Ray Diffraction (NXRD), which has been established and developed in our laboratory. This technique is based on standard Powder X-Ray Diffraction (PXRD), but is arranged into an in-operando setup and is coupled with Mass Spectrometry (MS). Our customised measurement strategy allows for acquisition of diffraction patterns (DP) while MS spectra are monitored on-line and other experimental parameters (including temperatures and gas flows) are logged at the same time. After extracting crystal structure description from DP the reversible changes of structure parameters of gold and support are presented as a function of time, chemical reaction output, etc.

Additionally, adsorbates on the surface will be identified by in-situ Infrared Spectroscopy (IR) and their interactions with the surface will be correlated with crystal structure evolution. Crystal lattice will be also investigated at the atomic level by Transmission Electron Microscopy (TEM).

The results of this research will show dynamics of the surface which is as a whole the active centre of the catalyst. New point of view on the catalytic systems together with new data are likely to be the crucial step towards development of this branch of chemistry.

The project summary is available also on the official site of the National Science Centre of Poland: http://ncn.gov.pl/sites/default/files/listy-rankingowe/2018-03-15/streszczenia/412873-en.pdf