Research strategy and topical outline

The main activity of the department is the design and characterisation of nanoscale composite catalyst systems including:

  • study of genesis and stability of supported nano-size mono- and bimetallic particles for use as catalysts;
  • elucidating the deeper insight into the scientific basis for the development of new, highly efficient nanostructured composite catalysts and their structure;
  • finding the relationship between catalyst structure and catalytic properties in a given reaction, manipulation of surface reactivity.

The morphology and electronic properties of nano-size (1-2 nm) metal and oxide particles (quantum dots) are fundamentally different from those of large particles in terms of short range ordering, valence band properties, surface coordination, etc. and their stability is much lower compared to their bulk-type counterparts. In combination with composite catalyst sytems, these are of primary importance in achieving special catalytic activity and selectivity in green chemistry, selective hydrogenation, in some oxidation reaction, etc. Beside the classsical catalyst preparation (wet impregnation) it is, therefore, desirable to apply non-classical chemical and physical procedures like deposition-precipitation, co-precipitation, liquid phase reduction/hydrolysis providing metal sols, oxide nanoparticles, particle formation in porous supports vapour phase deposition. Metal nano-particles can be chemically and physically functionalized. The modification can be attained by (i) addition of a second metal, (ii) by the presence of promoter molecules or (iii) by modifying the support.

Sophisticated experimental techniques are being applied at molecular level understanding the genesis of small mono- and bimetallic particles, their migration, segregation, oxidation state and stability to make recommendations about their overall behaviours.

Another important area of research is to have deeper insight into the surface science background of the preparation of highly selective catalysts for a given reaction. That is, what factors, like precursor deposition, calcination, reduction, support pretreatment, etc., affect the state of a catalyst.

The reactions are chosen from the fields of green chemistry (enantioselective hydrogenation), C1 chemistry (methane dry reforming), environmental chemistry (wet oxidation of waste materials, methane and N2O reaction) and alternative energy generation, (PROX, fuel cell anode catalyst).

Several sophisticated techniques are at our disposal, such as, X-ray fluorescence method (XRF) and ICP-MS are applied to measure the active component concentrations. The crystalline phases and crystallite sizes are characterised by X-ray diffraction (XRD). Temperature Programmed Spectroscopy comprises methods such as temperature programmed oxidation, reduction and decomposition (TPO, TPR, TPD), chemisorption and temperature programmed desorption (TPD) of hydrogen, oxygen and CO to characterize surface metallic sites. XPS UPS and AES with in situ atmospheric reaction chamber is used for the characterisation of the changes in the surface composition and valence state of the catalysts in different stages of pretreatment and under catalytic reaction. FT-IR spectrometer is applied for characterisation of the catalysts and surface interrmediates in adsorption or reaction conditions in a heatable transmission cell. Labelled experiments can also be carried out using deuterium, 13C, 14C and 35S labelled substances.

1. Asymmetric hydrogenation of C=C bond with Pd catalysts

A new research topic at our Department. The source of chirality can be a modifier or an auxiliary, the latter applied in stoichiometric amount. The asymmetric induction depends on the catalysts properties, so the preparation and treatment of the catalyst is investigated. The catalysts are characterized with different techniques (BET, chemisorption, TPD, TPR, XPS), so the relationship between enantioselectivity and structural properties can be established.

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2. Catalytic wet oxidation (CWO)

A part of environmental research is CWO, the partial oxidation of industrial process wastewaters is investigated in order to develop stable catalysts for this high pressure and temperature process (250oC, 50 bar), which takes place in a corrosive medium.

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3. Skeletal reactions of hydrocarbons on metal catalysts

Continuing earlier research on metal catalyzed dehydrocyclization, reactions of model C6 hydrocarbons (such as ring closure - ring opening - skeletal isomerization) were studied on metal catalysts. Various Pt, Pd and Rh based supported and unsupported catalysts have been prepared between 2005 and 2010 (in cooperation with the University of Poitiers). Their investigation with photoelectron spectroscopy was carried out together with the Fritz-Haber-Institut in Berlin. The deactivating effect of carbonaceous species in various chemical states (such as graphite, disordered carbonaceous deposits, and single C atoms on metal surfaces) is different. New studies were carried out regarding hydrogen effects on metal catalysts. Two methods were used to prepare bimetallic catalysts: organometallic grafting and electrochemical deposition. Inactive second metals (e.g. Sn, Ge) hindered deactivation by impeding the formation of a continuous carbonaceous overlayer. Test reactions on catalysts containing an active second component (such as Ir, Rh) the properties of both metals were observed in test reactions. In addition, peculiar bimetallic properties also appeared. The main results of Berlin-Budapest cooperation continuing for several years have been summarized in a review paper.

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4. Study of preferential oxidation of carbon monoxide in the presence of hydrogen (PROX reaction)

In Proton Exchange Membrane Fuel Cell (PEMFC) the CO content in the hydrogen feed to the anode of the PEMFC must be kept below 10-100 ppm, since CO poisons the nobel metal anode. The aim of preferential oxidation is to oxidize selectively CO in the presence of large hydrogen excess. Possible reactions in a realistic PROX system (H2, O2, CO, CO2, H2O, CH4), both CO and H2 oxidation as well as possible side reactions, mainly water-gas-shift (WGS) and reverse-water-gas shift (RWGS) are studied, examining the effect of catalyst structure (especially the role of reducible components). Differently prepared nobel metal (Pt, Pd, Au) containing various oxide (CeO2, TiO2, MnOx, CuO, FeOx etc.) supported catalysts are investigated and characterized using different methods (adsorption methods, TEM, XRD, XPS etc.). The kinetic tests are completed by in-situ spectroscopic techniques in cooperation with the Fritz-Haber Institute in Berlin, using high-pressure XPS and in-situ DRIFT spectroscopy.

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5. Studies on controlled formation of Au, Ag/MOx (M: Ti, Ce, Mn, Fe, Cu) nanocomposites with active interface

Investigation of the genesis of the system, structural characterisation and catalytic application in CO oxidation, PROX, deNOx reactions and selective glucose oxidation. Study on the effect of the morphology of the nanosized metal and oxide component and their interface on the efficiency of Au/MOx in catalytic reactions. Elucidation of the role of the crystalline polymorphs of TiO2 on the CO oxidation activity of Au/TiO2. Stabilisation of the Au-MOx nanostructures on SiO2 supports, confinement in mesoporous silicates in order to reach higher stability.

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6. Studies on Au-MOx (M: Fe, Ti, Ce) interaction on well defined model system and invers catalysts

Study of Au-MOx interaction and its effect on CO oxidation in model, SiO2/Si(100) supported layered systems of thin films or nanoparticles of the oxide and metal component formed by physical methods (pulsed layer deposition). In the MOx/Au/SiO2/Si(100), so called "inverse system" arrangement the effect of gold on the catalytic properties of the oxide covering gold can be studied. For the structural characterisation X-ray and UV photoelectron spectroscopy (XPS, UPS), atomic force and transmission electronmicroscopy (AFM, TEM), seconder ion mass spectroscopy (SIMS), X-ray diffraction (XRD) and sum frequency generation (SFG) techniques are used.

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7. Studies on controlled synthesis of Au-Pd, Au-Pt and Au-Ag bimetallic systems

Studies on controlled synthesis of Au-Pd, Au-Pt and Au-Ag bimetallic systems of different arrangements and morphologies as alloyed, core-shell particles or designed aggregates of mono- and bimetallic nanoparticles. In these preparation methods simultaneous reduction, successive reduction, seeded growth were applied considering the effect of the way of reduction such as reduction by ethanol or 2-propanol, tannic acid, citrate, borohydrid, gamma-irradiation or electron-pulse irradiation. Investigation of architecture and composition effects in semihydrogenation of highly unsaturated hydrocarbons (acetylene, diene) and in CO oxidation (PROX), deNOx reaction and selective glucose oxidation.

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8. Non-oxidative transformations of methane. The role of carbon nanospecies in deactivation of cobalt based catalysts in CH4 and CO transformation

Deactivation of Pt10Co90 catalyst supported on Al2O3 and NaY in non-oxidative methane transformation and CO disproportionation that may have importance in H2-deficient FT process was investigated in a constant flow system. Link can be found between deactivation of catalysts, especially of bimetallic Pt-Co nanoparticles and the formation, decomposition of meta-stabil CoCx (XRD) and formation of carbon nanotubes (TEM). The appearance of encapsulated Co particles inside the nanotubes (EDS) proves the restructuring of the Pt-Co bimetallic particles resulting in irreversible deactivation. The mechanism of the two processes is as follows. From the interaction of methane and the surface cobalt atoms CoCHx species are formed, which either are converted into C2+ hydrocarbons on the surface, or if they are grafted hard to the cobalt surface, they loose all hydrogen atoms and meta-stabile CoCx is created. At decomposition of the metastable CoCx carbon nanotubes and other carbon forms are generated on the catalyst surface. In the course of the nanotube growing cobalt particles are disrupted off the surface and encapsulated inside the tubes becoming inaccessible for the reactants. Since Pt could not be found in the carbon nanotubes the decomposition of Pt-Co bimetallic particles should be assumed. Due to this scenario the catalyst becomes irreversibly deactivated. The mechanism may be applied also for CO disproportionation.

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9. Design and development of extra active multifunctional bimetallic M/Ga/H-ZSM-5 (M-transition metal) catalysts for elimination of environmentally harmful N2O and CH4 gases

N2O and CH4 are strong greenhouse-effect gases with global warming potential (GWP) per molecule of about 296 and 23 times higher than that of carbon dioxide, respectively. N2O and CH4 is also identified as a contributor to the destruction of ozone in the stratosphere. It was demonstrated that addition of gallium to M/H-ZSM-5 (M=Fe, Co, Mo) samples increases the catalytic activity in various reactions of N2O/CH4 mixture. These results exceed the relating parameters of the Fe/H-ZSM-5 system recognised as the best in these reactions. The selective shift of the process into the formation of C2+ hydrocarbon, or oxygenates or towards the total oxidation of methane and reduction of dinitrogen-oxide is aimed. The N2O total reduction by CH4 can be utilized in catalytic combustion of nitrogen industry fumes, automotive exhaust gases and in afterburning systems of biomass generator. The outstanding low temperature activity of the M/Ga/H-ZSM-5 catalyst family offers possibility of development of novel environmentally friendly, energysaving fine chemical processes. The possibilites of the environmental and chemical technology application of the reaction between methane and dinitrogen-oxide will be searched.

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10. Methane dry reforming

Ni, NiRh and NiCo catalysts supported on Ce-Zr-oxide synthesised by pseudo sol-gel method have been investigated. Monometallic samples were performed with two different Ce/Zr ratios and by conventional impregnation. BET, XPS, TPR, TPO and TEM were applied for sample characterization and dry reforming of methane was carried out with a feed mixture consisted of CH4/CO2 = 70/30 ratio. Co and Rh containing samples were proved to be stable catalysts, the impregnated Ni catalyst only slightly, while sol-gel Ni samples slowly deactivated during the long term overnight run. The amount of carbon on the sample’s surface after catalytic runs varied between 1 and 12mg C/100mg of catalyst. The Ni samples prepared by sol-gel and impregnation method had a peak maximum in TPO at 400 oC and 600 oC, respectively. Upon high temperature pre-treatment and methane dry reforming reaction, alloyed NiRh, NiCo particles and sintered Ni were observed, with the simultaneous presence of carbidic carbon, carbon nanotubes and shell-type graphitic carbon deposition. Broad metal particle size distribution seems to play a role in long term stability.

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11. Investigation of hydrodesulfurization catalysts

A flow recirculation, isotopic tracer method has been developed and is applied to determine total and irrevesible sulfur uptake and equilibrium sulfur exchange between the catalyst and gas phase mainly for molybdenum-oxide based catalysts. Significant correlation (R2~0.9) was found between the extent of sulfur exchange and thiophene hydrodesulfurization activity of the catalysts. The activation energies of thiophene hydrodesulfurization, cyclohexene dehydrogenation and benzene hydrogenolysis were determined for different catalysts and based on these the C-catalysts, H-catalyst, S-catalyst binding energies were calculated.

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12. Study on the roles of subsurface carbon and hydrogen in palladium-catalyzed alkyne hydrogenation

Selective alkyne hydrogenation in the presence of carbon-carbon double bond compounds, for which Pd is an excellent catalyst, is a strategically important large-scale industrial process. Although in palladium, functionality and structure are closely interrelated, knowledge of the structure of Pd is insufficient as the interaction with the chemical environment causes drastic compositional changes near the subsurface region, as e.g. a result of intersticial carbon insertion (from the fragmented feed molecules) and hydrogen dissolution into the Pd lattice. On the basis of in situ x- ray photoelectron spectroscopic studies and in situ prompt gamma activation analysis measurements of hydrogen content of Pd under reaction conditions it could be elucidated that while unselective hydrogenation proceeds in the presence of a beta-hydride phase, selective hydrogenation can be achieved only in the presence of a near-surface Pd-C phase.
These studies were performed in cooperation between the Fritz-Haber-Institut in Berlin and Catalysis and Nuclear Research Departments of Institute of Isotopes.

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13. Development of stable, highly efficient electrode catalysts for direct methanol fuel cells

Recently commenced study on the modification of platinum based carbon supported multicomponent catalysts for increasing the stability of metal dispersion providing higher, stable electrocatalytic activity.

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