Temperature-programmed desorption study of NO reactions on rutile TiO₂(110)-1×1

Kim, Boseong,Dohná,lek, Zdenek,Szanyi, Já,nos,Kay, Bruce D.,Kim, Yu Kwon Elsevier 2016 Surface science Vol.652 No.-

<P><B>Abstract</B></P> <P>Systematic temperature-programmed desorption (TPD) studies of NO adsorption and reactions on rutile TiO<SUB>2</SUB>(110)-1×1 surface reveal several distinct reaction channels in a temperature range of 50–500K. NO readily reacts on TiO<SUB>2</SUB>(110) to form N<SUB>2</SUB>O, which desorbs between 50 and 200K (LT N<SUB>2</SUB>O channels), which leaves the TiO<SUB>2</SUB> surface populated with adsorbed oxygen atoms (O<SUB>a</SUB>) as a by-product of N<SUB>2</SUB>O formation. In addition, we observe simultaneous desorption peaks of NO and N<SUB>2</SUB>O at 270K (HT1 N<SUB>2</SUB>O) and 400K (HT2 N<SUB>2</SUB>O), respectively, both of which are attributed to reaction-limited processes. No N-derived reaction product desorbs from TiO<SUB>2</SUB>(110) surface above 500K or higher, while the surface may be populated with O<SUB>a</SUB>'s and oxidized products such as NO<SUB>2</SUB> and NO<SUB>3</SUB>. The adsorbate-free TiO<SUB>2</SUB> surface with oxygen vacancies can be regenerated by prolonged annealing at 850K or higher. Detailed analysis of the three N<SUB>2</SUB>O desorption yields reveals that the surface species for the HT channels are likely to be various forms of NO dimers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> N<SUB>2</SUB>O desorption from NO/TiO<SUB>2</SUB> is enhanced in the presence of oxygen vacancies (V<SUB>O</SUB>'s). </LI> <LI> Overall N<SUB>2</SUB>O yield saturates above a threshold NO dose. </LI> <LI> N<SUB>2</SUB>O yields on <I>h</I>-(or <I>r</I>-) TiO<SUB>2</SUB> are about the same with changes in desorption channels. </LI> <LI> Stabilization of NO in the presence of hydroxyls enhances LT and HT2 N<SUB>2</SUB>O channels. </LI> <LI> Oxidation of NO into NO<SUB>2</SUB> and NO<SUB>3</SUB> decreases the N<SUB>2</SUB>O desorption yield. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of H₂O on the Morphological Changes of KNO₃ Formed on K₂O/Al₂O₃ NO_<i>x</i> Storage Materials: Fourier Transform Infrared and Time-Resolved X-ray Diffraction Studies

Kim, Do Heui,Mudiyanselage, Kumudu,Szanyi, Já,nos,Hanson, Jonathan C.,Peden, Charles H. F. American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.8

<P>Based on the combined FTIR and XRD studies, we report here that H<SUB>2</SUB>O induces a morphological change of KNO<SUB>3</SUB> species formed on model K<SUB>2</SUB>O/Al<SUB>2</SUB>O<SUB>3</SUB> NOx storage-reduction catalysts. Specifically as evidenced by FTIR, the contact of H<SUB>2</SUB>O with NO<SUB>2</SUB> preadsorbed on K<SUB>2</SUB>O/Al<SUB>2</SUB>O<SUB>3</SUB> promotes the transformation from bidentate (surface-like) KNO<SUB>3</SUB> species to ionic (bulk-like) ones irrespective of K loadings. Once H<SUB>2</SUB>O is removed from the sample, a reversible transformation into bidentate KNO<SUB>3</SUB> is observed, demonstrating a significant dependence of H<SUB>2</SUB>O on such morphological change. TR-XRD results show the formation of two different types of bulk KNO<SUB>3</SUB> phases (orthorhomobic and rhombohedral) in an as-impregnated sample. Once H<SUB>2</SUB>O begins to desorb above 400 K, the former is transformed into the latter, resulting in the existence of rhombohedral KNO<SUB>3</SUB> phase only. On the basis of consistent FTIR and TR-XRD results, we propose a model for the morphological changes of KNO<SUB>3</SUB> species with respect to NO<SUB>2</SUB> adsorption/desorption, H<SUB>2</SUB>O and/or heat treatments. Compared with the BaO/Al<SUB>2</SUB>O<SUB>3</SUB> system, K<SUB>2</SUB>O/Al<SUB>2</SUB>O<SUB>3</SUB> shows some similarities with respect to the formation of bulk nitrates upon H<SUB>2</SUB>O contact. However, there are significant differences that originate from the lower melting temperature of KNO<SUB>3</SUB> relative to Ba(NO<SUB>3</SUB>)<SUB>2</SUB>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-8/jp410816r/production/images/medium/jp-2013-10816r_0008.gif'></P>

Polymer micro and nanocomposites: Structure, interactions, properties

Ja´nos Mo´czo,Be´la Puka´nszky 한국공업화학회 2008 Journal of Industrial and Engineering Chemistry Vol.14 No.5

The characteristics of all heterogeneous polymer systems including composites containing either micro or nanofillers are determined by four factors: component properties, composition, structure and interfacial interactions. The most important filler characteristics are particle size, size distribution, specific surface area and particle shape, while the main matrix property is stiffness. Segregation, aggregation and the orientation of anisotropic particles determine structure. Interfacial interactions lead to the formation of a stiff interphase considerably influencing properties. Interactions are changed by surface modification, which must be always system specific and selected according to its goal. Under the effect of external load inhomogeneous stress distribution develops around heterogeneities, which initiate local micromechanical deformation processes determining the macroscopic properties of the composites. In filled polymers the dominating deformation mechanism is usually debonding. Nanocomposites represent one of the new classes of materials, but further research and development is needed before they gain significant position in the market.

Dissecting the steps of CO₂ reduction: 1. The interaction of CO and CO₂ with γ-Al₂O₃: <i>an in situ FTIR study</i>

Szanyi, Já,nos,Kwak, Ja Hun The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.29

<P>The adsorption of CO<SUB>2</SUB> and CO was investigated on a pure γ-Al<SUB>2</SUB>O<SUB>3</SUB> support material that has been used in Pd and Ru catalysts for the reduction of CO<SUB>2</SUB>. The adsorption of CO<SUB>2</SUB> resulted in the formation of carbonates, bicarbonates and linearly adsorbed CO<SUB>2</SUB> species. The amount and the nature of the adsorbed species were dependent on the annealing temperature of the alumina support. On γ-Al<SUB>2</SUB>O<SUB>3</SUB> annealed at 473 K mostly bicarbonates formed, while no adsorbed CO<SUB>2</SUB> was seen on this highly hydroxylated surface. With increasing calcination temperature the amount of both surface carbonates and linearly adsorbed CO<SUB>2</SUB> increased, but still the most abundant surface species were bicarbonates. Surface carbonates and adsorbed CO<SUB>2</SUB> can readily be removed from the alumina surface, while bicarbonates are stable to elevated temperatures. The interaction of CO with γ-Al<SUB>2</SUB>O<SUB>3</SUB> is much weaker than that of CO<SUB>2</SUB>. At room temperature CO adsorbs only on Lewis acid sites, and can be readily removed by evacuation. At 100 K CO can probe different defect sites on the alumina surface. Under no conditions we have observed the formation of any carbonates or bicarbonates upon the interaction of CO with the pure alumina support. In co-adsorption experiments CO competes for adsorption sites with the linearly adsorbed CO<SUB>2</SUB> on the 773 K-annealed γ-Al<SUB>2</SUB>O<SUB>3</SUB> surface, but it does not result in the desorption of CO<SUB>2</SUB>, rather in the increased production of weakly held carbonates. After the removal of adsorbed CO, CO<SUB>2</SUB> moves back to its original adsorption sites, <I>i.e.</I>, Lewis acidic Al<SUP>3+</SUP> centers. The exposure of a CO<SUB>2</SUB>-saturated γ-Al<SUB>2</SUB>O<SUB>3</SUB> to H<SUB>2</SUB>O did not affect any of the adsorbed surface species. The findings of this study will be used to rationalize the results of our ongoing <I>in situ</I> and <I>in operando</I> studies on the reduction of CO<SUB>2</SUB> on supported Pd and Ru catalysts.</P> <P>Graphic Abstract</P><P>The adsorption of CO<SUB>2</SUB> on γ-Al<SUB>2</SUB>O<SUB>3</SUB> produces calcination temperature-dependent surface species. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp00616j'> </P>

What Big Data tells: Sampling the social network by communication channels

Tö,rö,k, Já,nos,Murase, Yohsuke,Jo, Hang-Hyun,Kerté,sz, Já,nos,Kaski, Kimmo American Physical Society 2016 Physical Review E Vol.94 No.5

Stylized facts in social networks: Community-based static modeling

Jo, Hang-Hyun,Murase, Yohsuke,Tö,rö,k, Já,nos,Kerté,sz, Já,nos,Kaski, Kimmo Elsevier 2018 PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIO Vol.500 No.-

<P><B>Abstract</B></P> <P>The past analyses of datasets of social networks have enabled us to make empirical findings of a number of aspects of human society, which are commonly featured as stylized facts of social networks, such as broad distributions of network quantities, existence of communities, assortative mixing, and intensity-topology correlations. Since the understanding of the structure of these complex social networks is far from complete, for deeper insight into human society more comprehensive datasets and modeling of the stylized facts are needed. Although the existing dynamical and static models can generate some stylized facts, here we take an alternative approach by devising a community-based static model with heterogeneous community sizes and larger communities having smaller link density and weight. With these few assumptions we are able to generate realistic social networks that show most stylized facts for a wide range of parameters, as demonstrated numerically and analytically. Since our community-based static model is simple to implement and easily scalable, it can be used as a reference system, benchmark, or testbed for further applications.</P>

Dissecting the steps of CO₂ reduction: 2. The interaction of CO and CO₂ with Pd/γ-Al₂O₃: an <i>in situ</i> FTIR study

Szanyi, Já,nos,Kwak, Ja Hun The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.29

<P>Alumina supported Pd catalysts with metal loadings of 0.5, 2.5 and 10 wt% were investigated by <I>in situ</I> FTIR spectroscopy in order to understand the nature of adsorbed species formed during their exposure to CO<SUB>2</SUB> and CO. Exposing the annealed samples to CO<SUB>2</SUB> at 295 K resulted in the formation of alumina support-bound surface species only: linear adsorbed CO<SUB>2</SUB>, bidentate carbonates and bicarbonates. Room temperature exposure of all three samples to CO produced IR features characteristic of both ionic and metallic Pd, as well as bands we observed upon CO<SUB>2</SUB> adsorption (alumina support-bound species). Low temperature (100 K) adsorption of CO on the three samples provided information about the state of Pd after oxidation and reduction. Oxidized samples contained exclusively ionic Pd, while mostly metallic Pd was present in the reduced samples. Subsequent annealing of the CO-saturated samples revealed the facile (low temperature) reduction of PdO<SUB><I>x</I></SUB> species by adsorbed CO. This process was evidenced by the variations in IR bands characteristic of ionic and metallic Pd-bound CO, as well as by the appearance of IR bands associated with CO<SUB>2</SUB> adsorption as a function of annealing temperature. Samples containing oxidized Pd species (oxidized, annealed or reduced) always produced CO<SUB>2</SUB> upon their exposure to CO, while no CO<SUB>2</SUB>-related surface entities were observed on samples having only fully reduced (metallic) Pd.</P> <P>Graphic Abstract</P><P>Surface species formed on Pd/γ-Al<SUB>2</SUB>O<SUB>3</SUB> upon CO<SUB><I>x</I></SUB> exposure will aid mechanistic studies of CO<SUB>2</SUB> reduction. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp00617h'> </P>

Pi2 pulsations in the inner magnetosphere simultaneously observed by the Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer and Dynamics Explorer 1 satellites : Pi2 OBSERVED BY AMPTE/CCE AND DE 1

Teramoto, M.,Takahashi, K.,Nosé,, M.,Lee, D.-H.,Sutcliffe, P. R. American Geophysical Union 2011 Journal of geophysical research Vol.116 No.a7

Spontaneous doping of the basal plane of MoS2 single layers through oxygen substitution under ambient conditions

Pető,, Já,nos,Ollá,r, Tamá,s,Vancsó,, Pé,ter,Popov, Zakhar I.,Magda, Gá,bor Zsolt,Dobrik, Gergely,Hwang, Chanyong,Sorokin, Pavel B.,Tapasztó,, Levente Nature Publishing Group 2018 Nature chemistry Vol.10 No.12

Ethanol dehydration on γ-Al 2 O 3 : Effects of partial pressure and temperature

Lee, Jaekyoung,Szanyi, Já,nos,Kwak, Ja Hun Elsevier 2017 Molecular catalysis Vol.434 No.-

<P>Ethanol dehydration was investigated using platelet gamma-Al2O3 over a wide range of reaction temperature (180-300 degrees C) and ethanol partial pressure (0.5-2 kPa) by X-ray diffraction, ethanol Temperature programmed desorption and reactions. The turnover frequencies for commercial and platelet gamma-Al2O3 were almost identical (1.2-1.3 x 10(-2) ethanol/site s) when normalized to the number of ethoxide quantified by ethanol TPD. The desorption barrier of ethoxide was 183.6 kj/mol, similar to the activation barrier of ethylene formation. These results demonstrate that ethoxide is a key intermediate rather than molecular ethanol, possibly suggesting an El mechanism for ethylene formation, consistent with recent spectroscopic studies. Detailed kinetic measurements demonstrate the nature of the species on alumina surface varied with reaction temperature. At low temperature (180 degrees C), the ethanol dimer, one of which would be the ethoxide, saturated the surface, leading to the inhibition of ethylene formation and constant ether formation rates with ethanol pressure. At high temperature (260 degrees C), the ethanol monomer became dominant, consistent with the constant ethylene formation rates and increased ether formation rates with ethanol pressure. The apparent activation energies also changed with reaction temperature and ethanol partial pressure. Especially, the inhibition by ethanol dimer clearly contributed the increased apparent activation barrier at 180 degrees C. (C) 2016 Elsevier B.V. All rights reserved.</P>