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>

¹⁵N₂ formation and fast oxygen isotope exchange during pulsed ¹⁵N¹⁸O exposure of MnO_<i>x</i>/CeO₂

Szanyi, J.,Kwak, J. H. The Royal Society of Chemistry 2014 Chemical communications Vol.50 No.95

<P>Pulsing <SUP>15</SUP>N<SUP>18</SUP>O onto an annealed 1% Mn<SUP>16</SUP>O<SUB><I>x</I></SUB>/Ce<SUP>16</SUP>O<SUB>2</SUB> catalyst resulted in very fast oxygen isotope exchange and <SUP>15</SUP>N<SUB>2</SUB> formation at 295 K. In the 1st <SUP>15</SUP>N<SUP>18</SUP>O pulse, due to the presence of large number of surface oxygen defects, extensive <SUP>15</SUP>N<SUB>2</SUB><SUP>18</SUP>O and <SUP>15</SUP>N<SUB>2</SUB> formations were observed. In subsequent pulses oxygen isotope exchange dominated as a result of highly labile oxygen in the oxide.</P> <P>Graphic Abstract</P><P>Molecular nitrogen formation and extensive isotope exchange between <SUP>15</SUP>N<SUP>18</SUP>O and surface <SUP>16</SUP>O on defect-rich MnO<SUB><I>x</I></SUB>/CeO<SUB>2</SUB> was observed. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cc05427j'> </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>

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>

Roles of Pt and BaO in the Sulfation of Pt/BaO/Al₂O₃ Lean NO<i>_x</i> Trap Materials: Sulfur K-edge XANES and Pt L_III XAFS Studies

Kim, D. H.,Kwak, J. H.,Szanyi, J.,Cho, S. J.,Peden, C. H. F. American Chemical Society 2008 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.112 No.8

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>

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>

Morphology-dependent phase transformation of γ-Al₂O₃

Lee, J.,Jeon, H.,Oh, D.G.,Szanyi, J.,Kwak, J.H. Elsevier 2015 Applied Catalysis A Vol.500 No.-

The phase transformations of platelet- and rod-shaped γ-Al<SUB>2</SUB>O<SUB>3</SUB> were investigated and compared to that of a commercial sample by XRD, BET surface area measurements, transmission electron microscopy (TEM), solid state <SUP>27</SUP>Al-NMR, and ethanol temperature programmed desorption (TPD) after sequential annealing in air up to 1100<SUP>o</SUP>C. After annealing at 1100<SUP>o</SUP>C, commercial γ-Al<SUB>2</SUB>O<SUB>3</SUB> mostly transformed into α-Al<SUB>2</SUB>O<SUB>3</SUB> with drastic surface area reduction (from 200m<SUP>2</SUP>/g to 25m<SUP>2</SUP>/g). Interestingly, platelet- and rod-shaped γ-Al<SUB>2</SUB>O<SUB>3</SUB> which showed exactly the same XRD patterns transformed into different phases upon the high temperature calcinations. Platelet-shaped γ-Al<SUB>2</SUB>O<SUB>3</SUB> transformed into θ-phase while the rod-shaped γ-Al<SUB>2</SUB>O<SUB>3</SUB> transformed into the δ-phase and not to the α-polymorph. Both platelet- and rod-shaped aluminas retained significantly higher surface area (~60m<SUP>2</SUP>/g) than the commercial one after the same treatment at 1100<SUP>o</SUP>C. These results suggest that the phase transformation in γ-Al<SUB>2</SUB>O<SUB>3</SUB> is strongly affected by not only the crystal structure of the starting material, but its morphology as well. Ethanol TPD from platelet- and rod-shaped alumina after 1100<SUP>o</SUP>C annealing, showed significantly different desorption profiles which suggest different surface characteristics even though they had almost the same surface areas. These different phase transformations were also supported by solid state <SUP>27</SUP>Al-NMR. After 1100<SUP>o</SUP>C annealing commercial alumina showed the presence of mostly octahedral Al<SUP>3+</SUP> ions, but the other two samples displayed even higher number of tetrahedral Al<SUP>3+</SUP> ions than the initial γ-Al<SUB>2</SUB>O<SUB>3</SUB>. Morphological changes were also confirmed by TEM. All these results consistently suggest the morphology-dependent phase transformations of γ-Al<SUB>2</SUB>O<SUB>3</SUB> and the improved thermal stability of platelet- and rod-shaped γ-Al<SUB>2</SUB>O<SUB>3</SUB> in comparison to a commercial γ-Al<SUB>2</SUB>O<SUB>3</SUB>.

Origin of temperature-dependent reduction channels of NO into N₂O on TiO₂(110) surfaces

Yu Kwon KIM,Zdenek DOHNALEK,Janos SZANYI,Bruce D. KAY 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.8

The Nested Variable Model of FDI Spillover Effects: Estimation Using Hungarian Panel Data

Ichiro Iwasaki,PÉTER CSIZMADIA,MIKLÓS ILLÉSSY,CSABA MAKÓ,MIKLÓS SZANYI 한국국제경제학회 2012 International Economic Journal Vol.26 No.4

A new empirical model is presented that considers the productivity spillover effects of foreign direct investment (FDI) by focusing on the multi-layered structure of industrial classifications. In this model, the market presence of horizontal FDI in a host country is expressed using multiple spillover variables with a nested structure corresponding to the aggregated level of industrial classification. Using large-scale firm-level data from Hungary, we estimated the nested variable model and verified horizontal FDI spillover effects that cannot be captured with the conventional model having a single horizontal variable.