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Low-Temperature Desorption of N<sub>2</sub>O from NO on Rutile TiO<sub>2</sub>(110)-1 × 1
Kim, Boseong,Li, Zhenjun,Kay, Bruce D.,Dohná,lek, Zdenek,Kim, Yu Kwon American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.18
<P>We find that NO dosed on rutile TiO<SUB>2</SUB>(110)-1 × 1 at substrate temperatures as low as 50 K readily reacts to produce N<SUB>2</SUB>O, which desorbs promptly from the surface leaving an oxygen adatom behind. The desorption rate of N<SUB>2</SUB>O reaches a maximum value after 1–2 s at an NO flux of 1.2 × 10<SUP>14</SUP> NO/cm<SUP>2</SUP>·sec and then decreases rapidly as the initially clean, reduced TiO<SUB>2</SUB>(110) surface with ∼5% oxygen vacancies (V<SUB>O</SUB>’s) becomes covered with oxygen adatoms and unreacted NO. The maximum desorption rate is also found to increase as the substrate temperature is raised up to about 100 K. Interestingly, the N<SUB>2</SUB>O desorption during the low-temperature (LT) NO dose is strongly suppressed when molecular oxygen is predosed, whereas it persists on the surface with V<SUB>O</SUB>’s passivated by surface hydroxyls. Our results show that the surface charge, not the V<SUB>O</SUB> sites, plays a dominant role in the LT N<SUB>2</SUB>O desorption induced by a facile NO reduction at such low temperatures.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-18/jp501179y/production/images/medium/jp-2014-01179y_0006.gif'></P>
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Ammonia Formation from NO Reaction with Surface Hydroxyls on Rutile TiO<sub>2</sub>(110)-1 × 1
Kim, Boseong,Kay, Bruce D.,Dohná,lek, Zdenek,Kim, Yu Kwon American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.2
<P>The reaction of NO with the hydroxylated rutile TiO2(110)-1 x 1 surface (h-TiO2) was investigated as a function of NO coverage using temperature-programmed desorption. Our results show that NO reaction with h-TiO2 leads to formation of NH3, which is observed to desorb at similar to 400 K. Interestingly, the amount of NH3 produced depends nonlinearly on the dose of NO. The yield increases up to a saturation value of similar to 1.3 x 10 (13) NH3/cm(2) at a NO dose of 5 x 10(-13) NO/cm(2), but subsequently decreases at higher NO doses. Preadsorbed H2O is found to have a negligible effect on the NH3 desorption yield. Additionally, no NH3 is formed in the absence of surface hydroxyls (HObs) upon coadsorption of NO and (HO)-O-2 on a stoichiometric TiO2(110) (s-TiO2(110)). On the basis of these observations, we conclude that nitrogen from NO has a strong preference to react with HObs on the bridge-bonded oxygen rows (but not with H2O) to form NH3. The absolute NH3 yield is limited by competing reactions of HOb species with titanium-bound oxygen adatoms to form H2O. Our results provide new mechanistic insight about the interactions of NO with hydroxyl groups on TiO2(110).</P>
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Kim, Boseong,Li, Zhenjun,Kay, Bruce D.,Dohná,lek, Zdenek,Kim, Yu Kwon American Chemical Society 2012 The Journal of Physical Chemistry Part C Vol. No.
<P>The interaction of N<SUB>2</SUB>O with oxygen vacancies (V<SUB>O</SUB>’s) on a partially reduced rutile TiO<SUB>2</SUB>(110)-1×1 surface was investigated using temperature-programmed desorption (TPD). Contrary to a common belief that V<SUB>O</SUB> on a rutile TiO<SUB>2</SUB>(110) is a dissociation site for N<SUB>2</SUB>O, our results indicate that N<SUB>2</SUB>O does not dissociate to form N<SUB>2</SUB>(g) and O(a). In TPD, N<SUB>2</SUB>O desorption shows two peaks with maxima at 135 and 175 K that are assigned to N<SUB>2</SUB>O desorption from Ti<SUP>4+</SUP> and V<SUB>O</SUB> sites, respectively, with absolute coverages determined to be 5.4 × 10<SUP>14</SUP> N<SUB>2</SUB>O/cm<SUP>2</SUP> and 2.3 × 10<SUP>13</SUP> N<SUB>2</SUB>O/cm<SUP>2</SUP>, respectively, on the TiO<SUB>2</SUB>(110)-1×1 surface used (V<SUB>O</SUB> concentration of 5%, 2.6 × 10<SUP>13</SUP>/cm<SUP>2</SUP>). When V<SUB>O</SUB>’s are passivated by dissociative adsorption of H<SUB>2</SUB>O, the N<SUB>2</SUB>O desorption peak at 175 K disappears, evidencing that the peak is related to V<SUB>O</SUB>-bonded N<SUB>2</SUB>O. The absence of N<SUB>2</SUB>O dissociation on V<SUB>O</SUB>’s is supported by a number of observations. First, the integrated amount of N<SUB>2</SUB>O desorbed from the substrate during TPD vs the amount of N<SUB>2</SUB>O dosed at 70 K shows a straight line with no offset, indicating no loss of N<SUB>2</SUB>O due to the N<SUB>2</SUB> formation. Second, N<SUB>2</SUB>O scattering experiments at 300–350 K indicate no change in the V<SUB>O</SUB> concentration as determined from the H<SUB>2</SUB>O TPD spectra. Third, N<SUB>2</SUB>O uptake experiments at 70–90 K show that the N<SUB>2</SUB> desorption feature is observed from TiO<SUB>2</SUB>(110) surfaces without V<SUB>O</SUB>’s, suggesting a possible contribution from background N<SUB>2</SUB> adsorption. On the basis of the above observations, we conclude that N<SUB>2</SUB>O does not dissociate on V<SUB>O</SUB> sites on TiO<SUB>2</SUB>(110), in contrast with the currently accepted view.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-1/jp210636j/production/images/medium/jp-2011-10636j_0007.gif'></P>
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