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Temperature-programmed desorption study of NO reactions on rutile TiO<sub>2</sub>(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>
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Kim, Boseong,Li, Zhenjun,Kay, Bruce D.,Dohná,lek, Zdenek,Kim, Yu Kwon The Royal Society of Chemistry 2012 Physical chemistry chemical physics Vol.14 No.43
<P>A series of NH<SUB>3</SUB> temperature-programmed desorption (TPD) spectra were taken after dosing NH<SUB>3</SUB> at 70 K on rutile TiO<SUB>2</SUB>(110)-1 × 1 surfaces with oxygen vacancy (V<SUB>O</SUB>) concentrations of ∼0% (p-TiO<SUB>2</SUB>) and 5% (r-TiO<SUB>2</SUB>), respectively, to study the effect of V<SUB>O</SUB>s on the desorption energy of NH<SUB>3</SUB> as a function of coverage, <I>&thetas;</I>. Our results show that in the zero coverage limit, the desorption energy of NH<SUB>3</SUB> on r-TiO<SUB>2</SUB> is 115 kJ mol<SUP>−1</SUP>, which is 10 kJ mol<SUP>−1</SUP> less than that on p-TiO<SUB>2</SUB>. The desorption energy from the Ti<SUP>4+</SUP> sites decreases with increasing <I>&thetas;</I> due to repulsive NH<SUB>3</SUB>–NH<SUB>3</SUB> interactions and approaches ∼55 kJ mol<SUP>−1</SUP> upon the saturation of Ti<SUP>4+</SUP> sites (<I>&thetas;</I> = 1 monolayer, ML) on both p- and r-TiO<SUB>2</SUB>. The absolute monolayer saturation coverage is determined to be about 10% smaller on r-TiO<SUB>2</SUB> than that on p-TiO<SUB>2</SUB>. Additionally, the trailing edges of the NH<SUB>3</SUB> TPD spectra on the hydroxylated TiO<SUB>2</SUB>(110) (h-TiO<SUB>2</SUB>) appear to be the same as that on r-TiO<SUB>2</SUB> while those on oxidized TiO<SUB>2</SUB>(110) (o-TiO<SUB>2</SUB>) shift to higher temperatures. We present a detailed analysis of the results and reconcile the observed differences based on the repulsive adsorbate–adsorbate dipole interactions between neighboring NH<SUB>3</SUB> molecules and the surface charge associated with the presence of V<SUB>O</SUB>s.</P> <P>Graphic Abstract</P><P>A series of NH<SUB>3</SUB> temperature-programmed desorption (TPD) spectra were taken after dosing NH<SUB>3</SUB> at 70 K on rutile TiO<SUB>2</SUB>(110)-1 × 1 surfaces with oxygen vacancy (V<SUB>O</SUB>) concentrations of ∼0% (p-TiO<SUB>2</SUB>) and 5% (r-TiO<SUB>2</SUB>), respectively, to study the effect of V<SUB>O</SUB>'s on the desorption energy of NH<SUB>3</SUB> as a function of coverage, <I>&thetas;</I>. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cp42754k'> </P>
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