294708 DFT Study of Coverage-Depended Adsorption of NH3 On TiO2-B (100) Surface

Monday, October 29, 2012: 2:20 PM
412 (Convention Center )
Xiaohua Lu1, Xiaojing Guo2, Lu Cai2, Weijia Liu2, Yudan Zhu2 and Linghong Lu2, (1)Department of Chemical Engineering, Nanjing University of Technology, Nanjing, China, (2)chemical engineering, Nanjing university of technology, Nanjing, China

The selective catalytic reduction (SCR) of NOx with NH3 to N2 and H2O is an efficient way to reduce the amount of NOx from industrial plants and vehicles. V2O5/TiO2 catalyst is the basis for the industrial reaction. Ammonia adsorption is critical for SCR of NO on the catalyst. It was reported that the SCR activity increases with the amount of NH3 chemisorption on TiO2 surfaces increasing [1]. However, the saturation coverage of NH3 on TiO2 surface such as rutile (110) surface was reported to be half a monolayer [2]. TiO2 surface with high NH3 chemisorption capacity is expected for SCR. Our previous study showed that TiO2-B (100) surface is very unique. It is with high activity and a loose structure. The fully dissociative adsorption of water at 1 ML coverage on TiO2-B (100) surface is still favored due to its unique open structure [3].

In order to investigate the NH3 chemisorption capacity of TiO2-B (100) surface, we studied the adsorption of ammonia on TiO2-B (100) surface at coverages ranging from 1/6 to 1 ML using ab initio density functional calculations. The results show that the decrease rate of average molecular adsorption energy of NH3 with coverage on TiO2-B (100) surface is substantially lower than that on rutile (011) surface above 1/2 ML coverage due to its open structure. The variation pattern of average molecular adsorption energy with coverage on TiO2-B (100) surface is different from that on other TiO2 surfaces. It shows a linear dependence on the coverage of  on TiO2-B (100) surface, but accelerated degradation on rutile (011). The possibility of NH3 molecule onto the Ti5c site is nearly equal to forming dimer with adsorbed NH3 on TiO2-B (100) surface at 5/6 ML coverage.

[1] Yamazoe S., et al., Development of the efficient TiO2 photocatalyst in photoassisted selective catalytic reduction of NO with NH3. Catalysis Today, 2006. 111(3-4): p. 266-270.

[2] Siu W.K., Bartynski R.A., and Hulbert S.L., The role of defects at low concentrations in the NH3/TiO2(110) adsorption system: An Auger-photoelectron coincidence spectroscopy study. The Journal of Chemical Physics, 2000. 113(23): p. 10697-10702.

[3] Liu W.J., et al., A shortcut for evaluating activities of TiO2 facets: water dissociative chemisorption on TiO2-B (100) and (001). Physical Chemistry Chemical Physics, 2010. 12(31): p. 8721-8727.

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