The effect of oxygen vacancies on the binding interactions of NH3 with rutile TiO2(110)-1 × 1

Abstract

A series of NH(3) temperature-programmed desorption (TPD) spectra were taken after dosing NH(3) at 70 K on rutile TiO(2)(110)-1 × 1 surfaces with oxygen vacancy (V(O)) concentrations of ~0% (p-TiO(2)) and 5% (r-TiO(2)), respectively, to study the effect of V(O)s on the desorption energy of NH(3) as a function of coverage, θ. Our results show that in the zero coverage limit, the desorption energy of NH(3) on r-TiO(2) is 115 kJ mol(-1), which is 10 kJ mol(-1) less than that on p-TiO(2). The desorption energy from the Ti(4+) sites decreases with increasing θ due to repulsive NH(3)-NH(3) interactions and approaches ~55 kJ mol(-1) upon the saturation of Ti(4+) sites (θ = 1 monolayer, ML) on both p- and r-TiO(2). The absolute monolayer saturation coverage is determined to be about 10% smaller on r-TiO(2) than that on p-TiO(2). Additionally, the trailing edges of the NH(3) TPD spectra on the hydroxylated TiO(2)(110) (h-TiO(2)) appear to be the same as that on r-TiO(2) while those on oxidized TiO(2)(110) (o-TiO(2)) 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(3) molecules and the surface charge associated with the presence of V(O)s.

A Heterojunction Design of Single Layer Hole Tunneling ZnO Passivation Wrapping around TiO2Nanowires for Superior Photocatalytic Performance

“…In principle there are four main types of defects on TiO 2 which can be classified as: oxygen vacancies (V O ’s), titanium vacancies (V Ti ’s) (surface defects), interstitials (Ti i and O i ), and antisites which are mostly formed in the bulk of material 31 53 55 83 92 95 . There are several reports which propose Ti i ’s as the active sites of TiO 2 surface 81 84 96 , while the others give this functionality to the V O ’s 7 60 97 98 . The fact that which of these defects is dominant depends on the preparation method of the material; under Ti reach conditions V O ’s are the most favorable defects to form 60 81 99 .…”

NH3 adsorption on anatase-TiO2(101)

“…We note that this method is valid strictly for first-order desorption. 33 This is fulfilled for non-dissociative adsorption, 20 despite the shift of maximum desorption to lower temperature with increasing coverages, which is otherwise typically related to second-order desorption. 34 E d is calculated iteratively from the following equation:…”

“…The strong coverage-dependent desorption energy is attributed to the repulsion between ammonia molecules. 20,21 A small tail is seen at the trailing edge at around 450 K, this is presumably caused by ammonia adsorption in vicinity of defects (subsurface donors), as only small affinity for adsorption at step edges is observed.…”

“…19,22,23,26 On r-TiO 2 (110), a full monolayer is therefore considered in some studies to be achieved by occupation of half the available 5f-Ti sites 1922 . However, Kim et al 20 reported by TPD that a full NH 3 monolayer on rutile TiO 2 (110) corresponds to occupation of all 5f-Ti sites.…”

Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 1. Individual Heats of Adsorption of Adsorbed NH3 Species on a Sulfate-Free TiO2 Support Using Adsorption Isobars

“…We limit the comparison to a recent study of Kim et al 68 Moreover the heat of adsorption at full coverage is in good aggrement with that obtained from the AEIR method for NH 3ads-L1 species which is the dominant species at low temperature..…”