Adsorption of CO and NO on Ceria- and Pt-Supported TiO<sub>2</sub>: <i>In Situ</i> FTIR Study

Abstract

Pt/TiO 2 , Ce/TiO 2 and binary system PtCe/TiO 2 catalysts were prepared by impregnation method and the structural properties of these catalysts were investigated by means of XRD, CO-TPD and UV-vis diffuse reflectance spectroscopy. As investigated by XRD, the composition of the prepared samples anatase and rutile phases with higher amount of anatase phase and its particle size was in the range of 19 -22 nm. The band gap also decreased from 3.1 to 2.85 after addition of metal to TiO 2 . The adsorption and interaction properties of NO and/or CO gases were monitored using an in situ FTIR technique. The intensity and position of the infrared peaks were strongly dependent on the composition of the catalyst. In presence of Pt, the main oxidative reductive products of (NO + CO) are CO 2 and NCO complex. The formation of NCO depends on not only the presence of platinum in the catalyst but also the presence of Lewis acid sites which is Ti 4+ in this study. However, the interaction between NO and CO gases increased in presence of CeO 2 . The optimum Ce content in PtCe/TiO 2 was 0.1% (Ce/TiO 2 ) at which the maximum peak intensity was observed for NCO and CO 2 .

Promotion effect of ultraviolet light on NO + CO reaction over Pt/TiO2 and Pt/CeO2–TiO2 catalysts

“…12b). Moreover, two new peaks at 2181 and 2210 cm −1 (assigned to β-type Ti 4+ -CO and α-type Ti 4+ -CO species) [18] appear, but the peak at 2296 cm −1 (attributed to the Ti 4+ -NO − ) disappears with the introduction of UV light. However, the formed Pt-NCO species (2200 cm −1 )…”

“…17 With the introduction of UV light (curve B in Fig. 11b), the increased peak of Pt 0 -CO shifts to a low wavenumber (from 2079 to 2076 cm −1 ), and is further split into a new absorption peak at about 2050 cm −1 which may be attributed to the Pt-CO-Pt [18]. Moreover, the intensity of CO 2 at peak of 2346 cm −1 is significantly increased, indicating that UV irradiation promote the oxidation of CO at Pt sites even in the absence of O 2 .…”

“…Moreover, UV light can make the peak of Pt 0 -CO shift to a lower wavenumber (from 2087 to 2077 cm −1 ) with a increased intensity, and lead to the formation of Pt-NCO and Pt 2+ -CO species (corresponding to the peaks at 2200 and 2138 cm −1 , respectively) [18]. This indicates that UV light can be conducive to the adsorption and activation of CO and NO at Pt and TiO 2 sites, consistent with the result of adsorbing single CO or NO in Fig.…”

“…TiO 2 -CeO 2 exhibits a catalytic activity for selective reduction of NO with NH 3 at low temperature [16], while the TiO 2 -CeO 2 supported Pd catalyst exhibits a high activity of oxidizing CO [17] and the TiO 2 -CeO 2 supported Pt catalyst shows a good performance for NO + CO reaction [18]. For the process of CO+NO reaction over Pt/TiO 2 -CeO 2 , Zeinhom et al [18] also suggested that the strong interaction between CeO 2 and TiO 2 can cause the increase in the oxygen vacancies and the surface active sites, which facilitates the adsorption of CO and its activation at Pt sites and then the formation of the NCO intermediate species. 6 Anpo et al [19] also reported that the transition metal modified TiO 2 -based catalyst can cause the reduction of NO by CO under UV irradiation.…”

FTIR and density functional study of NO interaction with reduced ceria: Identification of N3− and NO2− as new intermediates in NO conversion

“…Important peculiarities of CeO 2 are its high oxygen storage capacity and easy reducibility [05]. There are many studies of the nature of the species formed during interaction of NO x with ceria [05, 17,[19][20][21][22][23][24][25][26][27][28][29][30][31] and ceria-containing systems [05, 16,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49], and the proposed structures are summarized in Table 1. Based on the paper of Niwa et al [21] and a more recent work of Martinez-Arias et al [20], several authors reported formation of various species, such as NO - [16,19,20,[32][33][34]48], cis-and trans-hyponitrites [16,19,20,…”