DRIFTS study of photo-assisted catalytic CO + NO redox reaction over CuO/CeO2-TiO2

Abstract

Please cite this article in press as: N. Liu, et al., DRIFTS study of photo-assisted catalytic CO + NO redox reaction over CuO/CeO 2 -TiO 2 , Catal. Today (2015), http://dx. a b s t r a c tCuO/CeO 2 -TiO 2 catalysts have been widely studied for the thermocatalytic NO reduction with CO. Here, we examine to what extent this reaction can be photocatalytically enhanced beyond the mere thermocatalytic activity by irradiating the catalyst with UV light under reaction conditions while observing the reaction progress via DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy). The reaction was studied in a batch reactor at four temperatures (35, 65, 100, and 200 • C). The most pronounced effect of photocatalytic enhancement was observed at 65 • C where an enhanced CO conversion of 64.4% was achieved, compared with 11.5% CO conversion without UV irradiation. The photocatalytic enhancement of the CO conversion diminished as the temperature increased to 200 • C, where the CO conversion process became entirely dominated by thermal catalysis. The promoting effect of ceria on the CO + NO reaction has been revealed and rationalized on the basis of physical and chemical characterizations results. XPS and TPR results suggest that the electronic state interaction between Ce and the other two components (Ti and Cu) in the catalysts might lead to a higher oxygen vacancy concentration that facilitates oxygen transport from ceria to copper species resulting in the high catalytic activity for NO reduction by CO.

Effect of Surface Copper Species on NO + CO Reaction over xCuO-Ce0.9Zr0.1O2 Catalysts: In Situ DRIFTS Studies

“…. This implies that the zirconia dopant is contained within the CZ lattice and formed a solid solution while maintaining the fluorite structure [11,26]. For the xCuOCZ catalysts, no reflections characteristic of CuO structure were observed, which may be due to some copper being well dispersed as CuO nano-crystalline or to a limited amount of Cu ion being included in the surface structure [27].…”

“…Upon switching to 0.5 vol % CO/N 2 , the surface adsorbed NO x species nearly vanished, as shown in Figure 9b. At the same time, the monodentate carbonate and carboxylate bands at 1467 and 1392 cm −1 [11,47] formed. This illustrates that the nitrate and nitrite species are reduced by the adsorbed CO.…”

“…The former three peaks were ascribed to bidentate nitrate (ν(N=O)) and monodentate nitrate (ν as (NO 2 )), respectively [1,11,20,41,42]. The IR (Infrared Radiation) peak at 1346 cm −1 was assigned to cis-hyponitrites (N 2 O 2 2− ) [16,20,43], and the IR peak at 1215 cm −1 was ascribed to the bidentate nitrite adsorbed on Cu 2+ [11]. The surface adsorbed NO x species on the CZ catalyst was detected at 1562 and 1461 cm −1 as shown in Figure S5a.…”

“…In the literature [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], copper oxide supported on different oxides (e.g., SiO 2 , TiO 2 , Al 2 O 3 , CeO 2 ) has been tested in the reaction of NO + CO. Among these supports, CeO 2 has received special attention due to the role of the oxygen buffering center through the facile Ce 4+ /Ce 3+ redox cycle [1,25].…”

Effect of Calcination Temperature on NO–CO Decomposition by Pd Catalyst Nanoparticles Supported on Alumina Nanofibers

“…Typical supported catalysts have metal catalyst particles attached to the surface of an inert support structure. Many transition metals (Au, Ir, Fe, Ni, Pd, Pt, Rh, Zr and others) can be used as catalysts due to their inherent properties to selectively adsorb chemical species and to reduce activation energies of chemical reactions [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In many applications in the automotive industry, multi-metal catalysts are used simultaneously to introduce desired performances over a wide range of operating conditions (such as three-way noble metal Pt, Pd and Rh catalysts) [3][4][5][6]; metal oxide materials, which have multiple metal atoms such as Ce combined with transition metals (Fe, Au, Zr, Ti, Sn and others), can further enhance performance [7,[17][18][19].…”