Pt/CeO_x/ZrO_x/γ-Al₂O₃ Ternary Mixed Oxide DeNO_x Catalyst: Surface Chemistry and NO_x Interactions

Abstract

Surface chemistry and the nature of the adsorbed NO x species on a Pt/CeO 2 −ZrO 2 /Al 2 O 3 catalyst were investigated by IR spectroscopy, X-ray diffraction, H 2temperature programmed reduction, and NO x-temperature programmed desorption. Parallel studies were also carried out with benchmark samples such as CeO 2 /Al 2 O 3 , ZrO 2 /Al 2 O 3 , CeO 2 −ZrO 2 /Al 2 O 3 and Pt-supported versions of these materials. All samples were studied in their reduced and nonreduced forms. The use of CO as a probe molecule revealed that during the synthesis of the mixed-metal oxide systems, deposited zirconia preferentially interacted with the alumina hydroxyls, while deposited ceria was preferentially located at the Lewis acid sites. Despite the limited extent of Zr 4+ ions incorporated into the CeO 2 lattice, the reduction of ceria was promoted and occurred at lower temperatures in the presence of zirconia. When deposited on ZrO 2 /Al 2 O 3 , platinum formed relatively big particles and existed in metallic state even in the nonreduced samples. The presence of ceria hindered platinum reduction during calcination and yielded a high platinum dispersion. Subsequent reduction with H 2 led to the production of metallic Pt particles. Consequently, NO adsorption on nonreduced Pt-containing materials was negligible but was enhanced on the reduced samples because of Pt 0-promoted NO disproportionation. The nature of the nitrogen-oxo species produced after NO and O 2 coadsorption on different samples was similar. Despite the high thermal stability of the NO x adsorbed species on the ceria and zirconia adsorption sites, the NO x reduction in the presence of H 2 was much more facile over Pt/CeO 2 −ZrO 2 /Al 2 O 3. Thus, the main differences in the NO x reduction functionalities of the investigated materials could be related to the ability of the catalysts to activate hydrogen at relatively lower temperatures.

Low-Temperature Catalytic NO Reduction with CO by Subnanometric Pt Clusters

“…Besides, 13 CO bonded to Si–OH (2108 cm –1 ) and 13 CO bonded to Pt δ+ (2088 cm –1 ) and Pt 0 (2043 cm –1 ) were also observed (see Figure 3a,b). 27 Several types of NO x species can be observed in the IR spectra, including 15 NO bonded to Pt 0 surface sites (1850 cm –1 ), 28 15 N 2 O 4 (1710 cm –1 ), and nitrates (1553 cm –1 ). Because the sample was reduced in the IR cell before the introduction of 13 CO and 15 NO, the presence of Pt δ+ should come from 15 NO dissociation on Pt nanoparticles, where the resultant oxygen atom on the partially oxidized Pt surface would further react with 13 CO to form 13 CO 2 .…”

Effects induced by interaction of the Pt/CeOx/ZrOx/γ-Al2O3 ternary mixed oxide DeNOx catalyst with hydrogen

“…Parallel studies were also carried out with benchmark samples such as: CeO 2 /Al 2 O 3 , ZrO 2 /Al 2 O 3 , CeO 2 -ZrO 2 / Al 2 O 3 and Pt supported versions of these materials. Despite the high thermal stability of the NO x adsorbed species on the ceria and zirconia adsorption sites, we have shown [29] that the NO x reduction in the presence of H 2 is much more facile over the Pt/CeO 2 -ZrO 2 /Al 2 O 3 catalyst. It was concluded [29] that the main difference in the functionality could be related to the ability of the catalyst to activate hydrogen at relatively lower temperatures.…”

“…Along these lines, as a continuation of our previous report [29], current study focuses on the effects induced by the interaction of the Pt/ CeO x -ZrO x /γ-Al 2 O 3 system with H 2 . In this study, based on in-situ Fourier-transform infrared spectroscopy (FTIR) investigations, we report our results on the effect of H 2 or D 2 on the activated Pt/CeO x -ZrO x / γ-Al 2 O 3 catalyst and also provide data on the NO x reactivity of the investigated material pre-exchanged with D 2 .…”

“…Despite the numerous investigations on DeNO x processes carried out with Pt/CeO 2 -ZrO 2 /Al 2 O 3 mixed ternary oxide system [26][27][28], effects induced by the interaction of the catalyst with hydrogen used as a reducing agent in the NO x reduction process are still not sufficiently well known. Efforts in our previous work [29] were focused on the surface chemistry and elucidation of the nature of the adsorbed NO x species on the Pt/CeO 2 -ZrO 2 /Al 2 O 3 catalyst. Parallel studies were also carried out with benchmark samples such as: CeO 2 /Al 2 O 3 , ZrO 2 /Al 2 O 3 , CeO 2 -ZrO 2 / Al 2 O 3 and Pt supported versions of these materials.…”

Effect of oxygen storage materials on the performance of Pt-based three-way catalysts

“…However, Pt-based TWCs have attracted less attention than Pd-and Rh-based TWCs. [26][27][28][29][30] Therefore, the design and development of effective catalytic supports is urgently required to improve the activity and stability of Ptbased TWCs to replace Pd-and Rh-based TWCs or reduce their use.…”