Effects of Adding CeO2 to Ag/Al2O3 Catalyst for Ammonia Oxidation at Low Temperatures

Abstract

Abstract:The effects of adding CeO 2 to Ag/Al 2 O 3 on the selective catalytic oxidation of ammonia to nitrogen were investigated by activity test and N 2 physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis diffuse-reflectance spectroscopy, high resolution transmission electron microscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy of NH 3 adsorption, and O 2 -pulse adsorption. Adding a suitable amount of CeO 2 improved the catalytic activity of Ag/Al 2 O 3 for NH 3 oxidation at temperatures below 160 o C, and slightly influenced N 2 selectivity by improving the catalyst's ability to adsorb and activate O 2 and the adsorption and activation of NH 3 .Key words: ammonia; silver; cerium; alumina oxide; supported catalyst; oxygen uptake; high resolution transmission electron microscopy; in situ diffuse reflectance infrared Fourier transform spectroscopyThe selective catalytic oxidation (SCO) of NH 3 to nitrogen (N 2 ) and water can reduce NH 3 emissions from chemical processes such as the selective catalytic reduction (SCR) of NO x by NH 3 and from soda production [1][2][3][4][5]. In particular, the low temperature oxidation of NH 3 to N 2 has important environmental applications. Noble metals such as Pt and Ir are the most active but least selective [5][6][7]. Gang et al. [6,8] reported that an alumina-supported Ag (10 wt% Ag/Al 2 O 3 ) catalyst was extremely active for NH 3 oxidation at low temperatures, and was superior to the noble metals. Nonetheless, there is still a considerable need for better catalysts that are active at low temperatures. The addition of CeO 2 improves the NH 3 oxidation activities of Au-, Cu-, and Ag-based catalysts [2,3]. Lippits et al. [3] found that adding CeO x to Ag-based catalyst lowered the temperature for the onset of oxidation from 300 to 200 o C. However, the role of CeO 2 in the Ag-based catalyst has not been studied in detail. Recently, we investigated the SCO of NH 3 over a 10 wt% Ag/Al 2 O 3 catalyst and discovered that the Ag valence state and particle size were significant for activity and N 2 selectivity at low temperatures [7]. To further improve the catalytic performance at low temperatures, we investigated the catalytic effects and the role of CeO 2 addition on Ag/Al 2 O 3 for the oxidation of NH 3 . Experimental Catalyst preparation and H 2 -pretreatmentThe

Cu-Mg-Fe-O-(Ce) Complex Oxides as Catalysts of Selective Catalytic Oxidation of Ammonia to Dinitrogen (NH3-SCO)

“…According to the mechanisms of ammonia oxidation described in the literature the most probable mechanisms for Cu-Mg-Fe mixed metal oxides is the internal selective ammonia oxidation (i-SCR) that include oxidation of part of NH 3 to NO and further NO reduction by NH 3 to N 2 [13,16,17]. Because of that, possible improvement of Cu-Mg-Fe catalysts activity could be reached by the modification of their surface by other metals (e.g., noble metals, [16][17][18][19]59]) that are responsible for selective oxidation of ammonia to NO [60] and ensuring the accessibility of active species by structural promoters, e.g., aluminum [14,21,57,61].…”

Ag Size/Structure-Dependent Effect on Low-Temperature Selective Catalytic Oxidation of NH3 over Ag/MnO2

“…Therefore, the development of efficient and low-price alternatives is needed to improve the catalytic activity and N 2 selectivity of NH 3 -SCO. Compared with other precious metal catalysts, silver is abundant and has high oxidation activity, and its low-temperature NH 3 catalytic oxidation record has been constantly broken. ,− Therefore, Ag-based catalysts have great potentials for achieving the ideal objective of NH 3 -SCO.…”

Characterization of Ceria’s Interaction with NOx and NH3

“…In addition, CeO 2 -based SCR catalysts, such as ceria-supported Pt, Pd, and Rh, Cu/Ag/CeO 2 –ZrO 2 , CeO 2 –MnO x , Ce/TiO 2 , and Ce-promoted Fe-exchanged TiO 2 -pillared clay ,− have been studied. It has been proposed that their NH 3 –SCR activities are at least partially due to NO oxidation over, or associated with, ceria. , Also, a ceria-based catalyst has been studied for NH 3 –SCO, providing high activity at low temperature due to its oxygen adsorption capacity. Many studies suggest that ceria promotes activity through its oxygen storage and redox properties; however, the published literature mainly focuses on the role of other catalytic materials, typically the precious metal components when studying DOCs and NSR catalysts, with the ceria playing a supporting role.…”