De-NOx Performance and Mechanism of Mn-Based Low-Temperature SCR Catalysts Supported on Foamed Metal Nickel

Abstract

A series of manganese-based catalysts supported on foamed metal nickel (FMN) with various Mn/Ni ratios was prepared for low-temperature selective catalytic reduction (SCR) of NO with NH 3 (NH 3 -SCR). The effects of calcination temperature, amount of added Mn, optimal operating conditions, and H 2 O on the elimination of nitrogen oxides (de-NO x ) performance of catalysts were studied. The catalysts were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and temperature-programmed desorption experiments of NH 3 analyses. The experimental results revealed that the Mn 7.5 /FMN catalyst calcined at 350 °C exhibited the best NO conversion that was ca. 100% at 120-200 °C. Moreover, it had excellent H 2 O tolerance. The superior activity of the Mn 7.5 /FMN catalyst, which was calcined at 350 °C, was attributed to the presence of amorphous manganese oxide, more unsaturated Ni atoms and structural defects, an increase in NH 3 adsorbance, and the number of surface acid sites. Based on these studies, we established that the reaction of the NH 3 -SCR with Mn 7.5 /FMN catalyst mainly exhibits an Eley-Rideal mechanism.Keywords: de-NO x , low-temperature SCR, MnO x , foamed metal nickel, mechanism IntroductionNitrogen oxides (NO x ) such as NO and NO 2 resulting from fossil fuel combustion are one of the main pollutants in the atmosphere. NO x gases are responsible for acid rain, photochemical smog, and ozone layer depletion. At high levels, they affect the respiratory system, and long-term exposure can damage lung function.1-3 Currently, several methods are used to eliminate NO x (de-NO x ). Selective catalytic reduction (SCR) of NO with NH 3 (NH 3 -SCR) is one of the most effective ways to reduce NO x emissions. [4][5][6][7][8] The reactions are as follows: As a core link in this technology, the catalyst performance directly affects the de-NO x efficiency of the whole SCR system. 9,10 The V 2 O 5 -WO 3 (MoO 3 )/TiO 2 catalyst is a commonly used commercial SCR catalyst for NO x removal with an active temperature range of 300-400 °C. 11,12 However, this catalyst has many disadvantages including the toxicity of vanadium at high temperatures.13 Therefore, significant efforts should be devoted towards the development of non-vanadium catalysts for NH 3 -SCR processes. Mn-based catalysts have been studied due to their inherent environmentfriendly characteristics and excellent SCR activity at low temperatures. [14][15][16][17][18][19] Zhu et al. 1681 Vol. 29, No. 8, 2018 co-workers 22 studied the low-temperature de-NO x activity of Mn-Ce/TiO 2 and Mn-Ce/Al 2 O 3 catalysts. The results indicated that the de-NO x performance of the Mn-Ce/TiO 2 catalyst was better than that of the Mn-Ce/Al 2 O 3 catalyst at temperatures of 80-150 °C. Although the Mn-based catalysts exhibit high low-temperature activities, there are significant differences in their low-temperature SCR activity. [23][24][25] Moreover, the role of the carrier should not be ignored. 26,27 Foamed metal nickel (FMN) with...

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“…The adsorbed NH 3 is activated at the weak acid site on the surface of the catalyst, with the adsorption and activation of NH 3 as the critical step. For the L-H mechanism, the NO of the gas phase first interacts with O 2 and subsequently the NO x is adsorbed onto the surface of the catalyst where it is oxidized to nitrates and nitrites in the role of lattice oxygen [55][56][57][58][59]. The NO removal mechanism of the MnO x -Cu/AC catalyst can be seen in Figure 10.…”

A Review of Urea Pyrolysis to Produce NH3 Used for NOx Removal

“…In SCR and SNCR processes, reducing agents are injected into the flue gas to reduce NO x into harmless nitrogen (N 2 ). At present, the most popular reducing agent is ammonia (NH 3 ), principally in forms of aqueous ammonia and liquid ammonia [11][12][13]. Related NO x reduction reactions are as follows:…”