MnO_x-CeO_x Nanoparticles Supported on Graphene Aerogel for Selective Catalytic Reduction of Nitric Oxides

Abstract

Removal of nitric oxides (NOx) from stationary and transportation sources has been desired for environmental benefits. Selective catalytic reduction (SCR) of NOx by NH3 is attractive for its cost effectiveness and high efficiency but still technically challenging in consideration of operable temperatures. In this research, MnOx-CeOx hybrid nanoparticles supported on graphene aerogel (MnOx-CeOx/GA) are fabricated as the monolithic catalysts for potential applications to low-temperature SCR. The impacts of the particle size along with the amount and valency of catalytic elements in the nanocomposite on the catalytic activities are studied with the help of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The catalyst crystallites are a few tens of nanometers and uniformly disperse on the surface of three-dimensional (3D) directionally aligned hierarchical porous graphene aerogel (GA) networks. The novel nanocomposite catalysts exhibit over 90% NOx conversion rate in a broad temperature range (200–300°C). Addition of CeOx into the MnOx-GA catalysts significantly reduces the operational temperature at the same conversion rate. In addition to Mn4+ ions in the catalysts, the adsorbed oxygen species which can be increased by the presence of low-valence cerium contribute to high catalytic activities in the MnOx-CeOx/GA catalysts.

Fabrication and Characteristics of Mn@ Cu3(BTC)2 for Low-Temperature Catalytic Reduction of NOx with NH3

“…Xin et al [32] has suggested that Mn 3+ could activate NH 3 into NH 2 intermediate that will readily react with NO to produce N 2 . Previous studies also confirmed that ample amount of Mn 4+ ions is one of the key factors enhancing NH 3 oxidation in the NH 3 -SCR process due to the strong oxidizing state of Mn (IV) [15,16]. Figure 5 presents the mass change of Mn@CuBTC-0.05, compared with CuBTC, upon increasing temperature.…”

“…e concentration of NO 2 and N 2 O in the effluent gas was determined by a Nicolet iS50 FT-IR spectrometer. Details have been described elsewhere [15]. e NO conversion and N 2 selectivity were calculated as follows:…”

“…Manganese-based catalysts are superior, which can be attributed to the versatile valence states and excellent redox ability. Multiple catalytic oxides supported on stable highsurface materials can further enhance the low-temperature performances via modified active sites, synergistic effects between the two metal ions, and metal-support interaction [14,15]. For instance, MnO x -CeO x hybrid nanocatalysts supported on graphene aerogel exhibited 80% NO conversion at 150°C and 98% at 250°C [15].…”

“…Multiple catalytic oxides supported on stable highsurface materials can further enhance the low-temperature performances via modified active sites, synergistic effects between the two metal ions, and metal-support interaction [14,15]. For instance, MnO x -CeO x hybrid nanocatalysts supported on graphene aerogel exhibited 80% NO conversion at 150°C and 98% at 250°C [15]. Recently, Boningari et al reported metal oxide confined in titania nanotube (M/ TNT) system and noticed that the surface texture and tubular morphology greatly promote the NO x conversion in the temperature regime of 100-300°C [16].…”