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.
Highlights
Nitric oxides (NOx) have raised global awareness for their serious impacts on the environment such as acid rain, photochemical smog, ozone depletion, and greenhouse effects
The morphology and microstructure of the as-prepared nanocomposite catalysts graphene aerogel (GA)-Mn and GA-MnCe series are elucidated by FESEM and transmission electron microscopy (TEM)
The catalytic activity increases with Mn loading and appears to saturate when Mn loading is over 10 wt%
Summary
Nitric oxides (NOx) have raised global awareness for their serious impacts on the environment such as acid rain, photochemical smog, ozone depletion, and greenhouse effects. Mn-based catalysts are attractive candidates because they exhibit good low-temperature SCR activities [1, 2, 7,8,9,10,11]. Better performances using carbon-based supports such as activated carbons, carbon nanotubes, and graphene have been demonstrated in SCR under excess oxygen and temperatures around 200°C [11]. We recently fabricated MnOx-CeOx nanoparticles supported on three-dimensional graphene aerogel (GA), i.e., MnOx-CeOx/GA, of different compositions and explored their SCR performances at low temperatures. The hierarchical pore structure in GA provides high surface area for anchoring nanoparticles and good accessibility for gases to the active surface. These structure and property merits render GA an ideal catalyst support. The novel nanocomposite catalysts MnOx-CeOx/ GA were subjected to systematic morphological, structural, compositional, and chemical analyses in order to gain insights of the key factors correlated with their catalytic activities
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