Selective catalytic reduction

About: Selective catalytic reduction is a research topic. Over the lifetime, 10502 publications have been published within this topic receiving 226291 citations.

High efficiency conversion of nitrogen oxides in an exhaust aftertreatment device at low temperature

Abstract: A system and method for delivering reductant to a lean NOx catalyst receiving exhaust gases from an internal combustion engine operating at a lean air-fuel ratio in disclosed. Reductant supply is based on an amount of reductant stored within the catalyst. Furthermore, reductant is supplied under prescribed conditions including an exhaust gas concentration upstream of the catalyst of less than 25 ppm NOx or the catalyst at a temperature greater than 300° C.

Cobalt doped CuO nanoparticles as a highly efficient heterogeneous catalyst for reduction of 4-nitrophenol to 4-aminophenol

Abstract: We present here a simple thermal route for synthesizing 5.1 wt% cobalt doped CuO nanoparticles (NPs) as the optimized composition of the best heterogeneous CuO catalyst for catalytic reduction of toxic 4-nitrophenol to industrially beneficial 4-aminophenol. The reduction is completed in merely 3 min in the presence of 8 mM NaBH4 as reducing agent. The optimized catalyst dose was 2 mg/L for converting 0.12 mM 4-nitrophenol and the corresponding rate constant (k) for reduction reaction was 43.8 × 10−3 s−1 per mg of catalyst. The catalytic reduction reaction was monitored by UV–vis spectroscopy method and by HPLC analysis. The mechanism is discussed in the light of hydride transfer phenomenon facilitated by large surface area and positive surface charge of the cobalt doped CuO nanoparticles. The cobalt doping resulted in: (a) increasing surface area due to decrease in particle size of the CuO NPs to 10 nm, measured by HRTEM; (b) improve stability of the cobalt doped CuO NPs. The cobalt dopant occupied the grain boundaries of CuO to reduce the particle size as derived from positron annihilation lifetime spectroscopy. The X-ray photoelectron spectroscopy analysis of unused catalyst and the spent catalyst revealed occurrence of Co2+ and Co3+ states at the surface. While the X-ray diffraction studies of spent catalyst confirmed the inhibition of reduction of the surface CuO to metallic copper in the presence of NaBH4, attributable to cobalt doping. It was concluded that cobalt doping led to stable and efficient CuO NPs as catalyst for reduction reaction.

Characterization of highly active silver catalyst for NOx reduction in lean-burning engine exhaust

Abstract: A new Ag/Al2O3 catalyst for removing NOx in lean exhaust gas was developed. Oxidized Ag/Al2O3 catalyst is highly active for reduction of NOx with ethanol and propene, whereas reduced Ag/Al2O3 catalyst is less active for these reactions. Selectivity to N2 is also high on the oxidized Ag/Al2O3 compared to that on the reduced Ag/Al2O3. XRD and SEM studies of these two types of Ag catalysts suggest that oxidation induces an interaction between Ag and the support, where the particles are grown in large size. In contrast, the metallic Ag particles are finely dispersed by the reduction process. Although dispersion of Ag particles is decreased by the oxidation process, the catalytic activity is increased. This suggests that the Ag-alumina sites created in the high temperature oxidizing environment are active in catalytic reduction of NOx.