Performance For NO Reduction Research Articles

Effects of sodium modification, different reductants and SO 2 on NO reduction by Rh/Al 2O 3 catalysts at excess O 2 conditions

Although many catalysts of NO reduction have been developed, the presence of excess O 2 and SO 2 significantly inhibits their performance when they are used to treat the incineration flue gas. To solve such problem, this study prepared new Rh/Al 2O 3 catalysts and investigated the effects of Na modification, SO 2 and different reductants. Experimental results indicated that the average removal efficiency of NO at such high O 2 concentrations exceeded 80% when the Rh/Al 2O 3 catalysts were used. CO was a better reductant than C 3H 6 and the best concentration ratio of reductant/NO was equal to 1. Adding Na to modify Rh/Al 2O 3 catalysts significantly enhanced the removal efficiency of NO from 80 to 99% at 250–300 °C, especially at relative high SO 2 concentrations. Unfortunately, Rh–Na/Al 2O 3 catalysts do not have long-time activities for NO reduction, possibly because of the formation of NaNO 3. Both Rh/Al 2O 3 and Rh–Na/Al 2O 3 catalysts have good performance for NO reduction, they can feasibly be used to reduce NO in the flue gas from waste incineration.

Structure of Ga2O3-Al2O3 prepared by sol–gel method and its catalytic performance for NO reduction by propene in the presence of oxygen

Catalytic performance of Ga2O3-Al2O3 prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was investigated. The activity of Ga2O3-Al2O3 increased with an increase in Ga2O3 loading up to 50wt.%, and then decreased after that. The same tendency was observed for the specific activity normalized by BET surface area. The possibility of a synergistic effect between Ga2O3 and Al2O3 was suggested. X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) revealed that a composite oxide in the form of [GaxAl(1−x)]2O3 (x<1) is uniformly formed by substitution of Ga3+ for Al3+ in the Al2O3 lattice. A reaction pathway in which nitrate species (NO3−) formed on the catalyst surface is reduced to nitrogen by the reaction with propene was proposed on the basis of the experimental results of in situ Fourier transform infrared (FT-IR) spectroscopy.

Thermally stable alumina–gallia aerogel as a catalyst for NO reduction with C3H6 in the presence of excess oxygen

In order to improve thermal stability, an alumina–gallia aerogel was prepared and the catalyst performance for NO reduction with C3H6 was compared with that of an alumina–gallia xerogel. Basically, both were prepared by a sol–gel method with supercritical drying for the former, while with oven drying for the latter. Upon heating at 800, 900, and 1000 °C, the aerogel exhibited higher NO conversion than the xerogel at reaction temperature 500 °C. At 450 °C, NO conversion was almost the same for these two catalysts. A marked difference was observed upon heating them at 1100 °C: the aerogel still maintained quite a high activity, while the xerogel greatly lost it. After heating the aerogel at 1100 °C, γ-phase alumina remained untransformed with its surface area of 80 m2/g, while the xerogel was completely transformed to α-alumina with its surface area of 6 m2/g. The high activity remaining on the aerogel heated at 1100 °C was ascribed to its large surface area.

The characteristics of a copper-exchanged natural zeolite for NO reduction by NH 3 and C 3H 6

The catalytic performance of the natural zeolite mined from Youngil, Korea was investigated when two types of reductant such as NH 3 and hydrocarbons were employed for the reduction of NO. The determination of the structure of the natural zeolite has also been made to identify the type of zeolite and to examine its use as a catalytic material for NO removal reaction. The elementary analysis and electron probe microanalysis of the zeolite revealed that it typically consisted of an aluminosilicate. Although it mainly contains mordenite-type zeolite, heulandite was also included as well as the phases of quartz and feldspar as an impurity in the zeolite. This result could be also confirmed by the X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses. It should be noted that the acid treatment of the natural zeolite for its use as a catalytic material is essential for the high performance of NO reduction by selective catalytic reduction (SCR) technology. Copper ion-exchanged natural zeolite catalyst (CuNZA) exhibits a competitive NO reducing activity for the reduction of NO by NH 3 as well as hydrocarbons. It can be regarded as a promising catalytic system by NH 3 and hydrocarbons for the removal of NO x from stationary and mobile sources.