Simultaneous Control of NOx-Soot by Substitutions of Ag and K on Perovskite (LaMnO3) Catalyst

Abstract

The different Ag and K substituted perovskite catalysts including base catalyst were LaMnO3 by the solid state method and the diesel soot was prepared in the laboratory. Their structures and physicochemical properties were characterized by X-ray diffraction (XRD), BET, SEM, H2-TPR, and XPS techniques. The Ag Substituted at A-site perovskite structured catalysts are more active than other type of catalysts for the simultaneous soot-NOx reaction, When Ag and K are simultaneously introduced into LaMnO3 catalyst, soot combustion is largely accelerated, with the temperature (Tm) for maximal soot conversion lowered by at least 50 °C, moreover, NOx reduction by soot is also facilitated. The high activity of La0.65Ag0.35MnO3 perovskite catalyst is attributed to presence of metallic silver in the catalyst. The activity order of Ag doped LaMnO3 is as follows La0.65Ag0.35MnO3 > La0.65Ag0.2MnO3 > La0.65Ag0.4MnO3 > La0.65Ag0.1MnO3. The dual substitution of silver and potassium in place of La in LaMnO3 gives better activity than only silver doped catalyst. In a series of La0.65AgxK1-xMnO3, the optimum substitution amount of K is for x=0.25. The single and doubled substituted perovskite catalyst proved to be effective in the simultaneous removal of NOx and soot particulate, the two prevalent pollutants in diesel exhaust gases in the temperature range 350-480 °C.

Monitoring intermediate species formation by DRIFT during the simultaneous removal of soot and NOx over LaAgMnO3 catalyst

“…In general, it can be seen that all catalytic systems showed very good performance in soot oxidation compared to the non-catalytic one according to the following order in activity LaAgMnO3 (NO/O2) > LaMnO3 (NO/O2) > LaAgMnO3 (O2) > non-catalytic (NO/O2). Similar trends were obtained by Dhal et al [13], who evaluated the effect of Ag and K substitutions on LaMnO3 catalyst in the simultaneous removal of NOx and soot. They have found that soot combustion, as well as, the NOx reduction by soot greatly increase by the presence of metallic silver in the catalyst.…”

“…Exhaust-after-treatment devices and engine modifications have been implemented to reduce the NOx and soot emissions from diesel engines [5][6][7][8][9]. However, for the simultaneously removal of soot and NOx, it is not enough to consider only engine modifications, and the implementation of diesel particle filter combined with catalytic combustion technology appears to be the most practical method to reduce the emission of these harmful substances [9][10][11][12][13].…”

“…Generally, NO2-assisted catalytic combustion of soot (known as continuously regenerating trap-CRT) involves two steps. First, NO is catalytically oxidized to produce NO2, which is a strong oxidizer that reacts with soot collected on a filter placed downstream at a temperature much lower than that required for either NO and/or O2 combustion [9][10][11][12][13][14][15][16][17][18][19]. The main reaction products of the soot-NO2 reaction are NO and CO2, although few NOx can be reduced until N2.…”

Catalytic Soot Combustion─General Concepts and Alkali Promotion

“…The importance of the soot-to-catalyst ratio was systematically examined elsewhere . The effect of contact between soot and catalyst was specifically investigated in refs − , and a broad scope of the reported ranges of the soot-to-catalyst mass ratios can be classified into three arbitrary categories: Low soot content mixtures: 1:20, ,,,,, 1:19, and 1:15. , Medium soot content mixtures: 1:10, ,,,,,,,, 1:9, ,,,− ,,,, and 1:8. − High soot content mixtures: 1:5, 1:4, , and 1:1 …”

An Overview on the Catalytic Materials Proposed for the Simultaneous Removal of NOx and Soot

“…Additionally, the dual substitution of Ag and K in place of La in LaMnO 3 has been demonstrated giving improved activity in the simultaneous soot-NO x reaction [41]. As a matter of fact, soot combustion is largely accelerated, with the temperature for maximal soot conversion (T m ) lowered by at least 50 • C; moreover, the silver substitution at A site of perovskite increases the NO x reduction efficiency (Table 6).…”