Catalytic oxidation of diesel soot on mixed oxides derived from hydrotalcites

Abstract

MAlO (where M = Ni 2+ , Co 2+ and Cu 2+ ) mixed oxides derived from hydrotalcites and potassium-promoted MAlO catalysts (designated as K/MAlO; K: 5 wt.%) have been studied for diesel soot oxidation. The catalysts were characterized by XRD, N 2 adsorption, TPR, FT-IR and TPO techniques. The hydrotalcites calcined at 800°C have large surface areas in the range 17-88 m 2 / g and uniform mesoporous features, which resulted in high activity for diesel soot oxidation under the conditions of tight contact between soot and catalyst powders. Potassium increased the activity due to the improvement of surface mobility. The presence of NO x considerably enhanced the catalytic soot oxidation rate. The enhancement was attributed to the acceleration of soot oxidation due to NO 2 as a strong oxidizing agent and intermediates of nitrate and/or nitrite species formed on the catalyst surface.

Simultaneous soot combustion and nitrogen oxides storage on potassium-promoted hydrotalcite-based CoMgAlO catalysts

“…Although numerous investigations on the soot combustion catalysts have been conducted and theoretical models for NOx storage have been developed [4][5][6][7][8][9], some problems still remain. Among them, the too high temperature of soot combustion and the relatively low NOx storage capacity (NSC) are the main aspects.…”

Layered double hydroxide (LDH) derived catalysts for simultaneous catalytic removal of soot and NOx

“…A promising process to meet this demand is the simultaneous catalytic removal of NO x and soot. 17 Previous studies have shown that the oxidation of soot and the reduction of nitrogen oxides can be achieved in the same reaction temperature range. In addition, the existence of nitrogen oxides can lower the activation energy of soot combustion.…”

“…In the process of catalytic oxidation of soot, a high activity of the catalyst is a key factor. To date, various soot oxidation catalysts such as alkali metal titanates, 9 alkali metal zirconates, 10 alkali modified aluminosilicates, 11,12 transition metal oxides, [13][14][15][16] and rare earth-based catalysts 17 have been reported.…”

“…Copper-, cobalt-or nickel-based oxides derived from HT are known to be active catalysts for oxidation reactions. 17 On the other hand, some metals such as Mg and Ca are the storage center for NO x . In order to provide a clearer picture of this topic, we reviewed all the catalysts by classifying the LDH precursor according to the number of metals into binary, ternary, and quaternary, and discussed their advantages and disadvantages in detail.…”

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

“…LDHs represent suitable candidates for the simultaneous removal of NO x and soot, as summarized in Table 1. Being their catalytic activity strongly related to the nature of metals, their amount and calcination temperature, different formulations have been proposed and between them copper-, cobalt-, or nickel-based oxides have demonstrated high activity in oxidation reactions [19], like soot combustion. Moreover, it is well known that the addition of alkali oxides, and in particular K can further improve their activities favoring the reaction through the formation of low melting point compounds [20], or of eutectics with other catalyst components, thus improving the surface mobility of the active species [12,13,21] and hence favoring the soot-catalyst contact, which has been claimed as a key factor in the soot oxidation process.…”