Novel Pd promoted Ag/Al2O3 catalyst for the selective reduction of NOx

Abstract

A novel palladium promoted Ag/Al 2 O 3 catalyst (denoted Ag-Pd/Al 2 O 3 ) has been developed for the selective catalytic reduction of NO by C 3 H 6 . The Ag-Pd/Al 2 O 3 shows a higher NO x conversion than Ag/Al 2 O 3 , especially at the temperatures ranging from 300 to 450 • C. The addition of a small amount of Pd (0.01 wt.%) to Ag/Al 2 O 3 is considered to be favorable for the partial oxidation of C 3 H 6 . In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) suggest that the presence of Pd catalyzes the formation of enolic species which is converted from C 3 H 6 . The enolic species is very active towards NO 2 and NO 3 − , resulting in the formation of -NCO species which is the key reaction intermediate in the selective catalytic reduction of NO.

Selective catalytic reduction of NOx with C3H6 over an Ag/Al2O3 catalyst with a small quantity of noble metal

“…In this case, noble metal is one of the candidates because Obuchi et al [13] have found that NO is reduced with C 3 H 6 at lower temperatures over noble metal catalysts such as Pt/Al 2 O 3 and Pd/Al 2 O 3 . With respect to Ag catalysts, we previously found that the C 3 H 6 -SCR of NO x over the Ag/Al 2 O 3 catalyst was effectively enhanced below 500 • C even in the presence of water vapor by the addition of trace Pd [15,16]. The positive effect of Pd was also reported by Masuda et al [17] using Ag-Pd/mordenite.…”

“…The biggest difference is the intensity of peak at 1637 cm −1 on the Ag-Pd/Al 2 O 3 catalyst. According to our previous work [16,26,27], the peak at 1637 cm −1 in Fig. 7 can be assigned to a surface enolic structure (H 2 C=CH-O-M + ) which derived from the partial oxidation of C 3 H 6 .…”

“…According to the previous literatures [8,19,20], the bands at 1304, 1556, and 1610 cm −1 were attributed to bidentate, monodentate, and bridge nitrates, respectively. The bands at 1394 and 1377 cm −1 were attributed to δ(-CH 3 ) and δ(-CH 2 ) of adsorbed acetate [16,21]. The peaks at 1572 and 1466 cm −1 were assigned to ν as (COO) and ν s (COO) of the adsorbed acetate [19][20][21][22][23][24].…”

Poisoning effect of sulphate on the selective catalytic reduction of NO by C3H6 over Ag-Pd/Al2O3

“…The Ag/Al 2 O 3 (Ag 5 wt%) and Ag-Pd/Al 2 O 3 (Ag 5 wt%, Pd 0.01 wt%) catalysts were prepared by the impregnation method described in our earlier paper [8]. The poisoned Ag/Al 2 O 3 and Ag-Pd/Al 2 O 3 were prepared in the flow of 80 ppm SO 2 at 723 K for 10 h.…”

“…However, the activity of Ag/Al 2 O 3 at low temperatures needs to be improved for practical usage. Our recent work [8] showed that the addition of 0.01 wt% Pd into the 5wt% Ag catalyst (denoted as Ag-Pd/Al 2 O 3 ) increases its catalytic activity for the SCR of NO x at low temperatures; however, our work also showed the weak sulphur tolerance of the Ag-Pd/Al 2 O 3 catalyst in the presence of SO 2 [9]. It should be noted that the presence of SO 2 in the various exhausts is another serious problem in catalytic after-treatment [10].…”