Advantages of High-Siliceous Zeolites in the Reactivity and Stability of Diesel Oxidation Catalysts

Abstract

This study demonstrates a comparison of oxidation performance and sulfur poisoning/regeneration between zeolite- and alumina-supported Pt catalysts for their use as diesel oxidation catalysts (DOC). All three Pt/zeolite catalysts (β, Y, and ZSM-5) with a high siliceous content (SiO2/Al2O3 = 211–243) prepared by incipient impregnation had an average size of Pt particles from 15 to 24 nm after degreening at 700 °C. The Pt/BEA catalyst not only outperformed the benchmark Pt/Al2O3 in terms of the conversion and T 50 (e.g., lower by 13 and 72 °C for CO and C3H8, respectively) but also exhibited more stable conversion than the benchmark Pt/Al2O3 during five cycles of the activity test. All zeolite-based catalysts exhibited significantly higher conversions of C3H8 than Pt/Al2O3 possibly because of the better confinement of C3H8 in the zeolite pores in Pt/zeolites than Pt/Al2O3. SO2 inhibited the oxidation of CO and NO but promoted the oxidation of C3H8. Pt/zeolites were more susceptible to the poisoning with SO2 than Pt/Al2O3; nevertheless, they could be effectively regenerated in the same way as Pt/Al2O3. Another beneficial aspect of Pt/BEA was that it regained NO oxidation activity faster than Pt/Al2O3 when stopping the exposure to SO2.

The Effect of Pt/Pd Ratio on the Oxidation Activity and Resistance to Sulfur Poisoning for Pt-Pd/Bea Diesel Oxidation Catalysts with High Siliceous Content

“…These results suggest that Pt1 was more active than the Pd1 catalyst for CO oxidation under the reaction conditions in this study. Furthermore, in our previous work, we found that the T 50 of the second cycle was 206 and 245 • C for the Pd1 and Pt1, respectively, which were prepared by wet impregnation instead of incipient impregnation [32]. Both samples of the Pd1 had similar T 50 values regardless of the preparation method whereas the Pt1 prepared with the incipient impregnation showed a substantially lower T 50 value than the one prepared by wet impregnation.…”

“…b Determined with CO chemisorption measurements and the size for a spherical particle. c Data was cited from our previous work [32]. Therefore, it is not surprising the XRD showed only a metallic phase [40].…”

“…A commercial beta zeolite (CP811C300, H + form) purchased from Zeolyst was used as the support for the preparation of the catalysts. The silica-alumina ratio (SiO 2 /Al 2 O 3 ) determined by elemental analysis (ICP-SFMS) was approximately 217 [32]. The zeolite was calcined at 550 • C for 6 h and denoted as H-BEA.…”

“…Five catalysts with different loadings of Pt and Pd were prepared using an incipient impregnation method. Firstly, 2 wt% Pt/BEA and 1.1 wt% Pd/BEA which have the same total molar number of Pt and Pd were prepared using the same protocol described in our previous work [32]. The catalysts were dried in air at 80 • C for 24 h and then calcined at 550 • C for 2 h with a heating rate of 5 • C min − 1 .…”

“…In our previous study, we found that the use of beta zeolite as a support, in particular the one with high silica-alumina ratios, can enhance the oxidation performance of the DOC [31]. Especially, Pt/BEA was the promising catalyst in terms of the oxidation activity and sulfur regeneration, because it exhibited better performance than the benchmark Pt/Al 2 O 3 and other zeolite-based catalysts (Pt/ZSM-5 and Pt/Y) for CO, NO, C 3 H 6, and C 3 H 8 oxidation [32].…”