La_ (0.7) Sr_0.3Co_ (1-x) Fe_xO_3 rare earth perovskite oxides of nitrogen and sulfur trap NO_x storage properties

Title: La_ (0.7) Sr_0.3Co_ (1-x) Fe_xO_3 rare earth perovskite oxides of nitrogen and sulfur trap NO_x storage properties
　　Authors: Shao-Zeng
　　Degree-granting units: Tianjin University
　　Keywords: sol-gel method;; perovskite;; NOx storage;; sulfur
　　Summary:
　　First, the sol - sol-gel method different pH values ​​(pH = 4.6 and 9) of the catalyst precursor, and were used to muffle and tube furnaces were prepared by two different roasting La0.7Sr0.3Co1-xFexO_3 (x = 0, 0.2) series of samples, found that Fe element was added to make reunion of perovskite increased surface area decreased, the generation of samples SrCO_3 Neodymium magnets reduced. For La_ (0.7) Sr_ (0.3) Co_ (0.8) Fe_ (0.2) O_3 sample, using the tube furnace samples calcined at pH = 9, the formation of uniform particles with diameters in the 40 ~ 80 nm or so, has the largest surface area ( 21.9 m2 / g), a more complete mineral perovskite phase structure, SrCO_3 further decline in the generation, has good performance of NOx storage and oxidation.
　　For security reasons, determined by TG-DTA experiments, a first pre-300 oC in a muffle furnace, and then calcined in a tube furnace method of preparation of the new roasting two different pH values ​​of La_ (0.7) Sr_ (0.3) Co_ (0.8) Fe_ (0.2) O_3 samples. Catalyst XRD and SEM results show that the new method of preparation of the samples calcined at a greater surface area and better particle morphology, about 80 nm in diameter, SrCO_3 generation capacity less. Storage experiment found that two samples have a higher amount of NOx storage and NO conversion, which NSC pH = 9 sample maximum value (378μmol / g), the maximum NO conversion rate (69.8%). The SO_2 pretreatment, particle morphology of both samples showed no significant change, NSC has not decreased significantly, showing good anti-sulfur performance, including sample pH = 9 NO conversion remained unchanged before and after curing. Combination of FT-IR, H2-TPR, O_2-TPD and XPS analysis of means to get the following results: a new method of preparation of the catalyst in the formation of carbonate rarely, NOx nitrate mainly in bulk form (only the 1380 cm-1 IR vibration peak) stored in the surface of the perovskite phase, curing, it only formed a small amount of bulk sulfate, the active catalyst bulk storage remain intact, even after it has cured a large storage capacity and higher NO conversion rate.
　　Finally, pH = 9 samples for replacing different proportions of Fe and Fe = 0.2 samples for the depth of sulfide was found to increase with the proportion http://www.chinamagnets.biz/ of Fe to replace, the NSC decreased, and when replacing Fe ratio greater than or equal to 0.2, the catalyst it has a strong anti-sulfur ability. Fe = 0.2 samples after curing depth, the perovskite structure have been varying degrees of damage, the active sulfur species play a role of catalyst to poisoning inactivation, leading to curing depth of the sample in the conversion of NO and NOx storage capacity are produced dropped significantly. This may be due to NOx storage catalyst in the process of perovskite are "gas - solid" phase reaction, NOx active center of the main storage exists in the perovskite structure of the surface rather than bulk, long-term exposure to SO_2/O_2 atmosphere, perovskite surface was cause serious sulfate, although there are still a lot of body phase perovskite phase, but increase the amount of NOx storage contribute little, so after a long curing perovskite catalysts after the NOx storage performance significantly.
　　Degree Year: 2010