Catalytic Oxidation of Toluene Over LaNixB1-xO3 (B=Co, Cu) Perovskite Catalysts

: A series of LaNi x B 1 - x O 3 (B=Co, Cu) perovskite catalysts were prepared by 18 sol - gel method and employed in toluene degradation. The catalysts were characterized 19 by XRD, UV - Vis, SEM and XPS to investigate crystal structure, morphology and 20 composition of the catalyst. The effect of different calcination temperatures and time 21 on the performance of perovskite catalysts for toluene degradation were investigated. 22 And the CO 2 selectivity was also carried out on as - prepared catalysts. The results 23 showed that a small amount of Co - doping in B site of LaNiO 3 could significantly 24 improve its toluene degradation, while the substitution of Ni with Cu could not 25 effectively enhance its activity. When the Ni/Co molar ratio in LaNi x Co 1 - x O 3 26 perovskite was 3:1, LaNi 0.75 Co 0.25 O 3 catalyst exhibited the best activity, and it showed 27 relatively short time and low temperature for toluene conversion of 100%. Therefore, 28 LaNi 0.75 Co 0.25 O 3 catalyst has a broad prospect in the degradation of volatile organic 29 pollutants.

and Ni) were prepared by sol-gel method. The structure, morphology, element valence, 72 and oxidation properties of as-prepared La-series perovskites were first investigated.

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And then, their catalytic activity and CO2 selectivity were compared by toluene 74 degradation. On this basis of the experimental results, the possible formation 75 mechanism was also put forward finally. The purpose is to explore the preparation 76 conditions of the appropriate ABO3 perovskite, and to select the LaBO3 perovskite 77 with the best degradation rate of toluene, which is of great significance for the 78 degradation of volatile pollutants in daily life.  C6H8O7·H2O as a complexing agent was first mixed evenly, 6 g of PEG as a 92 dispersant was also added dropwise into above mixture, then about 150 mL of 93 anhydrous as a solvent was poured into it, followed by stirring to dissolve completely.

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The resulting solution was heated at a constant temperature of 85 ºC to obtain gel, 95 which was transferred into a crucible for preheating to remove the citric acid, and then    The toluene conversion rate and CO2 yield can be calculated as follows:           degradation rate of 100%. Although the degradation rate at 700 ºC is higher than 600 259 ºC, the reaction temperature required to reach the conversion rate of 100% is not 260 much different. On the contrary, when the calcination temperature is 500, 400, and 261 300 ºC, the degradation rate of toluene at the same reaction temperature is 262 significantly reduced due to non-catalytic effect of La on the toluene degradation.

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Obviously, the reaction temperature required to reach the highest conversion rate for 264 LaNiO3 catalysts with calcination temperatures of 500, 400 and 300 ºC is much higher.

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In addition, according to XRD pattern in Fig. 1B, the shorter the calcination time at 266 the calcination temperature of 700 ºC, the more impurities will be produced, and the 267 yield of LaNiO3 will undoubtedly decrease, which will also affect the catalytic 268 performance of the as-prepared catalysts. In order to verify the above deduction, the 269 activity of LaNiO3 prepared at different time is compared in Fig. 7B. It is obvious that 270 LaNiO3 prepared at 5, 6, and 7 h has similar catalytic effect on toluene degradation， 271 while the degradation rate of toluene over the catalyst prepared at 3 and 4 h is slower.

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Combining the catalytic activity and XRD results. The calcination temperature of 700 273 ºC and calcination time of 7 h were selected in this work so as to pursue a higher 274 toluene conversion rate at the same temperature.   Fig. 9A is CO2 selectivity of LaNixCo1-xO3 catalyst. Still the 300 CO2 selectivity of LaNixCo1-xO3 gradually increases from 0% to 100% as the reaction 301 temperature increases. Among which, the CO2 selectivity of LaNi0.75Co0.25O3 is the 302 best, and the CO2 selectivity of other LaNixCo1-xO3 also corresponds to its activity.

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However, it is worth noting that the initial reaction temperature of the CO2 selectivity 304 of each catalyst from 0% is higher than that of degradation rate of toluene. This is 305 because toluene degradation has intermediate products instead of being converted to 306 CO2 at the beginning of degradation. Similar as LaNixCo1-xO3, the CO2 selectivity of 307 LaNixCu1-xO3 corresponds to its activity. As shown in Fig. 9B, the CO2 selectivity of 308 LaNiO3 is the best, followed by LaNi0.75Cu0.25O3 and La2CuO4 again, the worst is 309 LaNi0.5Cu0. 5O3. From what has been discussed above, LaNi0.75Co0.25O3 exhibited the 310 best CO2 selectivity.

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