Catalytic Reduction of Nitric Oxide with Carbon Monoxide as a Reducing Agent over Nanosized Supported Metallic oxide Catalysts

• Main Authors: Tzu-Chen Ko, 柯子真
• Other Authors: Hung-Shan Weng
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/41501110193379959832

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 91 === The nano-particle technology is appropriate for producing high performance catalysts. These catalysts process a markedly higher activity and selectivity compared with the conversional ones. The catalysts can be also used for reacton at a relativity low temperature, thereby reducing energy consumption. In this study, the performance of the supported metallic oxide catalysts for catalytic reduction of nitric oxide with carbon monooxide as a reducing agent were investigated. First, we prepared various kinds of supported metallic oxide catalysts. Then the activities of the prepared catalysts were evaluated by a packet-bed reactor. Then these prepared catalysts were characterized with TPD, TPO,TPR, XRD, SEM, TEM and BET in order to understand the effects of the catalyst characters on the catalystic activities. Finally, a kinetic study on the NO reduction over the best catalyst with CO as a reducing agent was carried out to figure out a suitable reaction mechanism. The experimental results indicate that active species, supports, the different method of making the support, calcination temperature, reducing pretreatment, different concentration ratio of reaction gas(CO/NO) and oxygen are important factors affecting catalyst activity. NiO/CeO2 is the most active catalyst among CeO2-supported single metal oxide catalysts (Fe2O3、NiO、MnO2、MoO3、Cr2O3、Co3O4、CuO). CuO/CeO2 is the second one. With NiO as the active species, CeO2 is also found to be the most suitable support. When changing nickel loading ratio in NiO/CeO2, we discover that the NiO/CeO2 catalyst with 5 wt % nickel is the most active. When we use different kinds of method of making nano-CeO2 to, we found that NiO/CeO2 whose CeO2 is made by citric-acid sol-gel is the most active. Knowing that the feed concentration ratio of CO to NO might affect the reduction of NO, three different feed concentration ratios (CO:NO=1：1, 1.5：1, 2：1, 3：1) were tested. When NiO/CeO2 with 5 wt % Ni as the catalyst for the reducing of CO, experimental results reveal that the feed concentration ratio of CO to NO being 2 provides higher conversion of NO. However, the 5 wt %Ni/CeO2 prereduced by CO or H2 provides a lower activity than those not pretreated with CO or H2. The addition of O2 in the course of reaction would result losing the conversion. Comparing the catalysts calcined at different temperatures reveals that the catalyst calcined at 500℃ is the most active. We could realize that area of NiO/CeO2 whose CeO2 was made by citric-acid sol-gel method is bigger by BET analysis. So NiO/CeO2 which is made by citric-acid sol-gel method would be more active than others made by another methods. CeO2 and two catalysts (NiO/CeO2 and CuO/CeO2) were characterized by NO-TPD. The desorption patterns exhibit that adding NiO or CuO on the CeO2 would make catalyst adsorption more NO. The results of CO-TPR further indicate that CuO supported by CeO2 (CuO/CeO2) will be reduced easily at lower temperature than NiO supported by CeO2 (NiO/CeO2). This result indirectly indicated why CuO/CeO2 would be more active than NiO/CeO2 at low temperature. By the XRD results, we could know that catalysts made by citric-acid sol-gel method could use to compare activity without making another crystal we don’t want. By the SEM and TEM Patterns, we could realize that we could get nano-CeO2 by citric-acid sol-gel method, precipitation method, reverse micell method and PAA sol-gel method to obtain our purpose. At the end of this study, a kinetic study on the NO reaction over the NiO/CeO2 catalyst with CO as a reducing agent was carried out to obtain a rate expression and to figure out a suitable reaction mechanism. We can realize that the reduced beginning temperature of NiO/CeO2 is similar to the activity beginning temperature of NiO/CeO2. And with the NO-TPO of the reduced NiO/CeO2 result, all phenomena shown that the reaction mechanism should be the Mars-Van Krevelen model. The results show that four models, Langmuir-Hinshelwood model-NO and CO adsorbed on two different kinds of active sites, Langmuir-Hinshelwood model-NO and CO adsorbed on the same kind of the active sites, Mars-Van Krevelen model and Eley Rideal model could fit well the data we obtained. Besides, Mars-Van Krevelen would fit best. With NO-TPD、 CO-TPD、 CO-TPR and NO-TPO results, all phenomena shown that the Mars-Van Krevelen model is the main reaction model for NiO/CeO2 using on NO reducing reaction with CO as a reducing agent.