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Fabrication And Performance Of Modified Pt-based Catalysts For Ammonia Oxidation

Posted on:2015-01-30Degree:MasterType:Thesis
Country:ChinaCandidate:B J LiFull Text:PDF
GTID:2271330482979037Subject:Environmental engineering
Abstract/Summary:PDF Full Text Request
Recent years, excessive emissions of ammonia -containing wastewater has caused environmental deterioration. Hence, it is important to develop a highly efficient technology for ammonia-containing wastewater treatment. Electro-oxidation is a mild process, which is simple to handle and easy to control, and thus it has attracted much attention. The investigation of the electrode materials (with Pt as the most active one) remains a hot point. However, the application of ammonia electro-oxidation technologies have been strongly hindered by the insufficient performance and high cost of Pt. Accordingly, the development of Pt-base materials with improved activity and poisoning resistance is of paramount importance.In this paper, we adopted a simple and facile electrochemical method to fabricate a modified Pt-base catalysts. Therein CeO2, a rare-earth metal oxide, was applied as the modified material, Pt the active component and glassy carbon electrode (GCE) the substrate. SEM and ICP methods were applied to analysis the morphology and component of the catalysts. The preparation condition in this paper was optimized according to the ammonia oxide peak in CV.In addition, CV and I-t method was utilized to analysis the electrochemical ability of Pt-based catalysts. Major results are listed as follows:(1) By using CV method, Pt and CeO2 was co-electrodeposited onto GCE to prepare Pt-CeO2/GCE. CVs of the modified electrode in ammonia solution indicate it have an excellent electro-catalytic activity for ammonia. According to the feedback from ammonia oxide peak in CV, Preparation conditions was optimized the by changing the concentration of Ce (NO3)3 and scanning laps.(2) The morphology and component of the catalysts was analyzed through SEM and ICP methods. The result of SEM indicate that the modified CeO2 changed morphology and size of Pt. Spherical Pt particles changed into smaller sheet-like pieces. Therefore the introduction of CeO2 increased Pt dispersion and decreased Pt particle size. The Pt-loading and CeO2 was calculated according to the result of ICP, thus could normalize the ESA and catalytic activity of Pt later.(3) The result of electrochemical test in H2SO4 solution by different catalytic indicate that CeO2 modified Pt-based catalysts have higher ESA. When put in ammonia solution for 50 cycles, ESA of Pt-CeO2GCE lose much fewer than Pt/GCE. By comparing the electrochemical behavior of Pt/GCE and Pt-CeO2/GCE for ammonia in alkaline, we found that the introduction of CeO2 enhanced the electro-catalytic activity, long-term stability (durability), and deactivation resistance of Pt. This may due to the strong interaction between Pt and CeO2 improved the performance of Pt. In addition, the peak current of ammonia is linear to the square root of scanning rate suggesting that the redox process of ammonia on Pt-CeO2/GCE is diffusion-controlled, while the peak potential is proportional to the Log Koc of scanning rate indicating that the redox process is irreversible.(4) Removal experiment of ammonia was conducted on Pt-CeO2/GCE at different voltages, different KOH concentrations and different initial ammonia concentration. The best removal rate of 32% occur when applied -0.4V. The CVs in various concentrations of KOH indicate a competitive adsorption between OH- and ammonia on Pt. And the most NH3 was removed when the concentration of KOH was 1.0 mol L" 1. While when Pt-CeO2/GCE was put in different ammonia concentrations to reaction for a fixed time,the highest removal rate of 95.91% in 20 mg L-1 ammonia suggesting that Pt-CeO2/GCE may be more suitable for low concentrations.In conclusion, by using electrochemical method, the modified CeO2 and active component Pt was co-electrodeposited onto GCE to prepare a new Pt-based catalytic material with improved activity, stability (durability) and deactivation resistance. This findings were expected to provide a method for preparing low cost, high deactivation resistance noble metal catalytic for electro-oxidation of ammonia.
Keywords/Search Tags:Ammonia, Eletro-oxidation, Platinum, ceria
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