金属氧化物担载非贵金属纳米催化剂用于乙醇水蒸气重整制氢

发布时间：2018-03-31 12:02

本文选题：乙醇　切入点：制氢　出处：《天津大学》2015年博士论文

【摘要】：乙醇水蒸气重整制氢的技术核心是催化剂的研发,文献报道的催化剂具有很好的活性和氢气选择性,近几年来研究重点主要集中在提高催化剂稳定性上。低温下反应后积碳沉积和高温下活性组分烧结是导致催化剂失活的主要原因。针对乙醇重整的积碳和烧结问题,本论文提出了两种催化剂的设计思路以期改善催化剂的稳定性:一种是选择具有氧空位的氧化物作为催化剂载体;另一种制备成负载型双金属催化剂,考察了催化剂结构与性能之间的关系。首先分别利用柠檬酸络合法和改性浸渍法制备Ni-La-Ce三元氧化物。制备方法对催化剂结构影响很大。两种方法制备的催化剂用于乙醇水蒸气重整反应都能表现出很好的活性和氢气选择性,柠檬酸络合法制备的催化剂在反应温度为650°C,水醇比为3和空速为180,000 ml·gcat-1·h条件下反应8h后催化剂没有出现失活,该催化剂能表现出更好的稳定性是由于其具有更丰富的氧空位,提高了催化剂抗积炭性能。然后利用LaCoxNi1-xO_3作为前驱物,由于钙钛矿LaCoxNi1-xO_3中钴离子和镍离子还原性质相近,能同时从钙钛矿结构中还原成金属,XRD、TPR和TEM等表征结果表明还原后形成了Ni-Co合金颗粒。由于大部分金属离子都能形成钙钛矿结构,通过调控金属离子还原可以制备其他多种负载型纳米双金属或多金属催化剂。与文献中报道的催化剂性能相比较,La CoxNi1-xO_3用于乙醇水蒸气重整反应中表现出较好的活性和稳定性。550°C反应10h后催化剂表征结果显示富Ni催化剂反应后以纤维状积碳为主,金属颗粒位于纤维状积碳末端,可以暴露出活性位,不会造成催化剂快速失活;而富Co催化剂反应后主要生成无定型积碳,该种类型积碳会包裹住金属颗粒,导致催化剂严重失活。在700°C反应30h,所制得的催化剂都能表现出很好的稳定性,且双金属催化剂的抗烧结性能优于单金属催化剂。最后以CuO/LaNiO_3和CuO/LaCoO_3为前驱物制备了负载型的Cu-Ni和Cu-Co催化剂。在前驱物中CuO能高分散在钙钛矿表面,且其在较低温度下就能还原成金属铜,钙钛矿结构抑制了金属离子的还原,钙钛矿中镍离子或钴离子需要在较高温度下才能还原成金属单质,生成的金属Ni或Co聚集在优先还原生成的金属Cu表面,构筑成类似核壳结构的双金属颗粒。所制得的催化剂用于乙醇水蒸气重整反应能表现出较好的催化性能。
[Abstract]:The key technology of ethanol steam reforming to produce hydrogen is the research and development of catalyst. The catalyst reported in the literature has good activity and hydrogen selectivity. In recent years, the main research focus is on improving the stability of the catalyst. The carbon deposition after reaction at low temperature and the sintering of active components at high temperature are the main reasons leading to the deactivation of the catalyst. In this paper, two kinds of catalysts are proposed to improve the stability of the catalyst: one is to select oxide with oxygen vacancy as the catalyst carrier, the other is to prepare the supported bimetallic catalyst. The relationship between catalyst structure and performance was investigated. Firstly, Ni-La-Ce ternary oxide was prepared by citric acid complexation method and modified impregnation method respectively. The preparation method has great influence on the structure of the catalyst. In the steam reforming of ethanol, both of them showed good activity and hydrogen selectivity. The catalyst prepared by citric acid complexation method showed no deactivation after 8 h reaction under the conditions of reaction temperature of 650 掳C, ratio of water to alcohol of 3 and space velocity of 180000 ml gcat-1 h. The catalyst showed better stability because of its abundant oxygen vacancy. LaCoxNi1-xO_3 was used as precursor because the reduction properties of cobalt ion and nickel ion in perovskite LaCoxNi1-xO_3 were similar. The characterizations of XRDX TPR and TEM from perovskite structure show that Ni-Co alloy particles are formed after reduction. Because most metal ions can form perovskite structure, Various other supported nanometer bimetallic or polymetallic catalysts can be prepared by regulating metal ion reduction. Compared with the reported catalysts reported in the literature, La CoxNi1-xO_3 shows better activity in ethanol steam reforming reaction. The results of catalytic characterization of Ni rich catalyst after 10 h reaction showed that fibrous carbon deposition was dominant in Ni rich catalyst. Metal particles are located at the end of fibrous carbon deposition, which can expose the active sites and do not cause rapid deactivation of the catalyst. However, Co-rich catalysts mainly form amorphous carbon deposits, which cover the metal particles. The catalyst was deactivated seriously. At 700 掳C for 30 h, the prepared catalyst showed good stability. Finally, supported Cu-Ni and Cu-Co catalysts were prepared by using CuO/LaNiO_3 and CuO/LaCoO_3 as precursors. In the precursor, CuO can be highly dispersed on perovskite surface. The structure of perovskite inhibits the reduction of metal ions, and the nickel or cobalt ions in perovskite can be reduced to metal elements at a higher temperature. The metal Ni or Co was formed on the surface of Cu which was preferentially reduced to form bimetallic particles similar to the core-shell structure. The catalysts obtained showed good catalytic performance for the steam reforming of ethanol.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：O643.36;TQ116.2

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