铱基双金属催化剂-复合氧化物无机透氢膜耦合催化碘化氢分解的研究

The hydrogen iodide (HI) decomposition is the key reaction to produce hydrogen in the iodine-sulfur (IS) thermochemical cycle which is a promising candidate for massive hydrogen production with high efficiency and without CO2 emissions. The catalysts play the important role in the HI decomposition because this reaction occurs hardly in the absence of catalysts. The supported monometallic Pt catalysts have been most generally used to catalyze this reaction. However, the stability and lifetime of the Pt catalysts are unsatisfactory because of the sintering of Pt particles in the reaction. In addition, the thermodynamic equilibrium conversion of HI decomposition is limited to a very low value, only about 23% even at 500℃. Therefore, the HI decomposition becomes one of the bottlenecks restricting the development of the IS cycle..Our previous studies showed that the Ir-based catalysts not only had the same activity as the Pt-based catalysts at high temperature (550-600℃) , but also presented the better stability than the Pt-based catalysts. In addition, modification of Ir metal catalysts by introduction of the second metals would appear the combination of high stability and good activity due to the cooperative interactions between the two metals. Therefore, the supported Ir-based bimetallic catalysts will replace the supported Pt catalysts to catalyze the HI decomposition. Furthermore, the composite oxides inorganic hydrogen permeation membranes would be used to separate the hydrogen during HI decomposition so as to promote the HI conversion to exceed the equilibrium value. In this project, first, a series of supported bimetallic catalysts (such as Ir-Pd, Ir-Ni and so on）will be prepared. Promotion effects of the second metals on the Ir-based catalysts in HI decomposition will be studied systematically. Second, the inorganic hydrogen permselective membranes (ZrO2-based and SiO2-based composite oxides membranes) will be synthesized. Effects of the composition, structure, surface morphology and pore size distribution on the stability and hydrogen separation characteristics of composite membranes in HI-H2-I2-H2O gaseous mixture will be studied in order to obtain the composite membranes with good stability, hydrogen permeance and separation factor. Third, the Ir-based catalysts and the inorganic hydrogen permeation membranes will be integrated into the membrane reactors for coupling catalytic HI decomposition. The effects of the application of the hydrogen permselective membrane on the HI decomposition will be evaluated. The reaction kinetics and the mechanism of HI decomposition in the membrane reactor will also be investigated. Finally, the HI conversion and the ratio of extracting hydrogen will be correlated with the preparation, composition, structure and properties of the bimetallic catalysts and composite membranes. The above studies may be helpful to improve the efficiency of HI decomposition, so as to promote the development of IS cycle.

碘硫循环热化学分解水制氢由于具有高效、无CO2排放等优点而有望成为一种大规模的制氢方法。碘化氢分解是其中的产氢关键步骤。目前最常用的负载铂催化剂能够在500℃使碘化氢分解，但金属铂会烧结引起催化剂失活；并且仅有23%的热力学平衡转化率限制了碘化氢的高效分解。.本课题从改善催化剂稳定性和打破热力学平衡考虑，提出采用铱基双金属催化剂和复合氧化物（氧化锆基和氧化硅基）无机透氢膜，来使催化反应和氢分离耦合促进碘化氢分解。针对催化剂和透氢膜的组成与制备工艺、结构与性能、膜催化反应器件的组装及耦合催化碘化氢分解机理、反应动力学等方面进行深入的应用基础研究，旨在探明影响催化剂性能、透氢膜氢分离性能、耦合催化效果的关键因素及其关联调控规律，力图在碘化氢分解新型催化剂设计、耦合催化新工艺与机理方面取得突破，为解决碘化氢分解存在的转化率低、催化剂稳定性差等问题提供理论基础和实践上的指导，从而提高总体制氢效率。

由本森反应、碘化氢分解和硫酸分解组成的碘硫热化学循环制氢由于具有高效、环境友好等优点而被认为是极具发展前景的大规模制氢方法之一。碘化氢分解是该循环的产氢单元，该部分能耗高、腐蚀性强，且碘化氢分解热力学平衡转化率较低，是制约碘硫循环发展的瓶颈之一。. 本课题从改善碘化氢分解催化剂稳定性和打破热力学平衡考虑，围绕铱基双金属催化剂、复合氧化物无机透氢膜和耦合碘化氢膜催化分解三个方面开展系统研究。（1）采用改进的浸渍方法制备了负载型单金属催化剂（Ir、Ni、Pd和Pt等）和系列不同组成的铱基双金属催化剂（Ir-Ni、Ir-Pd、Ir-Pt），利用BET、XRD、TEM、HTEM和XPS等技术对反应前后的催化剂进行了表征分析，通过碘化氢催化分解反应评价了催化剂的活性，获得了制备因素（如焙烧温度）、组成、反应温度等对催化剂的影响规律，最优双金属催化剂的组成分别是4%Pd-1%Ir/C, 2.5%Pt-2.5%Ir/C和10%Ni-1.5%Ir/C，表征结果表明双金属催化剂性能优于相应单金属催化剂原因可归结为双金属相互作用产生的合金效应。（2）采用浸渍提拉的方法，在陶瓷片或陶瓷管上成功制备了SiO2膜和SiO2-TiO2、 SiO2-ZrO2复合氧化物无极透氢膜，优化了制备工艺参数，研究了制备工艺参数及复合氧化物组成等因素对膜性能的影响，结果表明Zr/Si摩尔比为0.075：1的ZrO2-SiO2复合膜和Ti/Si摩尔比为0.1：1的TiO2-SiO2复合膜表现出优异的透气性能和透氢选择性。(3)设计并建立了膜催化研究平台，通过浸渍提拉法在三氧化二铝陶瓷管上制备了Ti/Si摩尔比为0.1：1的TiO2-SiO2复合氧化物透氢膜，将其与活性碳催化剂耦合催化碘化氢分解，膜催化碘化氢分解实验现象和分析结果都表明，膜催化碘化氢分解转化率超过了热力学平衡转化率。. 这些研究结果为解决碘化氢分解存在的转化率低、催化剂稳定性差等问题提供了理论和实践上的指导，进而为提高碘硫循环整体制氢效率，形成具有我国自主知识产权的碘硫热化学核能制氢新技术奠定了基础。