【作者】 陈云；

【导师】 岑可法； 周俊虎； 王智化；

【作者基本信息】 浙江大学 ， 工程热物理， 2010， 博士

【摘要】 氢气由于具有资源丰富,来源多样性,环保再生,安全可储存等优点被认为是一种理想的能源载体,正在越来越引起社会各界的关注。利用氢能首先需要制取氢气,因此大规模低成本制氢是发展氢能经济的基础。热化学循环水分解制氢技术是一种较理想的清洁可持续制氢技术,其利用一系列热化学反应,最终将水分解为氢气和氧气。热化学分解水制氢的方法诸多,已见报道的就有100多种,热化学硫碘循环由于其高热效率,低成本等优势而较易实现工业大规模生产被作为制氢的理想循环。热化学硫碘循环系统主要包括三个反应过程：Bunsen反应过程：x12+SO2+2H20=2HIx+H2SO4HI分解过程：2HIx=xI2+H2H2SO4分解过程：H2SO4=SO2+H2O+O2结合中国国情,(1)作为SO2来源的硫铁矿资源丰富、价格便宜；(2)除氢气以外的产品硫酸有很好的经济和市场价值,我们提出了热化学硫碘开路循环联产氢气和硫酸的多联产系统。该系统主要包含以下两个主要反应过程：Bunsen反应过程：x12+SO2+2H2O=2HIx+H2SO4HI分解过程：2HIx=xI2+H2以上两个系统中,HI的分解过程均作为唯一的产氢步骤,其分解率直接影响到系统的热效率和产氢速率。通过模拟和实验研究发现,HI的均相分解率极低,这意味着在实际的工业应用中,需要通过催化剂来促进HI的分解。我们小组在之前的HI催化分解研究中,制备了一系列CeO2,Pt/Ce-Zr和Ni/Ce-Zr催化剂,并对这些催化剂做了详细的活性评价和表征研究,提出了相应的催化反应机理。为了得到更加高效而廉价的催化剂,本文以活性炭为基础,对其进行酸处理,氧化处理,热处理及金属负载处理等一系列改性处理,得到高效的HI分解催化剂。将不同原料水蒸气制备活性炭催化剂的活性进行对比,同时通过一系列催化剂表征发现：高碳、低灰分且孔隙结构发达的AC-CS和AC-STONE催化活性最高,孔隙结构不够发达的AC-BAMBOO和灰分含量较高AC-COAL催化活性相对较差,含碳量最低且灰分含量较高AC-WOOD催化活性最差。将不同制备方法木质活性炭催化剂的活性进行对比,同时通过一系列催化剂表征发现：含碳量最高的AC-WH,其催化活性也最高。因此推测高的含碳量,低的灰分,合适的孔隙结构对HI催化分解活性有利。对煤质活性炭进行了非氧化性酸(HCL和HF)处理后,对比其活性及表征结果后发现：灰分最低的COAL-CLF具有最高的催化活性。因此降低灰分可以有效提高活性炭催化活性。对COAL-CLF进行了氧化性酸(HNO3)处理后,对比其催化活性及表征结果后发现：表面含氧基团最少的COAL-CLF具有最高的催化活性。因此氧化处理会降低活性炭的催化活性。对AC-WH分别在氮气和氢气气氛下进行了不同温度的热处理后,对比其活性及表征结果后发现：随着热处理温度的上升,表面含氧基团数量下降,碱性增强,催化活性增加。因此热处理提高了活性炭的催化活性。在以上实验结果及分析的基础上,首次提出了活性炭催化分解HI机理。对五种物化特性各异的活性炭进行Pd改性,对比其活性变化及表征结果后发现：与改性前的活性炭相比,Pd/AC催化剂的催化分解HI的活性大幅度提高了。Pd分散度的变化对H1分解催化活性的影响比活性炭自身物化特性的变化带来的影响大。对经过非氧化性酸(HCL和HF)的煤质活性炭进行Pd改性,对比其活性变化及表征结果后发现：Pd分散度的变化对H1分解催化活性的影响比灰分的影响要大。对不同温度HN03处理的煤质活性炭进行Pd改性,对比其活性变化及表征结果后发现：Pd的分散度变化缩小了改性前活性炭之间催化活性的差距。在以上实验结果及分析的基础上,首次提出了Pd/AC催化分解HI机理。对五种物化特性各异的活性炭进行Ru改性,对比其活性变化及表征结果后发现：与改性前的活性炭相比,Ru/AC催化剂的催化分解HI的活性有了一定的提高。Ru在五种活性炭上都有较高的分散度,显示了很好的抗烧结性能。对HCL, HF和HNO3处理后的煤质活性炭进行Ru改性,对比其活性变化及表征结果后发现：经过不同的预处理,Ru分散度并未发生很大的改变,Ru的分散度变化对H1分解催化活性的影响不如活性炭自身物化特性改变造成的影响大。对五种物化特性各异的活性炭进行Ni改性,对比其活性变化及表征结果后发现：在高温下,Ni在活性炭表面烧结团聚现象很严重,这些团聚的大颗粒堵塞了一部分孔。因此Ni/AC的催化活性并未增加活性炭的催化活性,低温段甚至还略低未负载Ni的活性炭。在以上实验结果及分析的基础上,首次提出了Ru/AC催化分解HI机理。更多还原

【Abstract】 Hydrogen is considered as an ideal energy vector owing to abundant resource, various source, environmental protection, regeneration, safety and advantageous storage. Therefore, it has greatly attracted worldwide attention. Hydrogen production is the fundamental step for hydrogen utilization. Consequently, developing hydrogen economy depends on large-scale and low-cost hydrogen production. Thermochemical water splitting cycle is a promising technique for hydrogen production featuring cleanness and sustainability. Hydrogen can be achieved by the decomposition of water through a series of related thermal reactions. Over one hundred kinds of thermochemical water splitting cycle have been reported to this day. Iodine sulfur thermochemical cycle is the most promising one due to its superiority with high thermal efficiency, low cost and easy large-scale industrialization.Iodine sulfur thermochemical cycle mainly consists of following three reactions:Bunsen reaction:xI2+SO2+2H2O=2HIx+H2SO4HI decomposition reaction:2HIx=xI2+H2H2SO4 decomposition reaction:H2SO4=SO2+H2O+1/2O2With regard to China, two key factors must be focused on. Pyrites as SO2 source are abundant and inexpensive. On the other hand, byproduct sulfuric acid is valuable and marketable. Therefore, the open-loop iodine sulfur cycle for hydrogen and sulfuric acid production has been proposed. The whole process is composed of following two reactions:Bunsen reaction:xI2+SO2+2H2O=2HIx+H2SO4HI decomposition reaction:2HIx=xI2+H2HI decomposition process is the unique procedure for generating hydrogen in the foregoing two cycles. And its conversion ratio directly influences systemic thermal efficiency and hydrogen production rate. Simulant and experimental results indicate the conversion of HI homogeneous decomposition is extremely low. Hence, the catalyst for improving HI decomposition is intensively applied. The catalysts of CeO2, Pt/Ce-Zr and Ni/Ce-Zr were investigated in the prior study on HI catalytic decomposition. Moreover, the catalytic reaction mechanism has been proposed by the detailed activity estimation and characterization study. The modified treatment including acid, oxidation, heat and metal loaded on activated carbon as HI decomposition catalysts are investigated to get more efficient and inexpensive.The activated carbon catalysts with different raw materials and vapor treatment have been tested to evaluate their effect on HI decomposition. AC-CS and AC-STONE showed the best catalytic performance. And AC-WOOD had the worst catalytic performance. AC-BAMBOO and AC-COAL represented the intermediate catalytic performance comparing with prior activated carbon catalysts. Catalytic characterization results indicated AC-CS and AC-STONE were similarly composed of high carbon content and low ash content. Meanwhile, their pore structures were both advanced. Regarding AC-BAMBOO and AC-COAL, the chemical composition contained high carbon content. Whereas, AC-BAMBOO’s pore structure was less advanced, and ash content of AC-COAL was rather high. AC-WOOD contained the lowest carbon content and relatively high ash content.The wooden activated carbon catalysts with different preparation methods have been tested to evaluate their influence on HI decomposition. The results implied that AC-WH the highest catalytic performance, AC-WOOD the worst catalytic performance, and AC-WZ the intermediate catalytic performance. The characterization results showed AC-WH contained more carbon content and less oxygen-containing groups in comparison with AC-WZ. Both of them contained relatively low ash content and similar pore structure. AC-WOOD consisted of lowest carbon content and rather high ash content. Consequently, high carbon content, low ash content, appropriate pore structure and less oxygen-containing groups were in favor of HI catalytic decomposition.The coal based activated carbon catalysts with non-oxidative acid (HCl and HF) treatment have been tested to evaluate their influence on HI decomposition. It was found that COAL-CLF had the best catalytic performance. Characterization results demonstrated that crystallization, pore structure and superficial oxygen-containing groups didn’t change significantly. Whereas, the sample ash content decreased obviously. Therefore, decreasing ash content could effectively improve the catalytic performance of activated carbon. The COAL-CLF catalyst with oxidative acid (HNO3) treatment has been tested to evaluate its catalytic performance. The results showed that COAL-CLF had the supreme catalytic performance. Characterization results indicated that superficial oxygen-containing groups and acidity increased by continuous oxidization. High temperature treatment easily resulted in specific surface area and pore volume decrease. Hence, oxidation treatment could depress the catalytic performance of activated carbon. Phosphoric acid activation wooden activated carbons with heat treatment at nitrogen or hydrogen atmosphere have been tested. Then samples with and without treatment were characterized and evaluated. The catalytic activity results showed that the catalytic performance improved as the heat treatment temperature increase. The characterization results demonstrated that crystallization and pore structure didn’t change obviously due to high thermal stability. While superficial oxygen-containing groups decreased and alkalinity increased. Therefore, heat treatment enhanced the catalytic performance. Moreover, HI catalytic decomposition mechanism via activated carbon has been proposed.Five kinds of different physicochemical activated carbons as vector with Pd modified load have been tested. Activity and characterization results showed that Pd/C catalyst manifested the higher catalytic performance in HI decomposition reaction in comparison with activated carbon without Pd load. The influence of Pd dispersion on HI catalytic decomposition was greater than physicochemical characterization of activated carbon. The coal based activated carbons as vector with Pd load by HCl or HF non-oxidative acid treatment have been tested. Activity and characterization results demonstrated that Pd dispersion had the greater effect on HI catalytic decomposition in comparison with ash content. The coal based activated carbons as vector with Pd load by different temperatures and HNO3 oxidative acid treatment have been tested. The results indicated that the catalytic performance difference of activated carbons without Pd load was reduced by Pd dispersion variety. Moreover, HI catalytic decomposition mechanism via Pd/C catalyst has been proposed.Five kinds of different physicochemical activated carbons as vector with Ru modified load have been tested. Activity and characterization results showed that Ru/C catalyst manifested the higher catalytic performance in HI decomposition reaction in comparison with activated carbon without Ru load. Ru load manifested relatively high dispersion on each activated carbon. Therefore, activated carbons with Ru modified load had the outstanding anti-sintering property. The coal based activated carbons as vector with Ru load by HCl, HF or HNO3 treatment have been tested. Activity and characterization results demonstrated that Ru dispersion didn’t change greatly by different treatments. Meanwhile, the influence of Ru dispersion on HI catalytic decomposition was less than physicochemical characterization variety of activated carbon. Five kinds of different physicochemical activated carbons as vector with Ni modified load have been tested. The results indicated that Ni sintering and agglomeration on activated carbon surface was extremely serious at high temperature. Then the agglomerated large particles blocked up partial pores. Therefore, Ni/C catalytic performance was not advanced than activated carbon’s one. Catalytic performance of activated carbon with Ni load even slightly worse at low temperature comparing with activated carbon without Ni load. Moreover, HI catalytic decomposition mechanism via Ru/C catalyst has been proposed.更多还原