【作者】 刘建军；

【导师】 王翔；

【作者基本信息】 南昌大学 ， 应用化学， 2014， 硕士

【摘要】 当今世界，能源与环保问题日益严重。甲烷干气重整反应，可充分利用天然气资源，同时降低CO2的排放，缓解温室效应，因此越来越受到各国催化学家的广泛关注。Ni基催化剂价格低廉储量丰富且活性高，是理想的甲烷干气重整反应催化剂，但是由于积碳严重，失活快等原因限制了其工业应用。研究和开发抗积碳性能优良的Ni基催化剂是实现甲烷干气重整反应工业化的关键。本文以Sn以及稀土Ce和Nd作为助剂改性Ni基催化剂，通过系统研究，合理设计得到一系列抗积碳性能良好的催化剂，为更好的设计活性和抗积碳性能优良的催化剂提供理论依据和实际指导。本论文首先研究了Sn对Ni/Al2O3催化剂抗积碳性能的改善作用。采用共浸渍法制备了不同含量Sn改性的Ni/Al2O3催化剂，结果发现添加少量的Sn能大大提高Ni/Al2O3催化剂的抗积碳性能，同时会使得催化剂活性有所降低。催化剂的抗积碳性能和Sn的添加量成正比关系，当Sn/Ni摩尔比为0.02时催化剂在反应150h后无积碳产生。为了考察Sn添加提高催化剂抗积碳性能的本质原因，采用共浸渍和分步浸渍方法制备了Sn/Ni摩尔比为0.02的催化剂。结果发现不同的浸渍顺序对催化剂的抗积碳性能也有影响。共浸渍制备的催化剂抗积碳性能好于分步浸渍制备的催化剂。H2-TPR表明，Sn的加入能促进NiAl2O4的还原；CO2-TPD表明，Sn的加入降低了催化剂的CO2吸附能力；XPS结果表明Sn在Ni颗粒表面富集；而XRD和TEM都发现Sn改性的催化剂Ni晶粒和颗粒都变大，造成Ni晶粒和颗粒变大的原因是由于Ni-Sn表面合金的形成；同时STEM-EDX结果更进一步证明了Ni-Sn表面合金的形成。各表征结果表明，Ni-Sn表面合金是提高催化剂抗积碳性能，同时降低催化剂活性的主要原因。因此控制合适量的Ni-Sn表面合金，将有助于制备得到活性下降不大，但抗积碳性能大大提高的催化剂。其次研究了Ce和Nd改性的Ni/Mg/Al催化剂。采用共沉淀法制备镁铝水滑石。通过浸渍法分别以镁铝水滑石和γ-Al2O3作为载体负载Ni制备催化剂用于甲烷干气重整反应。结果发现以镁铝水滑石为载体的催化剂表现出更好的催化活性和抗积碳性能。XRD结果表明以镁铝水滑石为载体制备的催化剂Ni晶粒更小。H2-TPR结果表明镁铝水滑石为载体Ni更难被还原。结合XRD和H2-TPR结果，我们认为Ni与Mg形成固溶体，固溶体的形成阻止Ni聚集，从而得到晶粒更小的Ni，提高催化剂的抗积碳性能。采用共浸渍法制备稀土Ce和Nd改性的Ni/Mg/Al催化剂，结果发现添加稀土Ce和Nd能进一步提高Ni/Mg/Al催化剂的活性以及抗积碳性能。特别是添加Ce改性后催化剂，相比于未改性的NiMgAl催化剂，其活性提高，同时积碳速率由30mg·gcat.-1.h-1降到了7mg·gcat.-1.h-1。H2-TPR结果表明稀土Ce和Nd增强了Ni与载体的强相互作用，XRD结果表明稀土Ce和Nd进一步降低了Ni的晶粒大小，这可能是提高催化剂活性和抗积碳性能的本质原因。更多还原

【Abstract】 Nowadays, energy and environment protection become more and moreimportant topics for all of the world. Increasing attention has been paid to thecatalytic methane dry reforming with carbon dioxide (CRM). Dry reforming ofmethane has been considered as a good options, which makes a full use of methaneand at the same time consumes a significant amount of greenhouse gas, carbondioxide. Ni-based catalysts have been widely investigated due to their high activity,abundant source and low price, but there are also still some remained problems. Forinstance, severe coke deposition, which deactivates the Ni active sites and evenblocks the reactor, is a major problem to be solved. It’s very necessary to design acoke-resistant catalyst to industrialize dry reforming process. In this thesis Sn, Ce andNd have been used as promoters to modifiy Ni-based catalysts. With intentionaldesign, a series of coke-resistant catalysts have been obtained and the reasons leadingto the prohibiting of coke formation have been rationalized. These information mayhelp people to design and develop stable dry reforming catalysts for industrialapplication.First，the improvement of coke resistance for Ni/Al2O3by Sn addition wasstudied. Ni-based catalysts doped by a small amount of Sn were prepared usingco-impregnation method. It’s interesting to find that a small amount of Sn addition onNi could effectively decrease the carbon deposit formation with a minor loss ofreforming activity. With the increasing of the Sn/Ni molar ratio up to0.02, the cokingof the catalysts can be completely suppressed but at a reasonable loss of the reformingactivity. No any coke can be detected on the catalyst even after reaction with anextended period of150h.Catalysts with a Sn/Ni molar ratio of0.02were thus intentionally prepared byco-impregnation or two step impregnation, with the expectation to find the role of Snin the enhancement of coke resistant of the catalysts. It was found that the step ofimpregnation had a great influence on the catalytic performance. The catalystsprepared with co-impregnation had the best coke resistant but with the lowestreforming activity. The H2-TPR results show that Sn addition increased the reducibility of the NiAl2O4species formed on the fresh samples. Sn made thedesorption of CO2easier, as confirmed by CO2-TPD. XRD and TEM results showedthat the presence of Sn improved the crystallite and particle sizes of Ni active sites.The formation of Sn-Ni alloy increases the size of metallic Ni, and the results ofSTEM-EDX mapping testified this further. It was concluded that the formation ofsurface Ni-Sn alloys was the main reason for the improved coke resistance of thecatalysts. Based on the information here, reforming catalysts with superior cokeresistance and applicable activity could be designed and developed by adjusting theamount of surface Ni-Sn alloys.Second，Ce and Nd modified Ni/Mg/Al catalysts have been studied. Thehydrotalcite-type precursors with a Mg/Al molar ratio of2.5were prepared usingcoprecipitation method. Then the Ni catalysts were prepared by impregnation methodwith hydrotalcite-type precursors or γ-Al2O3as support. It was found that thecatalysts, which using hydrotalcite-type precursors as support, had a better reformingactivity and coke resistance than the catalysts with γ-Al2O3as support. The XRDresults showed that in Ni/Mg/Al catalysts, Ni was doped into MgO lattices and toform solid solution. The formation of solid solution indeed made Ni more difficult tobe reduced, which was testified by H2-TPR results. The formation of Ni-Mg-O solidsolution also made the catalysts have smaller Ni crystallite sizes than the Ni/Al2O3these may be the major reasons leading to the high coke resistance of the catalysts.The Ni/Mg/Al catalysts, which were modified by Ce and Nd, were prepared byco-impregnation method. It was found that using Ce and Nd as promoters couldfurther enhance the catalytic reforming activity and coke resistance of the catalysts.The addition of Ce was even more effecteve compared with the un-modified NiMgAl.Its coke formation rate drops from30to7mg·gcat.-1.h-1. It’s found that the addition ofCe and Nd enhances the strong interaction between Ni and the support, therefore,smaller Ni crystallite sizes were formed, which is believed to be the major reasonaccounting for the coke resistance improvement.更多还原