【作者】 艾沙·努拉洪；

【导师】 郭洪臣；

【作者基本信息】 大连理工大学 ， 工业催化， 2013， 博士

【摘要】 纳米金催化剂的制备和应用是近年来催化界的研究热点。沸石具有巨大的比表面积和独特的孔道结构,是制备负载金催化剂的重要载体。但由于沸石等电点低,因而在沸石上制备高分散催化剂还面临挑战。另一方面,将沸石负载金催化剂用于低碳烷烃活化转化方面的研究工作至今鲜有报道。因此本文开展了纳米HZSM-5沸石负载金催化剂的制备研究和正丁烷芳构化、异构化反应研究,主要得到以下结果和结论：1.采用负压沉积沉淀法并结合氮气气氛或氮气等离子体气氛焙烧处理,制备出了金颗粒比较均匀,金颗粒尺寸主要在2-10nm范围内的纳米Au/HZSM-5沸石催化剂。研究发现,焙烧处理条件(温度和气氛)是影响金颗粒在纳米HZSM-5沸石载体上分散尺度和均匀性的决定性因素。在空气气氛中焙烧时,金颗粒在200℃左右形成,在大约500℃以上烧结长大速度加快。在相同的焙烧条件下,惰性气氛(如氮气和氩气)优于空气气氛和还原性氢气气氛。在氮气等离子体气氛中焙烧优于氮气气氛中焙烧。2.纳米Au/HZSM-5沸石催化剂是一种金属-酸双功能催化剂。研究发现,在纳米沸石载体上负载金时B酸减少,L酸相对增加；载少量金时总酸度变化不大,载金量较高时总酸度小幅下降。在低于200℃下干燥时金主要以Au+3和Au+1态存在,可被氢气还原。随着焙烧温度的提高,Au+3消失,Au+1减少,金主要以零价态存在。金的负载方法和负载量也影响金的价态。相对于巯基保护法而言,沉积沉淀法有利于生成一价金,且低负载量时一价金比例相对较高。一价金对正丁烷有很强的低温吸附活化作用。3.在脉冲微反条件下,正丁烷在纳米HZSM-5沸石载体上反应活性很低,但在纳米Au/HZSM-5沸石催化剂上的反应活性显著提高。结合钾离子改性和XPS表征发现,载金催化剂的高活性与一价金离子有关。在高温下(如550℃),正丁烷在载金催化剂上可以进行芳构化反应。在氮气等离子体中焙烧的载金量为1.88%Au/HZSM-5沸石催化剂的正丁烷转化率可达64%左右,芳烃产率远高于载体,达到了24%左右。在低温下(如300℃-400℃),正丁烷在载金催化剂上进行异构化反应,在空气中焙烧的载金量为1.88%催化剂的正丁烷转化率可达7.2%左右,异丁烷选择性远高于载体,达到了85%。正丁烷在纳米Au/HZSM-5沸石催化剂上的异构化具有金属-酸双功能催化特征。4.在纳米Au/HZSM-5沸石催化剂(0.3%Au)上引入第二金属锌能显著提高正丁烷的芳构化活性。与正丁烷相比,异丁烷在金-锌双组份改性催化剂上不但芳构化活性显著提高,而且芳构化反应选择性也有提高。更多还原

【Abstract】 The application and preparation of nano-Au catalyst have been received extensive attention. Zeolite with high specific surface area and unique pore pathway was considered as an important support for Au, but the isoelectric point of zeolite is too low to obtain highly dispersed Au. So far, there were few publications about the activation of light-alkane molecules on Au catalyst. Here, systematic studies were carried out to investigate the preparation of HZSM-5supported Au catalyst and its application in aromatization and isomerization of n-butane.The results and conclusions are as following:1. Highly dispersed Au on HZSM-5was prepared by deposition precipitation method unver negative pressure, combined with plasmas treatment in N2or Ar atmosphere. And the size of Au is2-10nm. XRD, UV-vis and TEM results show that the condition (temperature and atmosphere) of calcination would influence the dispersion of Au on HZSM-5. In the condition of air atmosphere, the formation of Au crystal particles began at temperature about200℃, but the size of Au crystal particles aggregated quickly if temperature reached500℃. However, at the same condition, the calcination in N2or Ar atmosphere was better than that in air or H2atmosphere, and we also found that in the same N2atmosphere the plasma calcination was superior to the traditional calcination.2. Nano-Au/HZSM-5was bi-function catalyst. NH3-TPD, XPS, H2-TPR, FTIR with pyridine or n-butane and DFT calculations show that the acidic properties of HZSM-5with high Au loading was changed, the Br(?)nsted acid sites of HZSM-5were decreased, but the Lewis acid sites were increased. Au3+and Au+are two main species of Au in Au/HZSM-5with treatment lower200℃, which could be reduced in H2flow at128℃or585℃. But with calcination temperature increased, the state of Au was transformed from Au3+(disappearance) and Au+(decrease) into Au0, and Au+exhibits high n-butane conversion activity at relatively low temperature. In addition, the valence state of Au was influenced by the preparation method and Au loading, the deposition-precipitation method facilitates to the formation of Au+compared with the hydrosulfuryl protection method with low Au loading.3. Experiments on mini-scale pulse reactor show that the n-butane conversion activity on Au/HZSM-5was obviously enhanced compared with that on pure HZSM-5. Compared Studies about catalyst modified by K+further demonstrated that the activity of Au/HZSM-5depends on Au+. In the condition of550℃, the aromatization of n-butane occurred over1.88 wt%Au/HZSM-5calcinated in N2plasma. The conversion of n-butane was64%and the yield of aromatics was higher than that on HZSM-5.However, at lower temperature (300-400℃), the isomerization of n-butane occurred over1.88%Au/HZSM-5calcinated in air. The conversion of n-butane was7.2%and the selectivity of i-butane was84%, which are both higher than that on HZSM-5. The Au/HZSM-5catalyst exhibits the feature of bi-function metal catalyst for the isomerization of n-butane。4. Au/HZSM-5modified with Zn (0.3%Au,6.0%Au, impregnation method) could greatly improve the activity of n-butane conversion, but the selectivity of aromatics was slightly decreased. In comparison with n-butane,i-butane exhibits higher activities and aromatics selectivity on Au-Zn/HZSM-5.更多还原