【作者】 李军；

【导师】 胡仰栋；

【作者基本信息】 中国海洋大学 ， 海洋化学工程与技术， 2014， 博士

【摘要】 作为一种重要的化工基础原料，丙烯近年来需求不断上涨，其与丙烷的价格差也不断提高。丙烷脱氢是增产丙烯的重要工艺，目前制约其应用的主要瓶颈在于催化剂活性和稳定性有待提高。本文以制备丙烷脱氢制丙烯用高温稳定型纳米催化剂为目标，以期解决传统丙烷脱氢Pt基催化剂在苛刻条件下的Pt组分烧结、易积炭及失活的难题。结合液相合成和超声波震荡负载法制备了Pt纳米粒子催化剂，考察了Pt纳米粒子制备方法、负载方法和载体等对Pt纳米粒子结构性质及丙烷脱氢性能的影响。研究表明，不同制备条件对形成不同形貌的Pt纳米粒子具有很大的影响，用硼氢化钠化学还原法制备的Pt纳米粒子，粒径均匀；稳定剂PVP可以阻止Pt纳米粒子的聚集，当n(PVP)/n(Pt)=15：1时，Pt纳米粒子分布较窄；超声波振荡法制备的Pt纳米粒子催化剂表现出更好地丙烯选择性及丙烷转化率，催化剂稳定性更好。自制的γ-Al2O3-3载体孔道以介孔为主，孔径范围在6-10nm，通过超声波振荡法制备的Pt纳米粒子负载在自制γ-Al2O3-3负载催化剂上，Pt粒子分布均匀，平均粒径约为3nm，其丙烷脱氢性能更优。以氧化铝为载体，采用液相合成-超声波震荡法制备了Pt纳米粒子催化剂，结合丙烷脱氢实验及透射电镜（TEM）、X射线衍射（XRD）、X射线光电子能谱（XPS）以及CO红外吸附等表征方法，考察了助剂Sn、Ce对催化剂结构及其丙烷脱氢性能的影响。助剂Sn的添加，可以提高Pt/Al2O3催化剂的丙烯选择性；采用共还原法添加助剂Sn要比浸渍法得到的催化剂性能好。采用以助剂Ce修饰后的氧化铝为载体所得到的催化剂，其Pt纳米粒子平均粒径为2.9nm，粒径分布均匀；少量的Ce以Ce3+形式存在，Ce可以与载体、Pt纳米粒子之间产生相互作用，从而提高了Pt纳米粒子的抗烧结性能。采用液相还原法制备了SnO2包裹Pt纳米颗粒的新型Pt@SnO2/Al2O3催化剂，并对该催化剂的制备方法及其丙烷脱氢反应工艺条件进行了考察。研究表明，以PVP为稳定剂，PVP/Pt摩尔比为15：1，乙醇-水体系，Pt添加量为0.4wt%，Pt/Sn摩尔比为1：1.5时，Pt@SnO2/Al2O3催化剂拥有较高的反应活性、较优的稳定性能和较强的抗积炭性能。通过对其丙烷脱氢反应工艺进行优化，确定最佳反应工艺条件为：还原温度为500℃、还原时间为4h，反应空速为1400h-1，丙烷/氢气的进料比为1：1，脱氢反应温度为580℃。催化剂稳定性考察结果表明，Pt@SnO2/Al2O3催化剂在72h内丙烷转化率和丙烯选择性分别稳定在23%和93%以上，并且都优于商用PtSn催化剂。在液相还原法制备Pt@SnO2/Al2O3催化剂基础上，通过引入助剂K、Ce对Pt@SnO2/Al2O3催化剂进行了进一步的优化。相比于Pt@SnO2/Al2O3，经Ce改性后的催化剂初始转化率提高了5.2％左右，反应200min以后，催化剂仍然保持着93%的丙烯选择性和27%的丙烷转化率。经助剂K修饰后的Pt@SnO2/Al2O3，丙烷转化率和丙烯选择性达到最佳，分别为24.5%和97.5%。NH3-TPD、H2-TPR、Py-IR和H2-O2滴定等表征结果表明，经助剂K、Ce修饰后的催化剂，其金属纳米粒子的负载均匀性得到了提高，载体和活性组分之间的相互作用得到了加强，积炭量减少，深度脱氢性能降低，高温稳定性进一步提高。利用固定床微分反应器研究了Pt@SnO2/Al2O3催化剂上丙烷脱氢反应的本征动力学。从基于多相催化表面反应的Langmuir-Hinshelwood机理出发，推导出了4个丙烷脱氢反应速率模型。通过不同反应温度下Pt@SnO2/Al2O3催化剂上丙烷脱氢反应的实验数据对方程（Ⅱ）进行了拟合，得到该模型不同温度下的动力学参数，根据Arrhenius方程和Van’t Hoff方程进而得到了反应活化能、吸附活化能和指前因子等参数的估值。统计检验和Boudart准则表明，所建立的动力学模型是合理的。更多还原

【Abstract】 The demand of propylene, an important basic chemical raw material, growscontinuously. The price difference between propylene and propane also is rising.Propane dehydrogenation is an important process for producing propylene. At present,the bottleneck which restricts its application is the poor stability of catalyst. In thiswork, a stable nano-catalyst was prepared to relieve the deactivation problemassociated with the traditional propane dehydrogenation platinum-based catalyst.Platinum nanoparticle catalysts were prepared through a liquid-phase synthesisroute combined with ultrasonic vibration method. Effect of preparing methods,loading methods, and carriers on the structure and properties of platinumnanoparticles were investigated. Relationship between the dehydrogenationperformances with the structural properties was clarified. Results show thatpreparation conditions influence the morphologies of platinum nanoparticles.Platinum nanoparticles prepared are uniform using chemical reduction method usingNaBH4as a reducing agent. Stabilizer, PVP, prevents aggregation of platinumnanoparticles. The particle size distribution of platinum nanoparticles is narrow whenthe molar ratio of PVP to Platinum was15:1. Platinum nano-catalyst exhibits a highselectivity to propylene and a high conversion of propane when prepared by ultrasonicvibration method. The pore diameter of mesoporous alumina ranged from6to10nm.Br nsted acid sites exist on the surface of carrier. The platinum nano-catalyst preparedby ultrasonic vibration method exhibits good performance in propanedehydrogenation. The distribution of platinum nanoparticles is uniform, and theaverage diameter of particles is3nm.Effect of tin and cerium as promoters on the structure and dehydrogenationperformance of catalysts was investigated. The catalyst was characterized by using various techniques: TEM, XRD, XPS and CO-chemisorption. The tin promoterincreases the selectivity to propene of Pt/Al2O3catalyst. The dehydrogenationperformance of the catalyst prepared by reduction method is better than that ofcatalyst prepared by impregnation. The particle size distribution of platinumnanoparticles when using cerium modified alumina as the support is uniform with theaverage diameter centered at2.9nm. Cerium exists in the form of Ce3+at low content.It interacts with carrier and platinum nanoparticles, increasing the resistance tosintering.Pt@SnO2/Al2O3catalyst was obtained by liquid-phase reduction. Effect ofpreparing methods and reaction conditions was investigated. Resuts show thatPt@SnO2/Al2O3catalyst for the dehydrogenation of propane exhibits the highestactivity, stability and resistance to coke when prepared under conditions as follows:PVP as stabilizer, the molar ratio of PVP to Platinum as15:1, ethanol-water as thesolvents, platinum content of0.4wt%, the molar ratio of platinum to tin as1:1.5. Byinvestigating the influence of reaction conditions on the performance fordehydrogenation, the optimal conditions were determined as follows: reductiontemperature at500℃, reaction time of4h, space velocity of1400h-1,propane/hydrogen feed ratio of1:1and reaction temperature at580℃. The conversionof propane and selectivity to propene were23%and93%respectively after reactionof72h, which is superior to PtSn commercial catalyst.The catalysts were further optimized by introducing K, Ce promoters toPt@SnO2/Al2O3catalyst. Compared with Pt@SnO2/Al2O3catalysts, the initialconversion of the catalysts modified by Ce increased by about5.2%. The conversionof propane and the selectivity to propylene were27%and93%respectively afterreaction for200min. The Pt@SnO2/Al2O3catalyst modified by K promoter shows thebest performance, and the conversion of propane and the selectivity to propylene were24.5%and97.5%respectively. NH3-TPD, H2-TPR, Py-IR and H2-O2titration analysisshowed that the active component of catalyst was better dispersed after modified by K,Ce promoters. Besides, the interaction between the active components and carrier wasstrengthened, decreasing the amount carbon and preventing the reaction of deep dehydrogenation. Hence, the stability of the catalyst at high temperature is furtherimproved.The intrinsic kinetics of dehydrogenation reaction was studied using a fixed beddifferential reactor. Four propane dehydrogenation reaction models were deducedbased on Langmuir-Hinshelwood mechanism for heterogeneous catalytic surfacereactions. The kinetic parameters of the model were obtained by fitting the equationⅡwith experimental data. The activation energy, adsorption energy and pre-exponentialfactor were obtained according to the Arrhenius equation and Van’t Hoff equation.Statistical tests and Boudart guidelines indicate that the dynamic model is reliable.更多还原