摘要
烃类燃料催化裂解作为强吸热型反应，可有效解决高超音速器（HFV）的空气动力热问题，为飞行器主动冷却系统的设计提供了一种可行的方案。HZSM-5沸石是吸热型碳氢燃料超临界催化裂解常用催化剂，但由于超临界反应流体的特殊性，存在反应物及其产物在微孔分子筛孔道中扩散困难和积炭沉积严重的问题，导致其在超临界状态下的催化活性和使用寿命有限，因此对其进行孔道结构和酸性的调控是十分有必要。
本文通过离子交换法和碱中和法这两种减量法对HZSM-5分子筛的酸性调控研究发现，这两种方法都能有效调控HZSM-5酸性且对其晶体结构和孔道特性无显著影响。但碱中和法存在可操作性差、重复性弱的问题，而离子交换法很好的规避了这两个问题且可以有效调控HZSM-5的Brønsted酸性位。在正己烷常压裂解中，催化活性与HZSM-5质子交换度呈负相关，因此常压下HZSM-5酸含量越多越有利于催化活性的提高；但在超临界催化裂解中，过强的酸极易导致积炭沉积，使催化剂瞬间失活，因此只有适度的酸量和酸强度才有助于提高HZSM-5在超临界状态下有效的催化活性和使用寿命。
选用HZSM-5分子筛为原料，采用后合成法在水热条件下合成了具有微-介孔结构的复合分子筛HZSM-5/MCM-41，通过正交试验优化合成条件。选用离子交换减量法，在超声条件下NaCl溶液与HZSM-5/MCM-41复合沸石进行离子交换调控其酸性，优化其在正十二烷催化裂解中的活性。采用气相谱分析
裂解过程催化剂活性的变化，并用XRD、氮气吸附、NH3-TPD、程序升温氧化（TPO）和程序升温表面反应（TPSR）等方法对反应前后的催化剂进行了表征。
XRD和氮气吸附-脱附曲线表明，晶体晶型和孔道性质不受离子交换的影响；而NH3-TPD，正己烷裂解探针反应和正十二烷程序升温表面反应表明，通过与不同浓度NaCl溶液的离子交换强酸性位点不同程度的减少。虽然离子交换的复合沸石在正十二烷超临界催化裂解过程中的初始转化率略有降低，但其稳定性却大大增强，用0.8mol/L NaCl溶液进行离子交换后获得的复合沸石在反应3h后任没有明显失活。总之，通过减量法调控复合分子筛HZSM-5/MCM-41酸性后，不仅提高了超临界催化裂解活性和使用寿命，还不影响其晶体结构和孔道性质，是优化复合分子筛HZSM-5/MCM-41超临界催化裂解性能的有利探索。
最后基于结焦催化剂的焦炭分析，我们提出了吸附在复合沸石催化剂微孔和介孔上酸性位点的作用的机理：催化活性主要由微孔中的酸位点提供，而超临界催化裂解中焦炭对强酸性位的覆盖是一个快速的过程；介孔主要改善超临界状态
下反应物与产物的扩散性；微孔的损失与阻塞微孔的有效焦炭之间存在简单的线性关系。
关键词：HZSM-5/MCM-41，复合分子筛，离子交换，酸性，焦炭沉积
ABSTRACT
Catalytic cracking of hydrocarbon fuels as a strongly endothermic reaction can effectively solve the aerodynamic heat problem of hypervelocity (HFV) devices and provide a feasible solution for the design of active cooling systems for aircrafts. HZSM-5 zeolite is a commonly used catalyst for supercritical catalytic cracking of endothermic hydrocarbon fuels. However, due to the special nature of supercritical reaction fluids, there are problems in the diffusion of reactants and their products in the pores of microporous molecular sieves and serious deposition of carbon deposits. As a result, its catalytic activity and service life in the supercritical state are limited, so it is necessary to regulate the pore structure and acidity.
In this paper, we studied the acidity regulation of HZSM-5 by two methods of ion exchange and alkali neutralization. These two methods can effectively regulate the acidity of HZSM-5 and have no significant effect on the crystal structure and pore characteristics of HZSM-5. However, the alkali neutralization method has problems of poor operability and repeatability, and the ion exchange method evades these two problems well and can effectively regulate the Brønsted acidity of HZSM-5. In the normal pressure cracking of n-hexane, the catalytic activity is negatively correlated with the exchange degree of HZSM-5 protons, so the more acid content of HZSM-5 at atmospheric pressure is more conducive to the increase of catalytic activity, but in supercritical catalytic cracking, it is too strong. The
acid easily causes deposition of carbon deposits and deactivates the catalyst instantaneously. Therefore, only moderate acidity and acid strength can help increase the catalytic activity and service life of HZSM-5 in the supercritical state.
HZSM-5 molecular sieve was selected as raw material, and the composite molecular sieve HZSM-5/MCM-41 with micro-mesoporous structure was synthesized under hydrothermal conditions by post-synthesis. The synthesis conditions were optimized by orthogonal test. Ion exchange-reduction method was used. Under the ultrasonic conditions, NaCl solution and HZSM-5/MCM-41 zeolite were ion-exchanged to control their acidity and optimize their catalytic activity in n-dodecane catalytic cracking. Gas chromatography was used to analyze the change of catalyst activity during pyrolysis. The catalysts before and after the reaction were characterized by XRD, nitrogen adsorption, NH3-TPD, temperature programmed oxidation (TPO) and
temperature programmed surface reaction (TPSR).
The XRD and nitrogen adsorption-desorption curves show that the crystal form and pore properties are not affected by ion exchange. While NH3-TPD, n-hexane cleavage probe reaction and n-dodecane temperature-programmed surface reaction show that different degrees of reduction of strong acid sites
by ion exchange with different concentrations of NaCl solution. Although the initial conversion of the ion-exchanged composite zeolite in supercritical catalytic cracking of n-dodecane is slightly reduced, but its stability is greatly enhanced. The composite zeolite obtained after ion exchange with 0.8 M NaCl solution is after 3 hours of reaction, there was no apparent inactivation. In a word, by adjusting the acidity of the composite molecular sieve HZSM-5 / MCM-41 by the reduction method, not only the activity and service life of the supercritical catalytic cracking are improved, but also the crystal structure and the pore properties are not significant affected. It is an advantageous exploration to optimize the performance of the supercritical catalytic cracking of the composite molecular sieve HZSM-5/MCM-41.
Finally, based on coking analysis of the coked catalyst, we proposed a mechanism for the adsorption of acidic sites on the microporous and mesoporous of the composite zeolite catalyst: the catalytic activity is mainly provided by the acid sites in the microporous, and the coverage of strong acid sites by coke in supercritical catalytic cracking is a rapid process. There is a simple linear relationship between the loss of microporous and the effective coke blocking the pores, and mesoporous mainly improve the diffusion of reactants and products in the supercritical catalytic cracking.
Keywords:HZSM-5/MCM-41, Hierarchical zeolite, Ion exchange, Acidity, Coke deposition.
目录
中文摘要.......................................................................................................................................... I 英文摘要....................................................................................................................................... III 1 绪论.. (1)
1.1 引言 (1)
1.2 ZSM-5催化剂 (2)
1.2.1 ZSM-5的结构 (2)
1.2.2 ZSM-5的应用 (3)
1.3 HZSM-5/MCM-41复合分子筛 (4)
1.3.1 复合分子筛的合成 (4)
1.3.2 复合分子筛的优化 (5)
1.4 课题的研究内容和意义 (6)
2 实验部分 (9)
2.1 实验试剂及设备 (9)
2.1.1 实验试剂 (9)reaction diffusion
2.1.2 实验设备 (10)
2.2 催化剂的制备 (11)
2.2.1 HZSM-5的制备 (11)
2.2.2 HZSM-5的酸性调控 (12)
2.2.3 HZSM-5/MCM-41的制备 (12)
2.2.4 HZSM-5/MCM-41的酸性调控 (13)
2.3 超临界催化裂解装置及催化活性评价 (13)
2.3.1 超临界催化裂解装置及TPO分析装置 (13)
2.3.2 正己烷评价及TPSR分析装置 (14)
2.3.3 超临界催化裂解评价 (15)
2.4 催化剂结构表征 (15)
2.4.1 晶体结构表征（XRD） (15)
2.4.2 比表面积及孔径分析 (16)
2.4.3 扫描电子显微镜表征及能谱分析 (16)
2.4.4 氨程序升温脱附（NH3-TPD） (16)
2.4.5 程序升温表面反应（TPSR） (16)
2.4.6 正己烷探针分析 (17)

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