【作者】 刘会茹；

【导师】 李永丹；

【作者基本信息】 天津大学 ， 工业催化， 2007， 博士

【摘要】 近年来,随着环保法规的日益严格及对能源效率的深入认识,柴油中的芳烃加氢研究受到极大关注。贵金属催化剂由于有较高的加氢活性而成为研究的热点,但贵金属对硫极其敏感,提高贵金属催化剂的抗硫性是研究的重点。本文研究了硫存在下负载在超稳Y（USY）载体上的金属催化剂的加氢性能和抗硫性能。考察了含硫物种对Pd-Pt/HDAY（SiCl4脱铝的氢型Y载体）催化剂芳烃加氢性能及加氢产物分布的影响。以四氢萘加氢为探针反应,在固定床上评价了催化剂的活性和抗硫性。结果表明Pd-Pt/HDAY催化剂具有较好的加氢活性和抗硫性。含有噻吩与含有4,6-二甲基二苯并噻吩的物料反应体系中,催化剂的失活速率有较大差别。通过对反应后催化剂的X射线能量散射分析得出催化剂的失活是由HDAY分子筛对噻吩和4,6-二甲基二苯并噻吩的择形效应造成的。对反应后的产物进行分析,结果表明,产物中除十氢萘外,还有十氢萘的异构产物,开环产物,裂解产物。含有噻吩的物料中,裂解产物的选择性较小,开环产物的选择性与含4,6-二甲基二苯并噻吩的物料体系相似。三种物料中,催化剂的积碳量有所差别,造成裂解产物选择性的不同。研究了载体的酸量对催化剂芳烃加氢活性和抗硫性的影响。采用水蒸汽脱铝获得了不同酸量的Y型分子筛-USY1、USY2、USY3、USY4。以上述分子筛为载体制备了金属含量、金属组成、金属分散度相近的催化剂,研究了载体酸量对催化剂抗4,6-二甲基二苯并噻吩能力的影响。载体酸量较小的Pd-Pt/USY4催化剂和酸量较大的Pd-Pt/USY1催化剂抗硫性较低,表明载体的酸量过大或过小不利于提高催化剂的抗硫性。Pd-Pt/USY1催化剂抗硫性较低归因于酸量大时,相应酸性位上含硫物种的吸附增强,表面高浓度的含硫物种对金属活性位的毒化能力增强;Pd-Pt/USY4催化剂抗硫性较低与金属中心缺电子效应较小和酸性位浓度低有关。探讨了酸性位对芳烃加氢的贡献以及对产物分布的影响,另外考察了十氢萘的顺反异构化机理。以USY分子筛为载体,用吸附吡啶的方法获得了酸性位被毒化的催化剂。研究了不同金属含量的催化剂酸性位毒化前后四氢萘加氢活性和耐硫性的影响。对于同一金属含量的催化剂,未毒化前催化剂的活性和耐硫性始终高于毒化后催化剂的活性,说明载体的酸性有利于提高催化剂的加氢活性和耐硫性。溢流氢对芳烃加氢的贡献可以简单的表示为酸性位毒化前后催化剂的TOF值之差。酸性位和金属之间有一定的关系。考察了金属含量、载体酸性、四氢萘的转化率对十氢萘顺反异构化的影响。金属含量对十氢萘的顺反异构比影响不大,四氢萘对十氢萘的反顺异构化有一定的抑制作用,载体的酸性对十氢萘的顺反异构比有较大影响,酸性位是十氢萘反顺异构化的主要活性中心,十氢萘异构化机理主要为碳正离子机理。以萘、蒽、芘加氢为模型反应研究了Pd-Pt/USY催化剂多环芳烃加氢性能以及硫对芳烃加氢的抑制作用。结果显示,催化剂具有深度加氢的能力。以萘与蒽、萘与芘的混合体系为模型反应研究了它们之间竞争加氢的问题。萘与蒽之间竞争加氢的结果表明,蒽抑制萘加氢,而萘抑制了蒽加氢产物1-ring物质向0-ring物质的转化。这说明,对于分子动力学直径相当的混合体系中,多环物质抑制环少的物质的加氢。对于动力学直径相差较大的萘与芘体系,萘的转化率始终高于芘的转化率,并且单和混合体系中萘和芘的转化率变化程度不大。单纯以环的数目判断多环芳烃的加氢活性是不充分的,除此之外,分子能否扩散进入分子筛孔道内也是影响加氢活性的重要因素。噻吩对催化剂催化萘、蒽加氢有抑制作用。结果显示,噻吩对催化剂催化多环芳烃生成全氢物质的抑制作用比生成部分加氢物质的抑制作用更显著。采用离子交换法制得Y³⁺改性的USY载体,用TPR、NH₃-TPD等表征了载体和催化剂的性质。在金属含量、金属组成相近的前提下,研究了载体改性前后催化剂的四氢萘加氢活性和耐硫性。实验结果表明,少量Y³⁺的添加可以使负载金属催化剂的加氢抗硫性能得以改善;过量Y³⁺的添加不利于提高金属催化剂的活性和抗硫性。更多还原

【Abstract】 In recent years, a considerable attention had been focused on aromatics hydrogenation of diesel due to the increasingly stringent environmental legislation and the recognition of the importance of energy efficiency. Noble metal catalysts were highly active for aromatics hydrogenation. However,they were extremely sensitive to sulfur, it was paramount to improve the sulfur tolerance of the catalyst. In this work, fundamental research was conducted with tetralin hydrogenation utilizing USY supported noble metal catalysts in the presence of sulfur.The influence of sulfur compound on hydroconversion of tetralin and on product distribution over Pd-Pt/HDAY catalyst was investigated. The activity and thiotolerance for the hydrogenation of tetralin were examined in a high-pressure fixed-bed continuous-flow stainless steel catalytic reactor. The thiotolerance was tested with feeds containing 200 ppm sulfur in the form of 4, 6-dimethyldibenzothiophene and thiophene, respectively. It was found that thiophene was more effective for deactivating the catalyst than the former one. The diffusion barrier of the pores for the sulfur compound is likely the major reason for the different deactivation rate of catalysts.The products other than decalins were mainly decalin isomers （iso-DECS）, ring-open （RO） hydrocarbons and their hydrogenated derivatives. The selectivities of RO and iso-DECS in the two feeds with sulfur are almost the same to each other and to that of the clean feed, while there are significant differences in the selectivities of cracking product. The differences in product distribution observed are explained by the different poisoning ability for acid sites on which secondary acid-catalyzed reactions, mainly cracking and dealkylation, leading to lighter products occurs.The effects of acid site amount on tetralin hydrogenation activity and sulfur tolerance were studied. USY supports with different acid amount were obtained by steaming dealumination, and the noble metal catalysts with same metal content and same metal dispersion were prepared by an ion-exchange method. Hydrogenation activity and sulfur tolerance of catalysts was examined. It was shown that Pd-Pt/USY1 catalyst with very high acid amount and Pd-Pt/USY4 catalyst with low acid amount showed noticeable decrease in sulfur tolerance. The low sulfur tolerance of Pd-Pt/USY4 was related to its low acid amount and insignificant electron-deficiency of metal particles. The noticeable decrease in sulfur tolerance of Pd-Pt/USY1 catalyst was because the acid sites were more easily poisoned by sulfur when acid amount increased.The contribution of acid sites to aromatic hydrogenation and influence to the distribution of products was studied. Neutralization with pyridine of acid sites on catalysts with different metal content was performed in order to evaluate the contributions of acid sites to activity. The activity and thiotolerance of fresh catalysts were higher than that poisoned by pyridine in same metal content, indicating that acid sites were favor to increasing the activity of catalysts. The contribution of acid site to turn over frequency （TOF） was roughly estimated by subtracting the TOF of the samples before and after acid site neutralization.Influence of metal content, support acidity and tetralin on stereoisomerization of decalin was explored. It was shown that support acidity played a predominate role in stereoisomerization of decalin. The mechanism for stereoisomerization of decalin on proton-form zeolites involved a carbenium ion.The deep hydrogenation of polycyclic arenes on Pd-Pt/USY catalyst has been investigated. It was shown that catalyst promoted deep hydrogenation of polycyclic arenas. Competitive hydrogenation of naphthalene and anthracene system as well as naphthalene and pyrene system was examined. For the naphthalene and anthracene with same kinetic diameter, a strong inhibition existed in this reaction system. The results showed that the polycyclic arenes inhibits the hydrogenation of arenas with less number of aromatic rings. However, for naphthalene and pyrene the hydrogenation activity of naphthalene was obviously higher than that of pyrene. It is because that pyrene can not diffuse to the supercage of Y. Although its hydrogenation may occur on the active sites in mesopores and on the outer surface of the crystallites, a low hydrogenating activity than naphthalene was reasonable. Inhibition of polycyclic arenas hydrogenation activity by sulfur was investigated. It showed that sulfur has stronger inhibiting for hydrogenation of deeply hydrogenated compounds than that with less number of aromatic rings.Modified USY by adding yttrium was prepared by an ion exchange method. TPR and NH₃-TPD were employed to investigate the character of catalysts and supports. At the same metal content and metal composition, activity and sulfur tolerance of catalysts were analysed. The results showed that the activity and sulfur tolerance of the catalyst could be improved by adding a low content of yttrium, while it could be decreased when content of yttrium was high.更多还原