【作者】 陈爱平；

【导师】 杨意泉；

【作者基本信息】 厦门大学 ， 工业催化， 2008， 博士

【摘要】 甲硫醇（CH₃SH）是一种重要的有机化工原料和常用的有机中间体。传统的工业合成甲硫醇的方法是在钨系催化剂作用下由硫化氢与甲醇气相合成。近年来,高硫合成气（CO/h₂/h₂S）一步法合成甲硫醇引起人们的兴趣,与传统的合成方法相比,由于该法原料易得,且省去了合成甲醇的中间步骤,具有很好的工业应用前景。本文主要对高硫合成气合成甲硫醇的钼基催化剂的制备、催化剂结构和性能之间的关联及反应历程展开研究。以Mo作为活性组份,采用浸渍法制备了一系列用于催化高硫合成气合成甲硫醇的催化剂;对助剂、载体和制备过程进行了最优化,并且对优化的催化剂进行了实验室放大试验。采用BET、XRD、LRS、XPS、TG、TPR、TPD、ESR等谱学手段对催化剂进行了表征;讨论了催化剂的构-效关联。对产物分布和工作态催化剂进行了分析和表征,提出了高硫合成气制甲硫醇的反应网络和反应机理。主要结果归纳如下:（1）在Mo基催化剂中,必须添加碱才具有可观的合成甲硫醇活性,在IA和IIA族元素中,K是最佳的碱促进剂,当K/Mo摩尔比为2,前驱体为K₂CO₃,采用共浸法制备的K-Mo催化剂活性最高。H₂-TPR和LRS表征显示,碱的加入导致表面八面体钼氧物种向四面体转化,催化剂的低温还原峰发生分裂,碱助剂（B）与钼之间存在强相互作用形成了B-Mo“界面相”,该物种与合成甲硫醇密切相关。（2）在K-Mo催化剂助剂的筛选实验中,发现Fe、Co、Ni、Te对催化剂有较明显的促进作用,首先发现非金属Te对K-Mo催化剂的促进作用,其促进作用顺序为Ni≈Co>Te>Fe。Co/K₂MoO₄的摩尔比为0.33-0.35,采用共浸法制得的K-Mo-Co催化剂活性最高。催化剂中,Te/K₂MoO₄的摩尔比为0.5时,采用“先Te后Te/K₂MoO₄/SiO₂”浸渍顺序所制的K-Mo-Te催化剂具有最高的活性。在对Te和Co促进的K-Mo催化剂的构-效关联研究中发现,Te对KMo/SiO₂催化剂的促进作用本质是碲物种的“电子助剂效应”,而Co对KMo/SiO₂合成甲硫醇催化剂的促进作用是由于Co与Mo-S物种结合生成了有利于加氢反应的“Co-Mo-S”物种。（3）在三组份的K-Mo-Co合成甲硫醇催化剂的制备研究中,发现当载体为SiO₂,钾钼钴以原子比为2:1:0.35时,MoO₃的负载量为25%（wt%）,且在浸渍液中加入柠檬酸制得无煅烧的K₂MoCo_0.35O/SiO₂（CA）催化剂具有最高的合成甲硫醇活性。制备条件对催化性能的影响的研究表明,在弱酸性氧化物为载体制备的催化剂上,Mo以难于还原和硫化的四面体构型存在,硫化后主要以K₂O_xMoS_4-x的形式存在,这些物种与合成甲硫醇密切相关;柠檬酸的加入提高了活性组份的分散度,同时有利于形成“Co-Mo-S”物种;惰性气氛中400℃煅烧的催化剂与无煅烧的催化剂活性相当,惰性气氛中柠檬酸分解（>212℃）造成部分的Mo和Co被还原;而催化剂在空气气氛中高温（>400℃）煅烧时,柠檬酸分解,活性组份与载体相互作用增加,分散度下降并导致活性组份的流失,导致催化活性降低。（4）在300℃,0.2MPa,3000h^-1。下,在钾促进的钼基催化剂上,高硫合成气（CO/H₂/H₂S=1/1/2,v/v）反应主要生成了CH₃SH、COS、CO₂和H₂O,并生成了少量的CS₂、CH₄、C₂H₄、C₂H₆、CH₃SCH₃、CH₃SSCH₃和CH₃SSSCH₃。本文首先报道CH₃SSCH₃和CH₃SSSCH₃等产物的存在。对反应途径的研究发现,COS是一级产物,其加氢后生成CH₃SH和H₂O。水煤气换反应是CO₂的主要来源;CS₂是COS的分解产物;CH₃SH的二次反应导致碳氢化合物和硫醚的生成。本文提出了一个较为完善的反应网络图。（5）在对反应机理的研究中,提出碱修饰的Mo基催化剂是一种“双功能”催化剂,并提出了在K-Mo-（Co）-S和/或K-Mo-（Co）-S-O活性相的高硫合成气制甲硫醇的可能的反应机理:H2S、CO和H2在催化剂上吸附和解离;K⁺结合S^2-和/或SH^-生成K⁺-S^2-和/或K⁺-SH^-;然后Mo（CUS）上的非解离吸附的CO迁移至K-S键形成COS_ads和/或HSCO_ads中间物种;此中间物种被Mo⁴⁺-S^2-,Co-Mo-S,S₂^2-和S_x等物种提供的溢流氢加氢化,或者它们迁移到这些物种上被活泼氢加氢生成CH₃S_ads;CH₃S_ads继续加氢形成CH₃SH。（6）本文所优化的K-Mo-Co催化剂表现出较好的重复性和稳定性,放大实验表明,催化剂具有工业应用前景。（7）本课题为与德国Evonik Degussa GmbH公司的合作项目,现已申请欧洲、韩国、中国等多国发明专利和发表学术论文若干,双方对合作进展感到满意。更多还原

【Abstract】 Methanethiol （CH₃SH） is an important chemical raw material and common organic intermediate. Industrially, methanethiol is synthesized in the gas phase from methanol and hydrogen sulfide over tungsten-based catalysts. Recently, there is an increasing interest in the route of one-step synthesis of methanethiol from H₂S-rich syngas （CO/H₂/H₂S）. Compared to the CH₃OH-H₂S route for production of CH₃SH, this method is attractive and promising since it skips the step of the synthesis of CH₃OH from syngas, furthermore, the feedstock composition is simple and easily available.This dissertation focuses on the preparations of Mo-based catalysts, the analysis of structure-activity relationships and the studies of the pathway of the CH₃SH synthesis from H₂S-rich syngas. Mo-based catalysts were prepared by impregnation method and the promoters, supports and preparation conditions were investigated in detail. Thus optimized catalysts were tested in the scale-up experiments. To analyze the structure-activity relationship, we performed BET, XRD, LRS, XPS, TG, TPR, TPD and ESR characterizations for the selected catalysts. Moreover, to investigate the reaction network and the mechanism of the methanethiol formation from H₂S-rich syngas, we performed detailed analysis of the product distribution and characterizations of the sulfided catalysts. The results of the dissertation were concluded as follows:（1） It is essential to deposit a basic additive on the Mo-based catalysts for the synthesis of CH₃SH. The potassium-doped Mo-based catalysts exhibit the highest activity than that of the catalysts doped with the otherⅠA andⅡA group basic promoters. H₂-TPR and LRS characterizations suggest that the addition of a base leads to the transformation of octahedrally coordinated Mo to tetrahedrally coordinated Mo, thus leads to the split of low temperature reduction peaks. The interaction between the basic components （B） and Mo lead to the formation of B-Mo interface phase, which are closely correlated with the formation of CH₃SH.（2） It has been found that Fe, Co, Ni and Te have evident promoting effects for the K-Mo/SiO₂ catalysts. Interestingly, nonmetallic tellurium was found to have an effective promoting effect on the K₂MoO₄/SiO₂ catalyst for the CH₃SH synthesis from H₂S-rich syngas and the promoting effects of the promoters were in the order of Co （Ni） > Te > Fe. The K-Mo-Co/SiO₂ catalysts prepared by the co-impregnation method exhibited highest activity when the Co/K₂MoO₄ molar ratio was 0.33-0.35. However, the K-Mo-Te/SiO₂ catalysts prepared in the order that Te impregnated first and followed by K₂MoO₄ exhibited highest activity when the Te/K₂MoO₄ molar ratio was 0.5. The studies of structure-activity relationship for the Co- and Te-promoted K-Mo catalysts indicate that the promoting effect of Te can be interpreted in terms of "electronic effect promoter", while that of Co is explained as that Co combines with Mo-S species to form the so-called "Co-Mo-S" phase which favors the hydrogenation reactions in the formation of CH₃SH.（3） For the supported tri-component catalysts for CH₃SH synthesis, the preparation conditions are as follows: SiO₂ was chosen as the support, and K : Mo : Co molar ratio is 2 : 1 : 0.35, and MoO₃ loading is 25%（wt%）, and citric acid is added as a chelating agent. The K₂MoCo_0.35O/SiO₂（CA） catalyst prepared in those cases without calcinations exhibits the highest activity. The studies of the effects of the preparation conditions on activity were conducted. The results show that Mo species in the K-Mo-Co catalyst prepared with weak acidic supports exist in the form of tetrahedrally configuration, which is hard to be reduced and sulfided, and this effect results in K₂O_xMoS_4-x becoming dominant species after sulfidation, which are closely related with the formation of methanethiol. The addition of citric acid is favorable to improve the dispersion of active component and to form the "Co-Mo-S" species. The catalysts calcined at 400℃in inert atmosphere exhibit similar activity as the catalysts without calcinations. The decomposition of citric acid takes place in inert atmosphere above 212℃, which gives rise to partially reduction of Mo and Co species. While the decomposition of citric acid takes place in air above 400℃, which leads to the enhancement of the interaction between the active components and supports, and affects the dispersion of the Mo and Co species, thus results in the loss of the active components, leading to the decrease of the activity.（4） At CO/H₂/H₂S=1/1/2 （v/v）, 0.2 MPa, 3000 h^-1 and 300℃, mainly CH₃SH, COS, CO₂ and H₂O were formed, along with small amounts of CS₂, C_1-2 hydrocarbons （CH₄, C₂H₄ and C₂H₆） and thioethers （CH₃SCH₃, CH₃SSCH₃ and CH₃SSSCH₃） over potassium-promoted Mo-based catalysts. We firstly report that CH₃SSCH₃ and CH₃SSSCH₃ are produced from the H₂S-rich syngas under these reaction conditions. Studies of the reaction pathway show that COS is a primary product, which is then hydrogenated to CH₃SH and H₂O. The disproportionation of COS leads to the formation of CS₂. Most of CO₂ originates from water-gas shift reaction. The hydrocarbons and thioethers originate from the secondary reactions of CH₃SH. This dissertation gives a more clear illustration for the pathway of the CH₃SH synthesis from H₂S-rich syngas（5） The results of mechanism studies show that the base-doped Mo-based catalysts are the bifunctional catalysts. A possible mechanism for the CH₃SH synthesis over the K-Mo-（Co）-S and/or K-Mo-（Co）-S-O active phases was proposed as follows: H₂, CO and H₂S are adsorbed firstly, wherein H₂S is thought to be supply enough S^2- and/or SH^- groups, the function of potassium thus be suggested to furnish K-S and/or K-SH bonds, into which the non-dissociative adsorption of CO can insert. The formed carbonyl sulfide (COS_ads) and/or thioformate (HOCS_ads) can then be hydrogenated to methylthiolate (CH₃S_ads) by the spillover of active hydrogen atoms on the sulfided Mo or Co-Mo components (Mo⁴⁺-S^2-, Co-Mo-S, S₂^2-, or S_x species), or they are hydrogenated after migration from the potassium component, the subsequent hydrogenation of methylthiolate (CH₃S_ads) produces CH₃SH.（6） The most optimized K-Mo-Co catalyst shows a good repeatability and stability. The results of the scale-up experiments show that the catalyst has the prospects in industrial applications.（7） This work is sponsored by Evonik Degussa GmbH （Germany）. The related achievements have been granted by some European, Korean and Chinese patents and published in several papers. Both parties are satisfied with the progress of the cooperation.更多还原