|导师||高志贤 ; 吾满江·艾力|
|关键词||Ru基催化剂 催化加氢 马来酸二甲酯 丁二酸二甲酯 吸附-沉淀法|
与其它还原过程相比，催化加氢技术更加环保和高效，符合绿色化学发展的要求。加氢催化剂是催化加氢工艺的核心，因此其制备与改性方法就成为研究的重点。在贵金属加氢催化剂中，Ru基催化剂因其独特的优势而被更多的用于催化加氢过程中。本实验室前期开展了吸附-沉淀法制备Ru基催化剂的研究工作，制备出了具有优异催化性能的Ru催化剂，可在低温低压下高效实现马来酸及其酯的选择加氢。 结合前期研究工作，本论文以Ru基催化剂为核心研究内容，通过样品的制备、表征和催化性能评价，探讨了制备方法对催化剂性能的影响和吸附-沉淀法制备催化剂的的特性。在此基础上，采用吸附-沉淀法，通过添加不同的金属助剂对Ru催化剂进行改性，制备出了Ru-M/Al2O3(M:Ni、Fe)催化剂。以马来酸二甲酯加氢合成丁二酸二甲酯为探针反应，结合XRD、XPS、TPR、TPD等表征手段，对Ru-Ni/Al2O3与Ru-Fe/Al2O3催化剂的加氢性能及氧化还原性能进行了系统的研究。主要内容和结论如下： （1）Ru催化剂的制备、表征与催化性能 以Al2O3为载体，RuCl3.xH2O为活性组分前驱体，分别采用吸附-沉淀法与浸渍法制备了1.0 wt%Ru/Al2O3催化剂。以马来酸二甲酯催化加氢制丁二酸二甲酯为探针反应，考察了制备方法对催化剂性能的影响。 在反应温度70oC、压力1.0 MPa下，经相同活化方式处理后，采用吸附-沉淀法制备催化剂的活性高于浸渍法制备催化剂。 结合XRD、TPD、XPS等表征，揭示了催化剂制备方法与催化剂活性的关系。结果表明：催化剂中残留的氯离子覆盖了催化剂的活性中心，抑制了活性组分Ru对氢气的吸附与活化。与浸渍法相比，采用吸附-沉淀法制备样品可以有效的去除催化剂中的残留的氯离子，从而增强了活性组分Ru在反应温度下对氢气的吸附和活化能力，提高了催化剂活性。 （2）吸附-沉淀法制备Ru/Al2O3催化剂体系的特性 采用吸附-沉淀法制备了不同负载量的Ru/Al2O3催化剂，考察了还原活化条件和Ru的负载量对催化剂加氢性能的影响。结合TPR数据与活性评价结果，揭示了Ru的负载量、还原条件与催化剂活性的关系。结果表明：新鲜催化剂Ru/Al2O3上存在不同状态的Ru物种，催化活性主要来源于低温可被还原Ru物种（还原温度≤100oC），其所占比例随催化剂负载量增大而降低，即催化剂中Ru的利用效率随负载量增大而降低。基于以上结果，采用有效平均加氢速率可以更客观的反应催化剂活性的差别。 （3）Ru-Ni/Al2O3催化剂的制备、表征与催化性能 以Al2O3为载体，RuCl3.xH2O及Ni(NO3)2.6H2O为活性组分前驱体，采用吸附-沉淀法制备了系列Ru-Ni/Al2O3催化剂，考察了预处理条件和Ni的添加量对催化剂性能的影响。 随Ni负载量的升高，Ru-Ni双金属催化剂的活性呈现先升高后降低的趋势，在Ni:Ru的原子比为6:1时催化剂活最高。样品Ru1Ni6/Al-fresh在200oC还原所得催化剂活性与400oC还原所得催化剂无明显差别，平均转化速率达到了单组份Ru催化剂的1.5倍以上。 结合催化剂XPS、XRD、TPR表征，探讨了Ni的添加对催化剂性能影响的原因。结果表明: Ru与Ni之间的产生了相互作作用，Ni的加入促进了金属Ru在载体上的分散。 催化剂氧化还原稳定性测试的结果显示：高温还原活化Ru-Ni催化剂的氧化还原稳定性较好，原因可能是高温还原条件下Ru与Ni之间发生较强的相互作用，阻止Ru的烧结长大。 （4）Ru-Fe/Al2O3催化剂的制备、表征与催化性能 以Al2O3为载体，RuCl3.xH2O与FeCl3.6H2O为活性组分前驱体，采用吸附-沉淀法制备了系列Ru-Fe/Al2O3催化剂，以马来酸二甲酯催化加氢合成丁二酸二甲酯为探针反应，详细考察了Fe 的加入对Ru/Al2O3催化性能的影响。 评价结果表明，当Fe/Ru原子比小于2时，催化剂活性变化不大；但Fe/Ru 原子比大于或等于2时，催化剂活性有所增加；与Ru /Al2O3催化剂相比，Fe的加入改善了催化剂的氧化还原处理稳定性。 TPR、XPS及XRD表征的结果表明：Fe的加入，一方面提高了Ru在载体上的分散性；另一方面Ru与Fe之间相互作用，增强了Ru的给电子效应，可以提高催化剂对H2分子的活化能力，促进了加氢反应的进行。
Compared with other reduction processes, the catalytic hydrogenation technique is environmentally benign and more efficient, which can meet the requirements of the development of green chemistry. And the hydrogenation catalysts are the key point of the catalytic hydrogenation process, so investigations on the preparation as well as modification have been the main research topic. Among the noble catalysts, Ru-based catalysts can be used more and more widely due to its unique advantages. Previously, adsorption-precipitation method was developed by our research group to prepare the Ru catalysts, which demonstrated both high catalytic activity and selectivity for hydrogenation of dimethyl maleate under the mild conditions. Based on the previous results, the thesis focuses on the development of Ru catalysts. Hence, Ru catalysts are prepared, characterized and tested by hydrogenation of dimethyl maleate, aiming at in-depth understanding of the effects of preparation methods and the properties of the catalysts. Furthermore, using Fe and Ni as the modifiers, Ru-M/Al2O3 samples are prepared via the adsorption-precipitation method, and then characterized with XRD, XPS, TPR, TPD and other techniques. With hydrogenation of dimethyl maleate to dimethyl succinate as the probe reaction, catalytic behaviors of Ru-Ni/Al2O3 and Ru-Fe/Al2O3 were investigated. The main contents and conclusions are listed as follows: (1) Preparation, characterization and catalytic performance of Ru-supported catalysts Two methods, namely the incipient wetness impregnation and the adsorption-precipitation technique, were utilized to prepare 1.0 wt%Ru/Al2O3 samples, using Al2O3 as the support and RuCl3.xH2O as precursor. Effects of the preparation methods on the catalytic performances were investigated with selective hydrogenation of dimethyl maleate to dimethyl succinate as the probe reaction. The results demonstrated an enhanced catalytic activity with AP method as compared to IM technique, under mild hydrogenation conditions(70oC, 1.0 MPa). The relationship between preparation method and catalytic performance was discussed based on the results of XRD, TPD and XPS. It was found that the residual chlorine could cover the active centers on the catalyst, resulting in the suppression of hydrogen adsorption and activation on Ru. Compared with IM method, the AP technique could effectively eliminate residual chlorine, thus increasing the abilities of hydrogen adsorption and activation on Ru and improving the catalytic performance. (2) Properties of Ru/Al2O3 system prepared by AP method Ru/Al2O3 catalysts with different Ru content were prepared utilizing adsorption-precipitation method, and the effects of reduction conditions on the catalytic performance were investigated. The relationship between Ru content, reduction conditions and catalytic performance has been disclosed on the basis of TPR data and catalytic results. It was confirmed that several states of Ru on the fresh samples can be discerned. And Ru species that could be reduced at low temperature(reduction temperature≤100oC) may mainly contribute to the catalytic activity, the proportion of which decreased with increasing Ru loading, resulting in a decrease of the Ru utilization efficiency. On the basis of the above findings, the effective average hydrogenation rate was introduced to better evaluate the catalytic performance. (3) Preparation, characterization and catalytic performance of Ru-Ni/Al2O3 A series of Ru-Ni/Al2O3 catalysts were prepared via adsorption-precipitation method, using Al2O3 as the support and RuCl3.xH2O and Ni(NO3)2.6H2O as precursors. Effects of pretreatment conditions and the amount of Ni on the catalytic behaviors of the catalysts were investigated. The catalytic activities of Ni-modified Ru catalysts increased with the increase of the Ni content firstly and then decreased. The highest hydrogenation activity was obtained as the atomic ratio of Ni:Ru is 6:1. The catalytic activity of Ru1Ni6/Al-fresh subjected to reduction at 200oC has no significant difference with that reduced at 400oC, reaching to 1.5 times that of Ru/Al2O3 with the same pretreatment. Combination with the results of XPS, XRD and TPR, the reason for the promoted catalytic effect of Ni was disclosed. It was found that the dispersion of Ru could be improved as the promotion of Ni, resulting in the improvement of the catalytic performance of the Ru catalyst. It was also observed that the oxidation-reduction stability was improved when the sample was reduced at high temperature, because the sintering of Ru was inhibited as a result of the strong interaction between Ru and Ni. (4) Preparation, characterization and the catalytic performance of Ru-Fe/Al2O3 A series of Ru-Fe/Al2O3 catalysts were prepared via adsorption-precipitation method, using Al2O3 as the support and RuCl3.xH2O and FeCl3.6H2O as precursors. The effects of Fe addition on catalytic performance were studied using selective hydrogenation of dimethyl maleate to dimethyl succinate as the probe reaction. At a Fe/Ru atomic ratio above 2:1, enhanced catalytic performance and the stability of high temperature oxidation-reduction treatment were observed. Based on the results of TPR, XPS and XRD, the promotion effects could be ascribed to the increase of the dispersion of Ru and the change of electronic state of Ru as a result of Fe modification.
|王磊. Ru基催化剂的制备、表征及催化加氢性能研究[D]. 北京. 中国科学院大学,2014.|
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