【作者】 冯伟樑；

【导师】 曹勇；

【作者基本信息】 复旦大学 ， 物理化学， 2007， 博士

【摘要】 低碳烷烃制取高附加值的烯烃和含氧衍生物是当前催化领域内最富挑战性的课题之一。由资源丰富的烷烃转化成需求量日益增长的烯烃，更是这一领域内的研究前沿。目前工业丙烯主要来自炼油厂流化床裂解和乙烯裂解，其收率均比较低，难以满足增长的需求；而丙烷非临氧条件下直接脱氢制丙烯的反应由于反应温度高、能耗大、催化剂易结焦失活等原因，使其在工业生产中受到很大限制。而近年来丙烷氧化脱氢制丙烯的反应，由于其在热力学上有利，可以避免直接脱氢反应中存在的许多问题，成为一个有巨大应用前景的研究课题。然而，由于其产物丙烯活泼性远高于原料丙烷，在临氧条件下，丙烯很容易进一步转化成深度氧化产物，导致反应的选择性不高，所以经过数十年的努力，仍然没有能够工业化的催化剂问世。因此，开发新的催化材料用于丙烷氧化脱氢反应，不论在理论研究还是在工业应用方面都有重要的价值。近年来具有规整孔道结构和较窄孔径分布的介孔分子筛材料作为催化载体，其优良的性能被催化界所广泛关注。在介孔分子筛上引入高分散金属氧化物活性组分后，人为调节其表面性质，有望成为高效的丙烷氧化脱氢制丙烯的新型催化剂。过氧化氢是一种重要的无机化工产品，近年来随着现代电子行业的发展和环保绿色化工的需求，这些行业对高纯度，无有机污染物的过氧化氢需求量不断增加。然而，现有工业蒽醌法制得的过氧化氢产品中含有残留的烷基蒽醌等有机杂质，极大地限制了成品过氧化氢的应用范围。目前工业需求的高纯度过氧化氢，需要在蒽醌法成品的基础上，进行蒸馏，离子交换，活化吸附，萃取等步骤处理，此方法工艺复杂，能耗巨大，限制了高浓度过氧化氢的大规模生产。为避免传统生产方法带来的有机溶剂污染问题，采用直接法生产过氧化氢是近年来人们一直积极探索的课题。国外研究发现，采用负载型贵金属催化剂，可由氢气氧气直接合成过氧化氢。此方法采用纯水为介质，无需净化去除有机杂质，因此是极具前途的生产工艺。与国外相比，直接法制过氧化氢在我国的研究还是空白，应此，开展直接法制过氧化氢的研究，极富挑战性且具有重大社会意义。本论文分两部分，第一部分研究了丙烷氧化脱氢制丙烯的课题，我们将新型钴基介孔分子筛催化剂以及传统氧化硅载体上钒钼二元高分散金属氧化物模型催化剂用于丙烷氧化脱氢制丙烯的研究；第二部分研究了直接法制过氧化氢的课题，我们既采用贵金属钯催化剂进行了氢氧法直接制过氧化氢，也采用了较温和条件下以一氧化碳，氧气，水为原料制过氧化氢。本论文在这两个课题基础上，通过催化剂的制备，表征以及反应活性的测试，对两元金属氧化物模型催化剂以及纳米金属催化剂在上述两个反应过程中催化反应本质进行了不同程度的探讨。本论文主要内容如下：一Co-SBA-15系列催化剂的制备及其丙烷氧化脱氢性能采用浸渍法制备Co-SBA-15系列催化剂（Co-SBA-15），用不同Co前驱体制备了相同Co含量的系列催化剂（Co20-SBA-15-x），以柠檬酸钴络合物为前驱体制备了一系列不同Co含量的系列催化剂（Cox-SBA-15），还用不同含量的P，Ti，Zr等助剂对Co-SBA-15催化剂进行了修饰。小角XRD和透射电镜结果表明，所制备的SBA-15具有典型的六方孔结构及规整的孔道，Co氧化物颗粒进入SBA-15孔道，Co的引入并没有破坏SBA-15的孔结构。随着Co负载量的提高，Co的分散性变差，不能很好的分散在载体表面。XPS，H₂-TPR研究表明，催化剂中随着Co与载体相互作用的强弱差异，Co物种在催化剂表面分别以3种形式共存：团聚的Co₃O₄，与载体弱相互作用的CoO，与载体有强相互作用的硅酸钴。不同配体为前驱体制备的催化剂，其Co物种与载体作用按Cl^-＜H₂O＜柠檬酸＜NH₃的顺序由弱到强。随着Co负载量的增大，硅酸钴物种增多，Co与载体表面相互作用也逐渐变强。而加入助剂修饰后，Zr能使Co更好的分散在载体表面，Ti和P则使Co进一步形成CoTiO₃与Co₃（PO₄）₂物种，改变了Co与载体的作用强度，对催化活性也有影响。XRD的研究表明，催化剂表面Co主要以Co₃O₄形式存在，其颗粒粒径随负载量增大而增大，随前驱体配体变强而减小，导致Co分散度不同。此趋势也为TEM观察和XPS计算所证实。CO吸附红外研究表明，Co-柠檬酸配合物为前驱体制备的不同Co负载量的催化剂，与气相CO分子所形成的羰基钴红外振动波数略有不同，也预示着Co在载体表面不同的分散性和相互作用。用连续微反应装置考察活性结果表明，用Co-柠檬酸配合物为前驱体制得的Co-SBA-15催化剂具有最好的催化活性，当Co负载量为20wt％时，丙烷转化率和丙烯选择性达到最大值，此时(500℃，W=0.05 g，GHSV=72，000 L kg^-1cat h^-1，C₃H₈：O₂：N₂=1：1：8)丙烯收率为26.2％。而用不同组分修饰的催化剂活性测试表明，2wt％Zr修饰的催化剂活性好于Ti，P修饰以及未修饰的催化剂，主要原因是Zr的存在增加了Co的分散性，改变了Co与载体的相互作用，使之产生了较多的Co-载体弱相互作用物种。因此，可以认为，在制备Co-SBA-15催化剂用于丙烷氧化脱氢反应时，高活性，高选择性的催化剂，应使其具有较多的Co-载体弱相互作用物种，避免产生无活性的Co-载体强相互作用物种。二V-Mo二元金属氧化物模型催化剂的制备及其丙烷氧化脱氢性能用浸渍法制备了一系列不同V／Mo负载量的V-Mo-SiO₂二元金属模型催化剂（VxMoySiO₂）。按照V，Mo理论单层分散量的1／2，1，2倍调节负载量，并调整负载顺序，用作参比催化剂。H₂-TPR结果表明，随着Mo的加入，因V-Mo间的相互作用而产生新的V-Mo-O物种，VO_x的还原温度向低温方向移动。UV-RAMAN研究结果表明，在单层负载的Mo-SiO₂表面，仅存在MoO₆八面体物种以及Mo-O-Mo单层聚合物种。在单层负载的V-SiO₂表面，仅观察到VO₄四面体物种所具有的V=O振动峰，没有V₂O₅的特征峰存在。随着第二元金属组分的加入，780 cm^-1位置的峰强度逐渐变大，预示着形成了新的V-O-Mo聚合物种。而水汽的存在对催化剂表面金属氧化物物种配位情况和几何构型也有影响。催化剂酸性一般对反应选择性有较大影响，NH₃-TPD的研究表明，在固定单层Mo负载量的催化剂中，总体催化剂酸性较弱，随着V负载量的增加，酸强度略微减弱，而酸量增加。而丙烷脉冲实验研究了催化剂表面吸附氧和活性晶格氧的储量，吸附于催化剂表面的分子氧易把产物烯烃进一步氧化成深度氧化产物，而反应的高选择性转化则是通过催化剂内部晶格氧进行。通过脉冲测定，各为单层负载量的V-Mo-SiO₂催化剂中活性晶格氧储量最大，与TPR预测结果一致。活性测试结果表明，相比单一组分的催化剂，V-Mo二元金属模型催化剂有更好的催化活性，当V和Mo的负载量分别达到理论单层分散值时，丙烯收率最大。这一结果证实，二元金属氧化物模型催化剂由于V-Mo间的协同相互作用产生的V-O-Mo聚合物，相比一元金属氧化物催化剂更有利于丙烷氧化脱氢反应。三纳米Pd催化剂在H₂/O₂直接法制过氧化氢中的应用研究采用了微波加热，氢气，水合肼，甲醛等还原手段，用浸渍法制备了一系列Pd／C催化剂，用于H₂／O₂直接法制过氧化氢中的应用研究。TEM测试结果表明，对采用不同还原法制备的催化剂，微波法制得的催化剂金属Pd颗粒较小，粒径均一，高度分散，催化活性较好。而采用其他还原方法制得的催化剂，Pd颗粒都有不同程度的团聚现象，易长大形成较大晶粒。对煤质，杏壳，椰壳等不同种类活性碳载体材料的物理化学特性，还采用BET，SEM，XRD等手段进行了表征。结果发现，由于载体本身具有不同的表面积和孔结构以及杂质含量，对催化活性有较大影响，其中采用椰壳活性碳载体作为载体得的Pd／C催化剂，有较好的反应活性。进一步研究催化剂的XRD测试结果，我们发现采用不同还原法所制得的催化剂，其暴露的Pd的各类晶面比例差别较大，且与催化活性紧密相关。为此，我们采用理论计算方法，获得了不同晶面不同Pd位置上H，O以及OH，H₂O₂的吸附能。结果表明，反应基团若在Pd（110）面上进行吸附反应，在能量上较为有利，此结果初步解释了不同还原方法对催化活性的差别。这一结果也对我们下一步工作有一定的指导意义。四纳米Cu催化剂的制备及其CO/O₂/H₂O直接法制过氧化氢性能为在较温和条件下进行直接法制过氧化氢研究，我们选取了CO／O₂／H₂O作为反应体系。我们采用浸渍法制备了一系列含有不同金属的负载型催化剂，并对它们进行了研究。通过不同反应条件的活性测试，我们发现Cu／Al₂O₃有较好的催化活性。在此基础上，对氧化铝载Cu基催化剂进行了进一步研究。XRD结果表明，不同负载量的采用KBH₄还原的Cu／Al₂O₃系列催化剂，均观察到2θ值为43.3°和50.4°归属于Cu（100）及Cu（200）晶面的金属Cu特征衍射峰。所有样品中未出现CuO及Cu₂O的衍射峰，表明样品中的Cu（Ⅱ）前驱体已被完全还原。随着铜负载量的增加，可观察到Cu（100）及Cu（200）晶面的衍射峰强度逐渐增强，表明催化剂表面形成了尺寸较大的金属铜纳米晶粒。通过N₂O化学滴定所测得的金属铜表面数据及XRD结果，我们估算出各催化剂表面金属铜纳米晶粒的尺寸随Cu负载量的增加而变大，与TEM的观察结果相吻合。当Cu／Al₂O₃催化剂表面纳米金属铜平均粒径为15 nm左右时，有最高的H₂O₂生成速率，这一结果体现了在以CO／O₂／H₂)为原料直接合成H₂O₂反应中，Cu／Al₂O₃催化剂呈现出强烈的纳米尺寸效应。此外，我们还在反应中对铜基催化剂用量，原料气的分压，所使用的辅助酸，辅助溶剂等一系列影响反应活性的条件或参数进行了优化，结果发现，当使用1.0克催化剂，O₂：CO为2 MPa：2 MPa，采用0.01 M硫酸，三小时反应，可获得最佳活性结果。在此基础上，丙酮等有机溶剂的加入，有利于稳定反应生成的H₂O₂，从而可获得更高浓度的H₂O₂溶液。更多还原

【Abstract】 The research drive to develop an oxidation dehydrogenation （ODH） process for propane comes from the facts that the chemical industry depends heavily on the propylene and other alkenes feedstock. The major source of propylene currently is steam cracking and FCC, the steam cracking maximizes ethylene yield and in the FCC plant propylene is produced as a by-product, so propylene production from these sources will barely match the consumption. Thermal dehydrogenation suffers from several drawbacks, such as thermodynamics limited, rapid coking and high reaction temperature, from the industrial standpoint. ODH can be a viable route for production alkenes as the presence of oxygen counteracts the thermodynamic limitation and prevent coking. While this has been recognized for a long time, an industrially applicable process has not been developed, because secondary oxidation of alkanes to carbon oxides is very significant on most materials. Thus the yield of alkenes remained under 30%, far from satisfactory for commercial application. So it is necessary to develop other new efficient catalysis materials for the ODH of propane. Recently considerable interest has been focused on the potential applications porous solid of ordered mesoporous silica with pore walls of uniform width in the range 1-5 nm and controlled uniform pore diameters in the range 2.5-25 nm as periodic hosts for the preparation of mesoporous catalysts with chemically functionalized surfaces have been widely investigated in the past decade. SBA-15 is a newly discovered mesoporous silica molecular sieve with larger pore diameters, tunable uniform hexagonal channels and thick framework walls, which improve its thermal stability, so it is a promising new type of porous support for fabrication the catalyst for ODH of propane.As an important chemical product, hydrogen peroxide was widely used in many fields, such as the bleaching of the pulp and paper, environmental protection, chemical and food industry for it is an environmentally friendly oxidant. With the increase of the demand, the production of hydrogen peroxide has become more and more important. Currently, the commercial production of H₂O₂ is mainly based on a multistep process involving cyclic hydrogenation and oxidation of an alkyl anthraquinone in a complex working solution. This high-energy consuming process often has disadvantages, such as the cost of the quinone solvent system and the elaborate treatments required to remove degradation products due to non-selective hydrogenation. Hence, it is highly attractive to develop more economical and "green" processes that can allow the direct synthesis of H₂O₂. Although notable recent progress in this area is the use of noble metal based catalysts to achieve efficient production of H₂O₂ from mixtures of H₂/O₂, the latter process in particular has attracted recent interest due to its high safety.1 Mesostructured Co-SBA-15 Catalysts for Oxidative dehydrogenation of propaneThe influence of cobalt loading （10-30 wt%）, cobalt precursor on the physico-chemical and catalytic properties of mesoporous Co/SBA-15 catalysts for the light alkanes （propane and ethane） ODH reactions has been investigated. The combination of different techniques （LAXRD, WAXRD, Raman, TEM, and H₂-TPR） in the characterization of cobalt supported on mesoporous SBA-15 catalysts show that the disparity and the nature of the cobalt species depend strongly on the Co loading and cobalt precursor. Textural, TEM, and LAXRD results indicate that the ordered hexagonal mesoporous structure with large pore diameters of the support is retained upon the cobalt incorporation, and therefore high surface areas were obtained on the final catalysts. A maximum light alkenes （propylene and ethylene） yield was found for the sample with 20 wt% Co loading, though the activity test in the range of Co loading study. And with the similar cobalt loading （20wt%）, the catalyst prepared from cobalt nitrate and citric acid has a better light alkenes formation rate than using other precursors. The high performance of the catalyst （prepared from cobalt nitrate and citric acid） in light alkanes （propane and ethane） oxidative dehydrogenation has been attributed to a better Co dispersion and a stronger cobalt-support interaction in final samples, as evidenced by TEM, XPS, and TPR.Cobalt catalysts impregnated on Zr and Ti-doped mesoporous SBA-15 silica were characterized and investigated in the oxidative dehydrogenation （ODH） of propane. Catalysts supported on pure siliceous SBA-15 and conventional amorphous silica were also examined. The best performance in propane ODH is achieved with the Co/Zr-SBA sample with 2wt% Zr. The enhanced catalytic performance of the Co/Zr-SBA catalysts has been attributed to the beneficial generation of highly dispersed Co²⁺-riched Co₃O₄ nanocrystallites in the zirconium-containing materials.2 ODH of propane over silica supported binary V-Mo-O catalystThe catalytic performance of vanadia dispersed on silica containing a nominal molybdena near-monolayer coverage in the oxidative dehydrogenation （ODH） of propane was investigated. The surface structure of the MO_x species （M = Mo, V） was probed with UV-laser Raman spectroscopy, while the acidity and reducibility of the materials were investigated by temperature programmed NH₃ desorption and H₂ reduction. The lattice oxygen content was test by propane pulse reaction. The great activity of vanadia dispersed on molybdena modified silica reflects the high activity of propane dehydrogenation rate. The high dispersion of V and Mo species, the interaction between the V, Mo species and the support, as well as the medium strong acidity of the catalysts all account for the high activity of this material.Vanadia catalysts supported on molybdena modified silica at theoretical monolayer coverage were tested in the oxidative dehydrogenation of propane. Characterization of the materials showed that MoO_x and VO_x surface species are essentially amorphous in nature and well dispersed on the support surface in isolated and polymeric moieties. V/Mo/Si catalysts were more active than V/Si or Mo/Si catalysts in the oxidative dehydrogenation of propane. There were no correlation between reducibility, determined by TPR, and activity was established, since all catalysts exhibited similar reduction behavior with T_max ranging between 470 and 510℃, but different activity. Comparing catalysts on propane pulse reaction, we could correlate the lattice oxygen species and the catalytic property, which suggests that the dispersion of vanadia on Mo modified silica near monolayer coverage could increase the catalyst activity for propane ODH reaction. The high activity can be ascribed to the formation of V-O-Mo bonds between the dispersed vanadia and the Mo modified layer. The results also reveal that the metal oxide can be well dispersed on modified neutral support material.3 Direct synthesis of hydrogen peroxide from H₂ and O₂ over nano-Pd/C catalyst The influence of support physico-chemical properties and reduce method on the catalytic properties of Pd/AC catalysts for the direct synthesis of hydrogen peroxide from H₂ and O₂ has been investigated. The catalytic reactions of hydrogen and oxygen molecules with active metal atoms of a catalyst for direct formation of hydrogen peroxide product and water has been presented. The combination of different techniques （XRD, SEM, TEM） in the characterization of active carbon support and the corresponding Pd/C catalysts show that the disparity and the nature of the surface characteristics of the carbon support play important roles in determining the final properties of the palladium loaded catalyst.Coupled with the theoretical analysis of Pd nanocrystals having different surface structures, it is further revealed that the crystal phase （110） having a linear alignment of metal atoms on the crystals is more effective for selective H₂O₂ formation from H₂ and O₂, which is suggested to be one of the most important parameter that must be considered in designing highly effective Pd catalyst for direct H₂O₂ synthesis.4 Direct production of hydrogen peroxide from CO, O₂, and H₂O over a novel alumina-supported Cu catalystCurrently, the commercial production of H₂O₂ is mainly based on a multistep process involving cyclic hydrogenation and oxidation of an alkyl anthraquinone in a complex working solution. This high-energy consuming process often has disadvantages, such as the cost of the quinone solvent system and the elaborate treatments required to remove degradation products due to non-selective hydrogenation. it is highly attractive to develop more economical and "green" processes that can allow the direct synthesis of H₂O₂ from H₂ and O₂ or from CO, O₂ and H₂O, in particular the later process has attracted recent interest due to its high safety.The influence of support, reduction method, active metal for the direct synthesis of hydrogen peroxide from CO, O₂ and H₂O has been investigated. A series of environmentally benign nanocrystalline Cu/Al₂O₃ catalysts for the direct formation of H₂O₂ from CO, H₂O and O₂ have been developed by a novel liquid-phase chemical reduction method and characterized by TEM, XRD, and N₂O titration. A maximum H₂O₂ formation rate of 0.236 mmol（g-cat.）^-1h^-1 was achieved over the catalyst with average Cu particle size of ca. 15 nm, suggesting the presence of a significant size effect for the performance of the Cu/Al₂O₃ catalysts.更多还原