【作者】 李致伯；

【导师】 宋一兵；

【作者基本信息】 汕头大学 ， 工业催化， 2010， 硕士

【摘要】 碳酸二甲酯(DMC)是重要的绿色化工产品,具有广泛的应用前景,被誉为21世纪有机合成的“新基块”。在DMC合成方法中,甲醇气相氧化羰基化法以其成本低,污染小,产物选择性高和生产工艺简单等诸多优点倍受重视,被誉为是最有前途的DMC生产方法之一。然而,甲醇气相氧化羰基化法合成DMC存在的主要缺陷是甲醇转化率低,催化剂易于失活。本文从改变催化剂的助剂和载体两个方向出发,研究了多羟基化合物类助剂对甲醇气相氧化羰基化合成DMC催化剂性能的影响,并对助剂选择方法以及助剂的添加量等问题进行了探讨;同时,建立了载体的类型与催化剂反应活性、产物选择性之间的对应关系,研究了载体的材质及孔结构对催化剂性能的影响,主要研究结果如下:1.以多羟基化合物为助剂修饰活性炭(AC)负载的Pd-Cu双金属催化剂。活性评价结果显示:未添加助剂时,甲醇的转化率为2.8%,DMC对甲醇的选择性为88.9%。而添加适量的丙三醇后,甲醇的转化率达到26.1%,DMC对甲醇的选择性达到92.1%。XRD,SEM,XPS等表征结果表明:多羟基化合物助剂的添加,能有效提高金属活性组分的分散度,且焙烧后不会产生包裹活性组分或者挤占载体表面活性位的残余物,因此助剂改性后Pd-Cu/AC催化剂的反应性能较改性前有显著的提高。值得注意的是:多羟基化合物具有还原性,添加量过多将导致金属活性物种部分还原,造成催化剂活性下降。2.介孔材料的合成及其负载的Pd-Cu双金属催化剂的反应性能。以SBA-15为硬模板,蔗糖为碳源,合成出介孔炭材料。SEM,XRD和N2物理吸附测试结果显示:介孔炭呈棒状,质地疏松,有序度良好,表面积大,且孔道分布均匀,孔径集分布中在4nm左右。将合成的介孔炭作为载体应用于甲醇气相氧化羰基化反应中,活性评价结果显示:甲醇的初始转化率很高,达到了30%左右,可是产物对甲醇的选择性偏低,只有7%。随着反应的进行,转化率逐渐下降到17%,而DMC对甲醇的选择性在6h则升高到90%,且在随后的测试段内内保持稳定。对比活性炭负载的催化剂反应性能,可以看出炭质载体的孔结构的改变、孔径的增大并不能有效提高催化剂的反应性能,说明本反应体系所涉及的传质阻力较小,影响催化剂反应性能的关键因素应是金属活性物种的分散度。3.活性炭的预处理对催化反应性能的影响。测试的样品中,以0.5M硝酸处理的活性炭负载的金属催化剂性能最佳。在反应的初始阶段,甲醇最高转化率超过30%;进入稳定期后,转化率为25%, DMC对甲醇的选择性为90%。表征结果表明,硝酸处理能显著提高活性炭表面含氧基团的浓度,使得金属活性组分易于分散。而随着硝酸浓度的增加,高浓度的硝酸会氧化活性炭表面的不稳定碳分子,破坏活性炭的内孔壁表面,使得活性炭的部分微孔或中孔变大,从而降低了催化剂的活性。更多还原

【Abstract】 Dimethyl carbonate（DMC）, as an important green chemical intermediate, has considerable potential for green chemicals synthesis, and is known as a new benign building block of organic synthesis in the new century. There are several ways to the synthesis of DMC, in which vapor-phase oxidative carbonylation of methanol has many advantages, such as low erosion, relatively easier separation of products, attainable raw materials etc. However, the major drawback for this reaction is a low methanol conversion together with rapid deactivity of catalysts.In this paper, promoter and support were investigated to study the change of catalyst activity for synthesis of dimethyl carbonate by gas-oxidative carbonylation of methanol. The results are summarized as follows:1. In the reaction of gas-phase oxidative carbonylation of methanol, the activity of PdCl2-CuCl2/AC catalyst was low, the conversion of methanol and the selectivity of DMC to methanol are 2.8% and 88.9%. When the catalyst was modified by glycerol, its catalytic performance was improved significantly: the conversion of methanol and the selectivity of DMC to methanol are 26.1% and 92.1%. The catalysts use polyhydroxy compounds as promoter were characterized by means of XRD, SEM and XPS. The results showed that the addition of promoter can significantly enhance the dispersal of active species. And there would not have leftover after calcinations which will enwrap active component. However, the polyhydroxy compounds promoters would reduce the metal active component, and this situation would induce the deactivation of catalysts.2. Using SBA-15 as hard templates, sucrose as the carbon source, mesoporous carbon materials were prepared. The results of SEM and XRD showed that mesoporous carbon had a rod with loose texture, there were three XRD peaks which could be assigned to （100）, （110） and （200） diffractions of the 2-d hexagonal space group, it indicated that carbon materials had highly ordered structure. And the carbon material has uniform mesopores about 4 nm in size. Mesoporous carbon was used as catalyst support in the synthesis of dimethyl carbonate by gas-phase oxidative carbonylation of methanol. At the beginning, the conversion of methanol and the selectivity of DMC to methanol are 30% and7%. While the activity of catalyst remains stable, the conversion of methanol and the selectivity of DMC to methanol are 17% and 90%. Compare with the catalysts support on the AC, it appeared that the change of pore structure and the increase of pore diameter can enhance the catalytic activities. So it can conclude that the key factors is dispersion of metal active species.3. The activated carbon （AC） which treated with different methods were investigated to study the change of PdCl₂-CuCl₂/AC catalysts activity, and found that the AC treated with nitric acid （0.5M） had the best performance. At the beginning, the conversion of methanol was more than 30%; the conversion received 25% and the selectivity of DMC to methanol was more than 90% while catalyst remains stable. The results of characterization showed that the treatment of HNO3 can significantly increase the concentration of oxygen-containing groups on AC, so the dispersal of active species on AC will be enhanced. However, a too-large concentration of HNO3 will destroy the mesopore and micropore structure of AC which will decrease the activity of catalysts.更多还原