【作者】 孙鹏；

【导师】 邵刚勤；

【作者基本信息】 武汉理工大学 ， 材料学， 2005， 硕士

【摘要】 碳化钨由于表面碳的存在改变了钨的电子表面特性,使之类似于铂的电子表面特性。据此,设想钨的碳化物可以在一些重要的化学反应中代替铂、铑等贵重的过渡金属元素作为催化剂。人们发现WC在烃分解反应、烃的异构化、室温下氢氧化合反应、CO加氢生成甲烷、肼的分解反应等反应中表现出令人感兴趣的催化能力。因此碳化钨被认为是一种很有前途的、可以用来替代铂的类铂催化剂而被广为研究。本课题中,通过对苯加氢反应的实验,研究了纳米碳化钨粉末在反应中的催化性能。纳米碳化钨粉末具有巨大比表面积,可以为催化反应提供大量的活性中心。因此在碳化钨催化性能研究中,制备粒径小、比表面积大的纳米碳化钨粉末具有着十分重要的意义。实验中采用包埋-直接还原碳化法来制备碳化钨粉末。即:将按一定比例混合的三氧化钨和碳粉置于氧化铝制碳包埋装置中,在1300℃的温度下保温3小时制得碳化钨粉末;通过对碳化钨合成反应的温度和保温时间的优选,以及分别对反应物和产物粉末的高能球磨处理来控制碳化钨粉末的粒径,并制得纳米级碳化钨粉末。文中讨论了原料中两种组分的配比、反应温度、保温时间对碳化钨合成反应的影响,以及对反应物和合成后的产物的不同处理对碳化钨粒径的影响。苯加氢催化反应实验是在一个常压固定床中进行。用作催化剂的纳米碳化钨粉末用短切玻璃纤维分散,置于反应床中。反应物苯先由水浴加热至沸腾,再由氢气载入反应床中,产物由氢气载出,并经冷凝收集。收集到的不同测试温度下的反应产物,用红外光谱来表征其组分。由于苯中不含有-CH2-官能团,而其加氢产物中含有-CH2-官能团,因此通过考查测试实验收集的液体产物的红外光谱图中-CH2-官能团的特征吸收谱带及其强度可以初步确定碳化钨在反应中的催化效能。实验结果表明,在反应温度(实验中选择300、 350、 400、 450、更多还原

【Abstract】 The presence of carbon in tungsten carbide modifies the electronic surface properties of tungsten in such a way that they resemble those of platinum. Tungsten carbide has been assumed as a new catalyst that can be substituted for Pt and Ru because of its catalytic activities in some organic reactions. Results of research reported that tungsten carbide powders showed catalytic activities in hydrogenation, dehydrogenation and isomerization of hydrocarbons, oxidization of hydrogen at low temperature and oxidization of Hydrazine. So, tungsten carbide has been universally studied as a new promising platinum-like catalyst. In this research, catalytic activity of nano-sized tungsten carbide waspreliminarily studied through hydrogenation of benzene.Nano-sized tungsten carbide has huge surface area and can provide a large number of active centers （situ） for catalytic reaction. Preparation of nano-sized tungsten carbide powder with great surface area is meaningful to its catalytic activity. In this research , Embedment - Direct Reduction Carburization Process was selected to Synthesize Tungsten Carbide, which synthesized the WC powder by 4 hours’ heat preservation at 1300 ℃. In order to control the grain size of WC powders, planetary high-energy ball milling machine was applied in pretreatment of WO3 and C mixture and aftertreatment of WC powders. SEM showed that both pretreatment and aftertreatment contributed to reducing the grain size of WC powders. The effects of WO₃/C（wt）, synthesis temperature and heat-preservation time to tungsten carbide synthesis and the effects of pretreatment and aftertreatment to the size of produced tungsten carbide were discussed.The catalytic activity of tungsten carbide was studied through hydrogenation of benzene. The reaction occurred in a flow reaction equipment with atmospheric pressure. Tungsten carbide powders were dispersed by short-cut glass fibre and situated in reaction equipment. Benzene was heated to its evaporation temperature（80.1 ℃ ） and evaporated. Its vapor was carried into reaction equipment by hydrogen.The product of reaction was also carried out by hydrogen and collected after condensation in liquid. The collected liquid was characterized by infrared spectra. There is no group of -CH2- in benzene molecular. On the contrary, the products of benzene hydrogenation are constituted of group of -CH2-. So, the catalytic activity of tungsten carbide can be estimated through examining the characteristic absorption peak of -CH2- in curve of infrared spectra.The intensity of characteristic absorption peak of -CH2- of product with tungsten carbide catalyzing was stronger those without tungsten carbide when the reaction occurred in a certain temperature. In a certain range of temperature, it increased with reaction temperature increasing. This change would disappear when the reaction temperature continue increasing because of the further dehydrogenation of benzene hydrogenation product. It means that the catalytic activity of tungsten carbide in hydrogenation of benzene increases with reaction temperature increasing.The catalytic mechanism of tungsten carbide was demonstrated.更多还原