论文部分内容阅读
聚氯乙烯(PVC)是世界五大工程塑料之一,在工业、农业、建筑、电力及通信等领域有着非常广泛的应用.氯乙烯(VCM)作为合成PVC的单体,其生产工艺以源于煤化工路线的乙炔氢氯化法工艺为主,但是该工艺目前采用的是氯化汞催化剂,存在较为严重的环境污染问题.开发新型无汞催化剂成为电石法生产VCM亟待解决的问题.氮掺杂炭基非金属催化剂成本低廉,制备简单,在诸多反应中展现了较好的性能,成为近几年多相催化领域的一个研究热点,在乙炔氢氯化反应中也具有较好的活性,但是对活性中心的鉴别及制备方法的研究还有待深入.本文报道了一种一步原位尿素掺杂氮的中孔炭的制备方法,采用氮气吸附-脱附、高分辨透射电子显微镜、元素分析和X射线光电子能谱(XPS)等表征手段研究了氮掺杂中孔炭的结构、氮含量及存在形式,并与两步尿素改性方法做了对比,探究了氮掺杂形式与中孔炭乙炔氢氯化反应性能之间的关系,同时考察了尿素用量对氮掺杂中孔炭的氮含量和存在形式的影响.元素分析结果表明,原位合成法能有效地将氮掺杂进骨架中,随着制备过程中尿素用量增加,得到的氮掺杂中孔炭中的氮含量增加,可达3.6wt%.后处理法的掺氮效果较差,材料氮含量仅为0.2wt%.XPS测试进一步表明,一步法原位法可以得到石墨型氮占据主导地位的氮掺杂中孔炭,石墨型氮约占70%左右,后处理制备的氮掺杂中孔炭中石墨氮、吡啶氮和吡咯氮三种形式含量相差不大.对不同方法合成的氮掺杂介孔炭的乙炔氢氯化反应催化性能进行了评价,结果显示,无论是原位合成还是后处理制备的氮掺杂中孔炭,其活性均比中孔炭得到一定提升.氮的引入能有效提高材料的乙炔氢氯化反应性能.原位合成法制备的氮掺杂中孔炭在乙炔氢氯化反应中的催化性能远高于后处理法.对于原位合成的氮掺杂中孔炭,在一定范围内,随着氮含量的增加,催化活性提高,但当尿素用量过高时,虽然氮含量增加,催化活性却有所下降,这归因于孔结构坍塌和比表面积下降.
Polyvinyl chloride (PVC) is one of the world’s top five engineering plastics, and has a very wide range of applications in the fields of industry, agriculture, construction, power and communications, etc. As a monomer of synthetic PVC, However, the process currently used is a mercuric chloride catalyst, which poses serious environmental pollution problems. To develop a new mercury-free catalyst has become an urgent problem to be solved in the production of VCM by calcium carbide process. It is a hot research topic in the field of heterogeneous catalysis in recent years because of its low cost, simple preparation and good performance in many reactions. It also has good activity in the hydrochlorination of acetylene, However, the research on active center identification and preparation methods needs to be further studied.This paper reports the preparation of a one-step in-situ urea-doped mesoporous carbons by nitrogen adsorption-desorption, high-resolution transmission electron microscopy, elemental analysis And X-ray photoelectron spectroscopy (XPS) were used to characterize the structure, nitrogen content and existing forms of nitrogen-doped mesoporous carbon. Compared with the two-step urea modification method, Doped mesoporous carbon acetylene hydrochlorination reaction properties, and also investigated the effect of urea on nitrogen-doped mesoporous carbon nitrogen content and form of existence.Elemental analysis results show that in situ synthesis method can be effective Nitrogen into the framework of nitrogen, with the increase in the amount of urea used in the preparation of nitrogen-doped mesoporous carbon in the nitrogen content increased up to 3.6wt%. Post-treatment of nitrogen is less effective, the material nitrogen Content of only 0.2wt% .XPS test further shows that one-step in situ method can get graphite-type nitrogen dominated nitrogen-doped mesoporous carbon, graphite nitrogen accounted for about 70% of post-processing preparation of nitrogen-doped The contents of three forms of graphite nitrogen, pyridine nitrogen and pyrrole nitrogen in the pore carbon are not different.The catalytic properties of acetylene hydrochlorination of nitrogen-doped mesoporous carbon synthesized by different methods were evaluated.The results showed that both in-situ synthesis Or post-treatment preparation of nitrogen-doped mesoporous carbon, its activity than mesoporous carbon to get a certain degree of promotion. The introduction of nitrogen can effectively improve the acetylene hydrochlorination reaction performance. In-situ synthesis of nitrogen-doped mesoporous carbon Acetylene hydrochlorination in the catalytic performance far In the post-treatment method, the activity of in-situ synthesis of nitrogen-doped mesoporous carbon increased with the increase of nitrogen content in a certain range, but when the amount of urea was too high, the catalytic activity was increased although the nitrogen content increased This is attributed to the collapse of pore structure and the decrease of specific surface area.