【作者】 王国雄；

【导师】 孟祥举； 肖丰收； 王亮；

【作者基本信息】 浙江大学 ， 化学， 2018， 硕士

【摘要】 贵金属负载型纳米催化剂以其优异的催化性能,广受科研工作者的喜爱,但是在实际工业应用中,催化剂的使用条件往往十分严苛,需要高温高压等条件,这对催化剂的稳定性提出了巨大的挑战,如何在高温条件下保证贵金属纳米粒子不因团聚而失活,是催化剂领域的一个重点攻克的难题。传统负载型金属催化材料的制备过程中,其活性中心金属在载体上的分布是随机的,在经过高温处理或是经历高温反应后,活性中心的金属纳米粒子就会不可避免的发生迁移和团聚,进而极大地影响其反应活性。而本文巧妙地利用介孔沸石的表面缺陷位提供一个极性的环境来聚集溶液中的Pd前驱体,使之在载体沸石上选择性地分布,再通过前驱体有机阴离子自身的还原作用,在介孔沸石的缺陷部位形成定向负载的金属纳米粒子,有了介孔的阻隔作用,高温处理以及高温反应时,活性中心的金属纳米粒子便会限域在介孔内部,不发生团聚,从而具有较高的稳定性。本文介绍了一种新颖的Pd@分子筛催化剂的合成方法,并对其高温焙烧稳定性及高温反应稳定性进行了测试,结果表明该方法制备的催化剂在高温处理和高温反应条件下金属纳米粒子不团聚,具有良好的高温稳定性。本文首先研究了 Pd的前驱体醋酸钯溶解在极性溶剂中,发生自还原生成Pd纳米粒子的过程,并考察了合成条件对生成的纳米粒子的影响。研究表明,醋酸钯溶液中Pd离子能够被醋酸根离子还原,并被产物中的有机基团所稳定,从而形成Pd纳米粒子,该过程还受到温度和浓度等条件的影响。再在原有醋酸钯自还原体系中引入有缺陷的介孔沸石作为载体,通过介孔沸石的表面的介孔缺陷对Pd前驱体的富集作用以及钯源自还原,最终得到定向负载在介孔沸石缺陷里的,具有高温抗烧结性能的负载型Pd@zeolite催化剂。与普通负载的催化剂相比,该催化剂在600℃煅烧条件下能保持纳米粒子稳定不团聚,即使在80O℃煅烧后,催化剂的CO催化氧化活性也能很好的保持。此外,在长时间的高温CO氧化反应条件下,该催化剂也能保持纳米粒子不团聚,反应活性基本不降低。更多还原

【Abstract】 Due to their excellent catalytic performance,supported noble metal catalysts are widely explored by researchers.However,in practical industrial applications,the conditions for the many reactions are often very harsh,usually with high temperature or pressure,which provide a huge challenge to the stability of the catalysts.How to ensure that the noble metal nanoparticles are not deactivated by agglomeration under high temperature conditions,is a key problem in the field of catalysis.In the traditional synthesis process of the supported metal catalysts,the nano particles are randomly distributed on the support After the high temperature treatment or high temperature reaction,the active sites will inevitably migrate and agglomerate,which greatly decreases their activity.In this paper,we took use of the surface defects of mesoporous zeolite as traps to provide a polar environment to Pd precursor solution,so that they can be rationally distributed,and then the Pd nanoparticles were formed by self-reduction of the organic anion in Pd(OAc)2 in the traps of the zeolite.With Pd nanoparticles isolated by the zeolite framework,the Pd nanoparticles are sinter-resistant under high-temperature calcination and catalytic oxidation.A novel synthesis method of Pd@zeolite catalysts is introduced in this paper,and the test for high-temperature resistance and catalytic stability indicate that the catalysts prepared by this method have excellent high temperature stability,with no obvious agglomeration to the metal nanoparticles.In this paper,we first studied the self-reduction of the Pd(OAc)2 itself to forming Pd nanoparticles.The results indicated that the Pd ions in palladium acetate solution can be reduced by acetate ions and stabilized by the organic groups in the product to form Pd nanoparticles.The process is also affected by temperature and concentration conditions.Then the defected mesoporous zeolite was introduced into the system above as the support for supported catalysts.Pd precursor was enriched by the mesoporous traps on the surface of the zeolite,and after the self-reduction of the Pd(OAc)2 itself,the palladium nanoparticles were rationally positioned into traps of zeolite to obtain the Pd@zeolite catalysts with high sinter-resistant ability.Compared with the conventional supported catalyst,this catalyst can keep the nano-particles stable and non-agglomerated when calcined at 600℃.Even after calcination at 800℃,the CO catalytic oxidation activity of this catalyst can be well maintained.In addition,under the condition of prolonged high-temperature CO oxidation reaction,the catalyst can still keep the nanoparticles from agglomerating,with no obvious decrease of the reaction activity.更多还原