Structure, synthesis, and catalytic properties of nanosize cerium-zirconium-based solid solutions in environmental catalysis

铈锆固溶体的结构、合成及在环境催化领域中的应用（英文）

Nanosize cerium-zirconium solid solution(CZO)with a special fluorite structure has received an increasing research interest due to their remarkable advantages such as excellent oxygen storage capacity and great flexibility in their composition and structure.By partial metal(including rare earth,transition,alkaline earth or other metal)doping into CZO,the physicochemical properties of these catalytic materials can be controllable adjusted for the study of specific reactions.To date,nanosize CZO has been prepared by co-precipitation,sol-gel,surfactant-assisted approach,solution combustion,micro-emulsion,high energy mechanical milling,etc.The advent of these methodologies has prompted researchers to construct well-defined networks with customized micromorphology and functionalities.In this review,we describe not only the basic structure and synthetic strategies of CZO,but also their relevant applications in environmental catalysis,such as the purification for CO,nitrogen oxides(NOx),volatile organic compounds(VOC),soot,hydrocarbon(HC),CO2 and solid particulate matters(PM),and some reaction mechanisms are also summarized.

二氧化铈作为一种特殊的立方萤石结构,是应用最为广泛的稀土氧化物.同时,它也是一种合适的催化剂载体,可以促进活性组分的均匀分布,提高催化活性.但纯二氧化铈在高温下容易发生团聚,导致比表面积严重降低,而锆(Zr)掺杂所形成的铈锆固溶体(CZO)会显著提高铈基催化剂的稳定性.在Zr含量较低时,CZO主要呈现立方萤石结构,随着Zr含量增加,CZO结构逐渐由立方相转变为正方相,并最终形成单斜相.此外,与其它稀土氧化物不同,CZO由于其独特的结构性质、可控的组成、良好的氧化还原性能以及氧储存性能(OSC)而备受关注.截至目前,由于其特殊的物理化学性质和有序的空间形貌,纳米尺寸CZO格外引人关注.其形貌主要包括纳米粉末、一维纳米棒、纳米管、纳米带、纳米线、二维纳米薄膜、三维纳米笼、三维介孔、大孔和多级孔.基于其不同的形貌及有序的空间结构,CZO材料呈现不同的性质,并且已被广泛应用于多相催化领域.然而,不同形貌CZO材料的性能仍然有进一步提升的空间,例如:提高材料的稳定性及机械强度;探索环境友好型合成路径;考察反应时间、温度、溶液pH值、Ce和Zr源的浓度和构型、金属掺杂等对形貌的影响;研究不同形貌CZO纳米材料的物理化学性质;阐明CZO结构、形貌与其催化性能之间的关系.环境催化可将污染物转化为无害或有价值的物质,因而被认为是当今减少环境污染最有用的方法之一.而CZO作为活性组分、载体和氧存储材料具有优异的催化活性、较高选择性、高稳定性和极强的适应能力,是环境催化领域消除污染物过程中必不可少的组分,因而被广泛应用于催化CO、VOC、Soot、PM和HC燃烧、NOx选择性催化还原和直接降解、CO2转化等反应.研究发现:采用合适的制备方法能够改善CZO的结构和物理化学性质;调节Ce/Zr摩尔比能促进CZO基材料的氧化还原性能;负载活性金属如贵金属Pt、Rh、Pd或过渡金属Mn、Co、Cu等可提高CZO的催化性能;引入第三组分不仅可以增加CZO晶格氧缺陷,改善其OSC,进而提高其催化活性、选择性和稳定性,还可以抑制晶体转变,提高CZO催化剂的热稳定性.然而,自1970年代至今,进一步提高CZO基催化剂的OSC和热稳定性以满足日益严峻的环保要求迫在眉睫.