Pt掺杂CaTiO_3体系相平衡的理论研究  

A Theoretical Study of Phase Equilibria of Pt Doped Calcium Titanate

作　　者：李白海[1,2] 张秋杰[1] 陈亮[2] 

机构地区：[1]电子科技大学能源科学与工程学院,四川成都611731 [2]中国科学院宁波材料工程与技术研究所,浙江宁波315201

出　　处：《中国材料进展》2015年第4期264-271,288,共9页Materials China

基　　金：国家重点基础研究项目(2013CB934800);国家自然科学基金(11104287);宁波市自然科学基金(2012A610099)

摘　　要：已有实验表明贵金属Pt能够随外界氧化还原条件的改变,自发地在钙钛矿Ca Ti O3内部和表面之间迁移,有效抑制贵金属颗粒的烧结,使得贵金属长期保持高效的催化活性,因此该体系被称为汽车尾气"智能催化剂"。但当前对该体系中贵金属与载体之间的相互作用,以及贵金属迁移特性发生的条件以及程度的研究很少。采用第一性原理计算方法与集团展开法以及蒙特卡洛方法相结合构建Pt Ox-Ca O-Ti Ox三元相图,对可再生汽车尾气催化剂Pt掺杂Ca Ti O3体系进行了理论研究。第一性原理相图分析表明,Pt能够以不同浓度取代Ca Ti O3中的Ti原子;而热力学相图分析表明,Pt掺杂到Ca Ti O3中将形成固溶体,更重要的是Pt能够在氧化还原条件下与Ca Ti O3形成固溶体或者析出,与"智能催化剂"的概念相一致。此外,相图分析还预测了其它一些氧化物以及合金结构的存在,并得到了这些物质之间的相变规律。这些结果将为实验工作提供有益的帮助,有利于开发高效的汽车尾气催化剂。Previous Experiments reported that precious-metal Pt is able to migrate between perovskite CaTiO3 surface and bulk with change of the external redox conditions. This novel process can efficiently suppress the agglomeration of preciousmetal particles, and maintain the high performance of the so-called ＂intelligent catalysts＂ for a long period. However, the study of the interactions between precious-metal and CaTiO3 substrate is rather limited. The first-principles calculations combined with cluster expansion and Monte Carlo methods were employed to construct the PtOx-CaO-TiO3 pseudo-ternary phase diagrams to explore the properties of Pt-doped CaTiO3 system. The first-principles phase diagrams show that Pt can be doped in CaTiO3 and occupy the Ti-site at various concentrations, and the thermodynamic phase diagrams indicate that the doped CaTi1-xPtx 03 structures evolve to solid solutions at ambient temperatures. More importantly, Pt tends to dissolve into CaTiO3 substrate under oxidizing conditions while precipitating from the perovskite matrix and exist as metallic particles under reducing conditions, which is consistent with the concept of ＂intelligent catalyst＂. Furthermore, the investigations of the phase diagram indicate the existence of some other oxides and metal alloys in the catalyst system at various conditions. The results might inform the experiments and be helpful for preparing highly efficient catalysts for elimination of harmful exhaust gas.

关 键 词：催化剂 量化计算 相图 热力学平衡 Pt掺杂CaTiO3体系 

分 类 号：O643[理学—物理化学]