文章信息/Info

Title:

A Theoretical Study of Phase Equilibria of Pt Doped Calcium Titanate

作者:

李白海1; 2; 張秋杰1; 陳亮2

1能源科學與工程學院，電子科技大學，四川 成都 611731 2中國科學院寧波材料工程與技術研究所，浙江 寧波 315201

Author(s):

ZHANG Qiujie1;  LI Baihai1; 2;  CHEN Liang2

1School of Energy Science and Technology, University of Electronic Science and Technology of China, Chengdu, 611731, China 2Ningbo Institute of Materials Technology & Engineering, Chinese Academy of Sciences, Ningbo, 315201, China

關鍵詞:

催化劑; 量化計算; 相圖; 熱力學平衡

DOI:

10.7502/j.issn.1674-3962.2015.04.02

文獻標志碼:

A

摘要:

已有實驗表明貴金屬Pt能夠隨外界氧化還原條件的改變，自發地在鈣鈦礦CaTiO3內部和表面之間遷移，有效抑制貴金屬顆粒的燒結，使得貴金屬長期保持高效的催化活性，因此該體系被稱為汽車尾氣“智能催化劑”。但當前對該體系中貴金屬與載體之間的相互作用，以及貴金屬遷移特性發生的條件以及程度的研究很少。本文采用基于第一性原理計算與集團展開法以及蒙特卡洛方法相結合構建PtOx-CaO-TiOx三元相圖，對可再生汽車尾氣催化劑Pt摻雜CaTiO3體系進行了理論研究。第一性原理相圖分析表明Pt能夠以不同濃度取代CaTiO3中的Ti原子，而熱力學相圖分析表明Pt摻雜到CaTiO3中將形成固溶體，更重要的是Pt能夠在氧化還原條件下與CaTiO3形成固溶體或者析出，與“智能催化劑”的概念相一致。此外，相圖分析還預測了其它一些氧化物以及合金結構的存在，以及得到了這些物質之間的相變規律。這些結果將為實驗工作提供有益的幫助，有利于開發高效的汽車尾氣催化劑。

Abstract:

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 precious-metal 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-TiOx 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-xPtxO3 structures evolve to solid solutions at ambient temperatures. More importantly, Pt tends to dissolve into CaTiO3 substrate under oxidizing conditions while precipitate 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.