Unexpected trends in the enhanced Ce 3+ surface concentration in ceria–zirconia catalyst materials
Unexpected trends in the enhanced Ce 3+ surface concentration in ceria–zirconia catalyst materials
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二氧化铈-氧化锆催化剂材料中 Ce 3 表面浓度提高的意外趋势
DOI：
10.1039/d0ta02762f
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发表时间：
2020
影响因子：
11.9
通讯作者：
Haile, Sossina M.
中科院分区：
文献类型：
--
作者：
Yuan, Weizi;Ma, Qing;Liang, Yangang;Sun, Chengjun;Narayanachari, K. V.;Bedzyk, Michael J.;Takeuchi, Ichiro;Haile, Sossina M.
尽管二氧化铈-氧化锆固溶体在多相催化中具有巨大的重要性，并且越来越多的共识是催化活性与还原的Ce 3+物质的浓度和伴随的氧空位相关，但是在这些材料的表面处发生催化的还原程度是未知的。使用角分辨X射线吸收近边光谱（XANES），我们在技术相关的条件下量化在单晶氧化钇稳定的氧化锆YSZ（001）上生长的氧化铈-氧化锆膜的表面（2-3 nm）和体区域中的Ce 3+浓度。在所有情况下，我们观察到大量的Ce 3+富集在表面相对于散装。令人惊讶的是，在不存在Zr的情况下增强的程度最高。这种行为与其中Ce 3+浓度随着Zr含量的增加而单调增加的体相的行为形成直接对比。这些结果表明，虽然Zr提高了二氧化铈中的储氧能力，但未掺杂的二氧化铈可能具有更高的表面催化活性。他们进一步敦促谨慎使用整体性能作为表面特性和催化活性的替代描述符。
Despite the immense importance of ceria–zirconia solid solutions in heterogeneous catalysis, and the growing consensus that catalytic activity correlates with the concentration of reduced Ce3+ species and accompanying oxygen vacancies, the extent of reduction at the surfaces of these materials, where catalysis occurs, is unknown. Using angle-resolved X-ray Absorption Near Edge Spectroscopy (XANES), we quantify under technologically relevant conditions the Ce3+ concentration in the surface (2–3 nm) and bulk regions of ceria–zirconia films grown on single crystal yttria-stabilized zirconia, YSZ (001). In all circumstances, we observe substantial Ce3+ enrichment at the surface relative to the bulk. Surprisingly, the degree of enhancement is highest in the absence of Zr. This behavior stands in direct contrast to that of the bulk in which the Ce3+ concentration monotonically increases with increasing Zr content. These results suggest that while Zr enhances the oxygen storage capacity in ceria, undoped ceria may have higher surface catalytic activity. They further urge caution in the use of bulk properties as surrogate descriptors for surface characteristics and hence catalytic activity.