Acid and basic sites on monoclinic and tetragonal zirconia were investigated at the DFT level by computing IR and NMR properties of adsorbed probe molecules. Regular and stepped ZrO₂ surfaces as well as stoichiometric zirconia nanoparticles have been considered. Acidity and basicity were probed by the adsorption of carbon monoxide and pyrrole, respectively. CO adsorption shows a positive shift of the C–O stretching frequency in IR spectra while the C atom of CO is shielded and ¹³C chemical shifts moves to higher field as a function of the strength of the acid site. For the study of basic sites we used a pyrrole molecule, but the interaction between the pyrrole ring and the surface leads to adsorption modes that cannot be used to titrate the surface basicity. On the other hand, at high coverage the molecule assumes an upright position and the formation of a hydrogen bond of the pyrrole NH group with the oxygen atoms of the surfaces provides a proxy of the basic properties of these sites. In particular, we focus on changes of the N–H IR frequency, ¹H, ¹⁵N, and ¹⁷O NMR chemical shifts and their correlations with the surface basicity. Among the correlations found, that between the N–H stretching frequency of adsorbed pyrrole and the ¹⁷O NMR chemical shift of the O ion where the molecule is bound show a nice linear correlation. These two properties can provide useful information about the basic character of various O sites on the surface of zirconia.

Graphic Abstract

中文翻译：

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吸附探针分子表征氧化锆表面和纳米颗粒上的酸和碱性位点的理论研究

通过计算吸附探针分子的IR和NMR特性，在DFT级别上研究了单斜晶和四方晶氧化锆上的酸和碱性位。已经考虑了规则和阶梯状的ZrO ₂表面以及化学计量的氧化锆纳米粒子。分别通过一氧化碳和吡咯的吸附来探测酸度和碱度。在红外光谱中，CO吸附显示了C–O拉伸频率的正向偏移，而CO的C原子被屏蔽，而¹³C化学位移随酸性位点强度的变化而移向更高的场。为了研究碱性位点，我们使用了吡咯分子，但是吡咯环与表面之间的相互作用导致无法用于滴定表面碱性的吸附模式。另一方面，在高覆盖率下，分子处于直立位置，吡咯NH基与表面氧原子的氢键形成提供了这些位点的基本特性的代表。特别是，我们关注N–H IR频率，¹ H，¹⁵ N和¹⁷ O NMR化学位移的变化及其与表面碱度的相关性。在发现的相关性中，吸附的吡咯的NH延伸频率与分子所键合的O离子的¹⁷ O NMR化学位移显示出良好的线性相关性。这两个性质可以提供有关氧化锆表面上各种O位的基本特征的有用信息。

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