The coupling of biomass‐derived ethanol to n‐butanol is a topic of contemporary interest. Indeed, n‐butanol can not only be used as a higher energy‐density fuel additive, it is also a key component in perfumes and serves as a solvent for paints and dyes. Hydroxyapatite (HAP) emerged in the literature as a promising catalysts for this transformation, with n‐butanol selectivity reaching ∼75 % at 10 % ethanol conversion. However, the molecular‐level mechanism for this reaction is still unclear and several mechanistic questions remain unanswered. Here, we use diffuse reflectance infrared Fourier Transform spectroscopy, coupled with mass spectrometry following a modulation excitation approach (ME‐DRIFTS‐MS) that enables us to better understand the dynamic processes involved. Our approach allows for a vibrational characterization of the active surface species and the formulation of a consistent mechanism. Based on our experimental observations, Ca²⁺/OH⁻ can be put forward as the main active site for the aldol condensation. POH/OH⁻ acid‐base pair is proposed as the active site for the Meerwein‐Ponndorf‐Verley (MPV) direct hydrogen transfer of the aldol condensation product, crotonaldehyde.

中文翻译：

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调制激发操作红外光谱对羟基磷灰石上乙醇偶联的见解

生物质衍生的乙醇与正丁醇的偶联是当代关注的话题。的确，正丁醇不仅可以用作高能量密度的燃料添加剂，而且还是香水中的关键成分，并且可以用作油漆和染料的溶剂。羟基磷灰石（HAP）在文献中成为一个有前途的催化剂用于该转化，与Ñ乙醇转化率为10％时，丁醇的选择性达到〜75％。但是，该反应的分子水平机理仍然不清楚，并且仍然没有答案。在这里，我们使用了漫反射红外傅里叶变换光谱技术，以及采用调制激发方法（ME‐DRIFTS‐MS）的质谱技术，使我们能够更好地了解所涉及的动态过程。我们的方法允许对活性表面物质进行振动表征，并建立一致的机理。根据我们的实验观察，钙²⁺ / OH ^-都可以提出来作为主要的活性位点的羟醛缩合。POH / OH ^- 酸碱对被建议作为Meerwein-Ponndorf-Verley（MPV）醇醛缩合产物巴豆醛直接氢转移的活性位点。