Hydrogenation and dehydrogenation reactions were performed over hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAP) and magnesia (MgO) to explore their role in the reaction network for the Guerbet coupling of ethanol to butanol. In particular, the dehydrogenation of benzyl alcohol at 633 K and the hydrogenation of ethene and acetone at 473 K using both H₂ and ethanol as a hydrogen source were studied. The H₂–D₂ exchange reaction at room temperature and the Guerbet coupling of ethanol at 613–673 K in the presence of D₂ were also performed. Although there was no consequence of adding D₂ to the Guerbet coupling of ethanol in terms of rate or selectivity, incorporation of deuterium into product butanol was only observed over MgO. This was attributed to the rapid exchange of H₂–D₂ that can occur over MgO but not over HAP. Hydrogenation of acetone occurred with ethanol as a sacrificial hydrogen donor via an MPV-like reaction whereas hydrogenation with H₂ was not observed. Hydrogenation of ethene with H₂ or ethanol was not observed above background. Comparing the rate of benzyl alcohol dehydrogenation to the rate of ethanol coupling over HAP and MgO suggests that the MPV-like hydrogen transfer reaction over HAP is mostly responsible for generating intermediate acetaldehyde during the Guerbet reaction instead of direct dehydrogenation.

中文翻译：

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与醇在羟基磷灰石和氧化镁催化剂上的Guerbet偶联有关的氢转移反应

在羟基磷灰石（Ca ₁₀（PO ₄）₆（OH）₂，HAP）和氧化镁（MgO）上进行了氢化和脱氢反应，以探讨它们在乙醇与丁醇的Guerbet偶联反应网络中的作用。特别地，研究了使用H ₂和乙醇作为氢源在633 K下对苯甲醇的脱氢以及在473 K下对乙烯和丙酮的氢化。还进行了室温下的H ₂ -D ₂交换反应和存在D ₂的情况下在613-673 K的乙醇的Guerbet偶联反应。尽管没有添加D _2的后果对于乙醇的Guerbet偶合速率或选择性，仅在MgO上观察到氘掺入产物丁醇中。这归因于H ₂ -D ₂的快速交换，这种交换可以通过MgO发生，而不能通过HAP发生。通过乙醇作为牺牲氢供体，通过类似于MPV的反应发生丙酮的氢化反应，而未观察到H _2的氢化反应。H ₂加氢乙烯或在背景以上未观察到乙醇。将苄醇脱氢速率与乙醇在HAP和MgO上的偶联速率进行比较，表明在Guerbet反应中，类似于MPV的氢转移反应在HAP上主要负责生成中间乙醛，而不是直接进行脱氢。