The mechanism and kinetics of methyl isobutyl ketone synthesis from acetone over ion-exchanged hydroxyapatite
The mechanism and kinetics of methyl isobutyl ketone synthesis from acetone over ion-exchanged hydroxyapatite
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DOI：
10.1016/j.jcat.2018.07.005
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发表时间：
2018-09
影响因子：
7.3
通讯作者：
Christopher R. Ho;Steven Zheng;S. Shylesh;A. Bell
中科院分区：
文献类型：
--
作者：
Christopher R. Ho;Steven Zheng;S. Shylesh;A. Bell
在负载型金属催化剂上，丙酮在氢气存在下缩合合成甲基异丁基酮（MIBK）。以往的研究表明羟基磷灰石是一种优良的缩合反应催化剂。本调查进行，以阐明丙酮偶联到MIBK在羟基磷灰石和Pd/SiO2的物理混合物的反应机理和网站的要求。发现该反应通过连续的羟醛加成形成二丙酮醇（DAA）、DAA脱水成异亚丙基丙酮（MO）和MO氢化成MIBK来进行。通过进料DAA和MO形成的产物表明，丙酮的羟醛加成是快速和可逆的，并且随后的DAA脱水是限速的。吡啶和CO2滴定表明，羟醛脱水通过E1 cB机制发生在碱性位点上。采用离子交换法制备了一系列阳离子取代的羟基磷灰石样品，进一步考察了酸碱强度对催化剂性能的影响。通过PXRD、BET、ICP-OES、XPS、CO2-TPD和拉曼光谱对这些样品进行表征，表明所使用的交换程序不影响羟基磷灰石的本体性质。DFT计算表明，除了影响载体的刘易斯酸碱度之外，阳离子的大小在化学中起着重要的作用：太大（Ba 2+）或太小（Mg 2+）的阳离子由于中间物质的过度稳定而对反应速率产生不利影响。结果表明，锶交换羟基磷灰石能有效地促进DAA的α-吸氢和C-单键-O键的断裂，是最具活性的催化剂。
The synthesis of methyl isobutyl ketone (MIBK) can be carried out by the condensation of acetone in the presence of hydrogen over a supported metal catalyst. Previous studies have shown that hydroxyapatite is an excellent catalyst for condensation reactions. The present investigation was undertaken in order to elucidate the reaction mechanism and site requirements for acetone coupling to MIBK over a physical mixture of hydroxyapatite and Pd/SiO2. The reaction is found to proceed by consecutive aldol addition to form diacetone alcohol (DAA), dehydration of DAA to mesityl oxide (MO), and hydrogenation of MO to MIBK. The products formed by feeding DAA and MO reveal that aldol addition of acetone is rapid and reversible, and that the subsequent dehydration of DAA is rate-limiting. Pyridine and CO2titration show that aldol dehydration occurs over basic sites via an E1cBmechanism. A series of cation-substituted hydroxyapatite samples were prepared by ion-exchange to further investigate the role of acid-base strength on catalyst performance. Characterization of these samples by PXRD, BET, ICP-OES, XPS, CO2-TPD, and Raman spectroscopy demonstrated that the exchange procedure used does not affect the bulk properties of hydroxyapatite. DFT calculations reveal that in addition to affecting the Lewis acidity/basicity of the support, the size of the cation plays a significant role in the chemistry: cations that are too large (Ba2+) or too small (Mg2+) adversely affect reaction rates due to excessive stabilization of intermediate species. Strontium-exchanged hydroxyapatite was found to be the most active catalyst because it promoted α-hydrogen abstraction and Csingle bondO bond cleavage of DAA efficiently.