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首页> 外文期刊>ACS catalysis >Catalytic Pathways and Kinetic Requirements for Alkanal Deoxygenation on Solid Tungstosilicic Acid Clusters
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Catalytic Pathways and Kinetic Requirements for Alkanal Deoxygenation on Solid Tungstosilicic Acid Clusters

机译：固体钨硅酸团簇上烷烃脱氧的催化途径和动力学要求

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摘要

Kinetic measurements and acid site titrations were carried out to interrogate the reaction network, probe the mechanism of several concomitant catalytic cycles, and explain their connection during deoxygenation of light alkanals (CnH2nO, n = 3-6) on tungstosilicic acid clusters (H4SiW12O40) that leads to hydrocarbons (e.g., light alkenes, dienes, and larger aromatics) and larger oxygenates (e.g., alkenals). The three primary pathways are (1) intermolecular C=C bond formation, which couples two alkanal molecules in aldol-condensation reactions followed by rapid dehydration, forming a larger alkenal (C2nH4n-2O), (2) intramolecular C=C bond formation, which converts an alkanal directly to an n-alkene (C=H) by accepting a hydride ion from H donor and ejecting a H2O molecule, and (3) isomerization dehydration, which involves self-isomerization of an alkanal to form an allylic alcohol and then rapid dehydration to produce an n-diene (CnH2n-2). The initial intermolecular C=C bond formation is followed by a series of sequential intermolecular C=C bond formation steps; during each of these steps an additional alkanal unit is added onto the carbon chain to evolve a larger alkenal (C3nH6n-4O and C4nH8n-6O), which upon its cyclization-dehydration reaction forms hydrocarbons (CtnH2tn-2t, t = 2-4, including cycloalkadienes or aromatics). The intermolecular and intramolecular C=C bond formation cycles are catalytically coupled through intermolecular H-transfer events, whereas the intermolecular C=C bond formation and isomerization dehydration pathways share a coadsorbed alkanal-alkenol pair as the common reaction intermediate. The carbon number of alkanals determines their hydride ion affinities, the stabilities of their enol tautomers, and the extent of van der Waals interactions with the tungstosilicic clusters; these factors influence the stabilities of the transition states or the abundances of reaction intermediates in the kinetically relevant steps and in turn the reactivities and selectivities of the various cycles.
机译：进行了动力学测量和酸位滴定，以探究反应网络，探究几种伴随的催化循环的机理，并解释了轻质链烷烃（H4SiW12O40）上轻链烷烃（CnH2nO，n = 3-6）的脱氧过程中的联系，会导致碳氢化合物（例如，轻质烯烃，二烯和较大的芳烃）和较大的含氧化合物（例如，烯烃）。这三个主要途径是（1）分子间C = C键形成，该键在醛醇缩合反应中将两个链烷烃分子偶联，然后迅速脱水，形成较大的烯烃（C2nH4n-2O），（2）分子内C = C键形成，通过接受来自H供体的氢离子并喷射H2O分子将链烷醛直接转化为正烯（C = H），以及（3）异构化脱水，这涉及链烷醛的自异构化以形成烯丙醇，以及然后快速脱水以生成正二烯（CnH2n-2）。最初的分子间C = C键形成之后是一系列连续的分子间C = C键形成步骤;在这些步骤的每一个步骤中，都会在碳链上添加一个额外的链烷烃单元，以生成更大的链烯烃（C3nH6n-4O和C4nH8n-6O），在其环化-脱水反应后形成烃（CtnH2tn-2t，t = 2-4，包括环烷二烯或芳烃）。分子间和分子内C = C键形成循环通过分子间H转移事件催化偶联，而分子间C = C键形成和异构化脱水途径共享共吸附的链烷醇-链烯醇对作为常见反应中间体。链烷烃的碳原子数决定了它们的氢化物离子亲和力，烯醇互变异构体的稳定性以及范德华斯与钨硅团簇相互作用的程度。这些因素影响动力学相关步骤中过渡态的稳定性或反应中间体的丰度，进而影响各个循环的反应性和选择性。

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