...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Reactivity and Selectivity Descriptors for the Activation of C-H Bonds in Hydrocarbons and Oxygenates on Metal Oxides
【24h】

Reactivity and Selectivity Descriptors for the Activation of C-H Bonds in Hydrocarbons and Oxygenates on Metal Oxides

机译：金属氧化物上碳氢化合物和含氧化合物中C-H键活化的反应性和选择性指标

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

C-H bond activation at lattice O atoms on oxides mediates some of the most important chemical transformations of small organic molecules. The relations between molecular and catalyst properties and C-H activation energies are discerned in this study for the diverse C-H bonds prevalent in C-1-C-4 hydrocarbons and oxygenates using lattice O atoms with a broad range of H atom abstraction properties. These activation energies determine, in turn, attainable selectivities and yields of desired oxidation products, which differ from reactants in their C-H bond strength. Bronsted-Evans-Polanyi (BEP) linear scaling relations predict that C-H activation energies depend solely and linearly on the C-H bond dissociation energies (BDE) in molecules and on the H-atom addition energies (HAE) of the lattice oxygen abstractors. These relations omit critical interactions between organic radicals and surface OH groups that form at transition states that mediate the H atom transfer, which depend on both molecular and catalyst properties; they also neglect deviations from linear relations caused by the lateness of transition states. Thus, HAE and BDE values, properties that are specific to a catalyst and a molecule in isolation, represent incomplete descriptors of reactivity and selectivity in oxidation catalysis. These effects are included here through crossing potential formalisms that account for the lateness in transition states in estimates of activation energies from HAE and BDE and by estimates of molecule-dependent but catalyst-independent parameters that account for diradical interactions that differ markedly for allylic and nonallylic C-H bonds. The systematic ensemble-averaging of activation energies for all C-H bonds in a given molecule show how strong abstractors and high temperatures decrease an otherwise ubiquitous preference for activating the weakest C-H bonds in molecules, thus allowing higher yields of products with C-H bonds weaker than in reactants than predicted from linear scaling relations based on molecule and abstractor properties. Such conclusions contradict the prevailing guidance to improve such yields by softer oxidants and lower temperatures, a self-contradictory strategy, given the lower reactivity of such weaker H-abstractors. The diradical-type interactions, not previously considered as essential reactivity descriptors in catalytic oxidations, may expand the narrow yield limits imposed by linear free energy relations by guiding the design of solids with surfaces that preferentially destabilize allylic radicals relative to those formed from saturated reactants at C-H activation transition states.
机译：氧化物上晶格O原子处的C-H键活化介导了有机小分子的一些最重要的化学转化。在这项研究中，对于具有广泛H原子抽象性质的晶格O原子，对于C-1-C-4碳氢化合物和含氧化合物中普遍存在的各种C-H键，本研究发现了分子和催化剂性质与C-H活化能之间的关系。这些活化能又决定了所需氧化产物的可达到的选择性和产率，这与反应物的C-H键强度不同。 Bronsted-Evans-Polanyi（BEP）线性比例关系预测C-H活化能仅线性依赖于分子中的C-H键解离能（BDE）和晶格吸氧剂的H原子加成能（HAE）。这些关系忽略了有机自由基和表面OH基团之间的临界相互作用，这些基团在介导H原子转移的过渡态下形成，过渡态取决于分子和催化剂的性质。他们还忽略了过渡态的延迟导致的线性关系偏差。因此，HAE和BDE值，即特定于催化剂和孤立分子的特性，代表了氧化催化中反应性和选择性的不完整描述。这些影响包括在以下方面：跨越潜在的形式主义，这些形式主义解释了HAE和BDE活化能的估算中过渡态的晚期，以及估算了依赖分子但不依赖催化剂的参数，这些参数解释了双基相互作用对烯丙基和非烯丙基显着不同。 CH键。给定分子中所有CH键的活化能的系统集成平均显示了强抽象剂和高温如何降低了其他普遍存在的激活分子中最弱CH键的偏好，因此，与反应物相比，具有弱CH键的产物的产率更高比基于分子和抽象性质的线性比例关系所预测的结果要好。鉴于此类弱H吸收剂的反应性较低，这些结论与通过软氧化剂和降低温度来提高此类收率的现行指导原则背道而驰，这是一种自相矛盾的策略。双自由基型相互作用以前未被认为是催化氧化反应中必不可少的反应性描述子，它可以通过引导表面相对于饱和反应物形成的那些优先使烯丙基自由基不稳定的表面的固体设计来扩展线性自由能关系所施加的狭窄产率极限。 CH激活过渡状态。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号