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首页> 外文学位 >Liquid-phase hydrogenation reactions over supported group VIII metals (Silicon dioxide, Aluminum oxide, Titanium dioxide).
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Liquid-phase hydrogenation reactions over supported group VIII metals (Silicon dioxide, Aluminum oxide, Titanium dioxide).

机译：在负载的VIII族金属（二氧化硅，氧化铝，二氧化钛）上进行液相加氢反应。

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The kinetics of liquid-phase hydrogenation of benzene and citral (3,7-dimethyl-2,6-octadienal) were studied over SiO2, Al 2O3, and TiO2-supported catalysts with particular emphasis on obtaining quantitative kinetics free of transport limitations to probe the effect of solvent, process parameters, metal-support interactions, and metal specificity. Thermodynamic arguments indicated that solvent effects can influence the surface coverage of hydrogen. The rate of citral hydrogenation exhibited an activity minimum with respect to temperature, which was attributed to the relative rates of concurrent alcohol decomposition and CO desorption, with the decomposition reaction having a lower activation energy compared to CO desorption. Metal-support interactions also had a significant influence on reaction kinetics. Pt/TiO2-HTR (high temperature reduced at 773 K) exhibited a 50-fold enhancement in the initial TOF for citral disappearance compared to Pt/TiO2-LTR (low temperature reduced at 473 K) and 100-fold enhancement in TOF compared to Pt/SiO2. Similar to the kinetics exhibited by Pt/SiO2, Pt/TiO2-LTR exhibited an activity minimum with respect to temperature and a near zero and first order dependencies on citral concentration and hydrogen pressure, respectively. In contrast, Pt/TiO2-HTR exhibited conventional Arrhenius behavior and negative first and near zero order dependencies on citral concentration and hydrogen pressure, respectively. The initial TOF for citral hydrogenation over SiO2-supported Group VIII metals at 300 K and 1 atm H 2 varied 1000-fold and correlated with % d-character. The initial TOF for citral hydrogenation exhibited the following trend: Pd > Pt > Ir > Os > Ru > Rh > Ni > Co and no activity was detected with Fe/SiO2. There were significant differences in product distribution among the different metals, which was rationalized on the basis of the width of the d-band, which affects the relative contributions of the stabilizing two-electron interactions and destabilizing four-electron interactions. DRIFTS study of vapor-phase citral, citronellal, and geraniol decomposition revealed that all three organic compounds decomposed on Pt to yield adsorbed CO, and the activation energy for citronellal decarbonylation was the largest. Furthermore, qualitative arguments indicated that the apparent rate constant for geraniol decomposition at 300 K is greater than that for citral.
机译：在SiO2，Al 2O3和TiO2负载的催化剂上研究了苯和柠檬醛（3,7-二甲基-2,6-辛二烯）的液相加氢动力学，特别着重于获得不受运输限制的定量动力学溶剂，工艺参数，金属与载体的相互作用以及金属特异性的影响。热力学论点表明，溶剂效应会影响氢的表面覆盖率。柠檬酸氢化速率相对于温度表现出最小的活性，这归因于同时发生的醇分解和CO解吸的相对速率，与CO解吸相比，分解反应具有较低的活化能。金属与载体的相互作用也对反应动力学有重要影响。与Pt / TiO2-LTR（低温降低473 K）相比，Pt / TiO2-HTR（高温降低773 K）在初始TOF中显示出柠檬醛消失的50倍增强，而TOF增强则与柠檬酸相比。铂/二氧化硅。与Pt / SiO2表现出的动力学相似，Pt / TiO2-LTR表现出相对于温度的最小活性，并且对柠檬酸浓度和氢压的依赖性分别接近零和一阶。相反，Pt / TiO2-HTR表现出常规的Arrhenius行为，并且分别对柠檬酸浓度和氢压呈负一阶和近零阶依赖性。在300 K和1 atm H 2下，SiO2负载的VIII族金属在柠檬酸上的初始TOF变化了1000倍，并且与d-字符相关。柠檬酸加氢的初始TOF表现出以下趋势：Pd> Pt> Ir> Os> Ru> Rh> Ni> Co，Fe / SiO2未检测到活性。不同金属之间的产物分布存在显着差异，这是根据d波段的宽度合理化的，这影响了稳定的两电子相互作用和不稳定的四电子相互作用的相对贡献。 DRIFTS对柠檬酸，香茅醛和香叶醇的气相分解研究表明，这三种有机化合物均在Pt上分解以产生吸附的CO，而香茅醛脱羰基的活化能最大。此外，定性论据表明，香叶醇在300 K时的表观速率常数大于柠檬醛。

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