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首页> 外文期刊>ACS catalysis >Conceptual Frame Rationalizing the Self-Stabilization of H-USY Zeolites in Hot Liquid Water
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Conceptual Frame Rationalizing the Self-Stabilization of H-USY Zeolites in Hot Liquid Water

机译：H-USY沸石在热水中自我稳定化的概念框架

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摘要

The wide range of liquid-phase reactions required for the catalytic conversion of biomass compounds into new bioplatform molecules defines a new set of challenges for the development of active, selective, and stable catalysts. The potential of bifunctional Ru/H-USY catalysts for conversions in hot liquid water (HLW) is assessed in terms of physicochemical stability and long-term catalytic performance of acid sites and noble metal functionality, as probed by hydrolytic hydrogenation of cellulose. It is shown that zeolite desilication is the main zeolite degradation mechanism in HLW. USY zeolite stability depends on two main parameters, viz., framework and extra-framework aluminum content. The former protects the zeolite lattice by counteracting hydrolysis of framework bonds, and the latter, when located at the external crystal surface, prevents solubilization of the zeolite framework which is the result of its low water-solubility. Hence, the hot liquid water stability of commercial H-USY zeolites, in contrast to their steam stability, increased with decreasing Si/AI ratio. As a result, mildly steamed USY zeolites containing a high amount of both Al species exhibit the highest resistance to HLW. During an initial period of transformations, Al-rich zeolites form additional protective extra-framework Al species at the outer surface, self-stabilizing the framework. A critical bulk Si/AI ratio of 3 was determined whereby USY zeolites with a lower Si/AI ratio will self-stabilize over time. Besides, due to the initial transformation period, the accessibility of the catalytic active sites is extensively enhanced resulting in a material that is more stable and drastically more accessible to large substrates than the original zeolite. When these findings are applied in the hydrolytic hydrogenation of cellulose, unprecedented nearly quantitative hexitol yields were obtained with a stable catalytic system.
机译：将生物质化合物催化转化为新的生物平台分子所需的各种液相反应，为开发活性，选择性和稳定的催化剂提出了一系列新的挑战。通过理化稳定性，酸性位点和贵金属官能度的长期催化性能（通过纤维素的水解加氢探测），评估了双功能Ru / H-USY催化剂在热水中（HLW）转化的潜力。结果表明，沸石的脱硅作用是高放废物中主要的沸石降解机理。 USY沸石的稳定性取决于两个主要参数，即骨架和骨架外铝含量。前者通过抵消骨架键的水解来保护沸石晶格，而后者位于外晶体表面时，由于其低水溶性而阻止了沸石骨架的增溶。因此，与H / USY沸石的蒸汽稳定性相反，其热液体水稳定性随Si / Al比的降低而增加。结果，含有大量两种Al的轻度蒸煮的USY沸石对HLW的抵抗力最高。在转变的最初阶段，富铝沸石在外表面形成额外的保护性骨架外铝物种，从而使骨架自稳定。确定了3的临界堆积Si / Al比率，由此具有较低Si / Al比率的USY沸石将随时间自稳定。此外，由于初始转化期，催化活性位点的可及性得到了大大增强，从而导致与原始沸石相比，这种材料更稳定并且对于大型基材而言，其可及性更强。当将这些发现应用于纤维素的水解加氢时，利用稳定的催化系统可获得前所未有的几乎定量的己糖醇收率。

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