Bifunctional Catalysts Containing Sites of Controlled Accessibility

CTS-9629963这是一个旨在提高双功能催化剂选择性的催化剂设计新概念的探索。所提出的催化剂包含两种类型的活性位点：一种类型与流体（气体或液体）介质中的所有分子接触，另一种类型通常是金属簇，大多数反应物都无法接近，但氢等小分子却可以接近。这种情况应尽量减少不希望的反应，如金属催化的碳-碳键裂变。通过将金属团簇沉积在具有一维微孔的沸石中，这些微孔充满了物理吸附的蒸汽，可以实现金属团簇的受限可及性；期望得到具有单锉扩散特性的稳态条件。物理吸附的分子可以转化为碳质材料，这将更彻底地将金属团簇与大分子隔离开来，同时基本上保持它们解离氢的能力不变。然后，氢原子可以通过沸石表面迁移到更容易接近的位置（“溢出”）。如果成功，这种方法将应用于许多现有和潜在的工业过程，包括从羧酸中生产醛，从酯中生产醚，从硝基化合物中生产亚硝基化合物。它也可以用于对映选择性氢化或氢甲酰化。这些过程对化学、药物、化妆品和农用化学工业具有重要的经济意义。

ABSTRACT CTS-9629963 This is an exploration of a novel concept of catalyst design intended to improve selectivity in bifunctional catalysts. The proposed catalysts contain two types of active sites: one type that is in contact with all molecules in the fluid (gas or liquid) medium, and another type, typically metal clusters, effectively inaccessible to most reactants but reachable by small molecules such as hydrogen. This situation should minimize undesired reactions such as metal-catalyzed carbon-carbon bond fission. The restricted accessibility of the metal clusters is achieved by depositing them in a zeolite with one-dimensional micropores that are filled with a physisorbed vapor; it is desired to obtain steady-state conditions characteristic of single-file diffusion. The physisorbed molecules may be converted to carbonaceous materials which would more thoroughly isolate the metal clusters from large molecules while leaving largely unchanged their ability to dissociate hydrogen. The hydrogen atoms can then migrate over the zeolite surface to the more accessible site ("spillover"). This approach if successful would have application to many existing and potential industrial processes, including production of aldehydes from carboxylic acids, ethers from esters, and nitroso compounds from nitro compounds. It could also have utility for enantioselective hydrogenation or hydroformylation. These processes are of great economic importance to the chemical, drug, cosmetic, and agrochemical industries.