The behavior of a Pd(OAc)₂/P4VP catalyst submitted to different pretreatments (prereduced, preoxidized, and untreated) during the aerobic oxidation of 2-propanol to acetone in the gas phase has been investigated. Synchronous, time-resolved, SAXS/XAS/MS techniques coupled with operando DRIFT spectroscopy (which gave information on the destiny of the acetate ligands) and ex situ HR-TEM (to detect the formation of Pd nanoparticles and to obtain their size distribution) were employed to accomplish a dynamical picture of the changes occurring to the Pd phase under transient reaction conditions. In addition, the catalytic performances were qualitatively explored by means of a CATLAB microreactor, with the final aim to establish structure–activity relationships. Our approach clearly demonstrates that highly isolated Pd²⁺ cationic species, either atomically dispersed or in the form of ultrasmall Pd²⁺–oxo clusters, are efficient and very stable active sites for the gas-phase aerobic oxidation of 2-propanol to acetone. Noticeably, the behavior of the Pd(OAc)₂/P4VP catalyst in reaction conditions is influenced by the nature of the support. On one hand, the presence of the pyridyl functional groups is fundamental to stabilize the cationic Pd²⁺ species; on the other hand, the porous structure of the P4VP polymer efficiently confines the active Pd²⁺ species in the presence of the reagents. As such, our catalyst is situated at the confluence between its homogeneous and heterogeneous analogues.

中文翻译：

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Pd / P4VP催化剂在2-丙醇有氧氧化过程中的动态行为：同时进行SAXS / XAS / MS Operando研究

Pd（OAc）₂的行为研究了在气相中将2-丙醇氧化成丙酮期间，将P / P4VP催化剂用于不同的预处理（还原，预氧化和未处理）。同步，时间分辨的SAXS / XAS / MS技术与操作DRIFT光谱技术（提供有关乙酸盐配体的命运的信息）和非原位HR-TEM（检测Pd纳米颗粒的形成并获得其尺寸分布）用来完成瞬态反应条件下Pd相发生变化的动力学图。此外，通过CATLAB微反应器定性地探索了催化性能，最终目的是建立结构与活性之间的关系。我们的方法清楚地表明，高度隔离的Pd ²⁺阳离子物质，无论是原子分散还是呈超小Pd 2 ^+-氧代簇形式，都是有效且非常稳定的活性位点，可将2-丙醇气相好氧氧化为丙酮。值得注意的是，Pd（OAc）₂ / P4VP催化剂在反应条件下的行为受载体性质的影响。一方面，吡啶基官能团的存在对于稳定阳离子Pd ²⁺物种至关重要。另一方面，在试剂的存在下，P4VP聚合物的多孔结构有效地限制了活性Pd ²⁺物质。因此，我们的催化剂位于其均相和异相类似物之间的汇合处。