Dynamic Behavior of Pd/P4VP Catalyst during the Aerobic Oxidation of 2-Propanol: A Simultaneous SAXS/XAS/MS Operando Study

Abstract

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 Pd 2+ cationic species, either atomically dispersed or in the form of ultrasmall Pd 2+ −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 Pd 2+ species; on the other hand, the porous structure of the P4VP polymer efficiently confines the active Pd 2+ species in the presence of the reagents. As such, our catalyst is situated at the confluence between its homogeneous and heterogeneous analogues.

Operando X-ray absorption spectra and mass spectrometry data during hydrogenation of ethylene over palladium nanoparticles

“…EXAFS data collection. Experimental Pd K -edge EXAFS spectra were measured at BM26A beamline [14], [15] of European Synchrotron Radiation Facility (ESRF, Grenoble, France). The X-ray beam was monochromatized by Si(111) double-crystal monochromator and harmonic rejection was performed by Pt coated mirrors.…”

Electron-Rich Gold Clusters Stabilized by Poly(vinylpyridines) as Robust and Active Oxidation Catalysts

“…Au NPs (20 nm) embedded within the microparticles of poly­( N -isopropylacrylamide) (PNIPAM) were highly robust and active for the C–C bond-forming reactions . In this work, we investigated the potential of poly­(vinylpyridines), which have been used as templates for preparing metal and metal oxide NPs, − as effective stabilizers of Au clusters for their catalytic application. So far, poly­(vinylpyridine) and its copolymers have been used to tune the diameter of Au NPs in the range of 20–130 nm to enhance the long-term stability of Au NPs (4–7 nm) against aggregation and to produce anisotropic Au nanostructures of various shapes, such as octahedron, decahedron, tetrahedron, triangle, and triangular prism .…”

In situ formation of surface and bulk oxides in small palladium nanoparticles

“…Palladium-based materials are extensively investigated as catalysts for a wide range of important industrial reactions, such as methane combustion [1][2][3][4] and selective oxidation of alcohols. [5][6][7] Palladium oxide is generally considered to be the actual catalytic species in many of these reactions, however, the activity of metallic palladium or core-shell combinations of Pd and PdO were also reported. [8][9][10] A number of previous studies highlighted the importance of in situ detection of palladium oxides and their distribution in the bulk and at the surface of palladium particles to highlight the actual active phase in catalytic oxidation reactions.…”

“…[8][9][10] A number of previous studies highlighted the importance of in situ detection of palladium oxides and their distribution in the bulk and at the surface of palladium particles to highlight the actual active phase in catalytic oxidation reactions. 5,6 Oxidation and reduction of palladium phases are very complex process often associated with the formation of core-shell structures. 11,12 Generally, it was shown that the extent of oxidation increases with decreasing particle size and crystallinity of palladium.…”

“…However, bigger particles with defects and non-spherical shape may also result in the similar values of CN. 6 The remaining unfitted background below 2 Å (Fig. 2Figb) originates from the interaction of surface palladium atoms with the support, whose contribution to the spectra is considerable due to the small particle size.…”