Interstitial Boron Atoms in the Palladium Lattice of an Industrial Type of Nanocatalyst: Properties and Structural Modifications

Abstract

It is well established that the inclusion of small atomic species such as boron (B) in powder metal catalysts can subtly modify catalytic properties, and the associated changes in the metal lattice implies that the B atoms are located in the interstitial sites. However, there is no compelling evidence for the occurrence of interstitial B atoms, and there is a concomitant lack of detailed structural information describing the nature of this occupancy and its effects on the metal host. In this work, we use an innovative combination of high-resolution 11 B magic-angle-spinning (MAS) and 105 Pd static solid state NMR nuclear magnetic resonance (NMR), synchrotron X-ray diffraction (SXRD), in-situ X-ray pair distribution function (XPDF), scanning transmission electron microscopy-annular dark field imaging (STEM-ADF), electron ptychography and electron energy loss spectroscopy (EELS) to investigate the B atom positions, properties and structural modifications to the palladium lattice of an industrial type interstitial boron doped palladium nanoparticle catalyst system (Pdint B/C NPs). In this study we report that upon B incorporation into the Pd lattice, the overall face centered cubic (FCC) lattice is maintained, however short range disorder is introduced. The 105 Pd static solid-state NMR illustrates how different types (and levels) of structural strain and disorder are introduced in the nanoparticle history. These structural distortions can lead to the appearance of small amounts of local hexagonal close packed (HCP) structured material in localized regions. The short range lattice tailoring of the Pd framework to accommodate interstitial B dopants in the octahedral sites of the distorted FCC structure can be imaged by electron ptychography. This study describes new toolsets that enables the characterization of industrial metal nanocatalysts across length scales from macro-analysis to micro-analysis, which gives important guidance to structure-activity relationship of the system.

Investigating the structure–function relationship in triple cation perovskite nanocrystals for light-emitting diode applications

“…These observations mirror the findings from previous 195 Pt and 105 Pd NMR studies on Pt and Pd metal nanoparticle systems that report similar phenomena where the bulk component is clearly identified as a separate component to the disordered surface and sub-surface speciation of lower translational symmetry. [55][56][57] Fig . 1 High resolution transmission electron microscopy (HR-TEM) images of nanocrystals supporting, (a) 0 mol% Cs, (b) 5 mol% Cs, (c) 10 mol% Cs, and (d) 15 mol% Cs.…”

Carrier‐Induced Modification of Palladium Nanoparticles on Porous Boron Nitride for Alkyne Semi‐Hydrogenation

“…Boron atoms are known to be most stable in octahedral interstitial sites of palladium. [10,17] Our results show that the maximum density and spatial distribution of the dopant is likely determined by interatomic lateral repulsion ( Supporting Information, Figure S17), indicating that boron atoms are separated by at least three PdÀPd bonds. The enhanced selectivity could conceivably also result from modification with nitrogen, but boron can be better incorporated into the palladium lattice due to its smaller size and is also energetically more likely to be displaced from distinct defective sites in the carrier (Supporting Information, Figure S18).…”

Interstitial and substitutional light elements in transition metals for heterogeneous catalysis

“…Furthermore, for light-element dopants, additional care must be taken to avoid beam damage when using intense electron beams. In an investigation of an interstitially boron-doped palladium catalyst, Pd-int B, our research group used the emerging electron microscopy technique of ptychography to visualise boron at the octahedral sites of the Pd metal framework 6 . Along with other supporting techniques and simulations, certain atomic columns observed by microscopy were interpreted as interstitial boron atoms.…”

“…However, despite the dramatic alteration of the catalytic properties by such light-element doping, there is a lack of indepth understanding of the structure-activity relationship. Recent advances in analytical techniques such as electron ptychography in transmission electron microscopy, and highresolution synchrotron and neutron diffraction have made strong contributions to the understanding of these catalysts, and consequently the correlations between doping, structure and activity, allowing the rational design of this class of catalysts 6 . It is timely to summarize some recent breakthroughs in this area.…”