Atomic layer deposition of Pd and Pt nanoparticles for catalysis: on the mechanisms of nanoparticle formation

Abstract

The deposition of Pd and Pt nanoparticles by atomic layer deposition (ALD) has been studied extensively in recent years for the synthesis of nanoparticles for catalysis. For these applications, it is essential to synthesize nanoparticles with well-defined sizes and a high density on large-surface-area supports. Although the potential of ALD for synthesizing active nanocatalysts for various chemical reactions has been demonstrated, insight into how to control the nanoparticle properties (i.e. size, composition) by choosing suitable processing conditions is lacking. Furthermore, there is little understanding of the reaction mechanisms during the nucleation stage of metal ALD. In this work, nanoparticles synthesized with four different ALD processes (two for Pd and two for Pt) were extensively studied by transmission electron spectroscopy. Using these datasets as a starting point, the growth characteristics and reaction mechanisms of Pd and Pt ALD relevant for the synthesis of nanoparticles are discussed. The results reveal that ALD allows for the preparation of particles with control of the particle size, although it is also shown that the particle size distribution is strongly dependent on the processing conditions. Moreover, this paper discusses the opportunities and limitations of the use of ALD in the synthesis of nanocatalysts.

Low-temperature atomic layer deposition delivers more active and stable Pt-based catalysts

“…In brief, such ALD process, by relying on high oxygen partial pressures (i.e., 0.2 bar) and oxygen exposures on the order of minutes, enables the deposition of metallic Pt NPs at temperatures (e.g., 100°C) at which conventional ALD would otherwise lead to negligible deposition without resorting to powerful oxidizers such as ozone and oxygen plasma. 18,25,42,43 The Pt/GNP composites were obtained after 1, 3, and 10 ALD cycles carried out at both 100°C and 200°C. In addition, we also carried out 10 ALD cycles at 250°C to establish a worse case reference for the initial particle size distribution (PSD) span.…”

“…For example, increasing the number of cycles in thermal ALD of Pt and Pd has been reported to not only vary the average NP size but also broaden the size distribution. 21,[25][26][27] We have recently described the fate of adatoms on supports during ALD, showing that they indeed migrate, form clusters and sinter. 27 These processes are highly size-dependent (large clusters are less mobile), temperature-dependent (as holds for most sintering processes 1,2 ), and crucially depend also on the extent to which both surface reactions have run to completion.…”

Review Article: Catalysts design and synthesis via selective atomic layer deposition

“…ALD process adjustment from precursor pressure reduction During the ALD reaction, the growth rate of metal nanoparticles is strongly depended on the chemisorption of precursors with the substrate. 10 For example, the growth of Pt with the precursors of (methylcyclopentadienyl)-trimethylplatinum (MeCpPtMe 3 ) and O 2 is affected by the dissociation of chemisorbed O 2 . O 2 dissociation usually prefers to take place on a metal surface, leading to the formation of active oxygen atoms to decompose and activate MeCpPtMe 3 molecules for the following reactions.…”

“…Among various synthesis methods, atomic layer deposition (ALD) has been recently developed as an effective method to synthesize composite catalysts. [8][9][10][11][12][13][14] ALD is based on successive and alternative surface reactions from gas phase to fabricate thin films and overlayers in the nanometer range. So far, significant number of elements and their oxides can be synthesized via ALD.…”

Oriented Attachment and Nanorod Formation in Atomic Layer Deposition of TiO2 on Graphene Nanoplatelets

“…17,22 Because such mechanisms are a strong function of reaction conditions and adlayer–support interactions, control over the NP size can be achieved only under certain system-dependent conditions. 17,20,21 Nonetheless, if properly understood, unconventional growth pathways can expand the range of nanostructures that can be synthesized by ALD. 22,23 After achieving control over the NP size, the natural next step in the advancement of ALD of NPs is the synthesis of shape-controlled NPs and, in particular, of one-dimensional (1D) nanocrystals such as nanorods (NRs).…”