Design and Characterization of ALD-Based Overcoats for Supported Metal Nanoparticle Catalysts

Abstract

Supported metal nanoparticle (SMN) catalysts are enormously crucial for many catalytic applications. However, catalyst deactivation, caused by sintering and coke formation, is a ubiquitous problem that significantly undermines catalytic processing economics. The application of material overcoating onto supported metal nanoparticles by atomic layer deposition (ALD) offers the solution to inhibit catalyst deactivation. Herein, we discuss examples in which ALD has been used to stabilize SMN catalysts in gaseous and aqueous-phase reactions. We highlight the ALD tools and methods in coating high-surface-area catalysts. Besides, various techniques are introduced to understand better how to characterize the overcoating layer and the catalyst itself. Finally, the outlook for new techniques to characterize the ALD overcoated catalytic materials is discussed.

Unraveling Property‐Performance Relationships by Surface Tailoring of Oxidation Catalysts via ALD

“…Bottom‐up synthesis of supported metal nanoparticles was already successfully conducted for monometallic and multi‐metallic systems [33–38] . Also, catalyst modifications by ALD are already developed, e. g. deposition of a functional metal oxide overcoat on supported metal nanoparticles to prevent sintering or coke formation [36,39–42] . Despite recent developments of ALD in the field of catalysis, modifications of bulk catalysts are barely investigated yet.…”

Elucidating the Roles of Amorphous Alumina Overcoat in Palladium-Catalyzed Selective Hydrogenation

“…Atomic layer deposition (ALD) has been demonstrated as a powerful tool for encapsulating metal nanoparticles (NPs) to improve their catalytic performance in heterogeneous catalysis. − Superior selectivity and durability have been observed in many reactions, including alkane dehydrogenation, oxidative dehydrogenation, , selective hydrogenation of alkynes , /dienes and unsaturated aldehydes, , methanol decomposition, CO oxidation, , and methane combustion . The improvement in catalytic performance by an ALD overcoat has been mostly attributed to the following factors: (i) physical confinement of metal NPs, which restricts the coalescence/sintering; , (ii) selective blockage of certain crystal facets or low-coordinated sites; ,, (iii) confinement effect of diffusion and adsorption due to the microporous nature of the oxide overcoat; , (iv) size reduction of adsorption site ensembles; , and (v) unique active site structures at inverse metal–oxide interfaces. ,, …”

Manganese Oxide Overlayers Promote CO Oxidation on Pt

“…While it was developed primarily for semiconductor fabrication, ALD has also been shown to provide advantages for the synthesis of catalysts that are typically in particulate form . For example, ALD-coated oxide overlayers have been shown not only to stabilize the metal particle size following high-temperature sintering − but also to facilitate the selective production of desired products. , In other examples, conformal films of an oxide on a more stable support have exhibited the chemical properties of the film with the stability of the support. The Pd–ceria–Al 2 O 3 catalyst, discussed above, is one example of this.…”