Ultrasmall Cluster Model for Investigating Single Atom Catalysis: Dehydrogenation of 1-Propanamine by Size-Selected Pt₁Zr₂O₇ Clusters Supported on HOPG

Abstract

The selective dehydrogenation of hydrocarbons and their functionalized derivatives is a promising pathway in the realization of endothermic fuel systems for powering important technologies such as hypersonic aircraft. The recent surge in interest in single atom catalysts (SACs) over the past decade offers the opportunity to achieve the ultimate levels of selectivity through the subnanoscale design tailoring of novel catalysts. Experimental techniques capable of investigating the fundamental nature of the active sites of novel SACs in well-controlled model studies offer the chance to reveal promising insights. We report here an approach to accomplish this through the soft landing of mass-selected, ultrasmall metal oxide cluster ions, in which a single noble metal atom bound to a metal oxide moiety serves as a model SAC active site. This method allows the preparation of model catalysts in which monodispersed neutral SAC model active sites are decorated across an inert electrically conductive support at submonolayer surface coverage, in this case, Pt 1 Zr 2 O 7 clusters supported on highly oriented pyrolytic graphite (HOPG). The results contained herein show the characterization of the Pt 1 Zr 2 O 7 /HOPG model catalyst by X-ray photoelectron spectroscopy (XPS), along with an investigation of its reactivity toward the functionalized hydrocarbon molecule, 1-propanamine. Through temperature-programmed desorption/reaction (TPD/R) experiments it was shown that Pt 1 Zr 2 O 7 /HOPG decomposes 1-propanamine exclusively into propionitrile and H 2 , which desorb at 425 and 550 K, respectively. Conversely, clusters without the single platinum atom, that is, Zr 2 O 7 /HOPG, exhibited no reactivity toward 1propanamine. Hence, the single platinum atom in Pt 1 Zr 2 O 7 /HOPG was found to play a critical role in the observed reactivity.

Effect of a Single Platinum Atom within a Small Metal Oxide Cluster: Reaction of DMMP with Size-Selected Pt1Zr2O7 Supported on HOPG

“…Notably, no methane evolution is observed for DMMP exposed to bare HOPG without Pt 1 Zr 2 O 7 clusters present, and neither is it observed for Pt 1 Ti 2 O 7 clusters, which were found to decompose DMMP into H 2 O, CO, and H 2 . 31 Another previous study of ours investigating the adsorption and decomposition of DMMP by HOPG-supported (ZrO 2 ) 3 clusters, which can be viewed as a species in which the single Pt atom is switched with a Zr atom, likewise saw no methane evolution. In that case, DMMP was primarily decomposed into methanol, with relatively minor amounts of dimethyl ether and formaldehyde evolved as well.…”

“…These experiments revealed a decomposition chemistry distinct from the HOPG-supported (ZrO 2 ) 3 clusters studied previously, as well as recent experiments of ours involving another comparable SAC cluster model, Pt 1 Ti 2 O 7 . 31 Unlike those clusters, the HOPG-supported Pt 1 Zr 2 O 7 clusters were found to primarily evolve methane, directly resulting from DMMP decomposition. Similar to the reactivity observed for Pt 1 Ti 2 O 7 , evolution of CO and H 2 resulting from DMMP decomposition was observed as well.…”

“…A highly detailed description of the apparatus used to prepare sizeselected supported cluster samples and investigate their reactivity was reported previously. 32 An overview of the method used to synthesize, mass-select, and deposit the clusters onto a prepared substrate in UHV will thus be described here in brief. Cluster ions were synthesized in the gas phase via a combined magnetron sputtering/inert gas condensation source.…”

Single-atom nanozymes as promising catalysts for biosensing and biomedical applications

“…37 many SAzymes have been successfully prepared via both bottom-up and top-down synthetic procedures. The former mainly involves atomic layer deposition (ALD), 38,39 ball milling, 40,41 wet chemistry, 42,43 mass-selected soft landing, 44,45 and photochemical reduction, 46,47 while the latter entails high-temperature pyrolysis 48,49 and gas-phase migration. 50,51 Below is a summary of these synthetic methods.…”

Electronic Structure of Heteronuclear Cerium-Platinum Clusters

“…Spectroscopy of small molecule or cluster models can provide a back-door approach to understanding the fundamental electronic structure of these materials. Small clusters, 43,44 even diatomics, 45 provide an insight into bonding and atomicscale interactions 46−49 within the materials; they are also effective models of edges, corners, and defect sites. 50−54 A previous study from our group characterized several platinum-cerium oxide binary clusters, which gave insights into the strong support-catalyst interactions reported for ceria supported platinum and its impact on the water gas-shift reaction.…”