Preparation of Size- and Composition-Controlled PtnSnx/SiO2 (n = 4, 7, 24) Bimetallic Model Catalysts with Atomic Layer Deposition

Gorey, Timothy J.; Zandkarimi, Borna; Li, Guangjing; Baxter, Eric T.; Alexandrova, Anastassia N.; Anderson, Scott L.

doi:10.1021/acs.jpcc.9b02745

Cited by 29 publications

(65 citation statements)

References 124 publications

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“…We showed in a joint theory-experiment study that the effect of Sn is robust also in small clusters, and furthermore, the anti-coking mechanism is different from that induced by boration. 56,57 In contrast to PtB, PtSn clusters supported on amorphous silica and alumina have the unchanged or even increased affinity for ethylene from that of pure Pt clusters.…”

Section: Ensembles Of Catalyst States and Deactivationmentioning

confidence: 99%

Ensembles of Metastable States Govern Heterogeneous Catalysis on Dynamic Interfaces

2020

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Heterogeneous catalysis is at the heart of chemical industry. Being able to tune and design efficient catalysts for processes of interest is of an utmost importance, and for this, the molecular-level understanding of heterogeneous catalysts is the first step, and indeed a prime focus of the modern catalysis research. For a long time, a single most thermodynamically stable structure of the catalytic interface attained in reaction conditions had been envisioned as the reactive phase. However, some catalytic interfaces continue to undergo structural dynamics in the steady state, triggered by high temperatures, pressures, and binding and changing reagents. Among particularly dynamic interfaces are such widely-used catalysts as crystalline and amorphous surfaced supporting (sub-)nano metallic clusters. Recently, it became clear that this dynamic fluxionality causes the supported clusters to populate many distinct structural and stoichiometric states in catalytic conditions. Hence, the catalytic interface should be viewed as an evolving statistical ensemble of many (not one) structures. Every member in the ensemble contributes to the properties of the catalyst differently, and in proportion to its probability to be populated. This new notion flips the established paradigm and calls for new theory, modeling approaches, operando measurements, and updated design strategies. The statistical ensemble nature of surface-supported sub-nano cluster catalysts can be exemplified by oxide-supported and adsorbate-covered Pt, Pd, Cu, CuPd clusters, catalytic toward oxidative and non-oxidative dehydrogenation. They have access to a variety of 3D and quasi-2D shapes. The compositions of their thermal ensembles are dependent on the cluster size, leading to size-specific catalytic activities and the famous "every atom counts" phenomenon. The support and adsorbates affect catalyst structures, and state of the reacting species causes the ensemble to change in every reaction intermediate. The most stable member of the ensemble dominates the thermodynamic properties of the corresponding intermediate, whereas the kinetics can be determined by more active but less populated metastable catalyst states, and that suggests that many earlier studies might have overlooked the actual active sites. Both effects depend on the relative timescales of catalyst restructuring and reaction dynamics. The catalyst may routinely operate off-equilibrium. Ensemble phenomena lead to surprising exceptions from established rules of catalysis, such as scaling relations, and Arrhenius behavior. Catalyst deactivation is also an ensemble property, and its extent of mitigation can be predicted through the new paradigm. These findings were enabled by advances in theory, such as global optimization and subsequent utilization of multiple local minima, and pathways sampling, as well as operando catalyst characterization. The fact that the per-site and per-species resolution is needed for the description and predicting of catalyst properties gives theory the central role in ...

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Section: Ensembles Of Catalyst States and Deactivationmentioning

confidence: 99%

Ensembles of Metastable States Govern Heterogeneous Catalysis on Dynamic Interfaces

2020

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“…The selection of suitable reagents and processes makes ALD much more demanding than CVD and has been introduced for the synthesis of intermetallic compounds in 2016 for NiFe films [ 152 ]. Since then, it has been applied to synthesise PtSn/SiO2 [ 153 ], nanoparticles of PtIn [ 154 ] and PtSn [ 155 ] as well as thin films of Co 3 Sn 2 and Ni 3 Sn 2 [ 156 ].…”

Section: Developments In Synthesismentioning

confidence: 99%

Intermetallic compounds in catalysis – a versatile class of materials meets interesting challenges

Armbrüster

2020

Science and Technology of Advanced Materials

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The large and vivid field of intermetallic compounds in catalysis is reviewed to identify necessities, strategies and new developments making use of the advantageous catalytic properties of intermetallic compounds. Since recent reviews summarizing contributions in heterogeneous catalysis as well as electrocatalysis are available, this contribution is not aiming at a comprehensive literature review. To introduce the field, first the interesting nature of intermetallic compounds is elaboratedincluding possibilities as well as requirements to address catalytic questions. Subsequently, this review focuses on exciting developments and example success stories of intermetallic compounds in catalysis. Since many of these are based on recent advances in synthesis, a short overview of synthesis and characterisation is included. Thus, this contribution aims to be an introduction to the newcomer as well as being helpful to the experienced researcher by summarising the different approaches. Selected examples from literature are chosen to illustrate the versatility of intermetallic compounds in heterogeneous catalysis where the emphasis is on developments since the last comprehensive review in the field.

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“…In fact, a strong Pt-Sn interaction will improve the stability of the catalysts operating at harsher conditions, as was shown by Pastor-Pérez et al 24 We recently presented a method of preparation of model catalysts with size-selected Pt clusters decorated by controlled coverage of Sn atoms, which are shown to alloy upon heating. 25 The effects of Sn on catalytic activity and stability of sub-nano Pt clusters has been less studied. Smaller clusters are most prone to sintering, and that often precludes their use in practical catalysis, with the rate of sintering depending on particle size and support material.…”

Section: Introductionmentioning

confidence: 99%

Alloying with Sn Suppresses Sintering of Size-Selected Subnano Pt Clusters on SiO₂ with and without Adsorbates

Zandkarimi

Gorey

et al. 2020

Chem. Mater.

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Using Pt in the form of sub-nanometer dispersed clusters is a way to save precious metal in catalysis, but making such clusters stable against sintering is an uphill battle. Sn is a known agent used to increase the selectivity of dehydrogenation of alkanes on Pt. Through a joint experimental and theoretical approach, we show that adding Sn to the size-selected Pt clusters deposited on amorphous SiO 2 also dramatically enhances the thermal stability of the clusters against sintering.CO temperature programmed desorption (TPD) and He + ion scattering indicate that no Pt sites are lost, and XPS shows no change in the electronic structure of Pt, upon repeated system heating and cooling. DFT results indicate that the binding energy of Pt clusters to the support increases by >1 eV upon adding Sn, and Sn forms strong polar covalent bonds with Pt within the clusters and quenches all the unpaired spins. As a result, the energy needed to remove a Pt atom from Pt 4 Sn 3 /SiO 2 and put it on the support is 0.15 eV larger than that from Pt 4 /SiO 2 , and in fact it is significantly easier to dissociate a Sn atom. Both factors would tend to stabilize the Pt core of the clusters against sintering, as is observed experimentally. CO adsorbates further facilitate Ostwald ripening of the pure Pt clusters, and even in that case nano-alloying with Sn suppresses sintering.

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Preparation of Size- and Composition-Controlled Pt_nSn_x/SiO₂ (n = 4, 7, 24) Bimetallic Model Catalysts with Atomic Layer Deposition

Cited by 29 publications

References 124 publications

Ensembles of Metastable States Govern Heterogeneous Catalysis on Dynamic Interfaces

Ensembles of Metastable States Govern Heterogeneous Catalysis on Dynamic Interfaces

Intermetallic compounds in catalysis – a versatile class of materials meets interesting challenges

Alloying with Sn Suppresses Sintering of Size-Selected Subnano Pt Clusters on SiO₂ with and without Adsorbates

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Preparation of Size- and Composition-Controlled PtnSnx/SiO2 (n = 4, 7, 24) Bimetallic Model Catalysts with Atomic Layer Deposition

Cited by 29 publications

References 124 publications

Ensembles of Metastable States Govern Heterogeneous Catalysis on Dynamic Interfaces

Ensembles of Metastable States Govern Heterogeneous Catalysis on Dynamic Interfaces

Intermetallic compounds in catalysis – a versatile class of materials meets interesting challenges

Alloying with Sn Suppresses Sintering of Size-Selected Subnano Pt Clusters on SiO2 with and without Adsorbates

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Preparation of Size- and Composition-Controlled Pt_nSn_x/SiO₂ (n = 4, 7, 24) Bimetallic Model Catalysts with Atomic Layer Deposition

Alloying with Sn Suppresses Sintering of Size-Selected Subnano Pt Clusters on SiO₂ with and without Adsorbates