Dynamics and Site Isolation: Keys to High Propane Dehydrogenation Performance of Silica-Supported PtGa Nanoparticles

Abstract

Nonoxidative dehydrogenation of light alkanes has seen a renewed interest in recent years. While PtGa systems appear among the most efficient catalyst for this reaction and are now implemented in production plants, the origin of the high catalytic performance in terms of activity, selectivity, and stability in PtGa-based catalysts is largely unknown. Here we use molecular modeling at the DFT level on three different models: (i) periodic surfaces, (ii) clusters using static calculations, and (iii) realistic size silica-supported nanoparticles (1 nm) using molecular dynamics and metadynamics. The combination of the models with experimental data (XAS, TEM) allowed the refinement of the structure of silica-supported PtGa nanoparticles synthesized via surface organometallic chemistry and provided a structure–activity relationship at the molecular level. Using this approach, the key interaction between Pt and Ga was evidenced and analyzed: the presence of Ga increases (i) the interaction between the oxide surface and the nanoparticles, which reduces sintering, (ii) the Pt site isolation, and (iii) the mobility of surface atoms which promotes the high activity, selectivity, and stability of this catalyst. Considering the complete system for modeling that includes the silica support as well as the dynamics of the PtGa nanoparticle is essential to understand the catalytic performances.

Zeolite-confined subnanometric PtSn mimicking mortise-and-tenon joinery for catalytic propane dehydrogenation

“…Without Sn, the propene can readily further dehydrogenate to form the deep dehydrogenation products. The presence of Sn donates electron to Pt and helps to reduce the propene adsorption and dehydrogenation on Pt sites, which can also be realized by other metal dopants (e.g., Ga, Zn) 16 , 31 , 32 . Recently, Linic et al 6 also reported a silica-supported PtSn nanoparticles with excellent PDH activity, in which they initially introduce a heterometallic Pt-Sn coordination complex with intimate Pt and Sn contact.…”

A Robust and Efficient Propane Dehydrogenation Catalyst from Unexpectedly Segregated Pt2Mn Nanoparticles

“…As recently demonstrated by MTD calculations for a SOMC derived PtGa system, a strong effect of the support on the nanoparticle structure can be expected. 35 We thus investigated the role of the oxide support by building a more complex model placing the coreshell Pt2Mn particle -identified as the energetic ground state in the preceding calculation in vacuum -at the surface of an amorphous dehydroxylated silica support 49 bearing 5 Mn II sites (see supporting information for details on the construction of this oxide model). Along the simulation, the Mn-O MTD coordination number increases steadily at the expense of the Mn-Mn and Mn-Pt coordination numbers, which tend to decrease along the simulation, suggesting a strong affinity of Mn 0 for the oxide support (Figure 3, C)-right & Figure S54).…”

“…SiO2 is thus ideally suited to study structure-property relationships of surface species, avoiding interference from the support. This SOMC/TMP approach combined with detailed spectroscopic -including X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) -and computational studies -using in particular metadynamics (MTD) at the DFT level 35 -has enabled the development of PtGa-based PDH catalysts with high catalytic performances. Such analysis helped to derive structure-performance relationships, tracing back the catalytic performance to i) Pt site isolation at the nanoparticle surface and ii) increased dynamics of Pt sites in the alloyed nanoparticles.…”

“…While Ga itself exhibits catalytic activity in the PDH reaction [36][37][38] , we proposed that its main role in the PtGa system is the improvement of the stability of PtGa alloyed nanoparticles due to strong interaction with Ga III surface sites. 35 Considering the promising catalytic performances of recently reported PtMn systems discussed above and the need to constantly improve our understanding of PDH catalysts, we here explored the generation of tailored PtMn bimetallic systems using the SOMC/TMP approach in combination with MTD at the DFT level. First, we determined the composition of such particles via X-ray absorption near edge structure (XANES) and elemental analysis (EA).…”

Uncovering selective and active Ga surface sites in gallia–alumina mixed-oxide propane dehydrogenation catalysts by dynamic nuclear polarization surface enhanced NMR spectroscopy

“… 3 However, the role of platinum in PtGa catalysts is currently debated, ranging from a promoter of coordinately unsaturated Ga 3+ active sites, 4 to the active phase itself, such as site-isolated Pt atoms in metallic PtGa alloyed nanoparticles. 5 …”