First-Principles Calculations of Propane Dehydrogenation over PtSn Catalysts

The role of H2S addition on Pt/Al2O3 catalyzed propane dehydrogenation: a mechanistic study

Effects of H₂S addition on the Pt/Al₂O₃ catalyzed propane dehydrogenation.

The importance of direct reduction in the synthesis of highly active Pt–Sn/SBA-15 for n-butane dehydrogenation

Supported Pt–Sn bimetallic catalysts directly reduced by H₂ are highly active for the dehydrogenation of n-butane, while the catalysts calcined in air, followed by H₂ reduction are totally inactive.

Two-dimensional transition metal carbides as supports for tuning the chemistry of catalytic nanoparticles

Supported nanoparticles are broadly employed in industrial catalytic processes, where the active sites can be tuned by metal-support interactions (MSIs). Although it is well accepted that supports can modify the chemistry of metal nanoparticles, systematic utilization of MSIs for achieving desired catalytic performance is still challenging. The developments of supports with appropriate chemical properties and identification of the resulting active sites are the main barriers. Here, we develop two-dimensional transition metal carbides (MXenes) supported platinum as efficient catalysts for light alkane dehydrogenations. Ordered Pt₃Ti and surface Pt₃Nb intermetallic compound nanoparticles are formed via reactive metal-support interactions on Pt/Ti₃C₂T_x and Pt/Nb₂CT_x catalysts, respectively. MXene supports modulate the nature of the active sites, making them highly selective toward C–H activation. Such exploitation of the MSIs makes MXenes promising platforms with versatile chemical reactivity and tunability for facile design of supported intermetallic nanoparticles over a wide range of compositions and structures.

The performance of supported metal nanoparticle catalysts can be tailored by metal-support interactions, but their use in catalyst design is still challenging. Here, the authors develop two-dimensional transition metal carbides as platforms for designing intermetallic compound catalysts that are efficient for light alkane dehydrogenations.

The Effect of Sn Content in a Pt/KIT-6 Catalyst Over its Performance in the Dehydrogenation of Propane

Propylene is one of the most important commodity chemicals. Its future demand is expected to exceed its production. Alternative routes to obtain this product need to be implemented. Dehydrogenation of propane assisted with catalyst is a promising route to meet demands. The Pt and Cr supported catalysts are amongst the most effective possibilities. However, Pt catalysts are preferred over Cr due to the toxic nature of Cr species. Despite the high performance of the Pt catalysts, they deactivate during reaction, mainly due to coke deposits blocking the active site and/or pores. This effect can be reduced with a support having high connectivity and surface area, like KIT-6. In this work the mesoporous silica KIT-6 was employed as support in a series of Pt-Sn catalysts. The influence of adding or increasing the weight % of Sn to Pt catalyst was studied. There were species of SnO2 and metallic Pt in the fresh catalysts. After reaction, it was found that in the catalysts with the lowest wt % of Sn (0.5), there were metallic Pt and a Pt-Sn alloy. In the rest of the used catalysts (containing 1.0, 1.5 and 2.0 wt % of Sn) the only detected specie was the Pt-Sn alloy. In the two most active catalysts (having 0.5 and 1.5 wt % of Sn), it was observed a difference of three times the quantity of coke deposited on the surface. The catalysts containing the highest coke deposits maintained its activity due to the high connectivity of the support.

Mechanistic investigations of the Au catalysed C-H bond activations in on-surface synthesis

Recently, Au-based nanostructures have attracted extensive interest due to their excellent activities in heterogeneous catalysis. The reaction mechanisms have been interpreted qualitatively by the quantum confinement effect due to the low-coordination of Au atoms in nanostructures. In this work, systematic first-principles calculations were carried out to obtain an in-depth understanding of the origin of C-H bond activations with Au-based catalysts in on-surface synthesis. Combining density functional theory (DFT) calculations and scanning tunneling microscopy (STM) studies, we reveal that the d-band centre and the d-band width of the Au-5dz2 orbital in an energy window of -6.80 to 0.00 eV may serve as theoretical descriptors for the prediction of the activity of Au catalysts in C-H bond activations. This work may therefore inspire further investigations on the design of new catalysts.

Identification of Pt-based catalysts for propane dehydrogenation via a probability analysis

A probability-based computational screening study has successfully identified an optimal bimetallic alloy (Pt₃In) for the propane dehydrogenation reaction.

The intrinsic errors due to functionals are always a concern on the reliability of the predicted catalytic performance by density functional theory. This paper describes a probability-based computational screening study, which has successfully identified an optimal bimetallic alloy (Pt₃In) for the propane dehydrogenation reaction (PDH). Considering DFT uncertainty, Pt₃In was found to have an activity comparable to that of pure Pt and Pt₃Sn. Meanwhile, Pt₃In shows a considerable improvement in the propylene selectivity compared with pure Pt. After a complete and progressive potential energy, free energy and microkinetic analysis, Pt₃In was discovered to show a great balance between activity and selectivity and reach a maximum propylene formation performance. The first dehydrogenation step was found to be the rate-controlling step on most of the facets. Apart from separating Pt atoms and covering the low coordinated step Pt atoms, the role of In can also be attributed to an apparently increasing electron transfer from In to Pt. The adsorption energies of propylene that play a key role in selectivity and activity were correlated with the d-band center, which can be used to tune a more precise PtIn ratio for the PDH reaction in the future.

Metastable Structures in Cluster Catalysis from First-Principles: Structural Ensemble in Reaction Conditions and Metastability Triggered Reactivity

Reactivity studies on catalytic transition metal clusters are usually performed on a single global minimum structure. With the example of a Pt₁₃ cluster under a pressure of hydrogen, we show from first-principle calculations that low energy metastable structures of the cluster can play a major role for catalytic reactivity and that hence consideration of the global minimum structure alone can severely underestimate the activity. The catalyst is fluxional with an ensemble of metastable structures energetically accessible at reaction conditions. A modified genetic algorithm is proposed to comprehensively search for the low energy metastable ensemble (LEME) structures instead of merely the global minimum structure. In order to reduce the computational cost of density functional calculations, a high dimensional neural network potential is employed to accelerate the exploration. The presence and influence of LEME structures during catalysis is discussed by the example of H covered Pt₁₃ clusters for two reactions of major importance: hydrogen evolution reaction and methane activation. The results demonstrate that although the number of accessible metastable structures is reduced under reaction condition for Pt₁₃ clusters, these metastable structures can exhibit high activity and dominate the observed activity due to their unique electronic or structural properties. This underlines the necessity of thoroughly exploring the LEME structures in catalysis simulations. The approach enables one to systematically address the impact of isomers in catalysis studies, taking into account the high adsorbate coverage induced by reaction conditions.

Monitoring Reaction Paths Using Vibrational Spectroscopies: The Case of the Dehydrogenation of Propane toward Propylene on Pd-Doped Cu(111) Surface

Monitoring reaction paths is not only a fundamental scientific issue but also helps us to understand and optimize the catalytic process. Infrared (IR) and Raman spectroscopies are powerful tools for detecting particular molecules or intermediate products as a result of their ability to provide the molecular "finger-print". However, theoretical modeling for the vibrational spectra of molecular adsorbates on metallic surfaces is a long-standing challenge, because accurate descriptions of the electronic structure for both the metallic substrates and adsorbates are required. In the present work, we applied a quasi-analytical IR and Raman simulation method to monitor the dehydrogenation of propane towards propylene on a Pd-doped Cu(111) surface in real-time. Different Pd ensembles were used to construct the single-atom catalyst (SAC). We found that the number of sublayer Pd atoms could only affect the intensity of the peak rather than the peak position on the vibrational spectra. However, with the dehydrogenation reaction proceeding, both IR and Raman spectra were changed greatly, which indicates that every reaction step can be distinguished from the point of view of vibrational spectroscopies. Additionally, we found that the catalytic process, which starts from different initial states, shows different spectral profiles. The present results suggest that the vibrational spectroscopies obtained by the high-precision simulations pave the way for identifying different catalytic reaction paths.

Nanocatalysts for hydrogen evolution reactions

Hydrogen fuel is among the cleanest renewable resources and is the best alternative to fossil fuels for the future.

Thermally Stable and Regenerable Platinum-Tin Clusters for Propane Dehydrogenation Prepared by Atom Trapping on Ceria

Ceria (CeO₂) supports are unique in their ability to trap ionic platinum (Pt), providing exceptional stability for isolated single atoms of Pt. The reactivity and stability of single‐atom Pt species was explored for the industrially important light alkane dehydrogenation reaction. The single‐atom Pt/CeO₂ catalysts are stable during propane dehydrogenation, but are not selective for propylene. DFT calculations show strong adsorption of the olefin produced, leading to further unwanted reactions. In contrast, when tin (Sn) is added to CeO₂, the single‐atom Pt catalyst undergoes an activation phase where it transforms into Pt–Sn clusters under reaction conditions. Formation of small Pt–Sn clusters allows the catalyst to achieve high selectivity towards propylene because of facile desorption of the product. The CeO₂‐supported Pt–Sn clusters are very stable, even during extended reaction at 680 °C. Coke formation is almost completely suppressed by adding water vapor to the feed. Furthermore, upon oxidation the Pt–Sn clusters readily revert to the atomically dispersed species on CeO₂, making Pt–Sn/CeO₂ a fully regenerable catalyst.

Strong metal-support interaction between Pt and SiO2 following high-temperature reduction: a catalytic interface for propane dehydrogenation

Pt/SiO₂ directly reduced in H₂ at 1073 K exhibited a high catalytic activity in propane dehydrogenation, primarily attributed to the electronic modification of Pt nanoparticles by the SMSI effect.

Pd–In intermetallic alloy nanoparticles: highly selective ethane dehydrogenation catalysts

2 nm PdIn intermetallic alloy (cubic, CsCl type) nanoparticle catalyst was near 100% selective to ethane dehydrogenation at 600 °C (at 15% conversion) with a dehydrogenation TOR almost 10 times higher than that of monometallic Pd.

Insight into mechanism and selectivity of propane dehydrogenation over the Pd-doped Cu(111) surface

The Pd/Cu(111) surface demonstrates good balance between the activity, selectivity, thermal stability and the maximum use of the noble metal, showing great potential in the catalytic production of light olefins.

Catalytic dehydrogenation of isobutane over a Ga2O3/ZnO interface: reaction routes and mechanism

In this work, physical mixtures of ZnO and Ga₂O₃, even with a small amount of Ga₂O₃, were found to exhibit greatly enhanced catalytic performance for isobutane dehydrogenation compared to their individual components, namely solely ZnO or Ga₂O₃.

Molecular understandings on the activation of light hydrocarbons over heterogeneous catalysts

Due to the depletion of petroleum and the recent shale gas revolution, the dropping of the price for light alkanes makes alkanes an attractive feedstock for the production of light alkenes and other valuable chemicals. Understanding the mechanism for the activation of C-H bonds in hydrocarbons provides fundamental insights into this process and a guideline for the optimization of catalysts used for the processing of light alkanes. In the last two decades, density functional theory (DFT) has become a powerful tool to explore elementary steps and mechanisms of many heterogeneously catalyzed processes at the atomic scale. This review describes recent progress on computational understanding of heterogeneous catalytic dehydrogenation reactions of light alkanes. We start with a short description on basic concepts and principles of DFT as well as its application in heterogeneous catalysis. The activation of C-H bonds over transition metal and alloy surfaces are then discussed in detail, followed by C-H activation over oxides, zeolites and catalysts with single atoms as active sites. The origins of coking formation are also discussed followed by a perspective on directions of future research.

Dehydrogenation of propane over PtSnAl/SBA-15 catalysts: Al addition effect and coke formation analysis

Addition of Al to PtSnAl/SBA-15 catalysts inhibits the reduction of SnO_x and changes the acidity, which results in different coke formation rates.

Propane dehydrogenation over Pt-Cu bimetallic catalysts: the nature of coke deposition and the role of copper

This paper describes an investigation of the promotional effect of Cu on the catalytic performance of Pt/Al2O3 catalysts for propane dehydrogenation. We have shown that Pt/Al2O3 catalysts possess higher propylene selectivity and lower deactivation rate as well as enhanced anti-coking ability upon Cu addition. The optimized loading content of Cu is 0.5 wt%, which increases the propylene selectivity to 90.8% with a propylene yield of 36.5%. The origin of the enhanced catalytic performance and anti-coking ability of the Pt-Cu/Al2O3 catalyst is ascribed to the intimate interaction between Pt and Cu, which is confirmed by the change of particle morphology and atomic electronic environment of the catalyst. The Pt-Cu interaction inhibits propylene adsorption and elevates the energy barrier of C-C bond rupture. The inhibited propylene adsorption diminishes the possibility of coke formation and suppresses the cracking reaction towards the formation of lighter hydrocarbons on Pt-Cu/Al2O3, while a higher energy barrier for C-C bond cleavage suppresses the methane formation.