Classical
strong metal–support interactions (SMSI), which
play a crucial role in the preparation of supported metal nanoparticle
catalysts, is one of the most important concepts in heterogeneous
catalysis. The conventional wisdom for construction of classical SMSI
involves in redox treatments at high-temperatures by molecular oxygen
or hydrogen, sometimes causing sintered metal nanoparticles before
SMSI formation. Herein, we report that the aforementioned issue can
be effectively avoided by a wet-chemistry methodology. As a typical
example, we demonstrate a new concept of wet-chemistry SMSI (wcSMSI)
that can be constructed on titania-supported Au nanoparticles (Au/TiO2-wcSMSI), where the key is to employ a redox interaction between
Auδ+ and Ti3+ precursors in aqueous solution.
The wcSMSI is evidenced by covering Au nanoparticles with the TiO
x
overlayer, electronic interaction between
Au and TiO2, and suppression of CO adsorption on Au nanoparticles.
Owing to the wcSMSI, the Au–TiO
x
interface with an improved redox property is favorable for oxygen
activation, accelerating CO oxidation. In addition, the oxide overlayer
efficiently stabilizes the Au nanoparticles, achieving sinter-resistant
Au/TiO2-wcSMSI catalyst in CO oxidation.
As the commercial catalyst in the propane direct dehydrogenation (PDH) reaction, one of the biggest challenges of Pt catalysts is coke formation, which severely reduces activity and stability. In this work, a first-principles DFT-based kinetic Monte Carlo simulation (kMC) is performed to understand the origin of coke formation, and an effective method is proposed to curb coke. The conventional DFT calculations give a complete description of the reaction pathway of dehydrogenation to propylene, deep dehydrogenation, and C−C bond cracking. The rate-limiting step is identified as the dissociative adsorption of propane. Moreover, a comparison between different exchange-correlation functionals indicates the importance of van der Waals corrections for the adsorption of propane and propylene. The lateral interactions between the surface adsorbates are significant, which implies that mean field microkinetic modeling might not adequately describe the reaction process. There are two distinct stages in PDH, which are quick deactivation and steady state, respectively, as revealed from the kMC simulation. The precursor of coke mainly formed during the quick deactivation. The calculations indicate that the geometries of the active sites for the dehydrogenation and deep reactions are different. Therefore, the availability of surface sites is a crucial factor in the formation of propylene and side products. The active sites from quick deactivation are mainly occupied by C 2 /C 1 species, which are hard to remove. On the other hand, the surface sites that are left are mainly active toward dehydrogenation to propylene due to the geometry constraint. Therefore, a stable activity and selectivity is reached. Furthermore, the effect of hydrogen molecules in the input stream is also explored. The calculations indicate that the inclusion of hydrogen in PDH reactants not only enhances the forward reactions to the propylene formation but also reduces the consumption of the resulted propylene during the reaction. Therefore, hydrogen is very helpful to the selectivity increase in PDH in addition to other effects. Overall, the current study lays out a solid base for the future optimization of the Pt catalysts in PDH and we propose that the fine control of the surface sites on Pt has paramount importance in reducing coke formation.
Phosphorus-doped carbon shows superior performance for the CO2 electrochemical reduction reaction, revealing the crucial role of the phosphorus bonding configuration.
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