Lattice Strain and Surface Activity of Ternary Nanoalloys under the Propane Oxidation Condition

Abstract

The ability to harness the catalytic oxidation of hydrocarbons is critical for both clean energy production and air pollutant elimination, which requires a detailed understanding of the dynamic role of the nanophase structure and surface reactivity under the reaction conditions. We report here findings of an in situ/operando study of such details of a ternary nanoalloy under the propane oxidation condition using high-energy synchrotron X-ray diffraction coupled to atomic pair distribution function (HE-XRD/PDF) analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The catalysts are derived by alloying Pt with different combinations of second (Pd) and third (Ni) transition metals, showing a strong dependence of the catalytic activity on the Ni content. The evolution of the phase structure of the nanoalloy is characterized by HE-XRD/PDF probing of the lattice strain, whereas the surface activity is monitored by DRIFTS detection of the surface intermediate formation during the oxidation of propane by oxygen. The results reveal the dominance of the surface intermediate species featuring a lower degree of oxygenation upon the first C–C bond cleavage on the lower-Ni-content nanoalloy and a higher degree of oxygenation upon the second C–C bond cleavage on the higher-Ni-content nanoalloy. The face-centered-cubic-type phase structures of the nanoalloys under the oxidation condition are shown to exhibit Ni-content-dependent changes of lattice strains, featuring the strongest strain with little variation for the higher-Ni-content nanoalloy, in contrast to the weaker strains with oscillatory variation for the lower-Ni-content nanoalloys. This process is also accompanied by oxygenation of the metal components in the nanoalloy, showing a higher degree of oxygenation for the higher-Ni-content nanoalloy. These subtle differences in phase structure and surface activity changes correlate with the Ni-composition-dependent catalytic activity of the nanoalloys, which sheds a fresh light on the correlation between the dynamic change of atomic strains and the surface reactivity and has significant implications for the design of oxidation catalysts with enhanced activities.

Insights into Reaction Mechanisms in Liquid Metals from Density Functional Theory: CH4 Pyrolysis in BiNiX (X = Cu, Al) Molten Metals as a Case Study

“…Moreover, one can even explore the inclusion of a third species in the alloy, aiming to enhance the activity of the active metal even further. Several examples from the literature showcase the intriguing synergy exhibited by such ternary alloys. − For instance, Maluf and Assaf used a Mo promoter in a solid-phase Ni catalyst to improve its activity for methane steam reforming . These alloys have been previously investigated in such diverse areas as hydrocarbon conversion, dry reforming of methane, , and thermocatalytic decomposition of methane , which are similar to the reaction under consideration.…”

“…Several examples from the literature showcase the intriguing synergy exhibited by such ternary alloys. − For instance, Maluf and Assaf used a Mo promoter in a solid-phase Ni catalyst to improve its activity for methane steam reforming . These alloys have been previously investigated in such diverse areas as hydrocarbon conversion, dry reforming of methane, , and thermocatalytic decomposition of methane , which are similar to the reaction under consideration. Hence, the main objective of this study is to understand the effect of such a promoter on the reactivity of a Ni-based alloy within a low-melting-point solvent metal, namely Bi.…”

Stable Strain State of Single‐Twinned AgPdF Nanoalloys under Formate Oxidation Reaction

“…[ 6 ] However, the complicated evolution information of surface reconstruction makes it challenging to identify the structural model of actual active sites and, in turn, to conduct the substantial and reliable mechanism analysis. [ 7 ] To eliminate the impact of reconstructing, an effective strategy involves constructing the steady configuration during catalysis to directly trigger the catalytic cycle without structural transformation. For example, Sun et al reported the atomically dispersed Ru on Ni–V layered double hydroxide scaffold with the bifunctional reactive sites, which can preserve the surface configuration and suppress the occurrence of surface restructuring through a strongly atomic metal–support interaction.…”

Insights into Heterogeneous Catalysts under Reaction Conditions by In Situ/Operando Electron Microscopy

“…Many in situ/operando FTIR (Fourier transform infrared spectroscopy), Raman, XAS (X‐ray absorption spectroscopy), XPS (X‐ray photoelectron spectroscopy), XRD (X‐ray diffraction), etc., have been used for catalyst characterizations which largely capture the average molecular or atomic information under reaction conditions. [ 22–47 ] In comparison, in situ/operando TEM is relatively new, which enables the ability to capture individual atom or molecule information under the reaction conditions. In other words, it provides information with atomic, molecular and sometimes nanoscale/microscale resolutions depending on the complexity of the sample system and the instrumental measurement configuration.…”