Kinetics of Lifetime Changes in Bimetallic Nanocatalysts Revealed by Quick X‐ray Absorption Spectroscopy

Abstract

Alloyed metal nanocatalysts are of environmental and economic importance in a plethora of chemical technologies. During the catalyst lifetime, supported alloy nanoparticles undergo dynamic changes which are well‐recognized but still poorly understood. High‐temperature O2–H2 redox cycling was applied to mimic the lifetime changes in model Pt13In9 nanocatalysts, while monitoring the induced changes by in situ quick X‐ray absorption spectroscopy with one‐second resolution. The different reaction steps involved in repeated Pt13In9 segregation‐alloying are identified and kinetically characterized at the single‐cycle level. Over longer time scales, sintering phenomena are substantiated and the intraparticle structure is revealed throughout the catalyst lifetime. The in situ time‐resolved observation of the dynamic habits of alloyed nanoparticles and their kinetic description can impact catalysis and other fields involving (bi)metallic nanoalloys.

Propane to olefins tandem catalysis: a selective route towards light olefins production

“…26 Mixed phases and alloying can be monitored by in situ and operando X-ray absorption spectroscopy, drawing inspiration from work on Pt-In: changes in Pt-In alloys were monitored under O 2 -H 2 cycles, investigating the redox behavior and the sintering mechanism of the alloy under typical regeneration-reactivation conditions used in PDH. 118 The results showed that during oxidation, the Pt-In alloy simultaneously undergoes decomposition and Pt oxidation, the latter being the rate determining step, and that oxidation requires higher thermal activation compared to reduction. On the other side, the reduction step has a lower activation energy and involves the reduction of platinum and indium oxides with subsequent formation of the highly stable Pt 13 In 9 alloy.…”

Aligning time-resolved kinetics (TAP) and surface spectroscopy (AP-XPS) for a more comprehensive understanding of ALD-derived 2D and 3D model catalysts

“…10-20 nm metal nanoparticles. Previous reports on very similar catalysts derived from layered double hydroxides (LDH) and ALD-derived samples 36,71 suggest that aer several cycles of reduction/dehydrogenation/oxidation/re-reduction treatments, Pt and In form compositionally and structurally stable alloyed NPs, the degree of sintering of which depends on various preparation factors, that display consistent kinetic behavior in propane dehydrogenation. In order to prepare such a stable starting surface, the as-prepared 2D and 3D samples were subjected to the standard sequence of (ex situ and in situ) cycling pretreatments before further characterization.…”

Moving Frontiers in Transition Metal Catalysis: Synthesis, Characterization and Modeling

“…However, often the structure of the as‐prepared NPs and active sites changes during activation and exposure to the reaction conditions. [7c,8b] Supported NPs may change their size, shape, oxidation state, and composition also under dynamic reaction conditions . The transition metal NPs respond to the surrounding atmosphere and hence, they should usually be considered as “precursors.” The difficulty of predicting these changes necessitates the use of operando characterization techniques to measure the structure of the NPs as well as to track changes occurring under relevant reaction conditions.…”