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.

Formation and Functioning of Bimetallic Nanocatalysts: The Power of X‐ray Probes

“…Iglesias-Juez et al [74] simulated possible Pt-Sn NP structures based on Pt-Pt and Pt-Sn EXAFS coordination numbers [75] for different dehydrogenation-regeneration C 3 H 8 -O 2 -H 2 cycle(s), showing:1 )NPs ize increase,2 )progressive Sn-enrichment of the NP,a nd 3) increased mixing from core-shell-to random-type alloys (Figure 10 a). A gradual NP size increase is also observed by Filez et al [71] via adecreased XANES WL height under O 2 during 60 H 2 -O 2 redox cycles (Figure 10 b). In O 2 ,a nI n 2 O 3 /PtO x composite is formed in which PtO x consists of ametallic core with oxidized surface,t he latter yielding increased WL heights.W ith decreasing dispersion, which is due to sintering during redox cycling, the fraction of oxidized surface decreases,l eading to aW Ld ecrease.N otably,S olano et al [76] also studied Pt NP sintering with in situ GISAXS under different O 2 partial pressures to monitor the NP size and spacing in real time.The observed behavior indicates the key role of the outer PtO 2 shell, stable at low temperature,a nd its thermal reduction creating mobile species that trigger particle sintering.…”

“…Recently,F ilez et al [71] refined the steps involved in segregation alloying of Pt 13 In 9 into In 2 O 3 /PtO x and back to Pt 13 In 9 during high-temperature O 2 -H 2 redox cycling (Figure 9b). By kinetic modeling of QXANES data, partial reaction orders,r ate constants,a nd Arrhenius parameters were estimated, allowing to construct the kinetic reaction cycle that steers the dynamic restructuring of Pt 13 In 9 nanoalloys ( Figure 9c).…”

Nanoscale Chemical Diversity of Coke Deposits on Nanoprinted Metal Catalysts Visualized by Tip‐Enhanced Raman Spectroscopy

“…Particularly, disordered coke burns at significantly lower temperatures compared to graphitic coke during O 2 reactivation. [ 9 ] Lowering the reactivation temperature will thus free‐up the Pt surface necessary for reaction, but simultaneously prevent significant nanoparticle sintering inherently connected to high‐temperature O 2 reactivation, [ 17,67,68 ] thus extending the catalyst lifetime. In general, the demonstrated approach paves the way to a more general application of TERS on non‐conductive catalyst surfaces, such as zeolites and metal (oxide) catalysts, a field which is yet to be explored.…”

“…Frequent catalyst regeneration treatments are therefore required to free‐up the poisoned active sites by burning coke deposits into CO 2 and H 2 O, accelerating climate disruption. [ 8,15–17 ]…”