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1 Exsolution is an elegant process to produce catalytically active surfaces with well-dispersed metal nanoparticles. It is especially interesting for fast and simple catalyst preparation, that results in smaller and better dispersed nanoparticles compared t
Christoph Rameshan
 + 836 word(s) 836 2020-04-15 12:17:24 |
2 Exsolution is an elegant process to produce catalytically active surfaces with well-dispersed metal nanoparticles. It is especially interesting for fast and simple catalyst preparation, that results in smaller and better dispersed nanoparticles compared t
Christoph Rameshan
 Meta information modification 836 2020-04-16 18:50:42 | |
3 format correct
Camila Xu
 -1 word(s) 835 2020-11-01 10:32:46 |

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Lindenthal, L.; Rameshan, R.; Summerer, H.; Ruh, T.; Popovic, J.; Nenning, A.; Löffler, S.; Opitz, A.K.; Blaha, P.; Rameshan, C. Nanoparticle Exsolution on Perovskite-Based Catalysts. Encyclopedia. Available online: https://encyclopedia.pub/entry/590 (accessed on 15 November 2024).
Lindenthal L, Rameshan R, Summerer H, Ruh T, Popovic J, Nenning A, et al. Nanoparticle Exsolution on Perovskite-Based Catalysts. Encyclopedia. Available at: https://encyclopedia.pub/entry/590. Accessed November 15, 2024.
Lindenthal, Lorenz, Raffael Rameshan, Harald Summerer, Thomas Ruh, Janko Popovic, Andreas Nenning, Stefan Löffler, Alexander Karl Opitz, Peter Blaha, Christoph Rameshan. "Nanoparticle Exsolution on Perovskite-Based Catalysts" Encyclopedia, https://encyclopedia.pub/entry/590 (accessed November 15, 2024).
Lindenthal, L., Rameshan, R., Summerer, H., Ruh, T., Popovic, J., Nenning, A., Löffler, S., Opitz, A.K., Blaha, P., & Rameshan, C. (2020, April 16). Nanoparticle Exsolution on Perovskite-Based Catalysts. In Encyclopedia. https://encyclopedia.pub/entry/590
Lindenthal, Lorenz, et al. "Nanoparticle Exsolution on Perovskite-Based Catalysts." Encyclopedia. Web. 16 April, 2020.
Nanoparticle Exsolution on Perovskite-Based Catalysts
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This entry is adapted from the peer-reviewed paper 10.3390/catal10030268

In heterogeneous catalysis, surfaces decorated with uniformly dispersed, catalytically-active (nano)particles are a key requirement for excellent performance. Besides standard catalyst preparation routines—with limitations in controlling catalyst surface structure (i.e., particle size distribution or dispersion)—exsolution is a potential novel and time efficient route to precisely tailor catalyst surface morphology and composition of perovskites:

Perovskite-type oxides of nominal composition ABO3 with transition metal cations on the B-site can exsolve the B-site transition metal upon controlled reduction. In this exsolution process, the transition metal emerges from the oxide lattice and migrates to the surface where it forms catalytically active nanoparticles. Doping the B-site with reducible and catalytically highly active elements, offers the opportunity of tailoring properties of exsolution catalysts.

Exsolution Nanoparticles Perovskites Tailored Surfaces

1. Introduction

In heterogeneous catalysis, controllable surface properties and a maximum amount of stable uniformly-dispersed catalytically highly active sites on the surface of a porous material are of key importance. Typically, catalysts consist of metal, alloy, or oxide nanoparticles embedded in an oxide support material. Depending on the type of catalytic reaction, active sites are either just nanoparticles themselves or the combination of nanoparticles and oxide support. Ideally, catalysts exhibit long-term stability and activity during reaction. Therefore, resistance to catalyst poisons, inhibition of carbon deposition (blocking of active sites), and prevention of particle agglomeration and sintering (loss of active surface area) is essential.

Typically, these structures are prepared by deposition, impregnation or precipitation techniques[1][2] followed by catalyst activation prior to reactions via oxidation and reduction[3]. Although these approaches are applied widely, they offer limited control over size, distribution, and anchorage of deposited species, not only during preparation but also during catalyst activation or operation, and they might be time consuming and costly[4].

Alternatively, an emerging concept is to grow the nanoparticles in situ, by reduction or during catalytic reaction, directly from the (porous) oxide backbone support itself[4][5][6]. Perovskites (nominal composition ABO3 with A and B being a large and small cation, respectively, cf. Figure 1a) can incorporate catalytically highly active elements as cations on the B-site of the perovskite lattice (e.g., Ni[4][7], Fe [4][8], Co[9], Cu[4][9], Pt[10], Pd[10][11]). Upon exposure to reducing conditions, these elements can be partly exsolved as nanoparticles, thus opening the possibility of in situ growth of active catalysts[12], see sketch in Figure 1b. In comparison to traditional deposition techniques, this process produces finer and higher dispersed catalyst nanoparticles[4][13][14] and is more time- and cost-effective, as it does not require multiple "deposition" steps or expensive precursors[15]. Furthermore, it has been shown that nanoparticles formed by exsolution exhibit improved sintering stability during catalytic reaction[16]. In addition, due to a possible reversibility of the nanoparticle exsolution process, particle agglomeration can be avoided by reoxidation cycles[17], hence, greatly enhancing the catalyst lifetime[12][18].

 

Catalysts 10 00268 g001 550
Figure 1. (a) Perovskite lattice structure; (b) simplified exsolution process.

Mechanisms for nanoparticle exsolution from perovskites were investigated already by multiple groups[4][11][19][20][21]. It is generally accepted that exsolution catalysts need easily reducible dopant cations[22], such as Ru, Co, Pd, or Ni[23], that will form metallic deposits on the perovskite surface. Thus, depending on temperature and oxygen chemical potential in the gas phase (i.e., the strength of reduction), dopants and in some cases also lattice cations are reduced and exsolved as nanoparticles[8][24]. As an explanation for exsolution mechanisms, Neagu et al.[4] proposed that oxygen vacancies created by reduction destabilize the perovskite lattice, especially when their concentration is high and when additionally A-site cation vacancies are present. Such combined oxygen and A-site cation vacancy formations may locally cause spontaneous exsolution of B-site species in an attempt to re-establish stoichiometry across all sites. Oh et al.[19] implied that the morphological evolution of nanoparticles could be explained using a simple energy-based model, which accounts for interplay between surface free energy and strain energy induced by the included metal nucleate. By quantitative strain field modelling, they could demonstrate that this provides the driving force for exsolution processes. Similarly, Han and co-workers applied classical nucleation theory to the exsolution process and found the strain between metal particle and supporting oxide being a potential influencing factor for the particle size.

2. Conclusion

Usually, formation of nanoparticles on the surface is accomplished via a reductive treatment. For example, Arrivé et al.[25] showed for Ni doped LaSrTiO3 that pre-reduction in H2 at 1573 K leads to exsolution of Ni particles on the surface of solid oxide electrochemical cells leading to improved electrochemical performance. Additionally, Papargyriou and Irvine demonstrated Ni exsolution from Ni-doped La0.75Sr0.25Cr0.5Fe0.5O3 perovskite by H2 reduction[14]. Nanoparticles with a size of 30–50 nm were formed on the surface, leading to an improvement of catalytic properties of the material. Similarly, Sun et al.[13] could observe Ni nanoparticle exsolution from Ni-doped La0.7Sr0.3CrO3 upon pre-reduction in H2. Most of the recent studies on exsolution phenomena are reported and studied by the electrochemical community (mainly with respect to fuel cell technology), but utilization of this effect for preparing tailored heterogeneous catalyst materials is still rare—even though the initial idea came indeed from the catalysis community[12].

References

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  3. Séverine Rousseau; Olivier Marie; Philippe Bazin; Marco Daturi; Stéphane Verdier; Virginie Harlé; Investigation of Methanol Oxidation over Au/Catalysts Using Operando IR Spectroscopy: Determination of the Active Sites, Intermediate/Spectator Species, and Reaction Mechanism. Journal of the American Chemical Society 2010, 132, 10832-10841, 10.1021/ja1028809.
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  10. Hirohisa Tanaka; Mari Uenishi; Masashi Taniguchi; Isao Tan; Keiichi Narita; Mareo Kimura; Kimiyoshi Kaneko; Yasuo Nishihata; Jun’Ichiro Mizuki; The intelligent catalyst having the self-regenerative function of Pd, Rh and Pt for automotive emissions control. Catalysis Today 2006, 117, 321-328, 10.1016/j.cattod.2006.05.029.
  11. Michael B. Katz; George W. Graham; Yingwen Duan; Hong Liu; Carolina Adamo; Darrell G. Schlom; X. Q. Pan; Self-Regeneration of Pd–LaFeO3Catalysts: New Insight from Atomic-Resolution Electron Microscopy. Journal of the American Chemical Society 2011, 133, 18090-18093, 10.1021/ja2082284.
  12. Y. Nishihata; J. Mizuki; T. Akao; H. Tanaka; M. Uenishi; M. Kimura; T. Okamoto; N. Hamada; Self-regeneration of a Pd-perovskite catalyst for automotive emissions control. Nature 2002, 418, 164-167, 10.1038/nature00893.
  13. Yifei Sun; Jianhui Li; Yimin Zeng; Babak Shalchi Amirkhiz; Mengni Wang; Yashar Behnamian; Jing-Li Luo; A-site deficient perovskite: the parent for in situ exsolution of highly active, regenerable nano-particles as SOFC anodes. Journal of Materials Chemistry A 2015, 3, 11048-11056, 10.1039/C5TA01733E.
  14. D. Papargyriou; John T. S. Irvine; Nickel nanocatalyst exsolution from (La,Sr) (Cr,M,Ni)O3 (M Mn,Fe) perovskites for the fuel oxidation layer of Oxygen Transport Membranes. Solid State Ionics 2016, 288, 120-123, 10.1016/j.ssi.2015.11.007.
  15. Qian Zhao; Harald Lorenz; Stuart Turner; Oleg Lebedev; Gustaaf Van Tendeloo; Christoph Rameshan; Bernhard Klötzer; Jürgen Konzett; Simon Penner; Catalytic characterization of pure SnO2 and GeO2 in methanol steam reforming. Applied Catalysis A: General 2010, 375, 188-195, 10.1016/j.apcata.2009.12.027.
  16. Dragos Neagu; Tae-Sik Oh; David N. Miller; Hervé Ménard; Syed M. Bukhari; Stephen R. Gamble; Raymond J. Gorte; John M. Vohs; John T. S. Irvine; Nano-socketed nickel particles with enhanced coking resistance grown in situ by redox exsolution. Nature Communications 2015, 6, 8120, 10.1038/ncomms9120.
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  20. Jacob M. Haag; Scott A. Barnett; James W. Richardson; Kenneth R. Poeppelmeier; Structural and Chemical Evolution of the SOFC Anode La0.30Sr0.70Fe0.70Cr0.30O3−δupon Reduction and Oxidation: An in Situ Neutron Diffraction Study. Chemistry of Materials 2010, 22, 3283-3289, 10.1021/cm100609e.
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Subjects: Chemistry, Physical
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Lorenz Lindenthal
,
Raffael Rameshan
,
Harald Summerer
,
Thomas Ruh
,
Janko Popovic
,
Andreas Nenning
,
Stefan Löffler
,
Alexander Karl Opitz
,
Peter Blaha
,
Christoph Rameshan
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Revisions: 3 times (View History)
Update Date: 01 Nov 2020
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