M�ssbauer and X-ray photoelectron spectroscopic evidence for the structure of supported bimetallic catalysts: FeRu, FeRh, FePd, Felr, and FePt on SiO2

Niemantsverdriet, J.W.; KAAM, J. A. C. VAN; Flipse, C. F. J.; Kraan, A.M. van der

doi:10.1016/0021-9517(85)90360-4

Cited by 46 publications

(3 citation statements)

References 21 publications

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“…Our predictions on metal spin distribution and changes upon doping are in principle amenable to experimental validation via Mössbauer measurements on Fe single crystals. Our previous findings on N 2 bonding transformations from σ bond to π bond on the Fe-bcc(111) surface were consistent with scattering or spectroscopic experiments .…”

Section: Resultsmentioning

confidence: 86%

Discovery of Dramatically Improved Ammonia Synthesis Catalysts through Hierarchical High-Throughput Catalyst Screening of the Fe(211) Surface

et al. 2020

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In order to improve efficiency of ammonia synthesis using the Haber−Bosch (HB) process with Fe-based catalysts, we employed quantum mechanics (QM)-based hierarchical high-throughput catalyst screening (HHTCS) of 49 possible metal dopants. Here, we consider the Fe( 211) surface (one of the two most active iron catalyst facets) to identify dopants that dramatically increase the turnover frequency (TOF) for HB synthesis. We found that under HB conditions, this surface reconstructs to form the Fe(211)R missing-row surface. Focusing on dopants with a strong preference for the subsurface site, we found that Co is the most promising candidate among the 49. We then examined the full reaction pathway on this Co-doped Fe(211)R surface, considering all 19 important 2 × 2 configurations and calculated the free-energy barriers (ΔG ∫ ) for all 12 important reaction steps. At 673 K and 20 atm, we find a decrease, δ(ΔG ∫ ) = −0.19 eV, in the overall reaction free-energy barrier for the Co-doped case. We then carried out kinetic Monte Carlo simulations for 60−120 min using 100 replicas with the full reaction path using rates from QM free-energy reaction barriers to predict that the TOF for the Co-doped surface increases by a factor of 2.8 with respect to the undoped Fe(211)R surface. Thus, the Co-doped Fe(211)R system could lower the extreme HB pressure of 200 atm to ∼40 atm at 773 K while maintaining the same TOF as that of undoped Fe(211)R. We conclude that Co dopants in the Fe catalyst could significantly improve the catalytic efficiency of ammonia synthesis under industrial conditions. This excellent performance of the Co-doped system is explained in terms of a surface spin analysis on the N 2 -bonded configurations that show how Co dopants shift the N 2 surface-binding mode. This demonstrates that metal surface spins can be used as quantitative descriptors to understand reaction energetics. This study demonstrates that the HHTCS kinetic analysis of the free-energy reaction path in terms of essential configurations can enable discovery of the salient barriers to overcome and best dopant candidates for further improvements.

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Section: Resultsmentioning

confidence: 86%

Discovery of Dramatically Improved Ammonia Synthesis Catalysts through Hierarchical High-Throughput Catalyst Screening of the Fe(211) Surface

et al. 2020

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“…The addition of metal ions, such as Mn, Ti, Zr, Nb, and Fe, promotes the production of oxygenates, including alcohols and aldehydes, in CO hydrogenation on the modified Rh, Ir, and Pd catalysts. , EXAFS, Mössbauer, XPS, and FT-IR studies of such bimetallic catalysts suggest that the promotion is associated with CO activation on surface bimetallic sites of the catalyst and that this promotion enhances the migratory CO insertion into several intermediate adspecies such as methyl and carbene . The intrazeolitic bimetallic clusters are unique, bringing nanostructural alloys with encasing on a nearly molecular scale.…”

Section: Introductionmentioning

confidence: 99%

Intrazeolite Anchoring of Co, Ru, and [Ru−Co] Carbonyl Clusters: Synthesis, Characterization, and Their Catalysis for CO Hydrogenation

Shen

Ichikawa

1998

J. Phys. Chem. B

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This paper focuses on the intrazeolite anchoring of Co, Ru, and Ru-Co carbonyl clusters and their catalytic performances for CO hydrogenation. The synthesis of intrazeolite anchoring of [HRuCo 3 (CO) 9 (µ 2 -CO) 3 ] involves the adsorption of metal carbonyl species into zeolite cages followed by reductive carbonylation under a mixed CO and H 2 atmosphere. The physicochemical characterization used a multianalytical approach, including FT-IR and EXAFS spectroscopies and CO/H 2 gas chemisorption. The research concluded several key points as follows. (i) There is significant bimetallic interaction. (ii) The generation process of bimetallic carbonyl clusters was considered to occur through the interaction of [Ru-Co], Co(CO) 4 -, and Ru I carbonyls, and conversion into [HRuCo 3 (CO) 9 (µ 3 -CO) 3 ] and further to [HRuCo 3 (CO) 9 (µ 2 -CO) 3 ] isomer. (iii) Internal and external confinement of [HRuCo 3 (CO) 9 (µ 3 -CO) 3 ] were compared. (iv) The intrazeolite anchoring of [RuCo 3 ] carbonyl clusters shows a strong reaction with the extraframework Na + R-cage cations through involvement of the oxygen end of the bridging carbonyl ligands. (v) The bimetallic Ru-Co cluster catalyst shows higher CO conversion and oxygenates selectivity than the monometallic Co or Ru cluster. A high Co ratio in the Ru-Co cluster catalyst enhances the catalytic activity and the selectivity of oxygenates. (vi) The catalytic properities such as oxygenates selectivity depend on cluster size. Basic NaX is superion to NaY in enhancing oxygenates selectivity. (vii) Infrared spectra, 13 CO, D 2 isotopic exchange, and mass studies prove that a surface η 2 -formyl species adsorbed on Ru-Co interaction sites is an intermediate of oxygenate formation. The adjacent Ru-Co sites suppress η 2 -formyl adspecies dissociation and promote formyl species insertion into alkyl adspecies to enhance heavy oxygenate formation. (ix) The deactivated bimetallic Ru-Co cluster catalyst can be regenerated by hydrogen treatment, whereas the monometallic Co cluster catalyst cannot be regenerated.

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“…Bulk alloy behavior is not always a predictor for the structural behavior of supported bimetallic particles. Specifically, the interaction between the support and one of the metals in some systems can modify the behavior from that of the bulk alloy .…”

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confidence: 99%

Structure of Bimetallic Particles: Nonequimolar Graphite-Supported Fe−Pd

Wunder

Phillips

1996

J. Phys. Chem.

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This investigation established the effects of bulk immiscibility on the bulk and surface structure of FePd catalyst particles supported on graphite. By use of Mössbauer effect spectroscopy, X-ray diffraction and gas-adsorption microcalorimetry, it was shown that iron-rich FePd/Grafoil catalyst particles consist of thermodynamically stable segregated states of metallic iron and FePd alloy in accordance with the bulk immiscibility of the two phases. This indicates that manipulation of metal stoichiometry in bimetallic catalyst particles with weak metal support interaction provides another means to modify particle structure and hence catalytic chemistry.

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M�ssbauer and X-ray photoelectron spectroscopic evidence for the structure of supported bimetallic catalysts: FeRu, FeRh, FePd, Felr, and FePt on SiO2

Cited by 46 publications

References 21 publications

Discovery of Dramatically Improved Ammonia Synthesis Catalysts through Hierarchical High-Throughput Catalyst Screening of the Fe(211) Surface

Discovery of Dramatically Improved Ammonia Synthesis Catalysts through Hierarchical High-Throughput Catalyst Screening of the Fe(211) Surface

Intrazeolite Anchoring of Co, Ru, and [Ru−Co] Carbonyl Clusters: Synthesis, Characterization, and Their Catalysis for CO Hydrogenation

Structure of Bimetallic Particles: Nonequimolar Graphite-Supported Fe−Pd

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