Effect of Noble Metals on the Strength of Brønsted Acid Sites in Bifunctional Zeolites

Santi, Dominic; Rabl, Sandra; Calemma, Vincenzo; Dyballa, Michael; Hunger, Michael; Weitkamp, Jens

doi:10.1002/cctc.201200675

Cited by 25 publications

(20 citation statements)

References 30 publications

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“…Comparison of the Δδ 1H values of noble metalcontaining zeolites Y with those of the Si(OH)Al groups in zeolites H,Na−Y ( Table 2, top lines) hints at a lower acid strength for all noble metal-containing zeolites with low metal loadings. This finding agrees with that of Santi et al 15 With increasing metal loadings, except for zeolite 2.8Pd/H,Na−Y, the acetonitrile-induced low-field shifts, Δδ 1H , and, correspondingly, the acid strength of the noble metal-containing zeolites Y under study converge to those of the zeolites H,Na−Y ( Table 2, last column). Interestingly, this loading-dependent increase of the acid strength goes in line with an increase of the number The Journal of Physical Chemistry C Article of Si(OH)Al groups formed per metal atoms upon the reduction (Figure 3), which corresponds to a decrease of the cationic character of the metal species.…”

Section: Resultssupporting

confidence: 91%

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Generation and Properties of Brønsted Acid Sites in Bifunctional Rh-, Ir-, Pd-, and Pt-Containing Zeolites Y Investigated by Solid-State NMR Spectroscopy

et al. 2015

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In the present work, the generation and properties of Brønsted acidic bridging OH groups (Si(OH)Al) in Rh-, Ir-, Pd-, and Ptcontaining zeolites Y were quantitatively investigated by multinuclear solidstate NMR spectroscopy. The number of Si(OH)Al groups formed per noble metal atom upon their reduction was found to be 0.3 to 1.3 instead of the theoretically expected values of 2 (Pd 2+ , Pt 2+ ) or 3 (Rh 3+ , Ir 3+ ). For zeolites Y with low noble metal loadings, a significantly lower acid strength of Si(OH)Al groups in comparison with those of H,Na−Y zeolites occurred. Interestingly, noble metal-containing zeolites Y with lower acid strength have a significant content of not completely reduced noble metal atoms with partially cationic character. The spatial distribution of Si(OH)Al groups in noble metal-containing zeolites Y was found to differ significantly from that in H,Na−Y zeolites. This effect is explained by the migration of a significant content of noble metal atoms into the sodalite cages of zeolites Y already upon calcination of their noble metal complexes. Therefore, a much higher content of Si(OH)Al groups generated by the reduction of noble metal species in zeolites Y are located in sodalite cages compared to those in H,Na−Y zeolites.

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Section: Resultssupporting

confidence: 91%

“…15 The acid strength of Si(OH)Al groups was characterized by 1 H MAS NMR spectroscopy upon adsorption of deuterated acetonitrile (CD 3 CN) as probe molecule and by FTIR spectroscopy of the thermodesorption of pyridine. By both methods, a similar decrease of the acid strength of zeolites Y and Beta modified by noble metals was found.…”

Section: Introductionmentioning

confidence: 99%

Generation and Properties of Brønsted Acid Sites in Bifunctional Rh-, Ir-, Pd-, and Pt-Containing Zeolites Y Investigated by Solid-State NMR Spectroscopy

et al. 2015

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“…Because the interaction between ammonia and metallic cobalt was rather weak, the ammonia desorption peak at 673 K in Co/H‐ZSM‐5‐GR and Co/H‐ZSM‐5‐IR mainly originated from the interaction of ammonia with the Brønsted acid sites in the H‐ZSM‐5 zeolite. Compared with the parent H‐ZSM‐5, the strength of the Brønsted acid sites in Co/H‐ZSM‐5‐GR and Co/H‐ZSM‐5‐IR decreased significantly, that is, the ammonia desorption peak shifted from 743 to 673 K, which could be explained by the influence of adjacent metallic cobalt species …”

Section: Resultsmentioning

confidence: 97%

Construction of Bifunctional Co/H‐ZSM‐5 Catalysts for the Hydrodeoxygenation of Stearic Acid to Diesel‐Range Alkanes

Zhang

Dai

et al. 2018

ChemSusChem

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Bifunctional Co/H-ZSM-5 zeolites were prepared by a surface organometallic chemistry grafting route, namely, by the stoichiometric reaction between cobaltocene and the Brønsted acid sites in zeolites. The catalyst was applied to a model reaction of the catalytic hydrodeoxygenation of stearic acid (SA). The cobalt species existed in the form of isolated Co ions at the exchange positions after grafting, transformed to CoO species on the surface of the zeolite, stabilized inside the zeolite channels upon calcination in air, and finally reduced by hydrogen to homogeneous clusters of metallic cobalt species approximately 1.5 nm in size. During this process, the Brønsted acid sites of the H-ZSM-5 zeolites were preserved with a slightly reduced acid strength. The as-prepared bifunctional catalyst exhibited an approximately 16 times higher activity for the hydrodeoxygenation of SA (2.11 g g h ) than the reference catalyst (0.13 g g h ) prepared by solid-state ion exchange and a high C /C ratio of approximately 24. The remarkable hydrodeoxygenation performance of the bifunctional Co/H-ZSM-5 was owed to the effective synergy between the uniformed metallic cobalt clusters and the Brønsted acid sites in H-ZSM-5. The simplified reaction network and kinetics of the SA hydrodeoxygenation catalyzed by the as-prepared bifunctional Co/H-ZSM-5 zeolites were also investigated.

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“…[117] Generally,inac atalytic reaction, the confined noble metal in the acidic zeolite will strongly influence the state of the acid sites.F or example, Pt and Ir metal nanoparticles became involved in charge transfer with neighboring framework atoms of Beta and Y zeolites and thus affected the mean framework electronegativity of the zeolites as was shown by 1 Hmagic-angle spinning (MAS) NMR and FTIR spectroscopy. [118] At the same time, the zeolite framework will have ac onfinement effect to the electronic structure and coordination state of surface atom sites of noble metal clusters. [35] Therefore,b ifunctional catalysts could show advantageous synergistic effects in reducing the energy compared with the independent functions of acid sites and noble metal sites (Figure 6a).…”

Section: Synergy Effect For Multifunctional Design:f Rom Dual Sites Tmentioning

confidence: 99%

Confinement Effects in Zeolite‐Confined Noble Metals

2019

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Confinement of noble nanometals in a zeolite matrix is a promising way to special types of catalysts that show significant advantages in size control, site adjustment, and nano‐architecture design. The beauty of zeolite‐confined noble metals lies in their unique confinement effects on a molecular scale, and thus enables spatially confined catalysis akin to enzyme catalysis. In this Minireview, the confined synthesis strategies of zeolite‐confined noble metals will be briefly discussed, showing the processes, advantages, features, and mechanisms. The confined catalysis carried on zeolite‐confined noble metals will be summarized, and great emphasis will be paid to the confinement effects involving size, encapsulation, recognition, and synergy. Great progress of atomic sites in the size effect, supercage stabilization in the encapsulation effect, site adsorption in the recognition effect, and cascade reaction in the synergy effect are highlighted. This Minireview is concluded with challenges and opportunities in terms of the synthesis of zeolite‐confined noble metals and their applications to design multifunctional catalysts with high catalytic activity, selectivity, and stability.

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Effect of Noble Metals on the Strength of Brønsted Acid Sites in Bifunctional Zeolites

Cited by 25 publications

References 30 publications

Generation and Properties of Brønsted Acid Sites in Bifunctional Rh-, Ir-, Pd-, and Pt-Containing Zeolites Y Investigated by Solid-State NMR Spectroscopy

Generation and Properties of Brønsted Acid Sites in Bifunctional Rh-, Ir-, Pd-, and Pt-Containing Zeolites Y Investigated by Solid-State NMR Spectroscopy

Construction of Bifunctional Co/H‐ZSM‐5 Catalysts for the Hydrodeoxygenation of Stearic Acid to Diesel‐Range Alkanes

Confinement Effects in Zeolite‐Confined Noble Metals

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