Design and Use of Nanostructured Single-Site Heterogeneous Catalysts for the Selective Transformation of Fine Chemicals

Santo, Vladimiro Dal; Liguori, Francesca; Pirovano, Claudio; Guidotti, Matteo

doi:10.3390/molecules15063829

Cited by 64 publications

(35 citation statements)

References 151 publications

(131 reference statements)

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“…Here we report the combined application of solid-state 13 C-cross-polarization magic angle spinning nuclear magnetic resonance ( 13 C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η O rganometallic molecule-derived heterogeneous catalysts are of increasing interest owing to their enhanced thermal stability and activity vs. their homogeneous analogs, and their atomically precise tailorable metal-ligand structures vs. other heterogeneous catalysts (1,2). Furthermore, it is becoming increasingly evident that the inorganic support in many systems is noninnocent and can function as both a ligand and an activator, with the chemically important but poorly understood nature of the catalyst-support interaction strongly modulating catalytic activity and selectivity (3,4).…”

mentioning

confidence: 99%

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Williams

Guo

Motta

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Structural characterization of the catalytically significant sites on solid catalyst surfaces is frequently tenuous because their fraction, among all sites, typically is quite low. Here we report the combined application of solid-state 13 C-cross-polarization magic angle spinning nuclear magnetic resonance ( 13 C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η 5 O rganometallic molecule-derived heterogeneous catalysts are of increasing interest owing to their enhanced thermal stability and activity vs. their homogeneous analogs, and their atomically precise tailorable metal-ligand structures vs. other heterogeneous catalysts (1, 2). Furthermore, it is becoming increasingly evident that the inorganic support in many systems is noninnocent and can function as both a ligand and an activator, with the chemically important but poorly understood nature of the catalyst-support interaction strongly modulating catalytic activity and selectivity (3, 4). When adsorbed on Lewis acidic, dehydroxylated alumina surfaces, group 4 complexes such as Cp 2 ZrR 2 (Cp = η 5 -C 5 H 5 ; A, R = H; B, R = CH 3 ) and Cp*Zr (CH 3 ) 3 [C, Cp* = η 5 -C 5 (CH 3 ) 5 ] were argued on the basis of highresolution solid-state NMR spectroscopy to transfer an alkyl anion to unsaturated, Lewis acidic surface sites as in Fig. 1 (complexes B, C → qualitative model D) (5, 6). The resulting catalysts are extremely active for olefin hydrogenation and polymerization, and analogous ion-paired species form the basis for large-scale industrial polymerization processes (7,8). However, kinetic poisoning experiments in which the catalytic sites are titrated in situ with H 2 O or t BuCH 2 OH indicate that ≤5% of D-type sites are catalytically significant, likely reflecting, among other factors, the established heterogeneity of alumina surfaces (5, 6, 9), hence rendering active site structural and chemical descriptions necessarily imprecise. In contrast to these results, chemisorption of such organozirconium precursors on SiO 2 , Al 2 O 3 , and SiO 2 -Al 2 O 3 surfaces having appreciable coverage by weakly acidic OH groups predominantly yields covalently bound, poorly electrophilic Etype species via Zr-CH 3 protonolysis with CH 4 evolution (5, 6, 10, 11). Although the E-type sites may be characterized in some detail by high-resolution solid-state NMR and extended X-ray adsorption fine structure spectroscopy (EXAFS), they display minimal catalytic turnover in the absence of added, complicating activators [e.g., methylalumoxane or B(C 6 F 5 ) 3 ], and the fraction of catalytically significant sites is unknown (12, 13). In such situations, it is experimentally impossible to unambiguously distinguish catalytically significant sites from inactive "spectator" sites, hence to fully understand the catalytic chemistry.-In marked contrast to the above results, chemisorption of these same organozirconium molecules on highly Brønsted "super...

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mentioning

confidence: 99%

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Williams

Guo

Motta

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…that occupy substitutional sites in well-defined, three-dimensionally extended, open-structure silicates of the zeolite type. The well-known and most widely used are the 4-or 5-coordinated Ti(IV) ions accommodated within the crystalline phase of silica, silicalite (9)(10)(11)(12)(13)(14).…”

mentioning

confidence: 99%

On the dynamical nature of the active center in a single-site photocatalyst visualized by 4D ultrafast electron microscopy

Yoo

Thomas

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Understanding the dynamical nature of the catalytic active site embedded in complex systems at the atomic level is critical to developing efficient photocatalytic materials. Here, we report, using 4D ultrafast electron microscopy, the spatiotemporal behaviors of titanium and oxygen in a titanosilicate catalytic material. The observed changes in Bragg diffraction intensity with time at the specific lattice planes, and with a tilted geometry, provide the relaxation pathway: the Ti 4+ =O 2− double bond transformation to a Ti 3+ −O 1− single bond via the individual atomic displacements of the titanium and the apical oxygen. The dilation of the double bond is up to 0.8 Å and occurs on the femtosecond time scale. These findings suggest the direct catalytic involvement of the Ti 3+ −O 1− local structure, the significance of nonthermal processes at the reactive site, and the efficient photo-induced electron transfer that plays a pivotal role in many photocatalytic reactions.ultrafast electron microscopy | single-site photocatalysis | titanium based photocatalyst | ulatrafast phenomena | time-resolved microscopy S ingle-site catalysts of both the thermally and photoactivated kind now occupy a prominent place in industrial-and laboratory-scale heterogeneous catalysis (1-8). Among the most versatile of these are the ones consisting of coordinatively unsaturated transition metal ions (Ti, Cr, Fe, Mn. . .) that occupy substitutional sites in well-defined, three-dimensionally extended, open-structure silicates of the zeolite type. The well-known and most widely used are the 4-or 5-coordinated Ti(IV) ions accommodated within the crystalline phase of silica, silicalite (9-14).Titanosilicates, especially, are used extensively both industrially and in the laboratory for a wide range of chemo-, regio-, and shapeselective oxidations of organic compounds (15-18). These single-site heterogeneous photocatalysts are quite distinct from those typified by TiO 2 , SrTiO 3 , and other titaniferous photocatalysts where the Ti(IV) ions are in 6-coordination; and where, in interpreting the processes involved in harnessing solar radiation, electronic band structure considerations hold sway in preference to the localized states (see, e.g., refs. 19, 20). It has been demonstrated (16-18, 21, 22) that single-site, coordinatively unsaturated Ti(IV)-centered photocatalysts are especially useful in the aerial oxidation of environmental pollutants in the photodegradation of NO (to N 2 and O 2 ), of H 2 O (to H 2 and O 2 ), and in the photocatalytic reduction of CO 2 to yield methanol. There is an exigent need to explore the precise nature of the electronic, temporal, and spatial changes accompanying the initial act of photoabsorption that sets in train the ensuing elementary chemical processes that are of vital environmental significance in, for example, the utilization of anthropogenic CO 2 as a chemical feedstock (23).Here, we report the use of 4D ultrafast electron microscopy (UEM) (24-26) to trace the spatiotemporal behavior of the Ti(IV) and O ...

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“…Another example is the Ti(IV)-centred active site in the epoxidation of alkenes with alkylhydroperoxides--see Figs. 3 to 6 in Thomas et al [23] and later--see also the numerous examples highlighted by Guidotti and coworkers [24].…”

Section: The Oxyfunctionalization Of N-hexane To Adipicmentioning

confidence: 94%

Can a Single Atom Serve as the Active Site in Some Heterogeneous Catalysts?

2011

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We examine a number of distinct situations relating to heterogeneous catalysts where either a single atom (or ion), or a very small cluster of atoms functions as the locus of chemical turnover in various distinct kinds of conversion. There is little doubt that individual ions at certain crystallographic sites in nanoporous solids can indeed act as single-site catalysts. The situation concerning nanoclusters of pure metal (or bimetallic entities) is rather more ambiguous. What was hitherto thought to be an effective catalyst made up of a small cluster of Pt supported on c-Al 2 O 3 (for hydrogenation) now seems to be a single atom of Pt attached to a 5-coordinated Al III ion. And in the case of Au or Pt on other supports, there is evidence that a single Pt atom, positively charged, but surrounded by alkali-metal ions, is a powerful catalyst for the water-gas shift (CO ? H 2 O ? H 2 ? CO 2 ) reaction. We also report interesting results concerning the mobility of CeO 2 support material.

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Design and Use of Nanostructured Single-Site Heterogeneous Catalysts for the Selective Transformation of Fine Chemicals

Cited by 64 publications

References 151 publications

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

On the dynamical nature of the active center in a single-site photocatalyst visualized by 4D ultrafast electron microscopy

Can a Single Atom Serve as the Active Site in Some Heterogeneous Catalysts?

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Design and Use of Nanostructured Single-Site Heterogeneous Catalysts for the Selective Transformation of Fine Chemicals

Cited by 64 publications

References 151 publications

Surface structural-chemical characterization of a single-site d 0 heterogeneous arene hydrogenation catalyst having 100% active sites

Surface structural-chemical characterization of a single-site d 0 heterogeneous arene hydrogenation catalyst having 100% active sites

On the dynamical nature of the active center in a single-site photocatalyst visualized by 4D ultrafast electron microscopy

Can a Single Atom Serve as the Active Site in Some Heterogeneous Catalysts?

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Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites

Surface structural-chemical characterization of a single-site d ⁰ heterogeneous arene hydrogenation catalyst having 100% active sites