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Review
. 2018 May 22;30(10):3177-3198.
doi: 10.1021/acs.chemmater.8b01311. Epub 2018 May 7.

Engineering of Transition Metal Catalysts Confined in Zeolites

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Free PMC article
Review

Engineering of Transition Metal Catalysts Confined in Zeolites

Nikolay Kosinov et al. Chem Mater. .
Free PMC article

Abstract

Transition metal-zeolite composites are versatile catalytic materials for a wide range of industrial and lab-scale processes. Significant advances in fabrication and characterization of well-defined metal centers confined in zeolite matrixes have greatly expanded the library of available materials and, accordingly, their catalytic utility. In this review, we summarize recent developments in the field from the perspective of materials chemistry, focusing on synthesis, postsynthesis modification, (operando) spectroscopy characterization, and computational modeling of transition metal-zeolite catalysts.

Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Zeolite topologies with different pore architectures: SOD with 6-membered ring (6MR) pores of 2.8 Å; CHA (3.8 Å); MFI (∼5.5 Å); FAU (7.4 Å); UTL (∼9.5 Å); and ETR (10.1 Å).
Figure 2
Figure 2
Results of methane dehydroaromatization (MDA) tests over 5%Mo/zeolite catalysts with the same chemical composition. Benzene yields with the inset demonstrating pore openings of corresponding zeolites (a) and overall product distributions obtained during 16 h tests (b). Conditions: 700 °C, atmospheric pressure, 0.3 g of catalyst, CH4 WHSV 2.0 h–1. Adapted with permission from ref (26). Copyright 2016 American Chemical Society.
Figure 3
Figure 3
Substrate conversions (★) and product selectivities (colored columns and numerical values) for the hydrogenation of variously substituted nitroarenes and chlorobenzaldehyde on various catalysts. Adapted with permission from ref (27). Copyright 2017 Wiley.
Figure 4
Figure 4
Structure and location of [Cu3(μ-O)3]2+ cluster in mordenite predicted by density functional theory (DFT) modeling. The zeolite model contained paired (type I) and isolated (type II) Al atoms located at the pore mouth of the side pocket. The cluster is stabilized by two anionic centers due to AlISP lattice sites at the entrance of the MOR side pocket (b) so that the extraframework oxygens responsible for the initial C–H activation are pointing toward the main channel of MOR (a). The charge due to the remaining AlIISP is compensated by acidic protons resulting in BAS formation. Adapted with permission from ref (36). Copyright 2015 Macmillan Publishers Limited.
Figure 5
Figure 5
Transmission electron microscopy (TEM) images of Pt@nanoshell reduced at 500 °C for 2 h (a) and 750 °C for 10 h (b) under H2 and Pt particle size distributions of the two materials (c). TEM images of a commercial Pt/SiO2 catalyst reduced at 500 °C (d) and 750 °C (e) under the same conditions as those for Pt@hollow and Pt particle size distributions (f) of the two materials in (d) and (e). The particle size distributions have been modeled using a Normal law from the measurements on 400 particles. Adapted with permission from ref (39). Copyright 2015 Elsevier.
Figure 6
Figure 6
Number of indexed publications (average from Scopus and Web of Science), found as of November, 2017, searching for a term: “element name AND zeolite AND catalyst” in title, abstract, and keywords. For hydrogen, a term “proton” was used.
Figure 7
Figure 7
Possible zeolite–metal composite configurations.
Figure 8
Figure 8
(A) Illustration of the preparation of Pt@MCM-22. During the swelling process of layered MWW zeolitic precursors, a solution containing sub-nanometric Pt species is added. MWW layers are expanded by the surfactant (hexadecyltrimethylammonium, CTMA+OH−), and sub-nanometric Pt species are also incorporated into the internal channels between individual MWW layers. Removing the organic agents will lead to the formation of 3D Pt@MCM-22, in which sub-nanometric Pt species are confined in the external cups on the surface or encapsulated in the supercages of MCM-22. (B) HAADF-STEM images of Pt@MCM-22. Scale bars, 20 nm (left) and 5 nm (right). (C) HAADF-HRSTEM image of Pt@MCM-22, where two zoom-ins are shown in the square regions (marked in green (#1) and yellow (#2)). In these two areas, several single atoms have been highlighted. Scale bar, 2 nm. Adapted with permission from ref (101). Copyright 2017 Macmillan Publishers Limited.
Figure 9
Figure 9
Some possible configurations of Al distribution within MFI framework.
Figure 10
Figure 10
(A) Superimposed EFTEM mapping of annealed ZSM-5@silicalite-1 crystals prepared with a 10 nm silicalite-1 shell. The elements are color coded: Al (red) and Si (green). (B) HRTEM image of a core–shell crystal reveals the presence of lattice fringes that extend from the exterior to the interior of the particle without any discontinuity. The orientation of fringes (1.1 nm periodicity) is highlighted by the white lines. Gas-phase turnover frequency (TOF) in a flow reactor of (C) 1,3,5-triisopropylbenzene and (D) acetic acid over H-ZSM-5@silicalite-1 prepared with a 10 nm silicalite-1 shell, as well as the H-ZSM-5 core. The reactions were performed at 1 atm after pretreating the catalyst in He flow at 300 °C for 1 h to remove physisorbed water from the catalyst surface. Cracking of triisopropylbenzene (C) was done at 400 °C and ketonization of acetic acid (D) was done at 320 °C. Adapted with permission from ref (126). Copyright 2015 American Chemical Society.
Figure 11
Figure 11
SEM (a) and cross-sectional TEM (b) images of the of the unilamellar MFI nanosheet with unit cell thickness along the MFI b-axis of b = 1.9738 nm; (c) structure of tetrapropylammonium cation typically used for the synthesis of MFI zeolites and mesoporogen C22-6-6 applied by Ryoo and co-workers. Adapted with permission from ref (140). Copyright 2009 Macmillan Publishers Limited.
Figure 12
Figure 12
Aberration-corrected HAADF-STEM characterization of [Rh(C2H4)2]+ complexes on zeolite HY, before (left) and after (right) treatment in H2/He flow at 373 °C for 4 min. (A) HAADF-STEM images. (B) Magnified views of corresponding areas in (A), with the intensity surface plots shown in (C) and the three-dimensional intensity surface plots shown in (D). Bright features encircled on the left panel are examples of individual Rh atoms and on the right panel of both single Rh atoms (red circles) or Rh dimers (blue circles). Adapted with permission from ref (187). Copyright 2016 American Chemical Society.
Figure 13
Figure 13
Optical microscopy investigation of furfuryl alcohol conversion inside a hierarchical mordenite crystal. Scale bars: 3 μm. (A) NASCA reactivity map obtained for 50 × 50 × 800 nm3 voxels (xyz) for the duration of 500 s. False color scale shows the observed relative reaction rate; white rectangle indicates area enlarged in panel (B). (B) Magnification showing the scatter plot with locations of individual reaction events; yellow lines indicate distances taken for region width estimation. (C) Corresponding bright-field optical transmission image. Adapted with permission from ref (196). Copyright 2015 Wiley.
Figure 14
Figure 14
(a) Reconstructed needle of fresh Cu-SSZ-13 with Cu (red) and Al (blue) ions shown with Cu clusters overlaid in black. Bonding box dimensions are 63 × 67 × 115 nm3. (b) Radial distribution functions (RDFs) in fresh Cu-SSZ-13 for Al and Cu centers. Al–Cu affinity is indicated, which would be expected due to Cu exchanging onto paired Al sites, as indicated in the schematic. (c) Nearest neighbor distribution for fresh Cu-SSZ-13 for Cu showing a significant deviation from a random distribution and indicating the presence of Cu clusters. (d) RDFs in aged Cu-SSZ-13 for Al and Cu centers. Strong affinities are indicated between all species, pointing to the migration and aggregation of Cu with aging, and a Cu aluminate species is shown, though it was not quantitatively identified. (e) Normalized compositional histogram across 1.4% Cu isoconcentration surfaces in aged Cu-SSZ-13, with potential CuO species shown. (f) Reconstructed needle of aged Cu-SSZ-13 with 1.4% Cu isoconcentration surfaces shown. Bonding box dimensions are 49 × 52 × 90 nm3. Reproduced with permission from ref (203). Copyright 2017 Macmillan Publishers Limited.
Figure 15
Figure 15
(a) In situ XANES of Cu-CHA catalysts with different compositions (different samples are denoted with (Cu/Al; Si/Al) labels) during dehydration under He flow from 25 to 400 °C, heating rate 5 °C min–1. (b) Temperature-dependent abundance of pure Cu species in each of the catalysts as derived from multivariate curve reconstruction based on alternating least-squares (MCR-ALS) analysis of global temperature-dependent XANES data set collected for six Cu-CHA samples. (c) Proposed assignment of the five pure components to specific Cu species/sites formed in the Cu-CHA catalyst as a function of composition and activation temperature, using the same color code as in part (b). Blue (PC1): mobile Cu(II)-aquo-complexes [Cu(II)(H2O)n]2+/[Cu(II)(H2O)n−1(OH)]+ with n = 6; green (PC5): Cu(II) dehydration intermediate, possibly represented by mobile [Cu(II)(H2O)n]2+/[Cu(II)(H2O)n−1(OH)]+complexes with n = 4; black (PC3): 1Al Z[Cu(II)OH] sites in their oxidized form; red (PC2): 1Al ZCu(I) sites in their reduced form, resulting from self-reduction of 1Al Z[Cu(II)OH] species; orange (PC4): 2Al Z2Cu(II) sites. Atom color code: Cu: green; H: white; O: red; Si: gray; Al: yellow. Adapted with permission from ref (214). Copyright 2017 The Royal Society of Chemistry.
Figure 16
Figure 16
DNP-enhanced 119Sn spectra of hydrated (a) and dehydrated (b) natural abundance Sn-Beta zeolite. Spectra were acquired at 100 K for 18 and 21 h, respectively. 119Sn MAS NMR spectrum of natural abundant dehydrated Sn-Beta zeolite was acquired at 300 K for 246 h. Asterisks denote spinning sidebands. Adapted with permission from ref (226). Copyright 2016 American Chemical Society.
Figure 17
Figure 17
(A) Schematic representation of the reaction conditions of the partial oxidation of methane by water, involving the reduction of the dicopper site of mordenite and providing two electrons to stoichiometrically oxidize methane into methanol. Subsequent reduction of water into hydrogen returns two electrons for the rejuvenation of the mono(μ-oxo)dicopper active core. FTIR spectra of CO (B) and NO (C) adsorbed at 100 K onto CuMOR that was vacuum-activated (bottom), reacted with methane (middle), and reoxidized with water vapor (top). (D) Time-resolved in situ FTIR spectra of surface species formed during the interaction of CuMOR (pretreated in a flow of helium) with 7 bar of methane at 473 K. (E) Relative number of methoxy species versus number of Brønsted acid sites formed during the interaction of methane with CuMOR at 473 K within 5–120 min. Adapted with permission from ref (229). Copyright 2017 AAAS.
Figure 18
Figure 18
(a) Most stable bi- and trinuclear cationic Cu-oxo clusters in ZSM-5 zeolite as determined by ab initio thermodynamic analysis. Panel (b) shows a 2D projection of the lowest Gibbs free energy CuxOmHn species in ZSM-5 as a function of oxygen (ΔμO) and water (ΔμH2O) chemical potentials. Panel (c) shows a cross section of the 3D phase diagram at a fixed ΔμH2O, corresponding to 10–2 mbar H2O at 700 K. Adapted with permission from ref (239). Copyright 2016 Elsevier.

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