Bridging Zirconia Nodes within a Metal–Organic Framework via Catalytic Ni-Hydroxo Clusters to Form Heterobimetallic Nanowires

Abstract

Metal-organic frameworks (MOFs), with their well-ordered pore networks and tunable surface chemistries, offer a versatile platform for preparing well-defined nanostructures wherein functionality such as catalysis can be incorporated. Notably, atomic layer deposition (ALD) in MOFs has recently emerged as a versatile approach to functionalize MOF surfaces with a wide variety of catalytic metal-oxo species. Understanding the structure of newly deposited species and how they are tethered within the MOF is critical to understanding how these components couple to govern the active material properties. By combining local and long-range structure probes, including X-ray absorption spectroscopy, pair distribution function analysis, and difference envelope density analysis, with electron microscopy imaging and computational modeling, we resolve the precise atomic structure of metal-oxo species deposited in the MOF NU-1000 through ALD. These analyses demonstrate that deposition of NiOH clusters occurs selectively within the smallest pores of NU-1000, between the zirconia nodes, serving to connect these nodes along the c-direction to yield heterobimetallic metal-oxo nanowires. This bridging motif perturbs the NU-1000 framework structure, drawing the zirconia nodes closer together, and also underlies the sintering resistance of these clusters during the hydrogenation of light olefins.

Towards Generalized Noise-Level Dependent Crystallographic Symmetry Classifications of More or Less Periodic Crystal Patterns

“…One of the STEM images that the author of this paper was given has recently been published in ref. [95]. The faintly visible weak extra spots in the discrete Fourier transform of that image, which cannot be indexed on the basis of the alleged hexagonal lattice [86], have neither been mentioned nor discussed there [95].…”

“…The fact that these channels have been depicted to be empty in the form of cartoons in refs. [88][89][90][91]95] seems to be a direct consequence of this particular step in the original single crystals X-ray crystallography structure determination of this MOF [86].…”

“…This author's crystallographic image processing [19,20] analysis also showed that there is evidence for positionally ordered material in the meso-scopic channels of this MOF, which are depicted as empty in the corresponding structure cartoons [88][89][90][91]95]. To make matters worse, virtually everybody else seems to assume that the meso-scopic channels are indeed completely empty and there have been numerous attempts to incorporate small molecules (including rotaxanes [89], catenanes [90], and fullerene derivates [91]) into these channels.…”

“…The crystallographic analysis of a few low electron dose STEM images, see ref. [95] or [94b] for one of these images, of that structure (as mentioned briefly in appendix C3) proved to be crucial to this author's arrival at this conclusion on that structure's validity [94a].…”

Molybdenum (VI)‐functionalized UiO‐66 provides an efficient heterogeneous nanocatalyst in oxidation reactions

“…[1][2][3][4][5][6][7][8][9] Due to their high effective surface area and tuneability together with thermal and chemical stability, [10,11] they are well suited for a broad range of applications including ion-exchange, [12] nonlinear optics, [13][14][15] sensors, [16] gas separation or storage [17][18][19][20][21][22][23] and as support platform for heterogenization of homogeneous catalysts. [24][25][26][27][28] Approximately nine out of ten industrial chemical processes use heterogeneous catalysts, prompting an ongoing interest in the synthesis of new supported catalysts with a potential for direct impact on the global economy. [29] In recent years the catalytic activity of early transition metal complexes, especially molybdenum complexes (oxomolybdenum species) attracted intense attention due to their high catalytic activity and selectivity.…”