Highly Active, Ultra-Low Loading Single-Atom Iron Catalysts for Catalytic Transfer Hydrogenation

Abstract

Highly effective and selective noble metal-free catalysts attract significant attention. Here, a single-atom iron catalyst is fabricated by saturated adsorption of trace iron onto zeolitic imidazolate framework-8 (ZIF-8) followed by pyrolysis. Its performance toward catalytic transfer hydrogenation of furfural is comparable to state-of-the-art catalysts and up to four orders higher than other Fe catalysts. Isotopic labeling experiments demonstrate an intermolecular hydride transfer mechanism. First principles simulations, spectroscopic calculations and experiments, and kinetic correlations reveal that the synthesis creates pyrrolic Fe(I)-plN3 as the active center whose flexibility manifested by being pulled out of the plane, enabled by defects, is crucial for collocating the reagents and allowing the chemistry to proceed. The catalyst catalyzes chemoselectively several substrates and possesses a unique trait whereby the chemistry is hindered for more acidic substrates than the hydrogen donors. This work paves the way toward noble-metal free single-atom catalysts for important chemical reactions.

Single‐atom materials: The application in energy conversion

“…Recently, the isolate Pt or Au (i.e., single‐atom Pt or Au) systems attract much more attention, such as Pt/TiO 2 , Pt/CeO 2 , Au/FeO x , Au/La 2 O 3 , and so on, performing very well in the reaction. Based on abundant research, the relationship between activity and structure is further clarified both in width and depth, such as the work by Hensen et al [ 45 ] and Heydan et al [ 46 ] The metallic center and the support together contribute to the appropriate electronic and geometric structure, O vacancy on the support (Figure 2B), [ 42 ] for instance. What's more, it is the selectivity oxidation or reduction that can fully utilize the advantages of the SAMs.…”

Low-coordination M–N3 active sites with high accessibility and efficiency for electrocatalytic O2 and CO2 reduction

“…The majority of prior research on M-N 3 SACs utilized ZIFs as a carbon and nitrogen support for anchoring metal atoms using various methods, [71][72][73][74][75][76][77][78] as shown in Table 1. The in situ hydrolysis can form a stable M-N bond to obtain SACs by evaporating the metal in MOFs (or other porous carriers) at high temperature.…”

Tuning Active Site Flexibility by Defect Engineering of Graphene Ribbon Edge‐hosted Fe−N3 Sites

“…We consider the FeÀ N 3 site rather than the FeÀ N 4 site since the latter cannot bind the two reactants simultaneously, leading to poor activity for CTH. [12] Following on from prior work, [15] we embedded the FeÀ N 3 site in the edge of the zigzag graphene ribbon (ZGR) as an example of edge-hosted FeÀ N 3 sites (Figure 1a). Experimental studies have demonstrated that such edge-hosted, unsaturated MÀ N 3 sites can preferentially form in NH 3 atmosphere during pyrolysis.…”

“…[11] Compared to NiÀ NÀ C catalysts, a FeÀ NÀ C catalyst in our recent work exhibited a higher activity (TOF = 1882 h À 1 ) for the CTH of FF using isopropanol (IPA) as an H-donor. [12] These prior studies underline that MÀ NÀ C catalysts, especially FeÀ NÀ C catalysts, are promising candidates for biomassderived molecule transformation. Nevertheless, how to optimize the catalytic activity by purposely tailoring the local environment of the MÀ N x sites remains elusive.…”

“…This is possible at the flexible site because the Fe atom is displaced out of the plane of the support and coordinates both reactants. [12] Here, we explore the implications of the flexibility of active sites for their electronic behavior and the opportu-nities it affords for catalyst design. We consider FeÀ NÀ C and construct several edge-hosted FeÀ N 3 sites of varying flexibility by introducing divacancy carbon defects around the FeÀ N 3 site; we employ X-ray absorption near-edge structure (XANES) simulations to demonstrate that these sites are structurally distinguishable.…”