Synthesis of High Metal Loading Single Atom Catalysts and Exploration of the Active Center Structure

Abstract

Single‐atom catalysts (SACs) have been rising recently as a new frontier in the catalysis field. Due to maximum atom utilization efficiency and tunable electronic structures, SACs exhibit highly distinctive catalytic performance from bulk counterparts. SACs with high metal loading will facilitate practical applications. To that end, this Review focuses on recent strategies to maximize metal loading. An appropriate substrate, mainly heteroatom‐doped carbon materials, is the key to avoiding aggregation or sintering during synthetic procedures. The coordination site construction and spatial confinement strategies are adopted to prepare SACs with high metal loading. Advanced characterization techniques with atomic resolution are indispensable for identification of the exact structure of SACs. This is true, especially for the applications and challenges in developing in situ/operando characterization techniques at the atomic level, which are discussed in this Review. Moreover, it is fundamentally necessary to investigate the active center structure, which facilitates any design of efficient SACs that can maximize single‐atom catalytic activity. Furthermore, this Review highlights challenges and prospects for development of SACs.

Single‐Atom Catalysts (SACs) for Photocatalytic CO2 Reduction with H2O: Activity, Product Selectivity, Stability, and Surface Chemistry

“…This characterization technique is used to elucidate the atomic level dispersion of metals and catalyst active sites. [119] Isolated metal atoms on a support of light atoms are readily identifiable in ABF-STEM images; light elements, such as O or Li, appear as dark spots, whereas heavy elements, such as transition metals, appear as light spots. [120] Xu et al prepared a Cu-C 3 N 4 SAC and analyzed its morphology by HR-TEM.…”

Conversion of biomass-derived feedstocks into value-added chemicals over single-atom catalysts

“…117 The use of heteroatom-doped (such as N and S) carbon support is another effective approach to increase the metal loading. 118 Pyrolysis of metal complex or metal-organic framework (made by N-containing ligand) is now a well-known technique to synthesize SACs with increased metal loading for both transition metals (e.g., Fe, Co, Ni, Cu, etc.) and noble metals (e.g., Pd and Pt).…”

Metal Phosphides and Sulfides in Heterogeneous Catalysis: Electronic and Geometric Effects

“…16 This can help avoid agglomeration in post-treatment processes but is generally restricted to low metal loading (<1 wt %) and may result in an uneven distribution of the active metal sites which makes it difficult to reveal the catalytic mechanism. 17 Atoms like nitrogen and sulfur contain lone pairs of electrons which can coordinate metal atoms and serve as coordination sites to stabilize and isolate more metal atoms. 18 A spatial confinement strategy using porous materials like metal−organic frameworks is another promising approach to synthesize high-metalloading site-isolated catalysts.…”

“…Therefore, wet chemical techniques are often used to fix isolated metal atoms on the support surface since metal precursors already contain the metal dispersed on an atomic level. , A few studies have anchored metal atoms to defect sites of a support surface , or ion-exchanged metals supported on zeolites . This can help avoid agglomeration in post-treatment processes but is generally restricted to low metal loading (<1 wt %) and may result in an uneven distribution of the active metal sites which makes it difficult to reveal the catalytic mechanism . Atoms like nitrogen and sulfur contain lone pairs of electrons which can coordinate metal atoms and serve as coordination sites to stabilize and isolate more metal atoms .…”