Controlled synthesis of carbon-supported Co catalysts from single-sites to nanoparticles: characterization of the structural transformation and investigation of their oxidation catalysis

Abstract

Realizing accurate control of catalytically active centers on solid surfaces is one of the most essential goals in the development of functionalized heterogeneous catalysts. Controlled synthesis of carbon-supported Co catalysts from single-site to nanoparticles can be successfully achieved by the structural transformation of the deposited Co(salen) complex precursor under heat treatment. The obtained structures were characterized using techniques such as XRD, in situ XAFS, and TEM. The first decomposition of the Co(salen) complex is initiated by the dissociation of Co-O-C bonds at around 250 °C, which produces isolated single-atom Co species while retaining the Co-N-C bonds even up to 400 °C. When the heat treatment temperature exceeds 450 °C, the second decomposition of the Co-N-C bonds occurs to form Co oxide nanoclusters followed by the growth of Co NPs upon further increase of the heat treatment temperature. The single-site catalyst is highly dispersed and electronically deficient owing to the interaction with the carbon support, and shows activity and selectivity for the oxidation of ethylbenzene, as compared to the inherent Co(salen) complex and nanoparticle catalysts.

Controlled Pyrolysis of Ni‐MOF‐74 as a Promising Precursor for the Creation of Highly Active Ni Nanocatalysts in Size‐Selective Hydrogenation

“…In our previouswork, the Co species prepared from aC o(salen) complex supported onto AC also yielded electron-deficient Co species after heatt reatment at 400 8Ci na n inert gas atmosphere,w hich suggests that metal species supported on carbon materials tend to becomee lectronically deficient. [54][55][56] Considering the results of XPS in both previous work and this work, the contact area between Ni speciesa nd carbonaceous species in Ni-MOF-74-300 is larger than that in Ni/AC-300. The obtained Ni-MOF-74-300 likely has ac ore-shelllike structure that consists of aN iNPc ore and ac arbon/Ni-MOF-74 composite shell, which can be described asN iNPs@carbon/Ni-MOF-74 (Scheme 1).…”

“…Based on these results, the Ni species in Ni‐MOF‐74‐300 are electronically more deficient compared to those in Ni/AC‐300 due to the stronger interaction between Ni species and carbonaceous species derived from Ni‐MOF‐74. In our previous work, the Co species prepared from a Co(salen) complex supported onto AC also yielded electron‐deficient Co species after heat treatment at 400 °C in an inert gas atmosphere, which suggests that metal species supported on carbon materials tend to become electronically deficient . Considering the results of XPS in both previous work and this work, the contact area between Ni species and carbonaceous species in Ni‐MOF‐74‐300 is larger than that in Ni/AC‐300.…”

Scale‐Up Biomass Pathway to Cobalt Single‐Site Catalysts Anchored on N‐Doped Porous Carbon Nanobelt with Ultrahigh Surface Area

“…Searching for efficient catalysts has therefore become the main task. Recently, porous MNC (MFe, Co, and Ni) materials have emerged as superior heterogeneous catalysts mainly for their fascinating properties: i) good stability of graphitic carbon support against harsh catalytic conditions, ii) enriched active metal centers stabilized by heteroatom nitrogen, and iii) favorable mass adsorption and transportation facilitated by controllable porous structure with high surface area . Despite considerable achievements, the efficiency of the reported MNC catalysts is still unsatisfactory and the reactions generally require elevated temperature at 80–140 °C.…”

Specific Enhancement of Activity of Carbon-supported Single-site Co Catalyst in the Microwave-assisted Solvent-free Aerobic Oxidation

“…17 The Co(salen) complex (50 mg) was dissolved in acetone and activated carbon (Shirasagi, 450 mg) was added to the solution. After sonication and stirring, the solvent was removed under vacuum with a rotary evaporator.…”