Ionic-liquid-assisted synthesis of metal single-atom catalysts for benzene oxidation to phenol

Abstract

Ionic liquids (ILs) have the advantages of low cost, eco-friendliness, abundant heteroatoms, excellent solubility, and coordinated ability with metal ions. These features make ILs a suitable precursor for fabricating metal singleatom catalysts (SACs). Herein, we prepared various metal single atoms anchored on ultrathin N-doped nanosheets (denoted as Cu 1 /NC, Fe 1 /NC, Co 1 /NC, Ni 1 /NC, and Pd 1 /NC) by direct pyrolysis using ILs and g-C 3 N 4 nanosheets as templates. Taking benzene oxidation to phenol with H 2 O 2 as a model reaction to evaluate their catalytic performance and potential applications, Cu 1 /NC calcined at 1000°C (denoted as Cu 1 /NC-1000) exhibits the highest activity with a turnover frequency of about 200 h −1 in the first 1 h at 60°C , which is better than that of most metal SACs reported in the literature. High benzene conversion of 82% with high phenol selectivity of 96% and excellent recyclability were achieved using the Cu 1 /NC-1000 catalyst. This study provides an efficient general strategy for fabricating SACs using ILs for catalytic applications.

Understanding the Density-Dependent Activity of Cu Single-Atom Catalyst in the Benzene Hydroxylation Reaction

“…The highest H 2 O 2 utilization efficiency was about 50% on 2.4-Cu 1 /NOC, which exhibited even better activity and significantly higher phenol selectivity than commercial TS-1 (Figure c). In comparison to previously reported metal SACs, the 2.4-Cu 1 /NOC sample also demonstrated much higher mass specific activity and H 2 O 2 utilization efficiency for the benzene oxidation reaction (Figure d). − ,− After 10 circles, there was no decline in benzene conversion or phenol selectivity (Figure S26), indicating excellent stability of 2.4-Cu 1 /NOC during the reaction. AC HAADF-STEM image and XAFS spectra showed that Cu atoms remained atomically dispersed and maintained the original coordination structure after reaction (Figures S27, S28).…”

Regulating electron configuration of single Cu sites via unsaturated N,O-coordination for selective oxidation of benzene

“…SACs have been proved to be efficient for selective oxidation of benzene to phenol (SOBP), which is deemed to be the atomic economy and clean pathway for phenol production [1][2][3][12][13][14][15][16][17][18] . However, it generally needs large amount of H 2 O 2 for high benzene conversion (H 2 O 2 /Benzene molar ratio > 10) (SupplementaryTable 6) [12][13][14][15][16][17][18] , which makes it not practical in industry. Figure 4a and Supplementary Figs.…”

“…Besides the maximum atom utilization, the SAC can also present catalytic active sites with unique electron structure, thus producing excellent catalytic performance towards diverse reactions [7][8][9][10][11] . Fe, Co, Cu-based SACs have been applied in the SOBP reaction and show considerable catalytic performance [12][13][14][15][16][17][18] . However, the results show that the catalytic activity is very low at a low molar ratio of H 2 O 2 /benzene, and a 10:1 or even up to 48:1 of molar ratio of H 2 O 2 /benzene was used to obtain a high benzene conversion [12][13][14][15][16][17][18] .…”

“…Fe, Co, Cu-based SACs have been applied in the SOBP reaction and show considerable catalytic performance [12][13][14][15][16][17][18] . However, the results show that the catalytic activity is very low at a low molar ratio of H 2 O 2 /benzene, and a 10:1 or even up to 48:1 of molar ratio of H 2 O 2 /benzene was used to obtain a high benzene conversion [12][13][14][15][16][17][18] . If more than 10:1 of H 2 O 2 /benzene molar ratio is used for this reaction, the cost of H 2 O 2 is far beyond the value of the produced phenol, which leads to this SOBP process not practical application.…”

Engineering atomically dispersed single Cu–N3 catalytic sites for highly selective oxidation of benzene to phenol

“…Most of them showed good catalytic activity; however, there is still room for improvement. For example, the oxidation of benzene was catalyzed by Cu 1 N 3 /HCNS, 20 ISAS Fe/Co/Ni, 21 Cu/NC-1000, 22 Cu 1 N 2 /HCNS and Cu 1 N 3 /HCNS 23 at a relatively higher temperature (60 °C) which lowered the utilization rate of H 2 O 2 , therefore decreasing its industrial application potential. Some other SACs exhibited good catalytic performance at a lower (30 °C) or room temperature; nevertheless, either the phenol selectivity can still be increased ( e.g.…”