General Strategy toward Hydrophilic Single Atom Catalysts for Efficient Selective Hydrogenation

Abstract

Well dispersible and stable single atom catalysts (SACs) with hydrophilic features are highly desirable for selective hydrogenation reactions in hydrophilic solvents towards important chemicals and pharmaceutical intermediates. A general strategy is reported for the fabrication of hydrophilic SACs by cation-exchange approach. The cation-exchange between metal ions (M = Ni, Fe, Co, Cu) and Na + ions introduced in the skeleton of metal oxide (TiO 2 or ZrO 2 ) nanoshells plays the key role in forming M 1 /TiO 2 and M 1 /ZrO 2 SACs, which efficiently prevents the aggregation of the exchanged metal ions. The as-obtained SACs are highly dispersible and stable in hydrophilic solvents including alcohol and water, which greatly facilitates the catalysis reaction in alcohol. The Ni 1 /TiO 2 SACs have been successfully utilized as catalysts for the selective C=C hydrogenation of cinnamaldehyde to produce phenylpropanal with 98% conversion, over 90% selectivity, good recyclability, and a turnover frequency (TOF) of 102 h −1 , overwhelming most reported catalysts including noble metal catalysts.

Emerging materials for electrochemical CO2reduction: progress and optimization strategies of carbon-based single-atom catalysts

“…Ion-exchange strategies can successfully introduce metal elements into frameworks or polymers such as organic metal backbones (MOFs). 106–108 Metal ion precursors with framework or polymer as carriers are adsorbed or ion-exchanged with cations (Zn 2+ , Na + , K + , H + ) by impregnation and finally treated by high-temperature calcination to form SACs with unique coordination structures. 109,110 MOFs have advantages that cannot be compared to other polymers, such as well-defined metal nodes, well-developed pore structures, and tunable organic ligands, and therefore, play a non-negligible role in CO 2 RR.…”

The synthesis of single-atom catalysts for heterogeneous catalysis

“…Moreover, the combination of experiment and theory revealed that the benzene oxidation on the S, N dual-coordinated Cu SACs had an inferior activation energy barrier. Wu's group 73 also fabricated M SACs (M = Ni, Fe, Co, Cu) on the metal oxide (TiO 2 or ZrO 2 ) supports by the cation-exchange between metal ions and Na + ions introduced in the skeleton of nanoshells under mild conditions (Fig. 5f).…”

Elucidation of single atom catalysts for energy and sustainable chemical production: Synthesis, characterization and frontier science

“…• Carbon/Graphene [74,101,143,214,230,236,353] • Carbon nitride [101,[365][366][367] • CeO 2 [368] • Hydroxyapatite [369,370] • Ball milling [353] • Coordination site strategy [370] • Co-precipitation [368] • Electrochemical method [230] • CO 2 methanation [220] • CO 2 RR [74,101] • Cross-coupling [367] • Dry reforming [164,368,369,371] (continued on next page) reused more than six times TPD cycles with constant selectivity of butadiene to butene (~25%) as shown in Fig. 19(a) [257] In order to demonstrate the hydrogenation capability of the Pt-Cu SAC in different stressful conditions (with impurities), the authors tested the SAC in the presence of excess propylene and found that the propylene has no significant effect on the activity and selectivity of hydrogenation • TiO 2 [370] • Y 2 O 3 [220] • ZnO [361] • ZrO 2 [86] • Facile method [371] • Ion-exchange method [86] • Low temperature-induced strategy [220] • Mass-selected soft-landing [236] • Microwave-assisted method [367] • Pyrolysis-assisted method [101] • SEA [164,369] • Sol-gel method…”

“…Their applications have been extended to non-oxidative CH 4 conversion using Fe 1 /SiO 2 [61]; HER with Co 1 on N-doped graphene [59], graphitic carbon nitride [62], N-doped graphyne [63], and Ni 1 on α-SiX (X = N, P, As, Sb, Bi) [64]; ethylene benzene oxidation using Co 1 /CN [65]; electrocatalytic ethanol oxidation using a hybrid material of Pd nanoparticles and Ni 1 single atom [66]; oxidative desulphurization with Cr 1 /multiwalled carbon nanotubes [67]; CO oxidation using Ni 1 over FeO x [68], phosphorene nanosheet [69], Sc 1 and Fe 1 on honeycomb borophene/Al (111) heterostructure [70], and Ti 1 on MXene [71]; acetylene hydration using Zn 1 with S/N co-doped defective graphene supports [72]; the electrochemical CO 2 RR with Ni 1 on N-doped porous carbon [73], graphene nanosheets [74], carbon black [75] and other ZnN 4 -based SACs [76]; CO 2 hydrogenation with various non-noble metal-based SAC (Mn 1 , Fe 1 , Co 1 , Mo 1 ) supported on graphitic carbon nitride [77]; ORR has been carried out with Co 1 on defective N-doped carbon graphene [78], Fe 1 supported on N-doped porous carbon [79], hierarchically structured porous carbon [80], cellulose-derived nanocarbon [81] and phosphomolybdic acid cluster [82]; and the Oxygen Evolution Reaction (OER) has been carried out on Fe, Co and Ni-based SACs on N-doped graphene [83], N-doped biomass-derived porous carbon [84] as well as γ-graphyne monolayer [85]. Lastly, the production of H 2 O 2 was found to be effective via hydrogenation routes Ni-based SACs [86]. In fact, based on the comparative studies conducted in some of these works, the non-noble metal-based SACs were found to be more attractive and preferable.…”