Chirality plays a significant role in the manufacture of pharmaceuticals and fine chemicals. The use of chemical catalysts to control stereoselectivity relies on the use of chiral catalysts with labor–intensive synthesis and purification. Natural enzymes offer inherent stereoselectivity, making them attractive catalysts for this purpose. We report here chiral biocatalytic oxidations in microemulsions driven by horseradish peroxidase coupled with a synthetic Cu2+‐polymer catalyst. This hybrid system features crosslinked layer–by–layer (LBL) films composed of polyions with Cu2+‐containing pyrene–labelled poly(2‐hydroxy‐3‐dipicolylamino) propyl methacrylate (Py−PGMADPA) to drive oxygen reduction to form hydrogen peroxide. Peroxide in turn activates horseradish peroxidase (HRP) crosslinked in LbL films on magnetic particle beads to biocatalytically oxidize styrene, ethylbenzene, and methyl phenylacetate to chiral products. R‐stereoisomers of these reactants were selectively formed with a high enantiomeric excess of ≥80 % at 90 °C. The enzyme films show high thermal stability at 90 °C in cetyltrimethylammonium bromide microemulsion. Reactions at 90 °C were essentially complete in 2 hr. This hybrid approach opens a door to new designs of biocatalytic syntheses using a separate electrocatalyst for enzyme activation.
Cu‐containing metalloenzymes are known to catalyze oxygen activation through cooperative catalysis. In the current work, we report the design of synthetic polymer Cu catalysts using pyrene‐labelled poly(2‐hydroxy‐3‐dipicolylamino) propyl methacrylate (Py‐PGMADPA) to coordinate multiple Cu sites along polymer chains. The catalysts feature a pyrene end group that can form supramolecular π‐π stacking with conductive carbon to allow efficient immobilization of catalysts to the graphite electrode. Cu‐containing Py‐PGMADPA was examined for electrocatalytic oxygen reduction. The hybrid catalyst showed an onset potential of 0.5 V (vs. RHE) at pH 7 and 0.79 V at pH 13. The kinetic study indicated that the catalyst had a 2e−reduction of oxygen mainly mediated by Cu+centers. We demonstrated the importance of cooperative catalysis among Cu sites which did not exist for other transition metal ions, like Mn2+, Fe2+, Co2+, and Ni2+. The confinement of polymer chains promotes the activity and stabilizes Cu catalysts even at an extremely low Cu loading. The rational design of bioinspired polymer catalysts offers an alternative way to prepare synthetic mimics of metalloenzymes.
more » « less- Award ID(s):
- 1705566
- NSF-PAR ID:
- 10255751
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemCatChem
- Volume:
- 12
- Issue:
- 23
- ISSN:
- 1867-3880
- Page Range / eLocation ID:
- p. 5932-5937
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Ionic liquids (ILs) have shown to be promising additives to the catalyst layer to enhance oxygen reduction reaction in polymer electrolyte fuel cells. However, fundamental understanding of their role in complex catalyst layers in practically relevant membrane electrode assembly environment is needed for rational design of highly durable and active platinum-based catalysts. Here we explore three imidazolium-derived ionic liquids, selected for their high proton conductivity and oxygen solubility, and incorporate them into high surface area carbon black support. Further, we establish a correlation between the physical properties and electrochemical performance of the ionic liquid-modified catalysts by providing direct evidence of ionic liquids role in altering hydrophilic/hydrophobic interactions within the catalyst layer interface. The resulting catalyst with optimized interface design achieved a high mass activity of 347 A g−1Ptat 0.9 V under H2/O2, power density of 0.909 W cm−2under H2/air and 1.5 bar, and had only 0.11 V potential decrease at 0.8 A cm−2after 30 k accelerated stress test cycles. This performance stems from substantial enhancement in Pt utilization, which is buried inside the mesopores and is now accessible due to ILs addition.
-
Platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) with atomically dispersed FeN 4 sites have emerged as a potential replacement for low-PGM catalysts in acidic polymer electrolyte fuel cells (PEFCs). In this work, we carefully tuned the doped Fe content in zeolitic imidazolate framework (ZIF)-8 precursors and achieved complete atomic dispersion of FeN 4 sites, the sole Fe species in the catalyst based on Mößbauer spectroscopy data. The Fe–N–C catalyst with the highest density of active sites achieved respectable ORR activity in rotating disk electrode (RDE) testing with a half-wave potential ( E 1/2 ) of 0.88 ± 0.01 V vs. the reversible hydrogen electrode (RHE) in 0.5 M H 2 SO 4 electrolyte. The activity degradation was found to be more significant when holding the potential at 0.85 V relative to standard potential cycling (0.6–1.0 V) in O 2 saturated acid electrolyte. The post-mortem electron microscopy analysis provides insights into possible catalyst degradation mechanisms associated with Fe–N coordination cleavage and carbon corrosion. High ORR activity was confirmed in fuel cell testing, which also divulged the promising performance of the catalysts at practical PEFC voltages. We conclude that the key factor behind the high ORR activity of the Fe–N–C catalyst is the optimum Fe content in the ZIF-8 precursor. While too little Fe in the precursors results in an insufficient density of FeN 4 sites, too much Fe leads to the formation of clusters and an ensuing significant loss in catalytic activity due to the loss of atomically dispersed Fe to inactive clusters or even nanoparticles. Advanced electron microscopy was used to obtain insights into the clustering of Fe atoms as a function of the doped Fe content. The Fe content in the precursor also affects other key catalyst properties such as the particle size, porosity, nitrogen-doping level, and carbon microstructure. Thanks to using model catalysts exclusively containing FeN 4 sites, it was possible to directly correlate the ORR activity with the density of FeN 4 species in the catalyst.more » « less
-
Cobalt sulfide nanomaterials are among the most active and stable catalysts for the electrocatalytic oxygen reduction reaction in pH 7 electrolyte. However, due to the complexity and dynamism of the catalytic surfaces in cobalt sulfide bulk materials, it is challenging to identify and tune the active site structure in order to achieve low overpotential oxygen reduction reactivity. In this work, we synthesize isolated Co sites supported on colloidal WS 2 nanosheets and develop a synthetic strategy to rationally control the first-shell coordination environment surrounding the adsorbed Co active sites. By studying Co–WS 2 materials with a range of Co–S coordination numbers, we are able to identify the optimal active site for pH 7 oxygen reduction catalysis, which comprises cobalt atoms bound to the WS 2 support with a Co–S coordination number of 3–4. The optimized Co–WS 2 material exhibits an oxygen reduction onset potential of 0.798 V vs. RHE, which is comparable to the most active bulk phases of cobalt sulfide in neutral electrolyte conditions.more » « less
-
Oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are three critical reactions for energy-related applications, such as water electrolyzers and metal-air batteries. Graphene-supported single-atom catalysts (SACs) have been widely explored; however, either experiments or density functional theory (DFT) computations cannot screen catalysts at high speed. Herein, based on DFT computations of 104 graphene-supported SACs (M@C3, M@C4, M@pyridine-N4, and M@pyrrole-N4), we built up machine learning (ML) models to describe the underlying pattern of easily obtainable physical properties and limiting potentials (errors = 0.013/0.005/0.020 V for ORR/OER/HER, respectively), and employed these models to predict the catalysis performance of 260 other graphene-supported SACs containing metal-NxCy active sites (M@NxCy). We recomputed the top catalysts recommended by ML towards ORR/OER/HER by DFT, which confirmed the reliability of our ML model, and identified two OER catalysts (Ir@pyridine-N3C1 and Ir@pyridine-N2C2) outperforming noble metal oxides, RuO2 and IrO2. The ML models quantitatively unveiled the significance of various descriptors and fast narrowed down the potential list of graphene-supported single-atom catalysts. This approach can be easily used to screen and design other SACs, and significantly accelerate the catalyst design for many other important reactions.more » « less
