Nanoisozymes: The Origin behind Pristine CeO₂ as Enzyme Mimetics.

Area of Science:

• Heterogeneous catalysis
• Surface science
• Nanomaterials characterization

Background:

• Catalyst activity is governed by surface active sites and their electron density.
• Conventional surface analysis techniques lack sensitivity for the topmost catalyst layer.
• Previous studies on Cu2O suggest facet-dependent electron density influences CO2 reduction.

Purpose of the Study:

• To investigate the facet-dependent electron density of cerium oxide (CeO2) active sites.
• To correlate surface electron density with enzyme-mimicking catalytic activity.
• To clarify the role of surface area versus surface electron density in CeO2 catalysis.

Main Methods:

• Synthesis of pristine CeO2 with controlled surface facets.
• Nuclear Magnetic Resonance (NMR) spectroscopy utilizing a surface probe.
• Measurement of phosphatase- and peroxidase-like activities.

Main Results:

• Pristine CeO2 exhibited a 2506% increase in phosphatase-like and 1133% increase in peroxidase-like activity with optimized surface facets.
• NMR analysis revealed that the electron density of surface Ce is facet-dependent.
• Surface Ce electron density was identified as the primary determinant of enzyme-mimicking activity.

Conclusions:

• The electron density of surface Ce active sites is crucial for CeO2's enhanced catalytic performance.
• Facet engineering of CeO2 is a viable strategy to tune its enzyme-mimicking capabilities.
• Surface area is secondary to surface electron density for reactant activation in this system.