Selectively Adsorbed CO and O₂ on Transition-Metal-Incorporated Porphyrin

Area of Science:

• Computational Chemistry
• Materials Science
• Surface Science

Background:

• Porphyrins are versatile macrocyclic compounds.
• Transition metals (TMs) incorporated into porphyrins can alter their electronic and chemical properties.
• Understanding gas adsorption on functionalized porphyrins is crucial for applications like gas capture and catalysis.

Purpose of the Study:

• To investigate the adsorption behavior of carbon monoxide (CO) and oxygen (O2) on various transition-metal (TM)-incorporated porphyrins.
• To elucidate the factors governing the binding strength and adsorption capacity of these systems.
• To correlate adsorption properties with the electronic structure of the TM-incorporated porphyrins.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model the adsorption processes.
• Calculations focused on the interaction of CO and O2 molecules with porphyrins containing different transition metals (Sc, Ti, V, Cr, Mn, Fe, Co).
• Analysis of the highest occupied molecular orbital (HOMO) levels was performed to understand binding energies.

Main Results:

• The number of adsorbed CO molecules varied depending on the incorporated TM, with Sc-Mn porphyrins accommodating more CO than Fe-Co porphyrins.
• Only one O2 molecule adsorbed on all investigated TM-porphyrins.
• O2 exhibited stronger binding to Sc-Mn porphyrins compared to CO, while Fe-Co porphyrins showed weaker O2 binding than CO.
• Downward shifts in HOMO levels correlated with stronger binding energies for specific TM-porphyrin/gas combinations.

Conclusions:

• The adsorption capacity and binding strength of CO and O2 on TM-incorporated porphyrins are highly dependent on the specific transition metal.
• The electronic structure, particularly the HOMO level, plays a significant role in determining the interaction between the porphyrin and adsorbed gases.
• These findings provide insights into the rational design of TM-incorporated porphyrins for selective CO and O2 capture.