CO₂ Methanation Routes on Ni, Co, and NiCo (111) and (100) Surfaces

Area of Science:

• Heterogeneous Catalysis
• Computational Chemistry
• Surface Science
• Renewable Energy
• Carbon Capture and Utilization

Background:

• CO2 methanation is a key process for reducing greenhouse gas emissions and producing valuable energy carriers like methane.
• Understanding the catalytic mechanisms on different metal surfaces is crucial for designing efficient catalysts.
• Nickel (Ni), Cobalt (Co), and their alloys (NiCo) are promising candidates for CO2 methanation catalysts.

Purpose of the Study:

• To investigate the catalytic pathways for CO2 activation and subsequent methanation on Ni, Co, and NiCo surfaces.
• To elucidate the role of different crystallographic facets, specifically (111) and (100), in the reaction mechanism.
• To determine the structure sensitivity of the catalytic process and identify rate-limiting steps.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model the adsorption and reaction of surface species.
• Calculations focused on the (111) and (100) facets of Ni, Co, and NiCo alloys.
• Binding strengths of carbon (C) and oxygen (O) atoms were analyzed to understand surface species stability.

Main Results:

• Direct CO2 dissociation to CO and O is facile on all studied surfaces, with the highest energy barriers on Ni(111).
• Methane (CH4) formation is primarily limited by CO activation and CHx hydrogenation steps.
• The (100) facets exhibit lower activation barriers compared to (111) facets, suggesting their significant contribution to overall reaction rates. NiCo(100) showed higher barriers than Ni(100) and Co(100), aligning with experimental observations.

Conclusions:

• The (100) facets of Ni, Co, and NiCo play a significant role in CO2 methanation rates.
• Catalyst design should consider the specific facet properties, as NiCo(100) presents unique challenges for CO activation.
• Further studies should account for surface coverages and potential contributions from other facets for a comprehensive understanding.