Abstract
We present several in silico insights into the MAX-phase of early transition metal silicon carbides and explore how these affect carbon dioxide hydrogenation. Periodic density functional methodology is applied to models of Ti4SiC3, V4SiC3, Nb4SiC3 and Zr4SiC3. We find that silicon and carbon terminations are unstable, with sintering occurring in vacuum and significant reconstruction taking place under an oxidising environment. In contrast, the metal terminated surfaces are highly stable and very active towards CO2 reduction. However, we predict that under reaction conditions these surfaces are likely to be oxidised. These results are compared to studies on comparable materials and we predict optimal values for hydrogen evolution and CO2 reduction.
Highlights
We present several in silico insights into the MAX-phase of early transition metal silicon carbides and explore how these affect carbon dioxide hydrogenation
The H-(Hagg)phase of over 100 ternary carbides/nitrides was rst identi ed in the 1960s.1,2. This class of material is given the annotation “MAX”-phase, an abbreviation of the general formula of these 2D materials ‘Mn+1AXn’, where M denotes an early transition metal and A/X represent an A group element and carbon/nitrogen, respectively.[3,4,5]. These initial studies found that these materials possess a novel mixture of chemical properties, including the high thermo-/electrical-conductivity of a metal and a resistance to thermo/ oxidative shocks more typical of a ceramic.[1,6,7,8,9,10]
The MAX-phases of early transition metal silicon carbides represent an interesting class of materials, owing to both their novel mix of metallic, covalent and ionic properties, as well as their structural similarities to related redox catalysts for carbon utilisation reactions
Summary
The H-(Hagg)phase of over 100 ternary carbides/nitrides was rst identi ed in the 1960s.1,2 This class of material is given the annotation “MAX”-phase, an abbreviation of the general formula of these 2D materials ‘Mn+1AXn’, where M denotes an early transition metal and A/X represent an A group element and carbon/nitrogen, respectively.[3,4,5] Importantly, these initial studies found that these materials possess a novel mixture of chemical properties, including the high thermo-/electrical-conductivity of a metal and a resistance to thermo/ oxidative shocks more typical of a ceramic.[1,6,7,8,9,10] Owing to this set of novel properties these materials are called “metallic ceramics”.11 Interestingly, this same mixture of properties is present in the closely related monocarbide materials which in recent years have received a lot of interest from the catalytic aSchool of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK. The H-(Hagg)phase of over 100 ternary carbides/nitrides was rst identi ed in the 1960s.1,2 This class of material is given the annotation “MAX”-phase, an abbreviation of the general formula of these 2D materials ‘Mn+1AXn’, where M denotes an early transition metal and A/X represent an A group element and carbon/nitrogen, respectively.[3,4,5] Importantly, these initial studies found that these materials possess a novel mixture of chemical properties, including the high thermo-/electrical-conductivity of a metal and a resistance to thermo/ oxidative shocks more typical of a ceramic.[1,6,7,8,9,10] Owing to this set of novel properties these materials are called “metallic ceramics”.11.
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