Abstract
Metal–organic frameworks (MOFs) have received significant attention thanks to their promising features in the storage and separation of guest molecules. MOFs without open metal sites are emerging as they are often less susceptible to poisoning compared to those with open metal sites. However, a complete understanding of the binding and gas separation mechanisms in such materials is still missing. In this work, we perform a comparative study of two classes of vanadium-based MOFs without open metal sites: MFM-300-V^text{(III)} and MFM-300-V^text{(IV)}, as well as MIL-47-V^text{(III)} and MIL-47-V^text{(IV)}. We employ first-principles van der Waals density functional theory to find the optimal binding conformations and binding energies of a series of small hydrocarbons within the pores of the aforementioned MOFs. Our study provides insight into the host–guest interactions in such MOFs without open metal sites, especially the role played by the bridging hydroxyl group (mu _2–OH). We conclude that the bridging –OH group acts as a pseudo open metal site in these MOFs.Graphic abstract
Highlights
The separation of light hydrocarbons is a key step in the petroleum refining process
Our calculations are in good agreement with the literature: Ref. [56] reported that the lattice parameters of MIL-47-V(III) [MIL47-V(IV) ] are a =16.440 Å(17.434 Å), b =13.815 Å(13.433 Å), and c =6.886 Å(6.620 Å)
We systematically studied the binding of four small hydrocarbons—CH4, C 2H6, C 2H4, and C 2H2—with two families of vanadium-based metal–organic frameworks (MOFs) without open metal sites, namely the MFM-300 and the MIL-47 families
Summary
The separation of light hydrocarbons is a key step in the petroleum refining process. A classic and widely used approach for hydrocarbon separation is fractional distillation [1], which is energy-consuming and can be inefficient for mixtures with very similar boiling points This consideration led to the development of zeolites [2,3,4], a type of porous materials in which one of the main driving forces for separation is the difference in adsorption energies between guest molecules and the zeolite [5,6,7,8], i.e., the “adsorptive separation.”. Insights from accurate firstprinciples calculations are needed
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