Clathrates are well-known compounds whose low thermal stability makes them extremely rare and appreciated. Although their formation mechanism is still surrounded by many uncertainties, these ice-like structures have the potential to be an alternative for transport and storage of different gases, especially methane. For the formation of methane clathrates extreme pressure conditions and a narrow temperature window are needed. Microporous materials have been proposed to provide nucleation sites that, theoretically, promote clathrate formation at milder conditions. While activated carbons and Metal-Organic Frameworks (MOFs) have already been studied, very little is known about the role of zeolites in this field. In this work, we study the formation of methane clathrates in the presence of RHO zeolite. Experimental results based on adsorption and operando synchrotron X-Ray diffraction demonstrate the formation of clathrates at the surface of the zeolite crystals and reveal mechanistic aspects of this formation at mild conditions.

Purification of methane from other light hydrocarbons in natural gas is a topic of intense research due to its fundamental importance in the utilization of natural gas fields. Porous materials have emerged as excellent alternative platforms to conventional cryogenic methodologies to perform this task in a cost- and energy-efficient manner. Here we report a new family of isoreticular chiral MOFs, prepared from oxamidato ligands derived from natural amino acids l-alanine, l-valine and l-leucine, where, by increasing the length of the alkyl residue of the amino acid, the charge density of the MOF's channels can be tuned (1 > 2 > 3), decreasing the adsorption preference towards methane over light hydrocarbons thus improving this purification process. The validity of our rational design strategy has been proved by a combination of single-component adsorption isotherms, adsorption kinetics of CH₄, C₂H₆, C₃H₈ and n-C₄H₁₀, and breakthrough experiments of binary CH₄/C₂H₆ and CH₄/C₃H₈ mixtures.