Effects of textural and surface characteristics of metal-organic frameworks on the methane adsorption for natural gas vehicular application

• The methane adsorption and textural characteristics of 52 samples were measured.
• Ideal MOFs feature optimized surface area, micropore volume and packing density.
• Packing density is the major factor for the volumetric total capacity at 50 bar.
• The capacity changes due to metal effects in MOFs are observed at low pressure.
• Optimization of metal sites should avoid decreasing the deliverable capacity.

In this work, methane adsorption and textural and surface characteristics of selected 46 microporous metal-organic frameworks and 6 other adsorbents were measured experimentally. The objective of this work is to identify either the most relevant characteristics or a combination of multiple properties, which will qualify a given sample to be a good methane uptake material in a moderate pressure range (up to 70 bar) and at 298 K. It is found that there is an overall linear tendency between maximum excess methane adsorption and BET specific surface area. The micropore volume correlates to the maximum excess methane adsorption as well, irrespective of the chemistry and functionalities of materials. In addition, micropore size distribution has an impact on methane uptake. When considering the total methane uptake, special attention should be paid to the effect from packing density. The evaluation also focuses on the discussion of deliverable capacity and concludes that optimal adsorption enthalpy is desired to avoid large amount of methane retained at the minimum desorption pressure in practical vehicular applications.

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