Adsorption-based separation of CH4/N-2 mixture remains challenging. To this end, [Ni-3(HCOO) 6] frameworks were synthesized by a novel solvent-free method and used as adsorbent. CH4 and N-2 adsorption performances of the samples were examined separately by static adsorption, breakthrough and two-bed pressure swing adsorption (PSA) experiments. CH4 adsorption capacity was 0.82 mmol/g at 298 K and 100 kPa. The CH4/N-2 selectivity reached up to 6-7 at 298 K and 0.5 MPa, which was higher than that of most other adsorbents including activated carbon, zeolites, and metal-organic frameworks (MOFs). Two-bed lab-scale PSA experiments dealing with equimolar CH4/N-2 mixture showed that both CH4 purity and recovery exceeded 90% under optimized operation conditions. The remarkable performance in benchmarking experiments confirmed [Ni-3(HCOO)(6)] frameworks promising adsorbent for unconventional natural gas upgrading, owing to its high volume of uniform ultra-micropore and optimal polarizability. (C) 2017 Elsevier B.V. All rights reserved.