From the HaD Comments:
What zeolite to use?<p>13X zeolite 0.4 mm – 0.8 mm or JLOX 101 are both commonly used in o2 concentrators the second one is the most expensive. I used the 13X when rebuilding my craigslist o2 concentrator.<p>13x (10 angstrom pore size)<p><a href="https://catalysts.basf.com/files/literature-library/BASF_13X-Molecular-Sieve_Datasheet_Rev.08-2020.pdf" rel="nofollow">https://catalysts.basf.com/files/literature-library/BASF_13X...</a><p>5A (5 angstrom pore) molecular sieve can also be used. I think it’s a bit less selective for nitrogen but still usable.