Improving CO2 adsorption capacities and CO2/N2 separation efficiencies of MOF-74(Ni, Co) by doping palladium-containing activated carbon

• MOF-74(Co, Ni) were modified with Pd-loaded activated carbon.
• Pristine MOF-74(Ni) and MOF-74(Co) were adsorbed 11.06 and 10.28 mmol g−1 of CO2 at 298 K and 32 bar.
• CO2 adsorption capacities were enhanced to 12.24 and 11.42 mmol g−1 respectively, at same condition after modification.
• MOFs are capable to separate CO2 completely from the mixture of CO2/N2 gases.
• The CO2/N2 selectivity for MOF-74(Ni)-Pd and MOF-74(Co)-Pd were calculated as 14.6 and 12.4, respectively.

MOF-74(Ni, Co) were synthesized, characterized, modified with Pd-loaded activated carbon (AC) and evaluated for CO2 adsorption capacity and CO2/N2 separation efficiency. The BET specific surface areas of MOF-74(Ni) and MOF-74(Co) were measured as 1418 and 1404 m2 g−1 with the pore volumes of 0.86 and 0.82 cm3 g−1, respectively. CO2 adsorption capacity of these MOFs was enhanced with Pd containing AC doping. CO2 adsorption capacities of modified MOF-74(Ni)-Pd and MOF-74(Co)-Pd were 12.24 and 11.42 mmol g−1 respectively, measured at 298 K and 32 bar. The breakthrough curves of mixed CO2/N2 gases demonstrate the complete separation of CO2 from N2 stream. The adsorption and separation of CO2 were facilitated due the interaction between partially negative charge oxygen atoms of polarized CO2 molecule and partially positive Pd metal due to its low electronegativity. The fine structures of synthesized MOFs were further characterized with XANES and EXAFS. The bond distances of Ni–O, and Co–O in synthesized MOF-74(Ni) and MOF-74(Co) are 1.96 and 1.97 Å with the coordination numbers of 5.4 and 5.3, respectively.