The adsorption of molecular gases on La-MPBCP or
[La-MPBCP]+3 systems
The study for adsorption of biogas (CO2,
H2, N2 and CH4) on the
La-MPBCP or [La-MPBCP]+3 systems, we considered
that the gas molecule would interact with the lanthanum atom, because of
that the gas molecule was placed directly on the top of the lanthanum
atom, see Figure 4. The optimized structures shown Cs symmetry
for interactions by CO2, H2,
N2 and CH4 with neutral system. For the
case of the [La-MPBCP]+3 system, the
H2, and CH4 shown Cs symmetry and
C3v symmetry for interactions by CO2 and
N2 with perpendicular interaction gas-La
(CO2, La-O 2.50; N2, La-N 2.77 Å)
showing lower bond length than the neutral system see Table 3. On the
other hand, the La-H in H2 molecule has a similar value
for both systems (neutral, La-H 2.68-2.77 and
[La-MPBCP]+3 2.74 Å), those interactions are
significantly smaller than the sum of their van der Waals
radii.49
The calculated adsorption energies of the gas molecules adsorbed on
systems are listed in Table 3. It is observed that theEads are negative, indicating adsorption was
exothermic showing favorable interaction of those gas molecules. The
adsorption energy for the H2, N2,
CH4 and CO2 on the
[La-MPBCP]+3 system has a values of -7.51, -16.64,
-21.30 and -28.63 kcal/mol, these values are higher compared to neutral
system (-5.28, -9.90, -10.79 and -15.95 kcal/mol). The calculated
CO2 adsorption energy for
[La-MPBCP]+3 is similar to
La2O2CO3 systems
calculate with the PBE functional.50 The descending
order of those adsorption energies is the following:
CO2>CH4>N2>H2.
The adsorption of lanthanum atom on MPBCP induce to increase the
reactivity, causing the adsorption of gas molecule. We can clearly
observe that all gas molecules (N2, H2,
CO2, CH4) have coordinations with short
distances with the lanthanum atom (see Figure 5). Our results predicted
that these gas molecules are easy to be adsorbed on the La-MPBCP or
[La-MPBCP]+3 systems by physisorption. It is
important to highlight the computed adsorption energy for the
CO2 molecule on the [La-MPBCP]+3system is four times greater than adsorption energy for the
H2 molecule. These results suggested that the
[La-MPBCP]+3 system could serve as an
adsorber-separator of CO2/H2.