IR and Computational Characterization of CO Adsorption on a Model Surface, the Phenylene Periodic Mesoporous Organosilca with Crystalline Walls

Low-temperature adsorption of carbon monoxide on an ordered periodic mesoporous organosilica (1,4-phenylenesilica PMO) was studied by means of infrared spectroscopy and theoretical calculations on cluster models. Basically, three types of adsorbed CO species were found to be simultaneously formed at a low CO coverage: (i) physisorbed species having the CO molecule interacting only with a benzene ring, (ii) hydrogen-bonded species having the CO molecule interacting with a silanol group through the carbon atom, and (iii) hydrogen-bonded species having the CO molecule interacting with a silanol group through the oxygen atom. However, both hydrogen-bonded species showed also a residual (lateral) interaction of the CO molecule with a neighboring benzene ring. This residual interaction accounts for an overall adsorption enthalpy (ΔH0) that is significantly larger than that involving the interaction of CO with silica. Thus, the C-bonded species ii showed ΔH0 = −13.2 kJ mol−1 (as determined by variable-temperature infrared spectroscopy) to be compared with that of ΔH0 = −11 kJ mol−1 previously reported for the interaction between CO and silica silanol groups. Also remarkable is the relatively large value of adsorption enthalpy, ΔH0 = −10.6 kJ mol−1, showed by the physisorbed species involving only interaction between CO and a benzene ring.