PNNL

Abstract

The adsorption of a corrosive gas, SO¬2, into microporous pillared paddle-wheel frameworks M(bdc)(ted)0.5 [M = Ni, , Zn; bdc = 1,4-benzenedicarboxylate; ted=triethylenediamine] is studied by volumetric adsorption measurements and a combination of in-situ infrared spectroscopy and ab initio density functional theory (DFT) calculations. The uptake of SO2 in M(bdc)(ted)0.5 at room temperature is quite significant, 9.966 mol kg-1(63.8%) at room temperature/1.132 bar, which represents the highest SO2 uptake so far observed. Two different adsorption species are identified by infrared spectroscopy: one is typical physisorbed SO2 species, charac-terized by a modest red shift of S-O stretching bands (36 cm-1 for ?as and 7 cm-1 for ?s); the other characterized by adsorption bands at 1242 and 1105cm-1 and by a much higher (~150°C) temperature to completely remove. Theoretical calculations including van der Waals interactions (based on vdW-DF) indicate that the adsorption geometry of SO2 involves one molecule bonding of its sulfur atom to the oxygen atom of the paddle-wheel building unit and its two oxygen atoms to the C-H groups of the organic linkers by formation of hydrogen bonds. Such a configuration results in a large distortion of benzene rings, which is consistent with the experimentally observed shift of the ring deformation mode. The simulated frequency shift of the SO2 stretching bands by vdW-DF is in excellent agreement with spectroscopically measured value of physisorbed SO2. The IR absorptions at 1242 and 1105 cm-1 also suggest a stronger adsorption configuration, previously observed in SO4-like species involving two oxygen atoms of the paddle wheel building units. The adsorption configurations of SO2 into M(bdc)(ted)0.5 derived by infrared spectroscopy and vdW-DF calculations provide the understanding necessary to develop industrial processes for SO2 removal using microporous paddle-wheel frameworks materials.