Surface Chemistry of Sulfur Dioxide on Zr(OH)4 Powder: The Role of Water

Operando conditions, such as the presence of H2O, can dramatically alter the reaction pathways of molecular interactions on a surface. Here, we determine how water affects the decomposition chemistry of SO2(g) on dry and wet Zr­(OH)4 powder, a material being transitioned for battlefield chemical sequestration and decomposition. Diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy reveal that SO2 decomposition products on dry and wet Zr­(OH)4 differ significantly. Sulfites (sulfates) dominate on dry (wet) Zr­(OH)4 surfaces. Kinetic analysis of the wet surface shows that H2O interacts with SO2 initially and then with surface OH sites, indicating that the mechanism to form sulfates requires water molecules. The combined IR spectra and density functional theory calculations confirm that sulfites and sulfates bind to both surface terminal and bridging OH sites.