(603e) Fundamental Insights into Reactions for Trace Contaminant Removal

Natural gas and oil typically require purification before processing because these feedstocks contain a wide range of sulfur compounds that are hazardous. While metal oxides are used to remove these
contaminants via chemical reaction, these materials suffer from incomplete utilization that can lead to process shutdowns or emissions. More research is needed to understand these reactions at the molecular
level so that complete active phase utilization can be achieved. We combine reaction and characterization experiments across multiple length scales with computational studies to elucidate details of reactions of sulfur compounds with copper oxide.

Breakthrough studies showed that capacities are less sensitive to macroscopic size and intra-particle void space than to atomistic features such as crystallite size and the presence of dopants. In-situ X-ray
absorption spectroscopy revealed that capacities and kinetics measured from fixed beds are representative of those measured at individual particle scales and that introducing a foreign atom into
the CuO lattice can influence the reactivity of CuO towards sulfur by disrupting the lattice structure (manifested as perturbed Cu-O distances). The presence of foreign atoms could also alter the electronic
structure by changing the density of states at the fermi level which affects oxygen and cation reactivity. DFT calculations supported these conclusions and indicated that decreasing crystallite size exposes a
greater extent of reactive surface facets in CuO and increases O-vacancies. These open facets facilitate H-S bond cleavage which is necessary to produce S atoms that react with CuO moieties. Open facets
may also enhance the diffusion of sulfur atoms to fresh substrate layers allowing for a greater extent of propagation of the reaction front. This knowledge of the influence of crystallite size and composition on
CuO capacity for H₂S can serve as a guide for rational design or selection of copper oxide sources for sorbent materials.