Delafossite CuGaO2 surfaces: study of CO adsorption on Cu+ reactive sites

GUSTAVO E. MURGIDA; ESTEBAN FORNERO; MARTA BOSCO; JUAN C. HERNÁNDEZ GARRIDO; M. VERÓNICA GANDUGLIA-PIROVANO; ADRIAN L. BONIVARDI

La Plata

Workshop; X Woorkshop on Novel Methods for Electronic Structure Calculation; 2023

Noble metal catalysts are highly effective for oxidation reactions but are expensive, driving researchinto more affordable alternatives like Cu+. However, stabilizing Cu+ on surfaces is challenging,limiting its application in catalytic materials. Delafossite CuGaO2 is a promising alternative due toits stable Cu+ cations, but remains unexplored as a catalyst. In this study, we present experimentaland theoretical analyses of CuGa2 surfaces, CO adsorption at various active sites, CO oxidationperformance, and the impact of oxygen vacancies on these properties. By employing DFT withinthe PBE+U and HSE06 approximations, CuGaO2 surfaces were modeled alongside CO adsorptionand vibrational spectra of adsorbed CO. The findings were subsequently analyzed and compared toexperimental results obtained through HRTEM, XRD, XPS, and FTIR techniques.Porous CuGaO2 (111) nanoplates terminated with Ga were obtained via microwave-assisted hydrothermal synthesis. The edges of these plates are fundamental for the reactivity due to the presence of exposed Cu+ sites and due to their large surface area (greater than the (111) face). DFTcalculations of surface energy explained the Ga termination of the (111) faces and attributed the(110) termination to the edges of the nanoplates. CO adsorption on CuGaO2, followed by FTIR andsimulated via DFT, mainly occurs on Cu+ sites forming mostly carbonyl (t-Cu+), and also geminaldicarbonyl species (two CO molecules bound to the same Cu+, g-Cu+). In presence of oxygen vacancies, two types of copper are obtained (Cu+ and Cu+, where 0 < < 1), and the CO adsorptionenergy significantly increases. Furthermore, CO adsorbed on reduced CuGaO2 forms mainly g-Cu+dicarbonyl, and less frequently, t-Cu+ and t-Cu+ species.Under reducing conditions, the CO oxidation performance is also considerably enhanced. Our findings on CuGaO2 should be useful in the study of reactions activated by Cu+ and also to proposethe development of new technological catalysts.