Co-doped hydroxyapatite as photothermal catalyst for selective CO2 hydrogenation
Yong Peng, Horațiu Szalad, Pavle Nikačević, Giulio Gorni, Sara Goberna‐Ferrón, Laura Simonelli, Josep Albero, Núria López, Hermenegildo Garcı́a
Abstract
The rational design and in deep understanding of efficient, affordable and stable materials to promote the light-assisted production of fuels and commodity chemicals is very appealing for energy crisis and climate change amelioration. Herein, we have prepared a series of Co-doped hydroxyapatite (HAP) catalysts with different Co content. The materials structure has been widely investigated by XRD, FT-IR, HRTEM, XPS, XAS, as well as computational simulations based on Density Functional Theory (DFT) with PBE functional. At low Co loading, there is a partial substitution of Ca cations in the HAP structure, while higher loadings promote the precipitation of small (∼ 2 nm) Co nanoparticles on the HAP surface. For the optimal Co content, a constant CO rate of 62 mmol·g −1 ·h −1 at 1 sun illumination and 400 °C, with the material being stable for 90 h. Visible and NIR photons have been determined responsible of the light-assisted activity enhanced. Mechanistic studies based on both experimental and DFT simulations show that H 2 preferentially adsorbs to metallic Co, while CO 2 adsorbs to the HAP surface oxygen. Moreover, both direct photo- and plasmon-driven contributions have been separated in order to study their mechanisms independently. Co-doped hydroxyapatite has been demonstrated visible light photo-assisted activity of CO2 hydrogenation to CO. Experimental and computation investigation have confirmed the partial substitution of Ca ions in the hydroxyapatite structure. Mechanistic studies have determined both direct photo- and plasmon-driven catalysis occurs depending on the Co doping level. These materials have been also demonstrated to be very stable under operational conditions. • A series of Co-doped hydroxyapatite (CoHAP) at various Co loadings (3.46–11.38%) have been prepared. • Characterization indicates that Co 2+ replaces Ca 2+ in the HAP lattice up to 5.88%. • At higher loading Co 2+ migrates outside the HAP lattice and forms small Co 3 O 4 nanoparticles. • Under continuous flow at 400 °C, the optimal CoHAP produces 62 mmol CO·g −1 ·h −1 . • The material is stable for at least 90 h without activity decay