Light-assistance in nitrogen fixation to ammonia by highly dispersed Cs-promoted Ru clusters supported on ZrO2

Light-assisted N-2 fixation to NH3 under mild conditions is attracting massive attention to circumvent energy crisis and global warming. Herein, highly dispersed Cs-decorated Ru sub-nanometric clusters supported on ZrO2 NPs have been prepared by means of MOF-templated transformation method. The obtained catalyst exhibited N-2 hydrogenation activity of 1.6 mmolNH3 g(cat)(-1) h (-1) in the dark (350.C, 0.1 MPa). Remarkably this value increased by over 300 %, reaching 5.1 mmolNH3 g(cat)(-1) h (-1) (204 mmolNH3 g(Ru)(-1) h (-1)) under 1 Sun power illumination (1080 W/ m2) The influence of the incident light wavelength has been evaluated, revealing 81 % and 213 % enhancement in the NIR and visible region, respectively. DFT calculations were carried out to understand the static adsorption states of Ru sub-nanoclusters. Mechanistic studies have confirmed the co-existence of a photothermal and a nonthermal-hot electron mechanism. XPS, PXRD and FTIR analysis have determined that the Cs species block surface Zr4+ acidity, increasing the basicity of the ZrO2 support. Moreover, partially reduced Cs delta+ (0 <delta < 1) species surrounding the Ru active sites are donating electron density to the adjacent Ru sites, favoring N-2 adsorption and subsequent activation. Finally, this photocatalyst has shown an extended stability for 100 h irradiation under continuous flow.