Plasmonic Effects on CO 2 Reduction over Bimetallic Ni-Au Catalysts

Abstract The anthropogenic rise of carbon emissions has led to increased interest in the innovative utilisation of CO 2 . CO 2 reduction via the Sabatier reaction presents a thermodynamically favourable pathway to reduce CO 2 ; however, to date, there has been a lack of understanding of how plasmonic enhancement may be utilised for this reaction particularly with respect to the role of bimetallic catalysts. In this study, the effect of laser light illumination on Ni-Au/SiO 2 , at 520 nm and 660 nm, was studied for CO 2 reduction over a temperature range of 150 °C to 450 °C, with the catalytic performance being assessed by CO 2 conversion along with CH 4 and CO selectivity. Under laser light illumination, at 520 nm and 450 °C, CO 2 conversion for Ni–Au/SiO 2 increased by 79% whilst simultaneously lowering CH 4 selectivity, which was attributed to localised surface plasmon resonance effects and promotion of the reverse water-gas shift reaction by the Au. Laser light illumination at 660 nm also introduced a mild conversion increase, however not to the same extent as for 520 nm. XPS analysis of Ni-Au/SiO 2 implied that the observed photo-enhancement could be due to plasmonic mediated electron charge transfer from the Au deposits to the Ni deposits. Monometallic Ni and Au samples were examined and compared with the bimetallic system to elucidate the origin of the photo enhancement and to understand the plasmonic and catalytic interactions. The Au/SiO 2 and Ni/SiO 2 samples demonstrated that the photo-enhancement arose from the presence of the Au, with the increase in CO 2 conversion at 520 nm increasing with increasing Au content; Au (∼110%) > Ni-Au (∼80%) > Ni (∼21%). However, the overall better performance of the Ni/SiO 2 sample, facilitating high CO 2 conversion and CH 4 selectivity emphasises that, while plasmonic metal inclusion can induce synergistic effects, the benefits can be muted if it is unable to promote the target reaction.