Sunlight-Powered Reverse Water Gas Shift Reaction Catalysed by Plasmonic Au/TiO2 Nanocatalysts: Effects of Au Particle Size on the Activity and Selectivity

Abstract

This study reports the low temperature and low pressure conversion (up to 160 °C, p = 3.5 bar) of CO2 and H2 to CO using plasmonic Au/TiO2 nanocatalysts and mildly concentrated artificial sunlight as the sole energy source (up to 13.9 kW·m-2 = 13.9 suns). To distinguish between photothermal and non-thermal contributors, we investigated the impact of the Au nanoparticle size and light intensity on the activity and selectivity of the catalyst. A comparative study between P25 TiO2-supported Au nanocatalysts of a size of 6 nm and 16 nm displayed a 15 times higher activity for the smaller particles, which can only partially be attributed to the higher Au surface area. Other factors that may play a role are e.g., the electronic contact between Au and TiO2 and the ratio between plasmonic absorption and scattering. Both catalysts displayed ≥84% selectivity for CO (side product is CH4). Furthermore, we demonstrated that the catalytic activity of Au/TiO2 increases exponentially with increasing light intensity, which indicated the presence of a photothermal contributor. In dark, however, both Au/TiO2 catalysts solely produced CH4 at the same catalyst bed temperature (160 °C). We propose that the difference in selectivity is caused by the promotion of CO desorption through charge transfer of plasmon generated charges (as a non-thermal contributor).

Sunlight Powered Continuous Flow Reverse Water Gas Shift Process Using a Plasmonic Au/TiO2 Nanocatalyst

“…Other metals, such Ru and Ni have shown a strong selectivity towards CH 4 production [7a,d,h,15] . Recently, our group has reported plasmonic Au nanoparticles supported on TiO 2 that promote the rWGS reaction under sunlight irradiation without any external heating in a batch process [7e,f] . We reported a maximum CO initial production rate of 429 mmol ⋅ g Au −1 ⋅ h −1 (8525 mmol ⋅ m −2 ⋅ h −1 ) with a selectivity of 98% and an apparent quantum efficiency of 4.7% using mildly concentrated sunlight (1.44 W ⋅ cm −2 =14.4 suns) in a batch process.…”

Solar‐Driven Continuous CO2 Reduction to CO and CH4 using Heterogeneous Photothermal Catalysts: Recent Progress and Remaining Challenges

“…The light‐driven process obtained higher activity and selectivity in comparison to thermal reference experiments. Previous research based on experimental and theoretical analysis supported that the reaction was promoted by a synergistic contribution of (photo)thermal and photochemical processes [125,126] . Upadhye et al .…”

“…Previous research based on experimental and theoretical analysis supported that the reaction was promoted by a synergistic contribution of (photo)thermal and photochemical processes. [125,126] Upadhye et al ruled out localized heating effects based on reported literature [127] and the apparent activation energies found. [124] Here, the increase in productivity was predominantly attributed to a reduction in inhibition due to surface coverage of adsorbed species, which could be caused by either hot electrons or intense electromagnetic fields around the gold nanoparticles.…”

Light-assisted carbon dioxide reduction in an automated photoreactor system coupled to carbonylation chemistry

“…[22][23][24] To date, significant strides have been made in the development and evaluation of catalysts and reactor systems for the hydrogenation of carbon dioxide. [25][26][27][28][29][30][31][32][33] However, direct comparison of the performance and efficacy of these catalysts remains challenging due to the absence of standardized operational procedures. In this endeavor, we aim to tackle these challenges by introducing an automated, integrated, and modular reactor system.…”