Continuous-Flow Sunlight-Powered CO2 Methanation Catalyzed by γ-Al2O3-Supported Plasmonic Ru Nanorods

Jelle Rohlfs,Man Xu,Nicole Meulendijks,Marcel A Verheijen,Francesc Sastre,Koen W Bossers,Fidel Valega Mackenzie,Pascal Buskens

doi:10.3390/catal12020126

Abstract

Plasmonic CO2 methanation using γ-Al2O3-supported Ru nanorods was carried out under continuous-flow conditions without conventional heating, using mildly concentrated sunlight as the sole and sustainable energy source (AM 1.5, irradiance 5.5–14.4 kW·m−2 = 5.5–14.4 suns). Under 12.5 suns, a CO2 conversion exceeding 97% was achieved with complete selectivity towards CH4 and a stable production rate (261.9 mmol·gRu−1·h−1) for at least 12 h. The CH4 production rate showed an exponential increase with increasing light intensity, suggesting that the process was mainly promoted by photothermal heating. This was confirmed by the apparent activation energy of 64.3 kJ·mol−1, which is very similar to the activation energy obtained for reference experiments in dark (67.3 kJ·mol−1). The flow rate influence was studied under 14.4 suns, achieving a CH4 production plateau of 264 µmol min−1 (792 mmol·gRu−1·h−1) with a constant catalyst bed temperature of approximately 204 °C.

Highlights

In the last decade, the urge to reduce greenhouse gas emissions and to close the carbon loop has led to the promotion of synthetic fuels production, using CO2 and renewable energy as feedstock [1,2,3]
CH4 can be produced via hydrogenation of CO2 through the Sabatier reaction under solar light irradiation shown in Equation (1)
In order to determine the average size of the Ru NPs and the particle size distribution, we measured the dimensions of 200 NPs from the corresponding Transmission electron microscopy (TEM) micrograph, using the image analysis software ImageJ

Summary

Introduction

The urge to reduce greenhouse gas emissions and to close the carbon loop has led to the promotion of synthetic fuels production, using CO2 and renewable energy as feedstock [1,2,3]. Garcia et al studied the continuousflow photo-assisted CO2 methanation of a Ni-supported catalyst on Al2 O3 /SiO2 for a time period of 4 h They reported an increase of 3.7 times of the CH4 production rate compared to the process in dark with a 3.5% CO2 conversion under illumination at 240 mW·cm−2 and 225 ◦ C [38]. We present a catalyst consisting of Ru NRs supported on G-Al2 O3 , which successfully promoted full conversion for the CO2 methanation with complete selectivity for CH4 without conventional heating of the reactor and under a mild solar irradiation of up to 14.4 suns (14.4 kW·m−2 ) We selected this catalyst based on its broadband light absorption, which makes it capable of harvesting a large part of the solar energy, its high catalytic activity, and its ability to selectively convert CO2 and H2 to CH4 [25]. The catalyst showed negligible deactivation for at least 12 h of reaction

Thermal decomposition followed by reduction of the formed

Photomethanation without Conventional Heating

Thermocatalytic

Characterization

Gas-Phase Photocatalytic Experiments

Conclusions