CO2 Reduction on Supported Ru/Al2O3 Catalysts: Cluster Size Dependence of Product Selectivity
The catalytic performance of a series of Ru/Al2O3 catalysts with Ru content in the 0.1-5% range was examined in the reduction of CO2 with H2. At low Ru loadings (≤0.5 %) where the active metal phase is highly dispersed (mostly atomically) on the alumina support CO is formed with high selectivity. With increasing metal loading the selectivity toward CH4 formation increases, while that for CO production decreases. In the 0.1% Ru/Al2O3 catalyst Ru is mostly present in atomic dispersion as STEM images obtained from the fresh sample prior to catalytic testing reveal. STEM images recorded form this same sample following temperature programmed reaction test clearly show the agglomeration of small metal particles (and atoms) into 3D clusters. The clustering of the highly dispersed metal phase is responsible for the observed dramatic selectivity change during elevated temperature tests: dramatic decrease in CO, and large increase in CH4 selectivity. Apparent activation energies, estimated from the slopes of Arrhenius plots, of 82 kJ/mol and 62 kJ/mol for CO and CH4 formation were determined, respectively, regardless of Ru loading. These results suggest that the formation of CO and CH4 follow different reaction pathways, or proceed on active centers of different nature. Reactions with CO2/H2 and CO/H2 mixtures (under otherwise identical reaction conditions) reveal that the onset temperature of CO2 reduction is about 150 ºC lower than of CO reduction. We thank Dr. Feng Gao for carrying out the H2 chemisorption measurements on all the Ru/Al2O3 catalysts discussed in this work. The catalyst preparation and catalytic measurements were supported by a Laboratory Directed Research and Development (LDRD) project, while the TEM work was supported by the Chemical Imaging Initiative at the Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US Department of Energy by Battelle under contract number DE-AC05-76RL01830. JHK also acknowledges the support of this work by the 2013 Research Fund of UNIST (Ulsan National Institute of Science and Technology, Ulsan, Korea).
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1107482
- Report Number(s):
- PNNL-SA-98443; 47709
- Journal Information:
- ACS Catalysis, 3(11):2449-2455, Journal Name: ACS Catalysis, 3(11):2449-2455
- Country of Publication:
- United States
- Language:
- English
Similar Records
Influence of copper on nickel-based catalysts in the conversion of glycerol
The effect of CO on CO2 methanation over Ru/Al2O3 catalysts: a combined steady-state reactivity and transient DRIFT spectroscopy study