Synthesis and characterization of supported Sn/γ-Al2O3 and Sn/ZSM5 catalysts for CO2 reduction in electrochemical cell

- Sn supported on γ-Al2O3 and ZSM5 tested for CO2 electroreduction to organics.
- 20%Sn on γ-Al2O3 and ZSM5 gives highest CO2 reduction among all the loadings.
- Due to percolation limit 10%Sn gives low conversion whereas 40%Sn forms agglomerates.
- 20Sn/ZSM5 produced 190 mA cm−2 at −2 V higher than for 20Sn/Al2O3 160 mA cm−2.
- 20Sn/ZSM5 gives CH4 (FE 20.6%), CO and H2 as main product higher than for 20Sn/Al2O3.

To improve CO2 conversion efficiency at the cathode of an electroreduction cell, different loadings of Sn on high surface area supports, γ-Al2O3 and ZSM5, were synthesized by wet impregnation followed by hydrogen reduction. As synthesized catalysts were characterized using X-Ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscope (TEM) and cyclic voltammetry studies. By comparing voltammetry results it is found that 20 wt% Sn catalyst is electrochemically more active towards CO2 reduction than other lower and higher loadings of Sn on both the supports. The reason for such observation is explained based on physical characterization of γ-Al2O3 and ZSM5. In 20 wt% Sn catalyst, the Sn remains in dispersed form adhering to the porous wall of γ-Al2O3 and ZSM5 satifying percolation limit. Whereas, at lower loadings, electronic connectivity between Sn particles are lost and, at higher loadings, Sn particles agglomerate blocking the pores of the support. Reduction of CO2 using 20Sn/Al2O3 and 20Sn/ZSM5 catalyst is found to be selective towards methane and carbon monoxide formation from the product analysis of the electroreduction cell using gas chromatograph. In electroreduction cell, 20Sn/ZSM5 cathode produced higher current and more faradaic efficiency (20.4%) towards methane formation compared to 20Sn/Al2O3 cathode (12.9%).

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