(724d) Catalytic Conversion of CO2 into Vinyl Acetate with Activated Carbon Based Zn Acetate Catalyst

Conversion of CO₂ to high-value products is limited commercially due to the stability of the CO₂ molecule. Very few commercially significant reactions convert greenhouse gas like CO₂ to value-added products. The following is one such two-step process: the carboxylation of CH₄ to form acetic acid, which is reacted with acetylene to form vinyl acetate:

CO₂ + CH₄ → CH₃COOH; (2) CH₃COOH + C₂H₂ → vinyl acetate

This formation of acetic acid is thermodynamically limited, but can be addressed by coupling this reaction with a thermodynamically favorable reaction, e.g., reacting acetic acid with acetylene, and forming vinyl acetate monomer (VAM), a high-value industrial intermediate. The overall coupled reaction with CH₄ + CO₂ + C₂H₂ to VAM is thermodynamically feasible (ΔG_r^o= +6.4 kJ/mol). Previously, Wilcox et al. demonstrated the catalytic reaction of VAM from this reaction at temperature as high as 400⁰C under atmospheric pressure [1], but VAM formation was not stable at these conditions (Figure 1). The formation of VAM from CH₄ + CO₂ + C₂H₂ involves one, single reaction at low temperature and high pressure. The goal of this work is to investigate and synthesize an active and stable catalyst at thermodynamically favorable reaction conditions. Keeping this in mind, activated carbon based zinc acetate (ZnA/C) was synthesized and tested at different reaction conditions.

After characterizing ZnA/C with SEM-EDS, Raman and XRD, VAM reaction was run from temperatures as low as 130⁰C and at a pressure of 9 bar for ~15 hours. A stable VAM formation was observed. Acetaldehyde was observed as a side product of VAM. When the temperature was increased to 160⁰C, VAM Selectivity increased as well. VAM selectivity also increased with lower space velocity. Activity decreased slightly with time. Catalytic deactivation can be observed with the loss of acetate from the catalytic surface at high temperature.