Conversion of CO<sub>2</sub> to Formic Acid Using Silicon Sludge as a Reducing Agent

Utilizing Si sludge from wafer-production industries for synthesizing value-added chemicals using CO2 facilitates both the recycling of waste Si and the utilization of CO2 as a carbon resource. In this study, the reduction of CO2 to produce formic acid using Si sludge as a reducing agent is reported. Tetrabutylammonium fluoride effectively promotes the reduction. This approach is suitable not only for pure CO2 but also for the CO2 present in the exhaust gas from a thermal power plant. Reaction parameters such as CO2 pressure, temperature, water content, and amount of silicon sludge were optimized. Analyses of the Si sludge before and after the CO2 reduction reaction were performed using XPS and XRD, which indicated the conversion of the Si0 phase to SiO2 in the Si sludge. This is an environmentally friendly and possibly cost-effective approach for formic acid synthesis since CO2 is converted to formic acid by Si sludge.