Promoted aqueous ammonia is a potential solvent for CO2 separation processes. In this work, we investigated the effect of temperature, sarcosinate concentration, and CO2 loading on the mass transfer coefficients of CO2 absorption in a sarcosinate-promoted aqueous ammonia solution on a wetted-wall column. We further investigated the kinetics of the reaction between CO2 and a blended NH3/sarcosinate absorbent using stopped-flow spectrophotometric techniques, following the pH changes via coupling to pH indicators. Our study revealed that the mass transfer coefficient for CO2 absorption in a 3 M ammonia + 1.5 M sarcosinate blended solution at 288 K is close to that in 5 M monoethanolamine absorbent at 313 K. We did not observe any synergistic or catalytic effects between NH3 and sarcosinate in the blended solution; the mechanism of the reaction of CO2 with the NH3/sarcosinate mixture is the simple combination of the individual reactions of NH3 and sarcosinate with CO2.