The clumped isotope composition or the ∆47 value of CO2 relates the abundance of 13C18O16O among all the CO2 isotopologues to the formation temperature of a carbonate mineral or the equilibration temperature of CO2 gas. The ∆47 data typically requires several standardization steps and one of which heavily relies on true or equilibrium Δ47 values from different temperatures. However, they have not yet been experimentally quantified and only theoretically predicted Δ47 values are available to the community (e.g., Wang et al. 2004). In this study, a series of CO2 gases were cleaned using a custom-designed automated CO2 cleaning system, baked in a pre-cleaned dry quartz tube and then measured for their ∆47 values (the CBM protocol) to examine ∆47 change kinetics of CO2 gas over a heated quartz surface between 50 and 1100 °C. In another test, a series of CO2 gases were baked first, cleaned subsequently, and finally measured for their ∆47 values (the BCM protocol) to evaluate the effect of the CO2 cleaning on the ∆47 value in a routine ∆47 measurement. Our experimental results showed that ∆47 value of the CO2 gas over a heated quartz surface attained thermodynamic equilibrium in 191, 7, 0.23 and 0.1 h at 50, 100, 491 and 1000 °C, respectively. We also reported the first experimentally determined equilibrium ∆47–T relation in CO2 gas between 50 and 1100 °C as follows (∆47 in ‰, T in °C; R2 = 0.99, P < 0.0001): Absolute ∆ 47 = 0.9791 ± 0.0029 × e − 0.0045 T The comparison between the two CO2 preparation protocols also revealed that the CO2 cleaning step after the baking in the BCM protocol could alter the original ∆47 signature of CO2 gas by 0.04 and 0.07‰ at 100 and 1000 °C, respectively, increasing the empirical transfer function (ETF) slope to >1. Therefore, the isotope scrambling effect reported in the literature (e.g., Dennis et al. 2011) might be resulted from CO2 cleaning process because isolating the CO2 cleaning effect (before the baking) yielded an ETF slope of 1, implying that instrumental or analytical artifacts that could affect the measured ∆47 were not significant. We suggest using a set of heated CO2 gases prepared by the BCM protocol from several different temperatures as an alternative for the conventional use of heated and water-equilibrated CO2 gases to construct an absolute reference frame and standardize Δ47.