This paper presents thermal deactivation of beech wood chars during secondary pyrolysis in a drop-tube reactor. Pyrolysis temperature was varied between 1000 °C and 1600 °C at a constant residence time of 200 ms. The effect of pyrolysis conditions on initial conversion rate R₀ during gasification, graphitization of the carbon matrix and ash morphology was investigated. Gasification experiments for the determination of R₀ were conducted in a thermogravimetric analyzer using pure CO₂ at 750 °C and isothermal conditions. A linear decrease in initial conversion rate R₀ was observed between 1000 °C and 1400 °C. However, a strong increase of R₀ at 1600 °C was encountered. Micropore surface area of the secondary chars showed no correlation with the initial conversion rate R₀ during gasification with CO₂. Graphitization of the carbon matrix was determined using X-ray diffraction and Raman spectroscopy suggesting the growth of aromatic clusters and graphite-like structures for increasing pyrolysis temperatures up to 1600 °C. Furthermore, CaO dispersion was analyzed quantitatively and qualitatively using temperature-programmed reaction at 300 °C as well as SEM/TEM. CaO dispersion D_CaO decreases steadily between 1000 °C and 1400 °C whereas a strong increase can be observed at 1600 °C, which is in good accordance with the development of the initial conversion rate R₀ as a function of pyrolysis temperature. SEM/TEM images indicate the formation of a thin CaO layer at 1600 °C that is presumably responsible for the strong increase in initial conversion rate R₀ at this temperature. When excluding the catalytic activity of CaO via formation of the ratio R₀ D_CaO⁻¹, increasing graphitization degree has a linear negative influence on char reactivity at pyrolysis temperatures between 1000 °C and 1400 °C.