Display omitted •Using PTASA to promote PTL pyrolysis for high-quality syngas was firstly proposed.•The kinetic mechanism of PTASA in the pyrolysis of PTL was revealed.•PTASA mainly decreased the activation energy of Lignin in PTL by19%.•High-quality syngas increased evidently from 0.415 to 0.523 L/g with PTASA.•Inherent minerals in PTASA could break macromolecule bonds to promote PTL pyrolysis. To improve pyrolysis syngas of Phoenix Tree’s Leaves (PTL), the synergistic effect of Purified Terephthalic Acid Sludge Ash (PTASA) was comprehensively investigated. In kinetics analysis, the thermal decomposition of PTL could be divided into three pseudoreactions while PTL + PTASA was with four pseudoreactions owing to the decomposition of CaCO3 as well as the reduction of inherent metal compounds (Co(II), Mn(III, IV), etc). Meanwhile, the reaction models for pseudoreaction 1 (P1) ∼ pseudoreaction 4 (P4) were fitted as D3, R2 and D3, and A15, respectively. The Ea (average activation energy) of PTL + PTASA during pyrolysis (200 ∼ 600 °C) was 6.2 % lower than the monopyrolysis which was mainly caused by the decrease of Ea in the decomposition of lignin. In addition, the crystal structure e.g. CaMnO3 (ABO3), Ca3Co2O6 (A3BB’O6), and CoO in PTASA could effectively promote the production of high-quality syngas from 41.34 % to 61.76 %. Moreover, the reaction pathways in pyrolysis of PTL + PTASA showed that the PTASA could promote the CC bond, CO bond, and C–H bond breaking of the macromolecules, e.g. anhydrosugars, N-containing compounds, and aldehydes, to produce the small molecules and release syngas. This study could provide a useful strategy for clean, valuable, and sustainable resource utilization of waste resources.