CO₂-cofed catalytic pyrolysis of tea waste over Ni/SiO₂ for the enhanced formation of syngas

To valorize tea waste (TW), catalytic pyrolysis was done as a practical measure for recovering energy as a form of syngas. Considering CO₂ as a reactive gas medium in place of conventional pyrolysis gas, a sustainable pyrolysis platform was established. In addition, mechanistic effectiveness of CO₂ on TW pyrolysis was examined. In the presence of CO₂, homogeneous reaction with volatile organic compounds (VOCs) derived from TW pyrolysis contributed to CO formation. To enhance the formation of syngas at low pyrolysis temperature, catalytic pyrolysis over a Ni/SiO₂ was investigated. The synergistic effects of Ni/SiO₂ catalyst and CO₂ promoted thermal cracking of VOCs and further homogeneous reaction with CO₂, thereby resulting in the substantial enhancement (28 times more) of H₂ and CO production than non-catalytic pyrolysis. It was also confirmed that CO₂ could be considered a reactive gas medium to produce biochar (34–35 wt.% yield), having competitive porosity and surface area, in comparison to that from pyrolysis in N₂. Therefore, CO₂ can be employed to build a sustainable waste conversion platform for energy and biochar production through pyrolysis instead of using N₂.