In recent years, the development of efficient and sustainable adsorbents for CO₂ capture is critical for addressing climate change. This study aims to investigate the catalytic role of noble metals in hydrothermal carbonization (HTC) of loblolly pine (LP) to enhance biomass conversion efficiency and modify hydrochar properties by introducing metal oxide functionalities and microporosity to improve its CO₂ adsorption performance. The research work aims to perform HTC experiments of LP at different temperatures varying from 200°C to 260°C using 2 wt.% of Pd, Pt, and Ni, enabling a comparative analysis of their influence on hydrochar yield, chemical composition, and physical properties. Based on performance metrics, the optimal HTC conditions (260°C with Pd) were further examined by synthesizing hydrochars with 1 wt.% and 5 wt.% Pd. The produced hydrochars after HTC at 260°C with Pd in three different wt.% were marked as metal hydrochar composites (MHCs) and further superactivated using KOH in a ratio of 2:1 at 800°C to synthesize ultraporous activated char. The MHCs were evaluated for their elemental composition, surface functionalities, thermogravimetric behavior, BET surface area, and scanning electron microscopy morphology to assess the catalytic influence of Pd at varying concentrations. Pd incorporation during HTC enhanced carbonization efficiency and introduced oxygen-containing functional groups, while post-activation significantly increased surface area and microporosity, leading to improved CO₂ adsorption capacity. Notably, CO₂ uptake increased with Pd content, with the highest adsorption capacity recorded at 5.96 mmol/g for the H260 5% Pd T8 sample. The superior CO₂ capture performance is attributed to increased surface porosity, which facilitated enhanced physical adsorption mechanisms. This study highlights the potential of Pd-assisted HTC and activation strategies in developing high-performance carbon-based adsorbents for CO₂ capture applications.
