Influence of Hydrogen Pre-treatment at Different Temperatures on Copper Oxide Supported on Carbonised Oil Palm Empty Fruit Bunch (CuO/EFBC) for Low-Temperature Nitric Oxide Removal

Low-temperature nitric oxide (NO) removal by oil palm empty fruit bunch (EFBC) modified with phosphoric acid dehydration, followed by copper oxide (CuO) impregnation is a function of both surface chemical and physical properties of CuO/EFBC resulting from hydrogen (H2) pre-treatment at different temperatures. Subjecting CuO/EFBC sample to H2 pre-treatment at 400 °C initially reduces the NO adsorption capacity (q) (at C/Co = 0.95) from 1.65 to 1.57 mg/g although the BET specific surface area (SBET) increases from 4.81 to 160 m2/g, due to surface predomination by acidic oxygenated groups (e.g. carboxyl, lactone and phenolic groups). At 500 °C, q increases to 5.67 mg/g as some of the acidic surface groups are decomposed and the SBET improves to 466 m2/g. Further increase in the temperature to 600 and 700 °C respectively enhances the SBET to 448 and 516 m2/g, and decomposes most of the acidic groups, leaving unsaturated C to react with H and form stable basic sites e.g. aldehyde, alkane, alkyl and aromatic groups more favourable for NO adsorption, thus giving rise to q (at C/Co = 0.5) to 41.01 and 62.74 mg/g, with stable performance for more than 2 h of experiment. In addition, higher pore volume, smaller pore size and smaller crystallite size of CuO, Cu2O and Cu3P sites are observed in samples pre-treated at high temperatures (600 and 700 °C), leading to a condition more auspicious for dissociative NO adsorption. Graphic Abstract: [Figure not available: see fulltext.].