Removal of Nitric oxide (NO) by selective catalytic reduction over modified oil palm empty fruit bunch fibres (EFB)

Nitric oxide (NO) is one of the primary air pollutants emitted from combustion which could lead to many other global environmental problems such as acid rain and photochemical smog. Due to the associated risks, continuing effort to study the NO removal from industrial sources are necessary especially at low temperature. This work aims to investigate the NO removal by selective catalytic reduction (SCR) using activated carbon originated from oil palm empty fruit bunch fibres (EFB) as support material. The activated carbon (EFBC) was prepared by one stage chemical activation using phosphoric acid (H3PO4) and carbonized at temperature between 400-550°C for 4 hours. Higher carbonization temperature led to pore enlargement and resulted in lower NO adsorption capacity. The EFBC was then impregnated with metal additives i.e. copper (Cu), nickel (Ni) and iron (Fe) oxides/salts via wet incipient impregnation, and calcined at 400°C. Introduction of 5 wt.% CuO was found to be slightly more favourable for NO removal in comparison to the other two metals, and CuO at higher loading (10-20 wt.%). The physical and chemical properties of EFB and modified samples were characterized with surface area and pore analysis, proximate analysis, surface morphology and surface chemistry. The increase in the initial NO concentration and reaction temperature investigated between 300-1000 ppm and 100-300 ºC, respectively, were found to improve NO removal by both EFBC and CuO/EFBC. EFBC was also found to exhibit better performance in dissociative NO removal, with higher N2 production, while higher reaction temperature increased N2 production of EFBC from 13.99 % (100oC) to 62.56 % (300oC). The NO adsorption of both EFBC and CuO/EFBC at 100°C was best fitted to Sips isotherm, indicating the heterogenous nature of the adsorbent surface. On the other hand, the adsorption kinetic data of NO for both EFBC and CuO/EFBC were best fitted to Avrami kinetic model, suggesting that the NO adsorption were mainly governed by surface attachment and diffusional process. The NO adsorption data also fitted well with the intra-particle diffusion model via intraparticle diffusion and film diffusion. The reaction was endothermic in nature and nonspontaneous, involving both physisorption and chemisorption routes. The former route was mainly assisted by the physical characteristics such as higher surface area and smaller pore size while the latter were influenced by the surface chemistry on the carbon surface. Further hydrogen pre-treatment of CuO/EFBC at 600-700oC resulted in better specific surface area and pore properties, introduced more basic surface groups and induced the presence of smaller crystallite CuO, Cu2O and Cu3P, leading to higher metal dispersion favourable for NO removal. The research outcome will contribute to knowledge in NO removal and useful for post-combustion applications, especially for small medium industries who cannot afford high-temperature NO removal technologies.