Palladium nanoparticles impregnated activated carbon material for catalytic oxidation of carbon monoxide

Abstract

Synthesis of nanoparticles by green method is the most attractive alternative in nanoscience and technology as the process is environmentally benign, simple and cost effective. Metal nanoparticles (NPs) supported catalysts are effective for removing toxic gases such as carbon monoxide (CO). Activated carbon-based materials are generally used as support material for NP impregnation. This study investigates the room temperature oxidation of CO over palladium nanoparticles (PdNPs) impregnated on activated carbon fiber cloth (ACFC). For that, PdNPs impregnated activated carbon fiber cloth catalyst is prepared by a green method using ascorbic acid and green tea as reducing agents. The method utilizes spent Pd/C as a precursor for Pd. Atomic absorption spectroscopy (AAS), BET surface area analyzer, Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), Temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy techniques were used to characterize the prepared PdNPs impregnated carbon fiber cloth catalysts. The Pd/ACFC catalysts were then tested for its applicability for the oxidative removal of CO, one of the major air pollutants. The efficiency studies were carried out both in the presence and absence of moisture. The metal ions were found to reduce to metal NPs depending on the size of the biomolecules used in the study. As the size of green tea catechins are bigger compared to ascorbic acid and the surface of ACFC is mainly composed of micro pores, the conversion of Pd ions to metallic Pd is not favoured and the catalyst is inefficient for the removal of CO irrespective of the presence and absence of moisture. On the other hand, the surface of ascorbic acid reduced catalyst is composed of both Pd0 and Pd+2 with Pd+2 as the major species. Accordingly, the catalyst shows 100% efficiency for the oxidative removal of CO at 5% moisture over a period of 300 min. It was also observed that high moisture percentage has a retardation effect on the catalyst efficiency, irrespective of the oxidation state of Pd.