Enhancing S.I. Engine Performance with Metal-Doped Zeolite X Derived from Rice Husk

Abstract

The increasing emission of nitrogen oxides (NOx) from gasoline engines poses a major environmental concern and contributes significantly to air pollution, acid rain and photochemical smog. Traditional three-way catalytic converters (TWCs) have limited NOx reduction efficiency under oxygen-rich conditions, highlighting the urgent need for alternative emission control technologies to protect the environment. In this context, the present study explores the use of low-cost zeolites synthesized from rice husk ash as a sustainable catalyst material. Na-X zeolites were synthesized and characterized using X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) to determine their chemical composition, crystallinity and surface morphology. These zeolites were further modified through ion exchange with copper (Cu) and iron (Fe) ions to produce Cu-X and Fe-X catalysts. The prepared catalysts were wash-coated onto cordierite honeycomb monoliths, housed in steel casings and installed near the exhaust manifold of a twin-cylinder nano-engine. Engine emission tests were performed under various loads (4, 7, 10, 13 and 16 kW), with exhaust gases analyzed using an AVL DI gas analyzer to measure NOx, carbon monoxide (CO), unburned hydrocarbons (UHC), carbon dioxide (CO₂) and oxygen (O₂). The Cu-X and Fe-X zeolite converters demonstrated significantly enhanced NOx pollution reduction compared to conventional TWCs, while maintaining similar  performance for other pollutants. The improved catalytic activity is attributed to the porous structure of zeolites and the synergistic effects of Cu and Fe ions. This study presents a sustainable strategy to mitigate engine-related pollution and protect environmental quality using agricultural waste-derived materials.