Copper-Exchanged Philippine Natural Zeolite as Potential Alternative to Noble Metal Catalysts in Three-Way Catalytic Converters

Abstract

Natural and synthetic zeolites are microporous hydrated aluminosilicate minerals known for their high thermal stability and their use in various catalytic applications. In this study, the potential of modified Philippine natural zeolite as a cheap alternative to noble metal catalysts in three-way catalytic converters was investigated. The natural zeolite (Z) of the heulandite variety was treated using hydrochloric acid and then ion-exchanged with sodium (NaZ) and copper (CuZ) ions in succession. Energy-dispersive X-ray spectroscopy analysis revealed successful replacement of sodium and other exchangeable cations by copper in the zeolite at 1.19%. Morphological features using scanning electron microscope have shown uniform dispersion of copper as well as uniform particle distribution. In the emission study, a stationary two-stroke 125 cm3 spark-ignition gasoline engine motorcycle at three different speeds of 10 (low), 40 (medium) and 70 (high) kilometers per hour (kph) was used to investigate the catalytic properties of CuZ with the non-catalytic setup as baseline. Using the modified zeolite catalyst, emission test results have shown significant reduction in carbon monoxide (CO) and hydrocarbon (HC) emissions in all speeds, while nitrogen monoxide (NO) emission was significantly reduced from medium to high speeds, suggesting that NO reduction was highly influenced by reaction temperature. Highest reduction in CO emission was 59.61% at medium speed, while highest HC and NO emissions were 66.52% and 76.63%, respectively, at high speed. While further tests are recommended, results show the potential of modified Philippine natural zeolite as a cheap alternative material for three-way catalytic converters.