Metal substitution of natural zeolites clinoptilolite and mordenite via hydrothermal dealumination and atom planting for catalytic applications
Zeolites are mesoporous natural or synthetically prepared aluminosilicate materials widely used as adsorbates, waste remediation agents, and catalysts. Due to the complexity of the synthetic process, there has been growing interest to modify readily available natural zeolites, thus transforming them into valuable active zeolite materials. Dealumination of a parent zeolite material, achieved through chemical and physical processing, produces stable reactive defect sites that can be subsequently utilized to insert new desired atoms into the structure. This study performs an in-depth analysis of each intermediary step necessary for metal substitution of natural zeolites to be successful. The results presented shows the successful controlled dealumination of zeolite mordenite using a hydrothermal process followed by washing to remove the extra-framework aluminum. Successful "atom planting" of aluminum (III) using AlCl3 and titanium (IV) using TiCl4 was performed on the dealuminated material as well as the non-modified material. Attenuated Total Reflectance Infrared Spectroscopy (ATR FTIR), solid state Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy (ss MAS NMR), and Diffuse Reflectance Ultraviolet Spectroscopy (DRUV) was utilized to monitor the dealumination and atom-planting structural changes in the material throughout the modification process. The newly modified zeolite hopefully is expected to exhibit novel catalytic properties not shown by the starting material.