MCM-41 impregnated with active metal sites: Synthesis, characterization, and ammonia adsorption

Abstract

Active metal sites incorporated into nanoporous materials have shown potential as novel catalytic adsorbents for the removal of toxic industrial chemicals from air. This work explores the effects of the metal cation, anion, metal oxidation state, pH, solubility, and drying temperature on the ammonia capacity of MCM-41-impregnated samples. The nitrates, chlorides, sulfates, and carbonates of zinc, copper, and iron have been successfully impregnated using a solution method into a mesoporous silica material and characterized via XRD, XPS, adsorption isotherms, and ammonia capacity. The conditioning temperature was found to have a major impact on the ammonia capacity of the impregnated samples. At both 120 °C and 250 °C, the metal type and anion type were determined to be statistically significant predictors of ammonia capacity and the pH and metal oxidation state were not. The solubility of the metal salt in water was also determined to be an ammonia capacity predictor. Overall, ZnCl 2 was found to be most effective at enhancing the ammonia capacity; consequently, this metal salt was analyzed in more detail. Impregnation amounts from 20 to 50 wt% ZnCl 2 in MCM-41 gave high ammonia capacities. The highest capacity achieved was 8.8 mol ammonia/kg adsorbent, which is more than four times the capacity of the base, unimpregnated MCM-41 material.