Two-Step Hydrothermal Synthesis of Fly Ash-Based β Zeolite and Its Application in Catalytic Oxidation of NO with H2O2

Fly ash, a solid waste rich in silicon (Si) and aluminum (Al), offers significant potential for valorization through the high-value synthesis of zeolites, exemplifying the waste-to-wealth approach. We determined the optimal synthesis conditions for FA-β zeolite using the alkali fusion hydrothermal synthesis method, with fly ash as the primary raw material. The conditions included a NaOH/FA ratio of 1.2, a SiO2/Al2O3 ratio of 30, an H2O/Al2O3 ratio of 1200, a TEAOH/Al2O3 ratio of 14, a β-seed addition of 7.5%, and hydrothermal conditions of 140 °C for 72 h. XRD and FTIR analyses confirmed that the diffraction peaks of the synthesized fly ash-based zeolite align well with the standard pattern of commercial β zeolite. Removal experiments indicated that the efficiency of nitrogen oxides removal hinges on the adequate oxidation of NO. Under optimized conditions, the FA-β zeolite demonstrated a removal efficiency of 83%. ESR analysis revealed that the removal mechanism involves the oxidative elimination of NO, catalyzed by FA-β zeolite through the decomposition of H2O2 to OH radicals. This novel synthesis method, which utilizes fly ash as the raw material to prepare β zeolite, offers advantages in terms of cost-effectiveness and environmental protection. It holds significant potential for applications in environmental conservation.