Hierarchical ZSM-5 based on fly ash for the low-temperature purification of odorous volatile organic compound in cooking fumes

Hierarchical ZSM-5 (HZ) zeolites with different SiO 2 /Al 2 O 3 ratios (SiO 2 /Al 2 O 3 = 50, 100, 150, 200, 250 and 300) were synthesized using a two-step hydrothermal treatment method, and the Al and Si were obtained from fly ash by the alkali melting and acid leaching method. On this basis, the 10 wt% LaMnO 3 /HZ catalysts were prepared by impregnation. The all the synthesized catalysts were investigated for the low-temperature (200 °C) catalytic oxidation of pentanal, which was selected as a typical odorous volatile organic compound (VOC) in cooking fumes. In addition, the physicochemical properties of HZ zeolites were characterized by several techniques (XRD, N 2 physical adsorption–desorption, ICP-OES, SEM,TEM,NH3-TPD and 27 Al MAS-NMR). The results showed that the HZ zeolite, which was micro-mesoporous material and had high specific surface area, provided a higher diffuser efficiency for long-chain VOC gas. The catalytic performance of HZ zeolite was better than that of the traditional ZSM-5 zeolite. Compared with the dry atmosphere, HZ-100 zeolite, which possessed more proper medium strong acid sites and the appropriate amount of acid sites, had the higher pentanal catalytic combustion conversion of above 92% and the relatively superior stability with 2 V% water steam in air, indicating that the suitable acid sites can form the best synergistic catalytic effect with water molecules for purifying long-chainVOC gas. In addition, the catalytic conversion of pentanal on 10 wt% LaMnO 3 /HZ-100 was 100% with no deactivation, and compared with HZ under a dry atmosphere, the average CO 2 yields of 10 wt% LaMnO 3 /HZ catalysts in the steady catalytic oxidation stage under a dry atmosphere and 2 V% water steam in air were improved by 6–18% and 13–20%.