Textural and catalytic properties of Mo loaded hierarchical meso-/microporous lamellar MFI and MWW zeolites for direct methane conversion

The consequences of meso-/microporous zeolite structures on distribution and activity of active sites (Brønsted acid and metal sites) in molybdenum (Mo) impregnated lamellar MFI and lamellar MWW zeolites were investigated in direct methane aromatization (DMA) reactions. In comparison with their microporous analogies (Mo/MFI and Mo/MWW), the mesopores in the Mo/lamellar MFI and Mo/lamellar MWW zeolites facilitated the dispersion of Mo in zeolite micro-channels. The catalytic DMA reactions showed that the Mo loaded lamellar MFI and lamellar MWW zeolites enabled efficient methane conversion, aromatic product formation, and coke accumulation in the initial stage of reaction, while their performances were similar to those of Mo/MFI and Mo/MWW catalysts in the long term run. A plausible explanation to this scenario is that active sites in Mo/lamellar MFI and Mo/lamellar MWW can be accessed by reactants through both micropores and mesopores. The facilitated transport and accessibility to active sites by mesopores accounted for initial fast reaction and deactivation rates of Mo loaded lamellar zeolites. After mesopores were clogged by deposited coke in DMA reactions, micropores of zeolites were responsible for the long term catalyst performances, which were similar to Mo loaded microporous zeolites.