Study of W/HZSM-5-Based Catalysts for Dehydro-aromatization of CH4 in Absence of O2. I. Performance of Catalysts

With incorporation of Zn (or Mn, La, Zr ) into the W/HZSM-5 catalyst, highly active and heat-resisting W/HZSM-5-based catalysts were developed and studied. Under reaction conditions of 0.1 MPa, 1073 K, GHSV of feed-gas CH₄+10% Ar at 960 h^–1, the conversion of methane reached 18–23% in the first 2 h of reaction, and the corresponding selectivity to benzene, naphthalene, ethylene and coke was 56–48, 18, 5 and 22%, respectively. Addition of a small amount of CO₂ (2%) to the feed-gas was found to significantly enhance the conversion of methane and the selectivity of benzene, and to improve the performance of coke-resistance of the W/HZSM-5-based catalysts. Heavy deposition of carbon on the surface of the functioning catalyst was the main reason leading to deactivation of the catalyst. Reoxidation by air may regenerate the deactivated catalyst effectively. In comparison with the Mo/HZSM-5 catalyst, the promoted W/HZSM-5-based catalyst can operate under reaction temperature of 1073 K, and gain a methane conversion approximately two times as high as that of the Mo/HZSM-5 catalyst operating at 973 K. It can also operate at 973 K and have about the same methane conversion as that of the Mo/HZSM-5 catalyst at the same reaction temperature. Its main advantage is its heat-resistant performance; the high reaction temperature did not lead to loss of W component by sublimation.