Study of W/HZSM-5-based catalysts for dehydro-aromatization of CH4 in absence Of O-2. 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 stud ied. Under reaction conditions of 0.1 MPa, 1073 K, GHSV of feed-gas CH4 + 1 0% 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, similar to 18, similar to5 and similar to 22%, respectively. Addition of a small amount of CO2 (less than or equal to2%) to the feed-gas was found to significantly enhance the conversion of methan e and the selectivity of benzene, and to improve the performance of coke-re sistance of the W/HZSM-5-based catalysts. Heavy deposition of carbon on the surface of the functioning catalyst was the main reason leading to deactiv ation of the catalyst. Reoxidation by air may regenerate the deactivated ca talyst 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 th e Mo/HZSM-5 catalyst operating at 973 K. It can also operate at 973 K and h ave 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 per formance; the high reaction temperature did not lead to loss of W component by sublimation.