Research on the MgO-supported solid-base catalysts aimed at the sweetening of hydrogenated gasoline

The gas–liquid–solid heterogeneous base-catalyzed oxidation of n-octane thiol and tert-butyl thiol by molecular oxygen was investigated. The activity and stability of MgO-supported NaOH and monometallic Cu, Ni as well as bimetallic Cu–Ni catalysts were studied. The catalysts were further characterized by XRD, FT-IR, XPS and EPR. Compared with commercial cobalt phthalocyanine catalyst (CoPc catalyst), the MgO-supported bimetallic Cu–Ni catalyst displayed an enhanced stability to the oxidation of iso-mercaptan, and the catalytic lifetime is 10 h longer than that of CoPc catalyst. It is found that the superoxide anions result from defects and small crystalline size play an important role in conversion of the iso-mercaptans, the more the lattice distortion, the higher the amount of surface adsorbed oxygen, the better was the performance of the sweeten-catalyst. Moreover, compared with commercial CoPc catalyst, the NaOH-rich catalyst is more resistant to deactivation of the oxidation of long chain thiol, and the catalytic lifetime is 26 h longer than that of CoPc catalyst. The superbasicity of the NaOH-rich catalyst is responsible for the formation of mercaptide ion, which is the rate-controlling step for the oxidation of long chain thiol. The mercaptans of different structures conform to different reaction mechanisms.