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 10h 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 26h 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.