The identification of active chromium species to enhance catalytic behaviors of alumina-based catalysts for sulfur-containing VOC abatement

As to the treatment of sulfur containing VOCs (examples are compounds of CH3SH and C2H5SH), finding a catalyst with high performance is necessary. In this work, Cr-(x)-Al2O3 (x = 1.0, 2.5, 5.0, 7.5 and 10 wt%) catalysts were synthesized, and their behaviors toward CH3SH and C2H5SH abatement were investigated. The results indicated that Cr-(7.5)-Al2O3 exhibited higher activity than other samples and the reported catalysts, on which CH3SH could be almost completely converted at 375 degrees C, while the temperature for the reported catalysts was above 450 degrees C. Moreover, there was no obvious deactivation during 30 h on stream over Cr-(7.5)-Al2O3, while only about 10 h was found on the reported CeO2 and HZSM-5 catalysts. The improvement in the catalytic performance could be explained by the important role of the Cr6+ species, while the state of Cr3+ was suggested to be ineffective in the degradation process. The identification of the active Cr sites was proved by the characterization measurements, and the control experiments by using mechanical mixtures of CrO3 or Cr2O3 with Al2O3 as well as the comparison studies between spent Al2O3 and spent Cr-(7(.5))-Al2O3 catalysts.