Recycling the copper based spent catalyst for catalytic combustion of VOCs

The catalytic combustions of benzene, toluene and o-xylene (BTX) were investigated over the copper based spent catalyst and the pretreated copper based spent catalysts as well. Air, hydrogen and five different acid aqueous solution (HNO3, CH3COOH, H2SO4, HCl, and H3PO4) pretreatments were employed to recycle the spent catalyst from chemical industry. The properties of the pretreated spent catalysts were characterized by the Brunauer Emmett Teller (BET), elemental analyzer (EA), inductively coupled plasma (ICP), temperature programmed reduction (TPR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. The results showed that while the air pretreatment had an insignificant effect on the catalytic activity of the spent catalyst, the hydrogen pretreatment significantly enhanced that of the spent catalyst. The temperature of hydrogen pretreatment also made a significant difference in its catalytic activity. Furthermore, the increasing pretreatment temperature increased the catalytic activity of the spent catalyst, which was associated with the lower copper oxidation state (or reduced state). In acid pretreatment, the order of catalytic performance of the pretreated spent catalyst according to each acid aqueous solution was found to be HNO3 > CH3COOH > none > HCl > H3PO4 > H2SO4. Nitric acid or acetic acid pretreatment slightly improved the catalytic activity of the spent catalyst by regenerating the active sites on the pretreated samples. The XRD, XPS and TPR results clearly supported that all copper species such as CuO, Cu2O and Cu0 were active, among which Cu0 was the most active for the removal of toluene. Hydrogen pretreatment was superior to air or acid pretreatments for regenerating the spent catalyst because it favored the generation of metallic coppers. Based on the results of a long-term test and the catalytic activity of BTX, we suggested that the copper based spent catalyst pretreated with hydrogen could be recycled for the removal of volatile organic compounds (VOCs).