Preparation of Mn-Co/Ceramic Honeycomb Catalyst and Its Performance on Catalytic Ozonation of Hydroquinone

Abstract

In order to improve the activity and working life of metal catalysts in the heterogeneous catalytic ozonation of organic wastewater, four kinds of Mn-Co/ceramic honeycomb (CH) catalysts with different mass ratios of Mn and Co were prepared by coating method using cobalt nitrate hexahydrate [Co(NO3)2·6H2O] and manganese nitrate [Mn(NO3)2] as precursors, respectively, and CH as the carrier. The structure of the catalysts was analyzed via X-ray diffraction (XRD), N2 adsorption/desorption, field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). The mechanical properties of the catalysts were studied. The reaction kinetics model of O3 alone and catalytic ozonation of the hydroquinone were established and catalytic ozonation performance of catalysts was investigated. The results showed that the crystal phase of Mn0Co1/CH belonged to CoAl2O4 and that the crystal phase of the Mn-Co/CH catalyst (Mn1Co1, Mn2Co1, and Mn3Co1) mainly belonged to Mn3O4 and CoO. In particular, the Mn1Co1/CH catalyst had a large specific surface area of 190 m2·g-1, high pore volume of 0.25 cm3·g-1, and pore size of 4.8 nm. The highest catalytic activity was obtained when Mn∶Co was 1∶1 (Mn1Co1/CH catalyst). The catalytic activity of the Mn1Co1/CH catalyst was the highest, and removal efficiencies of hydroquinone and COD were 78% and 54%, respectively, using Mn1Co1/CH catalytic ozonation. The Mn-Co/CH catalyst had a high compressive strength (15.89-16.94 MPa). The degradation efficiency of hydroquinone decreased significantly after the addition of tert-butanol, which indicated that·OH played an important role in the Mn1Co1/CH catalytic ozonation. The catalytic ozonation process fitted the first-order kinetic model. The apparent rate constant k for O3 alone was only 0.0306. Furthermore, the Mn1Co1/CH catalyst had the highest rate, with an apparent rate constant k of 0.0535 min-1. The Mn-Co/CH catalyst was easy to industrialize owing to its lower consumption, excellent catalytic characteristics, and long working life.