Multi-walled carbon nanotubes (MWNTs) as an efficient catalyst for catalytic wet air oxidation of phenol
Introduction
Carbon nanotubes (CNTs) have attracted a lot of interests in the synthesis, characterization and applications due to their unique structural, mechanical and electronic properties since their discovery in 1991 [1], [2], [3]. In the catalytic field, CNTs have received extensive attention since they represent a novel class of advanced materials for catalytic applications [4]. As a support of heterogeneous catalysts, CNTs have shown more advantages than conventional supports in some catalytic reactions [4], [5], [6], [7], [8]. Wet air oxidation (WAO) is one of the chemical oxidation methods to convert organic pollutants to CO2, H2O and innocuous end products at high temperature (125–320 °C) and pressure (0.5–20 MPa) [9], [10]. The addition of catalysts could effectively decrease reaction temperature and pressure, and enhance the oxidation ratio of organic compounds [11], [12], [13]. Pt, Ru, and Cu catalysts supported on the multi-walled carbon nanotubes (MWNTs) exhibit good activity in catalytic wet air oxidation (CWAO) of nitrogen containing pollutants [14], [15], [16]. We focus our efforts on developing the effective catalytic systems to treat industrial wastewater using easily available catalysts.
In this paper, we present the MWNTs as a catalyst, treat the MWNTs with the different acid, and select phenol as the target compound for CWAO. The catalytic activity is obviously evaluated using the functional MWNTs at a bath reactor. The structure of the MWNTs is studied with SEM, TEM and FT-IR spectra. A mechanism in CWAO of phenol is also investigated and proposed.
Section snippets
Materials
The MWNTs, prepared by the chemical vapor deposition (CVD) over Fe/Al2O3 catalyst [17], were obtained from Tsinghua_Nafine nano-powder Commercialization Engineering Center. The MWNTs are ID 3–10 nm, OD 6–20 nm, ratio of length to diameter 100–1000, and specific surface area of 194 m2/g. The raw MWNTs contain amorphous carbon and catalyst particles, and the purity is >99.5%.
Purification and functionalization of the MWNTs
Fe/Al2O3 catalyst in the MWNTs was removed by sonicating the materials in 37% HCl during 20 min. The obtained mixture was kept
SEM of the MWNTs
SEM is used to observe the morphologies of the MWNTs. Fig. 1 illustrates SEM images of the MWNTs. Raw MWNTs contain some impurities [17]. In the morphologies of MWNTs-A and MWNTs-B, the impurities are not observed. Moreover, EDX analysis indicates that the metal catalyst attached to the nanotubes is removed. For the MWNTs treated with the acid, the length is not changed, and most of the nanotubes are several microns long. Fig. 1c shows the morphology of the MWNTs-B after CWAO of phenol. The
Conclusion
The effective oxidation reaction system with the MWNTs-B as a catalyst for CWAO of phenol is reported in the paper. It is observed that:
- •
The MWNTs-B are directly used as a catalyst, and exhibit an excellent activity in CWAO of phenol.
- •
About 100% phenol and 76% TOC are removed after 120 min reaction at a reaction temperature of 160 °C, oxygen partial pressure of 2 MPa and phenol concentration of 1000 mg/L.
- •
The MWNTs materials could be used not only as supports but also as the catalysts for the
Acknowledgement
The work is supported by the National Natural Science Foundation of China (No. 50508017).
References (27)
- et al.
J. Catal.
(2004) - et al.
Appl. Catal. A
(2003) - et al.
J. Catal.
(2006) - et al.
Chem. Phys. Lett.
(2006) Catal. Today
(1999)- et al.
Appl. Catal. B
(2003) - et al.
Appl. Catal. B
(2000) - et al.
Appl. Catal. B
(2004) - et al.
Catal. Commun.
(2006) - et al.
Appl. Catal. B
(2004)
Carbon
Chem. Phys. Lett.
Water Res.
Cited by (63)
Degradation and mineralization of oxalic acid using catalytic wet oxidation over carbon coated ceramic monoliths
2021, Journal of Environmental Chemical EngineeringMetal-free carbon materials as catalysts for wet air oxidation
2020, Catalysis TodayCarbon nanotubes catalysis in liquid-phase aerobic oxidation of hydrocarbons: Influence of nanotube impurities
2019, Journal of Physics and Chemistry of SolidsRuthenium-decorated carbon nanotubes as catalyst for wet air oxidation
2019, Journal of Environmental Chemical EngineeringIntegrated oxidation process and biological treatment for highly concentrated petrochemical effluents: A review
2018, Chemical Engineering and Processing - Process Intensification