Multi-walled carbon nanotubes (MWNTs) as an efficient catalyst for catalytic wet air oxidation of phenol

doi:10.1016/j.catcom.2007.04.015

Catalysis Communications

Volume 8, Issue 12, December 2007, Pages 2059-2063

https://doi.org/10.1016/j.catcom.2007.04.015 Get rights and content

Abstract

Multi-walled carbon nanotubes (MWNTs) were used as a catalyst for catalytic wet air oxidation (CWAO) of phenol in a batch reactor. SEM, TEM and FT-IR technique were applied to investigate the microstructure and the surface functional group of the MWNTs. When the carboxylic groups (–COOH) are grafted onto the surface of the MWNTs, the functionalized MWNTs exhibit a good catalytic activity in CWAO of phenol. At a reaction temperature of 160 °C, oxygen pressure of 2.0 MPa and a phenol concentration of 1000 mg/L, 100% phenol and 76% TOC are removed after 120 min reaction.

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:

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The MWNTs-B are directly used as a catalyst, and exhibit an excellent activity in CWAO of phenol.
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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.
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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).

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Multi-walled carbon nanotubes (MWNTs) as an efficient catalyst for catalytic wet air oxidation of phenol

Abstract

Introduction

Section snippets

Materials

Purification and functionalization of the MWNTs

SEM of the MWNTs

Conclusion

Acknowledgement

J. Catal.

Appl. Catal. A

J. Catal.

Chem. Phys. Lett.

Catal. Today

Appl. Catal. B

Appl. Catal. B

Appl. Catal. B

Catal. Commun.

Appl. Catal. B

Carbon

Chem. Phys. Lett.

Water Res.