Elsevier

Applied Catalysis A: General

Volume 451, 31 January 2013, Pages 282-288
Applied Catalysis A: General

Influence of calcination temperature on the structure and catalytic performance of CuOx-CoOy-CeO2 ternary mixed oxide for CO oxidation

https://doi.org/10.1016/j.apcata.2012.10.023Get rights and content

Abstract

Influence of calcination temperature (400−800 °C) on the structure and catalytic activity of CuOx-CoOy-CeO2 ternary mixed oxide (atomic Cu:Co:Ce ratio of 1:5:5) prepared by co-precipitation method is investigated by N2 physisorption, XRD, TPR, TEM, TG-DTA, XPS, and CO oxidation reaction. The as-synthesized CuOx-CoOy-CeO2 undergoes successive structural changes with the calcination temperature, involving the hydroxide dehydration below 400 °C, enhanced interaction between Co3O4 and CeO2 at ca. 600 °C, and Co3O4 decomposition to CoO at 700 °C. The catalyst calcined at 600 °C shows a relative enrichment of Cu+ on the surface of CuOx-CoOy-CeO2 and an enhanced interaction between Co3O4 and CeO2 along with the appearance of oxygen vacancies in CeO2, which seems to be responsible for its highest catalytic activity for CO oxidation among all the tested catalysts. The complete conversion of CO is obtained at 70 °C and about 50% of CO conversion is reached at 55 °C.

Highlights

► Mutual interaction between Co3O4 and CeO2 is involved during calcination of the catalyst. ► Oxygen vacancies are beneficial to achieve interaction between Co3O4 and CeO2. ► Enrichment of Cu and Co on the surface of as-prepared catalysts is found. ► Complete CO conversion over CCC600 is obtained at 70 °C and about 10% of CO conversion is reached at 30 °C.

Introduction

In the past decades, CeO2-based catalysts have received much attention because of their application in the three-way catalysts to eliminate vehicle exhaust [1], [2]. It has also been found that the CeO2-based catalysts doped with cobalt- and/or copper-oxides may achieve higher catalytic performance [3], [4], [5]. For example, Labhsetwar and co-workers [6] reported that a promotional effect of Co-oxide was responsible for the excellent catalytic activity of Co3O4-CeO2 for diesel soot oxidation. Liotta et al. [7] synthesized Co3O4/CeO2-ZrO2 for methane combustion. A stabilizing effect due to the presence of CeO2-ZrO2 against Co3O4 decomposition into CoO was observed.

Metal oxides with high thermal stability and surface area are usually good for use as catalysts and catalyst supports. Preparation conditions, especially calcination temperature, have a great effect on their physicochemical structure (e.g., texture, particle size, crystalline phase, surface composition, and oxidation state) and consequently catalytic performance [8], [9], [10], [11], [12], [13], [14], [15]. Galetti et al. [8] have studied the effect of calcination atmosphere and nature of catalytic precursors on the catalytic performance of Ni catalysts supported ZnAl2O4 modified by cerium addition for the ethanol steam reforming reaction. They claimed that the catalysts obtained from nitrate salt impregnation were the most carbon resistance and those obtained under reductive atmosphere were the most stable, compared with the catalyst obtained from acetate solution. Jung et al. [11] have investigated the influence of calcination on the properties of CeO2-based catalysts. And they found that the morphology and chemical properties of the catalysts heavily depend on the calcination temperatures. It is also reported that cobalt-oxides produced by thermal decomposition of their carbonates, nitrates or hydroxides at moderate temperatures of 400–600 °C were claimed to exist mainly as Co3O4 [16], [17]. However, Kang et al. [17] reported that the temperature higher than 700 °C leads to the decomposition of Co3O4 into CoO and simultaneously formation of surface CoAl2O4 spinel due to the diffusion of Co2+ ions into the lattice of Al2O3 support. Likewise, CuO and CeO2 are both sensitive to the temperature of thermal treatment [18], [19], [20]. Specifically, CuO is easy to aggregate and sinter when heated at high temperatures [18], which would give rise to the loss of its catalytic activity.

In the present work, we investigate the influence of calcination temperature on the structure and catalytic performance of CuOx-CoOy-CeO2 ternary mixed oxide. Catalytic CO oxidation is used as a probing reaction, and the catalyst structures are characterized by a variety of techniques such as N2 physisorption, XRD, TEM, TPR, TG-DTA, and XPS to understand the relationship between structure and catalytic activity.

Section snippets

Catalysts preparation

CuOx-CoOy-CeO2 with Cu:Co:Ce atomic ratios equal to 1:5:5 was synthesized by co-precipitation method. 0.2416 g Cu(NO3)2·3H2O and appropriate amounts of Ce(NO3)3·6H2O and CoCl2·6H2O were dissolved in 100 ml deionized water at room temperature and stirred for 15 min, followed by dropwise addition of 100 ml NaOH solution (0.375 M) under vigorous stirring. After stirring for 30 min, the obtained precipitate was centrifuged and washed with 150 ml deionized water and then 150 ml anhydrous ethanol. The

Catalytic CO oxidation

Fig. 1 shows the light-off curves of CO oxidation over CuO-Co3O4-CeO2 calcined at the temperatures from 400 to 800 °C. As expected, CO conversion for all the catalysts increases with the reaction temperatures. The catalyst activity is evaluated by the reaction temperature (T50) at which CO conversion reaches 50%, and has a strong dependence on the calcination temperature. T50 over CCC400 is 80 °C, and decreases to 55 °C with the elevation of calcination temperature to 600 °C. The further increase

Discussion

Calcination is of great importance for preparing nano-sized metal oxides and tuning their structure and catalytic performance for CO oxidation [13], [15], [28]. For the as-prepared CuOx-CoOy-CeO2 catalyst, its structure undergoes successive changes with the elevation of calcination temperature, including desorption of adsorbed water, dehydration of hydroxides, enhanced mutual interaction of oxides, and decomposition of Co3O4 to CoO. The desorption process of absorbed water occurs at the

Conclusions

In summary, calcination plays a significant role in the catalytic activity of CuOx-CoOy-CeO2 for CO oxidation. This process may shape the properties of the as-prepared catalysts. In accordance with the calcination temperatures, the processes may include several steps such as desorption of adsorbed water, dehydration of hydroxides, mutual interaction among the metal oxide species and decomposition of Co3O4 to CoO. In these steps, mutual interaction between Co3O4 and CeO2 plays a key role in

Acknowledgements

This research is sponsored by the Division of Chemical Science, Office of Basic Energy Sciences, U.S. Department of Energy. The research (ZL, YL, LJ) is also supported partly by the Heavy Oil State Key Laboratory in China.

References (43)

  • M.V. Twigg

    Appl. Catal. B

    (2007)
  • M. Shelef et al.

    Catal. Today

    (2000)
  • B. Thirupathi et al.

    Appl. Catal. B

    (2011)
  • A. Fuerte et al.

    J. Power Sources

    (2011)
  • Z.G. Liu et al.

    J. Mol. Catal. A

    (2007)
  • M. Dhakad et al.

    Catal. Today

    (2008)
  • L.F. Liotta et al.

    Catal. Commun.

    (2005)
  • A.E. Galetti et al.

    Appl. Catal. A

    (2011)
  • P. Li et al.

    Appl. Catal. B

    (2011)
  • X. Cui et al.

    J. Catal.

    (2011)
  • C.R. Jung et al.

    Catal. Today

    (2004)
  • K. Li et al.

    Int. J. Hydrogen Energy

    (2011)
  • E. Poggio et al.

    Int. J. Hydrogen Energy

    (2011)
  • A.L. Camara et al.

    J. Power Sources

    (2011)
  • J.L. Cao et al.

    Appl. Catal. B

    (2008)
  • H.C. Liu et al.

    J. Power Sources

    (2007)
  • M. Kang et al.

    Appl. Catal. A

    (2003)
  • T.J. Huang et al.

    Appl. Catal.

    (1989)
  • S.W. Oh et al.

    J. Power Sources

    (2007)
  • P. Djinovic et al.

    Appl. Catal. A

    (2008)
  • L.F. Liotta et al.

    Appl. Catal. B

    (2007)
  • Cited by (52)

    • Enhanced hydrothermal durability of Co<inf>3</inf>O<inf>4</inf>@CuO–CeO<inf>2</inf> Core-Shell catalyst for carbon monoxide and propylene oxidation

      2022, Applied Surface Science
      Citation Excerpt :

      This was attributed to the increased amount of Cu, which blocked the active sites of the interface. Furthermore, CuO was converted to Cu0 metal at a high temperature [65], and the catalyst was subsequently sintered [66–68]; thus, the oxidation activity was diminished. The T50 for the C3H6 are listed in Table 3; accordingly, the order of oxidation activity of the fresh catalysts was Co@2CeO2 < Co@1Cu–2CeO2 < Co@2Cu–2CeO2 < Co@4Cu–2CeO2 < CCC, and that at T90 was Co@2CeO2 < Co@2Cu–2CeO2 < Co@1Cu–2CeO2 < Co@4Cu–2CeO2 < CCC.

    • Preparation and reaction mechanism of novel Ce<inf>x</inf>Co<inf>y</inf>Cu<inf>z</inf> oxide composite catalysts towards oxidation of o-xylene

      2022, Journal of Rare Earths
      Citation Excerpt :

      As displayed in Fig. 4, the broad peak at 480 °C for Ce1Co1/3DOM corresponds to the reduction of surface Ce4+ to Ce3+. The two broad peaks at 274 and 331 °C are identified as the reduction of Co3O4 to CoO and CoO to metallic Co, respectively.29 The peak at 122 °C is attributed to the reduction of CuO species that interacted closely with Co3O4 and CeO2 for Ce1Co1Cu1/3DOM, as shown in Fig. 5.30

    View all citing articles on Scopus
    View full text