Elsevier

Catalysis Today

Volume 104, Issues 2–4, 30 June 2005, Pages 323-328
Catalysis Today

Preparation, performances and reaction mechanism for the synthesis of H2O2 from H2 and O2 based on palladium membranes

https://doi.org/10.1016/j.cattod.2005.03.054Get rights and content

Abstract

A series of new tubular catalytic membranes (TCM's) have been prepared and tested in the direct synthesis of H2O2. Such TCM's are asymmetric α-alumina mesoporous membranes supported on macroporous α-alumina, either with a subsequent carbon coating (CAM) or without (AAM). Pd was introduced by two different impregnation techniques. Deposition–precipitation (DP) was applied to CAM's to obtain an even Pd particles distribution inside the membrane pore network, whereas electroless plating deposition (EPD) was successfully applied to AAM's to give a 1–10 μm thick nearly-dense Pd layer. Both type of membranes were active in the direct synthesis of H2O2. Catalytic tests were carried out in a semi-batch re-circulating reactor under very mild conditions. Concentrations as high as 250–300 ppm H2O2 were commonly achieved with both CAM's and AAM's after 6–7 h time on stream, whereas the decomposition rate was particularly high in the presence of H2. Important features are the temperature control and pre-activation. In order to slow down the decomposition and favor the synthesis of H2O2 a smooth metal surface is needed.

Introduction

Hydrogen peroxide is a commodity which, today, is almost exclusively produced by the anthraquinone process [1]. This process is economically feasible only on large-scale plants. Additionally, the final price of H2O2 produced is deeply influenced by the complexity of the process and by the costly separation and concentration steps needed. Direct synthesis, which could be a more economic and “green” alternative, has been known since the beginning of the XXth century [2] and many patents have been filed even during the last 30 years [3], [4], [5], [6], [7], [8], [9], [10], [11], however only a few scientific papers have been published in the open literature [12].

To date, no industrial application has ever been accomplished, even if some successful attempts have been realized at DuPont during 1980's [3]. This is because two severe drawbacks have to be overcome: (i) the formation of explosive H2/O2 mixtures that should be avoided and (ii) the selectivity of the reaction (whose main product is water) that should be improved. Recently, the use of especially designed catalytic membranes could have been suggested to overcome both problems [10], [11], [12].

Section snippets

Experimental

Two types of tubular membranes have been prepared, loaded with Pd and tested in the direct synthesis of H2O2.

α-Alumina asymmetric membranes (AAM)

A dense Pd film was deposited on such supports by EPD, as stated in the Section 2.

After thermal treatment in inert atmosphere at different temperatures, two kind of surfaces could be obtained: (i) a rough and disordered surface after a thermal treatment in inert gas at 800 °C, as shown in Fig. 2(a) and (ii) a surface formed of well developed crystallites after a thermal treatment at 500 °C (Fig. 2(b)). A notable difference in reactivity was observed for these two different surfaces (Fig. 3):

Conclusions

Tubular catalytic membranes are able to catalyze H2O2 synthesis under mild conditions (2–3 bar H2, 5–25 °C) with a fair productivity (∼2 mmol H2O2 gPd−1 min−1). Regardless of the type of membrane, catalytic activity depends on: (i) the oxidation state of surface Pd atoms (a pre-oxidation step is needed); (ii) the temperature (temperatures as low as 2–5 °C favor H2O2 synthesis over decomposition). In addition, the decomposition of H2O2 on tested catalysts mainly proceeds via its reduction by H2.

Acknowledgements

Financial support from EU (contract No. G5RD-CT2002-00678) is gratefully acknowledged. The authors are indebted to HITK e.V. and Mast Carbon Ltd. for kindly providing the α-alumina tubular membranes and the carbon coating. Finally the authors thank Dr. Ing. Roland Dittmeyer and Mr. Karel Svajda from DECHEMA e.V. for useful discussions.

References (15)

  • L.A.M. Hermans et al.

    Stud. Surf. Sci. Catal.

    (1979)
  • A.J. van Dillen et al.
  • H.-J. Riedl, G. Pfleiderer, US Patent No. 2,215,883...
  • H. Henkel, W. Weber (Henkel & Cie), US Patent No. 1,108,752...
  • L.W. Gosser (Du Pont), US Patent 4,681,751...
  • L. Kim, G.W. Schoenthal (Shell Oil), US Patent No.4,007,256...
  • J. Van Weynbergh, J.-P. Schoebrechts, J.-C. Colery (Solvay Interox), PCT Patent No. WO92/15520...
There are more references available in the full text version of this article.

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