OF HYDROGEN PEROXIDE ON ANTIMONY AND BISMUTH ALLOYS 1055 Sept., 1958 THEDECOMPOSITION
THE DECOMPOSITION OF HYDROGEN PEROXIDE ON ANTIMONY AND BISMUTH ALLOYS BY P. P. CLOPPAND G. PARRAVANO’ T h e Franklin Institute Laboratories for Research and Development, Philadelphia, P a . Received March 3,1968
The rate of the decomposition of hydrogen peroxide on Sb and Bi alloys has been determined. Kinetic parameters have been correlated with changes in the electronic structure of Bi and Sb brought about by the alloying process. I n particular, the electronic electrochemical potential of Sb compounds can be qualitatively related to the activation energy of the catalytic reaction. These relationships are discussed in terms of present concepts on the catalytic activity of conducting surfaces.
The elucidation of the role played by the electronic structure of solid semi-conductors on their catalytic properties has been the subject of several recent investigations. These studies have been largely confined to metal oxides and related systems, while elemental semi-conductors and semi-metals have received less attention. The catalytic properties of germanium, tin, antimony and arsenic toward hydrogen and ammonia have been the subject of a thorough study.2 The activity of germanium, silicon and 111-V group compounds for the hydrogenation of formic acid also has been diswhile the chemisorption of several gases has been studied on semi-metals (As, Sb, Bi) and semi-conductors (Se, Te) . 4 From these studies correlations between the nature of the solid and catalytic activity have been deduced and a number of behavior patterns have emerged. It is, therefore, of interest t o explore additional systems in view of a critical evaluation of present concepts on the catalytic actian of conducting surfaces. We have investigated the reaction kinetics of the decomposition of hydrogen peroxide on bismuth and antimony alloys, because the general form of the electronic structure of these compounds is known and they occupy a bridge position between metals and metallic oxides. Experimental Materials.-Bi alloys were made from pure components (McKay), with nominal composition of 0.1 atom % of alloying element, which, in all cases studied, is known to be completely soluble in Bi within the above composition range. GaSb and InSb were formed by direct combination of zone refined elements,6 in approximately stoichiometric proportions, in a zone refining apparatus filled with dry hydrogen.6 Samples produced in this fashion exhibited p-type conductivity; n-type materials were formed by doping with 1% Te alloy. Conductivity and d.c. Hall coefficient of InSb and GaSb were measured on samples with dimensions of approximately 1.0 em. by 0.1 em. by 0.3 em. Catalytic activity of both Bi and Sb alloys was measured on samples prepared by grinding the original
material in a diamond mortar (Bi alloys) or an agate mortar (Sb alloys). The ground material was fractionated by means of a series of standard sieves. The fraction collected was found to have a BET surface area of about 0.02 m.2/g. for all Bi alloys and 0.04 me2/g.for all Sb alloys. Hydrogen peroxide (Merck, Superoxol) was diluted with triple distilled water, allowed to stand a week before use and handled in steam-cleaned vessels. Potassium permanganate solutions were prepared following the usual procedure and standardized with National Bureau of Standards sodium oxalate. Standardization was checked every two weeks. Procedure.-The decomposition reaction was followed in a Pyrex glass, stirred vessel, kept a t constant temperature (fl”). At different time intervals, samples were withdrawn from the reactor and the extent of decomposition determined by titration of the remaining hydrogen peroxide with KMn04 solution. Titrations were performed in a flask containing 5 ml. of 10% H804 and 20 ml. of freshly distilled water, and carried out in the usual manner to an end-point at which the color remained for 30 see. Experimental conditions were carefully chosen as to eliminate diffusion effects as controlling factors of the reaction rate. No homogeneous catalyst was present. This fact was checked by stopping an experiment, removing the catalyst and testing for decomposition over an extended period of time. Measurements of conductivity and Hall effect of Sb compounds were made with a conventional d.c. method.? The electromagnetic field for Hall constant determination was electronically controlled to an accuracy of 3~0.02% and could be varied from zero to 5000 oersteds. Potential measurements were made with a Wenner thermo-free potentiometer. Stainless steel whiskers were used as potential probes and lightly welded to the specimens by a high voltage discharge from a Tesla coil. Current contacts were made with large area stainless steel springs. Samples were cut from grown crystals with a diamond saw, and etched.with a dilute ”03-HC1 etch. The reported measurements of conductivity and Hall constant were obtained a t 300°K.
Results It was found that the decomposition of hydrogen peroxide on all samples tested could be expressed by a first-order rate equation, which has frequently been found in the past to describe accurately t.he course of the reaction _ -d[H20z1 =
dt
(1) Department of Cheniical Engineering. University of Notre Dame, Notre Dame, Indiana. 59,777 (1955); K. Tamaru, M. Bou(2) K. Tamaru, THIEJOURNAL, dart and H. Taylor, ibid., 69, 801 (1955); P. J. Fensham. K. Tamaru, M. Boudart and H. Taylor, ibid., 69, 806 (1955): H. Taylor, Can. J . Chem., 83, 838 (1955); I
