Hydrogen peroxide formation in the interaction of oxygen with boron-containing Pd catalysts prereduced by hydrazine in a
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Catalysis Letters Vol. 99, Nos. 1–2, January 2005 (Ó 2005)
Hydrogen peroxide formation in the interaction of oxygen with boron-containing Pd catalysts prereduced by hydrazine in aqueous acidic medium containing bromide anions Vasant R. Choudhary* and Chanchal Samanta Chemical Engineering and Process Development Division, National Chemical Laboratory, Pune 411008, India
Received 22 July 2004; accepted 15 September 2004
Interaction of molecular oxygen with Pd/BPO4 or ZrO2 (or Al2 O3 , CeO2 , TiO2 )–B2 O3 catalysts, prereduced by hydrazine hydrate, in an aqueous acidic (H2 SO4 or H3 PO4 ) reaction medium containing bromide ions leads to the formation of H2 O2 . However, in the absence of boron in the catalyst and also in the absence of acid and/or bromide ions in the reaction medium, almost no H2 O2 is formed. KEY WORDS: boron-containing Pd catalysts; hydrogen peroxide; oxygen–catalyst interactions.
1. Introduction Hydrogen peroxide is a versatile and environmentally friendly oxidizing agent. Its demand in the textile and paper/pulp industries as a bleaching agent, water purification/disinfection, wastewater treatment and catalytic oxidation processes for the synthesis of fine/bulk chemicals has been increasing day-by-day. It is mostly produced by the anthraquinone process [1], which is based on indirect oxidation of H2 , involving multiple reactions and processing steps, and also suffers from a number of drawbacks. This process is not environfriendly and the cost of H2 O2 produced is high. Hence, efforts are being made to produce H2 O2 by the direct catalytic oxidation of H2 by O2 using Pd catalysts [2–11]. However, because of the very broad explosion limits of O2 –H2 gas mixture (4–96% H2 in O2 ), the direct H2 –to– H2 O2 oxidation is highly hazardous one. It is, therefore, of great practical interest to find some non-hazardous new route for the production of H2 O2 . We report here our preliminary observations indicating the formation of H2 O2 in the interaction of O2 with boria containing supported palladium catalysts, prereduced by hydrazine, in aqueous acidic medium containing bromide ions. The H2 O2 formation is non-hazardous, but it requires the presence of boron in the catalyst, the prereduction of the catalyst by hydrazine, and also the presence. of mineral acid and bromide ions in the aqueous reaction medium. 2. Experimental The supported palladium catalysts with Pd loading of 2.5 wt% (Table 1) were prepared by impregnating PdCl2 *To whom correspondence should be addressed. E-mail: [email protected]; [email protected]
from its acetonitrile solution on boron phosphate or respective metal oxide support (with or without containing boron) by incipient wetness technique, drying the impregnated.mass in air oven at 100 C for 2 h and then calcining it at 500 C under static air for 3 h. The ZrO2 – B2 O3 , CeO2 –B2 O3 , TiO2 –B2 O3 and Al2 O3 –B2 O3 catalyst supports were prepared by mixing boric acid (H3 BO3 ) with respective metal oxide [ZrO2 (prepared from zirconyl nitrate by its hydrolysis to zirconium hyd
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