ChemInform Abstract: Electrocatalytic Reduction of Sulfuric Acid to Hydrogen Sulfide by a Trinuclear Niobium Cluster.

Abstract

It is thought that metal cluster compounds hold great potential as catalysts for the multiple-electron reduction of small molecules, since they contain several metal atoms in close proximity, available for multiside bonding. However, very few examples of catalysis by metal clusters have been documented so far. In the course of the electrochemical investigation of Nb(5+) in H{sub 2}SO{sub 4} and the mechanism for the formation of the trinuclear cluster anion [Nb{sub 3}O{sub 2}(SO{sub 4}){sub 6}(H{sub 2}O){sub 3}]{sup 5{minus}}, the authors found that the niobium cluster electrocatalyzes the reduction of 12 M H{sub 2}SO{sub 4} to H{sub 2}S on a Hg electrode at room temperature at -1.2 V vs Hg/Hg{sub 2}SO{sub 4} (-0.6 V vs NHE). The reduction of sulfate to sulfide is an important step in the sulfur biological cycle. In plants and some bacteria, the reduction is achieved through several intermediate steps, each requiring a different enzyme. Concentrated H{sub 2}SO{sub 4} can be reduced by a variety of metals at elevated temperatures (>230 {degrees}C) to H{sub 2} and SO{sub 2}. With Zn and Cd, some H{sub 2}S and elemental S depending upon the I{sup {minus}}/I{sub 2} concentrations. This latter reaction, however, required solid KI and was not established tomore » be catalytic.« less