THERMAL MULTIELECTRON TRANSFER CATALYSIS BY POLYOXOMETALATES - APPLICATION TO THE PRACTICAL PROBLEM OF SUSTAINED, SELECTIVE OXIDATION OF HYDROGEN-SULFIDE TO SULFUR

Novel polyoxometalate-based catalytic systems for the effective and se lective aerobic oxidation of H2S to S(O) are reported. The base stable catalysts TMA(9)[Nb3P2W15O62], 1, Li-33[H7P8W48O184], 2, K-10[Zn4P2W1 8O68], 3, and K-4[Nb2W4O19] produce 17, 135, 5.7 and 8.8 turnovers of S-8, respectively (23 degrees C; 1.0 atm O-2; 4 h; sealed vessel). The stability of these catalysts during sulfide oxidation are evaluated. The redox potentials of these polyoxometalates and the primary fragmen tation products pertinent to sulfide oxidation are given. Early time k inetics of the reduction of 1 by sulfide proceeds according to the rat e law +d[Nb3P2W15O6210-]/dt=k[1][HS-], with a complex pH dependence. T he buffering agent is shown to be non-innocent and at parity of reacti on conditions, the reduction of K-14[NaP5W30O110], 4, by sulfide in me dia buffered with PO43-, CO32-,B4O102-, and OH- (a blank) results in 4 0, 9.0, 49, and 10 turnovers of S-8, respectively.