ChemInform Abstract: Mechanistic Studies of the Catalytic Reduction of Nitric Oxide by Carbon Monoxide in the Presence of Platinum(II), Copper(I), and Copper( II).

Abstract

A rapid reduction of NO by CO to give N{sub 2}O and CO{sub 2} is catalyzed at low temperatures and pressures by an aqueous system comprised of K{sub 2}PtCl{sub 4}, CuCl{sub 2}, and CuCl, and HCl. Two platinum species , PtCl{sub 3}(CO){sup {minus}} and PtCl{sub 4}{sup 2{minus}}, were observed and characterized spectroscopically. Isotropic labeling studies by using {sup 18}O-enriched water as the solvent for the catalysis show that the CO{sub 2} evolved contains nearly the same {sup 18}O abundance as in the solvent. In contrast, no {sup 18}O from water is incorporated into the product N{sub 2}O. These observations clearly establish that both oxygens in Co{sub 2} strongly implies the presence of a rapid process of oxygen scrambling between coordinated CO and water. Indeed, PtCl{sub 3}(CO){sup {minus}} undergoes oxygen exchange with {sup 18}O-enriched water extremely rapidly without significant decomposition to give CO{sub 2} in the catalyst solution. The reaction of PtCl{sub 3}(CO){sup {minus}} with CO to give CO{sub 2} is also too slow to account for the CO{sub 2} production. However, by reaction with NO, PtCl{sub 3}(CO){sup {minus}} in the CuCl-CuCl{sub 2}-HCl system evolves CO{sub 2} and N{sub 2}O rapidly. The presence of CuCl{sub 2} or CuCl in the solutionmore » is required for the rapid gas production. This reaction is thought to be the process for N{sub 2}O and CO{sub 2} production in the catalysis. Consistent with the observed behavior of the system, the results of kinetic studies may be explained in terms of two kinetically distinguishable processes. One is the carbonylation of PtCl{sub 4}{sup 2{minus}} of which the rate shows first-order dependence on each of (PtCl{sub 4}{sup 2{minus}}), P{sub CO}, and (CuCl). The other process is the reaction of PtCl{sub 3}(CO){sup {minus}} with NO and water. Its rate is first order on (PtCl{sub 3}(CO){sup {minus}}), P{sub NO}, and (CuCl{sub 2}). 30 refs., 4 figs., 6 tabs.« less