The interaction of nitrogen oxides with metal-oxygen cluster compounds (heteropoly oxometalates)
Abstract Nitrogen dioxide is sorbed by the solid heteropoly acids, the first sorbates producing HNO 3 while those subsequently taken up remain strongly bound on the acid, up to three NO 2 per heteropoly anion. The sorption of NO 2 is shown to be dependent on the elemental composition of the anions of the solid acids and hence on the acid strengths of these materials. The sorbed NO 2 associates with both the surface and bulk protons to form HNO 2 + thus demonstrating that NO 2 is capable of penetrating into the crystallographic structure of the solid acid. Prior sorption of NO 2 facilitates the takeup of NO which forms N 2 O 3 . 12-tungstophosphoric acid (HPW) supported on silica produces quantitatively different but qualitatively similar results. The microporous ammonium salt of HPW produces markedly different results when exposed to NO 2 with the predominant product being N 2 evidently resulting from the ammonium cation functioning as a source of the reductant ammonia.