Impact of NO on the decomposition of supported metal nitrate catalyst precursors and the final metal oxide dispersion

In previous communications we have shown that the decomposition of nickel and cobalt nitrate in a flow of NO/He prevented agglomeration, yielding high nickel and cobalt oxide dispersions. We now report on the impact of NO on the decomposition of first row transition metal nitrates, i.e. Sc, Mn, Fe, Co, Ni, Cu, Zn, using thermal gravimetric analysis and mass spectrometry. It was found that NO decreased the temperature of decomposition significantly for all investigated metal nitrates. For cobalt, nickel and copper nitrate it was verified that decomposition in the presence of NO yielded high dispersions and narrow particle size distributions, whereas in Ar agglomeration resulted in broad particle size distributions. The beneficial effect of NO on the dispersion of Co, Ni and Cu coincided with a large difference in the decomposition profiles of these metal nitrates compared to that in Ar. It was found that NO induced fast and complete hydrolysis to highly dispersed cobalt, nickel and copper hydroxynitrates which decomposed to yield highly dispersed metal oxides. This is in contrast to literature reports that ascribe loss in dispersion to the formation of metal hydroxynitrate intermediates.