THERMAL-ANALYSIS OF CATALYST PRECURSORS .2. INFLUENCE OF SUPPORT AND METAL PRECURSOR ON THE REDUCIBILITY OF COPPER-CATALYSTS

The reductions of supported CuO and CuCl2 have been studied by thermal analytical methods. Upon calcination of Cu(NO3)2 impregnated onto SiO2 or Al2O3, there are formed both particles of non-interacting CuO, which are reduced over a narrow temperature range with T(max) approximately equals 490 K, and dispersed Cu(II) species, which are less easily reduced (T(max) approximately equals 560-610 K on SiO2 and 515-545 K on Al2O3). On TiO2, particulate CuO is reduced at a somewhat lower temperature (T(max) approximately equals 465 K) and there is evidence of a more easily reducible dispersed Cu(II) phase on anatase samples. However, the presence of residual additives on the surface of pigmentary anatase raises T(max) for CuO particles to approximately 525 K. Deposition-precipitation and ion exchange methods both lead to Cu(OH)2; this on calcination affords CuO, which is generally reduced in a single step, at a temperature characteristic of particulate CuO. On the other hand, reduction of supported CuCl2 proceeds in two clearly defined steps, the ratio of the peak areas being close to 1:1; an intermediate Cu(I) state is clearly implicated. Evolution of HCl does not however occur simultaneously with the H-2 uptake; little if any appears during the reduction of Cu(II) to Cu(I), but (except on Al2O3) the evolution is almost complete before the final reduction step starts. This is thought to be due to dissociation of Cu-Cl bonds and formation of Cl- on the support, this being the major intermediate in the formation of gaseous HCl.