The adsorption and interaction of HCN has been studied on (a) copper oxides on crystalline chromia, (b) mixtures of chromium (III) oxide and copper oxides on silica, and (c) mixtures of Cr(VI)O3 and CuO on silica. The adsorption and reaction of both HCN and C2N2 on Cr(VI)O3/SiO2 has also been studied. The work has involved gravimetric studies with a vacuum microbalance, infra-red spectroscopy of adsorbed species, and mass spectroscopic analysis of products. HCN contact at 293 K with both CuO/a-Cr2O3 and CuO-Cr2O3/SiO2 samples led to the slow release of cyanogen. The cyanogen reaction was shown to be occurring on the copper ions of the surface accompanied by reduction to cuprous hydroxide. Some HCN adsorption also occurred on this surface and on the chromia part of the surface without oxidation to cyanogen. On heating, some HCN was desorbed intact but most was oxidised to CO2 with some retention of nitrogen compounds on the surface. The infra-red work indicated that on the copper oxide part of the surface this oxidation occurred via an isocyanate, NCO, intermediate. On the chromia part of the surface HCN adsorption produced an amide species which decomposed to CO2 and N2. Pre-reduction of the surface suppressed cyanogen formation upon HCN adsorption, although considerable oxidation still occurred on heating. On Cr(VI)O3/Aerosil both HCN and C2N2 formed surface amides. On heating, there was some decomposition to CO2 and N2, as with Cr (III) oxide, but also in some cases sublimation of oxamide. With Cr(VI)O3-Cu(II)O/Aerosil, much less gaseous C2N2 was produced from HCN than on Cr2O3/CuO/Silica. This suggests that cyanogen was being preferentially adsorbed on the Cr(VI)O3. The results show the importance of the oxidation states of Cu and Cr in determining the surface reactions of HCN.
|Date of Award||1985|