HYDROGEN-CYANIDE SYNTHESIS ON POLYCRYSTALLINE PLATINUM AND 90 10-PLATINUM-RHODIUM SURFACES/

The synthesis of HCN from methane-based feedstocks has been studied at relatively low temperatures (up to 780 degrees C) and pressures (0.02 -0.15 Torr) over both pure Pt and Pt-10%Rh alloy model catalysts. Stea dy-state synthesis of HCN is observed over Pt from CH4-NH3-O-2 feed mi xtures with a maximum in activity observed using a 1:1:0.5 mixing rati o. The activity of the Pt-10%Rh alloy under comparable conditions is s ignificantly lower, indicating that Rh has an inhibiting effect on the synthesis reaction at these temperatures and pressures. Comparable st eady-state levels of activity were not observed over Pt for pure CH4-N H3, CH4-NH3-CO2 or CH4-NO feed mixtures; in particular, for CH4-NH3 fe eds in the absence of oxygen a high initial activity was seen to decay rapidly over time. The effects of various surface pretreatments of th e Pt were found to be transitory, with a gradual return of the HCN act ivity to its normal level in CH4-NH3-O-2 (1:1:0.5) mixtures in all cas es, and the most beneficial pretreatment effect was observed for a sim ple physical surface roughening induced by mild ion bombardment. By co ntrast, pre-exposure of the catalyst surface to ethylene or ammonia at elevated temperatures led to an initial inhibition or decrease in the synthesis activity.