Adsorption of CO and C2H4 on Rh-loaded thin-film praseodymium oxide

A praseodymium oxide thin-film was deposited on Ru(0 0 0 1) by vapor depositing Pr in 2 × 10−7 Torr O2 while the Ru was at 700 K. The film was approximately 5 nm thick and did not produce a LEED pattern. The adsorption and reaction of CO and C2H4 adsorbed on Rh supported on the PrOX film were studied by TPD and SXPS. The CO initially reacted with oxygen in the substrate to produce CO2. After this oxygen was removed, the CO adsorbed non-dissociatively in a manner similar to what is seen on Rh(1 1 1). C2H4 adsorbed on the Rh particles and underwent progressive dehydrogenation to produce H2 during TPD. The C from the C2H4 reacted with the O in PrOX to produce CO. CO dissociation on the Rh particles could be promoted by reducing the PrOX with C2H4 before CO exposure. The CO dissociation occurred over a narrow range of Pr reduction and occurred only at high degrees of reduction. No CO dissociation was seen for films with a Pr3+ content of up to 50%. Extensive treatment in C2H4 poisoned subsequent CO adsorption due to the build-up of C on the Rh particles.