AN INFRARED STUDY OF SUPPORT EFFECTS ON THE INTERACTION OF DIHYDROGENAND DINITROGEN WITH SUPPORTED RHODIUM FILMS

A substantial support effect exists for the interaction of N-2 and H-2 with supported Rh. Infrared spectroscopy was used to show that the in teraction of N-2 with Rh/TiO2 (average Delta H = -5.0 kcal mol(-1)) wa s stronger than that of N-2 with Rh/Al2O3 (average Delta H = -2.2 kcal mol(-1)). It was also demonstrated that H-2 dissociates to a greater extent over Rh/TiO2 than over Rh/Al2O3 to produce H2O on the support. Low coverages of Rh-H (Theta = 0.1-0.2) on the supported Rh caused an enhanced interaction of N-2 with Rh for both supports which was eviden t in enhancement of the intensity of the N-N stretching mode for the R h-N-2 surface species. Both weakly bound and strongly bound forms of h ydrogen were thought to be involved in the enhanced N-2 interaction wi th Rh. The interaction mechanism probably involves an electronic effec t transmitted between H and N-2 through the Rh metal centers, causing increased surface coverage of Rh-N-2 and possibly an increase in the N -N vibrational mode extinction coefficient.