THE NO + H2 REACTION ON PT(100) - STEADY-STATE AND OSCILLATORY KINETICS

The reaction of NO + H2 on Pt(100) was studied in the 10(-6) mbar range between 300 and 800 K with mass spectrometry, work-function measurements, and video LEED. Both multiple steady states and kinetic oscillations were found. The principal reaction products were N2, H2O and NH3, and the activity and selectivity of the reaction were seen to depend on the partial pressure ratio p(H2)/p(NO), on the surface temperature, and on the degree of surface reconstruction. Whereas the 1 x 1 surface of Pt was active for both N2 and NH3 formation, a well-annealed hex phase exhibited a low catalytic activity. The occurrence of defects during the 1 x 1 half-arrow-right-over-half-arrow-left hex transition was shown to lead to enhanced N2 formation. At low p(H2)/p(NO) ratios, N2 formation was favored while for large p(H2)/p(NO) ratios, NH3 production was enhanced. Kinetic oscillations, as determined from variations in the N2, H2O and work-function signals, were found between 430 and 445 K.