INFRARED STUDY OF HIGH-PRESSURE AND HIGH-TEMPERATURE COADSORPTION OF CO AND H2 ON CLEAN AND ON CARBIDED NI(100)

Fourier transform infrared reflection-absorption spectroscopy has been used to study CO adsorbed on clean Ni( 100) and on surfaces with coadsorbed H and/or carbidic C. Data showing high adsorbate coverages at high CO and/or H2pressures (up to 1.0 Torr) and at high temperatures (>300 K) are compared with previous results in which high coverages were attained in ultrahigh vacuum (UHV) at low temperatures (80–300 K). Under high pressures of CO carbidic C shifts the stretching vibration of terminally bonded CO to higher frequency and that of bridge-bonded CO to lower frequency. An H2ambient induces adsorption of CO from the residual gas background at bridged sites and subsequent evacuation of the H2leads to desorption of the CO. A CO ambient in the presence of preadsorbed H produces an inhomogeneous CO layer with some CO molecules possessing stretch frequencies of — 2100 cm −1Heating in a CO ambient causes the decomposition of adsorbed CO which is enhanced by the addition of H2. The correspondence between data obtained at low temperatures in UHV, on the one hand, and those obtained at high temperatures and high pressures, on the other, illustrates the transferrability of UHV results to the catalytic regime. © 1990, American Vacuum Society. All rights reserved.