Adsorption isobars for CO on Pd/Ta(110) at elevated pressures and temperatures using infrared reflection-absorption spectroscopy

Abstract

nfrared reflection-absorption spectroscopy (IRAS) has been used to study the adsorption of carbon monoxide on a Pd/Ta(110) surface. IRAS spectra were collected at pressures from 1 × 10 −9 to 1.0 Torr and at temperatures from 90 to 500 K. Adsorption isobars were constructed from the IRAS spectra that allowed the determination of isosteric heats of adsorption as a function of CO coverage. The heats of adsorption (Δ H) for CO on Pd/Ta(110) were determined to be ∼ 15 kcal mol lower than for CO adsorbed on a Pd(111) surface while the differential surface entropies ( s s) were comparable. The high coverage adsorption isosteres have a pronounced break that indicates that at high CO coverages and low substrate temperatures, the CO surface structures are not fully equilibrated.