The mechanism of palladium-catalyzed decomposition of ethanol - A comparison of chemical kinetic and surface science studies

The decomposition reactions of ethanol and ethanal over Pd/Al2O3 have been studied in pulse reaction mode at 200 degreesC in flowing helium and with added H-2, CO, and H2O. Ethanal decomposes to CH4 and CO with progressive coking that can be suppressed by Hz. The response times, as monitored by MS peaks at m/e = 16 for methane and m/e = 28 for CO2 are very similar. Ethanol decomposes to CH4/CO/H-2, the corresponding traces being either broad and unsymmetrical or resolved into two peaks. In H-2/He, the slower set of responses is suppressed, and those from CH4 and CO appear sharp and similar in shape to those observed from ethanal. Two independent mechanistic paths for the catalytic reaction of ethanol are proposed, based on a comparison with published TPR data from reactions on Pd(lll) and Pd(110) single-crystal surfaces. A comparison between the classical kinetic (LHHW) and surface science approaches is made.