Potential application of tungsten carbides as electrocatalysts: 4. Reactions of methanol, water, and carbon monoxide over carbide-modified W(110)

The reactions of methanol, water, and carbon monoxide over clean and carbide-modified W(110) are studied by using temperature-programmed desorption, high-resolution electron energy loss spectroscopy, and Auger electron spectroscopy. The product selectivity of methanol on unmodified W(110) is 67.5% toward complete decomposition, 8.5% toward CO, and 24% toward CH4. After the W(110) surface is modified by carbon, the complete decomposition pathway decreases to 58%, with the remaining methanol dissociating to produce approximately equal amounts of CO and CH4. On W(110), the number of H2O molecules undergoing dissociation is determined to be 0.320 water molecules per W atom. Upon carbon modification, the activity of water decreases by half to 0.153 molecules per W atom. The study of CO on W(110) shows three reaction pathways: decomposition to surface C and 0, formation of gas-phase CO2, and molecular desorption at 284 and 335 K. On the C/W(110) surface, only 7% of the adsorbed CO decomposes to produce surface C and O; additionally, no CO2 desorption is detected. The preadsorption of water onto C/W(110) does not appear to affect the amount of CO adsorption, but does lead to CO desorbing at the lower temperature of 271 K. These results are compared to our previous studies on W(111) and C/W(111) to determine the effect of substrate structure on the reaction pathways of methanol, water, and CO.