Selective decomposition of formic acid on molybdenum carbide: A new reaction pathway

Selective decomposition of formic acid is important as a prototype to study selective bond cleavage of oxygenates. We demonstrate that carbon-modified Mo(1 1 0), C-Mo(1 1 0), is up to 15 times more selective for the dehydrogenation of formic acid than Mo(1 1 0). Reflection absorption infrared spectroscopy (RAIRS) indicates that carbidic carbon blocks active sites for C-O bond cleavage, decreasing the rate of dehydration. Steady-state reactive molecular beam scattering (RMBS) shows that dehydration is the dominant reaction pathway on clean Mo(1 1 0), while C-Mo(1 1 0) selectively promotes dehydrogenation. Kinetic analysis of RMBS data reveals that formic acid dehydrogenation on Mo(1 1 0) has an activation energy of 34.4 +/- 3.3 kJ mol(-1) while the C-Mo(1 1 0) surface promotes distinct pathways for dehydrogenation with an activation energy of only 12.8 +/- 1.0 kJ mol(-1). RAIRS spectra suggest the new pathways include the formation of monodentate formate, and at temperatures of 500 K and greater, direct activation of the C-H bond to form carboxyl, both of which decompose via a CO2 delta- intermediate to evolve CO2 and H-2. (c) 2009 Elsevier Inc. All rights reserved.