Formic acid adsorption and decomposition on TiO2(1 1 0) and on Pd/TiO2(1 1 0) model catalysts

The reaction of formic acid with TiO2(1 1 0)-(1×1) and with model catalysts with Pd nanoparticles on that oxide has been investigated using a molecular beam reactor. On the oxide surface only the dehydration reaction is seen, and it proceeds at steady state with a very high reaction probability above 500 K. There is no evidence for a dehydrogenation pathway. However, when the surface is loaded with Pd nanoparticles then the dehydrogenation reaction is also seen, beginning at about 350 K. The rate of formic acid decomposition is slower than on a Pd single crystal because the nanoparticles are much less reactive than the bulk metal, probably due to alloying with Ti originating from interstitial Ti3+ cations in the oxide. This results in reduced electron density at the Fermi level of the nanoparticles. However, the adsorption probability of the formic acid with the Pd is higher than expected due to diffusion of formic acid, in a weakly held state, from the support to the metal particles.