Surface chemistry of polar oxide surfaces: formic acid on NiO (111)

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The adsorption and reaction of formic acid (HCO2H) on the NiO(111)/Mo(110) and MgO(111)/Mo(110) surfaces have been studied using temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). The adsorption of formic acid on the NiO(111) surface is dissociative even at 100 K, in contrast to the NiO (100)/Mo(100) surface, where molecularly adsorbed formic acid is stable up to 200 K. However, the species formed from formic acid decomposition is identical on the two surfaces and has been identified as a formate bonded in a Cs configuration. Upon heating the system to 600 K, both dehydration products, CO and H2O, and dehydrogenation products, CO2 and H2, have been detected in TPD experiments from the NiO(111)/Mo(110) surface; both channels have similar activation energies on this surface. On the MgO(111)/Mo(110) surface, however, dehydration is the only reaction pathway observed. The difference in reactivity between the NiO(111) surface and the MgO(111) surface towards formic acid is discussed.