Decomposition and combined reforming of methanol to hydrogen: a FTIR and QMS study on Cu and Au catalysts supported on ZnO and TiO2

Methanol decomposition and methanol combined reforming to hydrogen have been studied by in situ FTIR spectroscopy and quadrupole mass spectrometry (QMS) on Cu and Au catalysts supported on ZnO and TiO2 at increasing temperatures. Methoxy species on ZnO and TiO2 supported catalysts are produced by the reaction of methanol with OH surface groups already at room temperature. The evolution of the adsorbed species with the increase of the temperature is different on the four catalysts. The reaction mixture, the nature of the metal and the preparation method are the controlling parameters. Although both ZnO supported catalysts have been prepared by the same coprecipitation method, formate species are produced on Cu/ZnO, while they are completely lacking on the Au/ZnO sample during the same thermal treatment in pure methanol. On the contrary, the surface species on the TiO2 supported catalysts that have been both prepared by deposition– precipitation evolve quite similarly with the temperature. The different behaviour of the two coprecipitated ZnO based catalysts is mainly related to the formation of a solid solution precursor phase in the copper catalyst, not produced in Au/ZnO as a consequence of gold size. Therefore, gold is not able to activate the support towards the oxidative dehydrogenation of methanol to formaldehyde and it does not affect the defect equilibria of ZnO. In the methanol combined reforming reaction, the activity towards H2 production is beneficially influenced on the copper based catalysts and it is negatively affected by the presence of TiO2 as support.