Multilayer growth and chemisorbate reactivity of methanol on Pd{110}

Abstract

An electron energy loss spectroscopy study of resonance population in ethylene chemisorbed on Pd (110) The development of a methanol multilayer on Pd͕110͖ at 124 K has been examined with reflectionabsorption infrared spectroscopy ͑RAIRS͒. The spectra indicate that a crystalline multilayer grows in which hydrogen-bonded chains of molecules are parallel to the substrate. A ''sandwich'' phase is identified and consists of several physisorbed layers in between the chemisorbed layer and the crystalline phase. Methanol desorption and decomposition on heating have been followed with simultaneous temperature-programmed RAIRS and TPD measurements. Desorption of chemisorbed methanol is observed at 214 K, whereas the decomposition reaction yielding adsorbed CO and H proceeds at ϳ295 K on heating at 2 K s Ϫ1 . Spectral bands observed on adsorption at 180 K to low exposure, which precede the appearance of the CO signal, are tentatively attributed to chemisorbed methanol. No conclusive evidence for a methoxy intermediate in the decomposition reaction is found.

Reflection absorption infrared spectroscopy and temperature programmed desorption investigations of the interaction of methanol with a graphite surface

“…RAIRS was used to show that the multilayer consisted of a crystalline structure in which hydrogen bonded chains of molecules were formed. 15 In addition to the crystalline multilayer, a ''sandwich'' layer was also identified on Pd͕110͖ 15 which had a different RAIR spectrum to both the multilayer and the chemisorbed monolayer. The formation of crystalline multilayers has also been observed for CH 3 OH adsorbed on Ru͕001͖, 25 polycrystalline Pt, 32 Pt͕111͖, 34 Rh͕100͖, 28 Pd͕100͖, 22 and Cu͕110͖.…”

“…Electronic mail: w.a.brown@ucl.ac.uk talline multilayer was characterized by the observation of splitting in the O-H region of the infrared spectrum, with bands being observed at 3301 and 3193 cm Ϫ1 . 15,34 TPD studies of the desorption of CH 3 OH from a range of metal surfaces have also been performed. Pratt and co-workers 15 observed two main peaks in the TPD spectrum for CH 3 OH adsorbed on Pd͕110͖ at 143 and 230 K. The lower temperature peak did not saturate and was assigned to physisorbed CH 3 OH, while the higher temperature peak was assigned to the desorption of chemisorbed CH 3 OH.…”

“…15,34 TPD studies of the desorption of CH 3 OH from a range of metal surfaces have also been performed. Pratt and co-workers 15 observed two main peaks in the TPD spectrum for CH 3 OH adsorbed on Pd͕110͖ at 143 and 230 K. The lower temperature peak did not saturate and was assigned to physisorbed CH 3 OH, while the higher temperature peak was assigned to the desorption of chemisorbed CH 3 OH. 15 This TPD spectrum was in broad agreement with those observed for CH 3 OH desorption from other metal surfaces.…”

“…10,11 The adsorption and reaction of CH 3 OH with metal surfaces have been discussed in several review articles. 12-14 CH 3 OH has been shown to decompose to form methoxy (H 3 CO-) on most metal surfaces 12,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] and the decomposition can be promoted by coadsorbed oxygen, particularly on Au, Ag, and Cu surfaces. 20,21,27,30,31 At lower temperatures, physisorbed multilayers of CH 3 OH are observed, adsorbed on top of the underlying chemisorbed layer.…”

“…20,21,27,30,31 At lower temperatures, physisorbed multilayers of CH 3 OH are observed, adsorbed on top of the underlying chemisorbed layer. [15][16][17]19,[21][22][23][24][25]27,29,[32][33][34][35] A detailed RAIRS and TPD study of the adsorption of CH 3 OH on Pd͕110͖ at 124 K was performed by Pratt and co-workers. 15 Initial adsorption of CH 3 OH led to the formation of a chemisorbed layer.…”