The Role of Surface Defects in the Adsorption of Methanol on Fe3O4(001)

Oscar Gamba,Jiri Pavelec,Michael Schmid,Gareth S Parkinson,Roland Bliem,Jan Hulva,Ulrike Diebold

doi:10.1007/s11244-016-0713-9

Abstract

The adsorption of methanol (CH3OH) at the Fe3O4(001)−(√2 × √2)R45° surface was studied using X-ray photoelectron spectroscopy, scanning tunneling microscopy, and temperature-programmed desorption (TPD). CH3OH adsorbs exclusively at surface defect sites at room temperature to form hydroxyl groups and methoxy (CH3O) species. Active sites are identified as step edges, iron adatoms, antiphase domain boundaries in the (√2 × √2)R45° reconstruction, and above Fe atoms incorporated in the subsurface. In TPD, recombinative desorption is observed around 300 K, and a disproportionation reaction to form methanol and formaldehyde occurs at 470 K.

Highlights

IntroductionMethanol (CH3OH), the simplest alcohol, can be involved in several processes to produce hydrogen (oxidative reforming, decomposition, steam reforming) [1] and has received renewed interest for its importance in fuel-cell technology [2]
Methanol (CH3OH), the simplest alcohol, can be involved in several processes to produce hydrogen [1] and has received renewed interest for its importance in fuel-cell technology [2]
On the basis of the STM data the active sites for dissociation are identified as step edges, Fe adatoms, incorporated Fe defects, and antiphase domain boundaries (APDBs); we discuss these in turn in the following

Summary

Introduction

Methanol (CH3OH), the simplest alcohol, can be involved in several processes to produce hydrogen (oxidative reforming, decomposition, steam reforming) [1] and has received renewed interest for its importance in fuel-cell technology [2]. Studies of methanol adsorption on well-characterized metal-oxide surfaces have sought to correlate the atomicscale structure with chemical reactivity [3,4,5,6,7,8,9,10,11,12,13]. Oxygen vacancies (VOs) have been shown to be the major active sites on TiO2 [7, 8] and CeO2 [9, 10] surfaces, with adsorbed methoxy species (CH3O-) and hydroxyl groups formed at room temperature. Reaction products such as formaldehyde and methane are reported to emerge from this chemistry. As noted by Vohs in his recent review of oxygenate adsorption on metal oxides [4], little is known about the reactivity of isolated cation defects

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