Relating methanol oxidation to the structure of ceria-supported vanadia monolayer catalysts

• Published in: Journal of catalysis Vol. 272; no. 1; pp. 82 - 91
• Main Authors: Abbott, H.L., Uhl, A., Baron, M., Lei, Y., Meyer, R.J., Stacchiola, D.J., Bondarchuk, O., Shaikhutdinov, S., Freund, H.J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 25-05-2010; Elsevier; Elsevier BV
• Subjects: Catalysis; Catalysts; Ceria; Chemistry; Exact sciences and technology; General and physical chemistry; Infrared spectroscopy; Methanol; Oxidation; Photoelectron spectroscopy; Scanning tunneling microscopy; Selective methanol oxidation; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Vanadia; Scanning tunneling microscopy; Infrared spectroscopy; Selective methanol oxidation; Photoelectron spectroscopy; Vanadia; Ceria; Photoelectron; Monolayer; Infrared reflection; Binary compound; Infrared absorption; Alcohol; Cerium oxide; Silica; Supported catalyst; Formaldehyde; Thin film; Lanthanide compound; Particle; Alkanol; Vanadium oxide; Oxidation; Chemical reactivity; Structure; Low temperature; Methanol; Catalyst support; Vanadyl; Vibration; Transition element compounds; Thermodesorption; Infrared spectrometry; Heterogeneous catalysis; Models; Alumina
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2010.03.009

Methanol oxidation to formaldehyde was studied on well-defined VO
x
/CeO
2 model catalysts as a function of vanadia coverage. The results revealed a low temperature reaction pathway, which is assigned to isolated vanadyl species surrounded by a reduced ceria surface.
Vanadia “monolayer”-type catalysts supported on reducible oxides such as ceria previously have shown high activity for the selective oxidation of alcohols. Here, a model system consisting of vanadia particles deposited on well-ordered CeO
2(1
1
1) thin films has been employed. Scanning tunneling microscopy (STM), photoelectron spectroscopy (PES), and infrared reflection absorption spectroscopy (IRAS) were used to characterize the VO
x
/CeO
2 surface as a function of vanadia loading. The formation of isolated monomeric species as well as two-dimensional vanadia islands that wet the ceria support was directly observed by STM. The vanadia species exhibit V in a +5 oxidation state and expose vanadyl (V
O) groups with stretching vibrations that blue-shift from ∼1005
cm
−1 to ∼1040
cm
−1 with increasing coverage. Temperature programmed desorption (TPD) of methanol revealed three peaks for formaldehyde production. One is correlated with reactivity on the ceria support (565–590
K). Another is correlated with reactivity on large vanadia particles (475–505
K) similar to that previously observed on vanadia/silica and vanadia/alumina model systems. A low temperature reaction pathway (∼370
K) is observed at low coverage, which is assigned to the reactivity of isolated vanadia species surrounded by a reduced ceria surface. It is concluded that strong support effects reported in the literature for the real catalysts are likely related to the stabilization of small vanadia clusters by reducible oxide supports.