title: Nanostructured H(3+x)PW(12-x)NbxO40 (x = 0-3) Keggin heteropolyacid catalysts.
abstract: Nanostructured H(3+x)PW(12-x)NbxO40 (x = 0, 1, 2, 3) Keggin heteropolyacid (HPA) catalysts were investigated by scanning tunneling microscopy (STM) and tunneling spectroscopy to probe their redox property and oxidation catalysis. STM image showed that the HPAs formed two-dimensional well-ordered monolayer arrays on graphite surface. In tunneling spectra of the HPAs deposited on graphite, they exhibited a distinctive current-voltage behavior referred to as negative differential resistance (NDR). NDR peak voltage measured atop HPA molecule was then correlated with reduction potential and absorption edge energy determined by electrochemical method and UV-visible spectroscopy, respectively. It was revealed that NDR peak voltage of the HPAs appeared at less negative voltage with increasing reduction potential and with decreasing absorption edge energy. In order to correlate NDR peak voltage of H(3+x)PW(12-x)NbxO40 Keggin HPAs with oxidation catalysis, oxidative dehydrogenation of isobutyraldehyde to methacrolein was carried out as a model reaction. NDR peak voltage of the HPAs appeared at less negative voltage with increasing yield for methacrolein.
authors.affiliation: School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, Shinlim-dong, Kwanak-ku, Seoul 151-744, South Korea.
authors.forename: Jung Ho
authors.initials: JH
authors.lastname: Choi
authors.forename: Dong Ryul
authors.initials: DR
authors.lastname: Park
authors.forename: Sunyoung
authors.initials: S
authors.lastname: Park
authors.forename: In Kyu
authors.initials: IK
authors.lastname: Song
mesh_terms: D000143:Acids / Q000737:chemistry; D002384:Catalysis; D053768:Metal Nanoparticles; D016252:Microscopy, Scanning Tunneling; D018384:Oxidative Stress; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D000143:Acids