Regulating Photochemical Selectivity with Temperature: Isobutanol on TiO(110).

Selective photocatalytic transformations of chemicals derived from biomass, such as isobutanol, have been long envisioned for a sustainable chemical production. A strong temperature dependence in the reaction selectivity is found for isobutanol photo-oxidation on rutile TiO(110). The strong temperature dependence is attributed to competition between thermal desorption of the primary photoproduct and secondary photochemical steps.

Dual Lewis site creation for activation of methanol on FeO(111) thin films.

Despite a wide application in heterogeneous catalysis, the surface termination of FeO(111) remains controversial. Herein, a surface with both Lewis acid and base sites is created through formation of an FeO(111) film on α-FeO(0001). The dual functionality is generated from a locally nonuniform surface layer of O adatoms and Fe sites.

Reactions in the Photocatalytic Conversion of Tertiary Alcohols on Rutile TiO (110).

According to textbooks, tertiary alcohols are inert towards oxidation. The photocatalysis of tertiary alcohols under highly defined vacuum conditions on a titania single crystal reveals unexpected and new reactions, which can be described as disproportionation into an alkane and the respective ketone. In contrast to primary and secondary alcohols, in tertiary alcohols the absence of an α-H leads to a C-C-bond cleavage instead of the common abstraction of hydrogen.

Introducing catalysis in photocatalysis: What can be understood from surface science studies of alcohol photoreforming on TiO.

Mechanisms in heterogeneous photocatalysis have traditionally been interpreted by the band-structure model and analogously to electrochemistry. This has led to the establishment of 'band-engineering' as a leading principle for the discovery of more efficient photocatalysts. In such a picture, mainly thermodynamic aspects are taken into account, while kinetics are often ignored.

Why co-catalyst-loaded rutile facilitates photocatalytic hydrogen evolution.

As the conduction band edge of rutile is close to the reduction potential of hydrogen, there is a long-lasting discussion on whether molecular hydrogen can be evolved from this semiconductor. Our study on methanol photoreforming in the ultra-high vacuum reveals that photocatalysts comprising a TiO2(110) single crystal decorated with platinum clusters indeed enable the evolution of H2. This is attributed to a new type of mechanism, in which the co-catalyst acts as a recombination center for hydrogen and not as a reduction site of a photoreaction.

Photocatalytic selectivity switch to C-C scission: α-methyl ejection of tert-butanol on TiO(110).

The thermal and photochemical mechanistic pathways for tertiary alcohols on the rutile TiO(110)-surface are studied with the example of tert-butanol. While the thermal reaction is known to yield isobutene, the photochemical ejection of a methyl radical is observed at 100 K. The C-C scission, which is accompanied by the formation of acetone, is the only photochemical reaction pathway at this temperature and can be attributed to the reaction of photoholes that are created upon UV-light illumination at the surface of the n-type semiconductor.

Ethanol surface chemistry on MBE-grown GaN(0001), GaO/GaN(0001), and GaO(2¯01).

In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α-H abstraction from the dissociatively bound alcohol molecule.

Isomer-Selective Detection of Aromatic Molecules in Temperature-Programmed Desorption for Model Catalysis.

Based on three different molecules dosed on a Pt(111) single crystal the selectivity and sensitivity of REMPI-TPD in UHV is investigated for a potential application in heterogeneous catalysis. It is shown that the two structural isomers ethylbenzene and p-xylene can be discriminated by REMPI in a standard TPD experiment. The latter is not possible for the ionization with electrons in a Q-MS.

Ethanol photocatalysis on rutile TiO2(110): the role of defects and water.

In this work we present a stoichiometric reaction mechanism for the photocatalytic ethanol oxidation on TiO2(110). The reaction products are analyzed either under reaction conditions or after irradiation at lower temperatures. Water is identified as a quantitative by-product, which resides in a defect site.

Plasmons in supported size-selected silver nanoclusters.

The plasmonic behavior of size-selected supported silver clusters is studied by surface second harmonic generation spectroscopy for the first time. A blue shift of ∼0.2 eV in the plasmon resonance is observed with decreasing cluster size from Ag55 to Ag9.