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1.
Sci Rep ; 7(1): 8670, 2017 08 17.
Artigo em Inglês | MEDLINE | ID: mdl-28819324

RESUMO

The efficient conversion of light energy into chemical energy is key for sustainable human development. Several photocatalytic systems based on photovoltaic electrolysis have been used to produce hydrogen via water reduction. However, in such devices, light harvesting and proton reduction are carried separately, showing quantum efficiency of about 10-12%. Here, we report a nano-hybrid photocatalytic assembly that enables concomitant reductive hydrogen production and pollutant oxidation with solar-to-fuel efficiencies up to 20%. The modular architecture of this plasmonic material allows the fine-tuning of its photocatalytic properties by simple manipulation of a reduced number of basic components.

2.
Angew Chem Int Ed Engl ; 54(30): 8728-31, 2015 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-26069026

RESUMO

Identification of active species and the rate-determining reaction steps are crucial for optimizing the performance of oxygen-storage materials, which play an important role in catalysts lowering automotive emissions, as electrode materials for fuel cells, and as antioxidants in biomedicine. We demonstrated that active Ce(3+) species in a ceria-supported platinum catalyst during CO oxidation are short-lived and therefore cannot be observed under steady-state conditions. Using time-resolved resonant X-ray emission spectroscopy, we quantitatively correlated the initial rate of Ce(3+) formation under transient conditions to the overall rate of CO oxidation under steady-state conditions and showed that ceria reduction is a kinetically relevant step in CO oxidation, whereas a fraction of Ce(3+) was present as spectators. This approach can be applied to various catalytic processes involving oxygen-storage materials and reducible oxides to distinguish between redox and nonredox catalytic mechanisms.

3.
Phys Chem Chem Phys ; 17(7): 5078-83, 2015 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-25599521

RESUMO

The redox property of ceria is a key factor in the catalytic activity of ceria-based catalysts. The oxidation state of well-defined ceria nanocubes in gas environments was analysed in situ by a novel combination of near-ambient pressure X-ray Photoelectron Spectroscopy (XPS) and high-energy XPS at a synchrotron X-ray source. In situ high-energy XPS is a promising new tool to determine the electronic structure of matter under defined conditions. The aim was to quantitatively determine the degree of cerium reduction in a nano-structured ceria-supported platinum catalyst as a function of the gas environment. To obtain a non-destructive depth profile at near-ambient pressure, in situ high-energy XPS analysis was performed by varying the kinetic energy of photoelectrons from 1 to 5 keV, and, thus, the probing depth. In ceria nanocubes doped with platinum, oxygen vacancies formed only in the uppermost layers of ceria in an atmosphere of 1 mbar hydrogen and 403 K. For pristine ceria nanocubes, no change in the cerium oxidation state in various hydrogen or oxygen atmospheres was observed as a function of probing depth. In the absence of platinum, hydrogen does not dissociate and, thus, does not lead to reduction of ceria.

4.
Chem Commun (Camb) ; 47(23): 6590-2, 2011 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-21573273

RESUMO

Determination of metal oxidation state under relevant working conditions is crucial to understand catalytic behaviour. The reduction behaviour of Pt and Re was evaluated simultaneously as a function of support and solvent in a pressurized reactor (autoclave). The bimetallic catalysts are used in selective hydrogenation of carboxylic acids and amides. Gas phase reduction reduced the metals more efficiently, in particular Pt.


Assuntos
Gases/química , Platina/química , Rênio/química , Amidas/química , Ácidos Carboxílicos/química , Catálise , Hidrogenação , Oxirredução , Pressão , Solventes/química
5.
Chem Commun (Camb) ; 46(34): 6279-81, 2010 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-20664876

RESUMO

Selective hydrogenation of carboxylic acids to alcohols and alkanes has been achieved under remarkably mild reaction temperatures and H(2) pressures (333 K, 0.5 MPa) using Pt/TiO(2) catalyst.


Assuntos
Álcoois/química , Álcoois/síntese química , Ácidos Carboxílicos/química , Platina/química , Titânio/química , Alcanos/síntese química , Alcanos/química , Catálise , Hidrogenação
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