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Related Concept Videos

Catalysis02:50

Catalysis

The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
Catalysis01:27

Catalysis

Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...
Reduction of Alkenes: Catalytic Hydrogenation02:13

Reduction of Alkenes: Catalytic Hydrogenation

Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the surface of...
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
The Z-Scheme of Electron Transport in Photosynthesis01:34

The Z-Scheme of Electron Transport in Photosynthesis

The light reactions of photosynthesis assume a linear flow of electrons from water to NADP+. During this process, light energy drives the splitting of water molecules to produce oxygen. However, oxidation of water molecules is a thermodynamically unfavorable reaction and requires a strong oxidizing agent. This is accomplished by the first product of light reactions: oxidized P680 (or P680+), the most powerful oxidizing agent known in biology. The oxidized P680 that acquires an electron from the...
Heterogeneous Catalysis01:22

Heterogeneous Catalysis

Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...

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Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
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Photocatalytic hydrogen evolution with a self-assembling reductant-sensitizer-catalyst system.

Mirco Natali1, Roberto Argazzi, Claudio Chiorboli

  • 1Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara 17-19, 44121 Ferrara, Italy. mirco.natali@unife.it

Chemistry (Weinheim an Der Bergstrasse, Germany)
|June 5, 2013
PubMed
Summary

This study introduces a novel, metal-free system for photochemical hydrogen production using ascorbic acid, aluminum pyridyl porphyrin, and cobaloxime. The system

Keywords:
cobaloximeshydrogenporphyrinoidsself-assemblingsolar fuels

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Area of Science:

  • Photochemistry
  • Catalysis
  • Sustainable Energy

Background:

  • Developing efficient noble-metal-free systems for hydrogen production is crucial for sustainable energy.
  • Photochemical hydrogen evolution often relies on photosensitizers and catalysts.

Purpose of the Study:

  • To describe a novel noble-metal-free system for photochemical hydrogen production.
  • To elucidate the mechanism of hydrogen evolution in this system.

Main Methods:

  • Utilized ascorbic acid as a sacrificial donor, aluminum pyridyl porphyrin as a photosensitizer, and cobaloxime as a catalyst.
  • Employed nanosecond laser flash photolysis to study reaction kinetics and intermediates.

Main Results:

  • The active species is the free photosensitizer, not the docked complex.
  • The long-lived triplet state of the photosensitizer reacts with the ascorbate donor.
  • High turnover frequencies (TOF) and quantum yield (Φ) were achieved.
  • Turnover number (TON) was limited by sensitizer and catalyst hydrogenation at high donor concentrations.

Conclusions:

  • A functional noble-metal-free photochemical hydrogen production system was demonstrated.
  • The reaction mechanism involves bimolecular quenching and subsequent catalytic reduction.
  • System performance is promising but limited by degradation pathways.