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What is transition metal, and why it can be catalyst?

2019-06-11 来源:亚科官网
It is well known that the core of a fuel cell is a catalyst that converts fuel into energy. The better the catalyst, the higher the efficiency of the fuel cell, the higher the power and the higher the cost efficiency. Transition metal oxides are a kind of high-performance catalysts with great potential. Transition metal catalysts have become a research hotspot because of their abundant sources, low price and good catalytic performance.
What is transition metal?
The transition metal element refers to the d zone and the ds zone of the periodic table (the d zone element includes the elements of the period IIIB~VIIB, VIII group. Excluding the lanthanide and actinide elements. The ds zone includes the IB~IIB group of the periodic table.) This series of metallic elements, also known as transition metals. Generally speaking, this area includes elements of 10 to 12 families, but does not include the f-zone (the elements 58-71 in the periodic table are called transition elements within 4f, and the elements 90-103 are called transition elements within 5f, they both are internal transition elements of the f-zone element).
Due to the unfilled valence layer d orbital, the transition metal is significantly different from other elements based on the eighteen electron rule.
Since many of the elements in this region have many single electrons in the electronic configuration (the manganese family is particularly prominent, the d5 configuration), it is easier to lose, so these metals have variable valence, and some (such as iron) A variety of stable metal ions. The transition metal can display up to +7 (manganese) and +8 (osmium) oxidation states. The former is due to the presence of a single electron, and the latter is loose due to the high energy level. The high oxidation state is present in the acid or acyl group of the metal (eg, VO43-vanadate, VO22+ vanadyl).
Reasons for transition metals as catalysts
Because transition metals have d orbital electrons, or empty d orbitals, empty orbitals can be provided as electrophiles in chemical reactions, or lone pairs of electrons can be provided as nucleophiles to form intermediates, reduce reaction activation energy, and promote reaction. .
Characteristics of transition metal catalysts
1) The d-electron layer of the metal cation in the transition metal oxide easily loses electrons or captures electrons and has strong redox properties.
2) Transition metal oxides have semiconducting properties.
3) The inner valence orbit of the metal ion in the transition metal oxide may be cleaved by the foreign orbit.
4) Both transition metal oxides and transition metals can be used as redox reaction catalysts, while the former is more resistant to catalyst performance due to its heat resistance and toxicity, and is sensitive to photosensitivity, heat sensitivity and impurity sensitivity.
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Related Link: Transition metal catalysts
Edited by Suzhou Yacoo Science Co., Ltd.