Catalyst synergetic promotion

Synergetic promotion Here the support interacts energetically with the catalyst and produces a new kind of active entity. 

Phenomenologically, synergetic promotion is characterized by an increased reaction rate, accompanied by a decreased activation energy, compared with the catalyst alone. Structural promotion, on the other... 

Low-temperature activity promotion is an issue in mobile (diesel) applications, but may not be a critical issue in several stationary applications, apart from those where the temperature of the emissions to be treated is below 200°C (for example, when a retrofitting SCR process must be located downstream from secondary exchangers, or in the tail gas of expanders in a nitric acid plant). In the latter cases, a plasmacatalytic process [91] could be interesting. In the other cases, the use of NTP together with the SCR catalyst is not economically viable. However, the synergetic combination of plasma and catalysts has been shown to significantly promote the conversion of hazardous chemicals such as dioxins [92], Although this field has not yet been explored, it may be considered as a new plasmacatalytic SCR process for the combined elimination of NO, CO and dioxins in the emissions from incinerators. 

The effects of compositions and reaction conditions on product distribution were investigated over various metal promoted Cu-based catalysts to improve the performance for synthesis of hydrocarbons. The formation of carbon monoxide was suppressed and the formation of hydrocarbons increased with the increase in the amount of Fe. The synergetic effect between copper and iron was required for hydrocarbon synthesis. 

The first description of a synergetic effect due to a mixed cobalt-molybdenum catalyst (oxides and sulfides) was in 1933 by Pease and Keithon (11) at the Princeton University. Their catalytic system was active for the HDS of a mixture of benzene and thiophene. However, difficulty in reproducing their results already pointed out the complexity of this promotion effect, highly dependent on the conditions of preparation and pretreatment and the experimental conditions. 

The bi-functional mechanism, although simple, can explain very well the promoted MOR activity of Pt-Ru alloy catalysts. This mechanism is also well adapted by other binary alloys such as Pt-Sn [48]. It has been identified that CO does not bind to the Sn sites, with the result that OH can more easily adsorb on the Sn sites without competition from CO. The synergetic effect on Pt and Sn sites gives rise to Pt-Sn, a very active CO electrooxidation catalyst. However, the strong adsorption of OH species on Sn sites, particularly at high potentials, makes the Pt-Sn catalyst inferior to the Pt-Ru catalyst for the methanol oxidation reaction. 

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