Porous material supported nano alloy catalyst as well as preparation method and application thereof

Abstract

The invention relates to a porous material supported nano alloy catalyst as well as a preparation method and application thereof and belongs to the technical field of nano material application and catalysis. The preparation method for the porous material supported nano alloy catalyst is characterized comprising the step of reaction through taking a metallic compound as a precursor, a porous material as a carrier and a borane substance as a reducing agent under the action of supercritical carbon dioxide used as a fluid medium; in the catalyst, the types of nano alloy are selected from Pt, Au, Ag, Pd, Ru, Rh, Pb, Fe, Co, Ni, Ir, Cu and the like and can be arbitrarily matched and proportioned; the size of each of nano alloy particles is about 1-2 nm. The nano particles not only can be distributed on the surface of the carrier, but also can be distributed in holes, even mesopores; therefore, the catalyst has higher catalytic activity and stability.

Description

technical field [0001] The invention relates to a binary or multi-component nano-alloy catalyst supported by a porous material, a preparation method and application thereof, and belongs to the technical field of nano-material application and catalysis. Background technique [0002] Nanomaterials have unique crystal structures and surface properties, and their catalytic activity and selectivity are much higher than traditional catalysts. They can be used as new catalytic materials in many fields such as chemical industry, energy, environmental treatment, and biology. High catalytic activity, high stability, and low cost have always been the indicators to measure a nano-catalyst; at the same time, new technologies are constantly being used to prepare nano-catalysts with superior performance, among which nano-alloy catalysts are very popular catalysts in recent years; Although loading nano-alloys on supports such as carbon materials can effectively improve the stability of the ...

AI Technical Summary

Problems solved by technology

[0003]Pt is a very active catalyst, widely used in various chemical reactions including hydrogenation, NO reduction, CO oxidation and small organic molecule oxidation, oxygen reduction Not only that, but Pt is also the most important catalyst for fuel cells; with the continuous development of industry and technology, the importance of clean energy has become increasingly prominent, which is not only a challenge to energy technology, but also brings a huge impetus to energy science Proton exchange membrane fuel cell (PEMFC), as a new type of energy device, has many advantages such as low operating temperature, no pollution, high specific power, rapid start, etc., and has become a hot spot for research by countries all over the world; at present, most fuel cells The catalyst is mainly Pt / C catalyst, which faces three challenges: 1) Pt is easily poisoned and deactivated; 2) carbon materials are easily corroded when working in acidic conditions for a long time, which makes Pt nanoparticles fall off and agglomerate, thereby Cause catalyst deactivation and reduce its stability; 3) Pt is expensive

[0004] Aiming at the shortcomings of Pt catalysts, American scientist Raymond E. Schaak conducted research on the transformation of Pt nanocrystals into new catalysts for alloys and intermetallic compounds to improve catalytic properties. , Domestic scientists have also developed changeable Pt-based alloy catalysts, such as Pt-Fe, Pt-Co, Pt-Ni, Pt-Ru, Pt-Rh, Pt-Au, Pt-Pb, Pt-Pd, Pt-Ir etc.; there are many ways to prepare this type of alloy catalyst, among which the preparation of nanocatalyst by liquid phase chemical method has become one of the main directions of nanocatalyst preparation technology development, but for some more active metals, such as Fe, Co, Ni usually Need to react in the solution of oleic acid oil, the reaction temperature is higher and the time is longer

Purification and concentration are difficult, which will also cause waste of materials; in addition, the obtained nanomaterials and carbon materials still need to be loaded, and the binding force between nanoparticles and carbon materials is weak, which is not conducive to maintaining the stability of the catalyst

These determinations are not easy to achieve industrial production

[0005]Pt catalysts are usually supported on carbon black with good conductivity and high specific surface area, but as mentioned above, carbon black is prone to corrosion in acidic matrix , and make the Pt nanoparticles fall off and agglomerate, which seriously reduces the catalytic performance and stability of the catalyst. Therefore, seeking a more stable carrier is one of the keys to improving the stability of the catalyst; porous materials such as: mesoporous carbon, porous carbon, mesoporous Silicon and the very popular graphene aerosol, the porous structure not only maintains a high specific surface area, high mass and charge transfer capability, but also protects the particles and improves their stability; Porous graphene supports composite materials such as Au, Ag, Pd, Ir, Rh, Pt, etc. Qu Liangti's research group at Peking University uses the replacement method to obtain Pt-Au, Pt-Ag, Pt-Pb, Pt-Cu and other alloy supports Three-dimensional porous graphene composite materials; however, so far, these methods have some defects, first, it is difficult to obtain alloys of more active metals, such as Pt-Fe, Pt-Ni, Pt-Co; secondly, it is difficult to make nano Alloy particles are uniformly dispersed in the pores and on the surface of the carrier; finally, due to the surface tension, it is difficult for metal ions to enter the mesopores or even micropores, so it is impossible to load nanoparticles into the pores.

[0006]Supercritical CO2 is a kind of supercritical fluid, when CO2 exceeds the critical temperature and critical Above the pressure, the properties of gas and liquid will tend to be similar, and finally a homogeneous fluid phenomenon will be achieved. Supercritical CO2 is similar to gas that is compressible and can effluent like a gas. Moreover, it also has liquid-like fluidity; therefore, some metal precursors dissolved in supercritical CO2 can be fully homogeneous with supercritical CO2 and the carrier. After being reduced by the reducing agent, the nanoparticles will be separated from the supercritical CO2 and loaded on the carrier; Dr Wai's research group at the University of Idaho in the United States uses supercritical carbon dioxide technology and uses hydrogen as the reducing agent , successfully synthesized Pt-Pd, Pt-Ru, Pt-Rh, Pt-Ir and other alloys and carbon nanotubes, mesoporous silicon and other supports, the composite material has excellent catalytic performance; however, some active metals The reduction potential is too high, so hydrogen and some weak reducing agents such as ethanol and methanol cannot be used to obtain alloy nanoparticles of active metals, such as Fe, Co, Ni, Cu, etc.

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