Preparation method and application of rare earth modified Keggin-type heteropolyacid supported catalyst

Abstract

The invention relates to the technical field of preparation of catalysts, and discloses a preparation method of a rare earth modified Keggin-type heteropolyacid supported catalyst. A carbon nanotube is used as a carrier; the carbon nanotube is subjected to oxidation opening and is cut into short pipes through an acid solution; under the action of metal chlorides and alcohol solvent, the defect sites of the tail end or (and) the side wall of the carbon nanotube are combined with hydroxy, so that a hydroxylated carbon nanotube is obtained; the surface property of the carbon nanotube is changed,so that active ingredients can be more easily and firmly adsorbed; the stability of the catalyst is improved; meanwhile, the hydroxylated carbon nanotube has a large number of highly-delocalized Pi electrons, and strong attraction to rare earth metal elements is realized, so that a Lewis acid site is favorably formed; the activity of the catalyst is improved; and meanwhile, the stability of the catalyst is also improved.

Description

technical field [0001] The invention relates to the technical field of catalyst preparation, in particular to a preparation method and application of a rare-earth modified Keggin type heteropolyacid supported catalyst. Background technique [0002] Heteropolyacids are composed of heteroatoms or central atoms (P, Si, Fe, Co, etc.) and polyatoms with coordination (V, Nb, Mo, W, etc. transition metals) and oxygen atoms according to specific coordination bridges. The oxygen-containing polyacids formed together have high catalytic activity. Keggin-type heteropolyacid is the most widely used heteropolyacid at present, and its general molecular formula is H n XM 12 o 40 ·nH 2 O, such as phosphotungstic acid, phosphomolybdic acid, and silicotungstic acid, etc., which not only have redox properties, but also have strong Acidic, but also has the advantage of "pseudo-liquid phase" behavior, some smaller molecules can enter and exit freely inside and outside, and chemical reaction...

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Problems solved by technology

[0003] However, Keggin-type heteropolyacids are easily soluble in water, are not easy to recycle and reuse, and because they belong to Acid type solid acid, easy to react with water and lose activity

In order to improve the catalytic activity of Keggin-type heteropolyacids in aqueous reaction media, the prior art usually mixes and dopes heteropolyacids with alkali metals or rare earth element metals. For example, Chinese patent document CN105854943A discloses a rare earth modified heteropolyacid The preparation method of the acid catalyst is to modify the heteropoly acid by using the rare earth M compound under the condition of strong acid solution, so that a stable M-O bond is formed between the rare earth M and the O in the heteropoly acid, thereby improving the activity of the catalyst, but The catalyst is the same as the traditional homogeneous catalyst, but it also has the problem of difficulty in separating the catalyst from the product and difficult recovery.

For this reason, the prior art discloses a rare-earth modified heteropolyacid-supported catalyst, which uses multi-walled carbon nanotubes as a carrier, and removes carbon on the surface of carbon nanotubes by strong oxidizing acid, increases oxygen-containing functional groups, and makes the activity The components are firmly adsorbed on the functional groups to improve the stability of the catalyst. However, the acid-treated carbon nanotubes do not play a catalytic role in the subsequent reaction, and cannot further synergistically improve the catalytic activity of the catalyst. Therefore, by strong oxidizing acid Rare-earth modified heteropolyacid-supported catalysts obtained by treating carbon nanotubes show limited improvement in catalytic performance

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