Nano-gold catalyst supported on combined metal oxide, preparation method and application thereof

Abstract

The invention provides a nano-gold catalyst supported on combined metal oxide, a preparation method and an application thereof. The preparation method comprises the following steps: preparing layered double hydroxides (LDH) precursor crystal nucleus and dispersing the LDH precursor crystal nucleus into sucrose solution; then adding chloroauric acid solution in the obtained mixture so as to reduce Au3+ in HAuCl4 to Au single substances by using the reduction of glucose and fructose produced by sucrose hydrolysis; in the process of reduction, crystallizing the LDHs so as to obtain solid LDH supported on nano-gold; and carrying out high-temperature roasting on the solid LDH supported on the nano-gold so as to obtain the nano-gold catalyst supported on the combined metal oxide. The combined oxide of the catalyst is taken as a carrier on which the nanosize gold particles is supported, wherein the combined oxide refers to MgO or compound of ZnO and Al2O3, and the mole ratio of the MgO to the compound of ZnO and Al2O3 is 2-6:1; the gold capacity is 0.5 to 3 percent, the size of the gold particle is 8 to 15nm, and the gold particle is ellipsoidal or polyhedral. When the catalyst is used in the catalytic hydrogenation reaction of unsaturated aldehydes, the conversion rate of reactants reaches 60 to 97 percent, and the selectivity of cinnamyl alcohol is 40 to 75 percent.

Description

technical field [0001] The invention belongs to the field of composite metal oxide nanometer material and its preparation, and in particular relates to a supported gold catalyst and its preparation method, and its use as a catalytic hydrogenation catalyst for unsaturated aldehydes. Background technique [0002] Gold has traditionally been considered to be chemically inert and far less active than platinum group metals in terms of catalytic performance. However, since Haruta et al. have prepared nano-gold catalysts supported on transition metal oxides by co-precipitation and used them for carbon monoxide oxidation, they have shown excellent catalytic performance [Haruta M, Yamada N, Kobayashi T, Iijima S.Journal of Catalysis, 1989, 115(2), 301-309], this discovery broke the traditional idea that gold has no catalytic activity, and caused people to have great interest and attention to the catalytic properties of gold. Since then, research and development on gold catalysts has...

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Problems solved by technology

The gold catalyst prepared by the impregnation method has poor dispersion, small loading capacity, large gold particle size, and poor catalytic performance.

The gold-based catalyst prepared by co-precipitation method is wrapped in the inside of the carrier because quite a lot of gold particles, and the particles wrapped in the inside of the carrier cannot participate in the catalytic reaction, thus reducing the utilization rate of gold [Mamiko Yamashita, Hironori Ohashi, Yasuhiro Kobayashi, Yoshihiro Okaue, Tsutomu Kurisaki, Hisanobu Wakita, Takushi Yokoyama. Journal of Colloid and Interface Science 2008, 319, 25-29]

The deposition-precipitation method is a more effective method. The key to this method is to control the appropriate pH value by adding the amount of alkali dropwise, so that the gold hydroxide is deposited on the carrier to obtain low loading, small particle size, and high activity. High catalyst, but the too low pH value makes the gold hydroxide cannot be deposited, so this method is only applicable to specific supports [X.Yang, A.Wang, X.Wang, T.Zhang, K.Han, J. Li.J.Phys.Chem.C 2009, 113, 20918-20926.]

Utilize the hydroxyl on the support surface and the chlorine ion in chloroauric acid to exchange reaction, also can prepare loaded gold catalyst [G.Riahi, D.Guillemot, M.Polisset-Thfoin, A.A.Khodadadi, J.Fraissar d, Catalysis Today 2002, 72, 115-121], but the preparation process is not easy to control

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