Particle Size Effect of Ru-Zn Catalysts on Selective Hydrogenation of Benzene to Cyclohexene†

doi:10.7503/cjcu20150288

Abstract

Abstract:

Ru-Zn catalysts modified by water soluble polymers were prepared by a precipitation method. The catalysts after hydrogenation were characterized by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and N₂physisorption. It was found that the type of water-soluble polymers and the dosage of PEG-20000 imposed a remarkable effect on the particle size of Ru. With the Ru particle size in Ru-Zn catalysts increasing, benzene conversion decreased, and the maximum cyclohexene yield showed a volcanic-type variation tendency. When the Ru particle size of the Ru-Zn catalyst modified by 0.4 g PEG[m(PEG-20000)∶m(Ru)=0.2] was 4.8 nm, a maximum cyclohexene yield of 62.2% was obtained on this catalyst. The Ru particle size could produce an effect on the Zn/Ru atomic ratio on the catalyst surface, which was the primary reason why the Ru particle size could affect the performance of Ru-Zn catalysts.

Key words: Benzene, Selective hydrogenation, Cyclohexene, Water-soluble polymer, Particle size effect

CLC Number:

O643

TrendMD:

SUN Haijie, CHEN Lingxia, HUANG Zhenxu, LIU Shouchang, LIU Zhongyi. Particle Size Effect of Ru-Zn Catalysts on Selective Hydrogenation of Benzene to Cyclohexene^†[J]. Chem. J. Chinese Universities, 2015, 36(10): 1969.

Figures/Tables 10

Fig.1 XRD patterns of Ru-Zn catalysts modified by different water-soluble polymers before(A) and

Fig.2 FTIR spectra of Ru-Zn catalysts modified by different water-soluble polymers after hydrogenation(A) and the mechanism of the water-soluble polymers in preparing Ru-Zn catalysts with different particle sizes(B)a. Blank; b. 0.4 g PVA-1750; c. 0.4 g PEG-20000; d. 0.4 g PEG-10000; e. 0.8 g PEG-20000; f. 1.2 g PEG-20000.

Fig.3 TEM images of the Ru-Zn catalysts modified by different dosages of PEG-20000(A) 1.2 g PEG-20000; (B) 0.4 g PEG-10000; (C) 0.4 g PEG-20000; (D) 0.4 g PVA-1750; (E) blank.

Fig.4 Particle size distribution of the Ru-Zn catalysts modified by different dosages of PEG-20000 (A) 1.2 g PEG-20000; (B) 0.4 g PEG-10000; (C) 0.4 g PEG-20000; (D) 0.4 g PVA-1750; (E) blank.

Table 1 Particle size, compositions and texture properties of Ru-Zn catalysts modified by different water-soluble polymers after hydrogenation

Modifier	Particle size/nm	Zn/Ru(atomic ratio)		S_BET/(m²·g^-1)	d_pore/nm	V_pore/(cm³·g^-1)
Modifier	Particle size/nm	Bulk^a		S_BET/(m²·g^-1)	d_pore/nm	Surface^b
Blank	5.9	0.31	0.29	65	0.12	7.54
0.4 g PVA-1750	5.6	0.31	0.27	66	0.11	7.69
0.4 g PEG-20000	4.8	0.31	0.25	67	0.12	7.87
0.4 g PEG-10000	4.2	0.30	0.22	68	0.11	7.89
0.8 g PEG-20000	3.7	0.31	0.20	70	0.09	7.99
1.2 g PEG-20000	3.0	0.31	0.17	72	0.10	7.95

Fig.5 XPS spectra of the Ru-Zn catalyst modified by 0.4 g of PEG-20000(A) Ru3p32; (B) Zn2p32; (C) Zn LMM; (D) S2p32.

Fig.6 Performance of Ru-Zn catalysts modified by different water-soluble polymers for selective hydrogenation of benzene to cyclohexenea. Blank; b. 0.4 g PVA-1750; c. 0.4 g PEG-20000; d. 0.4 g PEG-10000; e. 0.8 g PEG-20000; f. 1.2 g PEG-20000.

Fig.7 Correlation of surface molar ratio of Zn/Ru and particle size with the maximum cyclohexene yield

Fig.8 Hückel molecular orbitals of benzene(A), the interaction between the d orbital of Ru and Hückel antibonding orbital(Ψ4 and Ψ5) of benzene(B) and the selective hydrogenation of benzene to cyclohexene over Ru-Zn catalyst surface(C)

Fig.9 Reusability of the Ru-Zn catalyst modified by 0.4 g of PEG-20000

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