Synthesis of Nitro-modified MOF-5 and Its Application on Catalyzing the Thermal Decomposition of Carbamates†

doi:10.7503/cjcu20130516

Abstract

Abstract:

Metal-organic frameworks(MOFs) are a new class of porous materials that are constructed from transition metal ions and organic ligands, and have potential applications in catalysis, separation and gas storage. MOF-5-NO₂, a metal-organic framework with nitro group, was synthesised by the direct mixing method at room temperature. Characterized by XRD, FTIR, N₂ adsorption and SEM, the crystalline structure and morphology of MOF-5-NO₂ were found resembled that of MOF-5, and both the MOFs exhibited microporosity with high specific surface area. However, the Lewis acidity of MOF-5-NO₂ was stronger than that of MOF-5 for the electron withdrawing effect of —NO₂, which was one of the reasons for the high activity of MOF-5-NO₂ on the synthesis of isocyanates by the thermal decomposition of carbamates. Under solvent-free condition, MOF-5-NO₂ significantly accelerated the reaction rate of the decomposition of methyl N-phenyl carbamate, and the turnover frequency(TOF) was seven times higher than that on ZnO. The intermediate product of the decomposition of methylene diphenyl di(phenylcarbamate) was decreased, and the yield of methylene diphenyl diisocyanate reached 81.6%. In conclusion, MOF-5-NO₂ prepared by the direct mixing method is a very effective catalyst for the thermal decomposition of carbamates, and is potentially better suited for other catalyses by modified with appropriate groups.

Key words: Metal-organic frameworks(MOFs), —NO2, Carbamate, Thermal decomposition, Lewis acid

CLC Number:

O643.3

TrendMD:

ZHANG Yi, YANG Xiangui, WANG Qingyin, YAO Jie, HU Jing, WANG Gongying. Synthesis of Nitro-modified MOF-5 and Its Application on Catalyzing the Thermal Decomposition of Carbamates^†[J]. Chem. J. Chinese Universities, 2014, 35(3): 613.

Figures/Tables 7

Fig.1 XRD patterns of MOF-5(b), MOF-5-NH2(c) and MOF-5-NO2(d) (A) Compared with simulated MOF-5(a); (B) compared with commercial ZnO(a).

Fig.2 FTIR spectra of MOF-5-NO2(a), MOF-5(b) and MOF-5-NH2(c) before(A) and after(B) pyridine absorbed

Fig.3 N2 adsorption isotherms(A) and H-K differential pore volume plots(B) of MOF-5(a), MOF-5-NO2(b) and MOF-5-NH2(c)

Table 1 Surface areas of MOF-5, MOF-5-NO2 and MOF-5-NH2 based on N2 adsorption isotherms

Sample	Surface area/(m²·g^-1)
Sample	BET	Langmuir	Micropore^*	External^*
MOF-5	331	410	300	31
MOF-5-NO₂	263	322	236	27
MOF-5-NH₂	231	287	206	25

Fig.4 SEM image of MOF-5-NO2

Table 2 Results of thermal decomposition of MPC*

Catalyst	Reaction time/min	Turnover frequency/min^-1	Yield of PI(%)
ZnO	180	0.153	51.3
MOF-5	140	0.453	51.8
MOF-5-NH₂	220	0.261	44.4
MOF-5-NO₂	70	1.086	51.5

Table 3 Results of thermal decomposition of MDPC*

Catalyst	Conversion(%)	Yield(%)
Catalyst	Conversion(%)	MDI	MPI
ZnO	99.2	68.7	18.8
MOF-5	99.4	74.3	14.1
MOF-5-NO₂	99.5	81.6	10.8

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