Selective catalytic oxidation of n-butylamine over Cu-zeolite catalysts
Graphical abstract
Introduction
Volatile organic compounds that contain amine, amide, nitro or nitrile groups, known as nitrogen-containing volatile organic compounds (NVOCs), are widely used in the petrochemical, pharmaceutical, and other industries [1,2]. However, they have the potential to cause odor nuisance and harm to the environment and human health [3]. Emissions of VOCs can be abated using techniques based on condensation, adsorption, absorption, thermal incineration, biological degradation, and photocatalysis [[4], [5], [6]], however, the most efficient technique is catalytic oxidation [7,8]. Catalytic oxidation of NVOCs may lead to excessive oxidation of nitrogen atoms, resulting in the formation of oxides of nitrogen (NOx). Hence, selective catalytic oxidation was developed to complete decomposition of NVOCs into CO2, H2O, and N2 as the final products.
Nanba et al. [[9], [10], [11], [12]] demonstrated the catalytic decomposition of acrylonitrile over various metal components supported on several metal oxides and ZSM-5. Pt and Pd showed the highest conversion activities with Cu and Ag achieving the highest N2 selectivity. Zhang et al. [13,14] also investigated Cu/SBA-15 and Cu-doped perovskite-typed LaB0.8Cu0.2O3 (B = Fe, Co, and Mn) catalysts for the selective catalytic combustion of acrylonitrile. Zhou et al. [[15], [16], [17]] investigated the catalytic performance of Ti-PILC-supported CrOx-CeO2 mixed-oxide (CrCe/Ti-PILC) catalysts for n-butylamine oxidation. Microporous zeolites are easily obtained and can act as a support to load and disperse metal nanoparticles [18,19]. The use of zeolites as a catalyst is effective for many reactions. Shen et al. [20] studied active Cu sites in the selective catalytic reduction of NO by NH3 over a Cu/SAPO-34 catalyst. Gervasini et al. [21] investigated the catalytic oxidation of NH3 by observing the NH3-SCO reaction on Cu/CHA samples.
In this work, a series of Cu-loaded zeolite catalysts (ZSM-5, MOR, Hβ, MCM-22, SAPO-34) were prepared by the impregnation method, and their catalytic activity for the selective oxidation of n-butylamine was evaluated. The physicochemical properties of these catalysts (i.e., porous structure, acidity, redox properties, and the existing forms of Cu), which could be responsible for the catalytic activity and N2 selectivity for selective catalytic oxidation of n-butylamine, were characterized using a number of techniques, such as X-ray diffraction (XRD), N2 adsorption-desorption, H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), UV–vis diffuse reflectance spectra (UV–vis-DRs) analyses, and X-ray photoemission spectroscopy (XPS).
Section snippets
Chemicals and materials
Commercial ZSM-5, Beta, and MOR zeolites with similar SiO2/Al2O3 ratio of 25, SAPO-34 zeolite with an SiO2/Al2O3 ratio of 0.5 and MCM-22 zeolite with an SiO2/Al2O3 ratio of 30 were supplied by the Nankai Catalyst Plant and selected as supports.
Cupric nitrate (Cu(NO3)2·3H2O, Sinopharm Chemical Reagent Co., Ltd., AR) were used as metal precursors.
The reaction feed consisted of 500 ppm n-butylamine and 20% of O2 in helium.
Synthesis of catalysts
Cu-loaded catalysts were prepared using an impregnation (IMP) method. The
X-ray diffraction and nitrogen adsorption-desorption results
The XRD patterns of Cu-zeolites (MOR, ZSM-5, MCM-22, Hβ, SAPO-34) and corresponding H-type zeolites are shown in Fig. 1, which show typical diffraction patterns and are in good agreement with the H-type zeolites. The crystal structure of the zeolites remains intact after the loading of Cu, however, the intensity of characteristic reflection decreased possibly due to interactions between Cu species and zeolites. In addition, the diffraction peak for CuO was not observed in Cu-zeolite samples [9
Conclusion
In this work, microporous Cu-modified zeolite (ZSM-5, MOR, MCM-22, Hβ, and SAPO-34) catalysts were investigated for selective catalytic oxidation of n-butylamine. The Cu-ZSM-5 catalyst displayed the best catalytic activity for n-butylamine selective catalytic oxidation, with T100 ≈ 300 °C and a N2 selectivity of more than 90%. The catalytic activity was governed by the dispersion of Cu and isolated Cu2+ species, which influence the redox properties of Cu-ZSM-5. In addition, the acidity of
Acknowledgement
This work is financially supported by the Natural Science Foundation of China (21477149, 21677160, and 21337003) and Beijing Municipal Science & Technology Commission (Z181100000118003).
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