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Frontiers of Environmental Science & Engineering

Front. Environ. Sci. Eng.    2016, Vol. 10 Issue (3) : 458-466
Enhanced performances in catalytic oxidation of o-xylene over hierarchical macro-/mesoporous silica-supported palladium catalysts
Nanli QIAO1,Xin ZHANG1,Chi HE2,Yang LI1,Zhongshen ZHANG1,Jie CHENG1,Zhengping HAO1,*()
1. Department of Environmental Nano-materials and Technologies, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
2. Department of Environmental Science and Engineering, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China
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A series of hierarchical macro-/mesoporous silica supports (MMSs) were successfully synthesized using dual-templating technique employing polystyrene (PS) spheres and the Pluronic P123 surfactant. Pd was next loaded on the hierarchical silica supports via colloids precipitation method. Physicochemical properties of the synthesized samples were characterized by various techniques and all catalysts were tested for the total oxidation of o-xylene. Among them, the Pd/MMS-b catalyst with tetraethoxysilane/polystyrene weight ratio of 1.0 exhibited superior catalytic activity, and under a higher gas hourly space velocity (GHSV) of 70000 h-1, the 90% conversion of o-xylene has been obtained at around 200°C. The BET and SEM results indicated that Pd/MMS-b catalyst possesses high surface area and large pore volume, and well-ordered, interconnected macropores and 2D hexagonally mesopores hybrid network. This novel ordered hierarchical porous structure was highly beneficial to the dispersion of active sites Pd nanoparticles with less aggregation, and facilitates diffusion of reactants and products. Furthermore, the Pd/MMS-b catalyst possessed good stability and durability.

Keywords hierarchical macro-/mesoporous      silica      palladium      VOCs catalytic oxidation     
Corresponding Authors: Zhengping HAO   
Online First Date: 17 July 2015    Issue Date: 05 April 2016
 Cite this article:   
Nanli QIAO,Xin ZHANG,Chi HE, et al. Enhanced performances in catalytic oxidation of o-xylene over hierarchical macro-/mesoporous silica-supported palladium catalysts[J]. Front. Environ. Sci. Eng., 2016, 10(3): 458-466.
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Nanli QIAO
Chi HE
Yang LI
Zhongshen ZHANG
Zhengping HAO
Fig.1  Low angle powder XRD patterns of the support
sample weight TEOS/PS SBETa/(m2·g-1) Vpb/(cm3·g-1) Dpc/nm d100d/nm a0e/nm Wf/nm
SBA-15 1:0 814 1.24 5.75 9.51 10.98 5.23
MMS-a 1:0.5 733 0.88 4.88 9.47 10.94 6.06
MMS-b 1:1 686 0.91 5.22 9.02 10.42 5.20
MMS-c 1:2 676 0.83 4.69 8.98 10.37 5.68
Tab.1  The physical and textural properties of catalyst supports
Fig.2  N2 adsorption/desorption isotherms (a) and pore size distribution calculated from the desorption branch (b) of the support
Fig.3  SEM images of the support: (a) SBA-15, (b) MMS-a (c) MMS-b and (d) MMS-c. The magnified SEM images of the MMS-d sample (e and f). TEM images of the MMS-b (g)
catalyst SBET/(m2·g-1) Vpb/(cm3·g-1) Pd loading/(wt.%) dispersion/% 42000 h-1 52500 h-1 70000 h-1
T10 T90 T10 T90 T10 T90
Pd/SBA-15 673 0.92 0.28 20 112 188 146 205 166 218
Pd/MMS-a 612 0.62 0.39 37 118 173 145 199 157 223
Pd/MMS-b 604 0.81 0.38 66 122 174 136 188 144 200
Pd/MMS-c 487 0.76 0.38 57 152 202 - - - -
Tab.2  Characteristic data and catalytic activity of the synthesized catalysts
Fig.4  TEM images of Pd/MMS-b catalyst
Fig.5  H2-TPR profiles of catalysts
Fig.6  Conversion profiles of o-xylene catalytic oxidation under different GHSV: (a) 42000h-1; (b) 52500h-1; (c) 70000h-1
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