็STO-117-06
Available online at www.buuconference.buu.ac.th
The 5th Burapha University International Conference 2016
“Harmonization of Knowledge towards the Betterment of Society”
NO Reduction in a Catalytic Al-MCM-41 Honeycomb
Reactor: Comparison of Mono-Metallic and Bi-Metallic
Catalysts
Pakkarada Sansuksoma , Paisan Kongkachuichayb*
a,b
Department of Chemical Engineering, Kasetsart University, Bangkok 10900, Thailand
Abstract
A series of supported monometallic Cu, Ce, Zn and bimetallic Cu-Ce, Cu-Zn catalysts on Al-MCM-41/cordierite
monolithic supports were synthesized, characterized, and evaluated for NO reduction reaction. Al-MCM-41 was
synthesized by a hydrothermal method on cordierite honeycomb monoliths as the base support material. Monometallic
(Cu, Ce and Zn) and bimetallic (Cu-Ce and Cu-Zn) catalysts were loaded onto Al-MCM-41/cordierite by a wet
impregnation method. The reduction of NO by hydrogen was conducted at 150–500 oC, 180 min, and GSHV 36,000 and
72,000 h–1. These catalysts were found to exhibit high NO conversion in a wide temperature range, and the maximum NO
conversion of 93% was achieved for the Cu-Ce/Al-MCM-41 at 350 oC and GHSV 36,000 h–1.
© 2016 Published by Burapha University.
Keywords: Al-MCM-41; Mesoporous Silica; Copper; Cerium; NO reduction
* Corresponding author. Tel.: +6627970999 ext. 1207
E-mail: paisan.k@ku.ac.th.
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Proceedings of the Burapha University International Conference 2016, 28-29 July 2016, Bangsaen, Chonburi, Thailand
1. Introduction
With increasing numbers of automobiles on the roadways, there are increasing detrimental effects on the
environment, including an increase in the amount of pollutants caused by exhaust gases such as nitrogen
oxides (NOx), carbon monoxide (CO) and unburned hydrocarbons by Chen and Chu, 2011. Some of the
exhaust gases of the most serious concerns are nitrogen oxides, which are a toxic pollutant gases that can
contribute to acid rain, form particulates affecting the human respiratory system, and produce toxic products
when they react with common organic chemicals by Caneghem et al., 2016; Fattah et al., 2014. There are
several catalysts and reactions proposed for NOx reduction in the literature. In automotive applications,
cordierite (2MgO∙2Al2O3∙5SiO2) honeycombs are widely used as a monolithic support material in catalytic
converters due to their superior properties, such as low pressure drop, low thermal expansion, high thermal
stability, high mechanical strength, high porosity, large relative surface area, uniform flow distribution and
easy scale- up in process by Bueno et al., 2005; Fang et al., 2015; Williams, 2001. This work utilized MCM41, a mesoporous silica mesoporous materials, which offer characteristics similar to zeolites except with larger
pores sizes. Incorporation of Al into MCM-41 can increase the BrØnsted acid sites and in turns to enhance the
H2-SCR by Wu et al., 2010; Chamnankid et al., 2011; Chamnankid et., 2012. The cordierite honeycomb
monolith support was coated with Al-MCM-41 by an in situ hydrothermal method.
This work focuses on monometallic and bimetallic catalysts for H2-SCR reaction. The monometallic
catalysts (i.e., Cu, Ce, and Zn) and bimetallic catalysts (i.e., Cu-Ce and Cu-Zn) were impregnated into AlMCM-41/cordierite by an incipient wetness impregnation method. The effects of adding cationic polymer,
crystallization time on morphology, and thickness of the deposited layer were investigated. The catalytic
activity for reduction of NO was tested and is reported.
2. Materials and methods
2.1. Catalyst preparation
Cordierite honeycomb monoliths (2MgO∙2Al2O3∙5SiO2: 30×100 mm, 62 cell/cm2: Jiangxi, PRC) was used
as a catalytic support. Before coating, it was cleaned by HCl (0.1 mol/L) in an ultrasonic bath for 30 min,
rinsed with deionized water, dried at 100 oC for 24 h, and then heated at 550 oC for 1 h to remove any
impurities. In order to enhance adherence between the support and catalyst, the surface of the support was
pre-washcoated with a cationic polymer, 0.45 mol/L polyamine solution (Sigma-Aldrich), for 24 h and then
dried at 100 oC for 24 h.
Al-MCM-41 was synthesized following by Chamnankid et al., 2011. The synthesis process was based on
MCM-41 gel composition (in molar units) of 1SiO2:0.2CTAB:100H2O, for which the Al2O3/SiO2 molar ratio
was fixed at 0.1. After the gel solution was formed, it was transferred into an autoclave where it was placed
inside a cordierite honeycomb monolith. Crystallization of Al-MCM-41 was controlled under hydrothermal
condition at 100 oC for 24 to 72 h. The autoclave was then cooled, and Al-MCM-41/cordierite was rinsed with
deionized water in an ultrasonic bath for 30 min, dried at 100 oC for 24 h, and calcined at 550 oC for 6 h. AlMCM-41/cordierite was subsequently coated with Cu, Ce, Zn, and Cu-Ce (1:1), Cu-Zn (1:1) by wet
impregnation method, using Cu(NO3)2, Ce(NO3)3 and Zn(NO3)2 as precursors and calcined at 400 oC for 6 h.
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Proceedings of the Burapha University International Conference 2016, 28-29 July 2016, Bangsaen, Chonburi, Thailand
2.2. Catalysts characterization
The formation of Al-MCM-41 in situ crystallized on to cordierite honeycomb was confirmed by using an
X-ray diffraction (XRD, Philips X-Pert) with Kα radiation in the 2 range of 0.5–80o.
Temperature-programmed reduction with hydrogen (H2-TPR) was performed in an Inconel tube reactor,
using samples about 1.25 g in each measurement. The mixture of H2 and Ar (9.6% H2 balanced with Ar) was
fed into a catalyst bed and heated up to 900 oC from room temperature at a heating rate 5 oC/min. The H2
consumption was measured by a thermal conductivity detector (TCD) in a gas chromatograph (GC:
Shimadzu, GC-2014).
2.3. Catalytic performance test
The Al-MCM-41/cordierite impregnated with metal oxide was tested for catalytic activity for NO
reduction using H2 as a reducer. Firstly, the impregnated metal oxides were reduced by H 2 at 350 C , and then
the reactant gases consisting of 250 ppm NO, 1,000 ppm H 2 and the balance He were fed at a total flow rate of
70 ml/min (Gas Hourly Space Velocity (GHSV) 36,000 and 72,000 h –1). The reduction of NO by hydrogen
was conducted at 150–500 oC and 180 min in the catalytic honeycomb reactor. Based on inlet and outlet
concentrations of NO analyzed by a gas chromatograph (GC: Shimadzu, GC-14A, equipped with a thermal
conductivity detector (TCD) and using Unibead-C packed column and He as a carrier gas), NO conversion
was then calculated.
3. Results and discussion
3.1. Characterization of catalysts
Figure 1 shows XRD patterns of coated Al-MCM-41/cordierite for different crystallization time,
confirming the formation of Al-MCM-41 on the cordierite surface (Chamnankid et al., 2011). However, the
low-angle pattern of Al-MCM-41 obtained from 72 h crystallization shows the highest intensity. This implies
that it has the highest structural order of hexagonal pores.
Figure 2 compares the TPR profile of five catalysts: Cu/Al-MCM-41, Ce/Al-MCM-41, Zn/Al-MCM-41,
Cu-Ce/Al-MCM-41, and Cu-Zn/Al-MCM-41. Cu/Al-MCM-41 shows a hydrogen consumption peak at 300
C, which is corresponded to one-step reduction of CuO to Cu (Intana et al., 2015). Ce/Al-MCM-41 shows
two small reduction peaks at 520 C and 724 C, which are corresponded to reduction of surface and bulk
CeO2, respectively (Yao, 1984). Zn/Al-MCM-41 shows a board reduction peak at about 450 oC, which is
assigned to reduction of ZnO. It is clearly observed that Ce enhanced the reduction of Cu of bimetallic system
in both ways-lowering the reduction temperature (from 300 to 250 C) and increasing the reducibility (from
59 to 66%, calculated from area under curve). However, this effect is not observed in Cu-Zn/Al-MCM-41,
and ZnO was found to be reduced to Zn only 5%.
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Proceedings of the Burapha University International Conference 2016, 28-29 July 2016, Bangsaen, Chonburi, Thailand
Al-MCM-41
Cordierite
Fig. 1. XRD patterns of cordierite honeycombs after coating Al-MCM-41 for different crystallization times: (a) 24h; (b) 48h; (c) 72h
Fig. 2. Temperature-programmed reduction profiles of catalysts: (a) Cu/Al-MCM-41; (b) Ce/Al-MCM-41; (c) Zn/Al-MCM-41;
(d) Cu-Ce/Al-MCM-41; (e) Cu-Zn/Al-MCM-41
3.2. Catalytic Performances
Catalytic performances of synthesized catalysts for NO reduction by H 2 were carried out in a honeycomb
monolith reactor. The obtained NO conversion at temperature range of 150 to 500 oC is shown in Fig. 3. It is
obviously seen that the reaction at 350 oC achieved the maximum NO conversion for all tested catalysts. For
Al-MCM-41/cordierite alone, it gave only about 15% conversion. For the mono-metallic catalysts, the
obtained conversion is in following order: Cu > Ce > Zn. It should be remarked that Zn/Al-MCM-41 gave
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Proceedings of the Burapha University International Conference 2016, 28-29 July 2016, Bangsaen, Chonburi, Thailand
very low performance, just slightly higher than that of Al-MCM-41/cordierite because of its low reducibility
as described in section 3.1. The catalytic activity was also directly related to the amount of loaded metal.
Fig. 3. NO conversion as a function of temperature (GSHV: 72,000 h –1)
For the bi-metallic catalysts, it was found that Cu-Ce/Al-MCM-41 performed much better than Cu-Zn/AlMCM-41, which is consistent with the results of H2-TPR. Additionally, the synergistic effect of bi-metallic
catalyst was clearly observed from the performance of Cu-Ce/Al-MCM-41 which gave significantly higher
NO conversion than that of Cu/Al-MCM-41 (about 15% higher). In order to increase the contact time
between reactant gases and catalyst, the GHSV was reduced to 36,000 h –1; as the matter of the fact that the
NO conversion at 350 C was increased from 88 to 93%.
4. Conclusions
H2-TPR indicates that the presence of Ce in the Cu-Ce/Al-MCM-41 enhanced the reducibility of Cu
forming the active Cu(I) species. After testing the catalytic performance for NO reduction, it was found that
Cu-Ce/Al-MCM-41 gave the highest NO conversion of 93%, at 350 C and GHSV 36,000 h–1.
Acknowledgements
This research was supported by the Faculty of Engineering, Kasetsart University (scholarship for
Pakkarada Sansuksom), the Synchrotron Light Research Institute (Public Organization), and the Kasetsart
University Research and Development Institute (KURDI).
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Proceedings of the Burapha University International Conference 2016, 28-29 July 2016, Bangsaen, Chonburi, Thailand
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