Reduction of Pd/HZSM-5 Using Oxygen Glow Discharge Plasma for a Highly Durable Catalyst Preparation
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Reduction of Pd/HZSM-5 Using Oxygen Glow Discharge Plasma for a Highly Durable Catalyst Preparation Dang-guo Cheng Æ Xinli Zhu
Received: 24 April 2007 / Accepted: 16 June 2007 / Published online: 17 July 2007 Springer Science+Business Media, LLC 2007
Abstract Pd/HZSM-5 catalyst prepared via glow discharge plasma reduction followed by calcination thermally showed enhanced stability for methane combustion. In order to investigate the plasma catalyst preparation mechanism, oxygen glow discharge, initiated at room temperature, has been employed for reduction of Pd/HZSM-5 catalyst. The catalyst characterization using XRD and XPS analyses demonstrates that oxygen glow discharge plasma is also able to reduce Pd/HZSM-5 catalyst. This suggests that the electronic effect plays an important role in the treatment of catalyst using glow discharge. This also confirms that the thermal effect of the glow discharge reduction can be ignored. A highly durable catalyst for methane combustion has been obtained from calcination of the glow discharge reduced sample. Keywords Pd/HZSM-5 Glow discharge Oxygen plasma Methane combustion
1 Introduction The catalytic combustion of methane has been considered as one of the major techniques for reducing NOx emission and also for the complete oxidation of unburned methane effluents of natural gas fueled vehicles. Palladium supported catalysts, esp., the zeolite supported catalysts, have been found to be the most active catalyst for the catalytic combustion of methane [1–9]. However, the low temperature
activity and stability of the developed palladium catalysts still need to be further improved. Most reported improvements were conducted using promoter elements [3, 4, 6, 8]. Previously Liu et al. [7] reported that glow discharge plasma reduction followed by calcinations thermally significantly improves the low-temperature activity and stability of Pd catalysts. Argon was previously used as the plasma forming gas. During the plasma catalyst treatment, Pd species was first reduced into metallic Pd species by argon plasmas [7, 10, 11]. A highly dispersed Pd catalyst was then obtained after further calcination thermally [7]. A temperature measurement of plasmas has also been conducted using IR imaging, which confirms that the temperature of catalyst powder during glow discharge plasma treatment remains around the room temperature. This means no thermal effect on catalyst during glow discharge reduction. Only electronic effect needs to be considered. It is reasonable to think that, if oxidative gas, like oxygen, is used as the plasma forming gas, it would be an excellent way to evaluate the electronic mechanism of the plasma catalyst treatment at room temperature. Therefore, in this work, we attempt to reduce Pd/HZSM-5 catalyst using oxygen glow discharge plasma. A plasma reduction of catalyst is indeed observed. The further calcination of this oxygen plasma reduced catalyst leads to a highly stable catalyst too for methane combustion.
2 Experimental D.-g. Cheng (&) X. Zhu Key Laboratory fo
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