The Influence of Rh Addition on the Catalytic Activity of Cubic Pt Nanocrystals Supported on Alumina for NO/CH 4 Reactio
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The Influence of Rh Addition on the Catalytic Activity of Cubic Pt Nanocrystals Supported on Alumina for NO/CH4 Reaction Ioan Balint Æ Akane Miyazaki
Received: 24 October 2007 / Accepted: 23 November 2007 / Published online: 13 December 2007 Ó Springer Science+Business Media, LLC 2007
Abstract The effect of the Rh addition to the well defined cubic (&70%) Pt nanocrystals of around 13 nm supported on alumina was investigated for NO/CH4 reaction. The impact of size and shape of Pt nanoparticles on the catalytic activity were also analyzed by comparing the results with a conventionally prepared catalyst. Keywords Platinum nanoparticles Rhodium deNOx catalysts Methane oxidative conversion
1 Introduction The catalytic removal of NO from different polluting sources by using hydrocarbon reductants became already a standard procedure for environmental protection. Methane is a convenient reductant because is relatively cheap but on the other hand is the least reactive among hydrocarbons. Under near stoichiometric or methane-rich conditions, platinum has been found to be the most active and stable catalyst [1] but gives relatively high selectivity to harmful products such as N2O and NH3. The NO reduction is a structure sensitive reaction [2], depending on the morphology of the supported metal particles. Recently, interesting
I. Balint (&) Institute of Physical Chemistry of Romanian Academy, Spl. Independentei 202, 060021 Bucharest, Romania e-mail: [email protected] A. Miyazaki Department of Chemical and Biological Sciences, Faculty of Science, Japan Women’s University, 2-8-1, Mejirodai, Bunkyo-ku 112-8681, Japan e-mail: [email protected]
morphological effects have been revealed by using welldefined Pt nanocrystals [3–5]. The aim of the present work was to investigate the effect of Rh addition on the catalytic behavior of the wellstructured (cubic) Pt nanocrystals supported on alumina for NO/CH4 reaction in methane-rich conditions. The purpose was to improve the selectivity to N2 without affecting the high catalytic activity of platinum. Another aim was to determine the intrinsic catalytic activity of Pt and Rh-added Pt nanoparticles (expressed as turnover frequency) as well as the associated activation energies for NO/CH4 reaction.
2 Experimental The synthesis method of the alumina supported Pt nanoparticles was already reported [4, 5]. The K2PtCl4 complex (10-4 M aqueous solution) was reduced with H2 at 40 °C in the presence of NIPA (N-isopropylacryl amide) capping polymer. The resulted Pt nanocrystals of around 13 nm and having mainly cubic shape (&70%) were supported on c-Al2O3 (Aerosil, 100 m2 g-1) to get a final metal loading of 1 wt%. After water elimination by freeze-drying the material was calcined air at 350 °C for 1 h to remove the capping polymer. This catalyst will be called hereafter Pt(NIPA). The Rh-added catalyst was prepared by impregnation of Pt(NIPA) with appropriate amounts of Rh3(CO)12 dissolved in tetrahydrofuran. After the solvent removal, the catalyst was calcined again in air at 35
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