Stability of WC Nanoparticles for NO x Reduction
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U8.7.1
Stability of WC Nanoparticles for NOx Reduction A.K. Rumaiz1, S.I. Shah1,2, H.Y. Lin3, I. Baldytchev2, J.G.Chen4
1 Department of Physics and Astronomy 2 Department of Materials Science and Engineering 3 Department of Civil and Environmental Engineering 4 Department of Chemical Engineering University of Delaware, Newark DE 19716 ABSTRACT WC nanoparticles where synthesized using various Physical Vapor Deposition (PVD) methods such as reactive sputtering and Pulsed Laser Deposition (PLD). In both the methods the metal flux obtained is condensed in the presence of He gas. The structural properties of the samples where investigated using X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The feasibility of using nano-WC as an alternative catalyst for Pt is determined. A comparative study on two sample of WC, as-prepared and carburized W, was done. The samples were used to check for the reduction of NOx in a simple reactor. The carburized W shows activity at temperatures around 400o C whereas the as-prepared WC shows activity towards NOx reduction at a slightly higher temperature. The stability of both the sample was studied by performing the same experiment at a fixed temperature for an extended period of time. XPS and XRD confirm the formation of oxide phase after de-NOx experiments. INTRODUCTION Transitional metal carbides, especially WC, have very interesting catalytic properties. In many cases it is supposed to mimic platinum like behavior [1,2]. This behavior is of great importance to automobile industry where Pt is extensively used in catalytic converters to reducing nitrogen oxides (NOx). The current regulations based on 1990 Clean Air Act Amendments (CAAA) require a vehicle NOx emission to be less than 0.6g/mile within 100,000 miles duration. However starting from 2004, a more stringent standard is enforced which requires the emission of NOx to be reduced to 0.2g/mile [3]. With the need for better emission norms and also the scarcity of Pt makes it important to look for alternate catalyst. Though bulk WC is also active, nano-WC is particularly interesting because of the catalytically favorable [4] more open 100 planes being formed.
U8.7.2
There have been various earlier works on the method of making WC nano particles [5,6] In this work we synthesized pure WC and carburized W nanoparticles using PVD techniques. We also report the results of some preliminary studies on the catalytic properties of these particles. EXPERIMENTAL DETAILS The particles were obtained using a Laser Ablation Inert Gas Condensation
He NO
catalyst
technique (LAIGC). A KrF excimer laser (1.2 J, λ = 248 nm) was used to ablate the material. The resulting flux is
Gas Sampling
To GC
carried out of the growth region by a circulating He gas. The particles are collected in a filter. The pure W particles prepared were later carburized
Figure 1: Reactor Set-up
o
in a CH4 atmosphere at 1000 C for an hour. The as prepared WC was obtained directly by ablating a pure WC target. XRD was done to analyze the crystalline
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