(600bl) Water-Treated Rh/γ-Al2O3 Catalyst for Methane Partial Oxidation

Water-treated Rh/?-Al2O3 catalyst for methane partial oxidation
Xia Xu1,2 and Alan M. Lane1,2*

1Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, AL

35487 USA.

2Department of Chemical and Biological Engineering, The University of Alabama, Tuscaloosa, AL 35487 USA.

Production of synthesis gas (H2 and CO gas mixture) by methane (CH4) partial oxidation is an important intermediate step in many existing energy conversion technologies, such as fuel cells and Fischer-Tropsch reaction. Decreasing the reaction temperature with an improved catalyst will increase the reaction efficiency and save energy. Our group in previous research [1-3] showed that pretreating a Pt/?-Al2O3 catalyst at 500 oC in a humid reducing (H2O/H2) environment significantly decreases the reaction temperature of catalytic CO preferential oxidation in H2. This is due to the decreased particle size and increased stability of Pt and decreased CO chemisorption strength after this treatment. In this work, we applied this water treatment to Rh/?-Al2O3 and investigated its effects on CH4 partial oxidation. Standard treatment is reduction under H2 at 500

oC. Water treatment involves taking this reduced catalyst back to room temperature, soaking it

with water, and then raising the temperature back to 500 oC under H2. TEM images of standard- treated and water-treated Rh/?-Al2O3 catalysts are shown in Figs. 1 and 2, respectively. The average Rh particle size decreases after water treatment. Both catalysts were used for CH4 temperature programmed partial oxidation and the results are shown in Fig. 3. Conversion is defined as the molar flow rate out of CO and CO2 divided by the total molar flow rate out
(including unreacted CH4). Selectivity is defined as the molar flow rate of CO or CO2 out divided by the molar flow rate out of all CO, CO2 and CH4. A negligible difference between the two catalysts is detected for CH4 conversation. However, the water-treated catalyst shows higher CO selectivity and lower CO2 selectivity when the reaction temperature is low than 650 oC. At higher temperatures, the selectivity of both products becomes similar for the two catalysts. This result can be used to improve CO selectivity of CH4 partial oxidation at low reaction temperature (< 650 oC).
This work was supported by U. S. Department of Energy (DOE) under contract GR23134, Institute for Sustainable Energy.

[1] I.H. Son, M. Shamsuzzoha, A.M. Lane, Promotion of Pt/gamma-Al2O3 by new pretreatment for low- temperature preferential oxidation of CO in H-2 for PEM fuel cells, J. Catal., 210 (2002) 460-465.

[2] M.C. Jo, G.H. Kwon, W. Li, A.M. Lane, Preparation and characteristics of pretreated Pt/alumina catalysts for the preferential oxidation of carbon monoxide, J. Ind. Eng. Chem., 15 (2009) 336-341.

[3] I.H. Son, A.M. Lane, D.T. Johnson, The study of the deactivation of water-pretreated Pt/gamma- Al2O3 for low-temperature selective CO oxidation in hydrogen, J. Power. Sources., 124 (2003) 415-419.

* Corresponding author contacted by telephone: +1-205-348-6367, fax: +1-205-348-7558 and email: alane@eng.ua.edu.

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Fig. 1. Rh/?-Al2O3 catalyst with standard

Fig. 2. Rh/?-Al2O3 catalyst with water treatment,

o

treatment, H2 reduction at 500 oC.

H2/H2O reduction at 500 C.

Fig. 3. The CH4 conversion, CO and CO2 selectivity of standard-treated and water-treated Rh/?- Al2O3catalyts in CH4 partial oxidation reaction (S: standard-treated catalyst, W: water-treated catalyst).

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