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Fuel Chemistry Division Preprints 2002, 47(1), 114

METHANE AND METHANOL STEAM REFORMING

TO PRODUCE HYDROGEN USING CATALYTICMICROCHANNEL REACTORS

Yong Wang, Robert Dagle, Ya-Huei Chin, Daniel Palo, Jianli Hu,

and Jamie Holladay

Chemical and Biological Processing GroupEnvironmental Technology Division

Pacific Northwest National Laboratory902 Battelle Blvd, Richland, WA 99352

Introduction

Steam reforming of hydrocarbons is conventionally used infuel processing to produce hydrogen. A fuel processor is a criticalreactor technology for the deployment of PEM-based fuel cells forportable, on-board, and stationary applications. Over the past severalyears, PNNL has developed microchannel chemical reactors for fuelprocessing applications, ranging from the power required for remoteelectronic device to that for automobile applications [1,2]. Inparticular, a series of steam reforming catalysts suitable formicrochannel reactors have been developed [3-5]. In this

presentation, we will present methane and methanol steam reformingcatalyst work recently developed at PNNL.

Experimental

Pd/ZnO catalysts were prepared from impregnating aqueousPd(NO3) solution containing 20.19 wt% Pd (Engelhard) onto ZnOpowder (Aldrich, 99%) using a solution/solid ratio of 0.58 ml/g. Theimpregnated samples were dried under vacuum at 110 oC for at least 8hrs prior to calcining in air. The calcination was conducted under a 2oC/min ramp followed by holding isothermally at 350 oC for 3hs.

Activity tests were carried out in a 4 mm I.D. quartz tubereactor. Approximately 0.200 g of catalyst was loaded between twolayers of quartz wool inside the reactor. A thermocouple was placedin the middle of the catalyst bed. A premixed 1:1wt % methanol-

water feed was introduced into the reactor by using a syringe pump.The feed rate was adjusted such that the reaction was conductedunder 100 ms contact time, which is in equivalent to a standardGHSV of 36000 h-1. Prior to entering the reactor, the feed was fullyvaporized through a vaporizer, operated at 200 oC. Prior to activitytestings, the catalysts were reduced in-situ under a 10 % H2/N2 at 350oC. A glass condenser at 0 oC was used to separate liquid productsfrom gaseous products. The product gases, CO, CO2, and H2, wereseparated using MS-5A and PPQ columns, and analyzed on-line bymeans of a Hewlett Packard Quad Micro GC (Model Q30L) equippedwith a TCD.

Results and Discussions

Methanol and methane are two popular and readily availablehydrocarbons. One way to extract hydrogen from methanol ormethane is via steam reforming reactions. Conventionally, CuZnAlcatalysts are used for methanol steam reforming and methane steamreforming catalysts are based on Ni. Although these two types ofcatalysts are suitable for conventional fixed bed-type reactors whereheat transfer is limiting, more active and selective catalysts are neededfor mcirochannel reactor applications where heat and mass transferadvantages are exploited.

Methanol is a unique fuel since it is sulfur-free and can beactivated at relatively low temperature (under 300 oC). This could bea significant advantage from system simplification and process heatrecovery points of view. We have investigated the steam reformingof methanol with Pd/ZnO under high throughput conditions (GHSVsranging from 18,000 to 144,000 hr-1). Pd, like other transition metals(Pt, Rh), exhibits high methanol decomposition activity to CO and H2.This is not surprising, since precious metal based catalysts typicallyexhibit different catalytic function than the Cu based catalytic

materials. However, when supporting the Pd on ZnO, the catalyticfunction of Pd can be greatly modified, resulting in a highly active andselective catalyst for methanol steam reforming, which was not foundpreviously on precious metal catalysts. Under steam reformingconditions, the Pd/ZnO catalyst produces mainly CO2 and H2 alongwith minimal amount of CO. The concentration of CO in the productstream was found to be at least as low as what reported for the well-studied Cu based catalyst. Hydrogen rich stream with low COcontent is highly desired since the electrocatalyst at the anode isextremely sensitive to CO poisoning at the operating temperature ofPEM fuel cells.

The methanol conversion and CO selectivity over 5, 10 and20 wt% Pd/ZnO catalysts are shown in Figure 1a and 1b, respectively.The experiments were repeated with the same catalyst, and nonoticeable catalyst deactivation was observed. As can be seen fromFigure 1a and 1b that increasing Pd loading from 5 wt% to 20 wt%results in a 10 oC shift of the conversion profile to the lowertemperatures. A complete conversion of methanol can be achieved ataround 300 oC. The CO selectivities of these catalysts were less than7 % over the entire temperature range studied. At 300 oC, thiscorresponds to a dry effluent consisting of approximately 1% CO,26% CO2, and 73% H2. Of the three catalysts examined, the 20%Pd/ZnO catalyst exhibited the lowest CO selectivity. In addition tocatalytic activity studies, we also attempted to elucidate the chemicaland physical properties of Pd/ZnO catalysts using TPR, TEM, H2chemisorption and XRD. It was found that PdZn alloy formed underreducing environment at moderate temperatures (

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Fuel Chemistry Division Preprints 2002, 47(1), 115

user facility sponsored by the US Department of Energys Office ofBiological and Environmental Research and located at PacificNorthwest National Laboratory in Richland, WA.

Figure 1a and 1b. Methanol conversion temperature profileunder steam reforming of methanol (a) and the corresponded

CO selectivity (b) for 5 wt% (triangle), 10 wt% (circle), and

20 wt% Pd on ZnO (both filled and open square). For

20%Pd/ZnO, the conversion profiles were acquired after two

separate reduction temperatures: reduction at 125oC (open

square) and after reduction at 350oC (filled square). All other

catalysts were tested after reduction at 350oC. Reaction

conditions: 0.1925g catalyst, 100 ms contact time or 36000

GHSV, H2O/C = 1.8, 1 atm.References

1. D.R. Palo, J.D. Holladay, R.T. Rozmiarek, C.E. Guzman-Leong, Y. Wang, J.Hu, Y.Chin, R.A. Dagle, and E.G.Baker,J. Power Sources (in press).

2. J.D. Holladay, E.O. Jones, M.R. Phelps, and J. Hu,submitted toJournal of Power Sources

3. Y. Chin, R. Dagle, J. Hu,A. C. Dohnalkova, and Y. Wang,submitted to Catalysis Today.

4. Y. Wang, D. VanderWiel, A.L. Tonkovich, U.S. Pat.,6,284,17B1 (2001).

5. J.Hu , Y. Wang, D.P. VanderWiel, Y. Chin, D.R.Palo, R.Rozmiarek, R.A. Dagle, J.D. Holladay, and E.G.Baker,submitted to Chemical Engineering and Technology.

6. N. Iwasa, S. Masuda, N. Ogawa, N. Takezawa, Appl.Catal. 125 (1995) 145.

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