연료전지 자동차용 가솔린 연료 개질기의 개발

: M1/M2/MgO/Al2O3 촉매상에서 가솔린의 부분산화 개질반응

류종우, 문동주, 이상득, 이병권, 안병성

CFC 대체연구센터, 한국과학기술연구원

Development of Gasoline Fuel Reformer for Fuel-Cell Powered Vehicles

: POX Reforming of Gasoline over M1/M2/MgO/Al2O3 catalysts

Jong Woo Ryu, Dong Ju Moon, Sang Deuk Lee,

Byung Gwon Lee and Byoung Sung Ahn

CFC Alternatives Research Center, Korea Institute of Science & Technology

Introduction

Recently, proton exchanged membrane (PEM) fuel cells operating with H2 from hydrocarbon reforming technologies are being increasingly accepted as the most appropriate power source for future generation vehicles. The successful development of a fuel-cell powered vehicle is dependent on the development of a fuel processor.

Hydrogen is the ideal fuel for a PEM fuel cell because it simplifies the system integration [1-2]. However, a direct hydrogen system has many disadvantages such as the lack of widespread refueling infrastructure and high storage volume compared to the hydrocarbon based fuels [3-4]. There is growing interest in the development of gasoline reformers, as this would allow fuel-cell vehicles to fit into the existing fuel infrastructure instantly [1, 4-5]. Considering the favorable factors required for the on-board generation of H2 in a fuel cell vehicle, POX (partial oxidation) reforming (or autothermal reforming, ATR) attracts much attention primarily because of a low energy requirement [1,6]. In our previous works [1,4,7,8], we found the problems of catalyst deactivation by carbon deposition and sulfur poisoning in the POX reforming reaction of iso-octane over the commercial reforming catalysts (ICI-naphtha reforming and Haldor Topsoe catalysts).

In this work, we investigated various supported transition metal formulations for ATR of iso-octane in order to develop a high performance catalyst with high activity and stability. The performance of the prepared catalysts were compared with the commercial reforming catalysts.

Experimental

The iso-octane as a fuel source was supplied from J.T. Baker. The standard iso-octane feeds containing 10 and 100ppm of sulfur were prepared by mixing of the iso-octane and thiophene (99%+, Acros Organics). Hydrogen  (99.999%), air (99.999%) and nitrogen (99.999%) were used in the reaction and pretreatment of the catalysts. Nickel nitrate, cobalt nitrate, ferric nitrate, molybdenum carbide and magnesium hydrate were provided by Aldrich Chemicals. □-alumina (2-3 microns) was obtained from High Purity Chemicals.

Several compositions of oxide-based formulations, represented as M/MgO/ Al2O3 and M1M2/MgO/Al2O3 (where, M, M1 and M2 = Ni, Fe, Co, Mo) have been prepared for the POX reforming of iso-octane. The catalyst formulations prepared in this work are summarized in Table 1. Various catalyst formulations have been prepared by modifying □-alumina with aqueous solutions of the corresponding metal nitrates using the incipient wetness technique. The solution containing the metal salts was added drop wise to precalcined alumina until incipient wetness was reached. The material is then slowly dried at 80□ for about 6 h. The resulting materials were calcined for 5 h at 650□ in dry air.

The performance of the commercial and the prepared catalysts were measured by a gasoline fuel processor system. The POX reforming catalyst of 1g was charged in the Inconel reactor and was pretreated for 1 h at 700□ under a hydrogen flow of 60 cc/min. All the runs were conducted in the temperature range of 550∼750oC, space velocity of 4,000∼43,000 h-1 and feed molar ratios of H2O/C = 0.5∼3 and O/C = 0.5∼2.0, at atmospheric pressure.  The gases were delivered by mass flow controllers, and H2O and iso-octane were fed by liquid delivery pumps (Young Lin Co., Model  M930). The gas effluent was analyzed by on-line gas chromatography (HP-5890 Series II) equipped with TCD and using a carbosphere 80/100, 10" x 1/8" SS column.

Table 1. The Characteristics of the prepared and the commercial catalysts [8].

Catalyst code	Catalyst formulation	Surface area	Total pore volume	Average pore diameter
		(m2/g)	(cc/g)	(□)
KIST-1	Ni / MgO / Al2O3	28.90	0.2067	286.0
KIST-2	Fe / MgO / Al2O3	87.80	0.2276	103.7
KIST-3	CO / MgO / Al2O3	65.74	0.3051	185.6
KIST-4	Mo / MgO / Al2O3	87.74	0.2942	134.1
KIST-9	Ni / Fe / MgO / Al2O3	73.55	0.2116	115.1
KIST-10	Ni / Co / MgO / Al2O3	61.61	0.1722	111.8
KIST-11	Ni / Mo / MgO / Al2O3	72.44	0.2585	124.4
ICI	NiO / CaO / Al2O3	35.32	0.0850	96.26
HT	(SiO2) / NiO / MgO / Al2O3	24.92	0.1541	286.5

Results and discussion

The characteristics of the commercial and the prepared catalysts are summarized in Table 1. The BET surface area, total pore volume and average pore diameter were measured by N2 physisorption using a sorption analyzer [Quantachrome Autosorb-1]. The surface areas of Ni(major) M(minor)/ MgO/Al2O3 catalysts are higher than that of Ni/MgO/Al2O3.

Many of the experimented catalyst formulations displayed reasonably good activity towards the POX reforming of iso-octane. The hydrogen selectivity of some systems was even higher than that of the commercial ICI and HT catalysts [1,4,7,8,].

Fig. 1 shows the product distribution of the catalysts represented by the general formula M(active)/MgO/Al2O3. The POX reforming reaction of iso-octane  was performed at a temperature of 700□ with a space velocity of 8776 h-1 and using the feed molar ratios of H2O/C=3 and O/C=1. The Fe-supported system showed better activity than the other supported system. Ni and Mo-supported systems displayed substantially low activity. However, the large amounts of CO and CH4 over the Fe and Co supported systems made these systems undesirable for POX reforming reactions.

Fig. 2 represents the effect of various minor components in Ni-based systems represented by the general formula Ni(major)M2(minor)/MgO/Al2O3. In the case of the systems possessing Ni as the major component, both Fe and Co are very effective components, which in very small amounts can considerably enhance the performance of the Ni-based systems. The considerable enhancement in the catalytic activities of the nickel based systems dopped with small amounts of other active components may be caused by a synergistic effect of the active components and of the supports, resulting in the proper dispersion of the active components and, thereby, providing more active sites for the reaction.

On the other hand, all molybdenum based systems (Mo(major)M(minor)/ MgO/Al2O3) containing small amounts of other components such as Ni, Fe or Co generated large amount of CH4. Incorporating the system with cations having stronger oxidizing properties such as Mo has significantly reduced the CO selectivity with a concomitant increase in the CO2 selectivity. However, there is a substantial reduction in the hydrogen selectivity over the Mo based systems. The screening test revealed that the formulations based on Ni as

Fig.1 POX reforming activity of KIST catalysts containing only one active component represented by the general formula M(active) MgO/Al2O3.. Reaction temperature = 700oC; space velocity = 8776h-1; feed molar ratios of H2O/C = 3 and O/C = 1

Fig.2 The effect of minor components  in Ni- based systems represented by the general formula Ni(major)M(minor)MgO/Al2O3. for the POX reforming of iso-octane. Reaction temperature = 700oC; space velocity = 8776h-1; feed molar ratios of H2O/C = 3 and O/C = 1.

the major active component and Fe or Co as the minor component are promising systems with comparable activity or even superior to the commercial systems [1,4,7,8].

Fig.3 Sulfur tolerance for the KIST 9 and commercial ICI-naphtha reforming catalysts in the POX reforming of iso-octane containing 100 ppm of sulfur. Reaction temperature = 700oC; space velocity = 8776h-1; feed molar ratios of H2O/C = 3 and O/C = 1.

Also, some KIST catalysts displayed better activity and sulfur tolerance than the commercial catalysts in the POX reforming reaction of iso-octane containing sulfur [8]. Fig. 3 shows the comparison of the KIST 9 with the commercial ICI catalysts for sulfur tolerance in the POX reforming of iso-octane containing 100ppm of sulfur. It was found that the KIST-9 catalyst displayed better sulfur tolerance than the commercial ICI catalyst, even though none of the systems was found to be completely sulfur resistant [9].

The results suggest the need of efficient desulfurization unit in a fuel processor unit in order to reduce the sulfur content of the feed to the tolerance level of the respective reforming catalysts. Alternatively, new sulfur  resistant catalysts have to be developed in order to operate even with feeds containing higher concentration of sulfur.

References

[1] D.J. Moon, K. Sreekumar, S.D. Lee, B.G. Lee and H.S. Kim, Studies on       Gasoline Fuel Processor System for Fuel-Cell Powered Vehicles              Applications, Appl. Catal. A, General 215 (2001) 1-9.

[2] P.J. de Wild, M.J.F.M. Verhaak, Catalysis Today, 60 (2000) 3.

[3] E. Borroni-Bird, Soc. Automotive Eng. 952762 (1995) 2118.

[4] D.J. Moon, S.D. Lee, B.G. Lee and B.S. Ahn, Partial Oxidation (POX)         Reforming of Gasoline for Fuel-Cell Powered Vehicles Applications, in        press Korean. J. of Chem. Eng. (2001).

[5] Y. Jamal, M.L. Wyszynski, Int. J. Hydrogen Energy, 19 (1994) 557-572.

[6] A. Docter, A. Lamm, J. Power Sources, 84 (1999) 194.

[7] D.J. Moon, K. Sreekumar, S.D. Lee and H.S. Kim, Studies on Partial         Oxidation Reforming of iso-octane, Proceeding of the 8th Japan-Korea        Symposium on catalysts. 263-266, May (2001).

[8] D.J. Moon, J.W. Ryu, S.K. Lee, B.G. Lee and B.S. Ahn, Transition metal      catalysts for the POX reforming of gasoline for fuel-cell powered vehicles     applications, in application to Korea and U.S. Patents, (2001)

[9] Arthur D. Little, Multifuel Reformers for Fuel Cells Used in                  Transportation-Assessment of Hydrogen Storage Technologies U.S. DOE     Report DOE/CE/50343-1, Mar. (1994).