연료전지 자동차용 가솔린 연료 개질기의 개발

: 전이금속계 촉매상에서 가솔린의 부분산화 개질반응

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

화학공학의 이론과 응용 제8권 제1호 2002년

류종우, 문동주, 이상득, 이병권, 안병성

환경공정연구부, 한국과학기술연구원

Development of Gasoline Fuel Reformer for Fuel-Cell Powered Vehicles

: POX Reforming of Gasoline over Transition Metal Catalysts

Jong Woo Ryu, Dong Ju Moon, Sang Deuk Lee, Byung Gwon Lee and Byoung Sung Ahn

Environment ＊ Process Technology Division , KIST

Introduction

Catalytic Partial Oxidation (POX) reforming of hydrocarbons for generating hydrogen has gained much attraction in recent years owing to its direct application in proton exchanged membrane (PEM) fuel cells which generate clean electrical energy. The successful development of fuel cell powered vehicles is dependent on the development of the fuel processor. The POX reforming process of gasoline is an attractive option for a fuel cell powered vehicles applications. Iso-octane is a principal component in gasoline and the results obtained over iso-octane feed can be extended to develop an on-board gasoline fuel processor. In our previous work [1,2], we found the problems of catalyst deactivation by iso-octane over the commercial Haldor Topsoe (HT) reforming catalyst. In this work, we investigated various supported transition metal formulations for POX reforming (autothermal reforming, ATR) reaction of iso-octane in order to develop a high performance catalyst with high activity and stability. The characteristics of HT and prepared catalysts are investigated by N2 physisorption and CO chemisorption. The contents of carbon and sulfur on catalysts were measured by elemental inorganic analyzer. The performance of the prepared catalysts was compared with that of the commercial reforming catalysts.

Experimental

1. Chemicals

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 the pretreatment of the catalysts. Nickel nitrate, cobalt nitrate, ferric nitrate, ammonium molybdate and magnesium hydrate were provided by Aldrich Chemicals. Also, □-alumina (2-3 microns) was obtained from High Purity Chemicals.

화학공학의 이론과 응용 제8권 제1호 2002년

2. Preparation of Catalysts

Several compositions of oxide-based formulations, represented as M/MgO/Al2O3 and MM1/ MgO/Al2O3, (where, M and M1, = 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. The various catalyst formulations were prepared by the method of incipient wetness of the □-alumina with aqueous solutions of the corresponding metal nitrates. The solution containing the metal salts was added drop wise to precalcined alumina until incipient wetness was reached. The materials were then slowly dried at 80℃ for about 6 h. The sample were calcined for 5 h at 650℃ in dry air.

화학공학의 이론과 응용 제8권 제1호 2002년

화학공학의 이론과 응용 제8권 제1호 2002년

3. Gasoline POX reforming system

The performance of the commercial and the prepared catalysts was 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 over the temperature range of 550∼750oC, space velocity of 4,000∼43,000 h-1, 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, 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 which use a carbosphere 80/100, 10" x 1/8" SS column.

4. Catalyst Characterization

BET surface area and total pore volume of catalysts before and after the POX reforming reaction were measured by N2 physisorption. The active metal surface area of HT and prepared catalysts was calculated by CO chemisorption using a sorption analyzer [Quantachrome Autosorb-1C]. The contents of carbon and sulfur on catalysts before and after the POX reforming of iso-octane were measured by elemental inorganic analyzer [Leco Co. CS-344, EIA).

Results and discussion

In our previous work [1,2], we identified the problems of catalyst deactivation by carbon deposition and sulfur poisoning in the POX reforming reaction of iso-octane over the commercial reforming catalysts. In order to figure out deactivation of HT catalyst, the characteristics of the catalysts before and after the reaction are investigated by N2 physisorption, CO-chemisorption and elemental inorganic analyzer. The results are summarized in Table 1. It was found that BET surface area and active metal surface area of catalysts after the reaction decreased 14% and 58%, respectively. It was found that carbon contents deposited on the catalyst after the POX reforming of sulfur-containing iso-octane (S=100ppm)  and sulfur free iso-octane (S＠5ppm) are 24% and 7%, respectively. These results interpreted that carbon deposition on the surface of catalyst was inclined to promote in the POX reforming of sulfur-containing fuels. Therefore, we investigated various supported transition metal formulations for POX reforming reaction of iso-octane in order to develop a high performance catalyst with coke and sulfur resistance.

The characteristics of the prepared catalysts are summarized in Table 2. BET surface area 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 much higher than that of the commercial ICI and HT catalysts tested under the same conditions [1,2,5,6]. The Fe-supported system showed better activity than the other supported system in the general formula M(active)/MgO/Al2O3. 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 [5,6]. Figure 1 shows 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 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 [3,4,5,6]. Also, some KIST catalysts displayed better activity and sulfur tolerance than the commercial catalysts in the POX reforming reaction of iso-octane containing sulfur [5,6]. Figure 2 shows the comparison of the KIST-9 with the commercial HT 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 HT catalyst. BET surface area of HT and KIST-9 catalysts after the POX reforming reaction of iso-octane (S＠5ppm) decreased 14% and 12%, respectively, and on the other hand, that of HT and KIST-9 catalysts after reaction of iso-octane containing 100ppm of sulfur decreased 34% and 17%, respectively. It was interpreted that KIST-9 catalyst is more sulfur tolerance than HT catalyst, even though, new high performance catalyst with coke- and sulfur-resistance are to be developed for applying in the POX reformer based on gasoline feed.

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] 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).

[3] 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).

[4] J.M. Ogden, T.G.Kreutz, A comparison of hydrogen, methanol and gasoline as fuels for      fuel cell vehicles, J. of Power sources 79, 143-168 (1999)

[5] 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, (2002)

[6] D.J. Moon, S.D. Lee, and B.G. Lee, Partial oxidation (POX) reforming of gasoline for       Fuel-Cell Powered Vehicles Applications, submitted to Korean. J. of Chem. Eng.             (2002).

Table 1. Characteristics of the HT catalysts before and after the POX reforming of iso-octane.

Catalyst	Surface area	Total pore volume	Active metal surface area	Carbon content	Sulfur content
	(m2/g)	(cc/g)	(m2/g)	(wt.%)	(wt.%)
before the reaction	24.92	0.1541	5.043×10-1	0.098	0.003
after the reaction of iso-octane (S＠5ppm)	21.92	0.1704	2.118×10-1	7.0	0.004
after the reaction of iso-octane (S 100ppm)	16.34	0.1749	1.999×10-1	24.0	0.006

Table 2. Characteristics of the prepared catalysts.

Catalyst code	Catalyst formulation	Surface area	Total pore volume	Active metal surface area
		(m2/g)	(cc/g)	(m2/g)
KIST-1	Ni/MgO/Al2O3	28.90	0.2067	1.030
KIST-2	Fe/MgO/Al2O3	87.80	0.2276	4.994×10-2
KIST-3	Co/MgO/Al2O3	65.74	0.3051	3.181×10-1
KIST-4	Mo/MgO/Al2O3	87.74	0.2942	2.812×10-1
KIST-9	Ni/Fe/MgO/Al2O3	73.55	0.2116	1.906
KIST-10	Ni/Co/MgO/Al2O3	61.61	0.1722	1.842×10-1
KIST-11	Ni/Mo/MgO/Al2O3	72.44	0.2585	2.187×10-1

Fig.1 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.

Fig.2 Sulfur tolerance for the KIST-9 and commercial HT 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.