Paper 11 EF 2009 WGS Thermodynamic Experimental OK

• Al
• Al

2 O), in the form of

• Cr
• CO

  (3) Jacobs, G.; Williams, L; Graham, U; Sparks, D.; Davis, B. H. Low- temperature water-gas shift: In-situ DRIFTS-reaction study of a Pt/CeO

²

catalyst for fuel cell reformer applications. J. Phys. Chem. B 2003, 107, 10398–10404 .

  (2) Wheeler, C.; Jhalani, A.; Klein, E. J.; Tummala, S.; Schmidt, L. D. The water-gas shift reaction at a short contact time. J. Catal. 2004, 223, 191–199 .

  (1) Panagiotopoulou, P.; Kondarides, D. I. Effect of morphological characteristics of TiO ^{2 -supported noble metal catalysts on their activity for} the water-gas shift reaction. J. Catal. 2004, 225, 327–336 .

  we demonstrated that noble metal catalysts, especially platinum (Pt) and ruthenium (Ru), and transition-metal catalysts [nickel (Ni)] showed good performance for the WGS reaction at high temperatures (700 °C). Because of its low price compared to noble metals, it is reasonable to develop further the Ni catalyst. Moreover, our observation was

  7,8

  In previous works,

  3-5%, while a LTS reactor with Cu-ZnO/Al

  2 O 3 catalysts further decrease the CO level to less than 1%.

  2 O 3 catalysts reduce the CO content from 8-10 to

  3

  2 O

  Typical designs of HTS WGS reactors with Fe

  4-6

  2 O 3 ) catalyst.

  (4) Qi, X; Flytzani-Stephanopoulos, M. Activity and stability of Cu- CeO ^{2 catalysts in high-temperature water-gas shift for fuel-cell applications.}

  (5) Quadro, E. B.; de Lourdes, M.; Dias, R.; Amorim, A. M. M.; do Carmo Rangel, M. Chromium and copper-doped magnetite catalysts for the high temperature shift reaction. J. Braz. Chem. Soc. 1999, 10 (1), 51– 59 .

  Ind. Eng. Chem. Res. 2004 , 43, 3055–3062 .

  ∆H

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  3097 10.1021/ef801076r CCC: $40.75  2009 American Chemical Society

  3097–3102

  Energy & Fuels 2009, 23,

  ) - 41.2 kJ/mol (1)

  298

  2

  (6) Bustamante, F.; Enick, R. M.; Killmeyer, R. P.; Howard, B. H.; Rothenberger, K. S.; Cugini, A. V.; Morreale, B. D.; Ciocco, M. V. Uncatalyzed and wall-catalyzed forward water-gas shift reaction kinetics.

  2

  CO + H

  (8) Haryanto, A.; Fernando, S.; Adhikari, S. H ^{2 yield from water gas} shift reaction over bimetallic Pt-Ru and Ni catalysts supported on ceria-alumina at high temperatures. Presented at the Institute of Biological Engineering (IBE) Meeting, St. Louis, MO, March 29-April 1, 2007.

  Catal. Today 2007 , 129, 269–274 .

  (7) Haryanto, A.; Fernando, S.; Adhikari, S. Ultrahigh temperature water gas shift catalysts to increase hydrogen yield from biomass gasification.

  AIChE J. 2005 , 51 (5), 1440–1454 .

  (LTS) section operating in a temperature range of 200-250 °C with copper-zinc oxide supported on an alumina (Cu-ZnO/ Al

  2 O 3 ) and a low-temperature shift

  3

  g

  Hydrogen Production through the Water-Gas Shift Reaction: Thermodynamic Equilibrium versus Experimental Results over Supported Ni Catalysts Agus Haryanto,

  †,‡ Sandun D. Fernando,*

  ,§ S. D. Filip To,

  † Philip H. Steele, ^| Lester Pordesimo,

  † and Sushil Adhikari

  ⊥ Agricultural and Biological Engineering Department, and Department of Forest Products, Mississippi State UniVersity, Mississippi State, Mississippi 39762, Agricultural Engineering Department, UniVersity of

  Lampung, Bandar Lampung 35145, Indonesia, Biological and Agricultural Engineering Department, Texas A&M UniVersity, College Station, Texas 77843, and Biosystems Engineering Department, Auburn UniVersity, Auburn, Alabama 36849 ReceiVed December 9, 2008. ReVised Manuscript ReceiVed March 5, 2009

  This paper discusses the experimental results of the water-gas shift reaction over supported nickel catalysts in comparison to thermodynamic equilibrium composition at the same reaction conditions. The effects of different supports on the performance of H

  2

  production over nickel-supported catalysts are also evaluated at both low and high temperatures. Ceria-promoted nickel catalyst supported on powder alumina (Ni/CeO

  2

  2 O 3 )

  demonstrated excellent performance. The catalyst was not stable at low temperature (250 °C) but showed good stability at high temperature (450 °C). At 450 °C, with a catalyst loading of 0.05 g, CO/S (S ) steam) ratio of 1:3, and gas hourly space velocity (GHSV) ≈ 200 L h ^-

  1

  cat ^-

  2 O

  1

  In industrial processes, it is important to have high reaction rates and to obtain maximum concentrations of the desired products. To produce high-purity hydrogen at the highest possible CO conversions, two-stage adiabatic reactors, with cooling in between, are used. These reactors consist of a high- temperature shift (HTS) section operated at 320-450 °C with a catalyst based on iron oxide structurally promoted with chromium oxide (Fe

  

2 ,

which is a fuel for hydrogen fuel cells.

  Recently, the WGS reaction has attracted renewed interest because of rapid innovations in fuel cell technology. CO existent in the synthesis gas produced via steam reforming of hydro- carbons (e.g., natural gas, petroleum, or renewable resources) and gasification of coal or biomass is poisonous to the catalysts used in fuel cells. The benefit of using the WGS reaction is that it reduces the CO concentration while producing extra H

  1-3

  2 ) and carbon dionoxide (CO 2 ). The reaction is presented below.

  steam, is reacted with carbon monoxide (CO) to produce hydrogen (H

  The water-gas shift (WGS) reaction is an established industrial technology, in which water (H

  Introduction

  2 yield of 52% and a H 2 selectivity of 73%.

  was 95% with a H

  3

  2 O

  2

  , the activity of Ni/CeO

2 O h H

• Cr
• To whom correspondence should be addressed. Telephone: +1-979- 845-9793. Fax: +1-979-845-3932. E-mail: sfernando@tamu.edu. _† Agricultural and Biological Engineering Department, Mississippi State University. _‡ University of Lampung. _§ Texas A&M University. _| Department of Forest Products, Mississippi State University. _⊥ Auburn University.

  Table 1. Composition of Prepared Nickel-Based Catalysts and Their BET Surface Areas catalyst number name composition BET (cm ² /g)

  6.44

  For an equimolar reaction, as presented by eq 1, equilibrium CO conversion (X) can be calculated using eq 3

  16

  and the compositions of output gases are determined using the mass balance principle where w is the number of moles of water and k

  1 K n i

  ∑ i)

  i

  ∆G

  1 K n i

  9.01 G ) ∑ i)

  9 Ni/CeO ^{2 -} Al ^{2 O 3 powder 4% Ni; 3% CeO 2 ; 93% Al 2 O 3}

  8 Ni/CeO ^{2 -} Al ^{2 O 3 monolith 4% Ni; 3% CeO 2 ; 93% Al 2 O 3}

  and the function can be expressed as follows: where G i is the Gibb’s free energy for species i at standard conditions, n i is the number of moles of species i, y i is the mole fraction of species i, R is the universal gas constant (8.3144 J mol ^-

  7 Ni/CeO ^{2 -}

Sm 4% Ni; 81.6% CeO

^{2 ; 14.4% Sm 425.00}

  6 Ni/CeO ^{2 -}

Gd 4% Ni; 76.8% CeO

^{2 ; 19.2% Gd 119.30}

  5 Ni/CeYO

^{5 4% Ni; 96% CeO}

^{2 -} Y 100.50

  4 Ni/CeZrO

^{4 4% Ni; 96% CeO}

^{2 -} ZrO ^{2 102.00}

  1.53

  3 Ni/Al ^{2 O}

^{3 monolith 4% Ni; 96% Al}

^{2 O 3}

  3.79

  2 Ni/Al ^{2 O}

^{3 powder 4% Ni; 96% Al}

^{2 O 3}

  80.79

  1 Ni/CeO

^{2 4% Ni; 96% CeO}

²

  1 K

• ^- 1 ), T is the absolute temperature, and P is the pressure (in atm).

  15

• RT
• RT

  11 The existence of Ni in the CeO

  i

  ∑ i)

  1 K n i

  ln P (2)

  reinforced by a recent review work by Davda et al. that reported that Ni catalysts had higher activity in WGS reactions than noble metals, such as Pt or Rh (rhodium).

  natural gas. However, Ni also plays an important role in the WGS reaction. For example, Willms reported that Ni was a good catalyst for producing H

  2

  either through the WGS reaction or the steam-reforming process.

  3098 Energy & Fuels, Vol. 23, 2009 Haryanto et al.

9 Nickel catalysts are commonly used in steam reforming of

  ln y

10 Cooper also noted that Ni, which

  forms a part of the anode composition, facilitated the WGS reaction to take place on the surface of the anode of solid oxide fuel cells.

• supported bimetallic Ni-Rh catalyst reportedly helped conversion of CO into CO

  and H

  

2

  2

  2 by the WGS reaction.

  12 Chu et al. observed that Ni/ceria had a higher activity for

  2

  X

  )

  k eq

  the WGS reaction than Fe/ceria. Nickel catalysts, however, seemed to be good for HTS than for the LTS reaction.

13 Li et

  6H

  . It was also observed that, at around 350 °C, the activity of the Ni-loaded catalyst surpassed the activity of the Cu-loaded one.

  Experimental Procedures. Nine nickel-based catalysts, with

  and

  17

  is the equilibrium constant and is determined using the following relations:

  eq

  composition of a reaction is accomplished when Gibb’s energy function (G) achieves a minimum point. The derivation of Gibb’s energy function was performed previously,

  Experimental Section Thermodynamic Equilibrium. Thermodynamic equilibrium

  9. Experiments were carried out at temperatures of 250 and 450 °C with a CO/steam (CO/S) molar ratio of 1:3.

  equilibrium compositions and experimental results of the WGS reaction using nickel catalysts. Analysis of thermodynamic equilibrium was performed over the temperature range of 27-1227 °C (300-1500 K) and CO/S molar ratios of 1:1-1:

  14 The aim of this research was to compare thermodynamic

  x

  4

  catalyst was much superior than the support itself, i.e., Ce(La)O

  x

  (1 - X)(w - X) (3)

  k eq

  ) exp[Z(Z(0.63508 - 0.29353Z) + 4.1778) + 0.31688] (4)

  Z ) (1000/T) - 1 (5)

  It was found that the Ni-Ce(La)O

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  1 and a temperature range of 150-550 °C.

  al. investigated the use of ceria-lantana-supported catalysts in the WGS reaction at gas hourly space velocities (GHSVs) of 8000 and 80 000 h ^-

  compositions as presented in Table 1, were prepared by an incipient wetness technique. Monolith alumina (from Vesuvius Hi Tech Ceramics, Champaign, IL) was crushed and sieved to obtain particle sizes of 20-60 mesh. Other supports including ceria-zirconia (CeZrO

  ), ceria-yttria (CeYO

  2 O] (Sigma-Aldrich).

  (17) Twigg, M. V. Catalyst Handbook, 2nd ed.; Wolf Publishing Ltd.: Frome, U.K., 1989; p 608.

  The Ni precursor was diluted with distilled water to make a solution with a Ni concentration of 3.85% (w/w). The solution was used for loading Ni into the supports. The Ni loading for all catalysts was 4% (w/w). The catalysts were dried at 75 °C overnight. For ceria-promoted catalysts, ceria (3%, w/w) was impregnated and dried prior to Ni loading. The catalysts were calcined at 500 °C in a muffle furnace for 3 h. Except for catalysts supported on monolith alumina, the catalysts were pelletized, crushed, and sieved to obtain particle sizes between 20 and 60 mesh.

  (9) Davda, R. R.; Shabaker, J. W.; Huber, G. W.; Cortright, R. D.; Dumesic, J. A. A review of catalytic issues and process conditions for renewable hydrogen and alkanes by aqueous-phase reforming of oxygenated hydrocarbons over supported metal catalysts. Appl. Catal., B 2005, 56, 171– 186 .

  (10) Willms, R. S.; Wilhelm, R.; Okuno, K. Performance of a palladium membrane reactor using a Ni catalyst for fusion fuel impurities processing. Presented at the Third International Symposium on Fusion Nuclear Technology, Los Angeles, CA, June 27-July 1, 1994.

  (11) Cooper, R. J.; Billingham, J.; King, A. C. Flow and reaction in solid oxide fuel cells. J. Fluid Mech. 2000, 411, 233–262 . (12) Kugai, J.; Velu, S.; Song, C. Low-temperature reforming of ethanol over CeO ^{2 -supported Ni-Rh bimetallic catalysts for hydrogen production.}

  Catal. Lett. 2005 , 101, 255–264 .

  (13) Chu, D.; Lee, I. C.; Pati, R. K.; Ehrman, S. H. Ceria based nano- scale catalysts for water-gas shift (WGS). http://www.asc 2004.com/ Manuscripts/sessionM/MP-03.pdf (accessed on Jan 5, 2004).

  (14) Li, Y.; Fu, Q.; Flytzani-Stephanopoulos, M. Low-temperature water-gas shift reaction over Cu- and Ni-loaded cerium oxide catalysts.

  Appl. Catal., B 2000 , 27, 179–191 .

  (15) Adhikari, S.; Fernando, S.; Haryanto, A. A comparative thermo- dynamic and experimental analysis on hydrogen production by steam reforming of glycerin. Energy Fuels 2007, 21, 2306–2310 .

  (16) Haryanto, A.; Fernando, S.; Adhikari, S. Ultrahigh temperature water gas shift catalysts to increase hydrogen yield from biomass gasifica- tion. Catal. Today 2007, 129 (3-4), 269–274 .

  2

  5

  )

  3

  Aldrich) was used as the ceria promoter for Ni supported on alumina catalysts. The Ni precursor for this experiment was nickel nitrate hexahydrate [Ni(NO

  2 O] (Sigma-

  6H

  ·

  3

  )

  3

  ), ceria-(20%) gadolinia, ce- ria-(15%) samaria [all from Sigma Aldrich (St. Louis, MO)], and ceria particles (NanoScale Materials, Manhattan, KS) were used as received. Cerium nitrate hexahydrate [Ce(NO

  ·

• [CO]

  2

  2

  yield. This provides evidence that the WGS reaction is favorable at low temperature. For instance, with the CO/S molar ratio of 1:3, the CO conversion was 99% at 250 °C and 94% at 450 °C. It can also be observed that increasing the number of moles of steam positively influenced CO conversion at the same temperature. For example, decreasing steam from 3 to 1 mol reduced the CO conversion from 99 to 90% and from 94 to 73%, respectively, at 250 and 450 °C. Increasing the steam flow Figure 1. Schematic of the experimental setup for the WGS reaction.

  Figure 2. Equilibrium CO conversion (XCO) of the WGS reaction at atmospheric pressure, at temperatures of 27-1227 °C, and at CO/steam molar ratios of 1:1-1:9.

  XCO ) [CO]

  in

  out

  [CO]

  in

  × 100% (6)

  SH

  ) [H

  2 yield, respectively.

  2

  ]

  yield

  [H

  2

  ]

  max

  × 100% (7) H

  2

  yield (%, v/v) )

  XCO 1 + XCO (8)

  From the figure, it can be observed that increasing the reaction temperature resulted in decreasing CO conversion and, therefore, H

  yield (vol %, dry) can be related to CO conversion (XCO) as follows: This means a 100 and 50% CO conversion results in 50 and 33% (v/v, dry) H

  Catalyst surface areas were measured using an Autosorb-1C (Quantachrome, Boynton Beach, FL) surface area analyzer. The surface areas were measured by the Brunauer-Emmett-Teller (BET) method using nitrogen adsorption isotherms. Prior to surface area measurements, samples were degassed at 300 °C for 3 h. In addition, to measure carbon deposits on the spent catalysts, a thermogravimetric analysis (TGA) were performed on a TG/DTA 6300 instrument (Perkin-Elmer Instrument, Wellesley, MA). The system was capable of measuring the change in mass of a sample as a function of the temperature up to 1100 °C. Temperature ramping of 20 °C/min with an air flow rate of 100 cc m

• ^- 1

  The catalyst performance is demonstrated by catalyst activity, H

  was used. The catalysts test setup is shown in Figure 1. The reactor consisted of a quartz tube from Technical Glass Products (Paines- ville Township, OH) with 12.51 mm outside diameter, 10.01 mm inside diameter, and 50 cm length. Bids of quartz wool were used to hold the catalyst in the tube. A tube furnace (Lindberg Blue M 33850-00, Cole Parmer, Vernon Hill, IL) capable of reaching 1100 °C was used as a heat source for the reactor. A thermocouple was inserted inside the tube to measure the actual reaction temperature. The testing was conducted at a low temperature (250 °C) and a high temperature (450 °C), at a CO flow rate of 15 cm

  3

  at a steam flow rate of 0.04 mL/min, and at a catalyst loading of 1 g diluted in 1.5 g of fused SiO

  2 (Sigma Aldrich). Water was delivered using

  a high-pressure liquid chromatograph (HPLC) pump (LC- 20AT, Shimadzu Scientific Instrument, Columbia, MD), while the CO flow rate was maintained using a mass flow controller (MFC, Cole Parmer). To avoid condensation of unreacted steam in the reactor tube, the section of the quartz tube protruding out from the furnace

  The output gas was cooled, dried, and then measured with another MFC. A large portion of the gas was vented, and a smaller portion was routed to the gas chromatograph (GC, GC6890N, Agilent Technologies, Inc., Palo Alto, CA). The GC used a thermal conductivity detector (TCD) to detect H

  2 and a flame ionization

  detector (FID) to detect CO, CH

  4 , and CO 2 . Helium and nitrogen

  were used as carrier gases for the FID and TCD, respectively. Three columns including HP-Molsiv (30 × 0.53), HP-Plot Q (30 × 0.53), and HP-Plot Q (15 × 0.53) were used in the GC.

  2 yield (vol %), and H 2 selectivity. The catalyst activity is

  2

  presented as CO conversion (XCO) and defined as follows: Hydrogen selectivity (SH

  2

  ) is defined as follows: Here, [H

  2

  ]

  max

  is the maximum H

  2

  yield based on thermodynamic equilibrium at the respected temperature and CO/S ratio.

  Results and Discussion

  Figure 2 presents thermodynamic CO conversion between 27 and 1227 °C for different CO/S molar ratios (1:1-1:9). On the basis of eq 1, it can be inferred that H

  Hydrogen Production through the WGS Reaction Energy & Fuels, Vol. 23, 2009 3099 Downloaded by UNIV OF MISSOURI COLUMBIA on August 16, 2009 Published on April 27, 2009 on http://pubs.acs.org | doi: 10.1021/ef801076r

  3100 Energy & Fuels, Vol. 23, 2009 Haryanto et al.

  activity of ceria-promoted Ni catalyst supported on powder alumina (96%) was quite close to the equilibrium CO conversion (99.6%) at the same temperature (250 °C) and CO/S molar ratio (1:3).Allofceria-supportedcatalysts(includingceria,ceria-zirconia, ceria-yttria, ceria-gadolinia, and ceria-samaria) showed a comparable activity of around 80%. The use of the monolith alumina as the support resulted in catalysts having the lowest activities (around 60%).

  As presented in Figure 4, the catalyst activity was related closely to the BET surface area. The higher the BET surface area, the more active the catalyst. The BET surface area, however, was not the only factor affecting catalyst activity. With a lower BET surface area, Ni supported on powder alumina still produced the highest activity. Atomic structure, which was

  Figure 3. Initial CO conversion with different nickel catalysts at 250 °C

  beyond our focus, was likely responsible for the behavior of

  (conditions: catalyst loading, 1 g; CO/steam molar ratio, 1:3; and GHSV, _{3 1 1}

• ^- these catalysts.

  7500 cm h ^- g ^{cat ).}

  All of the prepared Ni catalysts, however, were not stable at low temperature (250 °C). Figure 5 shows that the catalyst activity decreased quickly. The decrease in CO conversion led to a conjecture that the catalyst was deactivated because of carbon deposition. Therefore, a TGAs were performed to test the above supposition. The weight profiles resulting from TGAs (Figure 6), however, revealed that there were no dramatic mass changes above 400 °C, where carbon burned, for most catalysts. The only case for the presence of carbon deposits occurred with

  2 Sm). For this catalyst, carbon

• catalyst number 7 (Ni/CeO

  deposition was 4.77% (by weight). This implied that the deactivation for most catalysts was not due to carbon deposition. A better reason for catalyst deactivation was chemical changes at the catalysts surface because of CO binding. This happened,

  Figure 4. Initial CO conversion versus BET surface area of different

  for example, with platinum catalysts, which had a higher affinity

  Ni catalysts at 250 °C (conditions: catalyst loading, 1 g; CO/steam _{3 1 1}

• ^- toward CO at low temperatures, resulting in a binding of the
• ^- molar ratio, 1:3; and GHSV, 7500 cm h g ^{cat ).}

  18,19 catalyst active sites with CO.

  We observed that with 1 g of catalyst loading, some catalysts rate, however, has resulted in little effect on CO conversion. initially produced an extremely high activity. The activity was

  Besides, increasing the steam flow rate implies that more energy expected to be higher during the high-temperature (450 °C) test. is required to evaporate water. Therefore, we considered the

  For this reason, when testing at 450 °C, the catalyst loading CO/S ratio of 1:3 to be reasonable for use in our experiment. was reduced to 50 mg, while other conditions were kept

  Figure 3 shows the initial CO conversion for the prepared unchanged. The results of that experiment are presented in Ni catalysts at low temperature (250 °C). It can be seen that Ni Figure 7 (averaged over around 12 h). supported on powder alumina, with or without ceria promoter, showed the highest activity. With a catalyst loading of 1 g and It can be observed that at high temperature (450 °C) all catalysts

• _{- -}

  3

  1

1 GHSV of 7500 cm h g cat , the catalysts had activities of showed better performance than at low temperature (250 °C). Four

  Downloaded by UNIV OF MISSOURI COLUMBIA on August 16, 2009 Published on April 27, 2009 on http://pubs.acs.org | doi: 10.1021/ef801076r

  2 Al

• 96 and 92%, with and without ceria promoter, respectively. The catalysts including Ni/CeO

  2 O 3 (powder), Ni/CeO 2 , Ni/CeYO 5 , CO conversion versus time on stream for different Ni catalysts at 250 °C (conditions: catalyst loading, 1 g; CO/steam molar ratio, 1:3; _{- -} Figure 5. _{3 1 1} and GHSV, 7500 cm h g ^{cat ).}

  Hydrogen Production through the WGS Reaction Energy & Fuels, Vol. 23, 2009 3101 Figure 6. Catalyst weight profiles resulting from TGAs [catalysts are numbered as follows: (1) Ni/CeO ^{2 , (2) Ni/Al 2 O 3 powder, (3) Ni/Al 2 O 3 monolith,}

^{2 Al 2 O 3 monolith, and (9) Ni/CeO 2 Al 2 O} 3 powder].<
• (4) Ni/CeZrO ^{4 , (5) Ni/CeYO 5 , (6) Ni/CeO}
^{2 Gd, (7) Ni/CeO 2 Sm, (8) Ni/CeO}

  Figure 9. Average CH ^{4 yield for different catalysts at 450 °C} _- (conditions: catalyst loading, 0.05 g; CO/steam molar ratio, 1:3; and _{1 1} ^- GHSV, 207 L h ). g ^cat

  Figure 7. Average performance of Ni catalysts for the WGS reaction at 450 °C (conditions: catalyst loading, 0.05 g; CO/steam molar ratio,

  had an average activity of 95%, H yield of 52% (v/v), and H

• _{- 1 1 -}

  2

  2 1:3; and GHSV, 207 L h g ^{cat ). Note that the H 2 yield is expressed}

  selectivity of 73%. At the same conditions, the equilibrium CO in vol/vol. conversion was 94% with a H yield of 50%. The differences

  2

  may have been the result of inaccuracies with flow rate readings, which, in fact, fluctuated from the set point during the experiment. Our results, with an acceptable error, suggested that

  Downloaded by UNIV OF MISSOURI COLUMBIA on August 16, 2009 Published on April 27, 2009 on http://pubs.acs.org | doi: 10.1021/ef801076r

• 2

  the performance of the Ni/CeO Al O catalyst was extremely

  2

  3

  active in the HTS WGS reaction and achieved equilibrium CO conversion even at very little loading (0.05 g).

  It can also be observed that catalysts without ceria [catalyst number 2 (Ni/Al O , powder) and catalyst number 3 (Ni/Al O ,

  2

  3

  2

  3

  monolith)] had the lowest H yield, CO conversion, and H

  2

  2

  selectivity compared to those supported on or promoted with ceria. This observation provides evidence that the presence of ceria was advantageous for WGS catalysts. The beneficial role of ceria for WGS catalyst has been reported, among others, by

  Catalyst stability at 450 °C for about 12 h (conditions: catalyst

  20

  21

  22 Figure 8. _{1 -} Hilaire et al., Gorte and Zhao, and Swartz et al. loading, 0.05 g; CO/steam molar ratio, 1:3; and GHSV, 207 L h

  Most catalysts, however, produced unwanted CH . The evolution

  4 ^- g _cat ¹ ).

  of CH formation during the WGS reaction is presented below.

  4

  and Ni/CeO Gd exhibited very good activity. Except for Ni/

• 2 (18) Ralph, R.; Hogarth, M. P. Catalysis for low temperature fuel cells.
• 2

  CeO Gd, the other three catalysts demonstrated extremely high

  Part II: The anode challenges. Platinum Met. ReV. 2002, 46, 117–135 .

  (19) Si, Y.; Jiang, R.; Lin, J.-C.; Kunz, H. R.; Fenton, J. M. CO tolerance

  H yield and good stability over the 12 h test period. As can be

  2 of carbon-supported platinum-ruthenium catalyst at elevated temperature

• 2

  observed from Figure 8, Ni/CeO Gd also took a longer time to

  and atmospheric pressure in a PEM fuel cell. J. Electrochem. Soc. 2004,

• 2

  reach steady state. Two catalysts, Ni/CeO Al O (powder) and

  2

3 151

, A1820–A1824 .

  (20) Hilaire, S.; Wang, X.; Luo, T.; Gorte, R. J.; Wagner, J. A Ni/CeO , had H selectivity &gt; 70%.

  2

  2 comparative study of water-gas-shift reaction over ceria-supported metallic

  In general, the ceria-promoted Ni catalyst supported on catalysts. Appl. Catal., A 2004, 258, 271–276 . alumina powder demonstrated the best performance in the HTS

  (21) Gorte, R. J.; Zhao, S. Studies of the water-gas-shift reaction with WGS reaction. At 450 °C and a CO/S ratio of 1:3, the catalyst ceria-supported precious metals. Catal. Today 2005, 104, 18–24 .

  3102 Energy &amp; Fuels, Vol. 23, 2009 Haryanto et al.

  298

  h ) of a potential drawback of using monolith alumina as a support CO + 3H CH H O

• 2

  ∆H

  4

  2 for Ni catalysts.

  298

• Conclusions

  ) - 206 kJ/mol 142.2 kJ (9) ∆G

  298

• ) h

  CO

  4H CH

  2H O

  2

  2

  4 2 ∆H

  It can be concluded that ceria-promoted Ni catalyst supported

  298

  ) - 165 kJ/mol 113.7 kJ (10) on alumina powder (Ni/CeO Al O , Ni/CeO , and Ni/CeYO ) ∆G

  2

  2

  3

  2

  5

  demonstrated the best performance for the WGS reaction in

  298

  ) h

  2CO + 2H

• CH CO

  ∆H terms of activity, H yield, and H selectivity. The catalysts were

  2

  4

  2

  2

  2 298

  stable at high temperature (450 °C) but unstable at low ) - - 247 kJ/mol 170.8 kJ (11)

  ∆G temperature (250 °C). With catalyst loading of 0.05 g and GHSV

• _{- -}

  1

  1

• cat

  of 207 L h g , 4% Ni/CeO Al O showed the highest

  2

  2

  3

23 Tanaka and Iizuka suggested that, after the WGS reaction,

  performance, with activity of 95%, H yield of 52% (v/v), and

  2

  the formation of CH 4 occurred through the hydrogenation of H selectivity of 73% (averaged over 12 h).

  2 carbonaceous species formed by the dissociation of CO or CO .

2 EF801076R

  All of the aforementioned methanation routes require H

2 .

Therefore, the higher the CH yield, the lower the H yield.

  4 2 (22) Swartz, S.; Azad, A.-M.; Seabaugh, M. Ceria-based water-gas-shift catalysts. Presented at The 2002 Fuel Cell Seminar and Exposition, Palm

  Figure 9 shows that the monolith alumina-supported catalysts Springs, CA, Nov 18-21, 2002; pp 587-590. (with or without ceria promotion) produced the highest CH

  

4

(23) Tanaka, Y.; Iizuka, T. Methanation of carbon monoxide with water yield, around 5 vol % on average. This was another indicator over supported rhodium catalysts. Aust. J. Chem. 1985, 38, 293–296 .

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