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Title: Effect of nickel hexaaluminate mirror cation on structure-sensitive reactions during n-tetradecane partial oxidation

Abstract

Reforming studies were conducted on nickel-substituted hexaaluminate catalysts, ANi0.4Al11.6O19-δ (A = La, Sr and Ba), to reform liquid hydrocarbon fuels into H2-rich synthesis gas for fuel cell applications. The reaction conditions studied were the partial oxidation of n-tetradecane (I) and n-tetradecane with 50 ppmw sulfur as dibenzothiophene (II). Hexaaluminate catalyst activity toward reaction conditions (I) and (II) as well as the surface Ni concentration and dispersion was shown to correlate with the type of mirror cation substituted into the lattice. The Ni surface concentration was determined by XPS to be 5.3, <0.1 and 0.7 wt.% for LaNi0.4Al11.6O19-δ, BaNi0.4Al11.6O19-δ and SrNi0.4Al11.6O19-δ, respectively. SrNi0.4Al11.6O19-δ and BaNi0.4Al11.6O19-δ catalysts exhibited stable performance for reaction condition (I), while the loss in activity exhibited over time by LaNi0.4Al11.6O19-δ suggested site blocking by carbon deposition. Under reaction condition (II), additional activity loss was experienced by both LaNi0.4Al11.6O19-δ and Al11.6O19-δ catalysts due to the presence of dibenzothiophene. However, LaNi0.4Al11.6O19-δ experienced more severe and partially reversible site blocking where SrNi0.4Al11.6O19-δ experienced a less severe loss of activity, selectivity and irreversible site blocking. The behavior observed in nickel-substituted hexaaluminate catalysts suggests that the different mirror cations influenced the coordination of Ni sites within the lattice and adsorption of hydrocarbons tomore » the surface of the catalysts.« less

Authors:
; ; ; ; ;  [1]
  1. West Virginia University, Morgantown, WV
Publication Date:
Research Org.:
National Energy Technology Laboratory (NETL), Pittsburgh, PA, and Morgantown, WV
Sponsoring Org.:
USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
913355
Report Number(s):
DOE/NETL-IR-2007-109
Journal ID: ISSN 0926-860X
DOE Contract Number:
None cited
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Catalysis. A, General; Journal Volume: 323
Country of Publication:
United States
Language:
English
Subject:
Nickel; Hexaaluminate; Partial oxidation; Sulfur; Diesel; Fuel cell

Citation Formats

Gardner, T H, Shekhawat, D, Berry, D A, Smith, M W, Salazar, M, and Kugler, E L. Effect of nickel hexaaluminate mirror cation on structure-sensitive reactions during n-tetradecane partial oxidation. United States: N. p., 2007. Web. doi:10.1016/j.apcata.2007.01.051.
Gardner, T H, Shekhawat, D, Berry, D A, Smith, M W, Salazar, M, & Kugler, E L. Effect of nickel hexaaluminate mirror cation on structure-sensitive reactions during n-tetradecane partial oxidation. United States. doi:10.1016/j.apcata.2007.01.051.
Gardner, T H, Shekhawat, D, Berry, D A, Smith, M W, Salazar, M, and Kugler, E L. Mon . "Effect of nickel hexaaluminate mirror cation on structure-sensitive reactions during n-tetradecane partial oxidation". United States. doi:10.1016/j.apcata.2007.01.051.
@article{osti_913355,
title = {Effect of nickel hexaaluminate mirror cation on structure-sensitive reactions during n-tetradecane partial oxidation},
author = {Gardner, T H and Shekhawat, D and Berry, D A and Smith, M W and Salazar, M and Kugler, E L},
abstractNote = {Reforming studies were conducted on nickel-substituted hexaaluminate catalysts, ANi0.4Al11.6O19-δ (A = La, Sr and Ba), to reform liquid hydrocarbon fuels into H2-rich synthesis gas for fuel cell applications. The reaction conditions studied were the partial oxidation of n-tetradecane (I) and n-tetradecane with 50 ppmw sulfur as dibenzothiophene (II). Hexaaluminate catalyst activity toward reaction conditions (I) and (II) as well as the surface Ni concentration and dispersion was shown to correlate with the type of mirror cation substituted into the lattice. The Ni surface concentration was determined by XPS to be 5.3, <0.1 and 0.7 wt.% for LaNi0.4Al11.6O19-δ, BaNi0.4Al11.6O19-δ and SrNi0.4Al11.6O19-δ, respectively. SrNi0.4Al11.6O19-δ and BaNi0.4Al11.6O19-δ catalysts exhibited stable performance for reaction condition (I), while the loss in activity exhibited over time by LaNi0.4Al11.6O19-δ suggested site blocking by carbon deposition. Under reaction condition (II), additional activity loss was experienced by both LaNi0.4Al11.6O19-δ and Al11.6O19-δ catalysts due to the presence of dibenzothiophene. However, LaNi0.4Al11.6O19-δ experienced more severe and partially reversible site blocking where SrNi0.4Al11.6O19-δ experienced a less severe loss of activity, selectivity and irreversible site blocking. The behavior observed in nickel-substituted hexaaluminate catalysts suggests that the different mirror cations influenced the coordination of Ni sites within the lattice and adsorption of hydrocarbons to the surface of the catalysts.},
doi = {10.1016/j.apcata.2007.01.051},
journal = {Applied Catalysis. A, General},
number = ,
volume = 323,
place = {United States},
year = {Mon Apr 30 00:00:00 EDT 2007},
month = {Mon Apr 30 00:00:00 EDT 2007}
}
  • The catalytic partial oxidation (CPOX) of transportation fuels into synthesis gas (H2 + CO) for fuel cells is complicated by the large quantities of aromatics and sulfur-containing compounds commonly found in these fuels. Traditional supported metal catalysts are easily poisoned by these species which adsorb strongly onto the electron-rich metal clusters. The use of noble metal and/or oxide based catalyst systems may offer higher activity and stability, but only if the metal can be bound into a thermally stable structure. To that end, Rh metal was substituted into the structure of a lanthanum zirconate (LZ) pyrochlore to give La2RhyZr(2 y)O(7-j,)more » (LRZ) to produce a strongly bound, well-dispersed metal which is active for CPOX. A second catalyst was prepared in which Sr was substituted for a portion of La in the LRZ structure, producing La(2 x)SrxRhyZr(2 y)O(7-j) (LSRZ). Each of these pyrochlore catalysts, including the unsubstituted LZ, were characterized and screened for activity in the CPOX of ntetradecane (TD), which is a surrogate for linear paraffins typical of diesel fuel. Results were compared to a commercial Rh/g-Al2O3 catalyst. X-ray diffraction patterns of both the LZ and LRZ showed that each had the cubic unit-cell pyrochlore structure. However, substitution of Sr resulted in a binary perovskite-pyrochlore phase with a defect SrZrO3 phase. Hydrogen pulse chemisorption and temperature programmed reduction studies confirmed that Rh metal was substituted into the structure of the LRZ and LSRZ, and was reducible. Activity screening with the CPOX of TD showed that the Rh substituted in both LRZ and LSRZ is able to retain activity-producing essentially equilibrium synthesis gas yields, as was the Rh/g-Al2O3. Temperature programmed oxidation experiments performed after the CPOX of TD demonstrated that the amount of carbon was quantitatively similar for each catalyst (roughly 0.3 gcarbon/gcatalyst after each run), with the exception of LSRZ, which had significantly less carbon (0.17 gcarbon/gcatalyst). It is speculated that improved oxygen ion mobility in the LSRZ material, which resulted from Sr substitution, was responsible for the reduction in carbon formation on the surface.« less
  • The catalytic partial oxidation (CPOX) of transportation fuels into synthesis gas (H2 + CO) for fuel cells is complicated by the large quantities of aromatics and sulfur-containing compounds commonly found in these fuels. Traditional supported metal catalysts are easily poisoned by these species which adsorb strongly onto the electron-rich metal clusters. The use of noble metal and/or oxide based catalyst systems may offer higher activity and stability, but only if the metal can be bound into a thermally stable structure. To that end, Rh metal was substituted into the structure of a lanthanum zirconate (LZ) pyrochlore to give La2RhyZr(2 y)O(7-j,)more » (LRZ) to produce a strongly bound, well-dispersed metal which is active for CPOX. A second catalyst was prepared in which Sr was substituted for a portion of La in the LRZ structure, producing La(2 x)SrxRhyZr(2 y)O(7-j) (LSRZ). Each of these pyrochlore catalysts, including the unsubstituted LZ, were characterized and screened for activity in the CPOX of ntetradecane (TD), which is a surrogate for linear paraffins typical of diesel fuel. Results were compared to a commercial Rh/g-Al2O3 catalyst. X-ray diffraction patterns of both the LZ and LRZ showed that each had the cubic unit-cell pyrochlore structure. However, substitution of Sr resulted in a binary perovskite-pyrochlore phase with a defect SrZrO3 phase. Hydrogen pulse chemisorption and temperature programmed reduction studies confirmed that Rh metal was substituted into the structure of the LRZ and LSRZ, and was reducible. Activity screening with the CPOX of TD showed that the Rh substituted in both LRZ and LSRZ is able to retain activity-producing essentially equilibrium synthesis gas yields, as was the Rh/g-Al2O3. Temperature programmed oxidation experiments performed after the CPOX of TD demonstrated that the amount of carbon was quantitatively similar for each catalyst (roughly 0.3 gcarbon/gcatalyst after each run), with the exception of LSRZ, which had significantly less carbon (0.17 gcarbon/gcatalyst). It is speculated that improved oxygen ion mobility in the LSRZ material, which resulted from Sr substitution, was responsible for the reduction in carbon formation on the surface.« less
  • Catalyst deactivation by high levels of sulfur and aromatics limits the catalytic partial oxidation (CPOX) of diesel fuel into a H2-rich stream for fuel cells. These species poison traditional supported metal catalysts because they adsorb strongly to electron dense metal clusters and promote the formation of carbon on the surface. In this work, Rh + Sr are substituted into lanthanum zirconate (LZ) pyrochlore (La2Zr2O7) to give an La(2-x)SrxRhyZr(2-y)O(7- î) (LSRZ) catalyst. The resistance to deactivation and carbon formation were examined by the CPOX of a mixture of 5 wt% 1-methylnaphthalene + 1000 ppmw dibenzothiophene in n-tetradecane. The results were comparedmore » to a commercial Rh/ã-Al2O3 catalyst. In the presence of these contaminants, the activity of the LSRZ was only kinetically inhibited, which is thought to be attributable to the oxygen-ion conductivity that results from Sr substitution into the pyrochlore structure. Rh/ã-Al2O3 was deactivated, likely due to significant carbon accumulation on/near the Rh metal« less
  • Catalytic partial oxidation (CPOX) of liquid fuels is being widely studied as an option for producing a hydrogen-rich gas stream for fuel cells. However, deactivation of catalysts by carbon deposition and sulfur poisoning in this process is a key technical challenge. Here, the deactivation of Co0.4Mo0.6Cx has been compared to that of 1 wt % Pt/γ-Al2O3 in a fixed-bed catalytic reactor, using mixtures of n-tetradecane and either 1-methylnaphthalene (1-MN) or dibenzothiophene (DBT) to simulate diesel fuel. The results show that Co0.4Mo0.6Cx is stable and active for the CPOX of n-tetradecane at 850 °C, 50000 scc/(gcat h), and an O/C ratiomore » of 1.2. This catalyst produces slightly lower H2 and CO yields than Pt/γ-Al2O3, but still close to equilibrium values for 5 h. A low concentration of sulfur (50 ppmw as DBT) has little effect on either activity or selectivity for the carbide or Pt/γ-Al2O3 catalyst. However, the presence of 1-MN or a high sulfur concentration (1000 ppmw as DBT) deactivates both catalysts, resulting in reaction products that are typical of gas-phase reactions in a blank reactor. The addition of 1-MN or 1000 ppmw DBT to n-tetradecane produces qualitatively similar results on both catalysts: H2 production decreases continuously in the presence of either 1-MN or DBT, and CO drops to a stationary level. This drop in synthesis gas yields corresponds to an increase in steam, CO2, and olefin yields, suggesting that the contaminants deactivate sites that are active for steam and dry reforming reactions downstream of the reactor inlet, where rapid oxidation takes place. Once the contaminants are removed, initial activity returns more quickly for the carbide than for Pt/γ-Al2O3.« less
  • Catalytic partial oxidation (CPOX) of liquid fuels is being widely studied as an option for producing a hydrogenrich gas stream for fuel cells. However, deactivation of catalysts by carbon deposition and sulfur poisoning in this process is a key technical challenge. Here, the deactivation of Co0.4Mo0.6Cx has been compared to that of 1 wt % Pt/γ-Al2O3 in a fixed-bed catalytic reactor, using mixtures of n-tetradecane and either 1-methylnaphthalene (1-MN) or dibenzothiophene (DBT) to simulate diesel fuel. The results show that Co0.4Mo0.6Cx is stable and active for the CPOX of n-tetradecane at 850 °C, 50000 scc/(gcat h), and an O/C ratiomore » of 1.2. This catalyst produces slightly lower H2 and CO yields than Pt/γ-Al2O3, but still close to equilibrium values for 5 h. A low concentration of sulfur (50 ppmw as DBT) has little effect on either activity or selectivity for the carbide or Pt/γ-Al2O3 catalyst. However, the presence of 1-MN or a high sulfur concentration (1000 ppmw as DBT) deactivates both catalysts, resulting in reaction products that are typical of gas-phase reactions in a blank reactor. The addition of 1-MN or 1000 ppmw DBT to n-tetradecane produces qualitatively similar results on both catalysts: H2 production decreases continuously in the presence of either 1-MN or DBT, and CO drops to a stationary level. This drop in synthesis gas yields corresponds to an increase in steam, CO2, and olefin yields, suggesting that the contaminants deactivate sites that are active for steam and dry reforming reactions downstream of the reactor inlet, where rapid oxidation takes place. Once the contaminants are removed, initial activity returns more quickly for the carbide than for Pt/γ-Al2O3.« less