Methods of reforming hydrocarbon fuels using hexaaluminate catalysts

CATEGORY: CATALYSIS
PATENT
Methods of reforming hydrocarbon fuels using hexaaluminate catalysts
Patent number: 8142756
Issue date: Mar 27, 2012
Application number: 12/717,372
Inventors: Todd H. Gardner, David A. Berry, Dushyant Shekhawat
Original Assignee: The United States of America as represented by the U.S. Department of Energy
Abstract
A metal substituted hexaaluminate catalyst for reforming hydrocarbon fuels to synthesis gas of the general formula AByAl12-yO19-δ, A being selected from alkali metals, alkaline earth metals and lanthanide metals or mixtures thereof. A dopant or surface modifier selected from a transitions metal, a spinel of an oxygen-ion conductor is incorporated. The dopant may be Ca, Cs, K, La, Sr, Ba, Li, Mg, Ce, Co, Fe, Ir, Rh, Ni, Ru, Cu, Pe, Os, Pd, Cr, Mn, W, Re, Sn, Gd, V, Ti, Ag, Au, and mixtures thereof. The oxygen-ion conductor may be a perovskite selected from M′RhO3, M′PtO3, M′PdO3, M′IrO3, M′RuO3 wherein M′=Mg, Sr, Ba, La, Ca; a spinel selected from MRh2O4, MPt2O4, MPd2O4, MIr2O4, MRu2O4 wherein M=Mg, Sr, Ba, La, Ca and mixtures thereof; a florite is selected from M″O2.
FIELD OF THE INVENTION
The present invention relates to catalyst deactivation by carbon deposition.
BACKGROUND OF THE INVENTION
Catalyst deactivation due to carbon formation is one of the most difficult challenges in the design of catalysts for the reforming of hydrocarbon fuels. Carbon deposits decrease catalyst activity by blocking active sites, causing attrition of catalyst particles and results in increasing pressure drop and ultimately discontinuation of the process.
The formation of carbon on the catalyst initiates either by reaction of the hydrocarbon on the active metallic surface or by cracking on the support material. Carbon formation on metallic surfaces is a structure sensitive reaction that preferentially initiates on the step edges of the metal crystallites. While step edges are more reactive toward C4C and CiH bond scission, their surface geometry results in highly coordinated sites (a greater number of next-nearest-neighbors) that facilitate the multipoint adsorption of heavy hydrocarbon molecules and the formation of carbon. By dispersing the active metals in a mixed-metal oxide that has a strong metalsupport interaction; such as hexaalumina, the active metals are maintained in a state of low coordination, with few contiguous clusters; thereby, disrupting the carbon formation mechanism. Ensembles, or groups of active sites, are also nucleation sites for carbon growth. By dispersing the active metal crystallites, the nucleation sites are eliminated minimizing carbon deposition. In this invention, transition metals are doped directly into the structure of hexaalumina, a high temperature refractory support material. The hexaalumina serves to not only disperse the active metal crystallites, but also creates a strong metal-support interaction that prevents these crystallites from aggregating, sintering and vaporizing.
SUMMARY OF THE INVENTION
It is a principal object of the present invention to provide a catalyst, a method of making same and method of using the catalyst which retains its usefulness over a long period of time in the presence of hydrocarbon fuels that normally cause a reduction in catalyst deficiency due to coping sulfur poisoning.
It is another object of the present invention to a metal substituted hexaaluminate catalyst for reforming hydrocarbon fuels to synthesis gas, comprising a hexaaluminate of the general formula AByAl12_yOl9_;,, wherein A is selected from the alkali metals, the alkaline earth metals, the lanthanide metals or combinations thereof, B is selected from the transition metals or mixtures thereof, and a dopant or a surface modifier selected from a transition metal or a spinel or an oxygen-ion conductor and mixtures thereof,
wherein the dopant is selected from Ca, Cs, K, La, Sr, Ba, Li, Mg, Ce, Co, Fe, Ir, Rh, Ni, Ru, Cu, Pe, Os, Pd, Cr, Mn, W, Re, Sn, Gd, V, Ti, Ag, Au and mixtures thereof, the spinel contains a dopant metal, and wherein if Ni is present as a dopant without a spinel or an oxygen-ion conductor Ni is present in a concentration of greater than 2.3% by weight and less than 4.4% by weight of the catalyst.
Another object of the present invention is to provide a metal substituted hexaaluminate catalyst for reforming hydrocarbon fuels to synthesis gas, comprising a hexaaluminate of the general formula AByAl12_yOl9_.., wherein A is selected from the Li, K, Ca, Ba, Sr, La, Ce and combinations thereof, B is selected from the Ni, Rh, Mn, Pd, Cu, Pt or combinations thereof, and a dopant or a surface deposit of a spinel or a perovskite or an oxygen-ion conducting fluorite or mixtures thereof, wherein the dopant is selected from K, Ca, Ba, Sr, La, Ce, Ni, Rh, Mn, Pd, Cu, Pt, Co, Ru, and mixtures thereof, the spinel is selected from MRh2O4, MPt2O4, MPd2O4, MIr2O4, MRu2O4 wherein M':Mg, Sr, Ba, La, Ca and mixtures thereof, the perovskite is selected from M'RhO3, M'PtO3, M'PdO3, M'IrO3 M'RuO3 wherein M':Mg, Sr, Ba, La, Ca and mixtures thereof, the oxygen-ion conducting fluorite is selected from M"O2 wherein M" is M, M' or mixtures thereof, and wherein if Ni is present alone as a dopant without a spinel or a perovskite or fluorite Ni is present in a concentration of greater than 2.3% by weight and less than 4.4% by weight of the catalyst.
A further object of the invention is to provide a method of reforming a fuel containing hydrocarbons to produce a synthesis gas, comprising contacting the hydrocarbon containing fuel under reforming conditions with a catalyst of a hexaaluminate of the general formula AByAl12_yOl9_6, wherein A is selected from the alkali metals, the alkaline earth metals, the lanthanide metals or combinations thereof, wherein A is selected from the alkali metals, the alkaline earth metals, the lanthanide metals or combinations thereof, B is selected from the transition metals or mixtures thereof, and a dopant or a surface modifier selected from a transition metal or a spinel or an oxygen-ion conductor and mixtures thereof, wherein the dopant is selected from Ca, Cs, K, La, Sr, Ba, Li, Mg, Ce, Co, Fe, Ir, Rh, Ni, Ru, Cu, Pt, Os, Pd, Cr, Mn, W, Re, Sn, Gd,V, Ti, Ag, Au and mixtures thereof, the spinel is selected from MRh2O4, MPt2O4, MPd2O4, MIr2O4, MRu2O4 wherein M:Mg, Sr, Ba, La, Ca and mixtures thereof, the perovskite is selected from M'RhO3, M'PtO3, M'PdO3, M'IrO3 M'RuO3 wherein M':Mg, Sr, Ba, La, Ca and mixtures thereof, said oxygen-ion conducting fluorite is selected from M"O2 wherein M" is M, M' or mixtures thereof, and wherein if Ni is present alone as a dopant without a spinel or a perovskite or fluorite Ni is present in a concentration of greater than 2.3% by weight and less than 4.4% by weight of the catalyst, whereby to convert at least a portion of the hydrocarbon containing fuel to hydrogen and carbon monoxide.
A final object of the present invention is to provide a method of preparing a metal substituted hexaaluminate catalyst for reforming hydrocarbon fuels to synthesis gas, the hexaaluminate being of the general formula AByAl12_yOl9_f,, whereinA is selected from the alkali metals, the alkaline earth metals, the lanthanide metals or combinations thereof, B is selected from the transition metals or combinations thereof, and a dopant or a surface deposit of a spinel or a perovskite or mixtures thereof, wherein the dopant is selected from Ca, Cs, K, La, Sr, Ba, Li, Mg, Ce, Co, Fe, Ir, Rh, Ni, Ru, Cu, Pt, Os, Pd, Cr, Mn, W, Re, Sn, Gd, V, Ti, Ag, Au and mixtures thereof,
the spinel is selected from MRh2O4, MPt2O4, MPd2O4, MIr2O4, MRu2O4 Wherein M:Mg, Sr, Ba, La, Ca and mixtures thereof, the perovskite is selected from M'RhO3, M'PtO3, M'PdO3, M'IrO3 M'RuO3 Wherein M':Mg, Sr, Ba, La, Ca and mixtures thereof, the oxygen-ion conducting fluorite is selected from M"O2 Wherein M" is M, M' or mixtures thereof, and Wherein if Ni is present alone as a dopant Without a spinel or a perovskite or fluorite Ni is present in a concentration of greater than 2.3% by Weight and less than 4.4% by Weight of the catalyst, the method comprising forming an aqueous nitrate solution of the catalyst constituents containing Al ions in an acidic environment, adjusting the acidic environment to a pH suflicient to precipitate the constituents, filtering and rinsing the precipitated constituents to remove extraneous liquid and thereafter calcining the precipitate for a time and at a temperature sufficient to produce the catalyst or forming a metallo-isopropoxide of the desired constituents and adding same to Water folloWed by rinsing and drying to form a cake and calcining the cake at a temperature and for a time sufficient to form the catalyst or forming a mixture of the constituent oxides folloWed by addition of Water folloWed by drying and calcining oxides at a temperature and for a time sufficient to form the catalyst.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying draWings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made Without departing from the spirit, or sacrificing any of the advantages of the present invention.
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