Catalyst support of mixed cerium zirconium titanium oxide, including use and method of making
View Patent ↗A durable catalyst support/catalyst is capable of extended water gas shift operation under conditions of high temperature, pressure, and sulfur levels. The support is a homogeneous, nanocrystalline, mixed metal oxide of at least three metals, the first being cerium, the second being Zr, and/or Hf, and the third importantly being Ti, the three metals comprising at least 80% of the metal constituents of the mixed metal oxide and the Ti being present in a range of 5% to 45% by metals-only atomic percent of the mixed metal oxide. The mixed metal oxide has an average crystallite size less than 6 nm and forms a skeletal structure with pores whose diameters are in the range of 4-9 nm and normally greater than the average crystallite size. The surface area of the skeletal structure per volume of the material of the structure is greater than about 240 m 2 /cm 3 . The method of making and use are also described.
1. A catalyst for facilitating a water gas shift reaction, the catalyst comprising a noble metal on a mixed metal oxide, said mixed metal oxide comprising a homogeneous, nanocrystalline, mixed metal oxide of at least three metal constituents, the first metal constituent being cerium, the second metal constituent being selected from the group consisting of Zr, Hf, and a combination of Zr and Hf, and the third metal constituent being Ti, said three metal constituents comprising at least 80% of the metal constituents of said mixed metal oxide and said Ti being present in a range of 5% to 45% by metals only atomic percent of said mixed metal oxide, said mixed metal oxide having an average crystallite size less than 6 nm and agglomerated to form a skeletal structure with pores, average pore diameters being in a range between about 4 nm and 9 nm and greater than the average crystallite size, and wherein the surface area of the skeletal structure per volume of the material of the skeletal structure is greater than about 240 m 2 /cm 3 .
2. The catalyst of claim 1 wherein the noble metal on the mixed metal oxide comprises a combination of Pt and Re.
3. The catalyst of claim 2 wherein the weight % of the Pt as a percentage of both the noble metal and the mixed metal oxide is in a range of 1:1 to 4:1 of that of the Re.
4. The catalyst of claim 3 wherein the weight % of the Pt as a percentage of both the noble metal and the mixed metal oxide is in the range of 0.5 to 1.5%.
5. A catalyst for facilitating a water gas shift reaction, the catalyst comprising a noble metal on a mixed metal oxide, said mixed metal oxide comprising a homogeneous, nanocrystalline, mixed metal oxide of at least three metal constituents, the first metal constituent being cerium, the second metal constituent being selected from the group consisting of Zr, Hf, and a combination of Zr and Hf, and the third metal constituent being Ti, said three metal constituents comprising at least 80% of the metal constituents of said mixed metal oxide and said Ti being present in a range of 5% to 45% by metals only atomic percent of said mixed metal oxide, said mixed metal oxide having an average crystallite size less than 6 nm and agglomerated to form a skeletal structure with pores, average pore diameters being in a range between about 4 nm and 9 nm and greater than the average crystallite size, and wherein the surface area of the skeletal structure per volume of the material of the skeletal structure is greater than about 240 m 2 /cm 3 , the mixed metal oxide being prepared by a process including:
a. dissolving compounds of at least one of the group consisting of Ce, Zr, and Hf, and urea in water to form a first metal salt-urea solution;
b. converting an organic Ti precursor to a meta-stable Ti salt solution in acid;
c. combining the meta-stable Ti salt solution in acid with the first metal salt-urea solution;
d. heating the combined meta-stable Ti salt solution in acid and the first metal salt-urea solution nominally to boiling to crystallize and precipitate the mixed metal oxide;
e. recovering the crystallized mixed metal oxide as a solid;
f. washing the crystallized mixed metal oxide with water;
g. replacing the water existing in the crystallized mixed metal oxide with a water miscible, low surface-tension solvent that displaces water;
h. drying the crystallized mixed metal oxide to remove substantially all of any remaining water and solvent; and
i. calcining the dried coprecipitate at a moderate temperature below about 600° C. for an interval sufficient to remove adsorbed impurities and stabilize the skeletal structure.
6. A process for the preparation of the catalyst defined in accordance with claim 5 , the noble metal loaded on the mixed metal oxide comprising a combination of Pt and Re, and comprising the steps of:
a. loading the mixed metal oxide with the Pt;
b. placing the Pt-loaded mixed metal oxide in a solution;
c. introducing a source of Re in solution to the solution containing the mixed metal oxide with the Pt loading; and
d. removing the liquid phase of the combined solutions to provide a solid Re and Pt-loaded mixed metal oxide.
7. The process of claim 6 further comprising the additional steps of, between steps a) and b), calcining the Pt-loaded mixed metal oxide; between steps b) and c), pre-reducing, with dilute H 2 , the Pt on the Pt-loaded mixed metal oxide; applying mild heat under dilute H 2 gas to effect the removal of the liquid phase in step e), passivating the Re and Pt-loaded mixed metal oxide with N 2 gas containing a small amount of O 2 ; and exposing the solid, passivated Re and Pt-loaded mixed metal oxide to ambient air.