Mixed-conductor enhanced composite and core-shell oxides for cyclic redox production of fuels and chemicals
Compositions and methods for preparing and using ceramic mixed ionic-electronic conductor (MIEC) enhanced transition metals and metal oxides in composite or core-shell forms are disclosed. The presently disclosed compositions are stable at high temperatures and can carry as much as about 20 weight % oxygen.
1. A core-shell redox catalyst comprising:
(i) metal oxide core, wherein the metal oxide core comprises at least one transition metal oxide and mixtures thereof, wherein the at least one transition metal oxide is an oxide of a transition metal selected from the group consisting of Mn, Fe, Co, Ni, V, Mo, Cu, Zn and mixtures thereof, a spinel oxide having a formula A 2+ B 2 3+ O 4 2− , wherein A and B are each independently a metal cation, or combinations thereof:
(ii) A rigid mixed ionic-electronic conductive (MIEC) shell substantially enclosing the metal oxide core, wherein the rigid MIEC shell comprises a perovskite structure; and
(iii) A plurality of surface catalytic sites.
2. The core-shell redox catalyst of claim 1 , wherein the metal cation is selected from the group consisting of magnesium, zinc, iron, manganese, aluminum, chromium, titanium, and silicon.
3. The core-shell redox catalyst of claim 1 , wherein the rigid MIEC shell is selected from the group consisting of La x Sr 1-x FeO 3 , BaCe y Fe 1-y O 3 , and CaTi z Fe 1-z O 3 , wherein 0.2<x<0.8, 0.2<y<0.8, and 0.05<z<0.75.
4. The core-shell redox catalyst of claim 1 , further comprising an active metal.
5. The core-shell redox catalyst of claim 1 , wherein the core-shell redox catalyst has a lattice oxygen capacity of about 5 w.t. % to about 20 w.t. %.
6. The core-shell redox catalyst of claim 1 , wherein the rigid MIEC shell is selected from the group consisting of BaCe y Fe 1-y O 3 and CaTi z Fe 1-z O 3 , wherein 0.2<y<0.8, and 0.05<z<0.75.
7. The core-shell redox catalyst of claim 1 , wherein the metal oxide core comprises an iron oxide;
wherein the rigid MIEC shell comprises La x Sr 1-x FeO 3 , wherein 0.2<x<0.8;
wherein a ratio of the metal oxide of the core to the MIEC shell is about 4:1 to about 1:4;
wherein the core-shell redox catalyst has a lattice oxygen capacity of about 10 w.t. % to about 20 w.t. %; and
wherein a surface area of the core-shell redox catalyst is about 15 m 2 g −1 or less.
8. A method for generating syngas, the method comprising contacting methane, light hydrocarbons, or a mixture thereof with a redox catalyst according to claim 1 , thereby reducing the redox catalyst to produce a reduced redox catalyst and converting the methane and/or light hydrocarbons into syngas.
9. The method of claim 8 , further comprising contacting the reduced redox catalyst with H 2 O/O 2 to regenerate the redox catalyst and to produce H 2 and/or heat.