Method of manufacturing monolithic catalysts
The present invention is directed to a method of coating a substrate, such as a honeycomb having a plurality of parallel channels defined by the honeycomb walls. The honeycomb has different zones along the length of the channels. The zones are defined by their coating (or lack of coating) and extend for a length of the channel in which there is the same coating and architecture. Soluble components in coating compositions are fixed in their respective zones by forcing a heated gas stream through the channels.
1. A method of coating a substrate comprising an inlet end, an outlet end, wall elements extending between the inlet end to the outlet end and a plurality of axially enclosed channels defined by the wall elements, at least some of the channels having a channel inlet at the inlet end and a channel outlet at the outlet end, the method comprising:
passing at least a first inlet fluid composition into the inlet end of the substrate to form at least a first inlet end layer on the walls and extending for only part of the length from the inlet end toward the outlet end, the first inlet fluid composition comprising at least one first inlet base metal oxide component and at least one first inlet precious metal component; and
applying a vacuum to the outlet end while forcing a heated gas stream through the channels from the inlet end after the formation of each inlet end layer without significantly changing the length of each inlet layer, wherein the temperature of the heated gas is from about 200° C. to about 400° C. to fix the first inlet precious metal component.
2. The method as recited in claim 1 further comprising passing at least one outlet fluid composition into the substrate through the at least some of the channel outlets at the substrate outlet end to form at least one outlet end layer coating; and applying a vacuum to the inlet end while forcing a gas stream through the channels from the outlet end after the formation of each outlet end coating without significantly changing the length of each outlet layer coating.
3. The method as recited in claim 2 wherein at least one outlet end coating extends for only part of the length from the outlet end toward the inlet end.
4. The method as recited in claim 3 wherein at least one outlet layer comprises a first composition comprising at least one first outlet base metal oxide component and optionally at least one first outlet precious metal component.
5. The method as recited in claim 4 , further comprising passing at least a second inlet fluid composition into the inlet end of the substrate to form at least a second inlet layer on the first inlet layer and optionally on at least a portion of the first outlet layer.
6. The method as recited in claim 5 further comprising thermally fixing each layer after coating and prior to coating a subsequent layer.
7. The method as recited in claim 6 , wherein thermally fixing comprises applying a vacuum to one of the inlet end or the outlet end while forcing a heated gas stream through the channels from the other of the inlet end or the outlet end after the formation of each layer without significantly changing the length of each layer, wherein the temperature of the heated gas is from about 200° C. to about 400° C. to fix the precious metal component in each layer.
8. The method as recited in claim 4 , further comprising passing at least a second outlet fluid composition into the outlet end of the substrate to form at least a second outlet layer on the first outlet layer and optionally on at least a portion of the first inlet layer.
9. The method as recited in claim 8 further comprising thermally fixing each layer after coating and prior to coating a subsequent layer.
10. The method as recited in claim 9 , wherein thermally fixing comprises applying a vacuum to one of the inlet end or the outlet end while forcing a heated gas stream through the channels from the other of the inlet end or the outlet end after the formation of each layer without significantly changing the length of each layer, wherein the temperature of the heated gas is from about 200° C. to about 400° C. to fix the precious metal component in each layer.
11. The method as recited in claim 7 , wherein the thermal treatment is performed from about 1 second to about 10 seconds.
12. The method as recited in claim 10 , wherein the thermal treatment is performed from about 1 second to about 10 seconds.
13. The method as recited in claim 10 further comprising calcining the substrate upon completion of coating all layers.
14. The method as recited in claim 13 wherein the calcining is conducted at from 250° C. to 900° C. at from about 0.1 to about 10 hours.
15. The method as recited in claim 2 wherein there is an uncoated portion of the channel between the inlet layer and the outlet layer.
16. A method for coating a substrate comprising an inlet end, an outlet end, axial wall elements extending from the inlet end to the outlet end and a plurality of axially enclosed channels defined by the wall elements, with at least some of the channels having a channel inlet at the inlet end and a channel outlet at the outlet end, comprising:
partially immersing the substrate at the inlet end into a vessel containing a first coating composition containing a soluble component, at least once, to form at least one first layer located on the walls and extending for at least part of the length from the inlet end toward the outlet end, with at least one inlet end coating extending for only part of the length from the inlet end toward the outlet end;
partially immersing the substrate at the outlet end into a vessel containing a second coating composition containing a soluble component, at least once, to form at least one second layer located on the walls and extending for at least part of the length from the outlet end toward the inlet end; and
thermally treating the substrate after each immersion step, to form at least two zones, a first zone extending from the inlet end and a second zone, each extending along the channels wherein the second zone extends along a separate length of the channel than the first zone, the thermal treatment fixing the soluble component of the first zone in the first zone and the soluble component of the second zone in the second zone,
wherein the thermal treatment comprises applying a vacuum to one of the inlet end or the outlet end while forcing a heated gas stream through the channels from the other of the inlet end or the outlet end after the formation of each layer without significantly changing the length of each layer, wherein the temperature of the heated gas is from about 200° C. to about 400° C.
17. The method as recited in claim 16 further comprising thermally treating the substrate upon completion of coating all layers at from about 200° C. to about 400° C. at from about 1 to 10 seconds.
18. The method as recited in claim 13 further comprising calcining the substrate.
19. The method as recited in claim 18 wherein the calcining is conducted at from 250° C. to 900° C. at from 0.1 to 10 hours.
20. The method as recited in claim 1 wherein the at least one first inlet base metal oxide component is selected from the group consisting of a first inlet refractory oxide, a first inlet rare earth metal oxide, a first inlet transition metal oxide, a first inlet alkaline earth metal oxide, and a molecular sieve.
21. The method as recited in claim 4 wherein the at least one first outlet base metal oxide component is selected from the group consisting of a first outlet refractory oxide, a first outlet rare earth metal oxide, a first outlet transition metal oxide, a first outlet alkaline earth metal oxide, and a molecular sieve.