Use of a supplemental promoter in conjunction with a carbon-supported, noble-metal-containing catalyst in liquid phase oxidation reactions
This invention relates to the use of a supplemental promoter in conjunction with a noble-metal-containing catalyst comprising a carbon support in catalyzing liquid phase oxidation reactions, a process for making of an improved catalyst comprising such a supplemental promoter, and an improved catalyst comprising such a supplemental promoter. In a particularly preferred embodiment, a supplemental promoter (most preferably bismuth or tellurium) is used in conjunction with a noble-metal-containing catalyst comprising a carbon support in a liquid phase oxidation process wherein N-(phosphonomethyl)iminodiacetic acid (i.e., “PMIDA”) or a salt thereof is oxidized to form N-(phosphonomethyl)glycine (i.e., “glyphosate”) or a salt thereof. The benefits of such a process include increased oxidation of the formaldehyde and formic acid by-products, and, consequently, decreased final concentrations of those by-products as well as other undesirable by-products, most notably N-methyl-N-(phosphonomethyl)glycine (i.e., “NMG”).
1. A process for oxidizing a substrate selected from the group consisting of N-(phosphonomethyl)iminodiacetic acid or a salt thereof, formaldehyde, and formic acid, the process comprising contacting the substrate with an oxidation catalyst in the presence of oxygen, wherein the catalyst comprises a carbon support having a noble metal, iron and cobalt at a surface of the carbon support, the noble metal being selected from the group consisting of platinum, palladium, ruthenium, rhodium, iridium, silver, osmium, gold and combinations thereof.
2. A process as set forth in claim 1 wherein the catalyst comprises metal particles comprising said noble metal at a surface of the carbon support.
3. A process as set forth in claim 1 wherein the noble metal constitutes from about 2.5 to about 10% by weight of the catalyst.
4. A process as set forth in claim 1 wherein the noble metal constitutes from about 3 to about 7.5% by weight of the catalyst.
5. A process as set forth in claim 1 wherein the noble metal is platinum.
6. A process as set forth in claim 1 wherein the carbon support is activated carbon.
7. A process as set forth in claim 1 wherein the contacting is conducted in a continuous reactor system.
8. A process as set forth in claim 1 wherein the contacting is carried out at a pressure of from about 30 to about 130 psig.
9. A process as set forth in claim 1 wherein the contacting is carried out at a temperature of from about 80 to about 110° C.
10. A process as set forth in claim 1 wherein the contacting is carried out in a solution or slurry having a pH of less than 7.
11. A process as set forth in claim 1 wherein the contacting is carried out in a solution or slurry having a pH of less than 3.
12. A process as set forth in claim 1 wherein the contacting is carried out in a solution or slurry having a pH of from about 1 to about 2.
13. A process as set forth in claim 1 wherein the substrate comprises N-(phosphonomethyl)iminodiacetic acid or a salt thereof.