Method for catalytic generation of formic acid at an oxygen partial pressure below 1 bar and regeneration of the catalyst used therefor

A method for catalytic generation of formic acid at an oxygen partial pressure of less than 1 bar and regeneration of the catalyst used in this process, wherein a polyoxometallate ion of the general formula [PMoxVyO40]n−, which serves as the catalyst, is brought in contact with an alpha-hydroxyaldehyde, an alpha-hydroxycarboxylic acid, a carbohydrate, a glycoside or a polymer containing a carbon chain with at least one OH group bound repeatedly as a substituent to the carbon chain and/or an O, N or S atom occurring repeatedly in the carbon chain in a liquid solution (12) in a vessel (10), at a temperature above 70° C. and below 120° C., wherein 6≦x≦11 and 1≦y≦6 and 3<n<10 and x+y=12, wherein n, x and y each denote an integer, wherein the catalyst thereby reduced is returned to its starting state by oxidation, wherein the contacting takes place in the vessel (10) at an oxygen partial pressure of less than 1 bar, wherein a portion of the liquid solution (12) is discharged from the vessel (10) for oxidation of the catalyst, then is exposed to oxygen or a gas mixture containing oxygen at an oxygen partial pressure of 1 to 500 bar and next is fed back to the remainder of the liquid solution (12), wherein the oxygen partial pressure in the vessel is always kept below 1 bar, wherein the oxygen partial pressure acting on that portion of the liquid solution (12) is lowered from 1 to 500 bar to less than 5 bar before that portion of the liquid solution (12) is fed back to the remainder of the liquid solution (12).