OK, I see. As long as everything is kept neutral, no oximation can happen. (you didn't use any buffer, did you?)
And here's some nice advanced catalyst preparation for the enthusiastic C=C bond hydrogenationist ;) :
Activity Enhancement by the Support in the Hydrogenation of C=C Bonds over Polymer-Supported Palladium Catalysts
(Marco Zecca, Roman Fiera, Giancarlo Palma, Silvano Lora, Milan Hronec, Milan Králik)
Chemistry - A European Journal Volume 6, Issue 11, Date: June 2, 2000, Pages: 1980-1986
(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_imgs/pdf.gif)
Abstract
"Four synthetic ion-exchange resins (AH, BH, CH, DH) of different hydrophilic/hydrophobic properties were used as supports for heterogeneous palladium catalysts (A, B, C, D). The resins contained styrene (STY) and 2-(methacryloxy)ethylsulfonic acid (MESA) as the comonomers. Either divinylbenzene (DVB: CH, DH resins) or N,N-methylenebisacrylamide (MBAA: AH, BH resins) were used as the cross-linker. AH contained also N,N-dimethylacrylamide (DMAA) as the third comonomer. The catalysts (Pd 0.25-0.45 % w/w) were obtained by ion-exchanging the acidic forms of the resins with [Pd(OAc)2] and reducing palladium(II) with excess sodium borohydride. The use of NaBH4 also ensured the neutralization of the acidic sites of the supports. No effect of the hydrophilic/hydrophobic properties of the supports was observed in the hydrogenation of cyclohexene and 2-cyclohexen-1-one in methanol, at 25 °C and 0.5, 1, and 1.5 MPa, respectively. However, catalysts A and B, containing amido groups provided by either DMAA or MBAA, proved to be more active than C and D. The observed activity enhancement was directly proportional to the nitrogen/palladium molar ratio in the catalysts. This finding suggests that amido groups promote palladium through a direct interaction with the metal surface."
Interesting in particular is the following sentence: "The use of NaBH4 also ensured the neutralization of the acidic sites of the supports" - their special polymer-supported catalyst was rendered free from acidic ligands, too! And this effort in maintaining neutral conditions is done, I would guess, out of the same reason as Barium pointed out already...
indole_amine