the activity of the 0.33%Au-0.33%Pd/TiO 2
(Chloride-O) and TS-1 system (77% oxime yield)
markedly outperforming analogs consisting
of either monometallic catalysts or a physical
mixture thereof (Fig. 2A and fig. S10). Indeed,
the alloying of Au with Pd is known to be
highly effective in both suppressing O–O bond
dissociation (inhibiting H 2 O production) and
promoting the release of H 2 O 2 from catalytic
surfaces ( 23 , 24 ). It is therefore plausible to
consider that the role of Au is to facilitate the
desorption of H 2 O 2 (or peroxy species) from
the precious metal surface, enabling subse-
quent diffusion to TiIVsites present within
the TS-1 framework. TS-1 in turn catalyzes the
formation of the hydroxylamine intermediate,
with limited ammoximation activity observed
in the absence of either the titanosilicate or
AuPd-supported catalyst (≤15% oxime selec-
tivity; fig. S11). Further analyses of the 0.33%
Au-0.33%Pd/TiO 2 (Chloride-O) and TS-1 dual
catalyst system demonstrated that high H 2 se-
lectivity can be achieved when the reaction is
not limited by cyclohexanone availability, with
an H 2 selectivity of 98% observed at a reaction
time of 1 hour and a cyclohexanone conversion
of 30% (Fig. 2B).
We have also extended our studies to assess
the ammoximation of a small range of other
ketones (cyclopentanone, cycloheptanone,
cyclooctanone, and acetophenone), with many
of the corresponding oximes finding appli-
cation in the synthesis of pharmaceuticals
( 25 , 26 ). Using the 0.33%Au-0.33%Pd/TiO 2
(Chloride-O) and TS-1 catalysts (Fig. 2C), oxime
selectivities >95% were observed for all sub-strates, demonstrating the versatility of the
in situ approach to oxime formation. The var-
iation in the rate of ketone conversion is
primarily related to the differing intrinsic
reactivity of the ketones with hydroxylamine,
in addition to the limited ability of the larger
ketones to access the interior of the titano-
silicate pore structure ( 27 ).
Further optimization of the Au:Pd ratio
revealed an optimal composition with a
physical mixture of the 0.55%Au-0.11%Pd/
TiO 2 (Chloride-O) and TS-1 catalysts exhib-
iting a cyclohexanone oxime yield of 96%
and an apparent turnover frequency (TOF)
(223 moloximemolmetal−^1 hour−^1 ), far greater
than that of the physical mixture of the 0.33%
Au-0.33%Pd/TiO 2 (Chloride-O) catalyst and
TS-1 (143 moloximemolmetal−^1 hour−^1 )ina3-hourSCIENCEscience.org 6 MAY 2022•VOL 376 ISSUE 6593 617
Fig. 2. Catalytic activity of supported 0.66%AuPd/TiO 2 (Chloride-O) catalysts,
used in conjunction with TS-1, toward the ammoximation of cyclohexanone
through the in situ production of H 2 O 2 .(A) The synergistic effect of alloying Au
and Pd. (B) Time-on-line activity of the 0.33%Au-0.33%Pd/TiO 2 (Chloride-O)
catalyst. (C) Catalytic activity of the 0.33%Au-0.33%Pd/TiO 2 (Chloride-O) catalyst
toward the ammoximation of a range of ketones. (D) The effect of the Au:Pd ratio
on catalytic activity of 0.66%AuPd/TiO 2 (Chloride-O) toward cyclohexanone
ammoximation. Ammoximation reaction conditions: Ketone (2 mmol), NH 4 HCO 3
(4 mmol), 5% H 2 /N 2 (420 psi), 25% O 2 /N 2 (160 psi), 0.66%AuPd/TiO 2 (Chloride-O)
catalyst (0.075 g), TS-1 (0.075 g), t-BuOH (5.9 g), H 2 O (7.5 g), reaction time 3 hours,
reaction temperature 80°C, stirring speed 800 rotations per minute (rpm). Key:
Ketone conversion (black bar), selectivity toward oxime (red bar), oxime yield (blue
bar), selectivity based on H 2 (green bar), selectivity based on NH 3 (purple bar),
carbon balance (black circles). Note for Fig. 2A: Au refers to 0.66%Au/TiO 2
(Chloride-O), Pd to 0.66%Pd/TiO 2 (Chloride-O), Au+Pd to a physical mixture of the
two monometallic catalysts, and AuPd to 0.33%Au-0.33%Pd/TiO 2 (Chloride-O).RESEARCH | REPORTS