posted on 2021-09-03, 14:05authored byNating Yang, Samuel Pattisson, Mark Douthwaite, Gaofeng Zeng, Hao Zhang, Jingyuan Ma, Graham J. Hutchings
Stabilizers are commonly employed
to synthesize nanocrystals with
well-defined morphologies and size distributions, making them ideal
tools to study structure–activity relationships in heterogeneous
catalysts. While it is well documented that stabilizers can influence
both the structure and size of the nanocrystals, little emphasis has
been placed on how the properties of these species influence catalytic
performance. Herein, different polymers (poly-sodium acrylate (PNaA),
poly(vinyl alcohol) (PVA), and poly(vinyl pyrrolidone) (PVP)) and
the monomer sodium acrylate (NaA) were used as stabilizers for the
synthesis of Au nanoparticles supported on TiO2. The mean
Au particle size in all of the catalysts was comparable regardless
of the stabilizer used; however, the activity of these catalysts toward
CO oxidation differed markedly. The activity decreased in the sequence
Au/TiO2 (NaA) > Au/TiO2 (PNaA) > Au/TiO2 (none) > Au/TiO2 (PVA) > Au/TiO2 (PVP),
despite the Au/TiO2 (none) catalyst possessing a larger
Au mean particle size, suggesting active site blocking due to the
steric nature of the polymer species. According to UV–vis,
X-ray photoelectron spectroscopy (XPS), in situ diffuse reflectance
infrared Fourier transform spectroscopy (DRIFTS), high-resolution
transmission electron microscopy (HRTEM), X-ray absorption spectroscopy
(XAS), and composition analysis experiments, it was concluded that
the enhanced activity of Au/TiO2 (NaA) and Au/TiO2 (PNaA) catalysts were attributed to the large proportions of low
coordinate step/kink Au sites. It is to be noted that the electronic
interactions between NaA and HAuCl4 facilitated the production
of active Au nanoparticles. Our findings highlight that the physicochemical
properties of the stabilizer can profoundly influence the reactivity
of supported metal catalysts prepared by sol-immobilization. These
observations highlight the influence that various stabilizers have
on the morphology of supported metal nanoparticles and provides an
explanation for the low activity of catalysts prepared using common
forms such as PVA and PVP.