Superior Stability of Au/SiO₂ Compared to Au/TiO₂ Catalysts for the Selective Hydrogenation of Butadiene

Abstract

Supported gold nanoparticles are highly selective catalysts for a range of both liquid-phase and gas-phase hydrogenation reactions. However, little is known about their stability during gas-phase catalysis and the influence of the support thereon. We report on the activity, selectivity, and stability of 2–4 nm Au nanoparticulate catalysts, supported on either TiO2 or SiO2, for the hydrogenation of 0.3% butadiene in the presence of 30% propene. Direct comparison of the stability of the Au catalysts was possible as they were prepared via the same method but on different supports. At full conversion of butadiene, only 0.1% of the propene was converted for both supported catalysts, demonstrating their high selectivity. The TiO2-supported catalysts showed a steady loss of activity, which was recovered by heating in air. We demonstrated that the deactivation was not caused by significant metal particle growth or strong metal–support interaction, but rather, it is related to the deposition of carbonaceous species under reaction conditions. In contrast, all the SiO2-supported catalysts were highly stable, with very limited formation of carbonaceous deposits. It shows that SiO2-supported catalysts, despite their 2–3 times lower initial activities, clearly outperform TiO2-supported catalysts within a day of run time.

On the Limited Role of Electronic Support Effects in Selective Alkyne Hydrogenation: A Kinetic Study of Au/MOx Catalysts Prepared from Oleylamine‐Capped Colloidal Nanoparticles

“…Thus, the barrier to desorption from Au is likely lower than the barrier to further hydrogenation . However, Au is relatively poor at hydrogen activation, requiring process temperatures greater than 200 °C for acceptable alkyne conversion . Gold catalysts also lose activity within 12–24 h at operating temperatures between 180–400 °C ,,…”

“…Partial alkyne hydrogenation over supported Au catalysts has been evaluated for a variety of feedstocks ,,,. Much of the alkyne partial hydrogenation literature describes the manipulation of process variables such as reactor temperature and H 2 /alkyne feed ratios to achieve high alkene selectivity ,.…”

“…Few studies report detailed kinetic analyses or explore the underlying chemistry of alkyne hydrogenation. Hydrogen activation is often cited as the rate‐determining step in Au‐catalyzed hydrogenation ,,. There is also evidence suggesting that H 2 adsorption on Au may have a lower activation barrier at the metal‐support interface (MSI) .…”

“…Several studies claim that activity differences between several Au/MO x (metal oxide) catalysts were due to “support effects,” but differences in rate were not quantified under differential conversion ,. Other studies observed almost no difference in reactivity between Au/MO x catalysts ,. In this case, the authors hypothesized H 2 activation takes place on low‐coordinated Au sites on the NP surface rather than at the MSI ,.…”

“…Other studies observed almost no difference in reactivity between Au/MO x catalysts ,. In this case, the authors hypothesized H 2 activation takes place on low‐coordinated Au sites on the NP surface rather than at the MSI ,. Fujitani et al .…”