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Selective and Robust Ru Catalyst for the Aqueous Phase Aerobic Oxidation of Furfural to 2‑Furoic Acid
Synthesis of 2-furoic acid (FURA) via oxidation of furfural
(FAL)
is vital in evolving the biorefinery concept as FURA has numerous
important applications in the pharmaceuticals and optic areas. Though
few works on this reaction are done, those are marred with shortcomings
such as the nonrecyclability of catalyst, dilute solutions, lower
yields, or use of H2O2 as an oxidizing agent.
Herein, we report catalytic aqueous phase oxidation of FAL to FURA
using molecular oxygen as an oxidizing agent. For the synthesis of
FURA, various catalysts with a combination of metal (Pt, Pd, Ru) and
supports (carbon, Al2O3) were prepared and characterized
by multiple techniques (X-ray diffraction (XRD), scanning electron
microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller
(BET), X-ray photoelectron spectroscopy (XPS)). Oxidation of FAL carried
out over 5 wt % Ru/C catalyst in the presence of Na2CO3 yielded 83% of FURA at 120 °C and 15 bar oxygen pressure.
The catalyst could show potential for reusability as similar activity
was achieved after subjecting the spent catalyst to mild reduction
treatment (150 °C). Studies on the effects of temperature, pressure,
and time could help accomplish enhanced yields of FURA. Additionally,
learning about the effect of base (weak/strong/solid) revealed that
due to the weak basicity of Na2CO3, higher yields
could be achieved by maintaining approximately a pH of 11, which is
optimal for suppressing side reactions. Under the given conditions,
FURA is stable (>90%) and also adsorption studies divulge that
it
is immediately removed from the catalyst surface, and hence higher
yields could be achieved in our catalytic system. Using the initial
rates methodology, an activation energy of 21.91 kJ mol–1 was derived and also a high turn over frequency (TOF) (85.9 h–1) was observed under optimized conditions