3 research outputs found
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
Efficient, Stable, and Reusable Silicoaluminophosphate for the One-Pot Production of Furfural from Hemicellulose
Development of stable, reusable,
and water-tolerant solid acid
catalysts in the conversion of polysaccharides to give value-added
chemicals is vital because catalysts are prone to undergo morphological
changes during the reactions. With the anticipation that silicoaluminophosphate
(SAPO) catalysts will have higher hydrothermal stability, those were
synthesized, characterized, and employed in a one-pot conversion of
hemicellulose. SAPO-44 catalyst at 170 °C within 8 h could give
63% furfural yield with 88% mass balance and showed similar activity
up to at least 8 catalytic cycles. The morphological studies revealed
that SAPO catalysts having hydrophilic characteristics are stable
under reaction conditions
Lignin Depolymerization into Aromatic Monomers over Solid Acid Catalysts
It is imperative to develop an efficient
and environmentally benign
pathway to valorize profusely available lignin, a component of nonedible
lignocellulosic materials, into value-added aromatic monomers, which
can be used as fuel additives and platform chemicals. To convert lignin,
earlier studies used mineral bases (NaOH, CsOH) or supported metal
catalysts (Pt, Ru, Pd, Ni on C, SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, etc.) under a hydrogen atmosphere, but these methods face
several drawbacks such as corrosion, difficulty in catalyst recovery,
sintering of metals, loss of activity, etc. Here we show that under
an inert atmosphere various solid acid catalysts can efficiently convert
six different types of lignins into value-added aromatic monomers.
In particular, the SiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> catalyst gave exceptionally high yields of ca. 60% for organic solvent
soluble extracted products with 95 ± 10% mass balance in the
depolymerization of dealkaline lignin, bagasse lignin, and ORG and
EORG lignins at 250 °C within 30 min. GC, GC-MS, HPLC, LC-MS,
and GPC analysis of organic solvent soluble extracted products confirmed
the formation of aromatic monomers with ca. 90% selectivity. In the
products, confirmation of retention of aromatic nature as present
in lignin and the appearance of several functional groups has been
carried out by FT-IR and <sup>1</sup>H and <sup>13</sup>C NMR studies.
Further, isolation of major products by column chromatography was
carried out to obtain aromatic monomers in pure form and their characterization
by NMR is presented. A detailed characterization of six different
types of lignins obtained from various sources helped in substantiating
the catalytic results obtained in these reactions. A meticulous study
on fresh and spent catalysts revealed that the amorphous catalysts
are preferred to obtain reproducible catalytic results