724
synthesis of 2,6-DMP from 1,2-PDA and glycerol. The Cu-Cr-O catalyst performed
better in 2,6-DMP production although methanol and KOH were present in the
reaction mixture. The interaction (solid-solid) in Cu x O y –CuCr 2 O 4 due to CuO
resulted in easily reducible species (Cu-Cr from Cu-Cr-O) was the main reason for
high activity over this catalyst. It was also found to be more selective toward 2,6DMP as the individual bulk oxides showed less activity in comparison to
CuO-CuCr 2 O 4 .
In the following study, the influence of acid-base sites and metallic copper species was investigated on the activity of Cu-Cr catalysts [9]. A detailed study was
conducted on the role of acid-base sites (Lewis and Brønsted) on the product distribution using formic acid and pyridine as probe molecules for adsorbed IR spectroscopy combined with N 2 O pulse titration experiments to estimate the Cu active metal
surface area. The N 2 O titration measurements determined that the rate of 2,6-DMP
formation was linearly proportional to the active metal surface area with Cu 2 Cr 1
sample displaying the highest activity for 2,6-DMP. In addition, the selectivity of
2,6-DMP was dependent on both copper chromite and Cu
0
species.
To see the effect of preparation method, CuCr 2 O 4 catalyst was synthesized by
various methods, namely, mechanical mixing, sol-gel, and co-precipitation [10]. It
was observed that a high quantity of Cu particles interacted with Cr 2 O 3 in CuCr 2 O 4
resulted from the sol-gel method with a low ratio of Cu
2+
/Cu
0
exhibited better dehydrocyclization activity with high 2,6-DMP selectivity. Besides, dehydrocyclization
activities were examined under catalyst poisoning conditions to highlight the influence of acidic and basic sites (Lewis) responsible for the 2,6-DMP selectivity. The
HCOOH adsorbed IR spectroscopic data, and the N 2 O pulse titration results demonstrated that there is a higher proportion of basicity on the CuCr 2 O 4 surface (synthesized by the sol-gel method) than on CuCr 2 O 4 that is synthesized by mechanical
mixing and co-precipitation routes. The sol-gel-derived CuCr 2 O 4 catalyst was also
found to be stable even when crude glycerol was used as the reactant that was
received from the biodiesel plant. The Cu impregnated on Cr 2 O 3 exhibited segregated CuO and Cr 2 O 3 species that showed 2,6-DMP with high selectivity. It was
found that fine-tuning of surface acid-base sites could result in the desired products
with high selectivity in the dehydrocyclization process.
In the subsequent study, the Cu-Cr catalyst was calcined at different temperature
(from 400 to 750 °C) to study the role of copper dispersion and acid-base properties
on the product distribution [11]. The modified (with Na, K and Cs) Cu-Cr catalyst
studied their behavior in the vapor-phase synthesis 2,6-DMP from1,2-PDA and
glycerol. The results indicated that K-modified Cu-Cr sample efficiently minimizes
the by-product formation. The influence of calcination temperatures had a significant impact on the activity of Cu-Cr catalyst and found that 550 °C could be an
optimum temperature where a stable CuO-CuCr 2 O 4 was observed. Whereas at
400 °C calcination temperature, CuO-CuCr 2 O 4 exhibited low activity due to the less
number of Cu active sites available on the surface. The results also showed that the
dehydrocyclization rate was declined over CuO-CuCr 2 O 4 sample calcined at high
temperatures (>550 °C) due to low surface area of catalyst when calcined at high
temperature mostly due to sintering. On contrary, 2,6-DMP rate decreased
R. Sarkari et al.
synthesis of 2,6-DMP from 1,2-PDA and glycerol. The Cu-Cr-O catalyst performed
better in 2,6-DMP production although methanol and KOH were present in the
reaction mixture. The interaction (solid-solid) in Cu x O y –CuCr 2 O 4 due to CuO
resulted in easily reducible species (Cu-Cr from Cu-Cr-O) was the main reason for
high activity over this catalyst. It was also found to be more selective toward 2,6DMP as the individual bulk oxides showed less activity in comparison to
CuO-CuCr 2 O 4 .
In the following study, the influence of acid-base sites and metallic copper species was investigated on the activity of Cu-Cr catalysts [9]. A detailed study was
conducted on the role of acid-base sites (Lewis and Brønsted) on the product distribution using formic acid and pyridine as probe molecules for adsorbed IR spectroscopy combined with N 2 O pulse titration experiments to estimate the Cu active metal
surface area. The N 2 O titration measurements determined that the rate of 2,6-DMP
formation was linearly proportional to the active metal surface area with Cu 2 Cr 1
sample displaying the highest activity for 2,6-DMP. In addition, the selectivity of
2,6-DMP was dependent on both copper chromite and Cu
0
species.
To see the effect of preparation method, CuCr 2 O 4 catalyst was synthesized by
various methods, namely, mechanical mixing, sol-gel, and co-precipitation [10]. It
was observed that a high quantity of Cu particles interacted with Cr 2 O 3 in CuCr 2 O 4
resulted from the sol-gel method with a low ratio of Cu
2+
/Cu
0
exhibited better dehydrocyclization activity with high 2,6-DMP selectivity. Besides, dehydrocyclization
activities were examined under catalyst poisoning conditions to highlight the influence of acidic and basic sites (Lewis) responsible for the 2,6-DMP selectivity. The
HCOOH adsorbed IR spectroscopic data, and the N 2 O pulse titration results demonstrated that there is a higher proportion of basicity on the CuCr 2 O 4 surface (synthesized by the sol-gel method) than on CuCr 2 O 4 that is synthesized by mechanical
mixing and co-precipitation routes. The sol-gel-derived CuCr 2 O 4 catalyst was also
found to be stable even when crude glycerol was used as the reactant that was
received from the biodiesel plant. The Cu impregnated on Cr 2 O 3 exhibited segregated CuO and Cr 2 O 3 species that showed 2,6-DMP with high selectivity. It was
found that fine-tuning of surface acid-base sites could result in the desired products
with high selectivity in the dehydrocyclization process.
In the subsequent study, the Cu-Cr catalyst was calcined at different temperature
(from 400 to 750 °C) to study the role of copper dispersion and acid-base properties
on the product distribution [11]. The modified (with Na, K and Cs) Cu-Cr catalyst
studied their behavior in the vapor-phase synthesis 2,6-DMP from1,2-PDA and
glycerol. The results indicated that K-modified Cu-Cr sample efficiently minimizes
the by-product formation. The influence of calcination temperatures had a significant impact on the activity of Cu-Cr catalyst and found that 550 °C could be an
optimum temperature where a stable CuO-CuCr 2 O 4 was observed. Whereas at
400 °C calcination temperature, CuO-CuCr 2 O 4 exhibited low activity due to the less
number of Cu active sites available on the surface. The results also showed that the
dehydrocyclization rate was declined over CuO-CuCr 2 O 4 sample calcined at high
temperatures (>550 °C) due to low surface area of catalyst when calcined at high
temperature mostly due to sintering. On contrary, 2,6-DMP rate decreased
R. Sarkari et al.