Iycee Charles de Gaulle Summary Catalytic 11 20P-Y 41 80 10 20

Catalytic 11 20P-Y 41 80 10 20

Catalytic performance of H-USY, 10 to 30P-Y and 10 to 30S-Y were
evaluated for fructose conversion to 5-HMF reaction with biphasic (MIBK-Water) system
at 120oC for 5 h, the results including blank reaction are
summarized in Table 2.

Table 2: Catalytic performance
for Fructose to 5-HMF

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Catalyst

5-HMF
yield(%)

           5-HMF  

     Selectivity (%)                       

Furfural
yield
(%)

Furfural selectivity
(%)

Blank

11

    92

1

8

Parent  H-USY

32

     69

14

31

10P-Y

65

   89

8

11

20P-Y

41

  80

10

20

30P-Y

41

   87

6

13

10S-Y

30

   85

5

15

20S-Y

22

    88

3

12

30S-Y

20

  91

2

9

Reaction conditions: Temperature = 120? C ; Mole ratio of Fructose: Catalyst (1:1) ;
Volume ratio of MIBK: Water ((10:1), Time: 5h

The fructose
conversion was calculated using equation 2 and was observed to be same as that
of total yield of product (5-HMF and furfural) formed. There was no other by
product formation except furfural. The 5-HMF selectivity was found to be in the
range of 69 to 92%, based on the furfural formation. The selectivity of
furfural was varied from 31 to 8% (Table 1).  Amongst studied, all
catalysts has shown better 5-HMF yield than blank (without catalyst). Parent
H-USY was evaluated to be active than blank as can be seen from Table 2. This
increased in 5-HMF yield from 11% to 32% is due to the higher acidity and some
porosity. But this acidity and porosity also affected the further 5-HMF
conversion to furfural upto 14% due to loosing of formaldehyde in acidic
solution. Thus, if the parent H-USY can modify in such a way that the acidity
can reduce and mesoporosity can be created. In view to modify this parent
H-USY, the post synthesis acid treatment was employed by using H3PO4
and H2SO4. All modified catalysts were observed to be
less acidic (Table 1) and more mesoporosity due to dealumination of Al from
framework and/or from extra framework of parent H-USY without damaging the
structure (Fig. 1 A & B) is observed. This improved catalyst properties after
modifications help in enhancement of 5-HMF yield to 65% and selectivity of 89% (10P-Y)
from 32% (Yield) and 69% (Selectivity)
(parent H-USY), respectively with less formation of furfural (8%). This
improvement in 5-HMF formation with P-Y samples is due to the reduction in
total acidity and more dealumination (58%) from framework/extraframework of
H-USY.    Dealumination of zeolites like USY/Y enhances hydrothermal
stability, hydrobhobicity, along with creation of abundant mesopores .27

 Dealumination by H2SO4
treatment removes extraframwork alumina from supercavities of H-USY
without affecting zeolite framework, while dealumination by H3PO4
incorporate Phosphorous by two separate types: as monomeric phosphate
associated with framework aluminia atom at lower extraframework concentration
and as a polymeric phosphate generated from reaction of extraframework aluminia
with H3PO4 at high concentration of extraframework
alumina. Above 650oC calcination temperature, the concentration of extraframework
alumina is high. In the present study the calcination temperature was 500oC,
so the presence of extraframework alumina is low.  This monomeric phosphate linked with
framework alumina which form new bond of Al-O-P linkage by weakening the Al-O-Si
bond. 34

  This active Al-O-P linkage helps
in increase the 5-HMF yield to 65% (10P-Y). This is also confirmed by the fact
that, if 31P-NMR band width is wide and in the range of 0 to -40
then there is a presence of polymeric phosphate and it will interact with
extraframework alumina. Thus in the present work, phosphorous is in monomeric
form and it is linked with framework  Al
to get Al-O-P new bond.  Further
dealumination by H3PO4 multiple the linkages of Al-O-P,
which increases acidity. This was also confirmed by the fact that as P
incorporation increases then interaction with framework aluminium will be more
and contribution of 31P-NMR band will be closer to zero (Fig 4).
Identical results are also been reported by Corma et al37 However, this increased acidity
decreases 5-HMF yield due to formation of other products such as furfural.
Thus, the optimum combination of total acidity (both weak and strong (Fig. 2, Table
1), presence of B+L acid sites with contribution of AlPO species, new Al-O-P
bond with framework Al and dealumination (mesoporosity creation) is responsible
for the maximum formation of 5- HMF yield.
In case of H2SO4 treated H-USY, the 5-HMF yield was
decreased in comparison with parent H-USY (Table 2, entry 3-5). This means
that, H2SO4 treatment adversely affected on 5-HMF yield
formation.  This reduction in 5-HMF yield
with H2SO4 treated catalysts with respect to parent H-USY
is due to separation of
extraframework alumina and no creation of any new bond with framework alumina
like in case of H3PO4, which reduces acidity (Table 2).
This was also confirmed by
NH3-TPD  (Fig. 2) that , reduction in both weak
as well as strong acid sites reduces total acidity as compared to H3PO4
treated H-USY catalysts.

Thus, optimum
combination of moderate acidity (both weak as well as strong- 0.27mmol/g),
moderate dealumination (58%) of Al from extraframework as well as from
framework of H-USY; formation of new Al-O-P bond between framework Al,
existence of elemental monomeric phosphorous (0.0075%), Bronsted and Lewis
acidity availability and creation of mesopores are responsible for 10P-Y catalyst
to show maximum 5-HMF (65%) formation in comparison with other studied
catalysts. Further optimization of reaction parameters were done on the optimum
10P-Y catalyst aiming to get optimal process parameters for maximum 5-HMF
yield.