A.A. Greish et al.
Molecular Catalysis 502 (2021) 111398
Fig. 5. Arrhenius plot for the 1ꢀ CC formation rate over 12 %Re
2
O
7
+5%
B
2 3 2 3
O /Al O .
Fig. 6. Dependence of the 1ꢀ CC yield on the reaction time for 12 %Re
2
O
7
+10
0.398 h 1 and Ceq = 96 %, the latter is considered as the highest
ꢀ
◦
=
%B O /Al O (Re O : B O = 1 : 5.4). Conditions: 75 C, CH : heptane = 1 :
2
3
2
3
2
7
2 3
probable conversion of CH to 1ꢀ CC.
3.5, catalyst weight - 1 g.
The first-order of CH dimerization allows us to suppose the limiting
stage of the reaction to be likely the formation of -complexes of CH with
π
12 %Re O +10 %B O /Al O catalyst (Fig. 1), the yield of 1ꢀ CC rea-
2
7
2
3
2 3
rhenium. The absence of the denominator in the kinetic equation in-
dicates that the reaction is not inhibited by adsorption of the product
formed. This fact allows us to conclude that the concentration of 1ꢀ CC
on the surface is rather low, which can be caused by the fast desorption
of 1ꢀ CC from the catalyst surface into the solution. As shown in [9,10],
ches about 50 % and 75 %, respectively, while in the reaction over the
modified catalyst (Fig. 6), the same yields are somewhat higher and
approach 55 % and 88 %, respectively. This result points to the increase
in the reaction rate, which is not so remarkable as it could be expected. If
we consider the kinetic dependence obtained for the latter catalyst, it
can also fit to the equation of the first order reaction mentioned above
(SI, Fig. S6). In this case, the rate constant and equilibrium concentra-
the catalyst Re
2
O
7
+B
2 3 2 3
O /Al O exhibits the rather high activity in
alkene metathesis. However, at present we failed to find any publica-
tions devoted to CH transformations over metathesis catalysts where the
formation of CH metathesis products is observed, in particular
cyclododecadiene.
ꢀ 1
tion of 1ꢀ CC involved in the equation are equal to 0.425 h and 95 %,
respectively. As shown by our measurements of ammonia TPD, the
acidic properties of the catalyst due to the additional amount of B O
2
3
1
The H NMR analysis of the products (SI, Figs. S3, S4) showed that
change slightly (SI, Fig. 7), and this change in the catalyst acidity cannot
lead to the remarkable increase in the reaction rate. Noteworthy, not
only the yield of 1ꢀ CC but also the selectivity to this product increase. It
there is a small signal in the region of 5.5 ppm that can be attributed to
protons associated with carbon atoms located in a macrocycle contain-
ing double bonds. This fact can be considered as an evidence of cyclo-
dodecadiene formation in our conditions but in small amounts.
The data presented above demonstrate that there is a direct
connection between the catalyst activity in CH dimerization and the
acidic properties of the catalyst. In order to improve the performance of
is probably the -complexation of CH with rhenium that reduces the
π
tricyclic hydrocarbons formation and directs the reaction to the 1ꢀ CC
formation.
The dependence of the process on the presence of B O and Re O in
2
3
2 7
the catalyst allows us to consider the Re O +B O /Al O catalyst as a
2
7
2
3
2 3
the catalyst Re
content of B
maintain the CH : B
tion of CH in the initial heptane solution from 10 to 30 %. The results of
the runs carried out over the 12 %Re /Al catalyst in
+10 %B
these modified conditions are shown in Fig. 6.
2
O
7
+B
in the catalyst composition. At the same time, to
ratio, we increased accordingly the concentra-
2
O
3
/Al
2
O
3
, it was decided to increase two times the
2 3 2 7
bifunctional system, however the nature of B O and Re O actions in
2
O
3
the conversion of CH to 1ꢀ CC is fundamentally different. Indeed,
2
O
3
whereas B O is an acidic component responsible for the generation of
2
3
cyclohexyl carbocations, Re O creates active centers for -chemisorp-
2
7
π
2
O
7
2
O
3
2
O
3
tion of CH molecules and favors their interaction with cyclohexyl cations
followed by the formation of the target product. The molar ratio Re O :
2
7
It can be noticed that the yield of 1ꢀ CC on the modified catalyst in
B2O3
◦
the chosen conditions (T = 75 C) reaches about 94 %, while the selec-
: Al O = 1 : 5.4 : 37 in the catalyst 12 %Re O +10 %B O /Al O can
2
3
2
7
2
3
2 3
tivity to 1ꢀ CC in all experiments is close to 100 %. Thus, a conclusion
be considered as the value close to the optimal ratio for the selective
can be drawn that a simultaneous increase in both the content of B
2
O
3
in
formation of 1ꢀ CC. In addition, this catalyst can be easily regenerated in
the catalyst composition and CH concentration in the initial solution
leads to a positive effect on the catalyst performance in the synthesis of
the air flow at 500◦C for 1 h. Such regeneration can be repeated more
than 10 times without any loss of the initial activity.
1
ꢀ CC. However, this phenomenon is appeared mainly at the initial stage
of the reaction. Indeed, if the reaction is carried out for 2 and 4 h on the
4