727
with higher loadings of ZnO (10ZnO/Cr 2 O 3 and 15ZnO/Cr 2 O 3 ) have both ZnO and
ZnCr 2 O 4 phases along with Cr 2 O 3 . Diffraction signals at 2θ = 35.7°, 30.3°, 63.1°,
57.4°, and 43.4° corresponding “d” values of 0.251, 0.294, 0.147, 0.160, and
0.208 nm are confirmed as ZnCr 2 O 4 phase [ICDD #: 22-1107]. Diffraction lines at
2θ = 36.2°, 31.7°, 34.4°, 56.6°, and 62.8° with “d” values of 0.247, 0.281, 0.260,
0.162, and 0.147 nm are due to the presence of ZnO phase [ICDD #: 89-0510] [14,
15]. Diffraction signals due to Cr 2 O 3 [ICDD #: 85-0730] are appeared at 2θ = 33.6°,
36.1°, 24.4°, 54.8°, 41.5°, and 50.2° with “d” values of 0.265, 0.247, 0.362, 0.167,
0.216, and 0.181 nm [2, 16]. All the diffraction lines are in good correlation with
standard ICDD data.
3.2 FTIR Analysis
The FTIR spectra of various loadings of ZnO on Cr 2 O 3 are shown in Fig. 2. The
vibrational bands observed at 410, 445, 566, and 626 cm
−1
are characteristic of
chromium oxide with Cr
+3
oxidation state, and results are consistent with reported
literature [14–19]. The signal at 930 cm
−1
is characteristic vibration of CrO 4 tetrahedra due to Cr
6+
ions [19, 20]. The intensity of this band is decreased upon increasing
the ZnO loading on Cr 2 O 3 . Absorption bands at 410 and 445 cm
−1
were present in
all the samples except in 15ZnO/Cr 2 O 3 . However, a new band located at 507 cm
−1
is
found over 15ZnO/Cr 2 O 3 . The spinel structure of ZnCr 2 O 4 is considered to be originated from CrO 6 octahedral and ZnO 4 tetrahedral. ZnCr 2 O 4 spinels are expected to
have four phonon bands centered at 185, 367, 497, and 615 cm
−1
. Among these, the
two high-frequency IR bands originated due to F 1u symmetry of the ZnCr 2 O 4 spinel,
and they depend on position and shape on the chemical nature and stoichiometry of
Fig. 1 XRD patterns of various loadings of ZnO on Cr 2 O 3 (a) 2ZnO/Cr 2 O 3 , (b) 5ZnO/Cr 2 O 3 , (c)
7ZnO/Cr 2 O 3 , (d) 10ZnO/Cr 2 O 3 , and (e) 15ZnO/Cr 2 O 3
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with higher loadings of ZnO (10ZnO/Cr 2 O 3 and 15ZnO/Cr 2 O 3 ) have both ZnO and
ZnCr 2 O 4 phases along with Cr 2 O 3 . Diffraction signals at 2θ = 35.7°, 30.3°, 63.1°,
57.4°, and 43.4° corresponding “d” values of 0.251, 0.294, 0.147, 0.160, and
0.208 nm are confirmed as ZnCr 2 O 4 phase [ICDD #: 22-1107]. Diffraction lines at
2θ = 36.2°, 31.7°, 34.4°, 56.6°, and 62.8° with “d” values of 0.247, 0.281, 0.260,
0.162, and 0.147 nm are due to the presence of ZnO phase [ICDD #: 89-0510] [14,
15]. Diffraction signals due to Cr 2 O 3 [ICDD #: 85-0730] are appeared at 2θ = 33.6°,
36.1°, 24.4°, 54.8°, 41.5°, and 50.2° with “d” values of 0.265, 0.247, 0.362, 0.167,
0.216, and 0.181 nm [2, 16]. All the diffraction lines are in good correlation with
standard ICDD data.
3.2 FTIR Analysis
The FTIR spectra of various loadings of ZnO on Cr 2 O 3 are shown in Fig. 2. The
vibrational bands observed at 410, 445, 566, and 626 cm
−1
are characteristic of
chromium oxide with Cr
+3
oxidation state, and results are consistent with reported
literature [14–19]. The signal at 930 cm
−1
is characteristic vibration of CrO 4 tetrahedra due to Cr
6+
ions [19, 20]. The intensity of this band is decreased upon increasing
the ZnO loading on Cr 2 O 3 . Absorption bands at 410 and 445 cm
−1
were present in
all the samples except in 15ZnO/Cr 2 O 3 . However, a new band located at 507 cm
−1
is
found over 15ZnO/Cr 2 O 3 . The spinel structure of ZnCr 2 O 4 is considered to be originated from CrO 6 octahedral and ZnO 4 tetrahedral. ZnCr 2 O 4 spinels are expected to
have four phonon bands centered at 185, 367, 497, and 615 cm
−1
. Among these, the
two high-frequency IR bands originated due to F 1u symmetry of the ZnCr 2 O 4 spinel,
and they depend on position and shape on the chemical nature and stoichiometry of
Fig. 1 XRD patterns of various loadings of ZnO on Cr 2 O 3 (a) 2ZnO/Cr 2 O 3 , (b) 5ZnO/Cr 2 O 3 , (c)
7ZnO/Cr 2 O 3 , (d) 10ZnO/Cr 2 O 3 , and (e) 15ZnO/Cr 2 O 3
A Sustainable Process for the Synthesis of Alkylpyrazines by Dehydrocyclization…