Structural, Morphological, and Catalytic Properties …
61
ascertain their structural, morphologic, and textural properties, and effect of these
properties on the OMS-2 catalytic activity in the reaction of ozone decomposition.
2 Experimental
2.1 Cryptomelane Synthesis
Manganese oxide samples under study were synthesized by potassium permanganate reduction: with manganese acetate (solid-state reaction), OMS-2-SSt, with
manganese sulfate (reflux method), OMS-2-Ref, with maleic acid (sol–gel method),
OMS-2-SG, and via KNO 3 and MnSO 4 melting together, and OMS-2-MS. Detailed
procedures for their synthesis are presented below.
OMS-2-SSt. KMnO 4 and Mn(CH 3 COO) 2 ·4H 2 O were mechanically mixed in the
molar ratio of 2:3 in an agate mortar, and an appropriate amount of water was added to
the mixture to obtain a rheological phase. The rheological phase mixture was heated
at 100 °C for 12 h. The mixture was cooled down to room temperature and washed
with distilled water several times. Thus, a precursor was obtained. The precursor was
heated in air at 400 °C for 4 h [34].
OMS-2-Ref. A typical synthesis [35] was as follows: 5.89 g of KMnO 4 in 100 mL
of water was added to a solution of 8.8 g of MnSO 4 -H 2 O in 30 mL of water and
3 mL of concentrated HNO 3 . The solution was refluxed at 100 °C for 24 h, and the
product was filtered, washed, and dried at 120 °C.
OMS-2-SG. In a typical sol–gel synthesis [17], maleic acid (0.78 g (6.7 mmol))
and KMnO 4 (3.16 g (20 mmol)) were dissolved in deionized water (200 mL) at
the predetermined temperature of 40 °C. After stirring for 30 min, the mixture was
allowed to settle for 60 min. The sample obtained after this step was then filtered,
washed with deionized water, and dried at 120 °C for 12 h. Then, calcination at
450 °C for 2 h was carried out.
OMS-2-MS. The sample was synthesized via KNO 3 and MnSO 4 melting together
[36]. KNO 3 was put into a crucible and heated to 380 °C under stirring to form a
molten solution; MnSO 4 was added into it, and the weight ratio of KNO 3 to MnSO 4
was 15. After being maintained at 380 °C for 3 h, the crucible was cooled down to RT
under ambient conditions, and the product was obtained by washing with deionized
water, and drying at 90 °C for 12 h.
2.2 Characterization
The samples were investigated on a Siemens D500 powder diffractometer (CuK α
radiation, λ = 1.54178 Å) with a secondary beam graphite monochromator (Siemens
AG, Munich, Germany). After thorough grinding with a pestle, each sample was
61
ascertain their structural, morphologic, and textural properties, and effect of these
properties on the OMS-2 catalytic activity in the reaction of ozone decomposition.
2 Experimental
2.1 Cryptomelane Synthesis
Manganese oxide samples under study were synthesized by potassium permanganate reduction: with manganese acetate (solid-state reaction), OMS-2-SSt, with
manganese sulfate (reflux method), OMS-2-Ref, with maleic acid (sol–gel method),
OMS-2-SG, and via KNO 3 and MnSO 4 melting together, and OMS-2-MS. Detailed
procedures for their synthesis are presented below.
OMS-2-SSt. KMnO 4 and Mn(CH 3 COO) 2 ·4H 2 O were mechanically mixed in the
molar ratio of 2:3 in an agate mortar, and an appropriate amount of water was added to
the mixture to obtain a rheological phase. The rheological phase mixture was heated
at 100 °C for 12 h. The mixture was cooled down to room temperature and washed
with distilled water several times. Thus, a precursor was obtained. The precursor was
heated in air at 400 °C for 4 h [34].
OMS-2-Ref. A typical synthesis [35] was as follows: 5.89 g of KMnO 4 in 100 mL
of water was added to a solution of 8.8 g of MnSO 4 -H 2 O in 30 mL of water and
3 mL of concentrated HNO 3 . The solution was refluxed at 100 °C for 24 h, and the
product was filtered, washed, and dried at 120 °C.
OMS-2-SG. In a typical sol–gel synthesis [17], maleic acid (0.78 g (6.7 mmol))
and KMnO 4 (3.16 g (20 mmol)) were dissolved in deionized water (200 mL) at
the predetermined temperature of 40 °C. After stirring for 30 min, the mixture was
allowed to settle for 60 min. The sample obtained after this step was then filtered,
washed with deionized water, and dried at 120 °C for 12 h. Then, calcination at
450 °C for 2 h was carried out.
OMS-2-MS. The sample was synthesized via KNO 3 and MnSO 4 melting together
[36]. KNO 3 was put into a crucible and heated to 380 °C under stirring to form a
molten solution; MnSO 4 was added into it, and the weight ratio of KNO 3 to MnSO 4
was 15. After being maintained at 380 °C for 3 h, the crucible was cooled down to RT
under ambient conditions, and the product was obtained by washing with deionized
water, and drying at 90 °C for 12 h.
2.2 Characterization
The samples were investigated on a Siemens D500 powder diffractometer (CuK α
radiation, λ = 1.54178 Å) with a secondary beam graphite monochromator (Siemens
AG, Munich, Germany). After thorough grinding with a pestle, each sample was