Unpromoted and K O-Promoted
2
379
suspended in this solution. The mixture was then evaporated to dryness with continuous stirring over a
ꢂ
water bath. The resulting material was dried at 120 C in an oven for 24h. Finally, portions of the
ꢂ
catalyst were calcined in air for 5 h at 350, 400, 500, and 600 C. K O-promoted samples, denoted as
2
CoMo–K O (hyd) and CoMo–K O (nit), were prepared by the wet impregnation method. 10 w% K O
2
2
2
ꢂ
was added to 1.8g of CoMo-350, the calcined sample of cobalt molybdate at 350 C, from two sources
(
0.24 g KOH (BDH) and 0.43g KNO (BDH)) respectively, using few drops of deionized water. The
3
ꢂ
resulting homogeneous pasts were then dried and recalcined again at 350 C in air for 5 h.
Characterization
X-ray powder diffractograms (XRD) of the catalysts and two used catalysts were measured using a
D5000 Siemens diffractometer (Germany) at ambient temperature. The instrument used Ni-filtered
˚
CuK radiation (ꢂ ¼ 1.5418 A, 40kV, 30 mA). IR spectra of the unpromoted CoMoO =K O-promoted
ꢁ
4
2
CoMoO catalysts as well as two used catalysts were recorded by the KBr disk technique using a
4
Magna-FTIR-560 (USA) instrument operated by Nicolet Omnic software. The BET surface area was
obtained from nitrogen adsorption isotherms measured at liquid nitrogen temperature with an auto-
matic ASAP 2010 Sorptometer Micromeritics (USA). The total surface basic–acidic sites of the
catalysts were measured by temperature-programmed desorption of formic acid and pyridine, respec-
tively [12, 13]. The population of both surface acidic (ꢀ) and basic sites (ꢁ) were determined
ꢂ
thermogravimetrically [14] as follows: 100 mg portions of each sample were heated at 250 C in air
for 2 h, then kept in a desiccator together with an open beaker containing pyridine or formic acid at
ambient temperature for two weeks, prior to analysis. A 15-mg portion of each pyridine or formic acid-
ꢂ
ꢂ
covered sample was subjected to TG analysis on heating up to 350 C (at 20 C=min) in dry N
(40 ml=min) using an automatically recording Shimadzu Stand-Alone TGA-50H (Japan). The weight
2
loss, due to the desorption of pyridine and formic acid from the acidic and basic sites, was determined
as a function of both the acidity and the basicity of these catalysts.
Decomposition of acetic acid
The catalytic activity of all catalysts towards the decomposition of acetic acid was determined in the
gas phase in a fixed bed reactor. All experiments were conducted at atmospheric pressure in a
continuous flow mode, using a mixture of 0.74% CH COOH in dry N , obtained by passing N
3
2
2
ꢂ
3
À 1
through liquid acetic acid (Prolabo) in a saturator at 10 C. The total flow rate 147.7 cm (STP) min
3
was composed of 1.1 cm (STP) CH COOH and 146.6 cm (STP) min dry N . A catalyst sample of
3
À 1
3
2
ꢂ
1
00 mg was stabilized in a Pyrex glass reactor for 1 h at 200 C before measurements in a stream of dry
N . The reactor effluent was analyzed by a gas chromatograph (Shimadzu GC-14A) equipped with a
2
data processor model Shimadzu Chromatopac C-R4AD (Japan). TCD and SUS, PEG 6000 10% on
ꢂ
Shimalite TPA, 60=80 mesh (3mm i.d.ꢃ2 m) column at 150 C were used. Automatic sampling was
performed with a heated gas sample cock, type HGS-2. The retention time of acetic acid as a reactant,
and the expected decomposition products (CO and CH COCH ) have been calibrated in separate
2
3
3
experiments using pure authentic specimens. Conversion (%) and reaction rates during the decom-
position of CH COOH were calculated as explained in detail recently [15].
3
References
[
[
[
[
[
[
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4] Querini CA, Cornaglia LM, Ulla MA, Mir ꢂo EE (1999) Appl Catal B 20: 165
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