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Characterization of copper chromite catalysts for methanol dehydrogenation
Applied Elsevier
93
Catolysb, 11 (1984) 93-101 Science Publishers B.V., Amsterdam
OF COPPER
CHARACTERIZATION
S.P. TONNER, School
South Wales, aTo whom
Kensington,
of Chemistry,
(Received
12 October
CATALYSTS
FOR METHANOL
DEHYDROGENATION
D.L. TRIMM and N.W. CANTb
Engineering
correspondence
bSchool
CHROMITE
M.S. WAINWRIGHTa,
of Chemical
in The Netherlands
-Printed
and Industrial
N.S.W. should
Chemistry,
The University
of New
2033, Australia. be addressed
Macquarie
University,
1983, accepted
North Ryde,
5 March
N.S.W.,
2113, Australia.
1984)
ABSTRACT Copper chromite catalysts have been characterised by total and metal surface areas. X-ray powder diffraction, thermal gravimetric analysis and selective extraction of copper oxide in order to investigate the nature of the active catalyst for methanol dehydrogenation. After reduction in hydrogen at atmospheric pressure, the catalyst surface has been shown to consist essentially of copper metal crystallites supported on cuprous chromite. The mechanism of catalyst reduction has been identified.
INTRODUCTION Copper
chromite
the hydrogenation the hydrogenolysis cribed
in detail
chromites genation nickel, final
catalysts of a wide
were first
of esters
to alcohols
by the same authors
is their high selectivity of edible
product
which
feature
has been desof the copper
has been used to advantage hydrogenation
and inferior
has shown that copper
of alkyl
formates
in the hydro-
catalysts,
nutritional
chromite
in an alternative
thesis
[7,8], and for the dehydrogenation
of methanol
latter
reaction
importance
methyl
formate
xide
preparation
for
for
such as
quality
of the
[6].
in this laboratory
for the hydrogenolysis
formamide,
et al. to be active
Cl], and particularly
A particular
stronger
saturation
by Adkins
compounds
[2]. Catalyst
[3-51.
fats and oils, where
can lead to excessive
Research
reported
range of organic
has particular as a starting
acetic
acid,
industrial
material
formamide,
cyanide
are active
to methyl
formate
of formic
syn-
[9]. The
due to the emerging
in the synthesis
hydrogen
catalysts
two stage methanol
use of
acid, dimethyl
and high purity
carbon mono-
[lo].
Considerable sites,
work
has been done in determining
the distribution
catalyst
deactivation.
oxide
copper
(CuO) and copper
0166-9834/84/$03.00
on the catalyst
X-ray diffraction
that prior to reduction, copper
of copper
chromite
chromite
the nature surface,
of the active
and the reasons
Cl11 and magnetic
studies
catalysts
of intimate
(CuCr204).
consist Adkins
0 1984 Elsevier Science Publishers B.V.
[5] first
catalyst for
[12] have shown mixtures
suggested
of
94
TABLE
1
Catalyst
characterisation Composition (unreduced
Catalyst
Surface
catalysts)
Chromium
Copper Total
wt%
Crystallite size
(m2g-'1
Mol.Ratio
As CuO
Area
Total
cu E
Copper
Ratio
scu
sCU
'BET
/:
'BET
1. Harshaw
35.6
18.9
27.1
1.08
28.4
6.8
0.24
80
59.4
54.5
13.0
3.74
16.3
10.8
0.66
100
33.7
24.5
25.1
1.10
45.1
15.4
0.34
70
44.9
24.5
31.6
1.16
40.7
7.9
0.19
110
45.1
0.49
59.9
0.9
0.01
30
(1808) 2. Harshaw (0203) 3. Girdlera (G-22) 4. Laboratory preparation 5. CuCr204
27.3
-
a10% BaO
divalent
copper
tion of esters monovalent
to be the active and ketones,
and metallic pressure,
(Cu2Cr204).
Rabes and Schneck
copper metal on chromia hydrogenation chromia
Stroupe
the catalyst
and that further
in the high pressure
and that deactivation
states.
unspecified
initially
species
consisted
[13] believed
reduction
(Cr203).
was caused
[ll] proposed
(200 atm) hydrogenaby reduction
that after
of copper
metal
that cuprous
at high pressure
and cuprous
chromite
produced
reduction
at 200 atm proposed
is the true active
catalyst,
and that no other
dispersed
liquid
that copper
oxide
at an
chromite
was formed
highly
in simultaneous
Miya et al. [143,
and catalyst
to the
reduction
phases
phase
supported were
on
present
after reduction. Studies
of soyabean
rate data, X-ray shown eventual of maximum recently
reduction
activity
and chromia,
both metallic
extraction through
and monovalent
used to confirm elemental
oil hydrogenation,
and Cu(I), which
(6 atm),
combining
of copper
phases
an intermediate copper
copper
exist
state
[15,161.
as the active
eventually
reduces
have
More
species
to Cu(0) to
for isomerisation.
Our experiments methanol
at lower pressures
ESCA and selective
to copper
where
[I71 XPS has been
for vegetable be active
oil hydrogenation
diffraction,
have shown that copper
dehydrogenation
hydrogenation
activity
and a negative has been
identified
est, as well as fully characterising
metal
is also the active
contribution
of other
[9]. Hence
the catalyst,
component
components
it was of particular
to assess
the extent
for
to deinter-
and nature
95 of reduction the liquid
and to identify
phase
of the catalyst at elevated
phase present.
Conclusions
of esters
are of limited
value
and the hydrogenation
pressures
(> 6 atm).
lyst does not catalyse is necessary
the support
hydrogenation
In methanol
the reaction
for catalyst
and metal
surface
and selective the active
areas,
from
out simultaneously
dehydrogenation,
the unreduced
in pure hydrogen
cata-
at 220°C
activation.
employed
have been obtained
before
of copper
strictly
dehydrogenation,
X-ray powder
extraction
are carried
and pretreatment
In this study, reduced catalysts ions of pretreatment
reaction
derived
since the reduction
thermal
diffraction,
oxide
in order
under the condit-
and characterised gravimetric
to investigate
by total analysis
the nature
of
catalyst.
EXPERIMENTAL Catalysts Three Girdler
commercial
of basic oxides and Capece Cu(I).
copper
G-22) were used.
chromite
catalysts
(Harshaw
1808, Harshaw
catalyst
contains
10 wt% BaO. The addition
The Girdler
is believed
to inhibit
et al. Cl71 have recently
A copper
chromite
catalyst
complete
decomposition
of copper
2Cu(OH)NH4Cr04
t Cu0.CuCr204
+ N2 + 5H20
catalysts
were
reduced
of divalent
is achieved
was also prepared
[I41 involving
Powdered
reduction
shown this
ammonium
0203,
and
copper
[5],
by stabilization
by the method
of
of Miya et al.
chromate.
in a flow of hydrogen
(99.99%,
50 cm3 min-')
at
220°C and l-l.5 atm.
Characterisation The compositions
of the catalysts
scopy of acid digested were determined mixture
using samples
of HF, HC104 and HN03.
by washing filtrate
catalyst
[5].
The total
samples
prepared
single
point
at 363 K respectively. X-ray powder diffractometer. size by X-ray vent oxidation
by atomic
of total copper
by dissolution
The copper
present
was obtained
N
in a 60/10/30
were
Reduced
prior to examination.
of HCl and retaining by a similar
areas of reduced
in greater
carried
acid
catalyst
the leaching
samples
were
detail
elsewhere
were
oxide [18].
Geiger-Flex
for determining
coated
samples
with nitrous
out using a Rigaku
powder was used as a reference
line broadening.
volumetric
oxide was measured
at 77 K and reaction
is described
studies
spectro-
catalyst.
surface
adsorption
absorption
and total chromium
as copper
as a residue
chromite
metal
2 The latter
diffraction Silicon
obtained
copper
(BET) and copper
using
were determined
The amounts
with a hot 32 wt% solution
"Pure' CuCr204
of the laboratory
measured
samples.
crystallite
with collodion
to pre-
FIGURE
1
X-ray diffraction
a
patterns
of unreduced,
leached
and reduced
b
Harshaw
0203 copper chromite
catalyst
C
(Catalyst
2).
97 Thermal
Gravimetric
Analysis
(TGA) was carried out in atmospheres of pure nitro-1 (50 cm3 min ) using a Du Pont Series 99 Thermal Analyser.
gen and pure hydrogen A temperature thermal
range of 50-650°C
experiments
thoroughly
dried
was used with a heating
were also carried
before
out at 220°C over
rate of 10°C min -'. Iso12 hours.
Samples
were
analysis.
RESULTS Composition The compositions
of the unreduced
ite sizes of the reduced copper
and chromium
3 and 4 copper
to chromium
the ratio expected An alternative
chromite
Extraction
with
state
HCl indicates
copper
chromium
5, which
mole
of copper
followed
1. The values
ammonium
higher
copper
closely
chromate loading
can be prepared
has 90% of the Cu present
by reaction
1.
can be achiev-
[19]. Copper
[20].
53% of the total
from reaction
1,
to
by precipitation
at 500°C
CuO and Cr203
that approximately
for total
basis show for catalyst
by decomposition
between
as CuO, as expected
loading
areas and crystall-
of ca. 1.1. These correspond
in which
reaction
in Table
to a mole
2. Such catalysts
hydroxides
by solid
73% of the Cu exists Catalyst
mole ratios
by catalyst
lysts 1 and 4 is present has a higher
are presented
of preparation,
and chromium forms
and the surface
1 when converted
from the decomposition
method
ed is illustrated of copper
catalysts
in Table
catalysts,
copper
1. Catalyst
as CUD whilst
in cata-
2, which
in catalyst
3,
as CuO. was obtained
by leaching
ratio of 0.49, corresponding
catalyst
closely
4 with HCl, has a copper
to the stoichiometric
to
value of
0.50 for CuCr204.
Surface
areas
Copper
surface
areas,
have been discussed copper
and their effect
elsewhere
area to total surface
that there surface
is a relatively
area is obtained
on activity
[91. The high copper obtained
area,
high degree
for catalyst
for methanol
areas,
for catalysts
of copper 5, where
dehydrogenation,
and the high ratio of l-4 in this study show
dispersion.
A very
CuO has been removed
low copper prior
to
reduction.
X-ray diffraction The small copper reported
in Table
an easily loading, copper
sintered
crystallite
metal.
and low support
on decomposition
diffraction catalysts
sizes,
1, are indicative
This result
is surprising
area which would of the copper
was also used to identify using
as well as the high copper
of a relatively
lines with angles
over
high degree
salts during
the range
areas, for
in view of the high copper
be expected
different
surface
of dispersion
to lead to aggregation
catalyst
components
preparation. of unreduced
of
X-ray and reduced
10" < 28 < 70". For catalyst
5,
98
TABLE
2
Observed
and predicteda
weight
losses
due to catalyst
reduction
(w-t%)
50-650°C
Temperature Reduction Catalyst
of CuO
Obs
220°C
Pred
Reduction of Total Cu Obs Pred
(wt%)
Obs
1
4.5
4.76
10.8
8.96
4.8
2
13.2
13.71
15.2
14.97
12.9
3
6.2
6.17
12.6
8.50
7.5
4
6.2
6.17
11.6
11.31
6.0
9.0
6.86
< 1.0
5
aPredicted
from CuO loadings
no maxima
corresponding
ed closely standard
to CuO were reported,
to that recorded
for catalyst chromium
Silica
oxide
to total
[21]. Catalyst
were also greatly
ever, a 70-80X
reduction
fairly
distinct
maxima
are obtained
prior to reduction. more evident.
catalysts
to intensity
before
On reduction
2e = 36.3 emerges
were poorly
transition
from the cupric
The pattern indicating
for barium
decomposition
reduction.
corresponding
assessment
Only
38.9
to CuO had been of the CuCr204 difficult.
in catalyst
As Figure
of cuprous
to the cuprous
of the chromate
2 were
la shows,
(CuO) and 37.6
chromite,
throughout
phase
present
Howthe
intense
(CuCr204)
of CuCr204
had clearly
in catalyst
presumably
Cu2Cr204.
the spectra, taken
to be amorphous
oxide
the latter
(Cu20),
being most
copper
Although
place.
3, disappeared
on reduction
by the reaction
(2)
as no peaks were chromate
is
at
a significant
+ 3H2 + 2Ba0 + Cr203 + 3H20
BaO appears
and
of
is very poor and a broad maxima
and overlapped
chromate,
The presence
with HCl (lb), the contribution
the presence
defined
catalysts,
the high ratio of
The intensity
an overall
(Ic), definition
indicating
the maxima
that peaks
(CuO, CuCr204),
leaching
of CuO and CuCr204
3.
was evident.
and after
at 2e = 35.6
explains
had emerged.
making
correspond-
5 was thus used as a CuCr204
in the commercial
in catalyst
showed
obtained
essentially
than CuCr204
to copper
diminished,
After
consisted
of BaCr04 was observed.
rather
observed
corresponding
maxima
cuprous
pattern
copper
of reduced
and the pattern
(Si02) was identified
3, the distinct
XRD studies
2BaCr04
for CuCr204
in the form of BaCr04
lost and peaks maxima
1 and CuO + H2 -t Cu + H20
to show that all other catalysts
prior to reduction.
copper
in Table
evident.
(CuCr04)
likely also present
No interference
or chromia
in an amorphous
maxima
for
(Cr203) were detected, state.
99
FIGURE
2
Thermal
catalysts
Gravimetric
(catalysts
Analysis
in hydrogen
1 to 5 from top) showing
atmosphere
weight
of copper
chromite
loss due to reduction
of
copper.
Thermal
gravimetric
Figure hydrogen
analysis
2 shows the weight to 650°C.
and 25O"C,
Two distinct
and a slower
is attributed
to reduction
predicted the first
weight
values
in Table
values,
loss, a sharp
to 65O"C,
to reduction
from the data
in Table
a minor weight
200
of the chromthen
1. Actual
is obtained
loss, predicted
for catalysts
was observed
loss between
If the first stape
2, and close agreement
particularly
under
atom per atom of copper,
For the total weight
differences,
the catalysts
can be identified.
can be predicted
are compared
under nitrogen
to these
by heating
of CuO to Cu and the second
stage of reduction.
heated
ponding
of weight
the loss of one oxygen
losses
lower than observed were
stages
obtained
loss up to 55O"C,
ite to Cu, each involving the expected
loss curves
values
and
for are
1 and 3. When the catalysts
loss, approximately
and attributed
to thermal
corres-
decomposition
of the chromite. When catalyst
5 is reduced,
the first
stage of weight
the final weight
loss is again
in excess
of that predicted
This was also attributed As the catalysts necessarily carried shown
out. The first
catalysts loss
relevant,
in Table
to decomposition
are normally
so isothermal
closely
1, 2 and 4. No further
weight
loss for catalyst
weight
loss occurred
stage of reduction
rapidly
be attributed
is not
12 hours were also at 22O"C,
from the amounts took place,
5. The difference
3 could
and
content.
loss up to 650°C
at 220°C over
with that predicted
for catalyst
from copper
of the chromite. at 22O"C,
reductions
stage of weight
2, agreed
(< 1%) was recorded
served
reduced
loss is not present
between
and, as of CuO in
and minimal predicted
to decomposition
weight
and ob-
of BaCrO4
100 by reaction
2.
DISCUSSION The high copper crystallite
of reduction
dispersed
copper
of copper
since the copper
metal.
for methanol
with N20 and the small copper
suggest
that considerable
certainly
area in catalyst studies
appears
5 (reduced
of Cu2Cr204
aggregation to result
could
highly
of CuO reported be expected.
from reduction
of CuO
was very small.
to cuprous
can occur
that under the
relatively
high levels
CuCr204)
show reduction
The formation
data indicate
dehydrogenation,
This is despite
are formed.
surface
X-ray diffraction
by reaction
from XRD line broadening
employed
catalysts
1 which would
The source
copper
areas measured
sizes calculated
conditions
in Table
surface
chromite
as well as to
via two paths:
direct
reduct-
ion of CuCr204
2CuCr204
+ H2 + Cu2Cr204
or by a reverse
Cu + CuCr204
Thermal
disproportionation
gravimetric
analysis
The presence
The remaining
employed
surface copper,
which
in some previous
gradually
by XRD for samples reduction
by almost
as Cu2Cr204.
surface
are carried
of copper
after only
as Cu2Cr204,
reduction
reduced
at 220°C
then appears
immediate
to
incorporation by the
10 minutes
of
is left well disby nitrous
out at the higher
complete
is evid-
This is substantiated
areas obtained
rapid-
is observed
loss due to reduction
4. Catalyst
not incorporated
studies,
of this study
chromite
catalysts
of the catalyst
in which
ing essentially
of cuprous
dispersion
and CuCr204
hydrogen
of Cu2Cr204
oxide ad-
pressures
to Cu and Cr203
takes place.
The results of copper
metal
of free CuO takes place
areas can be obtained
for the high metal
For reductions
weight
of CUD accompanied
of the copper
that total copper
sorption.
copper
reduction
as shown
for by reaction
fraction
and accounts
complete
no further
of Cu2Cr204
take place via rapid reduction of a substantial
reduction.
between
shows that reduction
(55O"C),
can thus only be accounted
persed
reaction
at 220°C and although
temperatures
ent at 220°C.
finding
(3)
-f Cu2Cr204
ly and completely at elevated
+ Cr203 + H20
is achieved
show that the procedure for methanol
copper
crystallites
chromite,
for the activation
produces
are dispersed
Cu2Cr204.
by incorporation
employed
dehydrogenation
A relatively
an active
over a support high degree
of the bulk of the copper
form
consist-
of copper
as Cu2Cr204.
ACKNOWLEDGEMENTS Support
was provided
under the National
Energy
Research,
Development
and Demon-
101 stration
Programme
administered
by the Commonwealth
Department
of National
Develop-
ment.
REFERENCES
8
18 19 20 21
H. Adkins, R. Connor and K. Folkers, J. Amer. Chem. Sot., 53 (1931) 1091. H. Adkins, Organic Reactions, 8 (1954) 1. R. Connor, K. Folkers and H. Adkins, J. Amer. Chem. Sot., 54 (1932) 1138. R. Connor, K. Folkers and H. Adkins, ibid., 53 (1931) 2012. H. Adkins, E. Burgoyne and H. Schneider, ibid., 72 (1950) 2626. S.I. Gray and L.F. Russell, J. Amer. Oil Chemists Sot., 56 (1979) 36. J.W. Evans, N.W. Cant, D.L. Trimm and M.S. Wainwright, Appl. Catal., 6 (1983) 355. J.W. Evans, P.S. Casey, M.S. Wainwright, D.L. Trimm and N.W. Cant, ibid., 7 (1983) 31. S.P. Tonner, in preparation. M. Chono and T. Yamamoto, Shokubai, 23 (1981) 3. J.D. Stroupe, J. Amer. Chem. Sot., 71 (1949) 569. P.W. Selwood, F.N. Hill and H. Boardman, ibid., 68 (1946) 2055. I. Rabes and R. Schneck, Z. Elektrochem., 52 (1948) 37. B. Miya, F. Hoshino and I. Iwasa, J. Catal., 5 (1966) 401. L.E. Johansson and S.T. Lundin, J. Amer. Oil Chemists Sot., 56 (1979) 974. L.E. Johansson, ibid., 56 (1979) 987. F.M. Capece, V. Di Castro, C. Furlani, G. Mattogno, C. Fragale, M. Gargano and M. Rossi, J. Electron. Spectros. Relat. Phenom., 27 (1982) 119. J.W. Evans, M.S. Wainwright, A.J. Bridgewater and D.J. Young, Appl. Catal., 7 (1983) 75. H. Boerma, Scientific Bases for the Prepn. of Heterogeneous Catalysts, An Int. Symposium, Societe Chimique de Belgique, A7-1 (1975). H. Charcosset, P. Turlier and Y. Trambouze, Compt. Rend., 255 (1962) 1924. Von I. Schulz, I. Ebert and J. Scheve, Z. Anorg. Alleg. Chem., 346 (1966) 66.
93
Catolysb, 11 (1984) 93-101 Science Publishers B.V., Amsterdam
OF COPPER
CHARACTERIZATION
S.P. TONNER, School
South Wales, aTo whom
Kensington,
of Chemistry,
(Received
12 October
CATALYSTS
FOR METHANOL
DEHYDROGENATION
D.L. TRIMM and N.W. CANTb
Engineering
correspondence
bSchool
CHROMITE
M.S. WAINWRIGHTa,
of Chemical
in The Netherlands
-Printed
and Industrial
N.S.W. should
Chemistry,
The University
of New
2033, Australia. be addressed
Macquarie
University,
1983, accepted
North Ryde,
5 March
N.S.W.,
2113, Australia.
1984)
ABSTRACT Copper chromite catalysts have been characterised by total and metal surface areas. X-ray powder diffraction, thermal gravimetric analysis and selective extraction of copper oxide in order to investigate the nature of the active catalyst for methanol dehydrogenation. After reduction in hydrogen at atmospheric pressure, the catalyst surface has been shown to consist essentially of copper metal crystallites supported on cuprous chromite. The mechanism of catalyst reduction has been identified.
INTRODUCTION Copper
chromite
the hydrogenation the hydrogenolysis cribed
in detail
chromites genation nickel, final
catalysts of a wide
were first
of esters
to alcohols
by the same authors
is their high selectivity of edible
product
which
feature
has been desof the copper
has been used to advantage hydrogenation
and inferior
has shown that copper
of alkyl
formates
in the hydro-
catalysts,
nutritional
chromite
in an alternative
thesis
[7,8], and for the dehydrogenation
of methanol
latter
reaction
importance
methyl
formate
xide
preparation
for
for
such as
quality
of the
[6].
in this laboratory
for the hydrogenolysis
formamide,
et al. to be active
Cl], and particularly
A particular
stronger
saturation
by Adkins
compounds
[2]. Catalyst
[3-51.
fats and oils, where
can lead to excessive
Research
reported
range of organic
has particular as a starting
acetic
acid,
industrial
material
formamide,
cyanide
are active
to methyl
formate
of formic
syn-
[9]. The
due to the emerging
in the synthesis
hydrogen
catalysts
two stage methanol
use of
acid, dimethyl
and high purity
carbon mono-
[lo].
Considerable sites,
work
has been done in determining
the distribution
catalyst
deactivation.
oxide
copper
(CuO) and copper
0166-9834/84/$03.00
on the catalyst
X-ray diffraction
that prior to reduction, copper
of copper
chromite
chromite
the nature surface,
of the active
and the reasons
Cl11 and magnetic
studies
catalysts
of intimate
(CuCr204).
consist Adkins
0 1984 Elsevier Science Publishers B.V.
[5] first
catalyst for
[12] have shown mixtures
suggested
of
94
TABLE
1
Catalyst
characterisation Composition (unreduced
Catalyst
Surface
catalysts)
Chromium
Copper Total
wt%
Crystallite size
(m2g-'1
Mol.Ratio
As CuO
Area
Total
cu E
Copper
Ratio
scu
sCU
'BET
/:
'BET
1. Harshaw
35.6
18.9
27.1
1.08
28.4
6.8
0.24
80
59.4
54.5
13.0
3.74
16.3
10.8
0.66
100
33.7
24.5
25.1
1.10
45.1
15.4
0.34
70
44.9
24.5
31.6
1.16
40.7
7.9
0.19
110
45.1
0.49
59.9
0.9
0.01
30
(1808) 2. Harshaw (0203) 3. Girdlera (G-22) 4. Laboratory preparation 5. CuCr204
27.3
-
a10% BaO
divalent
copper
tion of esters monovalent
to be the active and ketones,
and metallic pressure,
(Cu2Cr204).
Rabes and Schneck
copper metal on chromia hydrogenation chromia
Stroupe
the catalyst
and that further
in the high pressure
and that deactivation
states.
unspecified
initially
species
consisted
[13] believed
reduction
(Cr203).
was caused
[ll] proposed
(200 atm) hydrogenaby reduction
that after
of copper
metal
that cuprous
at high pressure
and cuprous
chromite
produced
reduction
at 200 atm proposed
is the true active
catalyst,
and that no other
dispersed
liquid
that copper
oxide
at an
chromite
was formed
highly
in simultaneous
Miya et al. [143,
and catalyst
to the
reduction
phases
phase
supported were
on
present
after reduction. Studies
of soyabean
rate data, X-ray shown eventual of maximum recently
reduction
activity
and chromia,
both metallic
extraction through
and monovalent
used to confirm elemental
oil hydrogenation,
and Cu(I), which
(6 atm),
combining
of copper
phases
an intermediate copper
copper
exist
state
[15,161.
as the active
eventually
reduces
have
More
species
to Cu(0) to
for isomerisation.
Our experiments methanol
at lower pressures
ESCA and selective
to copper
where
[I71 XPS has been
for vegetable be active
oil hydrogenation
diffraction,
have shown that copper
dehydrogenation
hydrogenation
activity
and a negative has been
identified
est, as well as fully characterising
metal
is also the active
contribution
of other
[9]. Hence
the catalyst,
component
components
it was of particular
to assess
the extent
for
to deinter-
and nature
95 of reduction the liquid
and to identify
phase
of the catalyst at elevated
phase present.
Conclusions
of esters
are of limited
value
and the hydrogenation
pressures
(> 6 atm).
lyst does not catalyse is necessary
the support
hydrogenation
In methanol
the reaction
for catalyst
and metal
surface
and selective the active
areas,
from
out simultaneously
dehydrogenation,
the unreduced
in pure hydrogen
cata-
at 220°C
activation.
employed
have been obtained
before
of copper
strictly
dehydrogenation,
X-ray powder
extraction
are carried
and pretreatment
In this study, reduced catalysts ions of pretreatment
reaction
derived
since the reduction
thermal
diffraction,
oxide
in order
under the condit-
and characterised gravimetric
to investigate
by total analysis
the nature
of
catalyst.
EXPERIMENTAL Catalysts Three Girdler
commercial
of basic oxides and Capece Cu(I).
copper
G-22) were used.
chromite
catalysts
(Harshaw
1808, Harshaw
catalyst
contains
10 wt% BaO. The addition
The Girdler
is believed
to inhibit
et al. Cl71 have recently
A copper
chromite
catalyst
complete
decomposition
of copper
2Cu(OH)NH4Cr04
t Cu0.CuCr204
+ N2 + 5H20
catalysts
were
reduced
of divalent
is achieved
was also prepared
[I41 involving
Powdered
reduction
shown this
ammonium
0203,
and
copper
[5],
by stabilization
by the method
of
of Miya et al.
chromate.
in a flow of hydrogen
(99.99%,
50 cm3 min-')
at
220°C and l-l.5 atm.
Characterisation The compositions
of the catalysts
scopy of acid digested were determined mixture
using samples
of HF, HC104 and HN03.
by washing filtrate
catalyst
[5].
The total
samples
prepared
single
point
at 363 K respectively. X-ray powder diffractometer. size by X-ray vent oxidation
by atomic
of total copper
by dissolution
The copper
present
was obtained
N
in a 60/10/30
were
Reduced
prior to examination.
of HCl and retaining by a similar
areas of reduced
in greater
carried
acid
catalyst
the leaching
samples
were
detail
elsewhere
were
oxide [18].
Geiger-Flex
for determining
coated
samples
with nitrous
out using a Rigaku
powder was used as a reference
line broadening.
volumetric
oxide was measured
at 77 K and reaction
is described
studies
spectro-
catalyst.
surface
adsorption
absorption
and total chromium
as copper
as a residue
chromite
metal
2 The latter
diffraction Silicon
obtained
copper
(BET) and copper
using
were determined
The amounts
with a hot 32 wt% solution
"Pure' CuCr204
of the laboratory
measured
samples.
crystallite
with collodion
to pre-
FIGURE
1
X-ray diffraction
a
patterns
of unreduced,
leached
and reduced
b
Harshaw
0203 copper chromite
catalyst
C
(Catalyst
2).
97 Thermal
Gravimetric
Analysis
(TGA) was carried out in atmospheres of pure nitro-1 (50 cm3 min ) using a Du Pont Series 99 Thermal Analyser.
gen and pure hydrogen A temperature thermal
range of 50-650°C
experiments
thoroughly
dried
was used with a heating
were also carried
before
out at 220°C over
rate of 10°C min -'. Iso12 hours.
Samples
were
analysis.
RESULTS Composition The compositions
of the unreduced
ite sizes of the reduced copper
and chromium
3 and 4 copper
to chromium
the ratio expected An alternative
chromite
Extraction
with
state
HCl indicates
copper
chromium
5, which
mole
of copper
followed
1. The values
ammonium
higher
copper
closely
chromate loading
can be prepared
has 90% of the Cu present
by reaction
1.
can be achiev-
[19]. Copper
[20].
53% of the total
from reaction
1,
to
by precipitation
at 500°C
CuO and Cr203
that approximately
for total
basis show for catalyst
by decomposition
between
as CuO, as expected
loading
areas and crystall-
of ca. 1.1. These correspond
in which
reaction
in Table
to a mole
2. Such catalysts
hydroxides
by solid
73% of the Cu exists Catalyst
mole ratios
by catalyst
lysts 1 and 4 is present has a higher
are presented
of preparation,
and chromium forms
and the surface
1 when converted
from the decomposition
method
ed is illustrated of copper
catalysts
in Table
catalysts,
copper
1. Catalyst
as CUD whilst
in cata-
2, which
in catalyst
3,
as CuO. was obtained
by leaching
ratio of 0.49, corresponding
catalyst
closely
4 with HCl, has a copper
to the stoichiometric
to
value of
0.50 for CuCr204.
Surface
areas
Copper
surface
areas,
have been discussed copper
and their effect
elsewhere
area to total surface
that there surface
is a relatively
area is obtained
on activity
[91. The high copper obtained
area,
high degree
for catalyst
for methanol
areas,
for catalysts
of copper 5, where
dehydrogenation,
and the high ratio of l-4 in this study show
dispersion.
A very
CuO has been removed
low copper prior
to
reduction.
X-ray diffraction The small copper reported
in Table
an easily loading, copper
sintered
crystallite
metal.
and low support
on decomposition
diffraction catalysts
sizes,
1, are indicative
This result
is surprising
area which would of the copper
was also used to identify using
as well as the high copper
of a relatively
lines with angles
over
high degree
salts during
the range
areas, for
in view of the high copper
be expected
different
surface
of dispersion
to lead to aggregation
catalyst
components
preparation. of unreduced
of
X-ray and reduced
10" < 28 < 70". For catalyst
5,
98
TABLE
2
Observed
and predicteda
weight
losses
due to catalyst
reduction
(w-t%)
50-650°C
Temperature Reduction Catalyst
of CuO
Obs
220°C
Pred
Reduction of Total Cu Obs Pred
(wt%)
Obs
1
4.5
4.76
10.8
8.96
4.8
2
13.2
13.71
15.2
14.97
12.9
3
6.2
6.17
12.6
8.50
7.5
4
6.2
6.17
11.6
11.31
6.0
9.0
6.86
< 1.0
5
aPredicted
from CuO loadings
no maxima
corresponding
ed closely standard
to CuO were reported,
to that recorded
for catalyst chromium
Silica
oxide
to total
[21]. Catalyst
were also greatly
ever, a 70-80X
reduction
fairly
distinct
maxima
are obtained
prior to reduction. more evident.
catalysts
to intensity
before
On reduction
2e = 36.3 emerges
were poorly
transition
from the cupric
The pattern indicating
for barium
decomposition
reduction.
corresponding
assessment
Only
38.9
to CuO had been of the CuCr204 difficult.
in catalyst
As Figure
of cuprous
to the cuprous
of the chromate
2 were
la shows,
(CuO) and 37.6
chromite,
throughout
phase
present
Howthe
intense
(CuCr204)
of CuCr204
had clearly
in catalyst
presumably
Cu2Cr204.
the spectra, taken
to be amorphous
oxide
the latter
(Cu20),
being most
copper
Although
place.
3, disappeared
on reduction
by the reaction
(2)
as no peaks were chromate
is
at
a significant
+ 3H2 + 2Ba0 + Cr203 + 3H20
BaO appears
and
of
is very poor and a broad maxima
and overlapped
chromate,
The presence
with HCl (lb), the contribution
the presence
defined
catalysts,
the high ratio of
The intensity
an overall
(Ic), definition
indicating
the maxima
that peaks
(CuO, CuCr204),
leaching
of CuO and CuCr204
3.
was evident.
and after
at 2e = 35.6
explains
had emerged.
making
correspond-
5 was thus used as a CuCr204
in the commercial
in catalyst
showed
obtained
essentially
than CuCr204
to copper
diminished,
After
consisted
of BaCr04 was observed.
rather
observed
corresponding
maxima
cuprous
pattern
copper
of reduced
and the pattern
(Si02) was identified
3, the distinct
XRD studies
2BaCr04
for CuCr204
in the form of BaCr04
lost and peaks maxima
1 and CuO + H2 -t Cu + H20
to show that all other catalysts
prior to reduction.
copper
in Table
evident.
(CuCr04)
likely also present
No interference
or chromia
in an amorphous
maxima
for
(Cr203) were detected, state.
99
FIGURE
2
Thermal
catalysts
Gravimetric
(catalysts
Analysis
in hydrogen
1 to 5 from top) showing
atmosphere
weight
of copper
chromite
loss due to reduction
of
copper.
Thermal
gravimetric
Figure hydrogen
analysis
2 shows the weight to 650°C.
and 25O"C,
Two distinct
and a slower
is attributed
to reduction
predicted the first
weight
values
in Table
values,
loss, a sharp
to 65O"C,
to reduction
from the data
in Table
a minor weight
200
of the chromthen
1. Actual
is obtained
loss, predicted
for catalysts
was observed
loss between
If the first stape
2, and close agreement
particularly
under
atom per atom of copper,
For the total weight
differences,
the catalysts
can be identified.
can be predicted
are compared
under nitrogen
to these
by heating
of CuO to Cu and the second
stage of reduction.
heated
ponding
of weight
the loss of one oxygen
losses
lower than observed were
stages
obtained
loss up to 55O"C,
ite to Cu, each involving the expected
loss curves
values
and
for are
1 and 3. When the catalysts
loss, approximately
and attributed
to thermal
corres-
decomposition
of the chromite. When catalyst
5 is reduced,
the first
stage of weight
the final weight
loss is again
in excess
of that predicted
This was also attributed As the catalysts necessarily carried shown
out. The first
catalysts loss
relevant,
in Table
to decomposition
are normally
so isothermal
closely
1, 2 and 4. No further
weight
loss for catalyst
weight
loss occurred
stage of reduction
rapidly
be attributed
is not
12 hours were also at 22O"C,
from the amounts took place,
5. The difference
3 could
and
content.
loss up to 650°C
at 220°C over
with that predicted
for catalyst
from copper
of the chromite. at 22O"C,
reductions
stage of weight
2, agreed
(< 1%) was recorded
served
reduced
loss is not present
between
and, as of CuO in
and minimal predicted
to decomposition
weight
and ob-
of BaCrO4
100 by reaction
2.
DISCUSSION The high copper crystallite
of reduction
dispersed
copper
of copper
since the copper
metal.
for methanol
with N20 and the small copper
suggest
that considerable
certainly
area in catalyst studies
appears
5 (reduced
of Cu2Cr204
aggregation to result
could
highly
of CuO reported be expected.
from reduction
of CuO
was very small.
to cuprous
can occur
that under the
relatively
high levels
CuCr204)
show reduction
The formation
data indicate
dehydrogenation,
This is despite
are formed.
surface
X-ray diffraction
by reaction
from XRD line broadening
employed
catalysts
1 which would
The source
copper
areas measured
sizes calculated
conditions
in Table
surface
chromite
as well as to
via two paths:
direct
reduct-
ion of CuCr204
2CuCr204
+ H2 + Cu2Cr204
or by a reverse
Cu + CuCr204
Thermal
disproportionation
gravimetric
analysis
The presence
The remaining
employed
surface copper,
which
in some previous
gradually
by XRD for samples reduction
by almost
as Cu2Cr204.
surface
are carried
of copper
after only
as Cu2Cr204,
reduction
reduced
at 220°C
then appears
immediate
to
incorporation by the
10 minutes
of
is left well disby nitrous
out at the higher
complete
is evid-
This is substantiated
areas obtained
rapid-
is observed
loss due to reduction
4. Catalyst
not incorporated
studies,
of this study
chromite
catalysts
of the catalyst
in which
ing essentially
of cuprous
dispersion
and CuCr204
hydrogen
of Cu2Cr204
oxide ad-
pressures
to Cu and Cr203
takes place.
The results of copper
metal
of free CuO takes place
areas can be obtained
for the high metal
For reductions
weight
of CUD accompanied
of the copper
that total copper
sorption.
copper
reduction
as shown
for by reaction
fraction
and accounts
complete
no further
of Cu2Cr204
take place via rapid reduction of a substantial
reduction.
between
shows that reduction
(55O"C),
can thus only be accounted
persed
reaction
at 220°C and although
temperatures
ent at 220°C.
finding
(3)
-f Cu2Cr204
ly and completely at elevated
+ Cr203 + H20
is achieved
show that the procedure for methanol
copper
crystallites
chromite,
for the activation
produces
are dispersed
Cu2Cr204.
by incorporation
employed
dehydrogenation
A relatively
an active
over a support high degree
of the bulk of the copper
form
consist-
of copper
as Cu2Cr204.
ACKNOWLEDGEMENTS Support
was provided
under the National
Energy
Research,
Development
and Demon-
101 stration
Programme
administered
by the Commonwealth
Department
of National
Develop-
ment.
REFERENCES
8
18 19 20 21
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