C-X bond reactivity in the catalytic hydrodehalogenation of haloarenes over unsupported and silica supported Ni

Article abstract of DOI:10.1016/j.molcata.2004.08.038

The hydrodehalogenation (HDH) of fluorobenzene (FB), chlorobenzene (CB), bromobenzene (BB), iodobenzene (IB), 1,3-dichlorobenzene (1,3-DCB), 1,3-dibromobenzene (1,3-DBB) and 1,3-bromochlorobenzene (1,3-BCB) has been studied over Ni/SiO₂ at 573 K. In the case of the mono-haloarenes, HDH activity decreased in the order FB > CB > BB > IB, an effect that is discussed in terms of halogen inductive effects. The conversion of the di-substituted benzenes (at a common inlet X/Ni molar ratio) was significantly lower (by a factor of up to 2) than that recorded for the mono-haloarenes, i.e. the presence of a second electron withdrawing halogen substituent lowered the overall level of HDH. A decline in HDH activity with time-on-stream was observed in every instance. Catalyst activation via direct temperature-programmed reduction (TPR) has been monitored with on-line thermogravimetric/mass spectrometric/thermal conductivity analyses. The incorporation of a calcination step prior to reduction resulted in a marked decline in HDH activity. The pre- and post-reaction catalyst samples have been characterized by BET area measurements, X-ray diffractograms (XRD) and H₂ chemisorption/ temperature-programmed desorption. TPR analyses of the post catalysis (passivated) samples were also conducted and compared with the response recorded for the unused catalysts. The loss of activity is linked to halogen/Ni interactions resulting in a suppression of H₂ uptake with possible Ni sintering and a disruption of the H₂/catalyst interactions. In the hydrotreatment of 1,3-BCB, the level of debromination exceeded that of dechlorination, a result that we attribute to a surface hydrochlorination and Cl exchange with the Br substituent on the aromatic ring. This effect extends to reactions over bulk NiO and NiO + SiO₂ mixtures. Hydrodehalogenation over Ni/SiO₂ follows the order fuorobenzene > chlorobenzene > bromobenzene > iodobenzene. Catalyst activation is monitored by on-line TG/MS (see representative profile) with pre-/post-reaction characterization that links loss of catalyst activity to disruption of H₂/catalyst interactions. Debromination of 1,3-bromochlorobenzene exceeded dechlorination as a result of Cl/Br exchange.

Full text of DOI:10.1016/j.molcata.2004.08.038

Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
C–X bond reactivity in the catalytic hydrodehalogenation of haloarenes
over unsupported and silica supported Ni
a
b
a,∗
K.V. Murthy , Patricia M. Patterson , Mark A. Keane
a
Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506, USA
b
Center for Applied Energy Research, University of Kentucky, Lexington, KY 40506, USA
Received 3 June 2004; received in revised form 31 August 2004; accepted 31 August 2004
Available online 8 October 2004
Abstract
The hydrodehalogenation (HDH) of fluorobenzene (FB), chlorobenzene (CB), bromobenzene (BB), iodobenzene (IB), 1,3-dichlorobenzene
1,3-DCB), 1,3-dibromobenzene (1,3-DBB) and 1,3-bromochlorobenzene (1,3-BCB) has been studied over Ni/SiO at 573 K. In the case of
(
2
the mono-haloarenes, HDH activity decreased in the order FB > CB > BB > IB, an effect that is discussed in terms of halogen inductive effects.
The conversion of the di-substituted benzenes (at a common inlet X/Ni molar ratio) was significantly lower (by a factor of up to 2) than
that recorded for the mono-haloarenes, i.e. the presence of a second electron withdrawing halogen substituent lowered the overall level of
HDH. A decline in HDH activity with time-on-stream was observed in every instance. Catalyst activation via direct temperature-programmed
reduction (TPR) has been monitored with on-line thermogravimetric/mass spectrometric/thermal conductivity analyses. The incorporation
of a calcination step prior to reduction resulted in a marked decline in HDH activity. The pre- and post-reaction catalyst samples have been
characterized by BET area measurements, X-ray diffractograms (XRD) and H
analyses of the post catalysis (passivated) samples were also conducted and compared with the response recorded for the unused catalysts.
The loss of activity is linked to halogen/Ni interactions resulting in a suppression of H uptake with possible Ni sintering and a disruption of
the H /catalyst interactions. In the hydrotreatment of 1,3-BCB, the level of debromination exceeded that of dechlorination, a result that we
attribute to a surface hydrochlorination and Cl exchange with the Br substituent on the aromatic ring. This effect extends to reactions over
bulk NiO and NiO + SiO mixtures.
2004 Elsevier B.V. All rights reserved.
2
chemisorption/temperature-programmed desorption. TPR
2
2
2
©
Keywords: Hydrodehalogenation; Chlorobenzene(s); Bromobenzene(s); Fluorobenzene; Iodobenzene; Chlorobromobenzene; Nickel/silica
1
. Introduction
in use, i.e. incineration, pyrolysis, hydrolysis, chemical/bio-
degradation [4,5] but each can lead to the formation of other
halogenated toxins and do not constitute the best practicable
environmentaloption. Catalytichydrodehalogenation(HDH)
is now emerging as a viable alternative non-destructive treat-
ment that can generate compounds of economic value from
halogenated waste [6]; this report focuses on a Ni/SiO2 pro-
moted transformation of gaseous Cl-, Br-, I- and F- aromatics.
The hydrodechlorination (HDC) of aliphatic organochlorines
(C2H3Cl3, C2HCl3, C2Cl4, CH2Cl2, CHCl3 and CCl4) has
been investigated over Ni/SiO2 (50 atm/573 K) [7,8] where
significant catalyst deactivation was observed and attributed
to coke formation via reactant polymerization. In the HDH
(1 atm/523–563 K) of CH2Cl2 and CHClF2 over bulk Ni and
Organohalogens are classified as high priority pollutants
due to their toxicity, mutagenicity and carcinogenicity [1].
These compounds are of commercial significance in the man-
ufacture of pesticides, plasticizers and disinfectants, pro-
cesses that are potential sources of release into the environ-
ment [2] with associated ecological damage and atmospheric
ozone depletion effects [3]. As a direct consequence, the safe
handling/disposal of halogenated compounds is a pressing
remediation issue. There are several technologies currently
∗
Corresponding author. Tel.: +1 859 257 5857; fax: +1 859 323 1929.
E-mail address: makeane@engr.uky.edu (M.A. Keane).
1
381-1169/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2004.08.038

1
50
K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
Ni/C, Ni carbide formation was proposed and found to be
more active than the starting Ni phase [9]. The HDC of
2. Experimental
1
,2-C4H8Cl2, an epichlorohydrin production by-product, has
2.1. Catalyst preparation and activation
been examined over (5–40%, w/w) Ni/SiO2 where a high se-
lectivity (95%) to C4H8 was achieved and catalyst stability
was attributed to the formation of Ni-hydrosilicate that was
resistant to deactivation [10].
Focusing on haloarenes, HDC activity in the conversion
of chlorobenzene (CB) over Ni/SiO2 and Ni/C was found to
be dependent on the nature of the support, activation condi-
tionsandNiparticlesize, aresponsethatissuggestiveofHDC
structure sensitivity [11,12]. The gas phase HDC of polychlo-
rinated aromatics such as 1,2-dichlorobenzene (1,2-DCB),
A 10% (w/w) (determined by ICP-OES, Vista-PRO, Var-
ian Inc.) Ni on SiO2 (fumed, Aldrich) precursor was prepared
by standard impregnation, where an aqueous nickel nitrate
solution was added drop wise to the substrate at 343 K with
constant agitation; the catalyst precursor was washed with
deionized water and dried in air at 383 K. Prior to use in catal-
ysis, the precursor, sieved (ATM fine test sieves) into a batch
of 75 ␮m average particle diameter, was reduced directly in
3
−1
−1
a 60 cm min stream of ultra pure H2 at 10 K min to
23 ± 1 K, which was maintained for 12 h. Alternatively, the
catalyst precursor was subjected to a precalcination step, i.e.
7
1
,2,4-trichlorobenzene (1,2,4-TCB) and hexachlorobenzene
has been reported for Ni supported on Al2O3, NiAl2O4,
hydrotalacites, MCM-41 and Cr2O3 where a high selec-
tivity (>95%) to benzene has been linked to metal dis-
persion allied to the availability of surface reactive hydro-
gen [13–17]. Hydrodebromination (HDB), by comparison,
has received less attention in the literature and few pub-
lished articles of direct relevance could be found. The liq-
uid phase HDB of hexabromobenzene and tribromobenzenes
has been considered where a Pd metallocenyl diphosphine
complex served as the (homogeneous) catalytic agent [18].
Yu et al. [19] recorded HDB activity for Pd anchored on
polyvinyl pyrrolidone (PVP) and observed a decline in per-
formance that was ascribed to HBr poisoning. Pd supported
on SiO2/AlPO4, ZrO2 and MgO was found to be active
in the liquid phase HDH of 1,3-bromochlorobenzene (1,3-
BCB) [20,21]. We have shown elsewhere [22,23] that gas
phase HDH of a range of substituted bromo- and chloro-
arenes over supported Ni is 100% selective in terms of
C–X bond scission with no aromatic ring reduction, where
electron donating ring substituents serve to raise the over-
all reaction rate. Marques et al. [24] have studied the liq-
uid phase HDB of dibromobenzene(s) (DBB) over Pd/C
and Raney-Ni catalysts in mixed organic/aqueous media and
found the Pd/C to be significantly more active. An exhaus-
tive search through the literature failed to unearth any stud-
ies of gas phase HDH of iodobenzene (IB) or fluorobenzene
−
1
heating in air at 10 K min to 873 K (maintained for 1 h),
cooling in He to room temperature with a subsequent reduc-
tion in H2 (as above) but to a final temperature of 873 K.
Unsupported NiO, and a physical mixture (thorough mixing
was ensured) of NiO + SiO2 and Ni(NO3)2 + SiO2 were also
employed where the Ni content in the mixture = 10% (w/w)
Ni.
2.2. Catalyst characterization
After reduction (as above) or after catalysis, the sample
was flushed for 1 h in a stream of He, cooled (in He) to
3
−1
room temperature and passivated in (40 cm min ) 1% (v/v)
O2/He; there was no detectable temperature increase during
sample passivation. This treatment served to provide a protec-
tive oxide layer over the surface Ni that prevented bulk oxida-
tion upon exposure to the atmosphere. The BET surface area,
temperature-programmed reduction (TPR), H2 chemisorp-
tion and temperature-programmed desorption (TPD) asso-
ciated with the freshly activated (pre- and post-passivation)
and spent (passivated) samples were determined using the
commercial CHEM-BET 3000 (Quantachrome) unit. The
samples were loaded into a U-shaped Pyrex glass cell
3
−1
(10 cm × 3.76 mm i.d.) and heated in 20 cm min (mass
−1
flow controlled) 5% (v/v) H2/N2 to 723 K at 10 K min
.
(
FB) over supported Ni. It is, however, worth flagging stud-
The effluent gas passed through a liquid N2 trap and H2 con-
sumption was monitored by a thermal conductivity detec-
tor (TCD) with data acquisition/manipulation using the TPR
ies of liquid phase hydrodeiodination (with molecular hy-
drogen) of IB over Pd/C [25,26] and the liquid phase hy-
drodefluorination of FB and 1,2-difluorobenzene where Rh
complexes tethered to a silica support [27,28] and Zr-based
organometallics (homogeneous system) [29] served as the
catalytic agents.
In this investigation, we report reproducible activi-
ties/selectivities for the gas phase HDH of FB, CB, BB,
IB, 1,3-DCB, 1,3-DBB and 1,3-BCB over unsupported
and SiO2 supported Ni and focus on the relative reactivity
of the C Cl, C Br, C I and C F bonds for hydrogen
scission. We have carefully monitored catalyst activation
TM
Win software. The samples were maintained at 723 K for
12 hinasteadyflowofH2;TPRwasalsomonitoredfollowing
the precalcination outlined above (with an ultimate reduction
temperature = 873 K). The reduced samples were swept with
3
−1
a 20 cm min flow of N2 for 1 h at the final reduction tem-
perature, cooled to room temperature and subjected to H2
chemisorption using a pulse (50–100 ␮l) titration procedure:
3
detectable uptake >0.2 cm H2 at STP per gram Ni. The sam-
3
−1
)
ples were thoroughly flushed with pure N2 (20 cm min
for 30 min to remove physisorbed H2. Temperature-
programmed desorption was conducted in the N2 flow at
(
reduction with/without precalcination) and have examined
−
1
the changes to the catalyst structure that result during
HDH.
50 K min to 723 K. BET areas were recorded with a 30%
(v/v) N2/He flow; pure N2 (99.9%) served as the internal stan-

K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
151
dard. At least two cycles of nitrogen adsorption–desorption in
(αX) and
HX]out
the flow mode were employed to determine total surface area
using the standard single point method. BET surface area and
hydrogenuptakevalueswerereproducibletowithin± 5%and
the values quoted in this paper are the mean. BJH pore volume
analyses were performed using the commercial Micromerit-
ics TriStar 3000 unit; the catalyst precursor and activated
[
αX =
(X = F, Cl, Br, I)
X]in
(1)
[
benzene selectivity (Sbenzene), taking the conversion of 1,3-
DCB
[benzene]out
(
with and without precalcination) samples exhibited a cumu-
S
=
× 100
out
(2)
benzene
3
−1
[1, 3-DCB] − [1, 3-DCB]
in
lative pore volume = 2.2 ± 0.2 cm g with an average pore
radius = 22 ± 2 nm. Temperature-programmed treatment was
also undertaken using a Seiko Instruments Inc. TG/DTA 320
simultaneous thermo-gravimetric/differential thermal anal-
yser coupled to a micromass PC residual gas analyser. A
known quantity of catalyst (ca. 18 mg) was placed in a Pt
sample pan and subjected to the same temperature ramping
sequence(s), in either a reducing (20%, v/v, H2/He) or an
oxidizing (30%, v/v, air/He) flow, while monitoring the ef-
fluent gas over the mass range 10–100. Powder X-ray diffrac-
tograms (XRD) were recorded with a Philips X’Pert instru-
ment using Ni-filtered Cu K␣ radiation. The samples were
mounted in a low background sample holder and scanned at
where [X] represents the aromatic halogen concentration,
HX] the concentration of hydrogen halide product and in/out
[
refers to the inlet/outlet streams. A halogen (in the form of
HX) mass balance was performed by passing the effluent gas
−3
−3
through an aqueous NaOH trap (3.5–8.0 × 10 mol dm
,
kept under constant agitation at 400 rpm) with independent
pH (Hanna HI Programmable Printing pH Bench-Meter) and
potentiometric (Metrohm Model 728 Autotitrys) analyses.
Repeated (up to five separate) catalytic runs with different
samples from the same batch of catalyst delivered product
compositions that were reproducible to within ± 7%.
◦
−1
◦
a rate of 0.02 step over the 30 ≤ 2θ ≤ 90 range with a
−
1
scan time of 5 s step . The diffractograms were compared
with the JCPDS-ICDD [30] references for identification
purposes.
3. Results and discussion
3.1. Catalyst characterization: pre-reaction
The BET surface area of the freshly activated (unused)
2
.3. Catalysis procedure
catalyst is recorded in Table 1 along with the H2 chemisorp-
tion values. Hydrogen uptake on the Ni/SiO2 precursor re-
duced in situ was essentially the same as that recorded af-
ter TPR of the passivated/reduced sample, indicative of an
equivalency of both activation routes. The controlled room
Reactions were carried out under atmospheric pressure,
in situ immediately after activation, in a fixed bed glass re-
actor (i.d. = 15 mm) at 573 K. The catalytic reactor, and op-
erating conditions to ensure negligible heat/mass transport
limitations, have been described in detail elsewhere [31] but
some features, pertinent to this study, are given below. All the
chemicals (FB, CB, BB, IB, 1,3-DCB, 1,3-DBB and 1,3-BCB
supplied by Aldrich with >99.8% purity) were fed (undiluted
or in methanol) by means of a microprocessor controlled in-
fusion pump (Model 100, kd Scientific) via a glass/teflon air
tight syringe and a teflon line to the reactor in a stream of
Table 1
BET surface areas and H chemisorption values associated with the unused
2
and spent catalysts
Sample
BET surface
area (m g
H chemisorption
2
2
−1
3
−1
)
(cm g
)
Ni
a
Activated Ni/SiO , unused
2
190
195
185
10.4
10.7
1.5
b
Activated Ni/SiO2, unused
Precalcined/activated Ni/SiO2b,
unused
−
1
ultra pure H2 (GHSV = 1200 h ), the flow rate of which
was monitored using a Humonics 520 digital flow meter.
The reactant inlet molar flow rate was in the overall range
Ni/SiO2 after FB HDFa
183
180
173
6.1
4.6
0.8
Ni/SiO2 after CB HDCa
−3
−2
−1
9
× 10 to 2 × 10 mol h where H2 was maintained in
Precalcined and activated
Ni/SiO2 after CB HDCa
at least 20 times excess relative to stoichiometric quantities;
all the reactants were used without further purification. In a
series of blank tests, passage of each reactant in a stream of
H2 through the empty reactor, i.e. in the absence of catalyst,
did not result in any detectable conversion. Moreover, reac-
tion of the haloarenes over silica alone was not accompanied
by any detectable HDH: the presence of Ni (supported or
unsupported) is essential for H2 scission activity. The reac-
tion products were collected over a period of 24 h (6–8 h in
the case of the physical mixtures) and analyzed by capillary
GC as described elsewhere [32]. Catalytic HDH is quanti-
fied in this report on the basis of fractional dehalogenation
a
Ni/SiO2 after 1,3-DCB HDC
175
189
184
185
178
6
2.7
2.5
1.3
1.7
2.3
–c
Ni/SiO2 after BB HDBa
Ni/SiO2 after 1,3-DBB HDCa
a
Ni/SiO2 after 1,3-BCB HDH
Ni/SiO after IB HDI
Activated NiO , unused
Activated NiO + SiO2 physical
mix , unused
Activated Ni(NO3)2 + SiO2
physical mix , unused
a
2
b
c
185
–
b
190
–c
b
a
Analysis of a passivated sample.
In situ analysis.
Below detection limits.
b
c

1
52
K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
Fig. 2. (a) Mass (wt.%), water signal intensity and (b) nitrogen, nitrous
oxide and nitric oxide signal intensity as a function of temperature in the
direct reduction of the Ni/SiO2 precursor to 723 K. Inset to (a) H2O profile
generated during the heat treatment of the SiO2 support in flowing H2 under
the same conditions used in the direct reduction of Ni/SiO2.
Fig. 1. (a) TPR profiles generated for direct reduction of the Ni/SiO2 pre-
cursor to 723 K pre-passivation (I) and post-passivation (II) (inset shows
the results of repeated TPR runs) passivation. (b) TPR profiles generated
for reduction to 873 K of the precalcined (at 873 K) Ni/SiO2 precursor pre-
passivation (III) and post-passivation (IV).
Marcos and co-workers [37] linked their single TPR peak at
601 K for impregnated Ni/SiO2 directly to Ni(NO3)2 decom-
temperature passivation provided a protective oxide coating
over the supported metal, permitting storage/transfer for di-
rectly meaningful ex situ analyses. The TPR profiles gener-
ated for the direct reduction of the Ni/SiO2 precursor with-
out (to 723 K, profile I) and with (profile III) precalcination
position. We have extended our TPR analysis by monitoring
the decomposition (in H2) of the nitrate precursor by ther-
mogravimetic analysis where the effluent gas was analyzed
using on-line mass spectrometry: the results are included in
Fig. 2, wherein a weight loss in excess of 20% is in evidence.
Jackson et al. [38] have reported a similar TPR weight loss
profile, but without on-line MS analysis, for the activation of
1% (w/w) Ni/SiO2. Our MS results demonstrate that precur-
sor decomposition generated peaks at m/e of 18, 28, 30 and
44 amu which we assigned to H2O, N2, NO and N2O respec-
tively; NO2 (main fragment at m/e = 30) release cannot be
discounted. N2/NO/H2O predominate at T < 523 K with con-
comitant N2/N2O/NO/H2O release at T > 523 K. The occur-
rence of a H2O release maximum at 566 K (Fig. 2a) without
an accompanying N2/N2O/NO (Fig. 2b) evolution suggests a
(to 873 K) and those associated with a “re-reduction” of the
same samples after passivation (profiles II and IV) are given
in Fig. 1. The degree of TPR reproducibility is illustrated in
the inset to Fig. 1a which shows three separate TPR profiles,
taking the post-passivated direct TPR sample (profile II) as
a representative case. The direct reduction of the Ni/SiO2
generated a sharp H2 consumption peak at 560 K with an ill-
defined lower temperature (548 K) shoulder and a secondary
broader higher temperature H2 consumption with an associ-
ated Tmax = 615 K. The lower temperature peak(s) has(have)
been attributed [33,34] to the decomposition of nickel nitrate
0
reduction of NiO to Ni that precedes the higher temperature
0
to NiO. A subsequent reduction of NiO to Ni is responsible
reduction demonstrated by profile I in Fig. 1a. This is also
validated by the differential thermal analysis, (not shown),
where the presence of a sharp exotherm was associated with
the peak at 566 K. A generation of zerovalent Ni at yet lower
temperatures is possible but an explicit distinction between
precursor decomposition and metal formation is not possible
for the higher Tmax peak—Mizushima et al. [35] in their TPR
study of a 10% (w/w) impregnated Ni/SiO2 have attributed a
TPR Tmax at ca. 630 K to NiO reduction. Montes et al. [36]
likewise ascribed a TPR maximum at 651 K to reduction of
NiO on a 15% (w/w) impregnated Ni/SiO2 while Gonzlez-

K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
153
Fig. 4. (a) Mass (wt.%) and (b) water signal intensity resulting from the
reduction (to 873 K) of the precalcined (see Fig. 3 Ni/SiO2).
Fig. 3. (a) Mass (wt.%) and (b) water, nitric oxide and nitrous oxide signal
intensity as a function of temperature during the calcination of the Ni/SiO2
precursor in air to 873 K.
fluent (Fig. 3b), where the principal release of the nitrogen
oxides occurred at a similar temperature (540–550 K) to that
observed during precursor decomposition in H2 (Fig. 2b).
Mile et al. [34] observed weight loss maxima at 537 and
559 K in the thermal decomposition of silica supported nickel
nitrate and inferred, without any mass spectroscopic gas
analysis of the effluent gas, an associated decomposition of
Ni(NO3)(OH) 2.5H2O to NiO with release of HNO3 and
H2O. The mass of the calcined sample was 2.24% greater
(from TGA) than that after H2 treatment, which agrees well
at T < 560 K where the profiles represent composite temper-
ature effects. The decomposition/reduction of a supported
metal salt is a complex multi-step solid-phase reaction where
heterogeneity in nucleation site density/oxide particle size
will result in a range of temperature dependent reductions. It
is worth flagging the apparent emergence of a H2O peak at
the completion of the direct Ni/SiO2 reduction: see Fig. 2a. In
a separate run, we recorded the H2O profile generated during
the heat treatment of the SiO2 support in flowing H2 under
the same conditions used in the direct reduction of Ni/SiO2.
The resultant profile is recorded as an inset to Fig. 2a where
a H2O release at Tmax = ca. 740 K can be observed which
matches the emerging peak in Fig. 2a. This water loss can
be attributed to a thermally induced dehydroxylation of the
SiO2 support, as has been noted elsewhere [39–41].
The introduction of a calcination step prior to reduction
had a significant effect on the subsequent TPR profile (III, see
Fig. 1b), which was characterized by a broad T range (from
ca. 600 to >800 K) of H2 consumption with an ill-defined
Tmax at ca. 740 K. Geus et al. [42] have also recorded a broad
reduction peak (Tmax at 743 and 773 K) during the TPR of
Ni/SiO2 precalcined at 573 K. Our precalcination step alone
resulted in a 20% weight loss (Fig. 3a) with water, nitric
oxide and nitrous oxide the significant components in the ef-
0
with the expected mass difference between the NiO and Ni
content in the respective samples. Thermogravimetric/mass
spectrometric analysis of the reduction step that followed pre-
calcination revealed a slight weight loss (<5%, see Fig. 4a)
and water release (Fig. 4b), produced by the reduction of NiO,
over the temperature range corresponding to that observed for
H2 consumption (see Fig. 1b, profile III). It is evident, from a
comparison of profiles I and III in Fig. 1, that the incorpora-
tion of a precalcination step has rendered the supported nickel
phase more difficult to reduce, a response that finds agree-
ment in the literature where an increase in the precalcination
temperature is accompanied by a higher TPR Tmax [34,43].
The incorporation of a calcination step has been proposed to
generate nickel hydrosilicate that is more difficult to reduce
[33,38,44]. Both passivated samples are characterized by a
single reduction peak (Fig. 1) that arose at a lower tempera-
ture for the precalcined (ca. 450 K) when compared with the
uncalcined sample (ca. 510 K): a TGA/MS analysis of the

1
54
K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
TPR of the passivated samples revealed only the presence of
water in the effluent gas. As is to be expected, the reduction
of these passivated samples is far more facile than the acti-
vation of the starting catalyst precursors. Vos et al. [45] have
studied the TPR of (37 and 56%, w/w) Ni/Al2O3 samples
after passivation and recorded one peak at 473 K, which they
assigned to the reduction of the passivating oxide layer. Had-
jiivanov et al. [46] likewise noted a significant shift in the
reduction peak for 1.7% (w/w) Ni/SiO2 (prepared by a graft-
ing technique) to 489 K after passivation. It is known from the
literature [33,47,48] that a precalcination of an impregnated
Ni/SiO2 precursor results in an appreciable increase in Ni
particle size after reduction and this is borne out by the sub-
stantial reduction in H2 uptake (Table 1); the requirement of a
higher reduction temperature for the calcined sample should
also contribute to metal sintering. The lower TPR Tmax value
associated with the passivated precalcined sample is then di-
agnostic of a more facile reduction of the poorly dispersed
metal phase.
An interpretation of these TPR profiles is further facil-
itated by comparison with those generated (under identical
conditions)forbulkNiOandphysicalmixturesofNiO + SiO2
and Ni(NO3)2 + SiO2, which are included in Fig. 5. The sin-
gle H2 consumption peak associated with the direct reduction
of bulk NiO and the physical mix with SiO2 can be linked to
the higher Tmax recorded for the direct reduction of Ni/SiO2.
The discernible shift (to higher T) in the reduction peak for
the mixture may be attributed to some interaction of NiO with
SiO2 as has been observed by Ermakova and Ermakov [49].
A subsequent passivation resulted in a bulk oxide phase that
was readily reduced in a subsequent TPR as is evident from
a consideration of profiles (c) and (e) in Fig. 5. It should be
noted that the chemical interaction that is prevalent in the
passivated Ni/SiO2 (profile (a), Fig. 5) necessitates a higher
treatmenttemperaturefortheremovalofthepassivationlayer.
The direct reduction of Ni(NO3)2 + SiO2 generated a broad
region of H2 consumption where T > 540 K (profile (f), Fig. 5)
that can be attributed to a combined concomitant Ni(NO3)2
decomposition/NiO reduction (see Fig. 2); subsequent pas-
sivation and TPR again generated a low temperature indis-
tinct peak. Following TPR, there was no detectable hydro-
gen uptake on the starting bulk NiO or the NiO + SiO2 and
Ni(NO3)2 + SiO2 mixture; any H2 chemisorption was below
detection limits.
The XRD patterns for the passivated unused Ni/SiO2
samples, with/without precalcination are given in Fig. 6,
where the similarity of each is evident. The three peaks at
◦
◦
◦
44.5 , 51.8 and 76.3 , corresponding to (1 1 1), (2 0 0) and
(2 2 0) planes of metallic nickel present in each sample are
consistent with an exclusive cubic symmetry; the markers in-
cluded in Fig. 6 illustrate the position and relative intensity of
the XRD peaks for cubic Ni taken from the JCPDS standards
◦
[30]. Taking the signal at 44.5 , the peak width at half height,
i.e. the standard peak broadening approximation, suggests
a larger Ni particle size associated with the precalcined
sample, in accordance with the H2 chemisorption data. It is
instructive to note that there was no evidence of bulk NiO,
i.e. the reduction procedure was fully effective in reducing
the metal component to zero valent Ni while the passivation
step served to provide a protective oxide coating on the
metal with no bulk NiO formation. Hydrogen temperature-
programmed desorption (H2 TPD) can shed some light
on the electronic properties of supported metal particles
[50]; the H2 TPD profiles for the unused and spent (to be
discussed later) samples are presented in Fig. 7. A diversity
of H2 desorption patterns have been reported in the literature
Fig. 5. TPR profiles generated for: (a) passivated Ni/SiO2 (without precal-
cination), bulk NiO; (b) pre-passivation; (c) post-passivation, NiO + SiO2
Fig. 6. XRD patterns for the passivated unused activated Ni/SiO2 without
(a) and with (b) precalcination, the spent uncalcined (c) and precalcined (d)
sample after CB HDC and the spent uncalcined sample after (e) FB HDF, (f)
BB HDB and (g) IB HDI. Note: the solid lines indicate peak position (with
relative intensity) for cubic Ni.
(10%, w/w, Ni) physical mix; (d) pre-passivation; (e) post-passivation
and Ni(NO3)2 + SiO2 (10 %, w/w, Ni); (f) pre-passivation; and (g) post-
passivation.

K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
155
Fig. 8. Fractional dehalogenation (αX) as a function of time-on-stream for
the conversion of FB (×), CB (ꢀ), BB (᭹), IB (ꢁ), 1,3-DCB (ꢁ) 1,3-DBB
−
1
Fig. 7. H2-TPD profiles associated with passivated Ni/SiO2: (a) cal-
cined/reduced at 873 K and the passivated sample reduced directly at 723 K
without precalcination; (b) unused; (c) after CB HDC; (d) after BB HDB;
(ꢂ) and 1,3-BCB (ꢃ): W/F = 10 g mol h. Note: lines represent fits to Eq.
X
(3).
(
e) after 1,3-DCB HDC; (f) after 1,3-DBB HDB; (g) after 1,3-BCB HDH.
where αss represents the steady state fractional conversion
and β is a time scale fitting parameter. Fit convergence yields
values for α0, the initial fractional HDH and ꢀt0.8, the time
required for the fractional dehalogenation to decay to 80% of
its initial value, two indices on which to base a comparison
of haloarene reactivity: these values are recorded in Table 2.
Taking the α0 values as a measure of initial activity under
fixed bed plug-flow operation where H2 was maintained far
in excess, the following reactor/kinetic expression applies
with both low (<600 K) and high (>600 K) temperature
peaks where any associated Tmax is strongly influenced by
the desorption conditions/experimental procedures [51–55].
The H2 TPD profiles generated for activated unused Ni/SiO2
with/without precalcination are characterized by a principal
desorption peak (660–690 K) with a secondary lower
temperature release (500–560 K). Given the lower H2 uptake
associated with the precalcined sample, the TPD profile has
been magnified to aid comparison—it can be seen that the
combined precalcination/higher reduction temperature step
had little effect on the overall H2 release characteristics,
albeit the (ill-defined) Tmax was shifted to a lower value.
ꢀ W
ꢁ
ln(1 − α0)−1 = k
(4)
FX
−
1
where FX is the inlet molar halogen feed rate (molX h ) and
−1
W the catalyst mass; the parameter W/FX (units, g h molX
)
has the physical significance of contact time. From a con-
sideration of gas phase reaction equilibrium constants [59],
the dehalogenation step(s) under the stated reaction condi-
tions can be taken to be irreversible. The linear relationships
3
.2. Hydrodehalogenation activity/selectivity
−
1
Hydrodehalogenation of FB, CB, BB, IB, 1,3-DCB,
,3-DBB and 1,3-BCB over Ni/SiO2 at 573 K generated
between ln(1 − α0) and W/FX for each mono-haloarene
are shown in Fig. 9; each line passes through the origin,
diagnostic of adherence to pseudo-first order kinetics. The
extracted pseudo-first order rate constants support the fol-
1
benzene and, in the case of the di-substituted arenes,
CB and BB as the only products: secondary hydrogena-
tion to yield cyclohexene/cyclohexane or bromo-/chloro-
cyclohexane/cyclohexene was not observed. The latter sug-
gests that the dehalogenated products once generated desorb
from the catalyst without any ring reduction, as noted pre-
viously [56] for HDH over supported Ni. In contrast, a sec-
ondary ring reduction has been reported elsewhere [57,58]
for HDC over Pd, Rh and Pt-based catalysts. Fractional HDH
−
3
lowing sequence of increasing reactivity: IB (k = 11 × 10
−
1
−1
−3
−1 −1
mol h
g
) < BB (k = 15 × 10 mol h
g ) < CB (k = 12
−
2
−1 −1
−2
−1 −1
). On
× 10 mol h
g
) < FB (k = 22 × 10 mol h
g
the basis of C–X bond dissociation energy, the ease of
reductive dehalogenation should follow the reverse order,
i.e. C–I (53 kcal mol ) > C–Br (67 kcal mol ) > C–Cl
−
1
−1
Table 2
(
αX), over the directly reduced Ni/SiO2, under identical reac-
Initial fractional dehalogenation (α0) and the time required for the frac-
tion conditions is illustrated as a function of time-on-stream
for the four mono-halogenated arene reactants in Fig. 8. In
each case, there was a drop in the level of dehalogenation
before the ultimate attainment of a steady state conversion;
the precalcined/reduced Ni/SiO2 showed the same decline in
αX with time-on-stream. The temporal response of αX can be
expressed in terms of the empirical relationship
tional dehalogenation to decay to 80% of this initial value (ꢀt0.8): W/F = 10
−1
(
g mol h)
X
Reactant
α0
ꢀt0.8 (h)
FB
CB
BB
IB
0.89
0.71
0.13
0.10
0.64
0.11
0.30
1.3
3.1
1.0
0.3
1.1
0.7
0.8
1
,3-DCB
1,3-DBB
,3-BCB
αX − α0
αss − α0
ꢀt
=
(3)
1
β + ꢀt

1
56
K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
Table 3
Initial fractional dehalogenation (α0) of CB and BB over Ni/SiO2
with/without precalcination), bulk NiO, and NiO + SiO2 and
(
−
1
Ni(NO3)2 + SiO2 physical mixtures: W/F = 10 (g molX h)
Catalyst
α0
CB feed
BB feed
Ni/SiO2 reduced at 723 K
Ni/SiO2 precalcined/reduced at 873 K
NiO reduced at 723 K
NiO + SiO2 reduced at 723 K
Ni(NO3)2 + SiO2 reduced at 723 K
0.71
0.23
0.04
0.06
0.06
0.13
0.04
<0.01
0.01
0.01
over to the silica. Indeed, we have shown elsewhere [67]
that CB HDC kinetics can be accounted for on the basis
of reaction between non-competitively and dissociatively
adsorbed chloroaromatic and spillover hydrogen.
Fig. 9. Pseudo-first order relationships for the hydrodehalogenation of FB
(×), CB (ꢀ), BB (᭹), and IB (ꢁ).
The relationship between benzene selectivity (Sbenzene)
and the fractional conversion of the three di-halosubstituted
aromatics is shown in Fig. 10a. The greater reactivity of the
Cl substituents in DCB for hydrogen scission is immediately
apparent where both the fractional conversion of 1,3-DCB
(
81 kcal mol 1) > C–F (109 kcal mol ) [60,61]. Indeed,
−
−1
this reactivity sequence was found to hold in the liquid phase
dehalogenation of alkyl halides using both a homogeneous
Ni catalyst [62] and Raney Ni [63], a trend that has been
found to extend to the catalytic transfer hydrodehalogenation
of aliphatic halides (in 2-propanal/NaOH) over Pd/C [64] and
the dehalogenation of haloarenes by Pd/C in a mixed (isooc-
tane/KOH/quaternary onium salt) solution phase [24,25].
However, in gas phase heterogeneously catalyzed HDH, the
general consensus of opinion that is now emerging from the
literature [6,65–67] supports a surface mechanism involving
dissociative adsorption of the haloarene with the formation
of a surface σ-complex via the aromatic ring carbon with the
highest electron density. As the inductive effect associated
with halogen substituents increases from I to F, the electron
density of the ring (C–X) carbon in IB is lower than that
associated with FB with a consequent decrease in haloarene
reactivity [68], as observed in this study. The reactivity of
both DCB and DBB, on the basis of the tabulated α0 values, is
significantly lower than that associated with the correspond-
ing mono-haloarene while the degree of dehalogenation of
the BCB reactant falls within these two extremes. Catalyst
deactivation was more appreciable (see lower ꢀt0.8 values in
Table2)duringtheprocessingofthedisubstitutedhaloarenes.
The presence of the second electron withdrawing Cl and Br in
(α1,3-DCB) and associated benzene selectivity (Sbenzene) are so
much higher that there is no possible overlap with either the
,3-DBB and 1,3-BCB profiles, which are essentially equiv-
1
alent. The HDH of the di-haloarenes can proceed in a paral-
lel/series stepwise fashion where the mono-halorene serves
as a reactive intermediate [59]. The greater degree of dechlo-
1
,3-DCB, 1,3-DBB and 1,3-BCB has an overall deactivating
effect with the result that the entire halogen complement is
less susceptible to hydrogen cleavage. A precalcination of the
Ni/SiO2, which impacted on TPR/H2 uptake behavior (see
Figs. 1–3/Table 1), served to significantly lower the initial
HDH activity (by a factor of three), as revealed in Table 3.
Nevertheless, the latter was still greater than that generated
by bulk NiO. The mixed NiO + SiO2 (and Ni(NO3)2 + SiO2)
systems delivered slightly higher dehalogenation activities
than NiO alone, a response that can be linked to the inferred
Fig. 10. (a) Benzene selectivity (Sbenzene) as a function of the fractional
conversion (α) of 1,3-DCB (ꢁ) 1,3-DBB (ꢂ) and 1,3-BCB (ꢃ). (b) Ratio
of benzene (complete dehalogenation) to halo-benzene (CB or BB, i.e. par-
tial dehalogenation) in the reactor effluent, symbols as above: inlet molar
(from the TPR response in Fig. 5) metal/silica interaction
and/or involvement of spillover hydrogen [14,69,70] where
Ni acts as a dissociation center for hydrogen that then spills
−
1
W/F = 10 g molX h.

K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
157
Table 4
the aromatic host. The degree of debromination, in terms of
Outlet (out) to inlet (in) aromatic Br concentration ratio, at selected reaction
times for the conversion of BB and 1,3-BCB; W/F = 10 (g mol h)
the aromatic [Br]out/[Br] ratio was directly proportional to
in
−
1
Br
the fractional 1,3-BCB conversion (α1,3-BCB) where reaction
over supported and unsupported Ni with/without SiO2 addi-
tion delivered a common trend line, shown in Fig. 11c.
ꢀt (h)
[Br]out/[Br]in
BB feed
1,3-BCB feed
0
1
4
8
4
.25
0.79
0.84
0.87
0.90
0.91
0.58
0.63
0.78
0.82
0.85
3
.3. Catalyst characterization: post-reaction
BET surface area analysis (Table 1) before and after catal-
2
ysis demonstrated that there was no appreciable change in
overall area. Moreover, chemical analysis (ICP-OES) of the
activated catalysts pre- and post-reaction did not reveal any
measurable loss of Ni as a result of catalysis. However, the
TPR characteristics of the spent samples, used to promote an
array of HDH reactions, deviated significantly from the pro-
file associated with the unused sample: the passivated used
samples exhibited a principal TPR peak that arose at tem-
peratures up to 60 K lower when compared with the passi-
vated unused catalyst, as illustrated in Fig. 12. In addition,
the level of H2 chemisorbed on the spent samples, as recorded
in Table 1, was considerably lower. The latter response is in-
dicative of Ni particle growth during reaction and Ni sintering
as a result of HDC has been noted previously [10,23,74,75]
and can be ascribed to a halide-induced agglomeration of Ni
particles [76] due to the surface mobility of Ni–X species
[77]. In a recent study [78], we clearly demonstrated (from
TEM analysis) growth of Ni particles during hydrodehalo-
genation over Ni/SiO2. The shift in the TPR maximum peak
to lower temperatures is in line with a more facile reduc-
tion of the (HDH induced) sintered metal phase. The XRD
profiles associated with representative spent samples are in-
cluded in Fig. 6. There was no observable bulk NiO or Ni
halide phase in the catalysts after use but, as XRD is a bulk
structural characterization tool, we do not discount the pos-
sible formation of surface halide species. Indeed, we have
shown elsewhere [23,74] that supported metal catalysts bear
an appreciable surface HCl component during chloroarene
HDC, some of which is irreversibly held and resistant to ther-
mal desorption. Our XRD analysis confirm that an exclusive
cubic Ni symmetry was maintained as opposed to the find-
ings of Choi and Lee [10] which suggested a Ni (on SiO2)
phase transformation from cubic to hexagonal during 1,2-
dichloropropane HDC. Moreover, there was no evidence of
nickel carbide formation as has been reported by Morato et
al. [9] during the hydro-conversion of CFC-12 and HFC-22
over Ni on carbonaceous supports. We subjected the pas-
sivated spent samples to a high temperature (298–1273 K)
heat treatment in flowing H2 with on-line mass spectroscopic
analysis and recorded small weight changes (<2%). The lat-
ter was predominantly due to the loss of water associated
with removal of the passivating oxide layer. There was no
evidence of any significant methane generation—the latter
should result from a hydrogasification of a structural Ni3C
phase but can be discounted in this instance. All the spent
samples exhibited a shift in H2 TPD to lower temperatures
(see Fig. 7) and, with the exception of the sample used in CB
rination is further established in Fig. 10b where the temporal
response of total relative to partial HDH is plotted—total de-
halogenation is preferred in the case of 1,3-DCB whereas a
partial HDH predominates in the conversion of 1,3-DBB and
1
,3-BCB. One unexpected selectivity response was the ab-
sence of any BB component in the effluent from the 1,3-BCB
feed—the catalyst was 100% selective in terms of HDB and
CB was the only partially dehalogenated intermediate. Given
the appreciably higher reactivity of CB/DCB compared with
BB/DBB, it was expected that the organobromine content in
the effluent gas from BCB hydroprocessing should far ex-
ceed that of organochlorine. Rather, the presence of the Cl
substituent on the benzene ring served to promote HDB as can
be seen from the entries in Table 4 where Br removal (relative
to the inlet feed) is compared under identical reaction condi-
tions (same [Br] ) for the conversion of BB and 1,3-BCB. A
in
similar observation was recorded elsewhere for the HDH of
a mixed CB + BB feed over supported Ni and was ascribed
to a halogen exchange reaction [23]. This effect was further
probed by considering the HDH of 1,3-BCB over bulk NiO
and the NiO + SiO2 physical mix: the results are presented
in Fig. 11. The fractional dehalogenation over bulk NiO was
raised slightly with the addition of SiO2 (Fig. 11a), as ob-
served earlier (Table 3) for the conversion of CB and BB.
Indeed, the incorporation of SiO2 in the Ni/SiO2 bed also
served to raise αX when compared with the undiluted Ni/SiO2
(
see Fig. 11a). Spillover hydrogen can again be invoked to
account for the promotional effect of SiO2; a temporal loss of
activity was observed for each system. The ratio of aromatic
Br/Cl in the effluent stream fell below 1 for the conversion
of 1,3-BCB over the four catalyst systems. This is in marked
contrast to that expected on the basis of CB HDC and BB
HDB, as illustrated in Fig. 11b where the “predicted” ratio
far exceeds unity. There was no evidence of BB in the product
stream associated with reaction over NiO (with/without SiO2
addition). Any HDC must serve to chlorinate the surface, as
shown elsewhere [71], with a subsequent exchange reaction
where the adsorbed aromatic carbonium ion intermediate is
attackedbysurfaceHCl;HBrmustnotparticipateinananalo-
gousbrominationsteptothesameextent. Indeed, Brdisplace-
ment from aromatic nuclei has been found to be more facile
than that of Cl in catalyzed vapor phase halogen exchange
reactions [72,73]. The enhanced degree of debromination is
then the result of a combined HDB and hydrochlorination
(
Cl exchange) as composite steps in the removal of Br from

1
58
K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
Fig. 11. (a) Fractional dehalogenation (αX) as a function of time-on-stream for the conversion of 1,3-BCB over Ni/SiO2 (ꢃ), Ni/SiO2 + SiO2 (ꢁ), NiO (᭹)
and NiO + SiO2 (ꢂ); lines represent fits to Eq. (3). (b) Ratio of aromatic Br to Cl in the outlet stream ([Br]out/[Cl]out) as a function of time-on-stream, symbols
as above where (ꢁ) represents the predicted values based on CB HDC and BB HDB data. (c) Ratio of outlet to inlet aromatic Br concentration, ([Br]out/[Br]in)
−
1
as a function of fractional 1,3-BCB conversion (x1,3-BCB), symbols as above; W/F = 10 g molX h.
HDC, desorption was characterized by a single broad TPD
peak with Tmax in the range 500–560 K. It is known that halo-
gens can act as electron acceptors with respect to supported
transition metal systems [57,79] and the presence of Cl im-
pacts on H2 adsorption/desorption dynamics on Ni [51,52].
In this study, the shift in H2 TPD Tmax to lower values is
diagnostic of weaker H/Ni interactions that results from ex-
tended catalyst HDH use. The characteristics of the spent
catalysts that can be linked to the observed activity loss are
reduced H2 uptake that exhibits a weaker interaction with the
catalyst.
4. Conclusions
HDH of FB, CB, BB, IB, DCB, DBB and BCB over
Ni/SiO2 yields the partially dehalogenated mono-haloarene
(in the case of the di-substituted arenes) and benzene with no
ring reduction. Mono-haloarene reactivity decreases (from
FB to IB) with a decreasing halogen inductive contribution
that serves to activate the C–X bond for hydrogenolytic at-
tack. The presence of a second halogen ring substituent has
a deactivating effect that lowers the overall HDH. However,
the degree of debromination exceeded dechlorination in the
case of the BCB reactant as a result of the reactivity of sur-
face HCl which facilitates a hydrochlorination or Cl exchange
with aromatic Br. Bulk NiO exhibited HDH activity that was
raised with the addition of SiO2 and the same trend of higher
HDC relative to HDB for the conversion of mono (chloro-
or bromo-) aromatics with an apparent Cl/Br exchange in the
conversion of BCB. Activation of Ni/SiO2 in H2 involved a
decomposition of the supported nitrate precursor (to generate
Fig. 12. TPR profiles generated for passivated Ni/SiO2 reduced at 723 K
without precalcination: (a) unused; (b) after CB HDC; (c) after BB HDB;
(d) after 1,3-DCB HDC; (e) after 1,3-DBB HDB; and (f) after 1,3-BCB
0
N2, N2O, NO and H2O and concomitant Ni ) with a subse-
HDH.

K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
159
0
[
[
28] H. Yang, H. Gao, R.J. Angelici, Organometalics 18 (1999) 2285.
29] B.M. Kraft, R.J. Lachicotte, W.D. Jones, J. Am. Chem. Soc. 123
2001) 10973.
quent reduction of NiO to Ni . A precalcination of Ni/SiO2
resulted in an appreciable alteration to the TPR characteris-
tics, necessitating a higher reduction temperature leading to
Ni sintering and an ultimate lower HDH activity. HDH over
supported and unsupported Ni was subject to a temporal loss
of activity that was accompanied by a disruption to the H2
adsorption/desorption surface dynamics.
(
[
[
30] JCPDS—ICDD, PCPDFWIN, Version 2.2, June 2001.
31] M.A. Keane, P.M. Patterson, J. Chem. Soc., Faraday Trans. 92 (1996)
1413.
[32] G. Yuan, M.A. Keane, Chem. Eng. Sci. 58 (2003) 257.
[33] C. Louis, Z.X. Cheng, M. Che, J. Phys. Chem. 97 (1993) 5703.
[34] B. Mile, D. Stirling, M.A. Zammitt, M.A. Lovell, M. Webb, J. Catal.
114 (1988) 217.
[
[
[
35] T. Mizushima, K. Nishida, H. Ohkita, N. Kakuta, Bull. Chem. Soc.
Acknowledgements
Jpn. 75 (2002) 2283.
36] A. Diaz, D.R. Acosta, J.A. Odriozala, M. Montes, J. Phys. Chem.
B 101 (1997) 1782.
37] M.P. Gonz a´ lez-Marcos, J.I. Guti e´ rrez-Ortiz, C. Gonz a´ lez-Ortiz de
Elguea, J.R. Gonz a´ lez-Velasco, J. Mol. Catal. A: Chem. 120 (1997)
185.
The authors are grateful to Antonio de Lucas Consuegra
for his contribution to this work, which was supported in
part by the National Science Foundation through Grant CTS-
0
218591.
[38] S.D. Jackson, J. Willis, G.J. Kelly, G.D. McLellan, G. Webb, S.
Mather, R.B. Moyes, S. Simpson, P.B. Wells, R. Whyman, Phys.
Chem. Chem. Phys. 1 (1999) 2573.
[
[
39] V.I. Bogillo, L.S. Pirnach, A. Dabrowski, Langmuir 13 (1997) 928.
40] M.-A. Einasrud, L. Rørmark, S. Haereid, T. Grande, J. Non-Cryst.
Solids 211 (1997) 49.
References
[
1] H.R. Bauser, Chemosphere 7 (1979) 415.
[41] J.H. Zimnoch dos Santos, C. Krug, M. Barbosa da Rosa, F.C. Stedile,
J. Dupont, M. de Camargo Forte, J. Mol. Catal. A: Chem. 139 (1999)
199.
[2] D.G. Crosby, Environmental Toxicology and Chemistry, Oxford Uni-
versity Press, New York, 1998.
[
3] L.E. Manzer, Catal. Today 13 (1992) 13.
[42] J. van de Loosdrecht, A.M. van der Kraan, A.J. van Dillen, J.W.
Geus, J. Catal. 170 (1997) 217.
[4] C. Seignez, A. Vuillenium, N. Adler, P. Peringer, J. Hazard. Mater.
8
4 (2001) 265.
[43] K. Hadjivanov, M. Mihaylov, D. Klissurski, P. Stefanov, N. Abad-
jieva, E. Vassileva, L. Mintchev, J. Catal. 185 (1999) 314.
[44] M.A. Keane, Can. J. Chem. 72 (1994) 372.
[
[
[
5] J. Frimmel, M. Zdrazil, J. Chem. Technol. Biotechnol. 63 (1995) 17.
6] B.F. Hagh, D.T. Allen, Chem. Eng. Sci. 45 (1990) 2695.
7] K.A. Frankel, B.W.L. Jang, G.W. Roberts, J.J. Spivey, Appl. Catal.
A: Gen. 209 (2001) 401.
8] S. Ordonez, H. Sastre, F.V. Diez, Appl. Catal. B: Environ. 25 (2000)
4
9] A. Morato, C. Alonso, F. Medina, P. Salagre, J.E. Sueiras, R. Terrado,
A. Giralt, Appl. Catal. B: Environ. 23 (1999) 175.
10] Y.H. Choi, W.Y. Lee, Catal. Lett. 67 (2000) 155.
11] M.A. Keane, C. Park, C. Menini, Catal. Lett. 88 (2003) 89.
12] N. Lingaiah, M.A. Uddin, A. Muto, T. Iwamoto, Y. Sakata, Y. Ku-
sano, J. Mol. Catal. A: Chem. 161 (2000) 157.
[45] B. Vos, E. Poels, A. Bliek, J. Catal. 198 (2001) 77.
[46] K. Hadjiivanov, M. Mihaylov, D. Klissurski, P. Stefanov, N. Abad-
jieva, E. Vassileva, L. Mintchev, J. Catal. 185 (1999) 314.
[47] M. Montes, C. Pennemann de Bosscheyde, B.K. Hodnett, F. Delan-
nay, P. Grange, B. Delmon, Appl. Catal. 12 (1984) 309.
[48] G.A. Martin, C. Mirodatos, H. Praliaud, Appl. Catal. 1 (1981) 367.
[49] M.A. Ermakova, Y.D. Ermakov, Appl. Catal. A: Gen. 245 (2003)
277.
[
9.
[
[
[
[
[50] E.-J. Shin, A. Spiller, G. Tavoularis, M.A. Keane, Phys. Chem.
Chem. Phys. 1 (1999) 3173.
[
[
[
[
13] Y. Cesteros, P. Salagre, F. Medina, J.E. Sueiras, D. Tichit, B. Coq,
[51] J. Estelle, J. Ruz, Y. Cesteros, R. Fernandez, P. Salagre, F. Medina,
J.-E. Sueiras, J. Chem. Soc., Faraday Trans. 92 (1996) 2811.
[52] S. Smeds, T. Salmi, L.P. Lindfors, O. Krause, Appl. Catal. A: Gen.
144 (1996) 177.
[53] J.A. Konvalinka, P.H. van Oeffelt, J.J.F. Scholten, Appl. Catal. 1
(1981) 141.
[54] G.D. Weatherbee, C.H. Bartholomew, J. Catal. 87 (1984) 55.
[55] A.G. Boudjahem, S. Monteverdi, M. Mercy, M.M. Bettahar, J. Catal.
221 (2004) 325.
[56] G. Tavoularis, M.A. Keane, J. Mol. Catal. 142 (1999) 187.
[57] B. Coq, G. Ferrat, F. Figueras, J. Catal. 101 (1986) 434.
[58] P. Bodnariuk, B. Coq, G. Figueras, J. Catal. 116 (1989) 459.
[59] E.J. Shin, M.A. Keane, Chem. Eng. Sci. 54 (1999) 1109.
[60] F. Alonso, I.P. Beletskaya, M. Yus, Chem. Rev. 102 (2002) 4009.
[61] I. Imamoto, in: B.M. Trost, M.I. Fleming (Eds.), Comprehensive
Organic Synthesis, Pergamon Press, Oxford, 1991, p. 794.
[62] G.K. Lahiri, L.J. Schussel, A.M. Stolzenberg, Inorg. Chem. 31
(1992) 4991.
Appl. Catal. B: Environ. 32 (2001) 25.
14] Y. Cesteros, P. Salagre, F. Medina, J.E. Sueiras, Appl. Catal. B:
Environ. 25 (2000) 213.
15] Y. Cesteros, P. Salagre, F. Medina, J.E. Sueiras, Appl. Catal. B:
Environ. 22 (1999) 135.
16] Y. Cesteros, P. Salagre, F. Medina, J.E. Sueiras, Catal. Lett. 79 (2002)
8
3.
[
[
17] Y.A. Serguchev, Y.V. Belokopytov, Kinet. Catal. 42 (2001) 174.
18] B. Wei, S. Li, H.K. Lee, T.S.A. Hor, J. Mol. Catal. A: Chem. 126
(1997) 183.
[
[
19] Z. Yu, S. Liao, Y. Xu, React. Funct. Polym. 29 (1996) 151.
20] M.A. Aramendia, V. Borau, I.M. Garcia, C. Jimenez, J.M. Marinas,
J. Urbano, Appl. Catal. B: Environ. 20 (1999) 101.
[
[
[
[
21] M.A. Aramendia, V. Borau, I.M. Garcia, C. Jimenez, A. Marinas,
J.M. Marinas, J. Urbano, Appl. Catal. B: Environ. 43 (2003) 71.
22] C. Menini, C. Park, E.-J. Shin, G. Tavoularis, M.A. Keane, Catal.
Today 62 (2000) 355.
23] C. Park, C. Menini, J.L. Valverde, M.A. Keane, J. Catal. 211 (2002)
[63] A.F. Barrero, E.J. Alvarez-Manzaneda, R. Chahboun, R. Meneses,
J.L. Romera, Synletters (2001) 485.
4
51.
24] C.A. Marques, O. Rogozhnikova, M. Selva, P. Tundo, J. Mol. Catal.
A: Chem. 96 (1995) 301.
[64] Y. Usiku, T. Miyadera, Nippon Kagaku Kaishi (1998) 369;
Y. Usiku, T. Miyadera, Chem. Abs. 128 (1998) 308213.
[65] Y.A. Serguchev, Y.V. Belokopytov, Kinet. Catal. 42 (2001) 174.
[66] M.A. Keane, D.Y. Murzin, in: D.G. Morrell (Ed.), Catalysis of Or-
ganic Reactions, Marcel Dekker, New York, 2002, p. 595.
[67] M.A. Keane, D.Y. Murzin, Chem. Eng. Sci. 56 (2001) 3185.
[
[
25] C.A. Marques, M. Selva, P. Tundo, J. Org. Chem. 58 (1993) 5256.
26] Y. Ambroise, C. Mioskowski, G. Djega-Mariadassou, B. Rousseau,
J. Org. Chem. 65 (2000) 7183.
[27] S.D. Brown, T.G. Richmond, Chemtracts 13 (2000) 134.

1
60
K.V. Murthy et al. / Journal of Molecular Catalysis A: Chemical 225 (2005) 149–160
[
[
[
[
[
68] J.W. Bozzelli, Y.M. Chen, S.S.C. Chuang, Chem. Eng. Commun.
15 (1992) 1.
69] W.C. Conner Jr., G.M. Pajonck, S.J. Teichner, Adv. Catal. 34 (1986)
[73] J. Lindley, Tetrahedron 40 (1984) 1433.
1
[74] M.A. Keane, in: M.A. Keane (Ed.), Interfacial Applications in En-
vironmental Engineering, Marcel Dekker, New York, 2002, p. 231.
[75] A. Gampine, D. Eyeman, J. Catal. 179 (1998) 315.
[76] Y. Ohtsuka, J. Mol. Catal. 54 (1989) 225.
[77] C. Hoang-Van, Y. Kachaya, S.J. Teichner, J. Phys. Chem. B 101
(1997) 7060.
[78] K.V. Murthy, P.M. Patterson, G. Jacobs, B.H. Davis, M.A. Keane, J.
Catal. 223 (2004) 74.
[79] T. Halchev, E. Ruckenstein, J. Catal. 73 (1982) 171.
1.
70] F. Benseradj, F. Sadi, M. Chater, Appl. Catal. A: Gen. 228 (2002)
35.
71] G. Tavoularis, M.A. Keane, J. Chem. Technol. Biotechnol. 74 (1999)
0.
72] S. Imhaoulene, L. Vivier, M. Guisnet, G. Perot, Tetrahedron 50
1994) 12913.
1
6
(