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hydrocarbon, i.e. non-chlorine containing, products. How-
ever, there are some problems such as the improvement of
the stability of Pd catalysts and selectivities to target
products, i.e., C1–C5 hydrocarbons, remaining to be met.
The main drawback for practical application is rapid
deactivation of palladium catalysts during HdCl of CCl4
reaction, although they show a very high initial catalytic
activity [7–15]. Therefore, the development of new
catalysts with highly selective dechlorinating activity
and high stability becomes the strategy for the hydrode-
chlorination of chlorinated hydrocarbons.
As commonly observed in the hydro-treating catalytic
reactions, catalytic performance such as activity, selectivi-
ty, and resistance towards catalyst deactivation are
strongly dependent on the nature of the catalyst.
Therefore, various catalyst systems such as noble metals,
non-noble metals, and alloy catalysts have been investi-
gated for HdCl reactions. It is known that the HdCl activity
of supported palladium catalysts is affected by many
factors: the morphology of metal particles, the nature of
the support [16–18] and the presence of a second metal in
active phase [19–25].
microemulsion (especially water to surfactant molar ratio)
allow to obtain metal particles precisely predicted in size
in a very narrow range (which is difficult to obtain in
traditional synthesis routes, e.g., by impregnation). Our
recent studies showed that such prepared Pd–Au catalysts
are homogeneous and active in the reaction of hydrogena-
tion of cinnamaldehyde [36]. The present work is aimed at
the performance of similarly prepared carbon-supported
Pd–Au catalysts in the hydrodechlorination of tetrachlor-
omethane. High degree of alloy homogeneity attainable by
using the ‘‘water-in-oil’’ reverse microemulsion method
should allow us to establish more precisely the activity
pattern as a function of Pd–Au composition. Our previous
work [33] indicated a number of synergistic effects
associated with palladium alloying with Au in HdCl of
CCl4, however uncertainty as to the degree of Pd–Au
homogeneity did not allow us to render more rigorous
relations.
2. Experimental
2.1. Catalyst preparation characterization
Bimetallic catalysts are very promising as they feature
an interesting catalytic behaviour with respect to mono-
metallic systems [26]. Many bimetallic systems demon-
strate enhanced properties in terms of selectivity and
activity as well as resistance to poisoning and/or metal
sintering. Bimetallic palladium–gold catalysts find indus-
trial application, for instance in the selective hydrogena-
tion of various organic compounds [27], production of
vinylacetate [28], hydrodechlorination of chlorofluorocar-
bons [29] and trichloroethene [30].
The ultimate size of the metal particles and good
homogeneity of active metal phase (namely Pd–Au alloy)
are essential for improving the catalytic properties of
palladium. Our previous results show that for supported
Pd–Au catalysts prepared by impregnation techniques a
satisfactory extent of Pd–Au mixing was not achieved
[23,31]. The reductive deposition of gold to palladium
catalysts resulted in a significantly higher, although still
not perfect, degree of Pd–Au alloying [32]. Our recent
paper [33] deals with similarly prepared carbon-supported
Pd–Au catalysts investigated in CCl4 hydrodechlorination,
where attention was focused on the negative effect of alloy
inhomogeneity on the catalyst’s stability. Although this
defect could be largely reduced by removing unalloyed
palladium species (by treatment with nitric acid [33]),
nevertheless further progress in this research could be
made by application of another catalyst’s preparation
technique which would lead to a still better Pd–Au
alloying.
Two types of commercial active carbons were used as
catalyst’s supports: activated pyrocarbon Sibunit (Novo-
sibirsk, Russia) [37] and furnace black Vulcan XC-72 (Cabot
Corporation) [38]. Before preparation of catalysts, the
active carbon Sibunit was washed with a boiling mixture of
concentrated HCl and HF, rinsed with large amounts of
redistilled water and dried at 253 K in an air oven for
12 hours. Carbon Vulcan XC-72 was used without any
purification. The properties of the supports are given in
Table 1. It is evident that the Vulcan carbon is character-
ized by a larger average size of pores.
The catalysts consisting of the same palladium loading
equal to 2 wt% Pd and the growing Au content were
prepared by means of the reverse ‘‘water-in-oil’’ micro-
emulsion method according to the procedure described
previously [39,40]. In the PdAu/carbon catalysts the molar
ratio of Pd:Au ranges were from 95:5 up to 70:30. The
monometallic 2 wt%Pd/C (Pd100) and 2 wt%Au/C (Au100
)
catalysts (for catalyst notation, Table 2) were also prepared
using the same preparation procedure. The reverse
micellar solutions were prepared using surfactant dioctyl
sulfosuccinate sodium salt (AOT, pure 98%, Fluka) and
heptane (pure, Aldrich) as the oil phase. The aqueous
solutions of PdCl2 (99.9% Grade, Johnson Matthey) and
Table 1
Characteristics of active carbons used in this worka.
Measure
Sibunit Vulcan XC72
In the present work we decided to prepare palladium
and palladium–gold catalysts supported on mesoporous
active carbons by the ‘‘water-in-oil’’ reverse microemul-
sion method [34,35]. In this special method, nanoparticles
with precisely defined size are obtained. Nanoparticles are
formed by reduction/co-reduction of metal ions present
inside nanodroplets of aqueous solution of metal salts
stabilized by a surfactant in a non-polar solvent. Proper
adjusting of metals ions concentration, concentration
and type of reducing agent as well as composition of
Grain size,
m
m
ꢀ10
308
8
0.1–0.3
228
Surface area (BET), m2/g
t-plot micropore area, m2/g
24
Total pore volume (BJH desorption), cm3/g 0.890
1.770
1.722
0.048
0.74
14
Mezopore volume, cm3/g
0.841
0.029
0.97
5
H.-K. micropore volume, cm3/g
H.-K. micropore width, nm
Average pore width (BJH desorption), nm
a
The surface areas of the supports, their pore volumes and diameters
were determined from desorption isotherms of nitrogen adsorbed at 75 K
after evacuation at 623 K for 5 h on ASAP 2020 (Micromeritics, USA).
Please cite this article in press as: Bonarowska M, et al. Hydrodechlorination of CCl4 over carbon-supported palladium–
gold catalysts prepared by the reverse ‘‘water-in-oil’’ microemulsion method. C. R. Chimie (2015), http://dx.doi.org/
Bonarowska, Magdalena
