2
A.C. Badari et al. / Catalysis Communications 58 (2015) 1–5
Table 1
feeds. The sulfide catalysts are not favorable for processing bio-oils be-
cause these reactants, in contrast to those of fossil origin, are virtually
free of sulfur [12]. Precious metal and Ni catalysts are known to have
high hydrogenation activity also in the absence of sulfur, however,
this property is paralleled by hydrodecarbonylation and/or cracking
activity that is not desired if we want to get liquid with high yield.
The recent studies showed that modification of supported Ni/silica
catalysts by In or P generates surface Ni2In or Ni2P phases [9,13]. Present
work shows that introduction of In or P suppresses the undesired
side reactions proceeding over the Ni/silica catalyst. Both Ni2P and
Ni2In/silica catalysts are active and selective in the total HDN of amines
to hydrocarbon and ammonia, whereas only the Ni2In catalyst has
enhanced activity and selectivity in the hydrogenation of carboxylic
acids to alcohols.
Characterization of the catalysts.
Sample
SSA, m2 g−1a ΣVp, cm3 g−1b Ni, wt.% P, wt.% In, wt.% D, nmc
SiO2
Ni/SiO2
Ni2P/SiO2 268
Ni2In/SiO2 299
563
558
0.41
–
6.76
5.04
6.76
–
–
2–10 (11)
20–60 (49)
2–10 (10)
0.15
0.19
4.11
–
–
8.3
a
SSA = specific surface area, determined by the Brunauer–Emmett–Teller (BET)
method.
b
ΣVp, = total pore volume. The volume of liquid N2, equivalent with the saturation N2
adsorption capacity, was assumed to be equal with ΣVp.
c
Diameter of particles of the active phase observed in the TEM micrograph (particle
size determined from XRD by the Scherrer equation is given in parentheses).
were obtained by a FEI Morgagni 268D type microscope, whereas
the adsorption isotherms were determined by Quantachrome NOVA
Automated Gas Sorption Instrument. Before adsorption measurements
the samples were evacuated at 350 °C for 1 h.
The HDO and HDN reactions of acetic acid (AA) and propylamine (PA)
model compounds, respectively, were studied over silica-supported cat-
alysts using high-pressure flow-through microreactor. The HDO of AA
was carried out at 1.0 h−1 WHSV and 21 bar pressure, whereas the
HDN of PA was carried out at 1.0 h−1 WHSV and 30 bar pressure. The par-
tial pressures of PA and AA were 2.7 and 2.1 bar, respectively. Each cata-
lyst sample was tested for about two weeks in order to measure the
2. Experimental
A microporous silica gel (Sylobead B127, Grace Davison; diameter of
the pores: smaller than about 2 nm; specific surface area: 563 m2/g) was
applied as catalyst support. The silica-supported nickel phosphide
catalyst, Ni2P/silica, was prepared by incipient wetness impregnation
of the support by a solution of nickel phosphide precursor compounds,
followed by drying, calcination and controlled reduction according to
Ref. [9]. First an aqueous impregnating solution was prepared by adding
chemicals (NH4)2HPO4 (Fluka, +99%) and Ni(NO3)2 (Merck, +99%) to
water in an amount to set their concentrations to 4.6 and 2.3 mol/dm3
temperature (200–400 °C) and space time (0.25–2.0 h × gcatalyst/greactant)
,
respectively. Upon adding drops of concentrated nitric acid to the aque-
ous mixture a crystal clear green solution was obtained. Then, the dried
silica was contacted with the impregnation solution by adding 0.5 cm3
of solution to each gram of the silica. The impregnated silica was dried
at 120 °C for 6 h and calcined then at 400 °C for 4 h. The calcined sample
was used as the precursor of the Ni2P/silica catalyst. The supported Ni2P
was obtained by heating the precursor up to 650 °C at a heating rate of
2 °C min−1 in flowing H2 (100 cm3 min−1) and by continuing the H2
treatment at this temperature for 3 h. Finally, the sample was cooled
to room temperature in He flow (20 cm3 min−1) and contacted with
a flow of 1.0% O2/He (50 cm3 min−1) at room temperature for 4 h to
generate a phosphate-like surface layer over the pyrophoric Ni2P
particles to prevent the bulk of the particles from becoming oxidized
when exposed to air [14].
The silica supported Ni catalyst, Ni/SiO2, was prepared similarly as
the Ni2P/silica catalyst. The only difference was that the impregnating
solution did not contain (NH4)2HPO4. The impregnated silica was
dried at 120 °C for 6 h and calcined at 450 °C for 4 h to get the oxide
precursor of the Ni-catalyst. The catalyst was obtained by treating the
precursor in H2 flow at 500 °C for 3 h.
dependence of the reactions, while several measurements at a given set
of parameters were repeated in order to check the stability of the cata-
lysts. All the catalysts showed stable activity during this time period. No
coke deposition was perceptible to the eye on the catalysts removed
from the reactor. The carbon content of the feed and the products was
virtually equal.
The composition of the reactor effluent was analyzed by on-line gas
chromatograph (Shimadzu GC-2010 Plus) equipped with an Equity-1
fused silica capillary column (Supelco) and a flame ionization detector.
3. Results and discussion
The XRD patterns of the catalysts, obtained by in situ reduction of the
catalyst precursors are shown in Fig. 1. The Ni/SiO2 catalyst presents
weak reflection lines at 44.5° and 52.0° characteristic of Ni metal parti-
cles. The reflections at 2 degrees of 28.9 and 43.2o prove the presence of
the Ni2In phase in the Ni2In/SiO2 catalyst [13]. Note that neither In nor
Ni phase was detectable. The 40.6, 44.6, 47.3, 54.2, and 54.9° XRD reflec-
tions stem from the crystalline Ni2P phase of the Ni2P/SiO2 catalyst [9].
The Ni2In/silica catalyst was prepared from the Ni/silica catalyst
precursor. The incipient wetness impregnation method was applied to
introduce indium in the Ni-containing preparation. Each gram of the
Ni/silica precursor was impregnated with 0.5 cm3 In(NO3)3 solution,
having In concentration of 2.3 mol/dm3, i. e., the Ni to In atomic ratio
of the preparation corresponded to 2 to 1. The sample was dried and
calcined to get the oxide precursor of the Ni2In/silica catalyst. The cata-
lyst was obtained by the reduction of the precursor in H2 flow at 450 °C
for 1 h. The chemical composition and the specific surface area of the
catalyst samples are summarized in Table 1.
X-ray powder diffraction (XRD) examinations were carried out
using a Philips PW 1810/3710 diffractometer equipped with an XRD
cell that allowed in situ reduction of the catalyst precursors with hydro-
gen at selected temperatures. After H2 treatments the XRD patterns
were recorded at room temperature applying monochromatized CuKα
(λ = 0.15418 nm) radiation (40 kV, 35 mA) and a proportional counter.
The morphology of the samples was characterized by electron mi-
crograph (TEM micrograph), moreover, by SSA and pore size distribu-
tion (PSD). The SSA and PSD were derived from the low-temperature
(−196 °C) N2 adsorption isotherms of the samples. The TEM pictures
Fig. 1. X-ray diffractograms of catalyst (A) Ni2P/SiO2, (B) Ni/SiO2, and (C) Ni2In/SiO2. The
samples were pretreated in situ in H2 flow using a high-temperature XRD cell at the
indicated temperature prior recording the XRD patterns at room temperature.