353
phenol and other phenolic compounds using HZSM-5 catalysts
were not satisfactory [21–23]. The Fe/SiO2 catalyst [24] was used
to deoxygenate guaiacol. This compound was also deoxygenated
with Pt–Sn [25] and V2O5/Al2O3 catalysts [26], but phenol was the
main product in both cases.
drying and calcining at 550 ◦C. The final content of La in this case
was 0.03 wt%. This support was labelled LCH-B. A similar procedure
was followed to prepare another catalyst, LCL-B, using La(NO3)3
also in the second ion exchange, reaching a lanthanum content
of 4.2 wt%. Finally, H-B zeolite was exchanged with a solution of
NaOH 0.25 M for 3 h in reflux. Afterwards, it was filtered and dried
at 100 ◦C, and then calcined at 550 ◦C. The sodium content of this
zeolite was 1 wt%. This support was labelled Na-B. The chemicals
used for the ionic exchange were La(NO3)3·6H2O (Merck), NH4NO3
(Anedra) and NaOH (Ciccarelli). Na-B catalyst was exchanged with
NH4NO3 in order to go back to the original protonic form, and
compare with the sodic form, and also to verify if there was a
structural change during these ion-exchange steps, mainly dur-
ing the contact with the NaOH solution. This support was labelled
NaH-B.
In this work, the deoxygenation at atmospheric pressure of m-
cresol, taken as a model compound of the bio-oil phenolic fraction,
was studied using Pt supported on different materials. The use of
solid acid catalysts is particularly attractive because several of the
biomass deoxygenation reactions take place through decarbonyla-
tion, decarboxylation and dehydration followed by oligomerization
of olefins, as well as many other reactions such as cyclization,
hydrogen transfer, alkylation and cracking. Usually, a complex mix-
ture of hydrocarbons in the gasoline range (besides some shorter
tial amounts of aromatics, is obtained without the concomitant
consumption of hydrogen occurring on supported metal catalysts.
However, as above mentioned, the deoxygenation of phenolic com-
pounds requires the use of metallic catalysts. In previous works
[27], the deoxygenation of a phenolic compound (m-cresol) with
Pt supported on gamma alumina was studied. Toluene, benzene
and methylcyclohexane were the main reaction products. It was
shown that the yield of the desired product can be regulated by
changing the metal loading, the H2/cresol ratio and the reaction
temperature. The toluene hydrogenation to methylcyclohexane
was favoured at low temperature, while the toluene yield has a
maximum at an intermediate temperature level (around 300 ◦C),
zene by demethylation. The metal loading has a strong influence
in the product distribution, because as the ratio of metal/acid
sites increased, the toluene formation was favoured. It has been
proposed that a direct hydrogenolysis of the Caromatic OH bond
cannot occur [20]. The apparent direct hydrodeoxygenation may
involve a partial hydrogenation of the phenolic ring near the
Caromatic OH bond, resulting in the temporary removal of the delo-
calization effect, followed by rapid dehydration and a consecutive
dehydrogenation.
2.2. Catalysts characterization
Nitrogen adsorption was employed to determine BET surface
areas and pores volumes, using a Quantachrome Autosorb 1 ana-
lyzer. Micropores volumes were estimated by means of t-plots and
Saito-Foley method was used to estimate the average micropore
sizes. The determinations were carried out by pre-treating the cat-
alysts under vacuum at 350 ◦C for 3 h. The mesopores volumes were
calculated as the difference between the total pores volumes and
the micropores volumes.
Catalysts crystalline structures were characterized by X-ray
Diffraction (XRD). The X-ray diffractograms were obtained with
a Shimadzu XD-D1 instrument with monochromator using CuK␣
radiation (30 kV, 40 mA) at a scanning rate of 4◦ min−1 for Pt/␥-
Al2O3 and Pt/SiO2 catalysts, and at 0.5◦ min−1 for Pt/zeolites
catalysts, from 2ꢀ = 5–100◦. The crystallite size of Pt, determined
as the thickness of crystal in a direction perpendicular to the (1 1 1)
lattice plane (Lc) was determined by the following Scherrer’s equa-
tion:
K ꢁ
Lc =
(1)
ˇ cos ꢀ
where, ˇ is the full width at half maximum (FWHM) in radian, ꢁ is
the X-ray wavelength (0.154 nm), ꢀ is the Bragg angle, and K is the
Scherrer’s constant equal to 0.9.
In order to study the effect of the acidity required for cresol
deoxygenation, different supports were studied. Among them, sup-
ports with very low acidity such as gamma alumina and silica gel
were included, and also the mild-acid supports H-BEA, and H-BEA
modified with lanthanum and sodium by ion exchange. The effect
of the surface structure was also analyzed.
The metallic particles size for Pt/␥-Al2O3 and Pt/SiO2 catalysts
were determined by Transmission Electron Microscopy (TEM). The
reduced samples were dispersed in distilled water, and then one
drop of this suspension was placed on holey carbon supported on a
copper grid. The micrograph images of the samples were acquired
with a JEOL 100 CX model microscope at 100 kV, and a magnifica-
tion of 450,000×.
2. Experimental
Reducibility of metallic catalysts was studied by Temperature-
Programmed Reduction (TPR) analysis using a TCD detector. The
gas mixture was 5% H2 in Ar. The temperature was increased from
2.1. Catalysts preparation
The catalysts were prepared by wet impregnation of tetramine
platinum (II) nitrate (metal content 50 wt%) supplied by Alfa Aesar.
An aqueous solution of 1 wt% of Pt(NH3)4(NO2)3 was used to
prepare the Pt catalysts. The preparation procedure was the same
for all the catalysts, achieving a platinum loading of 1.7 wt%. A sus-
pension of the support in the metal precursor solution was stirred
on a hot plate at 110 ◦C until complete evaporation. The impreg-
nated catalyst was dried in an oven at 110 ◦C for 12 h. The dried
sample was calcined in an electric furnace at 350 ◦C for 2 h. The
supports used were ␥-Al2O3 (CK-300, Ketjen), SiO2 gel (Alfa Aesar)
and H-BEA zeolites from UOP, Si/Al = 13. This support was labelled
H-B. This zeolite was exchanged with a La(NO3)3 0.5 M aqueous
solution, during 3 h in reflux. Then it was filtered and dried at
100 ◦C, and finally calcined at 550 ◦C. This material was used for
a second ionic exchange with NH4NO3 0.5 M during 3 h in reflux,
20 to 700 ◦C with a heating rate of 11 ◦C min−1
.
The metallic dispersions were determined both by H2 and CO
chemisorption. The H2 chemisorption measurements were made
in volumetric equipment at room temperature. Each sample was
were measured at room temperature between 25 and 100 Torr.
In this range of pressure the isotherms were linear, and the H2
chemisorption capacity was calculated by extrapolation of the
isotherms to zero pressure [28]. The CO chemisorption experi-
ments were carried out in a fixed bed reactor. The sample were
reduced with H2 and then purged with N2 to desorb any hydro-
gen remaining on the metal. After this treatment, pulses of 250 l
of 2.5% CO in Ar were sent to the catalyst at room temperature.
The gas coming out of the cell was fed to a methanation reac-
tor, in order to increase the system sensitivity. In this reactor, CO