Tuning metal and acid properties of bifunctional Pt-USY
catalysts for the selective ring opening of decalin
Lech W. O. Soares1,2, Joan M. Faubel1, Maria A. Arribas1, Sibele B. C. Perguer2, Agustín Martínez1,*
aInstituto
de Tecnología Química, Universidad Politécnica de Valencia-Consejo Superior de Investigaciones Científicas, Valencia,
46015, Spain
bLaboratory of Molecular Sieves-LABPEMOL, Institute of Chemistry, Federal University of Rio Grande do Norte, Av. Senador
Salgado Filho 3000, Lagoa Nova, Natal, Rio Grande do Norte 59072-970, Brazil
Keywords: Selective ring opening; decalin; cetane upgrading; platinum; USY zeolite; acidity; metal dispersion
1. Introduction
Selective ring opening (SRO) of naphthenes is an
appealing, albeit challenging, catalytic approach for
upgrading poor quality distillates as a means of
meeting the global growing demand for diesel fuel
[1]. Dual-function catalysts comprising noble metals
(e.g. Pt and Ir) loaded on large-pore zeolites are
among the most prospective for the SRO of C6naphthenes [2]. For these catalysts, a proper balance
between the hydrogenolysis (related to the metal)
and acid (associated to the zeolite) functions is key
for promoting the selective formation of high-cetane
ring opening products with minimum cracking to
unwanted low molecular weight fractions [2, and
references therein].
In this work we applied high-silica ultrastable Y
(USY) zeolites as the acid component of
bifunctional Pt/zeolite SRO catalysts. Specifically,
USY-based catalysts with varying amounts of
Brønsted acid sites, Pt loadings, and metal
dispersions were prepared in order to assess the
impact of these parameters in the SRO reaction
using decalin as model feed.
adsorption (SEA) by adding the required amount of
Pt(NH3)4(NO3)2 to an aq. suspension of USY and
stirring the mixture at 25 ºC for 1 h while keeping
the pH at ca. 8 through dropwise addition of 1M
NaOH; Pt-NaUSY-5 (3 wt% Pt) was produced by
three sequential impregnations of NaUSY with
Pt(NH3)4(NO3)2 precursor introducing 1 wt% Pt in
each impregnation step, followed by drying. The
materials were characterized by ICP-OES, XRD, N2
sorption, IR-pyridine, and H2 chemisorption, and
evaluated in a fixed bed reactor for the SRO of
decalin (Dec) as model bi-naphthenic feed at T=280360 ºC, P=35 bar, H2/Dec=100 mol/mol, and
WHSV=0.44-3.22 h-1. Reaction products were
identified by GCxGC, and grouped as C9(cracking/hydrogenolysis products containing less
than 10 carbon atoms), isoDec (decalin isomers),
ROP (C10-alkylcycloalkanes formed by opening of
one Dec ring), OCD (open chain decanes, resulting
from the ring opening of ROP), and DHP
(dehydrogenated products, mainly tetralin and
naphthalene). Quantification of reaction products
was accomplished by online GC analyses.
2. Experimental Part
Two ultrastable Y zeolites, denoted here as USY
(CBV760, bulk Si/Al= 26.5, Zeolyst Int.) and
NaUSY (produced by submitting USY to 3
consecutive ionic exchanges with 0.1M NaNO3 at 25
ºC for 8 h) were used in the preparations. Catalysts
were then obtained by dispersing Pt on the USYtype zeolites as follows: Pt-USY-1 and Pt-NaUSY-3
(1.5 wt% Pt) were obtained by incipient wetness
impregnation (IWI) using H2PtCl6 precursor
followed by drying and air calcination at 500 ºC for
2 h; Pt-USY-2 (3 wt% Pt) was prepared by ionic
exchange (IE) of USY with a solution of
Pt(NO3)4Cl2 precursor at 80 ºC for 4 h under reflux;
Pt-USY-4 was prepared via strong electrostatic
3. Results and discussion
Table 1 summarizes the main physicochemical
properties of the prepared Pt-USY catalysts. For
USY zeolite and metal loading of 1.5 wt%, much
higher Pt dispersion (100%) is achieved via IE (PtUSY-2) than via IWI (DPt=21%, Pt-USY-1), both
catalysts exhibiting nearly the same concentration of
Brønsted acid sites (BAS). In turn, at equivalent Pt
loading (1.5 wt%), method of incorporation (IWI),
and dispersion (ca. 20-30%), the catalyst prepared
from NaUSY (Pt-NaUSY-3) exhibits, as expected, a
reduced Brønsted acidity compared to that obtained
from USY (Pt-USY-1). At higher Pt loading of 3.0
wt%, for which the IE method cannot be applied
given the limited ion exchange capacity of the
dealuminated USY zeolite, catalyst Pt-NaUSY-5
obtained by sequential impregnation shows higher
metal dispersion (39%) and lower amount of BAS
than Pt-USY-5 produced from USY via SEA method.
Table 1. Main properties of Pt-USY catalysts.
SBET
Smeso
Pt
DPta
BASb
Catalyst
(m2/g) (m2/g) (wt%) (%)
(mol/g)
Pt-USY-1
484
88
1.4
21
68
Pt-USY-2
510
90
1.7
100
67
Pt-NaUSY-3
465
86
1.6
28
20
Pt-USY-4
371
116
3.0
29
37
Pt-NaUSY-5
454
81
2.9
39
18
a Pt dispersion from H chemisorption.
2
b Density of Brønsted acid sites from IR-pyridine at a desorption
temperature of 250 ºC.
At the investigated conditions, the conversion of
decalin over Pt-USY catalysts is determined by the
density of BAS, as illustrated in Figure 1.
1.0
Relative activity
0.8
0.6
0.4
0.2
0.0
0
20
40
60
80
Density of BAS (ml/g)
Figure 1. Correlation between the relative activity for
conversion of decalin at 320 ºC and the density of BAS of
Pt-USY catalysts.
A simplified reaction scheme for the conversion of
decalin on bifunctional Pt-zeolite catalysts to the
main products defined as indicated in the
experimental part is presented in Scheme 1.
ring
isomerization
opening
Dec
isoDec
dehydrogenation
DHP
ROP
ring
opening
OCD
cracking
C9-
Scheme 1. Simplified scheme for the conversion of
decalin on bifunctional Pt-zeolite catalysts.
The yields to high-cetane ROP and OCD products
typically reach a maximum at decalin conversions of
80-90% under the studied conditions, after which a
decrease due to their cracking into C9- products
occurs. At constant conversion, catalyst Pt-USY-2
produced slightly higher yields to ROP and OCD
products than Pt-USY-1. This indicates that, at
constant Pt content and Brønsted acidity, an
improved catalytic performance is achieved by
increasing metal dispersion. The product yields for
Pt-USY-x (x=2 to 5) catalysts at their respective
maximum ROP+OCD combined yield as well as the
total selectivity to ROP+OCD products are given in
Table 2. Yields to dehydrogenated products (DHP)
were generally low (< 1%) at the condition of
maximum ROP+OCD yield and were thus not
included in the table.
Table 2. Product yields and selectivity to targeted
products at the maximum ROP+OCD combined yield.
Catalyst
C9Pt-USY-2a
14.0
Pt-NaUSY-3b 18.6
Pt-USY-4b
18.7
Pt-NaUSY-5b 9.8
a WHSV= 3.22 h-1.
b WHSV= 0.44 h-1.
Yields (wt%)
isoDec ROP
45.1
15.5
37.0
23.9
35.2
22.9
47.7
21.2
OCD
7.7
6.3
5.3
6.1
Sel. (wt%)
ROP+OCD
26.7
35.1
34.3
32.1
It is worth noting that Pt-NaUSY-3, with 1.6 wt% Pt
content and 28% dispersion, gives slightly higher
yield and selectivity to ROP+OCD than Pt-USY-4
and Pt-NaUSY-5 samples in spite of the higher
metal content and alike (or even higher) dispersion
of the latter. Nonetheless, the maximum ROP+OCD
yield over the least acidic Pt-NaUSY-5 catalyst is
achieved with the lowest yield to cracking (C9-)
products. Therefore, the Brønsted acidity of the PtUSY catalysts is concluded to be the most critical
parameter for maximizing the yield to ROP+OCD
products while keeping cracking at minimum levels.
4. Conclusions
At the investigated conditions, the activity for
decalin conversion as well as, to a high extent, the
maximum yield and selectivity to ring opening
products are driven by the Brønsted acidity of the PtUSY catalysts. Comparatively, the active metal area
(proportional to metal loading and dispersion) has a
much lower, albeit positive, impact on the SRO
reaction. Based on these results, current efforts are
focused on developing strategies for minimizing the
concentration of BAS while achieving high (>80%)
dispersions at high (>3 wt%) Pt loadings.
Acknowledgments
Financial support by the MINECO of Spain through the Severo
Ochoa project (SEV-2012-0267) and by the CNPq of Brazil
through project 401474/2014-3 (PVE 2014) is acknowledged.
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