Accepted Manuscript Effect of synthesis conditions on zeolite Beta properties and its performance in vacuum gas oil hydrocracking activity Cecilia Manrique, Alexander Guzman, Joaquín Pérez-Pariente, Carlos MárquezÁlvarez, Adriana Echavarría PII:
S1387-1811(16)30272-4
DOI:
10.1016/j.micromeso.2016.07.017
Reference:
MICMAT 7804
To appear in:
Microporous and Mesoporous Materials
Received Date: 17 May 2016 Revised Date:
1 July 2016
Accepted Date: 11 July 2016
Please cite this article as: C. Manrique, A. Guzman, J. Pérez-Pariente, C. Márquez-Álvarez, A. Echavarría, Effect of synthesis conditions on zeolite Beta properties and its performance in vacuum gas oil hydrocracking activity, Microporous and Mesoporous Materials (2016), doi: 10.1016/ j.micromeso.2016.07.017. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Graphical abstract
HCK 3780 3740
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Variation Si/Al ratio
NiMo/H-Zβ (5)-Al2O3
H-Zb (5)
Na-Zb(5)
H-Zb (6)
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Na-Zb(6)
H-Zb (7)
Na-Zb(7) 20
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Wavenumber (cm-1)
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2θ
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NiMo/H-Zβ (6)-Al2O3 (B)
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NiMo/H-Zβ (6)-Al2O3 (A) NiMo/H-Zβ (7)-Al2 O3
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Effect of synthesis conditions on zeolite Beta properties and its performance in vacuum gas
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oil hydrocracking activity
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Cecilia Manriquea, Alexander Guzmanb, Joaquín Pérez-Parientec, Carlos Márquez-Álvarezc, Adriana Echavarríaa
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a
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b
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c
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Grupo Catalizadores y Adsorbentes, Universidad de Antioquia-UdeA, A.A 1226, - Medellín, Colombia
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Instituto Colombiano del Petróleo - ICP, Ecopetrol S.A., km 7 vía a Piedecuesta, Piedecuesta, Colombia Instituto de Catálisis y Petroleoquímica, ICP-CSIC, C/Marie Curie 2, 28049 Madrid, Spain
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Corresponding author. Tel.: +57 4 2195667; fax: +57 4 2198654; postal address 050010, Calle 67 No 53-108- Medellín, Colombia
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E-mail address:
[email protected] (Cecilia Manrique)
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ABSTRACT
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The influence of synthesis conditions such as crystallization time, temperature and gel
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composition on crystallization of zeolite Beta was studied. Optimal temperature for the synthesis
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was 170°C. A crystallization time from 24 to 36 h and 25 and 70 SiO2/Al2O3 ratio in the
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synthesis gel were used. In this way, three pure zeolite Beta samples were obtained under
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hydrothermal conditions. Change of these conditions led to zeolites with different Si/Al ratio,
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with one composition with low SiO2/Al2O3 ratio (20
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materials were characterized by X ray diffraction, elemental analysis, thermal analysis, N2
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physisorption, 27Al solid-state NMR, ammonia temperature programmed desorption, and infrared
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spectroscopy of adsorbed pyridine.
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differences in the proportion of tetrahedral and octahedral aluminum. Hydrocracking catalysts
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Al MAS-NMR measurements showed no significant
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were prepared from the calcined zeolites. The evaluation of these catalysts in vacuum gasoil
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hydrocracking showed that textural properties such as mesopore volume and effects of solvation
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in zeolite voids have an impact on selectivity towards gasoline and middle distillates.
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Keywords: Hydrocracking, zeolite Beta, vacuum gas oil, middle distillates, mesoporosity,
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acidity
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1. Introduction
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Hydrocracking (HCK) of vacuum gas oils (VGO) is one of the most important refinery
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processes, which involves the conversion of high molecular weight hydrocarbons to lower
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molecular weight hydrocarbons. This technology is employed to obtain high-quality middle
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distillates from feeds that are very difficult to process [1]. Conventional catalysts used in
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hydrocracking are bifunctional, having both hydrogenation-dehydrogenation and acid functions
43
in the catalyst particle. Cracking activity is controlled principally by the acidic support, while the
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hydrogenation-dehydrogenation activity is due to the metals dispersed on the support [2].
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Nowadays, efforts are being directed towards developing new types of catalysts based on
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potentially useful zeolites in the hydrocracking reaction. Numerous research studies have been
47
published on HCK of VGOs, in particular with catalysts based on Y zeolite, which has proven to
48
be highly active for this reaction [2-5]. However, in spite of the previous efforts to increase
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intracrystalline mesoporosity and overcome diffusional limitations, stability issues with this
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zeolite remain unsolved [6]. This issue is less problematic in other materials such as porous
51
amorphous silica-alumina and alumina, materials that have applications in hydrocracking of
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VGOs. Large pore zeolites with Si/Al higher than that of Y zeolite have also been used as
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potential acidic materials in vacuum gas oil hydrocracking based on their intrinsic higher thermal
54
stability and Brønsted acid strength. Among them, zeolite Beta has been used for hydrocracking
55
of VGO owing to its catalytic properties and its high thermal stability [7].
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With the objective of increasing middle distillates selectivity and better understand
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aspects related to the catalytic performance, several studies have been conducted on VGO
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hydrocracking reaction using zeolite Beta-based catalysts. Among those studies, we can
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highlight the works on the influence of smaller zeolitic crystal size [8,9] ; the influence of
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location of NiMo phases in the final zeolite Beta-based catalyst [8]; the formation of hierarchical
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micro-/mesoporous zeolite crystals from mesoporous materials precursors [10]; and the study of
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binary catalysts composed of mixtures of zeolites Y-Beta [11,12]. However, to the best of our
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knowledge, studies on the modification of acidic properties of zeolite Beta from variation of the
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synthesis conditions and their effects on its catalytic performance in VGO hydrocracking have
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not been yet reported.
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Synthesis of zeolite Beta by hydrothermal method requires crystallization times above
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24h using gels containing TEAOH-Na2O-Al2O3-SiO2-H2O [13–22]. Using relatively dense gel
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systems and small amounts of template, Borade and Clearfield [23,24] synthesized zeolite Beta
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with Si/Al ratio = 5.2, in 24 h at 170°C, using in the synthesis gel fumed silica as silicon
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precursor; however, the solid obtained had low crystallinity. Zeolite Beta framework is formed
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by an intergrowth of three different polymorphs (polymorphs A, B and C). This stacking
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disorder causes high concentration of internal structure defects that generates diversity of acid
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sites [25,26]. NMR studies have shown three types of Al species: framework Al atoms that are
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responsible of formation of the bridging AlOHSi hydroxyls (Brønsted acid sites), distorted
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tetrahedral Al species or coordinatively unsaturated Al (structure defects), associated to Lewis
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acid sites and extraframework Al species (EFAL), generated during the transformation of the
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zeolite to its acid form [25,27]. The presence of these Al species depends strongly on the
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chemical composition of zeolite and the proportions of the polymorphs. Also, the concentration
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of Brønsted and Lewis acid sites, their interactions, and thermal stability of the zeolite Beta
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depend markedly on the Si/Al ratio [28]. All these zeolite properties affect ultimately the
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catalytic performance. Thus, in order to better understand the catalytic behavior of new zeolite
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Beta formulations it is necessary to combine structural and acid site characterization. Therefore,
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the present study details the effects of synthesis parameters such as gel composition,
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crystallization temperature, and time on the formation processes of the zeolite Beta. The
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influence of these conditions on the acidity and catalytic properties of the zeolite Beta as the
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active component in catalysts for VGO hydrocracking was also studied.
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2. Experimental
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2.1. Synthesis of zeolites All zeolites syntheses were carried out using the hydrothermal method. Some parameters
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of the preparation of the synthesis gel such as the Al2O3/Na2O ratio (0.5), stirring rate (400 rpm),
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aging time and temperature (3 h and 25ᵒC, respectively), were kept constant. Synthesis process is
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described as follows: Sodium hydroxide (NaOH, Merck) and sodium aluminate (Al2O3 50-56%,
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Na2O 40-45%, Sigma-Aldrich) were mixed with deionized water in a polypropylene flask and
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stirred for 5 min. Afterwards, a tetraethylammonium hydroxide solution (35 wt. % TEAOH,
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Sigma-Aldrich) was added to the previous solution and was stirred for 5 more minutes.
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Subsequently, a colloidal silica solution (30 wt.% SiO2, Ludox AM, Sigma-Aldrich) was added
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dropwise
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temperature for 3 h. Then, the resulting gel was introduced into a Teflon-lined autoclave and
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treated hydrothermally under static conditions. After the desired crystallization time, autoclaves
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were quenched, and the solid obtained was filtered and washed with deionized water until neutral
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pH was reached. Water content in the synthesis gel was varied using reaction mixtures with the
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composition 1.98Na2O: Al2O3: 6.24 (TEA)2O: 25SiO2: XH2O, where X was 603 and 398. These
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values correspond to samples labeled Na-Zβ(3) and Na-Zβ(5), respectively (see Table 1).
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Finally, the synthesized solid was dried at 100°C overnight. Table 1 shows the composition of
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the synthesis gels and the crystallization conditions.
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2.2. Preparation of the catalysts
stirring.
Next,
the
reaction
mixture
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was
stirred at room
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After washing and drying, a calcination procedure was carried out for all crystalline
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materials described above. These materials were calcined in air at 600 ºC for 2 h with a heating
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rate of 5ºC/min. Calcined zeolites were converted to their acid form by ammonium ion-exchange
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in a 0.2 M NH4NO3 solution during 3 h at 50 ºC (50 mL/g of zeolite). After three consecutive ion
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exchanges, the materials were washed, dried, and calcined at 600 ºC for 2 h with a heating rate of
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5ºC/min, in order to obtain the active proton-form. Results of chemical analyses confirmed that
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most of the sodium cations were exchanged and its content reduced to less than 0.01 wt.%. The
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zeolites in their acid form were label as H-Zβ(5), H-Zβ(6) and H-Zβ(7). Hydrocracking catalysts
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extrudates were prepared as follows. A mechanical mixture of zeolite in its acid form (40 wt. %),
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alumina binder, and support (Versal 250 pseudoboehmite alumina, surface Area (m2/g)= 320)
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were peptized using a 1 wt. % HNO3 solution as peptizing agent. The dough obtained was then
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extruded in cylindrical shapes (with diameter of 1.2 mm and length of 4-8 mm). The resulting
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material was dried at 110 °C during 2 h and calcined at 550 °C for 2 h. Subsequently, the
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extrudates were impregnated, firstly, with 15 wt% of oxide of molybdenum and, secondly, with
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1wt% of oxide of nickel by sequential incipient wetness impregnation with intermediate
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calcinations at 550 °C for 2 h. Nickel nitrate hexahydrate (99 wt.%, Merck) and ammonium
124
heptamolybdate tetrahydrate (99 wt.%, Merck) were used as metal precursors. Finally, the
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catalysts were identified as: NiMo/H-Zβ(5)-Al2O3, NiMo/H-Zβ(6)-Al2O3(A) and NiMo/H-Zβ(7)-
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Al2O3. One catalyst was prepared from the zeolite H-Zβ(6) with a zeolite to alumina weight ratio
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of 80:20, which was identified as NiMo/H-Zβ(6)-Al2O3 (B).
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2.3. Characterization methods
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Zeolites were characterized by XRD in a PANalytical Empyrean diffractometer using
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CuKα radiation (λ=1.5406 Å) using a X-ray tube operated at 45 kV and 40 mA emission current.
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Samples were analyzed at room temperature in a 2θ range between 5 and 50° with a step size of
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0.04°. Relative crystallinity of the solid was calculated as the sum of the intensities of X-ray
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peak positions at 2θ of 21.13º and 22.30º. The crystallinity of the sample with highest intensity at
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22.30° was considered as 100%.
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The Si, Al, and Na content of zeolites was determined by Atomic Absorption
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Spectroscopy (AAS) in a Thermo Scientific ICE Series 3000 equipment. All samples were
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treated with mineral acids (hydrochloric and hydrofluoric acids) to achieve a complete
138
dissolution. Interferences associated with each metal were eliminated using nitrous oxide-
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acetylene flame. Analyses were performed in duplicate.
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Thermogravimetric and differential thermal analyses of zeolites were performed with a
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heating rate of 10 °CC/min, in the 25-950 ºC range, under a 40 mL/min air flow in two
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equipment sets: TA Instruments Hi-Res 2950 and TA Instruments 1600, respectively.
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TEM images of the zeolite particles and catalysts were taken in a FEI Tecnai G2 F20
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microscope operating at 200 kV. Prior to measurements, the samples were suspended in ethanol,
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sonicated for 30 min, and placed over a carbon coated holey Cu microgrid.
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Surface analysis for catalyst was carried out using scanning electron microscopy (SEM)
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using a JEOL microscope (model JSM-6490LV) associated with energy-dispersive X-ray (EDX)
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analysis. Samples were loaded into the SEM holder using graphite tape and were covered with
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gold in a sputtering device
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Solid-state 27Al MAS NMR spectra of zeolites were obtained in a Bruker DMX400 NMR
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spectrometer equipped with a triple channel probe using 2.5 mm ZrO2 rotors at room
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temperature. The rotation speed was 20 kHz in all cases. The 27Al chemical shift was referred to
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a saturated Al(NO3)3 solution. In a typical experiment, about 10 mg of hydrated sample was
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packed in the zirconia rotor.
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The nitrogen sorption measurements at 77 K of both zeolites and catalysts were
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determined using a Micromeritics ASAP 2020 gas sorption system. Prior to the measurements,
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all samples were degassed under high vacuum conditions for 8 h at 400°CC. The value of
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micropore volume was determined on the t-plot method, while the apparent specific surface area
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was calculated by applying the Brunauer–Emmet–Teller (BET) method. Mesopore volume and
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mesopore size distributions were calculated based on the adsorption branch of the isotherm using
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the Barrett-Joyner-Halenda (BJH) method.
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Acid properties of both zeolites and catalysts were determined by ammonia temperature
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programmed desorption (TPD) and Fourier transformed infrared (FT-IR) spectra of adsorbed
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pyridine. NH3-TPD experiments were carried out in a Micromeritics TPD/TPR 2900 equipment
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with a thermal conductivity detector (TCD). Here, 0.3 ± 0.01 g of zeolite was placed in a quartz
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reactor and then heated up to 550°C with a temperature ramp of 8°C /min under He flow (50
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ml/min) for one hour. After cooling down to 150°C, ammonia adsorption took place through
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small pulses. Full saturation was verified and physically adsorbed ammonia was removed by
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flushing the sample with He flow for 1 h. Ammonia desorption was performed at a rate of 10°C
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/min starting at 150°C up to 550°C under He flow (50 ml/min) followed by a one-hour
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isothermal step.
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FT-IR spectra were recorded in a Thermo-Nicolet Nexus 670 FTIR spectrometer
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equipped with an MCT cryodetector. About 10 mg of zeolite powder samples were pressed into
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self-supported wafer discs of 13 mm diameter, which was placed into a self-made glass cell with
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CaF2 windows. The sample was heated under vacuum in the IR cell at a ramp of 5ºC/min up to
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450 ºC and kept at this temperature for 10 h. Subsequently, the cell was cooled down to room
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temperature and spectra were recorded between 4000 and 1000 cm-1 at 4 cm-1 resolution.
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Pyridine (Fluka) was then adsorbed on the zeolite at 30 ºC until reaching full saturation and later
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was desorbed at 250 ºC, 350 ºC, and 400 ºC during 1 h prior to recording spectra. The
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determination of the concentration of Brønsted and Lewis acid sites was carried out by using the
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extinction coefficients EBrønsted = 1.67 cm µmol-1 and ELewis = 2.22 cm µmol-1, respectively [29].
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The number of acid sites were obtained by integrating the area under the curve, as this area is
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proportional to the number of adsorbed pyridine molecules.
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Temperature programmed reduction (TPR) analyses of catalysts were performed in an
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AUTOCHEM II 2920, Automated Catalyst Characterization System (Micromeritics). 300 mg of
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each sample were supported on quartz wool in a quartz tube and heated in an electric furnace. All
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samples were pretreated in helium flow at 350 ºC for one hour before the TPR tests. After
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cooling down to room temperature, reduction processes were carried out under a 50 mL/min gas
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flow of 10 vol% H2/Ar in the temperature range of 25–1000 ºC at a heating rate of 10 ºC /min.
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Hydrogen consumption was monitored using a thermal conductivity detector (TCD).
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2.4. Catalytic tests
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Vacuum gas oil (VGO) hydrocracking was carried out in a fixed bed, continuous flow
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stainless steel tubular reaction system (Parr Instruments). The feedstock consisted of pretreated
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Colombian representative VGO whose properties are listed in Table 2. The catalysts were
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sulfided in situ during 24h using a mixture of 95 wt.% diesel, 4.5 wt.% of dimethyldisulfide and
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0.5 wt.% of aniline up to 350 °C, and then pressurized at 1500 psi under a weight hourly space
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velocity (WHSV) of 1 h−1. These conditions were further maintained for 12h before VGO
200
injection. Aniline was added with the purpose of simulating an ammonia rich atmosphere in
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order to partially neutralize the strongest acid sites of zeolite and to inhibit coke formation during
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sulfidation [5,30]. Hydrocracking tests were carried out at 350 °C, 10 MPa, 1250 NL/L of
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H2/feed ratio, and WHSV was 2 h− 1 during the first 18 h, and then was changed to 1 h−1. Time
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on stream was at least 100 h. Conversion was referred to the 370 °C+ cut in the feed. Selectivity
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to middle distillates was referred as the 180–370 °C fraction in the product. Products were
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analyzed by SIMDIS-GC in accordance with the ASTM D7213 standard test method. These and
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other parameters were similar to the ones described by Agudelo et al [31]. Coke content was
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determined after reaction by a LECO carbon analysis on the spent catalyst.
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3. Results and discussion
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3.1. Zeolites
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Fig. 1 presents the X-ray diffraction (XRD) patterns of synthesized solids. Only those
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zeolites with pure Beta type crystalline phase are shown. Diffraction patterns obtained for the
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materials were compared with the diffraction pattern reported in database of zeolite structures
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[32]. All synthetized zeolites have shown the characteristic diffractions of zeolite Beta, with
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main peaks at 2θ of 7.62º, 21.13º and 22.30º. After calcination at 600°C and ion exchange, all
216
zeolites maintained the same diffraction pattern, indicating a good thermal stability of zeolite
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Betas prepared. Moreover, XRD patterns showed that lower water content in the synthesis gel
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reduced the required crystallization time to form zeolite Beta crystals from 48 to 36 h (see Table
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1), without presence of other crystalline phases, since Na-Zβ(5) synthetized using 398 mol H2O
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produced a pure crystalline zeolite Beta phase in comparison to the synthesis Na-Zβ (1, 3) with a
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higher H2O/SiO2 ratio that have led to amorphous materials. In this regard, it has been reported
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that this effect is due to super-saturation within the precursor mixture that makes faster the
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nucleation process, which in turn increases the rate of crystal growth [33]. Crystallization
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temperature at 170°C favored the formation of Beta-type crystals, promoting rapid nuclei
225
formation and an increase in crystallization rate. This permitted the formation of much smaller
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crystals [28]. Difractograms of synthesized samples at temperatures between 130°C and 150°C
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did not show the characteristic diffraction peaks of the of zeolite Beta structure.
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Results shown in Table 1 indicate that an increase of the SiO2/Al2O3 molar ratio in the
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synthesis gel of zeolite Beta reduced their crystallization time. Na-Zβ(5) and Na-Zβ(6) samples
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showed a decrease in crystallization time from 36 down to 24 h, when the SiO2/Al2O3 ratio
231
increases from 25 to 50. Therefore, the reduction of the aluminum concentration in the gel
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decreases the induction period and increases the crystallization rate [33]. A further increase of
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the SiO2/Al2O3 molar ratio to 70 (sample Na-Zβ(7)) also allows the crystallization in 24 h. The
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variation of the SiO2/Al2O3 molar ratio in the synthesis gel had an important influence on the
235
Si/Al ratio of the synthesized zeolite. Table 1 shows that an increase of SiO2/Al2O3 ratio in the
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synthesis gel from 25 to 50 led to a Si/Al ratio increase from 10.4 to 15.9 for Na-Zβ(5) and Na-
237
Zβ(6), respectively. A further increase of the SiO2 /Al2O3 molar ratio in the synthesis gel to 70
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led to an increase of the Si/Al ratio to 20.6, sample Na-Zβ(7). Fig. 2 shows the TGA profiles and their corresponding DTA plots for as-synthesized
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zeolites Beta, Na-Zβ(5), Na-Zβ(6), and Na-Zβ(7). All samples had weight loss of about 5 wt% at
241
temperatures lower than 150 °C due to the desorption of physisorbed water. Between 150 °C and
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400 °C, Na-Zβ(5) zeolite presented a weight loss of 2 wt %, while weight losses of zeolites Na-
243
Zβ(6) and Na-Zβ(7) were higher, 6 wt % and 9 wt % respectively. These events correspond to
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the decomposition of TEAOH species occluded in the zeolite framework [34]. From this data, it
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can be concluded that a decrease of aluminum content in the zeolite crystals leads to an increase
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of the TEAOH species occluded in the zeolite framework. In the case of the third temperature
247
event between 400 ºC and 550 ºC, weight losses of 12.8 wt%, 10 wt%, and 9 wt% were observed
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for zeolites Na-Zβ(5), Na-Zβ(6), and Na-Zβ(7), respectively. This has been attributed to the
249
thermal decomposition of TEA+ species interacting with zeolite framework [34, 35].
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Consistently, the weight loss in this range decreases with the aluminum content of the zeolite. On
251
the other hand, differential thermal analyses showed exothermic events, being these events
252
consistent with the temperatures at which the observed weight losses occurred during the
253
thermogravimetric analysis. Moreover, the weight loss observed at T > 550 ºC corresponds to the
254
combustion of the carbon-rich residues resulting from the decomposition of the several occluded
255
TEA species.
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The TEM images of the zeolites (Fig. 3) revealed its crystalline nature. The crystal size is
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within the range 50 – 100 nm for all materials. The H-Zβ(5) and H-Zβ(6) zeolites gave square-
258
shaped single particles, while the crystals of H-Zβ(7) zeolite has a round shape.
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Al MAS NMR spectra were recorded for all zeolites in their acid form, as shown in Fig.
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4. The MAS NMR spectra were analyzed based on the usual Gaussian distribution. Spectra
261
deconvolution was done using a Dmfit2011 program. All spectra were deconvoluted using
262
identical parameters. Peak positions and areas are shown in Table 3. Fig. 4 shows a broad band
263
in the region between 65 and 40 ppm, attributed to tetrahedral Al species. At least four different
264
contributions to this band, labelled as AlT(1), AlT(2), AlT(3), AlT(4), were obtained after peak
265
deconvolution. Signals AlT(1) ( ~ 62 ppm) and AlT(4) (~ 44 ppm) were assigned to distorted
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tetrahedral Al species. Signals AlT(2), (~ 57 ppm) and AlT(3) (~ 53 ppm) were assigned to
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tetrahedral Al species incorporated into the framework. Extra-framework octahedral Al species
268
at 0 ppm were observed. At least two different contributions, labelled as AlO(1) and AlO(2), were
269
obtained after peak deconvolution. These species were attributed to dealumination during
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calcination and rehydration and/or ion exchange processes [26, 36].
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According to Table 3, zeolites H-Zβ(5) and H-Zβ(6) have shown very similar
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concentrations of total tetrahedral Al. This type of aluminum generated about 80% of the
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aluminum signal. Only sample H-Zβ(7) showed a significant difference with about 3% more
274
tetrahedral aluminum, i.e. lower octahedral aluminum concentration than the two zeolites. Such
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concentration in sample H-Zβ(7) may be due to its higher thermal stability determined by its
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higher Si/Al ratio of 20.6. The deconvolution results of
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Al MAS NMR of the present work shown in Table 3
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indicate that H-Zβ(5) and H-Zβ(6) samples with total Si/Al ratios of 10.6 and 15.9, respectively,
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produced no significant differences in the framework aluminum AlT(2) and AlT(3) species at ~ 54
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ppm and ~ 58 ppm, respectively. In contrast comparison of
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(Si/Al ratio of 15.7) and H-Zβ(7) (Si/Al ratio of 20.4) zeolites, have shown differences in terms
282
of peak shape and intensity of the tetrahedral AlT(1) and AlT(3) species, assigned to distorted
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tetrahedral Al and non-distored tetrahedral Al, respectively. As shown in Table 3, zeolite H-
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Zβ(7) with the highest Si/Al ratio produced an increase around 6% in the concentration of the
285
AlT(2) species. In case of EFAL species, especially those corresponding to the signal at ~ 15 ppm
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(AlO(2) in Table 3), were about 3% less for H-Zβ(7) with the highest Si/Al ratio, probably due to
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the fact that zeolites with less aluminum have a more stable framework against dealumination.
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NMR results will be further discussed and related with IR acidity measurements.
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Al MAS NMR spectra of H-Zβ(6)
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Table 4 shows the textural properties of the zeolites measured by nitrogen physisorption
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at 77K. As shown here, the total area for this samples set was around 690 and 600 m2/g, with
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zeolites H-Zβ(5) and H-Zβ(7) with the highest percentages of microporous to total surface areas,
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89 and 91%, respectively, while H-Zβ(6) with a significant lower percentage of 77% or in other
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words with the highest mesoporous area of the three zeolites of this study.
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The Amount and type of acid sites in zeolites are closely related to their catalytic
296
properties with respect to activity, deactivation rate, and product selectivity. The NH3-TPD
297
profiles (Fig. 5) show two distinct desorption peaks: one between 170°C and 320 °C, centered at
298
about 270°C, and the second one between 320 °C and 550 °C, centered between 380-400°C. The
299
first desorption peak has been attributed to weak acid sites (low temperature peak) while the
300
second was attributed to strong acid sites (high temperature peak). As expected, maxima and
301
intensity of these peaks are closely related with the Si/Al ratio. With decreasing aluminum
302
content, the intensity of ammonia desorption peaks at low-temperature decreased while the high-
303
temperature desorption peaks broadened and shifted to higher temperatures. Maximum for the
304
zeolite H-Zβ(7), with the highest Si/Al ratio, was approximately 20°C higher.
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Table 5 shows the acid strength distribution for each zeolite. Deconvolution of NH3-TPD
306
profiles using Gaussian function has provided the strong and weak total acid site concentrations.
307
Low and high temperature desorption peak concentrations were equal for H-Zβ(5) and H-Zβ(6)
308
zeolites while in case of H-Zβ(7) the low temperature desorption peak was less intense. The total
309
acid site concentration obtained by NH3 TPD are roughly close to the total amount of acid sites
310
estimated from the unit cell compositions (circa 1mmol/g for zeolites Beta with Si/Al ratio of 10
311
and 0.5 for those with Si/Al ratios of 20). In the case of acidity determined by pyridine
312
adsorption monitored byFT-IR, the quantitative results have shown (Table 5) much lower
313
concentration of acid sites based on pyridine adsorbed at 250°C. As can be seen in the IR spectra
314
(Fig. 6) bridging hydroxyl groups at about 3610 cm-1 assigned to tetrahedral aluminum in the
315
zeolite framework are fully saturated at this adsorption temperature. In case of bands at 3780 cm-
316
1
317
isolated extra-framework AlOOH+ species (3780 cm-1 band) and Al-OH groups [33–35], extra-
318
framework AlOOH+ at 3780 cm-1 is also fully saturated with pyridine adsorbed at 250°C, while
319
the band at 3665 cm-1 seems to be partially saturated since after pyridine adsorption at 250°C is
320
still observed. Silanol groups at 3740 cm-1 are also partially saturated with pyridine adsorbed at
321
250°C. Although ammonia TPD and IR of pyridine adsortion on zeolites are useful tools to
322
characterize acidity in zeolites [36], chemical reactions with model molecules have been used to
323
determine the number of active sites by measuring them directly and during catalysis as
324
requirement to obtain accurate rate constants [37]. It has been shown for ultra-stable and
325
chemically treated Y zeolites that catalysis is exclusively related to the number of protons, i.e.
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and the broader one at 3665 cm-1 commonly assigned to two different kinds of -AlOH groups:
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only H+ sites that correspond to the bridging hydroxyl groups and therefore sites that are
327
exchangeable by other ions as sodium. In addition to that, it is also shown that extra-framework
328
aluminum species do not play a role as catalytic sites but change the effective sizes of supercage
329
voids and therefore their solvation properties with no effect on the Brønsted acid strength.
330
Zeolites with larger amounts of EFAL sites occluded in the voids, and as a consequence reducing
331
their sizes, will experiment stronger van der Waals interactions that will be led to higher rate
332
constants, i.e. to a better catalytic performance.
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Based on the discussion above it is expected that zeolite H-Zβ(6) will be the one with the
334
lowest cracking activity since its mesoporous area was the highest of the three zeolites, i.e. larger
335
zeolite volume voids, that decrease its solvation power. On the contrary, its higher amount of
336
EFAL species possibly occluded and therefore decreasing the zeolite volume voids that leads to
337
an increase of the solvation properties. Thus, these two expected opposite effects will influence
338
its cracking activity. However, another factor that should be considered is that solvation power is
339
dependent of the number of protons associated to the ion exchangeable sites in the zeolite that in
340
case of the zeolite H- Zβ(6), were the lowest (0.145mmolpy/g). In this sense it will be very
341
useful to obtain a Brønsted/Lewis ratio by dividing the number of exchangeable protons obtained
342
either from model reactions as methylation of dimethylether or Na+ titration, and the total
343
amount of extra-framework species. This parameter will be analyzed along with VGO
344
hydrocracking results.
347 348
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3.2. Properties of NiMo supported catalysts
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Fig. 7 shows XRD patterns of all NiMo catalysts before and after of reaction. The peaks
349
centered at 2θ of 7.62º, 21.13º and 22.30º were contributed by Zeolite Beta while the peaks at 2θ
350
of 46º and 67º were due to alumina. In the NiMo/H-Zβ(6)-Al2O3 (B) catalyst, the peaks
351
contributed by alumina is not observed, because of the amount of alumina was only 20 wt%.
352
Even after impregnation with NiMo and reaction in HCK, both zeolite and alumina structure
353
remain. No metal phase was identified from the XRD pattern, indicating that nickel oxides and
354
molybdenum oxides were well dispersed on the support surface.
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The HRTEM micrographs shown in Fig. 8 of the catalysts permitted to determine that
356
crystalline structure of the zeolite remain after impregnation process with Ni and Mo. The black
357
spots in the images represent metallic well-dispersed particles (NiMo oxides) on the support, as
358
indicated by the white arrows. This observations are agreement with the results obtained by
359
SEM–EDX mapping as shown in Fig. 9. The metal nanoparticles are well dispersed on the
360
external surfaces of the catalysts and there are no evidence of agglomeration of particles.
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Table 6 show the textural properties (BET surface area, microporous area and pore
363
volume) of the supports and NiMo catalysts. The zeolite–alumina mixture causes a decrease in
364
the BET surface and microporous area, and increase the pore volume with respect to zeolites,
365
due to the presence of alumina. Impregnation of nickel and molybdenum on the supports,
366
decrease the textural properties due to blockage of the pores produced by these metals. An
367
enhanced in textural properties is observed when there is an increase in the zeolite content. The
368
pore-size distributions of the supports and the corresponding NiMo catalysts are shown in Fig.
369
10. Position of the maximum peak on the pore size distribution curve of the support and catalysts
370
with 40:60 zeolite–alumina ratio is 110 Å. However, when there is higher content of zeolite a
371
shift of the curve occurred. For the support and catalyst NiMo/H-Zβ(6)-Al2O3 (B) a slight shifted
372
toward lesser pore diameter (97 Å) is observed.
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It is well known that cracking properties of hydrocracking catalysts and middle distillate
375
yields strongly depend on their acidic characteristics [37]. In case of extrudates, the typical form
376
of hydrocracking commercial catalyst, activity should be mainly determined by the content of the
377
zeolitic portion in the catalyst, in spite of the expected contribution of alumina to the total
378
acidity. Total acidity measured with ammonia and FT-IR of pyridine adsorption is shown in
379
Table 7.
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In order to determine possible diffusional effects of zeolite for VGO components, an
381
enhanced zeolite concentration (doubled zeolite amount in extrudates) to prepare NiMo/ H-
382
Zβ(6)-Al2O3 (B) catalyst was used. This sample was also evaluated taking into account that
383
Zeolite Beta has a higher Si/Al ratio in comparison to Y zeolite, which is most widely used in
384
hydrocracking catalyst formulation. In this way, the expected acidity of Zeolite Beta must be
385
lower and concomitantly its activity [31]. Therefore, the increase in the zeolite content causes
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386
changes in the acidic properties of the catalyst (increase of number of acid sites) as well as in the
387
characteristics of the deposited metallic species on support (location and dispersion) since most
388
of the available surface comes now from the zeolite. In the case of extrudates, alumina contributes to total catalyst acidity. Meanwhile, zeolite
390
contributes to catalytic active acidity. Total acidity of alumina in the present study was about
391
0.22 mmol NH3/g. In fact, after impregnation of metals, total acidity, measured with NH3-TPD
392
and FT-IR, decreased with respect to the zeolites. This effect could be attributed to the
393
interaction of the surface OH groups with the metal precursors. On the other hand, it has been
394
reported that incorporation of metals in supported silica-alumina increased the acidity of the
395
catalyst [38,39]. Thus, results of the acidity measured by NH3-TPD on the NiMo catalysts could
396
be associated to Mo and Ni oxides, and not to the acidity provided by the bulk catalyst. On the
397
other hand, Ni and Mo species could be localize mainly on the external surface of support,
398
blocking the pore and difficult the accessibility of the pyridine to acid sites, producing a decrease
399
in the acidity of catalyst. Concentration and strength of Brønsted and Lewis sites of some NiMo
400
catalysts determined by FTIR of adsorbed pyridine are shown in Table 7. The concentration of
401
Brønsted acid sites decreased in the catalyst with respect to zeolite. However, acid strength
402
distribution in the catalysts has the same trend as in the zeolites. Table 7 shows that extrudates of
403
NiMo/ H-Zβ(6)-Al2O3 (B) with 80 wt.% zeolite presented a total ammonia acidity of 0.71
404
mmol/g. Extrudates of the same zeolite, but with lower content (40 wt.%), presented a value of
405
0.53 mmol/g.
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Fig. 11 presents H2-TPR results. The TPR profiles of the catalysts showed two reduction
407
bands: one between 350-600°C, and the second one centered around 900°C. The first reduction
408
band between 350°C-600°C was associated to octahedral molybdenum reduction (Mo6+ →
409
Mo4+). The second band at about 900 °C has been attributed, first, to the complete reduction of
410
the polymolybdate (octahedral) species (which were partially reduced at low temperature), and
411
secondly, to the complete reduction of tetrahedral species strongly bonded to the support [40–
412
42]. Due to the concentration difference between Ni and Mo, Ni2+ reduction was barely observed
413
in the TPR profile. Only in the NiMo/H-Zβ(6)-Al2O3 (A) catalyst, a shoulder was clearly
414
observed at about 600°C. In case of the catalyst based on the same zeolite but with 80%wt of
415
zeolite in the catalyst support, this shoulder was more notorious but slightly displaced to a lower
416
reduction temperature (about 550°C). In case of the reduction molybdenum peak associated to
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Mo6+ → Mo4+ is shifted to a lower temperature (by about 20°C) in comparison to the catalyst
418
with the same zeolite but with only 40% zeolite content in the catalyst formulation. This result
419
can be due to a lower interaction between the support and the metal, more specifically metal
420
dispersion on the zeolite’s external surface. Similarly, NiMo/H-Zβ(6)-Al2O3 (B) catalyst had a
421
high temperature signal with much lower intensity than NiMo/ H-Zβ(6)-Al2O3 (A) catalyst,
422
which had 40%/60% of zeolite to alumina ratio. This may be attributed to lower interaction
423
between support and the metal oxide phases. Similar results were observed by Solis et al. [43]
424
with NiMo catalysts based on Y zeolite, who attributed the lower reduction temperature to a
425
lower interaction of polymeric octahedral Mo species supported on zeolite, specifically on the
426
external surface. .
427
3.3. Catalytic activity of supported NiMo catalysts
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Fig. 12 presents the catalytic activity of the extradutes prepared with alumina and the
430
zeolites under study. As it can be seen, conversion for all catalysts, except for NiMo/H-Zβ(6)-
431
Al2O3 (B) (80% zeolite:20% alumina), showed a decrease at the window time monitored. For
432
industrial application, activation and stabilization procedures of commercial catalysts should
433
guarantee that steady state conditions be reached. The slight decrease observed during the
434
catalytic evaluation of the materials of this study can be the result of not enough aniline that was
435
used to control initial activity of fresh catalysts. The ammonia produced under the activation
436
conditions can partially neutralize the strongest zeolitic acid sites. This condition is intended to
437
simulate a rich ammonia atmosphere in the first reactor, as is the case in full conversion
438
hydrocracking units. Additionally, fresh catalysts are highly active and in spite of the high
439
hydrogen pressure in the reaction system, some amount of coke is formed that finally leads to
440
stable catalytic activity during the first days of use. Coke content after the catalytic tests was
441
about 30% higher for the zeolite-based catalysts with the lowest Si/Al ratio, indicating the
442
relation between Brønsted acidity and catalytic activity.
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Now, considering the difference in pore volume and the amount of Brønsted and Lewis
445
acid sites for the three zeolites, Brønsted/Lewis ratios were estimated from IR of adsorbed
446
pyridine at 250°C (this ratio is used here as a possible parameter to indicate the extent of
447
reduction in the zeolite voids by EFAL species occluded). These values were 3.5, 1.6 and 4.6 for
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448
H-Zβ(5), H-Zβ(6) and H-Zβ(7) zeolites, respectively, while the % of mesoporous were 11, 23
449
and 9. Fig. 12 of vacuum gasoil conversion with time of stream TOS has shown a faster
451
conversion decrease and lower conversion at the longest TOS for the extrudates based on the
452
zeolite H-Zβ(5). In light of the its relative high Brønsted/Lewis ratio and lower % of mesoporous
453
area, is to expect a better catalytic behavior than H-Zβ(6) since this would give to this catalyst
454
higher solvation properties. However, in case of bifunctional catalysts used in hydroconversion
455
of heavy crude oil fractions, other factors as metal dispersion and diffusional constrains of
456
molecules present for instance in vacuum gasoil to access protons in zeolite voids, should be
457
considered.
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Thus, on the one hand it is expected a higher solvation effect of the catalyst based on the
459
H-Zβ(5) with a relative lower amount of EFAL species and zeolite volume voids, on the other
460
hand reactant molecules in the vacuum gasoil will experience higher constraints to access the
461
zeolite pores and therefore the catalytically active zeolite protons. As can be seen in Fig. 12,
462
catalyst based on H-Zβ(5) has shown the faster deactivation decay in the first 60 h of time on
463
stream and its conversion was the lowest at the longest TOS monitored. On the contrary, catalyst
464
based on H-Zβ(6) with the lowest Brønsted/Lewis ratio and the largest mesoporous volume, with
465
potentially lower solvation properties, has shown a lower deactivation rate and a higher
466
conversion of the three catalyst, indicating that factor as accessibility to zeolite cavities are
467
favored by a higher mesoporous volume.
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In case of product selectivity, it is very likely that solvation properties play a more
469
determinant role on product yields. As can be seen in Fig. 12, for the same conversion level
470
(around 17%) reached at 35 h of time of stream, the selectivity to middle distillates of the three
471
catalysts with the same zeolite-alumina ratios was markedly different. The trend of selectivity for
472
the catalysts at this point of isoconversion is NiMo/ H-Zβ(7)-Al2O3 > NiMo/ H-Zβ(5)-Al2O3 >
473
NiMo/ H-Zβ(6)-Al2O3, has shown that the catalyst based on zeolite H-Zβ(6) with the highest
474
mesoporous volume and lowest Brønsted/Lewis ratio, was the one with the lowest middle
475
distillate selectivity or the highest gasoline selectivity. Considering that gasoline products can be
476
formed via overcracking of middle distillate molecules formed at the first reaction elementary
477
steps of the reaction cycle, it is possible that the better accessibility of zeolite pore volume of the
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478
zeolite with the highest mesoporous volume, will lead to improved cracking properties in spite of
479
its potentially lower solvation properties of the acid sites in the zeolite voids.
480 481
Now, catalytic results of the catalyst based on H-Zβ(6) but doubling the amount of zeolite in the catalyst formulation,
483
considered. Firstly, it is to remark that its VGO conversion reached 30%. This level almost
484
duplicated the conversion obtained with catalyst), with 40%/60% of zeolite to alumina
485
(conversion of 17%), which is an indicative for catalytic control of the reaction, favored by its
486
higher mesoporosity that probably diminishes diffusional constrains of VGO molecules in the
487
feed. As discussed before when comparing selectivity results between the catalysts based on the
488
three zeolites with a ratio 40%wt zeolite to 60% alumina in the catalyst preparation, the one
489
based on H-Zβ(6), showed higher gasoline selectivity than the other two catalysts (50% middle
490
distillate selectivity vs about 80-90% for catalysts based on H-Zβ(5) and H-Zβ(7)), possible due
491
to its better zeolite pore accessibility. However, when the proportion of zeolite in the catalyst
492
formulation was increased to 80%, conversion increased from 17% to 30% but its gasoline
493
product selectivity decreased to about 45%. This simultaneous increase of conversion and middle
494
distillate selectivity, or decrease of gasoline, has been attributed to the proximity effect of the
495
two catalytic functions in bifunctional catalysts [2,41]. This may be associated with the
496
preference of nickel to interact with the strong hydroxyl groups of the zeolite, as reported by
497
Fornes et al [40] in the case of Ni/Mo impregnated on ultrastable Y zeolite. In this report,
498
molybdenum oxides interacted with most of the zeolitic hydroxyl groups, while nickel precursors
499
showed the tendecy to interact with the most acidic OH groups. The above indicates that a good
500
metal dispersion could help to control the strong acidity in the hydrocracking catalyst, since
501
stronger acid sites are responsible of low middle distillate yields. At same time, a proper
502
dispersion could increase the probability to have metal and acid sites closer each other.
504
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NiMo/H-Zβ(6)-Al2O3 (B) (80%/20% of zeolite to alumina), are
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4. Conclusion
505 506
This paper introduced a new composition in the synthesis gel to prepare zeolite Beta with
507
low SiO2/Al2O3 ratio (20
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zeolites Beta differed significantly in their physicochemical properties as consequence of
509
synthesis conditions differences. Final compositions have shown important effects on the final
510
pore system and the acid properties after calcination treatments necessary to prepare the zeolites
511
in their acid form. Although acid strength and solvation on the reactivity of solid Brønsted acids
512
are desired property of catalyst for HCK of VGOs, mesoporosity characteristics should be
513
always taken into account. Acid sites of moderate strength may exert control over the gasoline
514
selectivity in the final product. Moreover, it has been shown that catalyst formulations with
515
higher proportions of zeolite, while considering appropriate pore properties, have influenced
516
metal deposition as well as dispersion. In spite of having double conversion with the catalyst of
517
higher zeolite proportion, middle distillate selectivity was maintained.
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Acknowledgements
The authors acknowledge financial support by Instituto Colombiano del Petróleo - ICP,
521
ECOPETROL S.A., for the development of this project, We also acknowledge Universidad de
522
Antioquia and 2014-2015 Sustainability Program and Instituto de Catálisis y Petroleoquímica –
523
CSIC. C. Manrique acknowledges COLCIENCIAS her doctoral fellowship.
524 525 526
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LIST OF FIGURES
607 608
Fig. 1. X-ray diffractograms of the synthesized samples
609
Fig. 2. TGA and DTA profiles of the zeolites
610
Fig. 3. TEM images of zeolites. A. Na-Zβ(5); B. Na-Zβ(6); C. Na-Zβ(7)
611 612
Fig. 4. 27Al MAS NMR spectra of zeolites in acid form and simulated spectra (dashed line) using standard deconvolution with symmetric function Gaussian
613 614 615
Fig. 5. NH3 TPD for zeolites in acid form
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Fig. 7. X-ray diffractograms of the catalyst (A) before and (B) after reaction
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Fig. 8. TEM images of zeolites. A. NiMo/H-Zβ(5)-Al2O3; B. NiMo/H-Zβ(6)-Al2O3 (A); C. NiMo/H-Zβ(6)-Al2O3 (B); D. NiMo/H-Zβ(7)-Al2O3
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Fig. 9. SEM-EDX images of catalyst
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Fig. 10. Pore size distribution in the catalysts and supports.
621 622 623 624 625
Fig. 11. TPR profiles of supported NiMo catalysts. a. NiMo/H-Zβ(5)-Al2O3; b. NiMo/H-Zβ(6)-Al2O3 (A); c. NiMo/H-Zβ(7)-Al2O3; d. NiMo/H-Zβ(6)-Al2O3 (B)
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Fig. 6. IR spectra in the region of OH groups vibration of zeolites
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Sample
SiO2/Al2O3 H2O/SiO2
Temperaturea (°C)
Timea (h)
Phaseb
XRD crystallinity (%)b 56 96 100 99
Si/Alc
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Na-Zβ(1) 25 24 130 48 amorphous Na-Zβ(2) 25 24 150 48 amorphous Na-Zβ(3) 25 24 170 48 Beta + MTW Na-Zβ(4) 25 16 170 24 Semicrystalline Na-Zβ(5) 25 16 170 36 Beta 10.4 Na-Zβ(6) 50 16 170 24 Beta 15.9 Na-Zβ(7) 70 16 170 24 Beta 20.6 a Crystallization temperature and time b Determined by X ray diffraction (XRD) c Determined by Atomic Absorption Spectroscopy (Na content (wt%): 0.3; 0.1;0.1 for Na-Zβ(5), Na-Zβ(6) and Na-Zβ(7) zeolites, respectively)
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Table 2. Properties of Colombian Vacuum Gas Oil
IBP(ºC)
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S(ppm) N(ppm) Density (15ºC) g/ml Gravity API Viscosity Paraffins (wt%) naphthenes Aromatic hydrocarbons distribution (wt%) Monoaromatics Diaromatics Polyaromatics
Value 155 n.d 25 0.91 23.7 n.d n.d n.d
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AlT(2) AlT(3) AlT(4) AlO(1)
H-Zβ(5) 61.7 2.3 57.8 14.8 53.6 48.2 42.8 14.9 0 5.9 -13.3 13.8 80.2 19.7
H-Zβ(6) 62.1 4.3 58.0 12.1 53.6 47.9 44.0 15.5 0 3.9 -14.9 16.3 79.8 20.2
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Parameter Position (ppm) Area (%) Position (ppm) Area (%) Position (ppm) Area (%) Position (ppm) Area (%) Position (ppm) Area (%) Position (ppm) Area (%) AlT total AlO total
Al MAS NMR and relative
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H-Zβ(7) 62.1 0.8 57.4 17.9 53.6 48.3 43.9 16.4 0 3.5 -15 13.3 83.4 16.8
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Table 3. NMR parameters from the deconvolution of content of Al species in each zeolite
ACCEPTED MANUSCRIPT Table 4. Textural properties of H-Zβ(5), H-Zβ(6), and H-Zβ(7) Sample
Smicro (m2/g) 534 529 581
Smeso (m2/g) 63 159 59
VTotal (cm3/g) 0.26 0.37 0.34
Vmicro Vmeso Smicro / SBET (cm3/g) (cm3/g) (%) 0.22 0.04 89 0.22 0.15 77 0.24 0.10 91
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H-Zβ(5) H-Zβ(6) H-Zβ(7)
SBET (m2/g) 597 687 641
ACCEPTED MANUSCRIPT Table 5. Acidity measured by NH3-TPD and Pyridine FT-IR
Brønsted 0.257 0.145 0.167
Lewis 0.073 0.093 0.036
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(a) NH3 temperature programmed desorption (TPD) (b) From deconvolution of NH3-TPD profiles. (c) Pyridine FT-IR (after desorption at 250ᵒC) (d) Pyridine FT-IR (after desorption at 400ᵒC)
Total acid sites, mmolPy/g(c)
Strong acidity, mmol Py/g(d) Brønsted 0.089 0.055 0.060
Lewis 0.022 0.012 0.009
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Acidic strength distribution by mmol NH3/g (b) Total acid Sample sites, mmol Low High NH3/g(a) temperature temperature peak peak H-Zβ(5) 1.20 0.60 0.60 H-Zβ(6) 0.91 0.45 0.46 H-Zβ(7) 0.66 0.29 0.37
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Support (Zeolite/alumina)
Smicro (m2/g) 244 235 420 250 143 149 160 158
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Catalysts
H-Zβ(5)-Al2O3 H-Zβ(6)-Al2O3 (A) 40 wt% zeolite H-Zβ(6)-Al2O3 (B) 80 wt% zeolite H-Zβ(7)-Al2O3 NiMo/ H-Zβ(5)-Al2O3 NiMo/ H-Zβ(6)-Al2O3 (A) 40 wt% zeolite NiMo/ H-Zβ(6)-Al2O3 (B) 80 wt% zeolite NiMo/ H-Zβ(7)-Al2O3
SBET (m2/g) 393 432 589 410 297 328 339 318
VTotal (cm3/g) 0.50 0.56 0.40 0.53 0.40 0.44 0.32 0.42
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ACCEPTED MANUSCRIPT Table 7. Acidity of the supported oxidic NiMo catalysts
NiMo/ H-Zβ(5)-Al2O3 NiMo/ H-Zβ(6)-Al2O3 (A) 40% wt zeolite NiMo/ H-Zβ(6)-Al2O3 (B) 80% wt zeolite NiMo/ H-Zβ(7)-Al2O3
10.6 15.9 15.9 20.6
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Strong acidity, mmol Py/g(d)
Brønsted Lewis Brønsted Lewis 0.057 0.086 0.012 0.023 0.041 0.098 0.008 0.013 0.089 0.169 0.010 0.078 n.d n.d n.d n.d
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(a) Si/Al ratio of zeolite (b) NH3 temperature programmed desorption (TPD) (c) Pyridine FT-IR (after desorption at 250ᵒC) (d) Pyridine FT-IR (after desorption at 400ᵒC)
0.730 0.526 0.714 0.740
Total acid sites, mmolPy/g(c)
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Total acid sites, mmol/g, (b)
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Research Highlights
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Synthesis of beta zeolite with different Si/Al ratio with optimal value of 15. Beta zeolite has been synthesized at 170 ºC at 24 hours of crystallization time. NiMo / beta - alumina catalysts for VGO hydrocracking.
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Catalysts exhibited high selectivity to middle distillates