Synthesis of NiMo Catalysts Supported on Gallium-Containing Mesoporous y Zeolites with Different Gallium Contents and Their High Activities in the Hydrodesulfurization of 4,6-Dimethyldibenzothiophene

Article abstract of DOI:10.1021/acscatal.7b02705

Mesoporous MY-xGa zeolites exhibiting both crystallized pore walls and narrowly dispersed mesopores with different Ga content were successfully synthesized. The synthesized samples were characterized by XRD, N₂ adsorption desorption isotherms, SEM, TEM, XPS, FTIR, ²⁹Si MAS NMR, ⁷¹Ga MAS NMR, and Py-FTIR methods. The results show that the synthesized samples exhibit unique open channel like mesopore systems and outstanding crystallite natures; no nonframework Ga species were observed over the MY-xGa series samples, and their acidic properties can be modulated by varying the Ga/Al ratio in the initial synthesis gel. The corresponding NiMo/HMY-xGa catalysts were prepared via the incipient wetness coimpregnation method; the morphologies of the sulfide catalysts were characterized by HRTEM, and the covalent states of the active metals were characterized by XPS. The catalytic activities of the investigated catalysts for the 4,6-DMDBT HDS reaction were assessed, and the collected products were analyzed by GC and GC-MS methods. The catalyst NiMo/HMY-0.5Ga showed the highest catalytic activity due to the synergistic effect of modulated acidic properties, excellent morphology, highest sulfidation degree, and proper proportion of NiMoS phase. More importantly, 4-MDBT, DBT, and BP were observed and identified as the products of the 4,6-DMDBT HDS reaction, designated as the demethylation pathway (DM) for the 4,6-DMDBT HDS reaction. Finally, a reaction network including DDS, HYD, ISO, and DM pathways for the 4,6-DMDBT HDS reaction over catalyst NiMo/HMY-0.5Ga was proposed.

Full text of DOI:10.1021/acscatal.7b02705

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Article
Synthesis of NiMo Catalysts Supported on Gallium Containing
Mesoporous Y Zeolites with Different Gallium Contents and Their High
Activities in the Hydrodesulfurization of 4,6-Dimethyldibenzothiophene
Wenwu Zhou, Meifang Liu, Qing Zhang, Qiang Wei, Sijia Ding, and Yasong Zhou
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b02705 • Publication Date (Web): 02 Oct 2017
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Synthesis of NiMo Catalysts Supported on Gallium
Containing Mesoporous Y Zeolites with Different
Gallium Contents and Their High Activities in the
Hydrodesulfurization of 4,6ꢀ
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Dimethyldibenzothiophene
Wenwu Zhou, Meifang Liu, Qing Zhang, Qiang Wei, Sijia Ding and Yasong Zhou*
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249,
PR China
KEYWORDS: Mesoporous Y zeolites; 4,6ꢀDMDBT HDS; NiMoS active phase; catalytic
activity; HDS pathway.
ABSTRACT
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Mesoporous MYꢀxGa zeolites exhibit both crystallized pore walls and narrow dispersed
mesopores with different Ga content were successfully synthesized. The synthesized samples
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were characterized by XRD, N adsorption desorption isotherms, SEM, TEM, XPS, FTIR, Si
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MAS NMR, Ga MAS NMR and PyꢀFTIR methods. The results show that the synthesized
samples exhibit unique open channel like mesopore systems and outstanding crystallite natures,
no nonꢀframework Ga species were observed over the MYꢀxGa series samples and their acidic
properties can be modulated by varying the Ga/Al ratio in the initial synthesis gel. The
corresponding NiMo/HMYꢀxGa catalysts were prepared via incipient wetness coꢀimpregnation
method, the morphologies of the sulfide catalysts were characterized by HRTEM and the
covalent states of the active metals were characterized by XPS. The catalytic activities of the
investigated catalysts for 4,6ꢀDMDBT HDS reaction were assessed and the collected products
were analyzed by GC and GCꢀMS methods. Catalyst NiMo/HMYꢀ0.5Ga showed the highest
catalytic activity due to the synergistic effect of modulated acidic property, excellent
morphology, highest sulfidation degree and proper proportion of NiMoS phase. More
importantly, 4ꢀMDBT, DBT and BP were observed and identified as the products of 4,6ꢀ
DMDBT HDS reaction which were designated as the demethylation pathway(DM) for 4,6ꢀ
DMDBT HDS reaction. Finally, a reaction network including DDS, HYD, ISO and DM
pathways for 4,6ꢀDMDBT HDS reaction over catalyst NiMo/HMYꢀ0.5Ga was proposed.
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1
. Introduction
In recent years, considerable attention have been paid on the complete reduction of the sulfur
compounds in inferior diesels owing to the stringent environmental legislations all over the
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world,
especially for certain of the major oil consumption regions, it is strictly limited to
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, 4
values as low as 10 ppm.
To reach such a low level, complete removal of highly refractory
organosulfur compounds like 4,6ꢀDMDBT is inevitable, and hydrodesulfurization(HDS) is
considered as one of the most promise methods for the removal of organosulfur compounds from
diesels. However, the hindrance caused by the methyl groups locate at 4 and 6 positions greatly
inhibits the adsorption and catalytic transformation of 4,6ꢀDMDBT which is among the most
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, 6
common organosulfur compounds in inferior diesel,
thus it remains difficult for ultraꢀdeep
desulfurization of inferior diesel via HDS method. One possible route to overcome this drawback
is employing zeolites which are very active in catalyzing highly refractory organosulfur
compounds like 4,6ꢀDMDBT into less refractory organosulfur compounds like 3,6ꢀDMDBT and
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,7ꢀDMDBT.
Y zeolite is considered as the best candidate due to its microporosity is
comparable to the size of 4,6ꢀDMDBT molecules, its controllable acidity and its superior
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hydrogen transfer ability.
Though it has been confirmed that the addition of Y zeolites to the
hydrotreating catalyst can promote the methyl groups at 4 and 6 positions migrate to 3 and 7
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positions to eliminate the hindrance. However, there are also some drawbacks: the size of
micropores in Y zeolites is about 7.4 Å which severely restricts the diffusion of both the
reactants and products, and the most commonly weight hourly space velocity(WHSV) used in
ꢀ1
FCC diesel hydrodesulfurization is 2 h , which is too fast for the 4,6ꢀDMDBT molecules to
diffuse in and adsorb on the active acid sites located in the narrow micropores of Y zeolites, thus
most of the active sites are inaccessible for the refractory reactant molecules; on the other hand,
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the acid density of Y zeolite is too high and the acid strength of Y zeolite is too strong for a
highly active bifunctional HDS catalyst, which would inhibit the formation of NiMoS active
phase over HDS catalyst and might has negative impact on both the stability of HDS catalyst and
the diesel yield.
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To overcome the aforementioned drawbacks and fully utilize the advantages of Y zeolites,
considerable strategies for the synthesis of hierarchical Y zeolites, or the so called mesoporous Y
zeolites, which exhibit both the high hydrothermal stability of Y zeolite and the mass transfer
ability of mesoporous materials, have been disclosed in the literatures and reported in several
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review articles.
Until now, strategy using soft templates is among the most commonly
methods in preparing mesoporous Y zeolites although it is still very difficult due to the challenge
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of dispersing the organic templates into the viscous Y zeolite precursor gel.
Recently, block
copolymers, P123 and F127, are reported to be used as soft templates in the synthesis of
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mesoporous Y zeolite by Zhao et al.
And the obtained materials products are reported to
exhibit mesoporous structure according to N adsorptionꢀdesorption analysis. However, the
2
materials they synthesized lack the typical small Xꢀray diffraction peak of ordered mesopores in
the 2θ range of 0.3~5° and the mesopore diameter distributions of their products are relatively
wide. Mesoscale cationic surfactant cetyltrimethylammonium bromide (CTAB) micelles is also
reported to act as a soft template in the synthesis of mesoporous Y zeolites by Gu and Zhu et al.,
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through their elaborate design of surfactant micelle by adding a swelling agentꢀ
trimethylbenzene(TMB) to swell the micelle to match the size of Y zeolite seeds and a
cosolventꢀbutyl alcohol to fortify the charge density of the micelle, after that, the assemble of
surfactant micelle and Y zeolite seeds is promoted and mesoporous Y zeolite can be successfully
synthesized. However, their synthesis route is still very complex and the synthesis conditions
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still need fine control, and the mesopore diameter distributions of their products are also
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relatively wide. In our recent study , through elaborate design of SiO @CTAB micelle,
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mesoporous Y zeolites with narrow mesopore diameter distribution can be successfully
synthesized in relative wide synthesis conditions, moreover, the average mesopore diameters of
the synthesized samples can be controlled by varying the amount of swell agent and cosolvent.
To adjust the acidity property of Y zeolite, the modification of Y zeolite using different metals
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have been proposed in literatures to improve its catalytic performance.
Among all of the
investigated metals, gallium(Ga) is considered as the most appropriate one due to the fact that the
27
average electronegativity value of 1.59 for Ga is lower than the value for Al (1.714), thus after
Ga modification, some of the strong acid sites(SiꢀO(H)ꢀAl) are substituted by weak acid sites(Siꢀ
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O(H)Ga).
The selective conversion of bioꢀbased dihydroxyacetone over Ga modified Y
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zeolite via postꢀsynthetic alkalineꢀassisted galliation method reported by Dapsens et al., and
they concluded that after FAU zeolite modified by Ga, it is highly efficient for the isomerization
of dihydroxyacetone. Our previous study also show that Ga modification of Y zeolite can
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modulate the acidity property, after Ga modification, the morphology of active Ni promoted
MoS2 slabs on the corresponding catalyst changed and the sulfidation of Mo species enhanced.
More importantly, Ga modification of Y zeolite can promote the formation of NiMoS phase on
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the corresponding catalyst.
However, all these studies are based on Y zeolite and all the
reported Ga modification of Y zeolites are via postꢀmodification method, there is no literature
focused on direct synthesis of Ga containing mesoporous Y zeolites and 4,6ꢀDMDBT HDS
performance over the corresponding NiMo supported catalyst at present.
In this paper, we propose a direct synthesis route to conquer the difficulties in the research
10, 13, 16, 31
reported in the literatures
to obtain Ga containing mesoporous Y zeolites with different
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Ga/Al ratios on the basis of our previous study. All of the synthesized samples were
characterized by the means of XRD, N adsorptionꢀdesorption, SEM, TEM, pyridine adsorbed
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FTIR(PyꢀFTIR), XPS, Si MAS NMR, Ga MAS NMR and ICPꢀAES. Finally, all of the
synthesized materials were pelleted and crushed into 20~40 mesh particles and impregnated with
an aqueous solution of Ni and Mo salts to form the corresponding hydrotreating catalysts. After
sulfided, the catalysts were characterized by means of HRTEM, XPS and finally assessed by a
model diesel to investigate the effect of Ga content on the active phase morphology and catalytic
performances of the corresponding catalysts.
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. Experimental Section
.1 Synthesis of Ga containing Mesoporous Y zeolites
All the mesoporous samples constructed by the type Y zeolite unit with different gallium
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content were synthesized via a continuous synthesis procedure. Typically, calculated amounts of
sodium hydroxide (Beijing Modern Oriental Fine Chemical Co. Ltd., no less than 99.8 %),
sodium silica (28 wt % SiO , 9.1 wt % Na O, and 62.9 wt % H O), sodium aluminate (Guangfu
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Fine Chemical Co. Ltd. no less than 99.8 %), aluminum sulfate (Beijing Modern Oriental Fine
Chemical Co. Ltd., no less than 99.8 %), gallium nitride(Beijing Modern Oriental Fine Chemical
Co. Ltd., no less than 99.8 %) and deionized water were mixed under vigorous agitation at a
temperature controlled between 0 °C and 10 °C with a composition of 7.5:1:16:240
Na O/(Al O +Ga O )/SiO /H O. After that, the resulting gel was agitated vigorously at room
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temperature for approximately 2 h, aged at 30 °C for 20 h and then preꢀhydrothermally
crystallized at 65 °C for some time in a Teflon autoclave. After the resulting colloidal product
was cooled to room temperature, a solution of 5 g of CTAB (Aladdin, no less than 99.9 %), 1.0 g
of sodium hydroxide, 5 g of 1,3,5ꢀtrimethybenzene (TMB) (Aladdin, no less than 99.9 %) as a
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swelling agent, 10 mL of ethyl alcohol (Beijing Modern Oriental Fine Chemical Co. Ltd., no less
than 99.8 %) as a cosolvent and 10 g of tetraethylorthosilicate (TEOS) (Guangfu Fine Chemical
Co. Ltd. no less than 99.8 %) in 20 g of distilled water, which was preꢀselfꢀassembled for
approximately 30 min, was added into the colloidal product. The obtained mixture was then
stirred at room temperature for 2 h and hydrothermally crystallized at 95 °C for 24 h. Finally, the
crystallized mixture was hydrothermally treated at 105 °C for 2 h, and the solid product was
collected by filtration, drying at 120 °C for no less than 6 h, and calcined at 550 °C for 6 h. The
final obtained samples were labeled MYꢀxGa, where x stands for molar ratio of Ga O /Al O .
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The synthesized mesoporous Y zeolites with different Ga contents were ion exchanged with 1.0
M NH NO aqueous solution at 90 °C for about 4 h and then dried at 120 °C for 6 h and calcined
Preparation of catalysts
4
3
at 550 °C for 5 h. After 3 times ion exchange and calcination, H form mesoporous Y zeolites
with different Ga contents were obtained and the obtained samples were labeled HMYꢀxGa. The
HMYꢀxGa zeolites were then pelleted at 30 MPa for 0.5 h and crushed into 20~40 mesh. The
corresponding NiMo/HMYꢀxGa catalysts were prepared via an incipient wetness coꢀ
impregnation method with an aqueous solution of nickel nitrate hexahydrate and ammonium
heptamolybdate tetrahydrate, the wet catalysts were dried at 120 °C for 6 h after water was
vaporized at room temperature overnight, then calcined at 550 °C in a muffle furnace in air flow
for 5 h. The total contents of NiO in the catalysts was 4 wt.%, and the total MoO contents was
3
12 wt.% in all the prepared catalysts.
2.3
Characterization of materials
The synthesized MYꢀxGa zeolites were characterized by the powder Xꢀray diffraction(XRD)
on a PANalytical advance powder diffractometer with Cu Kα radiation (40 kV, 40 mA) in the 2θ
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interval of 5~35° and the wideꢀangle XRD patterns were recorded. The lowꢀangle XRD patterns
of the synthesized MYꢀxGa zeolites were also recorded on the mentioned PANalytical Advance
powder diffractometer in the 2θ interval of 0.3~5°. After the synthesized MYꢀxGa zeolites were
completely degassed at 300 °C for 4 h, a Micromeritics ASAP 2010 volumetric analyzer was
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used to measure the N adsorptionꢀdesorption isotherms of the synthesized MYꢀxGa zeolites at ꢀ
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196 °C。The BrunauerꢀEmmettꢀTeller (BET) equation were used in calculating the surface areas
in the relative pressure(p/p0) range of 0.05~0.3; and the BarrettꢀJoynerꢀHalenda (BJH) method
was used in calculating the total pore volumes and pore diameters according to the amount of N2
adsorbed at the relative pressure of 0.99; the Density Functional Theory method was used in
calculating the pore size distribution according to the adsorption isotherm and the tꢀplot method
was used in calculating the micropore volumes. The TꢀOꢀT linkages were determined by FTIR
analysis after the IR spectra were recorded on A Magna 560 FTꢀIR analyzer, and it was also used
in assessing the acidity properties of all the synthesized HMYꢀxGa zeolites by using pyridine as
probe molecules. The Brönsted acid sites (BAS) and Lewis acid sites (LAS) were quantified
ꢀ1
based on the intensities of the bands at 1543 and 1453 cm , respectively, and using the molar
3
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extinction coefficients in the literature.
Si MAS NMR and Ga MAS NMR spectra were
recorded on a Bruker ADVANCE Ⅲ 600 spectrometer according to the method we formerly
3
3
used.
Transmission electron microscopy (TEM) images of all the synthesized MYꢀxGa
zeolites and the HRTEM images of all the sulfide catalysts were taken on a Philips Tecnai G2
F20 instrument with an operating electron voltage of 200 kV. At least 400 slabs taken from
different parts of each catalyst were counted to determine the size distribution of molybdenum
sulfide crystallites. We calculated the average length and stack number of MoS slabs using
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, 34
equations reported elsewhere as follows
:
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ꢂ
∑ꢁ
n l
ꢃꢄ ꢁ ꢁ
ꢀ
Average slab length: L =
ꢅ
ꢂ
(1)
∑
nꢁ
ꢃꢄ
ꢁ
ꢂ
∑ꢁ
nꢁNꢁ
ꢃꢄ
ꢆ
Average stack number: N =
ꢅ
ꢂ
(2)
∑
nꢁ
ꢁꢃꢄ
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where l is the length of the slab, n is the number of slabs with length l , and N is the number of
ꢁ
ꢁ
ꢁ
ꢁ
layers in slab i. The MoS dispersion fꢇꢈ was also calculated using the following equation
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35
reported in the literature :
∑ꢁꢌ
MoꢉꢊꢋꢉꢅMo
6(n − 1)
ꢁ
ꢃꢄ
fꢇꢈ
=
=
ꢅ
(3)
ꢌ
ꢏ
ꢌꢈꢌꢍꢎ
∑
(
3n − 3n + 1
)
ꢁ
ꢃꢄ
ꢁ
ꢁ
where Moꢉꢊꢋꢉ is the number of Mo atoms located on the edges of NiMoS slabs, Moꢌꢈꢌꢍꢎ is the
total number of Mo atoms, n is the number of Mo atoms along one edge of a MoS slab
ꢁ
2
determined from its length (L = 3.2(2ni ꢀ 1)Å), and t is the total number of slabs determined by
at least 300 MoS slabs taken from HRTEM images of different catalysts.
2
A VG ESCA Lab 250 spectrometer was used in Xꢀray photoelectron spectroscopy (XPS)
analysis to determine the covalent state of Ni, Mo and Ga in the corresponding materials, prior to
which, the C 1s peak with binding energy of 284.6 eV was used to calibrate the binding energy
scale.
2.4
Catalyst evaluation
HDS reactions of 4,6ꢀDMDBT were performed on a fixedꢀbed reactor (8 mm inner diameter
and 200 mm in length) loaded with 1.0 g of catalyst with a particle size of 0.59ꢀ0.84 mm in
diameter diluted to 2 mL by quartz sand with the same particle size. Before the assessment, the
catalyst was presulfided using a solution of 6.0 mL CS dissolved in 500 mL of cyclohexane at
2
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20 °C and 4 MPa for 4 h in a H flow of 20 mL·min with a liquid hourly space velocity
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LHSV) of 10 h . After that, the reactor temperature was decreased to 290 °C, and a mixture of
.5 wt.% of 4,6ꢀDMDBT dissolved in cyclohexane was pumped to the reactor using an SZBꢀ2
doubleꢀpiston pump. The 4,6ꢀDMDBT HDS evaluations were conducted at temperature of
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290 °C, a total pressure of 4.0 MPa, weight hourly space velocity (WHSV) of 10.0 h to 120 h ,
and a H /oil ratio of 120 (v/v). The liquid reaction products were carefully collected after a full
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stabilization period of 5 h. Then, the collected products were immediately analyzed offꢀline on
an Agilent 4890D gas chromatograph equipped with a 60 m capillary Rtxꢀ1 column (0.25 mm,
ꢀ1
RESREK) with a N pressure of 0.3 MPa and flow velocity of 30 mL·min as the column
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ꢀ1
temperature increased from 50 °C to 320 °C with a heat rate of 15 °C min after staying at 50 °C
for 1 min. To further identify each of the compounds in the liquid products, a Finnigan Trace
GCꢀMS consisting of a Trace Ultral Gas Chromatograph (60 mꢀ0.25 mmꢀ0.5 ꢁm) capillary
column and an MS detector HP 5973 was used to analyze the collected products.
3. Results and Discussion
Wide angle Xꢀray diffraction charactrerization of the synthesized samples were performed to
determine whether the synthesized samples consisted of a mixture of Y crystals and amorphous
gallosilicates. Figure 1 displays the wide angle XRD patterns of the samples MYꢀ0Ga, MYꢀ
0
.25Ga, MYꢀ0.5Ga, MYꢀ1Ga and MYꢀ2Ga in the 2θ range of 5°~35°. The results show that all
the synthesized samples exhibit the typical diffraction characteristics of type Y zeolite,
suggesting the formation of intact Y crystals. Compared to sample MYꢀ0Ga, the intensities of all
the diffraction peaks of sample MYꢀ0.25Ga increased and those of samples MYꢀ0.5Ga, MYꢀ
1
Ga, MYꢀ2Ga decreased, indicating that the substitution of small amounts of Al (SO ) by
2 4 3
Ga(NO ) can promote the formation of intact Y crystals, but too much gallium species has a
3
3
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negative impact on the formation of intact Y crystals. This is possibly because of the average
2
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electronegativity value of 1.59 for Ga is lower than the value for Al (1.714), the interaction
between gallium species and silicon species is stronger than that between aluminum species and
silicon species, so it is easier for the formation of SiꢀOꢀGa bonds than the formation of SiꢀOꢀAl
bonds, thus appropriate amount of gallium can promote the formation of intact Y crystals. To
confirm the existence of Ga species on the synthesized samples, Ga 3d XPS spectra were
recorded and the deconvolution results were displayed in Figure S1. It shows that the Ga
contents over the synthesized samples increased with the Ga/Al ratio. And the relative
crystallinities of the synthesized samples were calculated by the same method we reported
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earlier and the results were summarized in Table 1. It can also be observed from Figure 1 and
Table 1 that the diffraction peaks attributed to Y zeolite decreases with the increase of gallium
species(MYꢀ2Ga < MYꢀ1Ga < MYꢀ0.5Ga < MYꢀ0.25Ga), suggesting that the crystallinity and
the integrity of Y zeolite decreases obviously with the increase of gallium contents. This can be
explained by the theory that GaO tetrahedron is bigger than AlO tetrahedron in size, thus GaO
4
4
4
tetrahedrons are less compatible to the even smaller SiO tetrahedrons in Y framework than AlO4
4
tetrahedrons. It can also be explained by the theory held by Fernandez and other researchers that
the substitution of framework atoms in zeolite skeleton would cause a disorder in both
36
amorphous and crystalline solids. However, in our case, due to the similarity between Al and
Ga and the fact that the Ga substitution degree is relative low, the intensities of the diffraction
peaks of are similar for samples MYꢀ0Ga, MYꢀ0.25Ga, MYꢀ0.5Ga and MYꢀ1Ga; for the case of
MYꢀ2Ga, the intensities of the diffraction peaks decreased obviously due to the disorderliness
caused by Ga species substitution of Al species.
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Theta, degree
Figure 1. Wideꢀangle XRD patterns of the synthesized MYꢀxGa samples with different Ga
contents: (a) MYꢀ0Ga, (b) MYꢀ0.25Ga, (c) MYꢀ0.5Ga, (d) MYꢀ1Ga, (e) MYꢀ2Ga.
e
d
c
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Theta, degree
Figure 2. Smallꢀangle XRD patterns of the synthesized MYꢀxGa zeolites with different Ga
contents: (a) MYꢀ0Ga, (b) MYꢀ0.25Ga, (c) MYꢀ0.5Ga, (d) MYꢀ1Ga, (e) MYꢀ2Ga.
To confirm the pore structure of the synthesized samples, small angle XRD measurements
were also carried out. Figure 2 shows the small angle XRD patterns of the samples MYꢀ0Ga,
MYꢀ0.25Ga, MYꢀ0.5Ga, MYꢀ1Ga and MYꢀ2Ga in the 2θ range of 0.3°~5°. All the patterns
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displayed in Figure 2 exhibit typical diffraction peaks with 2θ of about 0.8°, indicating the
existence of highly ordered mesopores in all the synthesized samples. With the increase of Ga/Al
ratio, the intensities of the diffraction peaks increased in the order of MYꢀ0Ga < MYꢀ0.25Ga <
MYꢀ0.5Ga < MYꢀ2Ga < MYꢀ1Ga, suggesting that appropriate amounts of gallium species(with
Ga/Al ratio of 1) can promote the formation of mesostructures in the synthesized samples to the
maximum extent.
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e
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.0
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Relative Pressure, p/p0
Figure 3. N adsorptionꢀdesorption isotherms of the synthesized MYꢀxGa zeolites with different
2
Ga contents: (a) MYꢀ0Ga, (b) MYꢀ0.25Ga, (c) MYꢀ0.5Ga, (d) MYꢀ1Ga, (e) MYꢀ2Ga.
The details of the pore distributions, pore volumes and surface areas of the synthesized were
determined by employing the N adsorptionꢀdesorption characterization. Figure 3 shows the N2
2
adsorptionꢀdesorption isotherms of samples MYꢀ0Ga, MYꢀ0.25Ga, MYꢀ0.5Ga, MYꢀ1Ga and
MYꢀ2Ga. The results clearly show that all the synthesized samples exhibit type Ⅳ curves with a
capillary condensation step at relative pressure between 0.5 and 0.8 with a type H2 hysteresis
loop. Figure 4 displays the pore size distribution of samples MYꢀ0Ga, MYꢀ0.25Ga, MYꢀ0.5Ga,
MYꢀ1Ga and MYꢀ2Ga. Clearly, all the samples exhibit narrow dispersed mesopores with pore
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diameter of 5~8 nm, and with the increase of Ga/Al ratio, the mesopore size slightly increased
from that of about 5.7 nm for sample MYꢀ0Ga to that of about 6.8 nm for sample MYꢀ0.5Ga;
then the mesopore size slightly decreased with the increase of Ga/Al ratio to that of about 6.2 nm
for sample MYꢀ2Ga(Table 1). It is possible because of the charge density of gallium containing
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Y crystals is higher than that of Y crystals composed only by SiO tetrahedrons and AlO4
4
tetrahedrons, and thus the interaction between gallium containing Y crystals and the pore
directing agent(cation micelle) is stronger than that between those Y crystals don’t contain
gallium and the pore directing agent; however, for the cases that the Ga/Al ratio is higher than
0
.5, there are too much GaO tetrahedrons in the Y crystals, leading to a unit cell expansion and
4
an increase in the crystalline size of Y crystals. In order to confirm that, the sizes and Zetaꢀ
potentials of the prepared mesoscale micelles and the MYꢀxGa precursors with different Ga/Al
ratios were tested and the results are summarized in Table S1. It shows that the diameter of the
mesoscale micelles is about 82.4 nm and its Zetaꢀpotential is about ꢀ12.8 mV. The sizes and the
Zetaꢀpotentials of the synthesized MYꢀxGa precursors are increase in the order of MYꢀ0Ga(33.9
nm, 15.3 mV) < MYꢀ0.25Ga(35.8 nm, 18.5 mV) < MYꢀ0.5Ga(36.4 nm, 20.2 mV) < MYꢀ
1Ga(45.6 nm, 21.6 mV) < MYꢀ2Ga(56.5 nm, 22.8 mV). The sizes of the synthesized MYꢀ0Ga,
MYꢀ0.25Ga and MYꢀ0.5Ga slightly increased, however, the Zetaꢀpotentials increased
profoundly; the sizes of the synthesized MYꢀ1Ga and MYꢀ2Ga profoundly increased while the
Zetaꢀpotentials slightly increased, and because the size and Zetaꢀpotential of the synthesized
TMB swelled SiO @CTAB is unchanged, thus the interaction between Y crystals and the pore
2
directing agent is weakened and both the mesopore diameter and mesopore volume decreased
with the increasing of Ga/Al ratio.
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b
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Pore diameter, nm
Figure 4. Mesopore diameter distribution of the synthesized MYꢀxGa zeolites with different
Ga/Al ratio: (a) MYꢀ0Ga, (b) MYꢀ0.25Ga, (c) MYꢀ0.5Ga, (d) MYꢀ1Ga, (e) MYꢀ2Ga.
To make a more detailed comparison of the synthesized samples, the surface areas and pore
volumes of the samples MYꢀ0Ga, MYꢀ0.25Ga, MYꢀ0.5Ga, MYꢀ1Ga and MYꢀ2Ga were
calculated and summarized in Table 1. Clearly, the surface areas of the synthesized samples
decreased with the increasing Ga/Al ratio but the mesopore surface areas of the samples followed
the order MYꢀ0Ga < MYꢀ0.25Ga < MYꢀ2Ga ~ MYꢀ0.5Ga < MYꢀ1Ga. Both the total pore
volumes and the mesopore volumes of the samples increase in the order of MYꢀ0Ga < MYꢀ2Ga
~ MYꢀ0.25Ga < MYꢀ1Ga < MYꢀ0.5Ga, which is in good agreement with the results observed
from small angle XRD. More interestingly, the total surface areas of the synthesized samples is
closely related to the mesopore volume of the samples: sample MYꢀ0.5Ga and sample MYꢀ1Ga
3
ꢀ1
exhibit the largest mesopore volume (up to about 0.45 cm ·g ) and the lowest surface area
2
ꢀ1
(
about 520 m ·g ), and sample MYꢀ0Ga exhibits the smallest mesopore volume (only about 0.3
3
ꢀ1
2
ꢀ1
cm ·g ) and the highest surface area (about 600 m ·g ). This is probably because of that on the
one hand, after the introduce of mesopores into Y crystals, it is much easier for the desorption of
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the N molecules adsorbed in the short narrow micropores, thus the calculated micropore volume
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and micropore surface decreased; on the other hand, the introduce of mesopores into Y crystals
has a negative impact on the formation of intact Y crystals(see XRD results) and thus lead to a
decrease in the amount of micropores, micropore volumes and micropore surface areas.
0
1
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Table 1
Textural properties of the synthesized mesoporous MYꢀxGa zeolites
a
b
c
Mesopore
SBET
Smeso
Vtotal
Vmeso
Samples
Cryst. (%)
2
ꢀ1
2
ꢀ1
3
ꢀ1
3
ꢀ1
(
m ·g ) (m ·g ) (cm ·g ) (cm ·g )
diameter（nm）
MYꢀ0Ga
MYꢀ0.25Ga
MYꢀ0.5Ga
MYꢀ1Ga
595
569
524
518
559
274
298
304
312
303
0.66
0.69
0.74
0.71
0.69
0.36
0.39
0.48
0.44
0.42
5.7
6.4
6.8
6.5
6.2
100
109
102
96
MYꢀ2Ga
88
a
b
c
Calculated by the BET method.
Obtained at a relative pressure of 0.99.
Calculated by the BJH method.
To further confirm the pore structure of sample MYꢀ0.5Ga, SEM and TEM analysis were
performed. Figure 5 shows the representative SEM and TEM images of sample MYꢀ0.5Ga. The
SEM image displayed in Figure 5 revealed that the morphology of the synthesized sample is
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octahedron like particles, which is the same with the morphology of Y crystals, also indicating
that Y crystals were formed and there is no sign of amorphous mesoporous particles. More
importantly, the particle size is smaller than 300 nm, suggesting the synthesized samples are
nanocrystalline zeolites. Compared with the SEM image of industrial Y zeolite(Figure S2), the
external surface of the synthesized sample is much rougher due to that the synthesized samples
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were obtained by the selfꢀassemble of mesostructured SiO @CTAB surfactant micelle and
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nanostructured Y microcrystals; moreover, the existence of mseopores also leads to an increase
in the roughness of the external surfaces of the synthesized samples. The TEM image displayed
in Figure 5 revealed that one dimension narrow dispersed mesostructures are formed. To confirm
whether the mesopore wall is crystallized or not, a more detailed TEM image was taken and
displayed in Figure S3. Both the lattice fringes(with intervals of about 0.25 nm) of Y crystals and
the mesostructures can be clearly observed in Figure S3, suggesting that the mesopore walls are
crystallized. These results are in consistent with those observed from smallꢀangle XRD and
wideꢀangle XRD.
Figure 5. Representative SEM (left) and TEM (right) images of sample MYꢀ0.5Ga.
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To confirm the TꢀOꢀT linkages(where T represents Si, Al or Ga) in the synthesized MYꢀxGa
series samples, FTIR spectra were recorded and the results are displayed in Figure S4 and the
ꢀ1
details of the FTIR results in the wavenumber range of 600 to 1500 cm are displayed in Figure
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. The IR band at wavenumber lower than 500 cm is associated to the TꢀO bending mode; the
ꢀ1
band at about 580 cm is associated to the structureꢀsensitive double fiveꢀring vibration; the
ꢀ1
weak band at around 850 cm is associated to the symmetric TꢀOꢀT stretching; the broad strong
ꢀ1
band at 900 to 1250 cm is associated to the asymmetric TꢀOꢀT stretching; the bands at 1380(the
ꢀ1
stronger one next to the oliveꢀgreen dash line) and 1400 cm (the weaker one at the oliveꢀgreen
ꢀ
dash line) are associated to the Al species and Ga species; the broad strong band above 3000 cm
1
27
is associated to the vibration of the hydroxyl species.
a
b
c
d
e
600
900
1200
1500
ꢀ1
Wavenumber, cm
ꢀ
Figure 6. FTIR spectra of the synthesized samples in the wavenumber range of 600 to 1500 cm
1
:
(a) MYꢀ0Ga, (b) MYꢀ0.25Ga, (c) MYꢀ0.5Ga, (d) MYꢀ1Ga, (e) MYꢀ2Ga.
The most profoundly change in Figure S4 before and after the introduction of gallium is
observed for the structureꢀsensitive double fiveꢀring vibration: with the increase of Ga content,
the intensity of this IR band decreases, indicating a decrease in the amount of structureꢀsensitive
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double fiveꢀring in the synthesized sample; for samples MYꢀ1Ga and MYꢀ2Ga, this IR band
disappeared, indicating the absence of structureꢀsensitive double fiveꢀring in these two samples.
ꢀ1
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The shape of the IR band above 3000 cm slightly changed after the introduction of Ga ,
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ꢀ1
especially the evidence that the intensity at about 3620cm become stronger, indicating the
existence of SiꢀOHꢀGa groups in the Ga containing samples. The framework vibrations(in the
ꢀ1
wavenumber range of 600 to 1300 cm ) of the synthesized samples were carefully analyzed,
there are two obvious changes in the FTIR spectra before and after the introduction of Ga
species: one is the bands ascribed to the symmetric TꢀOꢀT stretching shifted to lower
wavenumbers, indicating the formation of SiꢀOꢀGa linkages in the synthesized samples due to
that the wavenumber of the IR bands of SiꢀOꢀSi and SiꢀOꢀAl linkages are higher than that of Siꢀ
OꢀGa linkages; another obvious change in the FTIR spectra is the emerge of the vibration band at
ꢀ1
about 1020 cm (the band at the red dash line in Figure 6), which is higher than the IR band of
ꢀ1
GaꢀOꢀGa(often lower than 1000 cm ) and lower than the IR bands of SiꢀOꢀAl(the band at the
blue dash line in Figure 6) and SiꢀOꢀSi(the band at the purple dash line in Figure 6), which can
be taken as another evidence of the formation of GaꢀOꢀSi linkages. The decline in the intensities
ꢀ1
of the bands at about 1380 cm ascribed to the Al species with the increase(or incorporation) of
Ga species implying decreases in the amounts of Al species on the Y crystal framework, and the
ꢀ1
slightly increase in the intensities of the bands at about 1400 cm ascribed to the Ga
species(marked with olive dash line in Figure 6) indicating the amounts of Ga species increase
with the Ga/Al ratio, which is highly agree with the result observed from Ga 3d XPS(Figure S1).
Although both the Ga 3d XPS characterization and FTIR characterization provide enough
proofs for the successful incorporation of Ga onto Y zeolite or even the existence of framework
Ga species on the synthesized MYꢀxGa samples. However, whether all the incorporated Ga
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29
species are framework Ga species or not needs to be further confirmed, thus the Si MAS NMR
7
1
and Ga MAS NMR characterizations were carried out and the results are displayed in Figure 7
2
9
71
29
(
Si MAS NMR) and Figure S5 ( Ga MAS NMR). The Si MAS NMR spectra displayed in
0
1
2
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4
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0
Figure 7 of sample MYꢀ0Ga shows five signals: the weak peak at ꢀ113±0.5 ppm is ascribed to
the Si(0Me) groups; the medium peak at ꢀ105±0.5 ppm is ascribed to the Si(1Al) groups; the
strong peak at ꢀ98.5±0.5 ppm is ascribed to the Si(2Al) groups; another stronger peak at ꢀ
9
4.5±0.5 ppm is ascribed to the Si(3Al) groups; another medium peak at ꢀ89.5±0.5 ppm is
2
7, 36
29
ascribed to the Si(4Al) groups;
respectively. After incorporation of Ga species, the Si
MAS NMR signals of Si species shift to lower field and with the increasing of Ga/Al ratio, the
2
9
Si MAS NMR signals shift to even lower field. This phenomenon can be explained by the
theory that the electronegativity of Ga atoms is lower than that of Al atoms, thus the substitution
of Al species by Ga species causes an increase in the TꢀOꢀT angels at the replacement site which
has to be balanced by a decrease of neighboring TꢀOꢀT angels. More interestingly, the ratio of
Si(2Me) groups to Si(3Me) groups, which can be used to estimate the Si/Me ratio of the
synthesized MYꢀxGa samples, firstly increase with the Ga/Al ratio in the raw materials and the
highest value was observed over sample MYꢀ0.5Ga, then it decrease with the Ga/Al ratio in the
raw materials, indicating that sample MYꢀ0.5Ga is the most stable one among the synthesized
MYꢀxGa samples since it is concerned that zeolite crystals with higher Si/Me ratios are more
stable. The result agrees well with those(the relative crystallinities of the synthesized samples in
Table 1) observed from wide angel XRD characterization. For sample MYꢀ2Ga, a weak signal at
about ꢀ77.5 ppm which is ascribed to the Si(4Ga) groups can been clearly observed, indicating
7
1
the Si(4Ga) linkages can also be formed on the synthesized MYꢀxGa samples. The Ga MAS
NMR spectra displayed in Figure S5 clearly show that there is only one main signal for all of the
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synthesized MYꢀxGa(x≠0) at 172 ppm ascribed for Ga(4Si) groups, indicating that all the
incorporated Ga species are on the zeolite framework.
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Si(4Ga)
e
Si(0Me)
d
Si(3Me)
c
Si(2Me)
Si(4Me)
b
Si(4Al)
Si(1Al)
a
-50
-60
-70
-80
-90
-100 -110 -120 -130 -140 -150
Chemical Shift, ppm
2
9
Figure 7. Si MAS NMR spectra of the synthesized MYꢀxGa samples with different Ga/Al
ratio: (a) MYꢀ0Ga, (b) MYꢀ0.25Ga, (c) MYꢀ0.5Ga, (d) MYꢀ1Ga, (e) MYꢀ2Ga.
A
BAS
B
LAS
LAS
BAS
e
d
c
e
d
c
b
a
b
a
1400
1450
1500
1550
1400
1450
1500
1550
ꢀ1
Wavenumber, cmꢀ1
Wavenumber, cm
Figure 8. FTIR spectra of pyridine adsorbed on the synthesized HMYꢀxGa samples with
different Ga/Al ratio: (a) HMYꢀ0Ga, (b) HMYꢀ0.25Ga, (c) HMYꢀ0.5Ga, (d) HMYꢀ1Ga, (e)
HMYꢀ2Ga; (A) after pyridine desorbed at 200 °C, (B) after pyridine desorbed at 350 °C.
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Table 2
Amounts of Brönsted and Lewis acid sites determined by pyridineꢀFTIR of the HMYꢀxGa
samples
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o
ꢀ1
o
ꢀ1
2
00 C, ꢁmol·g
350 C, ꢁmol·g
Samples
Total
BAS/LAS
LAS BAS LAS+BAS LAS BAS LAS+BAS
HMYꢀ0Ga
HMYꢀ0.25Ga
HMYꢀ0.5Ga
HMYꢀ1Ga
224 268
250 248
262 228
278 221
288 217
492
498
490
499
505
112 126
238
208
198
204
207
730
706
688
703
712
1.17
1.04
0.89
0.80
0.74
96
112
96
102
112
121
92
HMYꢀ2Ga
86
Since the acidity plays a very important role in the active phase morphology and activity of the
bifunctional hydrotreating catalysts. And in order to differentiate the acid types, quantify the
amounts of each types of acid sites and investigate the acid strength of the synthesized HMYꢀ
xGa samples, the FTIR spectra of the pyridine adsorbed(PyꢀFTIR) on the synthesized HMYꢀxGa
samples with different Ga/Al ratios were recorded at 200 °C and 350 °C, respectively, and the
ꢀ1
spectra was displayed in Figure 8. The vibration peak with wavenumber of about 1543 cm is
ascribed to the pyridine ions adsorbed on the Brönsted acid sites(BAS) and the vibration peak
ꢀ1
with wavenumber of about 1453 cm is ascribed to the pyridine combined with the Lewis acid
6
, 37
sites(LAS), respectively.
Both the amounts of BAS and LAS with different acid strength
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were quantified according to the PyꢀFTIR results and the details are summarized in Table 2. The
results show that the total amounts of acid sites of all the synthesized materials, which were
quantified by the pyridine adsorption FTIR spectra after degassing at 200 °C, are similar: with
the introduce of low content of Ga to the synthetic system, the total amount of acid sites slightly
decreased, with the increasing of the Ga content, this variation trend reversed. The amounts of
medium and strong acid sites, which were quantified by the pyridine adsorption FTIR spectra
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ꢀ1
after degassing at 350 °C, are varied with the Ga/Al ratio: HMYꢀ0.5Ga(198 ꢁmol·g ) < HMYꢀ
ꢀ1
ꢀ1
ꢀ1
1Ga(204 ꢁmol·g ) ≈ HMYꢀ2Ga(207 ꢁmol·g ) ≈ HMYꢀ0.25Ga(208 ꢁmol·g ) < HMYꢀ0Ga(238
ꢀ1
ꢀ1
ꢁ
mol·g ). Sample HMYꢀ0Ga exhibits the lowest amounts of LAS(weak: 224 ꢁmol·g ; medium
ꢀ1
ꢀ1
and strong: 112 ꢁmol·g ) and the largest amounts of BAS(weak: 268 ꢁmol·g ; medium and
ꢀ1
strong: 126 ꢁmol·g ), after the incorporation of Ga into the framework of the synthesized
ꢀ1
samples, the amounts of weak LAS increased from 224 ꢁmol·g of sample HMYꢀ0Ga to 278
ꢀ
1
ꢁ
ꢁ
mol·g of sample HMYꢀ2Ga and the amounts of strong LAS straightly decreased from 112
ꢀ1
ꢀ1
mol·g of sample HMYꢀ0Ga to 96 ꢁmol·g of HMYꢀ0.25Ga, however, with the increase of the
Ga/Al ratio, the amounts of strong LAS slightly increased. Both the amounts of weak BAS and
ꢀ1
ꢀ1
strong BAS decreased in the following order: HMYꢀ0Ga(268 ꢁmol·g ; 126 ꢁmol·g ) > HMYꢀ
ꢀ1
ꢀ1
ꢀ1
ꢀ1
0
.25Ga(248 ꢁmol·g ; 112 ꢁmol·g ) > HMYꢀ0.5Ga(228 ꢁmol·g ; 96 ꢁmol·g ) > HMYꢀ
ꢀ1
ꢀ1
ꢀ1
ꢀ1
1
Ga(221 ꢁmol·g ; 92 ꢁmol·g ) > HMYꢀ2Ga(217 ꢁmol·g ; 86 ꢁmol·g ). The ratios of the
amount of total BAS to the amount of total LAS(BAS/LAS) were also calculated and the results
are also summarized in Table 2, it clearly shows that the BAS/LAS ratios decrease with the
Ga/Al ratios: HMYꢀ0Ga(1.17) > HMYꢀ0.25Ga(1.04) > HMYꢀ0.5Ga(0.89) > HMYꢀ1Ga(0.80) >
HMYꢀ2Ga(0.74). All these results can be explained by the theory that the acid sites are only
generated at the Al or Ga sites in the zeolite frameworks, and the electronegativity value of 1.59
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for Ga is lower than the value for Al (1.71), implying GaꢀOHꢀSi and GaꢀOH groups(which are
+
correlated to BAS) are more inclined to form Ga caves(which are correlated to LAS) through
dehydration after calcination than AlꢀOHꢀSi and AlꢀOH groups(which are correlated to BAS) to
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form Al caves(which are correlated to LAS). Additionally, the existence of both nonframework
Al species and nonframework Ga species(confirmed by the FTIR and NMR results) lead to
increases in the amounts of LAS, which results in decreases in the BAS/LAS ratios.
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Figure 9. Representative HRTEM images of the sulfided NiMo/HMYꢀxGa series catalysts: (a)
NiMo/HMYꢀ0Ga, (b) NiMo/HMYꢀ0.25Ga, (c) NiMo/HMYꢀ0.5Ga, (d) NiMo/HMYꢀ1Ga, (e)
NiMo/HMYꢀ2Ga.
The morphology of the active metal sulfides is considered to be very important for the activity
3
8
of the bifunctional HDS catalysts, especially for the activity of the catalysts in removal of
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9
highly refractory organosulfides such as 4,6ꢀDMDBT. HRTEM characterizations of the sulfide
NiMo/HMYꢀxGa series catalysts were performed to visualize the morphologies of the NiMoS
active phase and to compare the dispersion of active metals. Figure 7 shows the representative
HRTEM images of the sulfide NiMo/HMYꢀxGa series catalysts. The statistical stacking layer
2
numbers distribution and the slab length distribution of MoS crystals by counting on 400 MoS2
crystals are presented in Figure S6 and Figure S7 and the statistical results are summarized in
Table 3. It is clearly show that before the incorporation of Ga, there are large amounts of MoS2
crystals with low stacking numbers(1 to 2 layers), thus the average stacking number for catalyst
NiMo/HMYꢀ0Ga is only 2.4; after incorporation of small amount of Ga into the zeolite
framework, the amounts of MoS crystals with low stacking numbers sharply decreased, the
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Table 3
Average length, layer number and fMo of Ni promoted MoS crystals for the NiMo/HMYꢀxGa
2
series catalysts
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Catalysts
Average length (nm)
Average stacking number
fMo
NiMo/HMYꢀ0Ga
NiMo/HMYꢀ0.25Ga
NiMo/HMYꢀ0.5Ga
NiMo/HMYꢀ1Ga
NiMo/HMYꢀ2Ga
4.9
4.4
4.2
4.1
3.9
2.4
3.3
3.6
3.8
3.9
0.26
0.29
0.30
0.31
0.31
stacking number distribution become narrowed and the average stacking number increased to
.3. With the increase of Ga/Al ratio, the stacking number distribution become more narrowed
3
and the main stacking number of MoS crystals firstly changed from 3 layers(NiMo/HMYꢀ
2
0.25Ga) to 3~4 layers(NiMo/HMYꢀ0.5Ga), and then to 4 layers(both NiMo/HMYꢀ1Ga and
NiMo/HMYꢀ2Ga); and the average stacking number slightly increased from 3.3(NiMo/HMYꢀ
0.25Ga) to 3.9(NiMo/HMYꢀ2Ga). The slab lengths also change with the Ga/Al ratio: After the
incorporation of Ga, the slab length distribution of MoS crystals also become narrowedꢀthe
2
numbers of long MoS crystals decreased and the proportion of MoS crystals with slab length in
2
2
the range of 3~5 nm increased; the average slab length of the MoS crystals firstly sharply
2
decrease from 4.9 nm(NiMo/HMYꢀ0Ga) to 4.4 nm(NiMo/HMYꢀ0.25Ga), then with the increase
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of Ga/Al ratio, it slightly declined from 4.4 nm(NiMo/HMYꢀ0.25Ga) to 3.9 nm(NiMo/HMYꢀ
2
Ga). All these changes are beneficial for the formation of more corner and edge Mo atoms
which is evidenced by the fMo value increased in the following order: NiMo/HMYꢀ0Ga(0.26) <
NiMo/HMYꢀ0.25Ga(0.29) NiMo/HMYꢀ0.5Ga(0.30) NiMo/HMYꢀ1Ga(0.31) and
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<
<
NiMo/HMYꢀ2Ga(0.31), which are considered to be necessary for the formation of the highly
active “Type II NiMoS” active phases.
The covalent states and sulfidation degree of active metals also play important roles in the
catalytic activities of the bifunctional HDS catalysts. In order to observe the changes in the
covalent states, sulfidation degrees of the active metals and investigate how the Ga species affect
the active phase, the sulfide NiMo/HMYꢀxGa series catalysts were characterized by XꢀRay
photoelectron spectroscopy(XPS) and the Ni 2p XPS spectra and their deconvolution results and
the Mo 3d XPS spectra and their deconvolution results are displayed in Figure 10 and Figure S8,
the deconvolution details are summarized in Table 4. The fitting standard for each Mo species is
4
+
as follows: the binding energies of the Mo (MoS species) are in the ranges of 227.5 to 227.9
2
eV for Mo 3d5/2 level and 230.6 to 231.0 eV for Mo 3d3/2 level, respectively; while those for the
5
+
Mo (MoOS species) are in the ranges of 228.4 to 228.7 eV for Mo 3d level and 234.7 to 234.8
5/2
4
0
6+
eV for Mo 3d3/2 level, respectively ; and for the Mo (MoO species), the binding energies are
3
230.2±0.2 eV for Mo 3d5/2 level and 234.7±0.5 eV for Mo 3d3/2 level, respectively. The Mo
4
+
sulfidation degree(Mosulfidation), defined as the percentage of Mo /Mototal, was calculated and is
also summarized in Table 4. The fitting standard for Ni species is as follows: the binding energy
2
+
of Ni (NiO) species is 857.5±0.2 eV, it is 853.3±0.1 eV for NiS species and 855.3±0.2 eV for
x
7
NiMoS species. The sulfidation degrees of Ni species(Nisulfidation), defined as the percentage of
(
NiS +NiMoS)/Nitotal, were also calculated and the details are summarized in Table 4. It is
x
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clearly show that after incorporation of small amount of Ga, the sulfidation degrees of both Ni
and Mo species increase profoundly: the Mosulfidation increase in the following order:
NiMo/HMYꢀ0Ga(82%) < NiMo/HMYꢀ0.25Ga(86%) < NiMo/HMYꢀ2Ga(88%) ≈ NiMo/HMYꢀ
0
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0
.5Ga(89%) ≈ NiMo/HMYꢀ1Ga(90%); and the Nisulfidation increase in the following order:
NiMo/HMYꢀ2Ga(86%) < NiMo/HMYꢀ0Ga(88%) < NiMo/HMYꢀ0.25Ga(91%) < NiMo/HMYꢀ
.5Ga(94%) ≈ NiMo/HMYꢀ1Ga(95%). Indicating that proper amount of Ga can promote the
0
sulfidation of both Ni and Mo species but superfluous Ga species would prevent the sulfidation
7
of Mo precursors. It can be explained by the theory proposed in our previous work : the strong
interaction between the active metals and the support often through the formation of MoꢀOꢀAl
linkages and the formation of NiAlO species, after the incorporation of small amount of Ga
4
species, the Al species in the synthesized samples declined, thus the probability for the formation
of both MoꢀOꢀAl linkages and nickel aluminate species is lower and results in the enhanced
sulfidation degrees of both Ni and Mo species. For catalyst NiMo/HMYꢀ2Ga, the sulfidation
degree of both Ni and Mo species sharply declined compared to those for catalyst NiMo/HMYꢀ
41
1
Ga. It is possible by employing the theory proposed by Johnson and coauthors that the active
metal atoms are inclined to interact with the acid sites, especially with those strong LAS via Mꢀ
OꢀL linkages(where M represents the metal atoms, L represents the strong LAS). In our case,
with the increase of Ga/Al ratio, the amount of nonframework Ga species increases(confirmed by
the FTIR results and NMR results), which lead to an increase in the amount of strong
LAS(confirmed by the PyꢀFTIR results), and thus strong MoꢀOꢀGa linkages or nickel gallium
+
spinel species might be formed when the density of the strong Ga caves(strong LAS) is high
enough, which results in a decline in the sulfidation degree of both Ni and Mo species. The most
profound changes in the deconvolution results of Ni 2p spectra is the proportion of NiMoS
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phase: NiMo/HMYꢀ0Ga(48%) < NiMo/HMYꢀ2Ga(54%) ≈ NiMo/HMYꢀ0.25Ga(54%) <
NiMo/HMYꢀ0.5Ga(76%) < NiMo/HMYꢀ1Ga(88%). Indicating that incorporation of proper
amount of Ga species can promote more Ni atoms doped into the MoS crystals to form the real
2
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NiMoS active phase, which is highly in accordance with the results reported elsewhere.
Table 4
XPS characterization results of the sulfide NiMo supported catalysts
a
b
2+
Catalysts
Mosulfidation (%) Nisulfidation (%) NiSx (%) NiMoS (%) Ni (%)
NiMo/HMYꢀ0Ga
NiMo/HMYꢀ0.25Ga
NiMo/HMYꢀ0.5Ga
NiMo/HMYꢀ1Ga
NiMo/HMYꢀ2Ga
82
86
89
90
88
88
91
94
94
86
40
36
18
6
48
55
76
88
54
12
9
6
6
32
14
a
4+
4+
5+
6+
Mosulfidation defines as Mo /(Mo +Mo +Mo )*100%.
b
2+
Nisulfidation defines as (NiS +NiMoS)/(NiS +NiMoS+Ni )*100%.
x
x
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