Synthesis of NiMo Catalysts Supported on Gallium-Containing

Subscriber access provided by UNIV OF ESSEX

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 Downloaded from http://pubs.acs.org on October 3, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Synthesis of NiMo Catalysts Supported on Gallium Containing Mesoporous Y Zeolites with Different Gallium Contents and Their High Activities in the Hydrodesulfurization of 4,6Dimethyldibenzothiophene 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; 4,6-DMDBT HDS; NiMoS active phase; catalytic activity; HDS pathway.

ABSTRACT

1

ACS Paragon Plus Environment

ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 45

Mesoporous MY-xGa zeolites exhibit both crystallized pore walls and narrow dispersed mesopores with different Ga content were successfully synthesized. The synthesized samples were characterized by XRD, N2 adsorption desorption isotherms, SEM, TEM, XPS, FTIR, MAS NMR,

71

29

Si

Ga 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 non-framework 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 incipient wetness co-impregnation 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 4,6-DMDBT HDS reaction were assessed and the collected products were analyzed by GC and GC-MS methods. Catalyst NiMo/HMY-0.5Ga 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, 4-MDBT, DBT and BP were observed and identified as the products of 4,6DMDBT HDS reaction which were designated as the demethylation pathway(DM) for 4,6DMDBT HDS reaction. Finally, a reaction network including DDS, HYD, ISO and DM pathways for 4,6-DMDBT HDS reaction over catalyst NiMo/HMY-0.5Ga was proposed.

2


Page 3 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

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 world,

1, 2

especially for certain of the major oil consumption regions, it is strictly limited to

values as low as 10 ppm.

3, 4

To reach such a low level, complete removal of highly refractory

organosulfur compounds like 4,6-DMDBT 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 4,6-DMDBT which is among the most common organosulfur compounds in inferior diesel,

5, 6

thus it remains difficult for ultra-deep

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 4,6-DMDBT into less refractory organosulfur compounds like 3,6-DMDBT and 3,7-DMDBT.

7

Y zeolite is considered as the best candidate due to its microporosity is

comparable to the size of 4,6-DMDBT molecules, its controllable acidity and its superior hydrogen transfer ability.

1, 8

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 positions to eliminate the hindrance.

9

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 FCC diesel hydrodesulfurization is 2 h-1, which is too fast for the 4,6-DMDBT 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,

3


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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. 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 review articles.

10-17

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 of dispersing the organic templates into the viscous Y zeolite precursor gel.10, 13 Recently, block copolymers, P123 and F127, are reported to be used as soft templates in the synthesis of mesoporous Y zeolite by Zhao et al.

18, 19

And the obtained materials products are reported to

exhibit mesoporous structure according to N2 adsorption-desorption analysis. However, the materials they synthesized lack the typical small X-ray 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., 10

through their elaborate design of surfactant micelle by adding a swelling agent-

trimethylbenzene(TMB) to swell the micelle to match the size of Y zeolite seeds and a cosolvent-butyl 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

4


Page 4 of 45

Page 5 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

still need fine control, and the mesopore diameter distributions of their products are also relatively wide. In our recent study20, through elaborate design of SiO2@CTAB micelle, 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 have been proposed in literatures to improve its catalytic performance.

21-26

Among all of the

investigated metals, gallium(Ga) is considered as the most appropriate one due to the fact that the average electronegativity value of 1.59 for Ga is lower than the value for Al (1.714),

27

thus after

Ga modification, some of the strong acid sites(Si-O(H)-Al) are substituted by weak acid sites(SiO(H)Ga).

7, 28

The selective conversion of bio-based dihydroxyacetone over Ga modified Y

zeolite via post-synthetic alkaline-assisted galliation method reported by Dapsens et al.,

29

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 modulate the acidity property,

7

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 the corresponding catalyst.

30

However, all these studies are based on Y zeolite and all the

reported Ga modification of Y zeolites are via post-modification method, there is no literature focused on direct synthesis of Ga containing mesoporous Y zeolites and 4,6-DMDBT 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 reported in the literatures10, 13, 16, 31 to obtain Ga containing mesoporous Y zeolites with different

5


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Ga/Al ratios on the basis of our previous study. All of the synthesized samples were characterized by the means of XRD, N2 adsorption-desorption, SEM, TEM, pyridine adsorbed FTIR(Py-FTIR), XPS,

29

Si MAS NMR,

71

Ga MAS NMR and ICP-AES. 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. 2. Experimental Section 2.1

Synthesis of Ga containing Mesoporous Y zeolites

All the mesoporous samples constructed by the type Y zeolite unit with different gallium 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 % SiO2, 9.1 wt % Na2O, and 62.9 wt % H2O), sodium aluminate (Guangfu 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 Na2O/(Al2O3+Ga2O3)/SiO2/H2O. After that, the resulting gel was agitated vigorously at room temperature for approximately 2 h, aged at 30 °C for 20 h and then pre-hydrothermally 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 1,3,5-trimethybenzene (TMB) (Aladdin, no less than 99.9 %) as a

6


Page 6 of 45

Page 7 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

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 pre-self-assembled 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 MY-xGa, where x stands for molar ratio of Ga2O3/Al2O3. 2.2

Preparation of catalysts

The synthesized mesoporous Y zeolites with different Ga contents were ion exchanged with 1.0 M NH4NO3 aqueous solution at 90 °C for about 4 h and then dried at 120 °C for 6 h and calcined 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 HMY-xGa. The HMY-xGa zeolites were then pelleted at 30 MPa for 0.5 h and crushed into 20~40 mesh. The corresponding NiMo/HMY-xGa catalysts were prepared via an incipient wetness coimpregnation 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 MoO3 contents was 12 wt.% in all the prepared catalysts. 2.3

Characterization of materials The synthesized MY-xGa zeolites were characterized by the powder X-ray diffraction(XRD)

on a PANalytical advance powder diffractometer with Cu Kα radiation (40 kV, 40 mA) in the 2θ

7


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 45

interval of 5~35° and the wide-angle XRD patterns were recorded. The low-angle XRD patterns of the synthesized MY-xGa zeolites were also recorded on the mentioned PANalytical Advance powder diffractometer in the 2θ interval of 0.3~5°. After the synthesized MY-xGa zeolites were completely degassed at 300 °C for 4 h, a Micromeritics ASAP 2010 volumetric analyzer was used to measure the N2 adsorption-desorption isotherms of the synthesized MY-xGa zeolites at 196 °C。The Brunauer-Emmett-Teller (BET) equation were used in calculating the surface areas in the relative pressure(p/p0) range of 0.05~0.3; and the Barrett-Joyner-Halenda (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 t-plot method was used in calculating the micropore volumes. The T-O-T linkages were determined by FTIR analysis after the IR spectra were recorded on A Magna 560 FT-IR analyzer, and it was also used in assessing the acidity properties of all the synthesized HMY-xGa zeolites by using pyridine as probe molecules. The Brönsted acid sites (BAS) and Lewis acid sites (LAS) were quantified based on the intensities of the bands at 1543 and 1453 cm-1, respectively, and using the molar extinction coefficients in the literature.

32 29

Si MAS NMR and

71

Ga MAS NMR spectra were

recorded on a Bruker ADVANCE Ⅲ 600 spectrometer according to the method we formerly used.

33

Transmission electron microscopy (TEM) images of all the synthesized MY-xGa

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 MoS2 slabs using equations reported elsewhere as follows6, 34:

8


Page 9 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

∑ nl Average slab length: L = ∑ n

= ∑ n N Average stack number: N ∑ n

(1)

(2)

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 MoS2 dispersion f was also calculated using the following equation reported in the literature35: f =

Mo ∑ 6(n − 1)

Mo =

(3) ∑ (3n − 3n + 1)

where Mo is the number of Mo atoms located on the edges of NiMoS slabs, Mo is the total number of Mo atoms, n is the number of Mo atoms along one edge of a MoS2 slab determined from its length (L = 3.2(2ni - 1)Å), and t is the total number of slabs determined by at least 300 MoS2 slabs taken from HRTEM images of different catalysts. A VG ESCA Lab 250 spectrometer was used in X-ray 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 4,6-DMDBT were performed on a fixed-bed reactor (8 mm inner diameter and 200 mm in length) loaded with 1.0 g of catalyst with a particle size of 0.59-0.84 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 CS2 dissolved in 500 mL of cyclohexane at 9


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 45

320 °C and 4 MPa for 4 h in a H2 flow of 20 mL·min-1 with a liquid hourly space velocity (LHSV) of 10 h-1. After that, the reactor temperature was decreased to 290 °C, and a mixture of 0.5 wt.% of 4,6-DMDBT dissolved in cyclohexane was pumped to the reactor using an SZB-2 double-piston pump. The 4,6-DMDBT HDS evaluations were conducted at temperature of 290 °C, a total pressure of 4.0 MPa, weight hourly space velocity (WHSV) of 10.0 h-1 to 120 h-1, and a H2/oil ratio of 120 (v/v). The liquid reaction products were carefully collected after a full stabilization period of 5 h. Then, the collected products were immediately analyzed off-line on an Agilent 4890D gas chromatograph equipped with a 60 m capillary Rtx-1 column (0.25 mm, RESREK) with a N2 pressure of 0.3 MPa and flow velocity of 30 mL·min-1 as the column temperature increased from 50 °C to 320 °C with a heat rate of 15 °C min-1 after staying at 50 °C for 1 min. To further identify each of the compounds in the liquid products, a Finnigan Trace GC-MS consisting of a Trace Ultral Gas Chromatograph (60 m-0.25 mm-0.5 µm) capillary column and an MS detector HP 5973 was used to analyze the collected products. 3. Results and Discussion Wide angle X-ray 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 MY-0Ga, MY0.25Ga, MY-0.5Ga, MY-1Ga and MY-2Ga 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 MY-0Ga, the intensities of all the diffraction peaks of sample MY-0.25Ga increased and those of samples MY-0.5Ga, MY1Ga, MY-2Ga decreased, indicating that the substitution of small amounts of Al2(SO4)3 by Ga(NO3)3 can promote the formation of intact Y crystals, but too much gallium species has a

10


Page 11 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

negative impact on the formation of intact Y crystals. This is possibly because of the average electronegativity value of 1.59 for Ga is lower than the value for Al (1.714),

27

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 Si-O-Ga bonds than the formation of Si-O-Al 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 earlier7 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(MY-2Ga < MY-1Ga < MY-0.5Ga < MY-0.25Ga), 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 GaO4 tetrahedron is bigger than AlO4 tetrahedron in size, thus GaO4 tetrahedrons are less compatible to the even smaller SiO4 tetrahedrons in Y framework than AlO4 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 amorphous and crystalline solids.

36

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 MY-0Ga, MY-0.25Ga, MY-0.5Ga and MY-1Ga; for the case of MY-2Ga, the intensities of the diffraction peaks decreased obviously due to the disorderliness caused by Ga species substitution of Al species.

11


ACS Catalysis

Relative Intensity, a.u.

e

d

c

b

a

5

10

15

20

25

30

35

2 Theta, degree

Figure 1. Wide-angle XRD patterns of the synthesized MY-xGa samples with different Ga contents: (a) MY-0Ga, (b) MY-0.25Ga, (c) MY-0.5Ga, (d) MY-1Ga, (e) MY-2Ga.

e


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

d

c

b a

0

1

2

3

4

5

2 Theta, degree

Figure 2. Small-angle XRD patterns of the synthesized MY-xGa zeolites with different Ga contents: (a) MY-0Ga, (b) MY-0.25Ga, (c) MY-0.5Ga, (d) MY-1Ga, (e) MY-2Ga. 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 MY-0Ga, MY-0.25Ga, MY-0.5Ga, MY-1Ga and MY-2Ga in the 2θ range of 0.3°~5°. All the patterns 12


Page 12 of 45

Page 13 of 45

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 MY-0Ga < MY-0.25Ga < MY-0.5Ga < MY-2Ga < MY-1Ga, 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.

e 3 -1

d

Relative Pore Volume, cm g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

c

b

a

0.0

0.4

0.8

Relative Pressure, p/p0

Figure 3. N2 adsorption-desorption isotherms of the synthesized MY-xGa zeolites with different Ga contents: (a) MY-0Ga, (b) MY-0.25Ga, (c) MY-0.5Ga, (d) MY-1Ga, (e) MY-2Ga. The details of the pore distributions, pore volumes and surface areas of the synthesized were determined by employing the N2 adsorption-desorption characterization. Figure 3 shows the N2 adsorption-desorption isotherms of samples MY-0Ga, MY-0.25Ga, MY-0.5Ga, MY-1Ga and MY-2Ga. 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 MY-0Ga, MY-0.25Ga, MY-0.5Ga, MY-1Ga and MY-2Ga. Clearly, all the samples exhibit narrow dispersed mesopores with pore 13


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 45

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 MY-0Ga to that of about 6.8 nm for sample MY-0.5Ga; then the mesopore size slightly decreased with the increase of Ga/Al ratio to that of about 6.2 nm for sample MY-2Ga(Table 1). It is possible because of the charge density of gallium containing Y crystals is higher than that of Y crystals composed only by SiO4 tetrahedrons and AlO4 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 GaO4 tetrahedrons in the Y crystals, leading to a unit cell expansion and an increase in the crystalline size of Y crystals. In order to confirm that, the sizes and Zetapotentials of the prepared mesoscale micelles and the MY-xGa 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 Zeta-potential is about -12.8 mV. The sizes and the Zeta-potentials of the synthesized MY-xGa precursors are increase in the order of MY-0Ga(33.9 nm, 15.3 mV) < MY-0.25Ga(35.8 nm, 18.5 mV) < MY-0.5Ga(36.4 nm, 20.2 mV) < MY1Ga(45.6 nm, 21.6 mV) < MY-2Ga(56.5 nm, 22.8 mV). The sizes of the synthesized MY-0Ga, MY-0.25Ga and MY-0.5Ga slightly increased, however, the Zeta-potentials increased profoundly; the sizes of the synthesized MY-1Ga and MY-2Ga profoundly increased while the Zeta-potentials slightly increased, and because the size and Zeta-potential of the synthesized TMB swelled SiO2@CTAB is unchanged, thus the interaction between Y crystals and the pore directing agent is weakened and both the mesopore diameter and mesopore volume decreased with the increasing of Ga/Al ratio.

14


Page 15 of 45

3 -1

e

Pore Volume, cm g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

d

c

b

a

0

10

20

Pore diameter, nm

Figure 4. Mesopore diameter distribution of the synthesized MY-xGa zeolites with different Ga/Al ratio: (a) MY-0Ga, (b) MY-0.25Ga, (c) MY-0.5Ga, (d) MY-1Ga, (e) MY-2Ga. To make a more detailed comparison of the synthesized samples, the surface areas and pore volumes of the samples MY-0Ga, MY-0.25Ga, MY-0.5Ga, MY-1Ga and MY-2Ga 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 MY-0Ga < MY-0.25Ga < MY-2Ga ~ MY-0.5Ga < MY-1Ga. Both the total pore volumes and the mesopore volumes of the samples increase in the order of MY-0Ga < MY-2Ga ~ MY-0.25Ga < MY-1Ga < MY-0.5Ga, 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 MY-0.5Ga and sample MY-1Ga exhibit the largest mesopore volume (up to about 0.45 cm3·g-1) and the lowest surface area (about 520 m2·g-1), and sample MY-0Ga exhibits the smallest mesopore volume (only about 0.3 cm3·g-1) and the highest surface area (about 600 m2·g-1). 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

15


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 45

the N2 molecules adsorbed in the short narrow micropores, thus the calculated micropore volume 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. Table 1 Textural properties of the synthesized mesoporous MY-xGa zeolites SBETa

Smeso

Vtotalb

Vmesoc

Mesopore

3

3

Samples

Cryst. (%) 2

-1

2

-1

-1

-1

(m ·g )

(m ·g )

(cm ·g )

(cm ·g )

diameter（nm）

MY-0Ga

595

274

0.66

0.36

5.7

100

MY-0.25Ga

569

298

0.69

0.39

6.4

109

MY-0.5Ga

524

304

0.74

0.48

6.8

102

MY-1Ga

518

312

0.71

0.44

6.5

96

MY-2Ga

559

303

0.69

0.42

6.2

88

a

Calculated by the BET method.

b

Obtained at a relative pressure of 0.99.

c

Calculated by the BJH method. To further confirm the pore structure of sample MY-0.5Ga, SEM and TEM analysis were

performed. Figure 5 shows the representative SEM and TEM images of sample MY-0.5Ga. The SEM image displayed in Figure 5 revealed that the morphology of the synthesized sample is

16


Page 17 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

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 were obtained by the self-assemble of mesostructured SiO2@CTAB surfactant micelle and 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 small-angle XRD and wide-angle XRD.

Figure 5. Representative SEM (left) and TEM (right) images of sample MY-0.5Ga.

17


ACS Catalysis

To confirm the T-O-T linkages(where T represents Si, Al or Ga) in the synthesized MY-xGa series samples, FTIR spectra were recorded and the results are displayed in Figure S4 and the details of the FTIR results in the wavenumber range of 600 to 1500 cm-1 are displayed in Figure 6. The IR band at wavenumber lower than 500 cm-1 is associated to the T-O bending mode; the band at about 580 cm-1 is associated to the structure-sensitive double five-ring vibration; the weak band at around 850 cm-1 is associated to the symmetric T-O-T stretching; the broad strong band at 900 to 1250 cm-1 is associated to the asymmetric T-O-T stretching; the bands at 1380(the stronger one next to the olive-green dash line) and 1400 cm-1(the weaker one at the olive-green dash line) are associated to the Al species and Ga species; the broad strong band above 3000 cm1

is associated to the vibration of the hydroxyl species. 27

a b

Relative Transmission, %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 45

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 cm1

: (a) MY-0Ga, (b) MY-0.25Ga, (c) MY-0.5Ga, (d) MY-1Ga, (e) MY-2Ga. The most profoundly change in Figure S4 before and after the introduction of gallium is

observed for the structure-sensitive double five-ring vibration: with the increase of Ga content, the intensity of this IR band decreases, indicating a decrease in the amount of structure-sensitive

18


Page 19 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

double five-ring in the synthesized sample; for samples MY-1Ga and MY-2Ga, this IR band disappeared, indicating the absence of structure-sensitive double five-ring in these two samples. The shape of the IR band above 3000 cm-1 slightly changed after the introduction of Ga27, especially the evidence that the intensity at about 3620cm-1 become stronger, indicating the existence of Si-OH-Ga groups in the Ga containing samples. The framework vibrations(in the wavenumber range of 600 to 1300 cm-1) 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 T-O-T stretching shifted to lower wavenumbers, indicating the formation of Si-O-Ga linkages in the synthesized samples due to that the wavenumber of the IR bands of Si-O-Si and Si-O-Al linkages are higher than that of SiO-Ga linkages; another obvious change in the FTIR spectra is the emerge of the vibration band at about 1020 cm-1(the band at the red dash line in Figure 6), which is higher than the IR band of Ga-O-Ga(often lower than 1000 cm-1) and lower than the IR bands of Si-O-Al(the band at the blue dash line in Figure 6) and Si-O-Si(the band at the purple dash line in Figure 6), which can be taken as another evidence of the formation of Ga-O-Si linkages. The decline in the intensities of the bands at about 1380 cm-1 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 slightly increase in the intensities of the bands at about 1400 cm-1 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 MY-xGa samples. However, whether all the incorporated Ga

19


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 45

species are framework Ga species or not needs to be further confirmed, thus the 29Si MAS NMR and 71Ga MAS NMR characterizations were carried out and the results are displayed in Figure 7 (29Si MAS NMR) and Figure S5 (71Ga MAS NMR). The

29

Si MAS NMR spectra displayed in

Figure 7 of sample MY-0Ga 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 94.5±0.5 ppm is ascribed to the Si(3Al) groups; another medium peak at -89.5±0.5 ppm is ascribed to the Si(4Al) groups;

27, 36

respectively. After incorporation of Ga species, the

29

Si

MAS NMR signals of Si species shift to lower field and with the increasing of Ga/Al ratio, the 29

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 T-O-T angels at the replacement site which has to be balanced by a decrease of neighboring T-O-T 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 MY-xGa samples, firstly increase with the Ga/Al ratio in the raw materials and the highest value was observed over sample MY-0.5Ga, then it decrease with the Ga/Al ratio in the raw materials, indicating that sample MY-0.5Ga is the most stable one among the synthesized MY-xGa 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 MY-2Ga, a weak signal at about -77.5 ppm which is ascribed to the Si(4Ga) groups can been clearly observed, indicating the Si(4Ga) linkages can also be formed on the synthesized MY-xGa samples. The

71

Ga MAS

NMR spectra displayed in Figure S5 clearly show that there is only one main signal for all of the

20


Page 21 of 45

synthesized MY-xGa(x≠0) at 172 ppm ascribed for Ga(4Si) groups, indicating that all the incorporated Ga species are on the zeolite framework.

Si(4Ga) Relative Intensity, a.u.

e

Si(0Me) d

Si(3Me) c

Si(2Me)

Si(4Me)

b

Si(1Al)

Si(4Al)

a

-50

-60

-70

-80

-90

-100

-110

-120

-130

-140

-150

Chemical Shift, ppm

Figure 7.

29

Si MAS NMR spectra of the synthesized MY-xGa samples with different Ga/Al

ratio: (a) MY-0Ga, (b) MY-0.25Ga, (c) MY-0.5Ga, (d) MY-1Ga, (e) MY-2Ga.

B

BAS

LAS

BAS

LAS

e d c


A


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

e d c b

b

a a 1400

1450

1500

1550

1400

1450

1500

1550 -1

Wavenumber, cm

Wavenumber, cm-1

Figure 8. FTIR spectra of pyridine adsorbed on the synthesized HMY-xGa samples with different Ga/Al ratio: (a) HMY-0Ga, (b) HMY-0.25Ga, (c) HMY-0.5Ga, (d) HMY-1Ga, (e) HMY-2Ga; (A) after pyridine desorbed at 200 °C, (B) after pyridine desorbed at 350 °C.

21


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 45

Table 2 Amounts of Brönsted and Lewis acid sites determined by pyridine-FTIR of the HMY-xGa samples 200 oC, µmol·g-1

350 oC, µmol·g-1

Samples

Total

BAS/LAS

LAS

BAS LAS+BAS LAS BAS LAS+BAS

HMY-0Ga

224

268

492

112

126

238

730

1.17

HMY-0.25Ga

250

248

498

96

112

208

706

1.04

HMY-0.5Ga

262

228

490

102

96

198

688

0.89

HMY-1Ga

278

221

499

112

92

204

703

0.80

HMY-2Ga

288

217

505

121

86

207

712

0.74

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 HMYxGa samples, the FTIR spectra of the pyridine adsorbed(Py-FTIR) on the synthesized HMY-xGa samples with different Ga/Al ratios were recorded at 200 °C and 350 °C, respectively, and the spectra was displayed in Figure 8. The vibration peak with wavenumber of about 1543 cm-1 is ascribed to the pyridine ions adsorbed on the Brönsted acid sites(BAS) and the vibration peak with wavenumber of about 1453 cm-1 is ascribed to the pyridine combined with the Lewis acid sites(LAS), respectively.

6, 37

Both the amounts of BAS and LAS with different acid strength 22


Page 23 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

were quantified according to the Py-FTIR 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 after degassing at 350 °C, are varied with the Ga/Al ratio: HMY-0.5Ga(198 µmol·g-1) < HMY1Ga(204 µmol·g-1) ≈ HMY-2Ga(207 µmol·g-1) ≈ HMY-0.25Ga(208 µmol·g-1) < HMY-0Ga(238 µmol·g-1). Sample HMY-0Ga exhibits the lowest amounts of LAS(weak: 224 µmol·g-1; medium and strong: 112 µmol·g-1) and the largest amounts of BAS(weak: 268 µmol·g-1; medium and strong: 126 µmol·g-1), after the incorporation of Ga into the framework of the synthesized samples, the amounts of weak LAS increased from 224 µmol·g-1 of sample HMY-0Ga to 278 µmol·g-1 of sample HMY-2Ga and the amounts of strong LAS straightly decreased from 112 µmol·g-1 of sample HMY-0Ga to 96 µmol·g-1 of HMY-0.25Ga, however, with the increase of the Ga/Al ratio, the amounts of strong LAS slightly increased. Both the amounts of weak BAS and strong BAS decreased in the following order: HMY-0Ga(268 µmol·g-1; 126 µmol·g-1) > HMY0.25Ga(248 µmol·g-1; 112 µmol·g-1) > HMY-0.5Ga(228 µmol·g-1; 96 µmol·g-1) > HMY1Ga(221 µmol·g-1; 92 µmol·g-1) > HMY-2Ga(217 µmol·g-1; 86 µmol·g-1). 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: HMY-0Ga(1.17) > HMY-0.25Ga(1.04) > HMY-0.5Ga(0.89) > HMY-1Ga(0.80) > HMY-2Ga(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

23


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 45

for Ga is lower than the value for Al (1.71), implying Ga-OH-Si and Ga-OH groups(which are correlated to BAS) are more inclined to form Ga+ caves(which are correlated to LAS) through dehydration after calcination than Al-OH-Si and Al-OH groups(which are correlated to BAS) to 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.

24


Page 25 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Figure 9. Representative HRTEM images of the sulfided NiMo/HMY-xGa series catalysts: (a) NiMo/HMY-0Ga, (b) NiMo/HMY-0.25Ga, (c) NiMo/HMY-0.5Ga, (d) NiMo/HMY-1Ga, (e) NiMo/HMY-2Ga. The morphology of the active metal sulfides is considered to be very important for the activity of the bifunctional HDS catalysts,

38

especially for the activity of the catalysts in removal of

highly refractory organosulfides such as 4,6-DMDBT. 39 HRTEM characterizations of the sulfide NiMo/HMY-xGa 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/HMY-xGa series catalysts. The statistical stacking layer numbers distribution and the slab length distribution of MoS2 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/HMY-0Ga is only 2.4; after incorporation of small amount of Ga into the zeolite framework, the amounts of MoS2 crystals with low stacking numbers sharply decreased, the

25


ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 45

Table 3 Average length, layer number and fMo of Ni promoted MoS2 crystals for the NiMo/HMY-xGa series catalysts Catalysts

Average length (nm)

Average stacking number

fMo

NiMo/HMY-0Ga

4.9

2.4

0.26

NiMo/HMY-0.25Ga

4.4

3.3

0.29

NiMo/HMY-0.5Ga

4.2

3.6

0.30

NiMo/HMY-1Ga

4.1

3.8

0.31

NiMo/HMY-2Ga

3.9

3.9

0.31

stacking number distribution become narrowed and the average stacking number increased to 3.3. With the increase of Ga/Al ratio, the stacking number distribution become more narrowed and the main stacking number of MoS2 crystals firstly changed from 3 layers(NiMo/HMY0.25Ga) to 3~4 layers(NiMo/HMY-0.5Ga), and then to 4 layers(both NiMo/HMY-1Ga and NiMo/HMY-2Ga); and the average stacking number slightly increased from 3.3(NiMo/HMY0.25Ga) to 3.9(NiMo/HMY-2Ga). The slab lengths also change with the Ga/Al ratio: After the incorporation of Ga, the slab length distribution of MoS2 crystals also become narrowed-the numbers of long MoS2 crystals decreased and the proportion of MoS2 crystals with slab length in the range of 3~5 nm increased; the average slab length of the MoS2 crystals firstly sharply decrease from 4.9 nm(NiMo/HMY-0Ga) to 4.4 nm(NiMo/HMY-0.25Ga), then with the increase

26


Page 27 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

of Ga/Al ratio, it slightly declined from 4.4 nm(NiMo/HMY-0.25Ga) to 3.9 nm(NiMo/HMY2Ga). 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/HMY-0Ga(0.26) < NiMo/HMY-0.25Ga(0.29)

Synthesis of NiMo Catalysts Supported on Gallium-Containing

Recommend Documents