Facile Synthesis of Mesoporous Zeolite Y with Improved Catalytic

Research Note pubs.acs.org/IECR

Facile Synthesis of Mesoporous Zeolite Y with Improved Catalytic Performance for Heavy Oil Fluid Catalytic Cracking Junsu Jin,† Chaoyun Peng,† Jiujiang Wang,‡ Hongtao Liu,*,† Xionghou Gao,*,‡ Honghai Liu,‡ and Chunyan Xu† †

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing, 100029, P. R. China Petrochemical Research Institute, Petrochina Company Limited, Beijing, 100195, P. R. China

‡

ABSTRACT: A facile and direct approach for the synthesis of mesoporous zeolite Y by using [(CH3O)3SiC3H6N(CH3)2C18H37]Cl as template is presented. Under the basic condition of the Y synthesis system, (CH3O)3Si− bonds hydrolyze to −Si− OH, and yield −Si−O−Al− and −Si−O−Si− linkages that anchor the template in zeolite framework. Afterward, micelles formed by −C18H37 lead to the formation of mesoporosity within zeolite Y crystals. This material, which introduces intracrystalline mesoporosity into zeolite Y, shows superior catalytic performance when used in heavy oil catalytic cracking. the final framework through −Si−O−Al− and −Si−O−Si− linkages. I n t h i s s t ud y , a bi fu nc t io n a l a m m o n iu m sa lt [(CH3O)3SiC3H6N(CH3)2−C18H37]Cl, denoted as TPOACl, which is a highly commercialized product, was used as template of mesoporous zeolite Y. The bifunctional template contains (CH3O)3Si− on one side that can undergo hydrolysis and polycondensation, and thus enable the formation of construction of −C18H37 as the source of mesopores in the framework of zeolite Y. In this approach, phase separation between the template and aluminosilicate gel was avoided thanks to the hydrolysis and anchoring of (CH3O)3Si− groups. Therefore, the bifunctional template is believed to be the key in in situ introduction of mesoporosity in zeolite Y, which has puzzled researchers for a long time in the synthesis of mesoporous zeolite Y.

1. INTRODUCTION Zeolite Y has been the primary active component of fluid catalytic cracking (FCC) catalysts for more than 50 years due to its high surface area, high hydrothermal stability, strong acidity, and low cost. However, its micropores at less than 0.74 nm cannot fulfill the particular application in heavy oil catalytic cracking catalysts,1,2 because the cracking reaction and the mass transfer of the large molecules of heavy oil are severely limited in the micropores of zeolite Y. Therefore, the introduction of mesopores into zeolite Y is the key to heavy oil cracking. To fulfill this requirement, a considerable amount of work has been done to introduce mesopores into zeolite Y and thus enhance the accessibility of active sites in zeolite Y.3−13 A number of approaches to introduce mesopores into zeolite Y have been developed besides the desilication14−17 and dealumination18,19 by hydrothermal treatment.20 For example, hard templates21−23 such as modified carbon,4,5 cationic or silylated polymer, and amphiphilicorganosilane have been employed as templates,24−27 leading to the successful introduction of mesopores into FAU-type (such as zeolite X and Y) and ZSM-5. Unfortunately, such templates are unavailable on the market and have to be specially designed and synthesized.28,29 Therefore, it is still a great challenge to develop a direct and facile synthetic approach of mesoporous zeolite Y. All the preparation methods used have a common basis, tha is, templates employed have to be grafted into the aluminosilicate gel in the synthesis of zeolite Y,24 which can lead either to a relatively low crystallinity of the final zeolite or to phase separation between the template and aluminosilicate gel, such as carbon black outside of the framework. The principle reason for these defects is the difficulty of dispersing and reactivity of templates in the viscous aluminosilicate gel used in the zeolite Y synthesis system.30 It is generally accepted that the presence of RO−Si− is the key to anchoring the template in the framework of zeolite.24 Therefore, the question can then arise as to whether a single-source molecular template already containing RO−Si− bonds can be used as templates in the synthesis. Using such a single-source template, we can expect a molecular and homogeneous template distribution in © 2014 American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Synthesis Procedure. Dimethyloctadecyl[3(trimethoxysiyl)propyl] ammonium chloride (TPOACl, Mw = 496.28) was purchased from Sigma-Aldrich Co. Water glass (containing 32.5 wt % SiO2 and 13.2 wt % Na2O) was obtained from Beijing Hongxing Sodium Silicate Company. The preparation of initiator was as follows: 8.17 g of NaOH and 2.92 g of NaAlO2 were desolved in 53.27 g of deionized water. The solution was mixed with 35.65 g of water glass. After stirring at 25 °C for 1 h, the gel mixture was aged at 45 °C for 4.5 h to obtain the initiator. A 6.48 g portion of the initiator (with molar composition 16Na2O/Al2O3/15SiO2/320H2O) was added dropwise to 22.32 g of water glass. After the addition of 3 mL of deionized water under stirring for 0.5 h, 3.68 g of TPOACl was added to the mixture. After this mixture was stirred for 1 h, Al2(SO4)3 and NaAlO2 were added, and the entire solution with a molar Received: Revised: Accepted: Published: 3406

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composition 0.125Al2O3/SiO2/0.625Na2O/25H2O/xTPOAC (x = 0.02, 0.03, 0.04, and 0.05) was obtained. After being stirred for 1 h, the mixture was placed in an autoclave at 100 °C for 24 h. The crystallization products were collected by filtration, dried in air, and calcinated at 570 °C for 5 h to remove the template. The resulting mesoporous NaY with x = 0.02, 0.03, 0.04, and 0.05 were denoted as MY-a, MY-b, MY-c, and MY-d (MY is short for mesoporous NaY), respectively. For comparison, the conventional NaY was obtained by the same procedure as the MYs except for the addition of TPOACl and denoted as “classical NaY”. 2.2. Characterization. X-ray diffraction (XRD) patterns of the synthesized zeolite were obtained with a Shimadzu XRD7000 diffractometer using Cu Kα radiation at 40 kV and 30 mA. The XRD patterns were collected in the range of 5−45° in 2θ/ θ scanning mode with a 0.02° step and scanning speed of 6°/ min. The morphology of the synthesized zeolite was investigated by HITACHI S4700 scanning electron microscope (SEM). Transmission electron microscopy (TEM) images were recorded by JEOL JEM-3010 with an acceleration voltage of 200 kV. All samples subjected to TEM measurements were dispersed in ethanol ultrasonically and were dropped on the microgrid. The isotherms of nitrogen were measured at the temperature of liquid nitrogen using a QuadraSorb SI system. The Brunauer−Emmett−Teller (BET) equation was used to calculate the specific surface area (Stotal) from the adsorption data obtained (p/p0 = 0.05−0.25). The mesopore volume (Vmeso) and mesopore size distribution were calculated using the Barrett−Joyner−Halenda (BJH) method on the adsorption branch of the isotherm. The micropore area (Smic) and micropore volume (Vmic) were calculated from the t-plot curve. XRF was performed on a PANalytical B.V. X’Pert PRO X-ray fluorescence spectrometer (XRF). 2.3. Catalytic Cracking Performance Tests. To decrease the Na content of zeolite Y and thus increase its acidity, La3+ and H+ were used for ion-exchange of Na+ in zeolite NaY, and thus zeolite Y containing La3+ and H+ (denoted as LaH-form) was obtained The LaH-form (the rare earth and H form) samples of MY-c were obtained by repeated procedure of ion exchange with NH4Cl and LaCl3·7H2O solution. After calcination at 550 °C for 2 h, the LaH-form classical NaY was obtained by the same procedure as MY-c. The LaH-form samples of MY-c and NaY were denoted as LaH-MY-c and LaH-Y, respectively. Cat-1 was prepared from kaolin (60%), alumina gel (10%), LaH-Y (5%) and USY (25%). Cat-2 was prepared from kaolin (60%), alumina gel (10%), LaH-MY-c (5%), and USY (25%). The two catalysts were crushed, sieved to 20−40 mesh, and finally steamed in 800 °C water vapor for 2 h before use. Heavy oil catalytic cracking tests were carried out in a fixedfluidized bed reactor by the pulse method. The heavy oil feedstock used was Xinjiang vacuum gasoline. The physical and chemical properties of the feedstock are shown in Table 1. The heavy crude oil catalytic cracking tests were performed under standard conditions: catalyst loading, 25 g; reaction temperature, 540 °C; 2.5 g of the heavy crude oil was introduced to the reactor through an injection tube within 36 s, then purging nitrogen was followed for 5 min. The reaction products were collected in a gas collector and a liquid collector, respectively, through a cooling bath. The component analysis of the cracking products were carried out using an Agilent gas chromatographer equipped with a flame ionization detector. Xinjiang

Table 1. Properties of the Xinjiang Vacuum Gas Oil property

Xingjiang vacuum gas oil

density (20 °C), kg/m3 kinematic viscosity at 100 °C, mm2/s average molecular weight, g/mol conradson carbon residue, wt% lumped composition, wt% saturated alkanes aromatics resins

898.40 12.05 449 0.39 76.59 21.01 4.08

vacuum gas oil was selected as the feed oil, and its properties were listed in Table 1.

3. RESULTS AND DISCUSSION The nitrogen isotherms of mesoporous Y exhibit a step at a relative pressure of 0.75−0.95, which is direct evidence for the presence of a mesostructure (Figure 1). Compared to the

Figure 1. N2 adsorption−desorption isotherms of (a) MY-a, (b) MYb, (c) MY-c, and (d) MY-d (the isotherms have been shifted).

classical NaY, the surface area of all the mesoporous NaY decreased. In addition, the surface area of mesoporous NaY increased with the increase of TPOACl addition (from MY-a 638 m2·g−1 to MY-c 696 m2·g−1). When TPOACl/SiO2 = 0.05, both the micropores and mesopores surface area of MY-d decreased compared to those of MY-c. Moreover, the relative crystallinity of MY-d is also decreased. It can be concluded that the presence of too low and too high TPOACl concentration prevent the complete zeolite growth and facilitate the formation of disordered mesoporous aluminosilicate.31 Interestingly, it can be seen from Figure 1 and Table 2 that MY-c exhibits a BET surface area of 696.2 m2·g−1 (Table 2). More remarkably, 144.4 m2·g−1 is from the external surface, which is from crystal external surfaces and intracrystalline mesopores. These are believed to be the results of the increased mesopore volume (0.29 cm3·g−1). Correspondingly, the pore size distributions of MY-a, MY-b, and MY-d show mesopores in the range of 2−10 nm (Figure 2), in accordance with the size of the surfactant micelles ([(CH3O)3SiC3H6N(CH3)2−C18H37]Cl).31 As comparison, Xiao has synthesized mesoporous Y and the pore size of mesopores centered at 18 nm.30 It is demonstrated in Table 2 that a synthesis system consisting of TPOACl in proper proportions can lay a foundation for directly synthesizing mesoporous zeolite Y.31 SEM images (Figure 3) indicated that the morphology of zeolite Y crystals was obtained without the formation of 3407

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Figure 2. BJH pore size distribution of (a) MY-a, (b) MY-b, (c) MY-c, and (d) MY-d.

separate amorphous mesoporous crystals. TEM images (Figure 4) revealed that the intracrystalline mesopores were present within the same crystal. These results are consistent with those of other literature.30,32−34 From the SEM images and XRF results, it is indicated that a zeolite Y with typical octahedral morphology, an average size of about 700 nm and a SiO2/Al2O3 molar ratio of 5.2 can be obtained. Moreover, from the TEM images at high magnification (Figure 4), the observation of wormlike mesostructure confirms the presence of mesopores. By the carefully controlled addition of TPOACl, a zeolite Y with typical octahedral morphology, a uniform size of about 700 nm, and a SiO2/Al2O3 molar ratio of 5.2 can be obtained. The observations described above show that the intracrystalline mesoporosity could be generated through the anchoring and templating mechanism of the bifunctional template TPOACl. The plausible scheme of this process is illustrated in Figure 5. Under the strong basic condition of the typical Y synthesis system, some of the (CH3O)3Si− bonds hydrolyze to −Si−OH, and yield −Si−O−Al− and −Si−O−Si− linkages that anchor the template in the zeolite framework. Strikingly, we observed sticky gel formation with the addition of TPOACl, which was associated with the hydrolyzing and anchoring of TPOACl. The phenomena suggested that possibly sequential anchoring-assembly proceed. Afterward, electrostatic interaction between the positively charged surfactants and these negatively charged aluminosilicate gels, and micelles formed through self-assembly, led to the formation of mesoporosity within the zeolite Y crystals. A similar process has been reported by Xiao et al.30 Different from the present investigation, Ying et al. obtained the mesoporosity from zeolite Y through the assembly of CTMABr in the crystalline pore wall.32 XRD patterns exhibit well-resolved peaks in the high-angle zone in the range of 5−45° with the zeolie Y structure (Figure 6), indicating that the mesoporous Y has a high crystallinity.

Figure 3. SEM images of MY-c.

But the sample MY-c exhibits no peak in the range of 0.5−5° (Figure 7), indicating that the mesopores obtained are not ordered. From XRD results, it was calculated that the unit cell sizes (a0) were almost the same (Table 2), suggesting the formation mechanism of mesoporous Y is similar with that of classical Y. Catalytic cracking properties of steam-deactivated catalysts Cat-1 and Cat-2 are studied using vacuum gas oil (VGO) as the feed oil in a fixed-fluidized bed reactor. A significant increase of yields of gasoline and reduction of yields of coke and dry gas were achieved with the mesoporous Y derived Cat-2 as compared with the classical Y derived Cat-1 (Table 3). The greatly improved catalytic performance could be attributed to the introduction of mesopores into zeolite Y that enhanced accessibility in the resulting catalysts. The intracrystalline mesopores would promote the primary cracking to yield more gasoline, meanwhile the undesirable secondary cracking is reduced since the formation of dry gas and coke is mainly due to the secondary cracking and condensation polymerization reactions of product molecules. Moreover, higher C3=/∑C3 and C4=/∑C4 ratios (Table 4) can also be explained by the reduction of hydrogen transfer

Table 2. The Specific Surface Area and Pore Structure Parameters of the Samples

a

Stotal

Smic

Smeso

Vtotal

Vmic

Vmeso

unit cell size, a0

samples

m2·g−1

m2·g−1

m2·g−1

cm3·g−1

cm3·g−1

cm3·g−1

nma

n(SiO2/Al2O3)

MY-a MY-b MY-c MY-d classical NaY

638 651 696 602 755

563 564 552 476 711

75 87 144 126 44

0.48 0.53 0.59 0.49 0.39

0.30 0.30 0.30 0.23 0.35

0.18 0.23 0.29 0.26 0.04

2.465 2.478 2.483 2.469 2.477

5.23 5.22 5.21 5.21 5.25

a0 = λ(h2 + k2 + l2)1/2/2 sin θ; h, k, l are the crystal plane index, λ is the wavelength of X-ray. 3408

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Figure 6. XRD patterns for (a) MY-a, (b) MY-b, (c) MY-c, (d) MY-d, and (e) classical NaY.

Figure 4. TEM images of MY-c.

(another secondary reaction) due to the introduction of intracrystalline mesopores. As we know, the hydrogen transfer reaction is a bimolecular reaction. It depends on both acidity density and pore structure of the catalyst. In this investigation, it is reasonably deduced that the reduction of hydrogen transfer (another secondary reaction) is mainly due to the introduction of intracrystalline mesopores.35

Figure 7. Small-angle XRD patterns for MY-c.

Figure 5. Scheme of the mesoporous zeolite Y synthesis. 3409

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(6) Groen, J. C.; Moulijn, J.; Perez-Ramirez, J. Desilication: On the Controlled Generation of Mesoporosity in MFI Zeolites. Mater. Chem. 2006, 16, 2121. (7) Wang, D.; Liu, Z.; Wang, H.; Xie, Z.; Tang, Y. Shape-Controlled Synthesis of Monolithic ZSM-5 Zeolite with Hierarchical Structure and Mechanical Stability. Microporous Mesoporous Mater. 2010, 132, 428. (8) Perez-Ramirez, J.; Abello, S.; Bonilla, A.; Groen, J. C. Tailored Mesoporosity Development in Zeolite Crystals by Partial Detemplation and Desilication. Adv. Funct. Mater. 2009, 19, 164. (9) Jacobsen, C. J. H.; Madsen, C.; Houzvicka, J.; Schmidt, I.; Carlsson, A. Mesoporous Zeolite Single Crystals. J. Am. Chem. Soc. 2000, 122, 7116. (10) Davis, M. E. Ordered Porous Materials for Emerging Applications. Nature 2002, 417, 813. (11) Ferey, G. The Simplicity of ComplexityRational Design of Giant Pores. Science 2001, 291, 994. (12) Corma, A.; Diaz-Cabanas, M. J.; Martinez-Triguero, J.; Rey, F.; Rius, J. A Large-Cavity Zeolite with Wide Pore Windows and Potential as an Oil Refining Catalyst. Nature 2002, 418, 514. (13) Guldin, S.; Kolle, M.; Stefik, M.; Langford, R.; Eder, D.; Wiesner, U.; Steiner, U. Tunable Mesoporous Bragg Reflectors Based on Block-Copolymer Self-Assembly. Adv. Mater. 2011, 23, 3664. (14) Orgura, M.; Shinomiya, S. Y.; Tateno, J.; Nara, Y.; Kikuchi, E.; Matsukata, H. Formation of Uniform Mesopores in ZSM-5 Zeolite through Treatment in Alkaline Solution. Chem. Lett. 2000, 29, 882. (15) Groen, J. C.; Peffer, L. A. A.; Moulijn, J. A.; Perez-Ramirez, J. Mechanism of Hierarchical Porosity Development in MFI Zeolites by Desilication: The Role of Aluminium as a Pore-Directing Agent. Chem.Eur. J. 2005, 11, 4983. (16) Groen, J. C.; Bach, T.; Ziese, U.; Paulaime-van, A. M.; de Jong, K. P.; Moulijn, J. A.; Perez-Ramirez, J. Creation of Hollow Zeolite Architectures by Controlled Desilication of Al-Zoned ZSM-5 Crystals. J. Am. Chem. Soc. 2005, 127, 10792. (17) Perez-Ramirez, J.; Verboekend, D.; Bonilla, A.; Abello, S. Zeolite Catalysts with Tunable Hierarchy Factor by Pore-Growth Moderators. Adv. Funct. Mater. 2009, 19, 3972. (18) Van Donk, S.; Janssen, A. H.; Bitter, J. H.; de Jong, K. P. Generation, Characterization, and Impact of Mesopores in Zeolite Catalysts. Catal. Rev. 2003, 45, 297. (19) Triantafillidis, C. S.; Vlessidis, A. G.; Evmiridis, N. P.; Dealuminated, H-Y Zeolites: Influence of the Degree and the Type of Dealumination Method on the Structural and Acidic Characteristics of H-Y Zeolites. Ind. Eng. Chem. Res. 2000, 39, 307. (20) Kim, S. S.; Shah, J.; Pinnavaia, T. J. Colloid-Imprinted Carbons as Templates for the Nanocasting Synthesis of Mesoporous ZSM-5 Zeolite. Chem. Mater. 2003, 15, 1664. (21) Zhu, H.; Liu, Z.; Wang, Y.; Kong, D.; Yuan, X.; Xie, Z. Nanosized CaCO3 as Hard Template for Creation of Intracrystal Pores within Silicalite-1 Crystal. Chem. Mater. 2008, 20, 1134. (22) Christensen, C. H.; Schmidt, I.; Carlsson, A.; Johannsen, K.; Herbst, K. Crystals in Crystals Nanocrystals within Mesoporous Zeolite Single Crystals. J. Am. Chem. Soc. 2005, 127, 8098. (23) Lopez-Orozco, S.; Inayat, A.; Schwab, A.; Selvam, T.; Schwieger, W. Zeolitic Materials with Hierarchical Porous Structures. Adv. Mater. 2011, 23, 2602. (24) Wang, H.; Pinnavaia, T. J. MFI Zeolite with Small and Uniform Intracrystal Mesopores. Angew. Chem., Int. Ed. 2006, 45, 7603. (25) Xiao, F.-S.; Wang, L.; Yin, C.; Lin, K.; Di, Y.; Li, J.; Xu, R.; Su, D.; Schlögl, R.; Yokoi, T.; Tatsumi, T. Catalytic Properties of Hierarchical Mesoporous Zeolites Templated with a Mixture of Small Organic Ammonium Salts and Mesoscale Cationic Polymers. Angew. Chem., Int. Ed. 2006, 45, 3090. (26) Choi, M.; Cho, H. S.; Srivastava, R.; Venkatesan, C.; Choi, D. H.; Ryoo, R. Amphiphilic Organosilane-Directed Synthesis of Crystalline Zeolite with Tunable Mesoporosity. Nat. Mater. 2006, 5, 718.

Table 3. Catalytic Evaluation of Catalyst Cat-1 and Cat-2 product yield/mass %

Cat-1

Cat-2

dry gas liquefied gas C5+gasoline (C5, 210 °C) LCO (light cycle oil) heavy oil coke

13.7 9.7 32.4 13.7 23.1 7.4

13.3 10.0 35.4 13.1 23.5 4.7

Table 4. Liquefied Gas Composition Analysis for Catalyst Cat-1 and Cat-2 composition of product (m%)

Cat-1

Cat-2

propane propene i-butane n-butane t-2-butene n-butene-1 i-butene c-2-butene C3=/∑C3 C4=/∑C4

0.83 3.85 2.04 0.27 0.59 0.56 1.13 0.43 0.82 0.54

0.76 3.94 1.94 0.32 0.68 0.60 1.28 0.48 0.84 0.57

4. CONCLUSIONS In summary, zeolite Y with intracrystalline mesoporosity has been prepared using TPOACl as a mesoporous template. Moreover, the ratio of mesoporosity can be adjusted by varying the addition of the template addition amount. A catalyst derived from MY-c shows better catalytic performance than a classical Y-derived catalyst. It is believed that this synthesis strategy can be extended to synthesis of other hierarchical zeolites such as Beta and ZSM-5.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (H. Liu), gaoxionghou@ petrochina.com.cn (X. Gao). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge financial support from the Natural Science Foundation of China (Grant No. 20606003), Petrochina Limited Company (Grant No. 2012A-2102-01), and PetroChina Innovation Foundation (Grant No. 2013D-50060403).

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REFERENCES

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(27) Inayat, A.; Knoke, I.; Spiecker, E.; Schwieger, W. Assemblies of Mesoporous FAU-Type Zeolite Nanosheets. Angew. Chem., Int. Ed. 2012, 51, 1962. (28) Dhainaut, J.; Daou, T. J.; Chappaz, A.; Bats, N.; Harbuzaru, B.; Lapisardi, G.; Chaumeil, H.; Defoin, A.; Rouleau, L.; Patarin, J. Synthesis of FAU and EMT-type Zeolites Using Structure-Directing Agents Specifically Designed by Molecular Modeling. Microporous Mesoporous Mater. 2013, 174, 117. (29) Lopez-Orozco, S.; Inayat, A.; Schwab, A.; Selvam, T.; Schwieger, W. Zeolitic Materials with Hierarchical Porous Structures. Adv. Mater. 2011, 23, 2602. (30) Fu, W.; Zhang, L.; Tang, T.; Ke, Q.; Wang, S.; Hu, J.; Fang, G.; Li, J.; Xiao, F. Extraordinary High Activity in the Hydrodesulfurization of 4,6-Dimethyldibenzothiophene over Pd Supported on Mesoporous Zeolite Y. J. Am. Chem. Soc. 2011, 133, 15346. (31) Koekkoek, A. J.; Tempelman, C.; Degirmenci, V.; Guo, M.; Feng, Z.; Li, C.; Hensena, E. Hierarchical Zeolites Prepared by Organosilane Templating: A Study of the Synthesis Mechanism and Catalytic Activity. Catal. Today 2011, 168, 96. (32) Garcia-Martinez, J.; Johnson, M.; Valla, J.; Li, K.; Ying, J. Y. Mesostructured Zeolite Y-High Hydrothermal Stability and Superior FCC Catalytic Performance. Catal. Sci. Technol. 2012, 2, 987. (33) Garcia-Martinez, J.; Li, K.; Krishnaiah, G. A; Mesostructured, Y. Zeolite as a Superior FCC Catalyst-from Lab to Refinery. Chem. Commun. 2012, 48, 11841. (34) Chal, R.; Cacciaguerra, T.; van Donk, S.; Gerardin, C. Pseudomorphic Synthesis of Mesoporous Zeolite Y Crystals. Chem. Commun. 2010, 46, 7840. (35) Gao, Y.; Zhang, Y. Study on Hydrogen Transfer Reaction in Catalytic Cracking. Chin. J. Pet. Refin. Eng. 2000, 30, 34.

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