Metals on a Novel USY Zeolite after Hydrothermal Aging

Studies in Surface Science and Catalysis, Vol. 139 J.J. Spivey, G.W. Roberts and B.H. Davis (Editors) 9 2001 Elsevier Science B.V. All rights reserved.

351

Metals on a Novel USY Zeolite after Hydrothermal Aging Huiping Tian, Congjun Huang, Zhongbi Fan Division 14, Research Institute of Petroleum Processing, 18 Xueyuan Rd., Beijing 100083, RR. China

Abstract A novel USY zeolite (EAH-USY), characterized by its high crystallinity and hydrothermal stability, was prepared by elaborately adjusting hydrothermal conditions. The behavior of Ca, Fe, Ni and V on this zeolite was studied. It was found that V interacted with EAH-USY at high temperature and thoroughly destroyed the structure. Fe destroyed the zeolite structure over a wide temperature range, but the structure of EAH-USY did not completely collapse due to the interaction between Fe and zeolite. The crystal lattice constant for Ca/Y samples (Ca in EAH-USY) did not change evidently. Ca was not uniformly distributed in the EAH-USY zeolite, while V uniformly distributed in the zeolite. Ni interacted readily with framework AI. The interaction between V and zeolite was caused by the solid-state reaction between V and framework A1, leading to the destruction of the zeolite structure by the interaction of V with the framework Si. The interaction between Fe and EAH-USY depended on Fe loading amount and hydrothermal temperatures. KEYWORDS: Y zeolite, metal loading, hydrothermal aging, interaction mechanism, structure model 1.Introduction RFCC (resid fluid catalytic cracking) is one of the processes for the conversion of heavy oils in modem refineries. The problem with vacuum residue as FCC feedstock is quick deactivation of catalysts by the coking of asphaltene fractions and the deposition of metals involved in metallorganic polycyclic compounds. Therefore, developing novel zeolites to achieve metal tolerance has long been a goal of catalyst researchers [~'2, 31. Ca is mainly from synthesized additives used in petroleum exploring and exploitation. Meyer et al. [41 has reported hydration and dealumination phenomenon by Ca in zeolites. Ni catalyzes both dehydrogenation reactions in FCC riser reactors, leading to high coke and dry gas yields, and oxidation reactions in FCC regenerators, resulting in high CO2/CO ratio. There were two types of Ni species in catalysts, i.e., nickel oxides and nickel aluminates or silicates-[51. Nickel aluminates had lower activity than nickel oxides. Shen [61 studied Ni migration from zeolite to matrices in hydrothermal conditions. FeY dealuminated faster than NH4Y did under same hydrothermal conditions, finally forming mesopores with Fe-A1 complex oxides [7]. V in crude oil was in the +3 and +4 valence state in porphrin compounds and remained in residue after distillation. After decomposition in riser reactors, low valence V deposited on the catalyst. The high melting points of low valence V oxides made them less harmful to the catalysts. In the regenerator, these V oxides were oxidized to +5 valence V oxides, which had low melting point and were able to destroy the structure of zeolites and catalysts. High valence V oxides such as V20 5 and its hydrate H3VO 4 could easily migrate in catalysts, block pore apertures and cover active sites, causing catalysts permanent deactivation [8,9, ~0l. In this paper, a novel ultrta-stable Y zeolite (EAH-USY) are reported. The state of metal contaminants (Ca, Fe, Ni, V) and their influence on this novel USY zeolite are investigated.

2.Experimentals 2.1 Sample Preparation USY was ion-exchanged with ammonium chloride to remove sodium. Then incipient wetness methods were used to impregnate calcium nitrate, iron nitrate,

352

nickel nitrate and vanadium naphthenate (individually, in petroleum ether) into the EAH-USY zeolite. The concentration of these solutions was designed to impregnate the desired amount of metal in the zeolite as listed in Table 1. The samples were then calcined in a muffle furnace at 803 K for 4 h. The flesh metal/Y samples were treated in 100% steam for 4 h at 823 K, 973 K, 1023 K or 1073 K. Table 1. Experimental samples and their metal levels (wt%)

Samples Ca/Y FefY Ni/Y V/Y

Ca 1.57 / / /

Fe / 1.61 / /

Ni / / 1.65 /

V / / / 1.79

2.2 Measurement of the Physicochemical Properties of Zeolite Samples Metal content in zeolite was detected by XRF (X-ray fluorimetry) using a tungsten target. Excitation voltage was 40 kV. Blaze current was 50 mA. The spectral line intensity was recorded on a proportional counter. The crystal lattice constant and relative crystallinity of Y zeolite were measured by XRD (X-ray diffraction) method on a D/max-IIIA diffractometer. CuKa was used as radiation source with Ni filter. Tube voltage was 30 kV. Tube current was 25mA. Step scanning span was 0.01 o in 23.4-24.6 ~ A Dupont 160 differential thermal analyzer was used to detect the crystal lattice collapse temperature. The measurement was conducted in 140 mL/min airflow at 10 K/min heating rate. Specific surface area was measured by the N2-BET (Brunner-Emmett-Teller) method on a Micromeritics ASAP2400 automatic adsorption meter. Samples were pretreated in a muffle furnace at 573 K for 1 h. The sample in system was outgassed at 523 K for 4 h, then, cooled down in liquid nitrogen. Nitrogen adsorption isotherms were recorded for BET calculation. 2.3 Temperature-Programmed Reduction Procedure TPR (temperature-programmed reduction) of these samples was conducted following a conventional procedure EIll. 0.20 gram samples were put into the reactor in each run. 0.20 gram quartz particles were placed upon the samples to eliminate the backmixing of the gas flow. Before heating, the system was treated with flowing nitrogen for 20 min, then, H2/N2 mixture was introduced at 30 mL/min flow rate. The reactor was heated to 423 K and kept at this temperature for 20 min. Then, the temperature was raised to 1323 K at a rate of 15 K/min and held for 20 min at 1323 K. The TPR curve was recorded. Different TPR curves for one sample were measured by changing the heating rate to 11 K/min or 20 K/min. Activation energy of reduction was calculated according to TPR profiles of different heating rates Ill, r~I. 3.Results and Discussion

3.1. Physicochemical Properties of EAH-USY Zeolite EAH-USY was made by elaborately adjusting the hydrothermal condition t131. Its properties are listed in Table 2. There was no peak on EAH-USY TPR curves due to the chemical stability of A1203 and SiO2 in reductive atmosphere. Table 2. Physieoehemieal properties of EAH-USY and traditional USY

Crystallinity (I/I0),% Lattice Constant (a0), angstrom Specific SurfaceArea, m2/g Zeolite CollapseTemperature,K 9 (SiO2/A12O3)Framework, mo!/mo!

EAH-USY 78 24.50 676 1067 9.5 ......

Traditional USY 67 24.45 643 1004 11.8

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(A1203)Non-Framework/(A1203)Total#, % 45 61 (SiO2)Non-F . . . . rk/(SiO2)Total #, % 14 24 #: (A12Oa)No,-F. . . . . k/(AI203)Tmtt~ZJ=lOO-(O.591*ao-14.305)*(I/Io)*(CAI/27+C.si/29+CM/M)/(CAt/27) ( SiO2)Non-F........ k/(SiO2)Totalt"J=100-(15.305-0.591*ao)*(Vlo)*(CA/27+Csi/29+Cu/M)/(Csi/29) in which, CAI, Csi and Cu were respectively the weight percentage of A1, Si and Metal. M was atomic weight of the metal. Table 3. Influence of h~,drothermal aBin ~ on EAH-USY and traditional USY zeolite ,

EAH-USY Traditional USY Hydrothermal Temperature, K 823 973 1073 823 973 1073 Crystallinity, % 77 72 63 75 70 59 Lattice Constant, nm 24.49 2 4 . 4 6 2 4 . 4 0 24.49 24.46 24.39 Specific Surface Area, m2/g 663 620 544 647 608 525 Zeolite Collapse Temperature, K 1064 1050 1028 1060 1050 1025 (SiO2/A1203)F....... k, mol/mol 9.9 11.3 15.3 9.9 11.3 16.3 (A1EO3)Non-F. . . . . . k/(Al203)Total, % 48 56 71 49 57 74 RMAS # 1.5 1.6 1.7 1.8 1.9 2.1 #: RMAS(Ratio of migration speed Of A1 to Si)t,z,=(Alr_Alo)/(Sir.Sio)' in which, AIr was (AI203)No,. F. . . . rk/(Al203)Total of the zeolite sample hydrothermal aged at T temperature. Alo was (AI203)NonFra,.... k/(Al203)Tot~l of the zeolite sample befdre hydrothermal aging. SiT was (SiO2)No,_ F. . . . . . k/(SiO2)Toai of the zeolite sample hydrothermal aged at T temperature. Sio was (SiO2)No,. F....... k/(SiO2)Tot~mof the zeolite sample before hydrothermal aging.

Table 3 lists the properties of EAH-USY and traditional USY after hydrothermal aging at 823 K, 973 K, and 1073 K. EAH-USY zeolite showed high crystallinity with notable lattice shrinkage and preferable hydrothermal stability. From the framework composition changes, the migration rate of Si and A1 was calculated. It was noted that the RMAS (ratio of migration rate of A1 to that of Si) of the EAH-USY zeolite was less dependent on the aging temperature than that of the conventional USY zeolite. However, RMAS of the EAH-USY was about 1.7 for aging at 1073 K, indicating an ample room for further optimization of the EAH-USY synthesis conditions. 3.2. Influence of Metal Contaminants on EAH-USY Structure The crystallinity changes of metals/EAH-USY after hydrothermal aging are depicted in Figure 1 (left). Note that the curves for the metal/Y samples are lower than the curve of EAH-USY, indicating more rapid collapse of the structure with treatment temperature for the metal/Y samples. Crystallinity is inversely proportional to hydrothermal aging temperatures. The crystallinity o f V/Y sample after hydrothermal treating at 823 K had slight changes. A sharp crystallinity drop o f V/Y was observed after hydrothermal treating at 973 K. The whole structure was destroyed at 1023 K or higher hydrothermal temperatures. A significant crystallinity decrease is also observed on the Fe/Y sample steam-aged at 823 K, but the framework structure o f Fe/Y zeolite did not completely collapse even at a steam-aging temperature o f 1073 K. The crystallinity o f Ni/Y decreased 40% after aging at 1073 K. Ca/Y samples had the smallest changes after steam-aging. Figure 1 (fight) shows the specific surface area changes after hydrothermal aging. Surface areas o f V/Y and Ni/Y samples were sensitive to the hydrothermal temperatures. Ca/Y showed smallest effect o f hydrothermal temperature on the surface area o f the E A H - U S Y zeolite. Fe/Y samples had a little larger decrease in surface area than the Ca/Y and Ni/Y samples. 80 *~ 60

<: 400

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~ 2o 0 800 ~.

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:

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900 1000 HydrothermalTemperatures,K Ca/Y

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Fe/Y

~

0 800

, 1100 V/Y

r

Y

=

i ... 900 1000 1100 HydrothermalTemperatures,K Ca/Y, & NirY X FeZY ~ V/Y

354

Figure 1. Crystallinity (left) and specific surface area (right) of metal/EAH-USY after hydrothermal aging at different temperatures.

Figure 1 shows that, even though specific surface area was roughly proportional to the crystallinity, this relationship among four metals was quite different. Fe/Y samples had the highest value of specific surface area relative to crystallinity, possibly due to their loose amorphous structure. The facile fusion and migration properties of V complex oxides resulted in the rapid sintering and caused the amorphous structure in V/Y samples, leading to the lowest specific surface area to crystallinity ratio. Figure 2 (left) depicts the variance of lattice constant with hydrothermal aging temperature. V/Y samples showed the largest decrease in lattice constant due to the rapid dealumination by V. Ca/Y samples had little lattice shrinkage. The lattice constant variance of Fe/Y and Ni/Y were similar to each other, and much smaller to the V/Y samples. 24.55

1100

24.45

"~ M~ 1050

24.35

~

1000

24.25

~ 950 900

"~ 24.15 800 Y

800

900 1000 1100 Hydrothermal Temperatures, K

_-- Ca/Y

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Fe/Y

~

V/Y

~,

Y

~

900 1000 Hydrothermal Temperatures, K CIgY

&

Ni/Y

X

Fe/Y

~

1100 V/Y

Figure 2. Lattice constant (left) and structure collapse temperature (right) of metal/EAH-USY after hydrothermal aging at different temperatures.

The dependence of structure collapse temperature on hydrothermal aging temperature is depicted in Figure 2 (fight). Fe decreased the Y zeolite structure stability, V had an even more severe effect. Ca and Ni had less influence on the structure collapse temperature. Figure 2 shows that the framework SIO2/A1203 ratio increased with increasing hydrothermal aging temperature, while structure collapse temperature decreased. This was attributed to the imbalance between dealumination and Si migration into the A1 defects. The structural vacancy resulting from rapid dealumination decreased the zeolite structural stability. 3.3. TPR Profile of Metal/Y Zeolite Samples CaO did not reduced in TPR experiments due to the positive standard Gibbs free energy associated with the reduction of CaO (375.41kJ/mol) [141. NiO could be reduced to metal Ni. Fe203 was usually reduced to FeO. V205 was reduced to V203 or VO2 in TPR processes. Figure 3 (left) shows TPR curves of Ni/Y samples. There was one reduction peak in each curve. The peak temperature increased and peak area decreased with increasing hydrothermal aging temperature. The degree of reduction calculated on the basis of peak area is listed in Table 4. More than 50 wt% of NiO was reduced to metallic Ni, while the remaining nickel is present as NiO. With a greater degree of reduction, violet samples turned black. The reduction activation energy in Table 4 varied with hydrothermal aging temperature and was proportional to the peak temperature. NiO reduction temperature ranged from 603 K to 1223 K. Ni/Y sample aged at 823 K were reduced at the lower part of this temperature range, but a portion of the NiO was not reduced. This meant the interaction between NiO and EAH-USY zeolite existed in all samples conducted at different hydrothermal aging temperatures. Furthermore, the increase of the reduction peak to high temperatures with increasing aging temperature indicated the enhancement of NiO and EAH-USY zeolite interaction. Therefore, NiO is in three forms in EAH-USY zeolite, i.e. multiple layers

355 NiO in super cage (reducible at low temperatures), monolayer NiO in super cage and beta cage (reducible at high temperatures), NiO-AI203 complex oxides such as spinel in zeolite mesopores (not reduced in TPR experiments). Figure 3 (middle) depicts TPR profiles of Fe/Y samples. After TPR, brown Fe203 had been reduced to black Fe oxides at low valence, corresponding to the reduction peak in each curve. The reduction peak temperature, average valence and reduction activation energy are presented in Table 4. Fe/Y had lower degree of reduction, lower reduction temperature and smaller reduction activation energy than Ni/Y, even though similar results were observed in Table 4. This difference resulted from the positive standard Gibbs free energy for deep reduction of Fe203 [14] and difference in metal interaction with EAH-USY zeolite. Fe destroyed the EAH-USY zeolite structure after hydrothermal aging at high temperature (Figure 1 and 2), enhancing the tendency to form complex FezO3-A1203 oxides. Ni/Y

Fe/Y o.

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z

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I

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723 1023 13231323 Temperature, K

Figure 3. TPR profiles of Ni/Y samples (above l e f t ) , F e / Y samples (above middle) and V / Y samples (above right). The numbers on these curves were hydrothermal aging temperatures.

.

Table 4. Reduction state and activation energy of Metal/EAH,USY samples Hydrothermal a g i n g Reductionpeak Average valence of Reductionactivation temperature, K temperature, K metals . . . . energY, kJ/mol .......................... Ni/Y Fe/Y V/Y N i / Y Fe/Y V/Y NEY Fe/Y V/Y 823 903 803 873 +0.73 +1.75 +3.04 134 84 97 973 973 913 885 +0.76 +1.79 +3.07 199 154 102 1023 1003 923 893 +0.80 +1.82 +3.05 211 162 106 1073 1013 963 898 +0.85 +1.87 +3.09 219 183 115 .

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Figure 3 (right) depicts TPR profiles of V/Y samples. Hydrothermal aging temperature had little influence on TPR peak position and area. V in all samples was reduced to near +3 valence state with color changing from shallow yellow to gray. Quantitative analysis of the TPR curves is listed in Table 4. V/Y reduction activation energy was much smaller than Ni/Y and Fe/Y, consistent with the facile reduction of V205. The peak soanned a larger temperature range than the case of V205 reduction on A1203 support F151,probably due to the intricate state of V205 in EAH-USY zeolite. The structure of this zeolite and amorphous SIO2-A1203 are much more complicated than an A1203 support, resulting in the multiple states of V205 in the V/Y samples. This is the reason that only one peak in TPR curves of Fe/Y samples, instead of several individual peaks for reduction of Fe203--->Fe304---,FeO--,Fe. 3.4. Comment Even though the conclusion that the severity of metal destruction of the EAHUSY structure decreases in the sequence of V>Fe>Ni>Ca is well known, the interaction mechanism is shown here to be very different among the four metals. Figure 4 depicts the variation of non-framework A1 content with non-framework Si content after hydrothermal aging. The non-framework A1 content is more than 40 % in the zeolite at low non-framework Si content, indicating the easy reaction of metals with A1. Therefore, the collapse of the structure was probably induced by the

356 interaction between metal and A1. Thus these four metals interact differently with EAH-USY zeolite. V tended to interact with Si, while Ni interacted with A1. Fe preferred to react with Si at low hydrothermal aging temperature, and react with A1 at high hydrothermal aging temperature. Ca behaved like V and Ni. These processes are illustrated by following equations: V+Z (fast)-,(V-A1)+Z v" (fast)--+(V-A1-Si)+Zv'" Ni+Z (fast)---~(Ni-A1)+ZNi' (moderate)-,(Ni-A1-A1)+ZNi" Fe+Z (fast)-*(Fe-A1)+ZFe, high" (fast)---~(Fe-Al+Si)+ZFe,high" Fe+Z (fast)---,(Fe-A1)+ZFe,low" (fast)---~(Fe-Al+A1)+Zve,low'" Ca+Z (slow)--->(Ca-A1)+Zca" (slow)---~(Ca-A1-A1)+(Ca-A1-Si)+Zca'" In which, Z stands for EAH-USY zeolite. Z with superscript and subscript stands for different states of EAH-USY after interaction with metals. CaO has high melting point and is stable in steam. The radius of Ca2+ is 0.099 nm [14]. Hence, Ca did not drastically destroy EAH-USY structure. Because of the pore structure of Y zeolite, Ca should mainly stay in the super cage. It was observed that surface area decreased faster than the crystallinity in the samples containing more Ca (see Figure 5), resulting from the Ca blockage in EAH-USY. Therefore, Ca obeyed non-uniform distribution model in EAH-USY, which was schematically drawn in Figure 6. ~1.1

io.= 1

~h

'~ 0.9

0.7 ,~0.6 0.5

Figure 4. Variation of nonframework Al content with nonframework Si content.

0.2

0.4

0.6

0.8

Sinon. framework/Sitotal ,

c~v+F~v

A N~

•

wv

o-e.60 "E 40 o 0 100

300

5OO

700

Figure 5. Variation of crystallinity and specific surface area of CAP/" samples. The number in legend was Ca weight percentage content in zeolite.

Specif i c surf ace area, n~/g # 1.57 ---11--4.46 A 6.86

/ ~ , @

Uniform ,. Distribution" G

@" Mn'~

(~

Non-Uniform Distributioff ~

Figure 6 Metal distribution models in EAH-USY.

357 The low melting point and easy migration of high valence V oxide attributed to the destructive effect of V on EAH-USY structure. Furthermore, the similar radius of V5+(0.052 nm) and A13+(0.051 nm) [141allowed the diffusion of V 5+ into the beta cage, which accelerated EAH-USY structural collapse. The rate of specific surface area loss was approximately linear with the decrease in crystallinity (see Figure 7). V content in EAH-USY only changed the range of specific surface area and crystallinity decrease, i.e., the higher the former, the wider the latter. This accounted for the uniform distribution of V in EAH-USY as presented in Figure 6. Increasing V content in EAHUSY equally added the number of initiation centers for destroying the zeolite structure. The physicochemical properties of Fe and Ni were between Ca and V, leading to an intermediate interaction of Fe or Ni with EAH-USY compared to that of Ca and V. 60

,

o~ 50 40 :r

O

Figure 7. Variation of crystallinity and specific surface area of V/Y samples. The number in legend was V weight percentage content in zeolite.

30

0 -

'

'

~

200

'

';

400

600

,.~:~eci f i c sur f ace area, #

1.79

~

3. 63

800 r~/g

--= 6. 56

8O

Figure 8. Variation of crystallinity with the valence of metal ions. The number in legend was hydrothermai aging temperature.

~ 20 O

0

~

2((N)

' 2( N )

I~tal r

823~973

3(Fe) i o n valence A

1023

5(V) X

1073

Moreover, the structure destruction of EAH-USY by metals was found to be related to the valence state of the metal ions. As shown in Figure 8, the higher the valence of metal ions, the more serious the structural effect of these metals. This might be explained either by the repulsive force between metal ions or the difficulty of diffusion of low valence metal ions in zeolite inner channels due to their large radius. In commercial RFCC units, it is useful to alleviate metal contamination by controlling the excess oxygen concentration in regenerator in order to keep the metals deposited on catalysts in a low valence state. 4 Conclusion

EAH-USY is a novel zeolite with high crystallinity, hydrothermal stability and metal-tolerant properties. Metals in this zeolite were mainly in three states: in the

358

super cage in multiple layer forms, in monolayer form in super cage, or in the beta cage. Other metals formed complex oxides with A1203 in zeolite mesopores. Ca in EAH-USY did not evidently affect the crystal lattice constant. Reduction of Ni oxide in EAH-USY zeolite required higher temperature than Fe and V. V interacted with EAH-USY at high temperature and completely destroyed the structure. Fe destroyed the zeolite structure over a wide temperature range, but the structure of EAH-USY did not completely collapse due to the interaction between Fe and the zeolite. A mechanism and models are proposed for the distribution and interaction of metals in EAH-USY zeolite. V was easily distributed in the zeolite and obeyed a uniform distribution model, while Ca possibly followed a non-uniform distribution model. The interaction between metals and the EAH-USY zeolite was caused by the chemical reaction of metals with A1 in the zeolite. Then, in various ways, depending on the type of metals, the metals destroy the zeolite structure. After reacting with A1, V tended to react with Si to affect the structure, while Ni continuously reacted with framework A1 of zeolite. 5 References 1. CarlosA.Trujillo, J. Catal., 168, 1-15(1997). 2. RunshengZhuo, Fangzhu Wang, Wenru Wu, Prepr.-Am. Chem. Soc., Div. Pet. Chem., 43(2), 332333(1998). 3. Lori T. Boock, Joanne Deady, Catalyst Deactivation, 1997, pp367-374. 4. JinhaiHe, Jiasheng Ai, Chinese J. Petroleum Processing, 12(1), 49-55(1996). 5. H. Geoffrey, L. Woolery, D. Maria, Prepr.-Am. Chem. Soc., Div. Pet. Chem., 41(2), 403409(1996). 6. YanfeiShen, Fluid Catalytic Cracking, 1994, pp209-229. 7. P. Hudec, A. Smieskova, Stud. Surf. Sci. Catal. 105(C), 2043-2050(1998). 8. P. O'Connor, E. Brevoord, Prepr.-Am. Chem. Soc., Div. Pet. Chem., 41(2), 428-432(1996). 9. F. Hemandez, R. Garcia, De. Leon, Catalyst Deactivation, 1997, pp455-462. 10. P. O'Connor, A. C. Pouwels, Stud. Surf. Sci. Catal., 88, 129-144(1994). 11. Nicholas W. Hurst, Sthphen J. Gentry, Alan Jones, Catal. Rev.-Sci. & Eng., 24, 233-309(1982). 12. CongjunHuang, Metals on USY Zeolites, Master Thesis, RIPP, Beijing, China, 2001. 13. Huiping Tian, CN Appl. No. 99110995.3. 14. J.A. Dinn, Handbook of Chem., Chinese Version, Science Press, Beijing, 1991, pp 117-123. 15. Yixin, Liu, V/A1203under Hydrothermal Conditions, Master Thesis, RIPP, Beijing, China, 1999.