CeO2–Al2O3 by Adding

Jul 8, 2014 - Catalytic cracking of Chinese number 3 jet fuel (RP-3) was used to examine the catalytic activities and thermal stabilities of the as-pr...
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Catalytic Cracking of RP‑3 Jet Fuel over Pt/CeO2−Al2O3 by Adding Cu/ZSM‑5 Yi Jiao,† Jianli Wang,*,† Quan Zhu,‡ Xiangyuan Li,‡ and Yaoqiang Chen† †

Key Laboratory of Green Chemistry and Technology of the Ministry of Education, College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, People’s Republic of China ‡ College of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, People’s Republic of China ABSTRACT: Cu/ZSM-5 (CZ) zeolite and Pt/CeO2−Al2O3 (PCA) composite catalysts (PCA, PCA + CZ, and CZ) were prepared using the impregnation method, the as-prepared catalysts were characterized using an automatic adsorption instrument, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). Catalytic cracking of Chinese number 3 jet fuel (RP-3) was used to examine the catalytic activities and thermal stabilities of the as-prepared catalysts. It was found that PCA + CZ had better catalytic cracking activities and high-temperature stabilities compared to the other catalysts. This is in well accordance with an increase in the strong acid amount and the appearance of a bimodal structure of PCA + CZ. Rapid deactivation of the heat sink over CZ at 700 °C was possibly caused by their poor stabilities under high temperatures. The addition of CZ onto PCA to form a composite catalyst may be an effective approach to maintain both catalytic activity and thermal stability (>650 °C).

1. INTRODUCTION Because of high thermal loads in hypersonic flight vehicles, the regenerate cooling of the scramjet has been on the agenda of engine design in recent years. Physical heat sinks of hydrocarbon fuels have not accounted for the conditions of engine cooling in hypersonic flight vehicles. The fuel must precede thermal cracking and catalytic cracking to generate a larger chemical heat sink before entering into the combustion chamber, and therefore, it is an important factor in realizing the engine regenerative cooling design.1−4 However, thermal cracking reactions require higher temperature and are readily subject to coking, leading to catalytic cracking becoming a major research topic in this field. An appropriate cracking catalyst could enhance the endothermic effects through improving the selectivity of preferred products (low-carbon alkenes) and stabilities under high temperature.5−7 In recent years, ZSM-5 zeolite catalysts have been developed at low prices, with unique pore structure, adjustable acidity, high activity, and selectivity for hydrocarbon cracking.8−13 Liu et al.9 investigated the catalytic activity and stability by a series of wall-coated HZSM-5 zeolite catalysts (ZC) with a Si/Al molar ratio of 25−140 on catalytic cracking of supercritical ndodecane (4 MPa and 550 °C), and they found that the catalytic cracking activities and stabilities of the coatings increased in the order: ZC25 < ZC50 < ZC100 < ZC140 (with the numbers representing the Si/Al ratio). Sicard et al.10 compared the catalytic cracking of n-dodecane over HZSM-5 and HY zeolites with thermal cracking in a stirred batch reactor heated to 425 °C under pressures up to 15 MPa and found that, at lower temperatures (375 °C−400 °C), the conversion for cracking over the HZSM-5 catalyst was approximately 1 time higher than that for thermal cracking. Xing et al.14 investigated the cracking reaction of tricyclo[5.2.1.02.6]decane (JP-10) over the HZSM-5 catalyst. In the temperature range of 500−650 °C, the conversion rate by catalytic cracking was 60−70% higher © 2014 American Chemical Society

than thermal cracking. Even so, many researchers focused on the improvement of shape-selective effects, acidity, and stability mainly by modifying HZSM-5. The transition metals, such as La, Ag, and Cu, were introduced into HZSM-5 to create both a relatively good stability and high yield of low-carbon alkenes.15,16 Zhang et al.17 investigated the cracking reaction of the endothermic fuel NNJ-150 over USY, exchanging ZSM-5 catalysts with Ag and La. The Ag- and La-modified catalysts had a higher selectivity for low-carbon alkenes (600 °C, 47.2%). A partially Cu-modified HZSM-5 provides an optimum balance between the number/strength of acid sites and the type/ amount of metals as a fluidized catalytic cracking (FCC) catalyst additive for maximization of low-carbon alkenes and low coke formation.18 However, up to now, little work has been performed on hydrocarbon cracking using ZSM-5 and modified ZSM-5 zeolites at high temperatures (>650 °C). Our early research concerning the application of Pt/CeO2−Al2O3 (PCA) in the kerosene cracking reaction revealed some useful findings (good high-temperature stability but poor alkene selectivity).19,20 Therefore, it is important to enhance the alkene selectivity of PCA by strengthening acid sites and hightemperature stabilities of ZSM-5 through the thermal modification of existing catalysts. In this work, the Cu-modified ZSM-5 zeolite was added to PCA and their catalytic activities were tested at the conditions of 600−750 °C and 3.5 MPa using Chinese number 3 jet fuel (RP-3) as the model fuel. The aim of this work will provide insight into cracking catalyst screening for the catalytic heat exchangers for the advanced aircrafts. Received: February 11, 2014 Revised: July 7, 2014 Published: July 8, 2014 5382

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2.3. Catalyst Characterization. The textural properties of the catalysts were measured using a QUADRASORB SI automated surface area analyzer (Quantachrome Instruments, Boynton Beach, FL). The samples were evacuated for 1 h at 300 °C and then cooled to −196 °C using liquid N2, at which point N2 adsorption was measured. X-ray diffraction (XRD) diffractograms were obtained using a DX-2500 Xray diffractometer (China Dandong Fangyuan Instrument Co., Ltd.) with a graphite monochromator and Ni filter, using Cu Kα radiation, operated at 40 kV and 25 mA. The samples were scanned in the 2θ range of 5−80° with a step size of 0.03°/s. X-ray photoelectron spectroscopy (XPS) was performed using a XSAM-800 spectrometer (Kratos Co., U.K.) with Mg Kα excitation under a high voltage (13 kV) and current (20 mA), calibrated internally by the carbon deposit C1s binding energy at 284.8 eV. The surface acidity of all of the catalysts was tested by using a TP-5076 temperature-programmed desorption (TPD) experimental device. The sample (100 mg) was heated to 400 °C with a heating rate of 8 °C/min in a flow of N2, kept at that temperature for 45 min, and then cooled to room temperature. The gas flow was then switched to NH3 (2%) in N2 (flow rate of 20 mL/min). The surface acidity was carried out from room temperature to 650 °C, at a heating rate of 8 °C/min (thermal conductivity detector).

2. EXPERIMENTAL SECTION 2.1. Support and Catalyst Preparation. CeO2−Al2O3 was prepared by the co-precipitation method.21,22 Ce(NO3)3 and Al(NO3)3 were dissolved in water at a molar ratio of n(Ce)/n(Al) = 1:1, and then precipitation was induced with a buffer solution containing NH3 and (NH4)2CO3. The precipitate was aged, dried, and heated for 3 h at 600 °C to form the support material, denoted by CA. Cu/ZSM5 (CZ) zeolite was prepared using the impregnation method. HZSM-5 (Si/Al ratios of 38) zeolite catalyst was purchased from the Nankai University Catalyst Plant (Tianjin, China), impregnated using a CuCl2· 2H2O solution, then dried at 120 °C, and heated for 2 h at 500 °C to obtain Cu/ZSM-5 catalyst powder. The PCA catalyst (Pt content was 0.50 wt %) was prepared by the impregnation method and then heated for 2 h at 500 °C. CZ (10%) was added to PCA, mixed with water to obtain a pot of slurry by ball milling, then coated on the inner wall of a stainless-steel tube by vacuum, with loads and uniformity of the catalyst being controlled by adjusting the vacuum pressure and slurry viscosity, then dried at 120 °C, and heated for 2 h at 500 °C to obtain a tube coated with catalyst, denoted by Cat2 (PCA + 10% CZ). PCA was labeled as Cat1. Cu/ZSM-5 catalyst was named as Cat3 (CZ). The catalyst loading on the inner surface of the tube is 0.2 ± 0.005 g/70 cm, which lies in each catalyst. 2.2. Catalytic Activity Evaluation. The catalytic cracking of RP-3 was carried out on a custom-built reactor. The experimental apparatus includes a feed system, flow-control system, temperature-control system, pressure sensor, reaction chamber, condensing column, and an analyzer, as shown in Figure 1. The reaction tubes were SS304

3. RESULTS AND DISCUSSION 3.1. Influence of Adding Cu/ZSM-5 on Catalytic Activity. 3.1.1. Gas Yield. The thermal cracking and catalytic

Figure 1. Schematic diagram of the apparatus: (1) feed tank, (2) highpressure metering pump, (3) check valve, (4) mass flow meter, (5) pressure system, (6) heating system, (7) cold trap, (8) filter, (9) backpressure valve, (10) gas−liquid separator, (11) liquid receiver, (12) gas chromatograph, and (13) wet gas flow meter.

Figure 2. Gas yield of thermal cracking and catalytic cracking of RP-3 fuel.

Table 1. Gas-Phase Product Distribution and Ratio of Alkene/Alkane of the Cracking Reaction of RP-3 Fuel stainless steel (2 mm inner diameter × 700 mm) and coated with the catalyst (0.2 g). The catalytic performance measurement was carried out from 600 to 750 °C, and the pressure was kept at 3.5 MPa. The fuel was injected into the reaction tubes at the flow rate of 76 mL/min using a dosing pump. The reaction effluent was quenched by passing through a water condenser and was separated by a gas−liquid separator. The volume of the gaseous product was quantified by the water displacement method, and the liquid residues were collected with a conical flask and weighed. A six-port valve sampled the gaseous products, which came from the gas−liquid separator in pulses and were analyzed by gas chromatography (GC, GC2000 III, Shanghai Institute of Technology and Computing), equipped with a HP-Al/s capillary column (Agilent Technologies Co., 50 m × 0.53 mm) and a flame ionization detector (FID). H2 was analyzed by GC−TCD using a 2 m packed column (TDX-01). The liquid products were identified by HP-6890/5973 gas chromatography−mass spectrometry (GC−MS, Agilent Technologies, Inc., Santa Clara, CA) with a FID and a HP-5/ MS column (50 m × 0.25 mm). The gas yield and heat sink were determined at different reaction temperatures. The error of the mass balance was less than 3.0% between feeds and products involving gas, liquid products, and coke.

mole fraction (%) temperature (°C) 600

650

700

750 a

5383

sample none PCA PCA + CZ none PCA PCA + CZ none PCA PCA + CZ PCA PCA +

CZ

CZ

CZ

CZ

H2

alkane

alkene

ene/anea

3.9 3.9 10.9 9.8 8.5 9.4 8.5 11.8 8.5 13.9 9.7 10 9.8 11

60.2 59.1 50.8 42.6 65.6 56.3 51.4 47.0 56.3 50.3 44.9 50.7 52.6 46

35.8 37.0 38.3 47.6 25.9 34.3 39.1 41.2 35.2 35.7 45.4 39.3 37.5 42.8

0.594 0.625 0.755 1.150 0.396 0.609 0.761 0.876 0.620 0.710 1.014 0.775 0.712 0.929

ene/ane instead of alkene/alkane. dx.doi.org/10.1021/ef500374c | Energy Fuels 2014, 28, 5382−5388

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had improved an extra 30% compared to Cat1 at each corresponding reaction temperature, and Cat3 (CZ) showed no obvious improvement in the gas yield. To achieve the same gas yield, the reaction temperature of catalytic cracking was lower than that needed for thermal cracking, which shows that the catalyst reduced the cracking reaction temperature. The addition of catalysts also increased the severity of the cracking reaction by lowering the activation energy of the reaction and increasing the reaction rate,23,24 while enhancing the yield of small hydrocarbons and hydrogen. It was observed that Cat3 (CZ) was not an efficient cracking catalyst relative to PCA above 600 °C; however, when mixed with PCA, the hightemperature activity improved. 3.1.2. Gas−Liquid Phase Distribution and Selectivity of Low-Carbon Alkenes. The major gaseous products obtained from the catalytic cracking of RP-3 were hydrogen, low-carbon alkanes (methane, ethane, propane, and butane), and lowcarbon alkenes (ethylene, propylene, isobutylene, and butadiene), as shown in Table 1. The selectivity of alkenes in the gaseous products was defined by the alkene/alkane ratio. The gaseous product composition from cracking RP-3 changed with the temperature and the addition of catalysts. The H2 content from catalytic cracking was higher than thermal cracking because of the dehydrogenation role of Pt.25,26 Thermodynamic analysis shows that, if unsaturated hydrocarbons, such as ethylene, propylene, and butylene, and hydrogen are produced during the cracking reaction, the heat absorption of the reaction is large. The lower the molar mass, the larger the heat absorption, and a higher chemical heat sink will be obtained, which results in good ignition performance of the cracking gas.5−7 We can see from Table 1 that the alkane content decreases, while the alkene content increases with the addition of CZ onto PCA, which is due to the improvement of the alkene selectivity through increasing the ratio of the carbon cation mechanism in catalytic cracking.27,28 The alkene selectivity of CZ was good at 600 and 650 °C but decreased at 700 °C. However, PCA + CZ shared improved alkene selectivity between 600 and 750 °C, while the contrast was observed for PCA, which is in accordance with the increased amount of strong acid and proportion of strong acid. The amount of strong acid and the proportion of strong acid in the PCA + CZ catalyst are increased by the addition of CZ, which is good for improving the alkene selectivity. The alkene selectivity is a guarantee of higher endothermic effects of fuel cracking. Therefore, PCA + CZ had an excellent contribution to the heat absorption of fuel. Table 2 compares the major liquid product distribution of RP-3 jet fuel from thermal cracking and catalytic cracking at different temperatures, and the major liquid products were divided into four categories: alkenes, alkanes, cycloalkanes, and arenes. Clearly, for both thermal and catalytic cracking of RP-3, the major liquid products are alkanes at 600, 650, and 700 °C. As a result of a rising temperature, the yield of alkenes increased for thermal cracking and the PCA, PCA + CZ, and CZ catalytic

Table 2. Liquid-Phase Product Distribution of the Cracking Reaction of RP-3 Fuel mass (%) temperature (°C) 600

650

700

liquid product

thermal cracking

PCA

CZ

PCA + CZ

alkenes alkanes cycloalkanes arenes alkenes alkanes cycloalkanes arenes alkenes alkanes cycloalkanes arenes

12.54 45.97 13.58 27.91 13.42 43.86 11.59 31.13 20.25 24.43 4.72 50.59

8.09 51.83 12.71 27.44 9.65 45.51 16.66 28.19 13.29 48.7 12.58 25.43

5.94 57.67 18.32 18.08 9.51 41.64 13.56 35.3 19.05 28.55 8.95 43.47

3.31 52.75 13.55 30.39 5.61 56.36 17.02 21.02 6.11 51.85 14.34 27.69

Figure 3. Heat sinks (Qm) of thermal cracking and catalytic cracking of RP-3 fuel.

cracking experiments based on RP-3 were carried out. The observed gas yield of RP-3 was defined as gas yield =

initial mass of RP‐3 − final mass of residues initial mass of RP‐3 (1)

× 100%

and the results are shown in Figure 2. It is shown that the gas yield of RP-3 is evidently heightened by adding CZ catalyst into PCA. The results show that the gas yields (56.9%, 750 °C) of catalytic cracking are higher than thermal cracking over Cat2 (PCA + CZ). Thermal cracking and catalytic cracking over Cat3 (CZ) were stopped at 700 °C because carbon deposition blocked the stainless-steel microchannel (passivation of the inner wall could decrease carbon deposition of the thermal cracking and made sure that the reaction proceeded at higher temperatures). At 600, 650, and 700 °C, the gas yields over Cat1 (PCA) increased respectively by 284, 33, and 64% compared to thermal cracking, respectively. Cat2 (PCA + CZ) Table 3. Textural Performance of Catalysts

crystallinity (%) sample

surface area (m2/g)

pore volume (mL/g)

average pore diameter (nm)

600

650

700

750

PCA PCA + CZ CZ

129.4 121.9 327.5

0.34 0.25 0.19

5.3 4.2 1.1

41.0 45.0 59.7

47.4

51.7

57

5384

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Figure 4. N2 adsorption−desorption isotherms and pore diameter distributions of catalysts.

Figure 6. NH3-TPD results for different catalysts.

at an elevated temperature. A good endothermic effect (the higher heat sink) is a synergistic effect of higher gas yield and better alkene yields in the cracking product. The Qm over Cat3 (CZ) increased by 0.34 and 0.30 MJ/kg compared to thermal cracking at 600 and 650 °C, respectively. However, a significant decrease was observed for Cat3 (CZ) at 700 °C. The CZ catalyst has a poor gas yield compared to PCA + CZ < 650 °C, but the alkene yield is better than PCA + CZ. This implies that CZ has good endothermic effects at 600 and 650 °C. The Qm for Cat2 (PCA + CZ) reached 3.18 MJ/kg (increased by 0.68 MJ/kg compared to thermal cracking) and 3.96 MJ/kg at 700 and 750 °C, respectively. The introduction of PCA, which has high-temperature stability and has the ability to form a new catalyst (CZ can highly disperse into PCA), can improve the cracking reaction to generate the low-carbon alkenes > 650 °C. 3.2. Texture Properties of Catalysts. Table 3 lists the surface area, pore volume, and average pore size of catalysts. The surface area and average pore diameter changed little after adding CZ to the PCA catalyst; therefore, the surface area is not the main reason for the difference between PCA + CZ and PCA but the appearance of the bimodal pore size by adding CZ. Small-molecule hydrocarbons pass through the small pores easily in catalytic cracking reactions, and carbon deposition can

Figure 5. XRD patterns of different catalysts.

cracking. It is worth noting that the amount of arenes for thermal creaking and catalytic cracking of CZ were gradually increased with the temperature and was much more than that for the catalytic cracking of PCA and PCA + CZ. 3.1.3. Heat Sink. Heat absorption of a fluid (heat sink) is equivalent to the heating power (W) multiplied by the thermal efficiency (η). The heat sink (Qm) can be determined by heat absorption divided by the mass flow rate, with the computational formula as shown Wη UIη = (2) G 1000G where Qm is the heat sink (kJ/kg), G is the mass flow rate (kg/ s), W is the heating power (kW), η is the thermal efficiency, U is the voltage (V), and I is the current (A). The error of the method was less than 3.0% compared to the heat absorption of a standard material, and the error of repetitive experiments of each group of catalysts at different temperature spots was less than 2.5%. Figure 3 shows that the heat sinks (Qm) of catalytic cracking are higher than those of thermal cracking at each temperature and increase significantly Qm =

Table 4. Electronic Binding Energies and Surface Contents of Pt, Al, Ce, O, and Si in Different Catalysts Eb (eV)

surface concentration (%)

catalyst

Al 2p

Ce 4f7/2

O 1s

Pt

Al

Ce

O

Si

PCA PCA + CZ

74.2 74.2

882.4 882.6

529.5 529.6

0 0

5.20 4.82

39.63 36.59

55.17 57.38

0 1.21

5385

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Table 5. Acidity of Catalysts temperature (T, °C) catalyst PCA PCA + CZ CZ

weak acid site (mmol/g) medium acid site (mmol/g) 0.075 0.062 0.061

strong acid site (mmol/g)

total acid site (mmol/g)

first peak

second peak

third peak

0.01 0.244 0.231

0.182 0.410 0.451

156 154 146

252 264 208

480 509 440

0.097 0.104 0.159

are not obvious. The Al, Ce, and O atomic ratios of Cat1 (PCA + CZ) are close to those of Cat2 (PCA), showing that the addition of Cu/ZSM-5 cannot change the surface concentration of the catalyst. Pt was not seen on the catalysts. 3.6. NH3-TPD. NH3-TPD techniques were used to study the acidities of the catalysts, such as total amount, nature, and distributions, and to find the possible explanations for the above experimental results. Figure 6 shows the NH3-TPD profiles of the catalysts. Adsorbed NH3 on the catalyst surface appears to be in a continuous desorption state and shows that the surface acidic center is homogenized. The profiles for each catalyst show a strong desorption peak in the low-temperature area (100−400 °C), and the order of the desorption peak of the weak−medium acid is Cat3 (CZ) > Cat2 (PCA + CZ) > Cat1 (PCA). High-temperature (400−650 °C) desorption peaks of Cat2 (PCA + CZ) and Cat3 (CZ) are significantly larger than those of Cat1 (Pt/CA). The C−C fracture needs to occur in strongly acidic centers of the catalysts,36−39 while hydrogentransfer reactions are in competition with the C−C fracture and can occur at different acidic centers (weak, medium, and strong acids). However, the hydrogen-transfer reaction mainly produces alkanes and aromatic macromolecules and can also contribute to carbon deposition.40,41 Therefore, an improved surface acidity of catalysts increased the proportion of strong acidic centers, at the same time improving the alkene selectivity. Table 5 shows that the amount of acidity is twice than that of Cat1 (PCA) after adding Cu/ZSM-5 zeolite into Pt/CeO2− Al2O3. The amount of strong acidity reached 0.244 mmol/g and was much larger than Cat1 (PCA). Cat1 (PCA) is mainly composed of weak−medium acid. The acidic strength is strong for Cat2 (PCA + CZ) and Cat3 (CZ). The addition of Cu/ ZSM-5 zeolite obviously strengthens the desorption peak of strong acid of Pt/CeO2−Al2O3 and increases the surface acidity of catalysts and the density of the strong acidic center of the Pt/ CeO2−Al2O3 catalyst, which increase the possibility of the C− C fracture and inhibits the hydrogen-transfer reaction. Thus, the strong acidic center density is more concentrated and increases the alkene selectivity of the cracking reaction,36,37 and therefore, a larger heat absorption can be obtained.

easily accumulate inside the big pore to prevent the catalytic reaction.29 3.3. N2 Adsorption−Desorption Isotherms and Pore Diameter Distributions of Catalysts. Figure 4a shows the N2 adsorption−desorption isotherms of the catalysts. All of the samples with typical IV-type adsorption isotherms have an obvious hysteresis loop caused by the capillary condensation phenomenon.30 The isotherms of these samples are typical H2type, suggesting that the pore shapes are slit or bottle type.31 It can also be seen that the adsorption amount increases rapidly at P/P0 = 0.8−0.9, which indicates that the samples have large average pore openings and relatively narrow pore size distributions (Figure 4b). Figure 4b shows that the pore size of each catalyst is concentrated in the region of 2−14 nm. The most probable pore size of Cat1 (PCA) is 6 nm. The most probable pore size of Cat3 (CZ) is 2 and 4 nm. When they mixed together by ball milling at high speeds, CZ may enter into the pore of PCA or hide between the PCA particles. The pore size decreases and appears bimodal because of adding Cu/ ZSM-5 zeolite. The bimodal pore size is conducive to different sizes of activated molecules of the cracking reaction reacting in different sizes of pores; it is beneficial to the cracking reaction.32,33 3.4. XRD. The XRD technique was used to study the hightemperature stabilities of catalysts. Figure 5 shows the XRD diffractograms of the catalysts. The diffractograms show peak located at 28.8°, 32.9°, 47.4°, 56.4°, and 76.7°, indicating the presence of the cubic fluorite structure of the CeO2 crystal. The diffraction peak at 67.1° is caused by the presence of γ-Al2O3. The Cat3 (CZ) shows the standard diffraction peak of ZSM-5 and is highly crystallized. The CZ phase is not found in the Cat2 (PCA + CZ) XRD spectrum and suggests that Cu/ZSM-5 was highly dispersed in the CeO2 cubic fluorite crystals and γAl2O3 phase.34 The crystallinity of PCA + CZ (Table 3) increases with the temperature, and it is still less than 60% at 750 °C. As everyone knows, the crystallization and collapse of the pore structure of the catalysts under higher temperatures will decrease both the surface acidity and the surface area. However, the addition of PCA inhibits the crystallization and collapse of the pore structure of the CZ catalysts and prevents the degradation of the surface area and surface acidity, thus making CZ keep the superior performance at higher temperatures. The diffractograms of Cat3 (CZ) show no peaks associated with Cu. This suggests that Cu species may be in the cation site of ZSM-5. In the Pt catalysts, no peak is observed for Pt, indicating that Pt is amorphous or highly dispersed on the support,35 which is beneficial to the catalytic activity. 3.5. XPS. The XPS binding energies and atomic ratios of Cat1 (PCA) and Cat2 (PCA + CZ) are listed in Table 4. It can be seen that the Al 2p, Ce 4f7/2, and O 1s binding energies of Cat1 (PCA) are 74.2, 882.4, and 529.5 eV, respectively, while the values are 74.2, 882.6, and 529.6 eV for Cat2 (PCA + CZ) respectively. The XPS binding energies are changed slightly. It shows that the impacts of Cu/ZSM-5 on the electronic valence

4. CONCLUSION Catalytic cracking of RP-3 jet fuel was successfully achieved in a catalyst-coated (PCA, PCA + CZ, and CZ) tube reaction. The catalytic cracking activity and stability of the coating catalyst was evidently heightened by adding CZ to PCA. Different sizes of pores in PCA + CZ can be adjusted. CZ is highly dispersed in the PCA lattice composed of CeO2 cubic fluorite crystals and the γ-Al2O3 phase. PCA + CZ acidity increases catalytic performance and low-carbon alkene selectivity derived from the increased strong acid amounts. Catalytic cracking of RP-3 was dependent upon the activity of the PCA + CZ catalyst and also the pore structure and acidity. 5386

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AUTHOR INFORMATION

Corresponding Author

*Telephone/Fax: +86-028-85418451. E-mail: wangjianli@scu. edu.cn. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The research was supported by the National Natural Science Foundation of China (91016002, J1103315) and the National High-Tech Research and Development Program of China (2006AA01A119).

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