Catalytic Cracking of Methylcyclohexane on FAU, MFI, and Bimodal

10486

Ind. Eng. Chem. Res. 2010, 49, 10486–10495

Catalytic Cracking of Methylcyclohexane on FAU, MFI, and Bimodal Porous Materials: Influence of Acid Properties and Pore Topology Rhona Van Borm,† Marie-Françoise Reyniers,*,† Johan A. Martens,‡ and Guy B. Marin† Laboratorium Voor Chemische Technologie, Ghent UniVersity, Krijgslaan 281 (S5), B-9000 Gent, Belgium, and Centrum Voor OpperVlaktechemie en Katalyse, Katholieke UniVersiteit LeuVen, Kasteelpark Arenberg 23, B-3001 HeVerlee, Belgium

Catalytic cracking of methylcyclohexane has been studied on eight commercially available zeolites, five FAUs and three MFIs, and on two newly developed zeotype materials with bimodal porous structure, BIPOMs. Both BIPOMs are composed of an MFI ultramicropore (99%) dissolved in 40 wt % aqueous tetrapropylammonium hydroxide (TPAOH; Alfa) and tetraethyl orthosilicate (TEOS; Acros, 98%) in a molar Al:TEOS:TPAOH:H2O ratio of 0.5:25:9:400. BIPOM3 was obtained by replacing 20 mol % TEOS with phenyltrimethoxysilane (PhTMS; Acros), leading to a clear solution with a molar Al:PhTMS:TEOS:TPAOH:H2O ratio of 0.5:5:20:9:400. In this way, zeotype materials were synthesized with a bimodal pore network, distributed over super-

10487

and ultramicropores. Ultramicropores of both BIPOMs are of the MFI type.15 The supermicropores have larger dimensions. The particle size of BIPOM1 was 1-6 µm, while that of BIPOM3 was around 1 µm. BIPOM1 did not show long-range order or wide-angle X-ray diffraction (XRD). BIPOM3, on the contrary, does display the XRD pattern of the MFI zeolite. Details of the synthesis procedure and characterization of both zeotype materials are given elsewhere.17,35-37 The main features of the BIPOMs are also given in Table 1. The unusually high micropore volume of BIPOM1 (0.64 cm3 g-1) is attributed to the large contribution of supermicropores with estimated dimensions 1.3-2.1 nm.35 BIPOM3 has a total pore volume of 0.28 cm3 g-1, 0.18 cm3 g-1 micropores and 0.10 cm3 g-1 mesopores with diameter up to 10 nm. Compared to the reference colloidal MFI obtained via the clear solution method without PhTMS substitution, displaying a total micropore volume of 0.13 cm3 g-1,35 BIPOM3 presents an enhanced microporosity of 0.05 cm3 g-1 because of templating with the organosilane compound PhTMS. Catalytic Experiments. Cracking experiments have been performed in a recycle electrobalance reactor.38 In this type of reactor, the weight of the catalyst basket is measured and registered continuously. The reactor operates gradientlessly at high conversion because of the use of external recirculation. Activity and selectivity are determined via online gas chromatographic (GC) analysis of the reactor effluent in two gas chromatographs. Dimethyl ether is added to the effluent after exiting the reactor and is used as the internal standard. A Chrompack CP-9003 gas chromatograph with a flame ionization detector (GC-FID) is used to identify and quantify the individual hydrocarbons in the effluent after separation on a capillary CPSil PONA CB for ASTM D 5134-90 fused-silica column. The temperature program applied (1 min at 223 K, +6 K min-1, 10 min at 473 K) allows one to detect acyclics, cyclics, aromatics, and cycloaromatics with a maximum of 10 carbon atoms. A Chrompack CP-9000 gas chromatograph with a thermal conductivity detector (GC-TCD) is used to quantify the amount of nitrogen in the effluent. A good separation of the components on the packed Alltech SS Porapak N column is obtained using a temperature program (2 min at 373 K, +10 K min-1, 8 min at 423 K). An extensive description of the operating procedure can be found elsewhere.17 Typically, during an experiment, five samples of the reactor effluent obtained after different times on stream are analyzed with a GC-FID to quantify the individual hydrocarbon species present. The first sample is taken shortly after the transient hydrodynamic phenomena have decayed (switching from pure N2 during the pretreatment to a feed mixture of methylcyclohexane + N2 during the reaction causes pressure imbalances), the next three samples are taken at relatively short times on stream (3, 6, and 11 min after the first sample), and finally the last sample is taken at a relatively long time on stream (roughly at 1 h 30 min). Prior to its use in catalytic experiments, the zeolite powder is pelletized (500-710 µm diameter) and pretreated (heating at +5 K min-1 and keeping it at 773 K for 1 h under a N2 flow) to remove adsorbed water and other contaminants and to convert zeolites supplied in ammonium form to those in hydrogen form. Table 2 gives an overview of the experimental conditions investigated and the range of conversion obtained for each catalyst. The reaction temperature was fixed at 748 K, the methylcyclohexane partial pressure was set at 7 kPa, the catalyst mass was varied from 60 to 350 mg, and the methylcyclohexane flow rate ranged from 1.9 to 8.4 µmol s-1. The reaction temperature was chosen somewhat below industrial operating

10488

Ind. Eng. Chem. Res., Vol. 49, No. 21, 2010

Table 2. Range of Cracking Conditions zeolite LZ-Y20 Y62 CBV500 CBV720 CBV760 CBV3020E CBV5524G CBV8014 BIPOM1 BIPOM3 a

0 0 a T (K) pmch (103 Pa) W/Fmch (kgcat s mol-1) X (mol %)

748 748 748 748 748 748 748 748 748 748

7 7 7 7 7 7 7 7 7 7

13-82 8-103 34-100 30-83 7-114 13-83 13-107 11-107 64-187 30-113

29-54 7-39 64-72 43-55 9-45 29-58 17-45 4-25 2-5 5-12

The catalyst mass W refers to the fresh zeolite before pretreatment.

temperatures in order to avoid interference of thermal cracking, occurring via radical chemistry, with the mechanism of catalytic cracking. The reactant partial pressure is high enough to allow both monomolecular and bimolecular cracking reactions. The molar flow rate of any species i is obtained from the GC peak area, Ai, the calibration factor, CFi, the molecular masses of both species i, MWi, and the internal standard, MWDME, and the molar flow rate of the latter, FDME, via MWDMEAiCFi Fi ) FDME MWiADMECFDME

(1)

The conversion of methylcyclohexane is calculated as the number of moles of reactant converted per mole of reactant fed Xmch ) 100

F0mch - Fmch F0mch

(2)

0 and Fmch respectively the feed and outlet molar flow with Fmch rates of methylcyclohexane. The selectivity toward a product i is computed as the number of moles of product i formed per mole of methylcyclohexane converted

Si ) 100

Fi F0mch

- Fmch

(3)

Note that, because the selectivity is expressed on a molar basis, the total sum of the product selectivities can be higher than 100%. Activities of the various catalysts are compared based on the number of active sites available, NH+. The number of acid sites used in this expression is obtained by multiplying the catalyst mass, W, with the total acid site concentration, Ct, given in Table 1 for the investigated catalysts. NH+ ) WCt

Figure 1. Elementary steps involved in the catalytic cracking of cycloalkanes on zeolites.

(4)

The site time yield is defined as the number of moles of reactant converted per mole of acid sites and per second, i.e., 0 ). X/(NH+/Fmch The absence of external mass and heat transfer limitations was verified previously in 2,2,4-trimethylpentane cracking17 by using correlations from the literature39 and performing test experiments with different pellet sizes. Note that both methods only allow one to study the absence of mass and heat transfer limitations at the pellet level, not inside the zeolite crystal. Because methylcyclohexane is a smaller molecule than 2,2,4trimethylpentane (the kinetic diameters are 0.60 and 0.62 nm, respectively40), it can be expected that external mass and heat transfer limitations will be absent in methylcyclohexane cracking as well.

The data reported in this paper refer to the fresh catalyst and were obtained by extrapolating the values of conversion and product selectivities, observed as a function of the time on stream, to a time on stream of zero in order to exclude the effect of coke formation on the observed catalyst behavior, which falls beyond the scope of this work. Because coke formation is inhibited on MFI zeolites41 and plays therefore only a minor role, the deviation from the trendlines due to extrapolation of both the conversion and selectivity values toward a time on stream of zero is much less pronounced for MFI than for FAU, which is highly susceptible to coke formation during catalytic cracking. To obtain these extrapolated values, the conversion and selectivity of each product, calculated using eqs 1-3, are plotted as a function of the time on stream. A trendline is then added (generally a second-order polynomial curve) to evaluate the conversion and selectivities at a time on stream of zero. Results and Discussion Reaction Mechanism. Catalytic cracking of cycloalkanes on zeolites is a complex autocatalytic process involving many steps.18 The elementary reaction families occurring in cycloalkane cracking are well-known. The reactions occurring in the alkyl side chain are similar to those occurring in alkane cracking, while reactions occurring in the ring are specific for cycloalkanes. The exact nature of the intermediate surface species involved in hydrocarbon conversion processes, alkoxides or carbenium ions, is still a subject of discussion in the literature.42-48 In this work, a reaction mechanism based on carbenium ion chemistry is assumed.49 Figure 1 represents the elementary steps involved in cycloalkane cracking. To avoid an overload of reactions, only those steps related to methylcyclohexane cracking are presented. Starting from a cycloalkane in the gas phase, the catalytic cycle can be initiated in two ways, via a monomolecular protolytic scission or via a bimolecular hydride transfer reaction.50,51 Which mechanism prevails depends on the reaction conditions and on the zeolite used,52 as in alkane cracking.9,44,53 In protolytic scission, a C-C or C-H bond of a gas phase cycloalkane is protonated by the zeolite acid site. This can occur in the alkyl side chain (exocyclic protolytic scission, step a) or in the ring (endocyclic protolytic scission, step b). The latter leads to an adsorbed alkylcarbenium ion via opening of the ring,


10489

Figure 2. Fresh catalyst methylcyclohexane conversion on five FAU zeolites as a function of the site time at 748 K and 7 kPa partial pressure. Experimental: [, Y62; 9, LZ-Y20; 2, CBV500; b, CBV720; 1, CBV760. The solid lines represent trendlines obtained by fitting the data series to a logarithmic curve.

Figure 3. Fresh catalyst methylcyclohexane conversion obtained on three MFI zeolites as a function of the site time at 748 K and 7 kPa partial pressure. Experimental: ], CBV3020E; 0, CBV5524G; 4, CBV8014. The solid lines represent trendlines obtained by fitting the data series to a logarithmic curve.

and the former produces a gas phase alkane or hydrogen and the complementary cycloalkylcarbenium ion. In cycloalkanes with longer alkyl side chains than methylcyclohexane, exocyclic protolytic scission may also produce a cycloalkane with a smaller alkyl side chain in the gas phase and the complementary alkylcarbenium ion. Once the initial carbenium ions are formed on the surface, a gas phase cycloalkane can undergo a hydride transfer reaction with these species (step g). If cycloalkenes are present in the feed, these can be protonated by the zeolite acid site (step c), producing cycloalkylcarbenium ions on the surface. These cycloalkylcarbenium ions can rearrange into skeletal isomers. Step e represents an isomerization, altering the degree of branching, while step f represents a ring contraction or expansion, preserving the degree of branching. Both types of isomerization occur via a protonated cyclopropane intermediate. In cycloalkylcarbenium ions with longer alkyl side chains than methylcyclohexyl, isomerization may also occur in the side chain. Cycloalkylcarbenium ions can also undergo β-scission reactions, either in the ring or in the alkyl side chain. The former is called endocyclic β-scission or ring opening and produces an alkenylcarbenium ion (step d). The latter can only occur in cycloalkylcarbenium ions with longer alkyl side chains than methylcyclohexyl and is referred to as exocyclic β-scission. It produces a gas phase cycloalkene and the complementary alkylcarbenium ion or a gas phase alkene and the complementary cycloalkylcarbenium ion. Cycloalkylcarbenium ions can also be alkylated with a gas phase alkene (the reverse reaction of exocyclic β-scission), producing cycloalkylcarbenium ions with a higher carbon number than the feed (oligomeric cracking). In turn, alkylcarbenium ions can undergo isomerization, β-scission, alkylation, hydride transfer, or deprotonation,17 while alkenylcarbenium ions can undergo cyclization (or ring closure, step d) or hydride transfer, leading to gas phase alkadienes. Termination of the catalytic cycle occurs when the cycloalkylcarbenium ion desorbs from the surface, either via hydride transfer, leading to a gas phase cycloalkane (step g), or via deprotonation, leading to a gas phase cycloalkene and a restored acid site (step c). Activity. Because the catalysts used in this work contain a different number of acid sites, the catalytic activity is expressed on an acid site basis and not on a mass basis because the latter can lead to erroneous interpretation when their activities are compared. Therefore, Figure 2 depicts methylcyclohexane conversion on the fresh faujasites as a function of the site time, NH+/F0mch, to compare the activity of the individual sites. Because no distinction is made between weak or strong acid sites, the reported activities are “average” values for a catalyst with a given Si/Al ratio. Conversions range from 7 to 72 mol % (see Table 2). Y62 containing no EFAl shows the lowest cracking activity, while CBV500 possesses the highest activity. Although Y62, LZ-Y20, and CBV500 contain an equal bulk Si/Al ratio

Table 3. Range of Site Time Yields Obtained on FAU and MFI at 748 K, 7 kPa Partial Pressure, and a Site Time of around 65 mol H+ s mol-1 When Cracking 2,2,4-Trimethylpentane and Methylcyclohexane site time yield (s-1) reactant

FAU

MFI

2,2,4-trimethylpentanea methylcyclohexane

2.2 × 10-4-8.9 × 10-3 3.0 × 10-3-1.1 × 10-2

5.7 × 10-4-2.2 × 10-3 4.5 × 10-3-1.0 × 10-2

a

Data from previous work.17

of 2.6, their cracking activities are very different, implying that the Si/Al ratio is not the only controlling factor. The acid sites of CBV720, CBV760, and LZ-Y20 display a similar activity in methylcyclohexane cracking. Ordering the five faujasites according to increasing site time yield leads to Y62 (Si/Albulk ) 2.6) , CBV760 (Si/Albulk ) 30) ≈ LZ-Y20 (Si/Albulk ) 2.6) ≈ CBV720 (Si/Albulk ) 15) < CBV500 (Si/Albulk ) 2.6). This activity order is consistent with that observed in 2,2,4-trimethylpentane cracking,17 isobutene cracking,33 hydroisomerization of decane and heptanes,26 and m-xylene transformation.28 At 748 K, 7 kPa partial pressure, and site time 63 mol H+ s mol-1, the site time yields obtained in methylcyclohexane cracking on the faujasites range from 3.0 × 10-3 to 1.1 × 10-2 s-1. Figure 3 presents methylcylohexane conversion on MFI zeolites as a function of the site time. Conversions between 4 and 58 mol % have been achieved (see Table 2). Within the MFI series, the activity of the individual sites increases with a decreasing Si/Albulk ratio: CBV8014 (Si/Albulk ) 40) < CBV5524G (Si/Albulk ) 25) < CBV3020E (Si/Albulk ) 15). At 748 K, 7 kPa partial pressure, and site time 37 mol H+ s mol-1, the site time yields obtained in methylcyclohexane cracking on MFI zeolites range from 6.6 × 10-3 to 1.6 × 10-2 s-1. The same activity order of the zeolites was observed when cracking 2,2,4trimethylpentane.17 However, methylcyclohexane cracks much faster than 2,2,4-trimethylpentane on MFI. To ensure that methylcyclohexane does not suffer from mass transfer limitations inside MFI, one can compare the site time yields obtained on FAU and MFI framework types at equal reaction conditions (Table 3). The site time yields for methylcyclohexane cracking on MFI have been calculated via extrapolation of the trendlines represented in Figure 3 toward higher site times. First, it can be seen that methylcyclohexane cracks faster than 2,2,4trimethylpentane on both framework types at equal reaction conditions, indicating that methylcyclohexane is more reactive. Second, the ranges of site time yields of methylcyclohexane cracking on FAU and MFI are very similar, demonstrating that methylcyclohexane does not suffer from diffusion limitations and can move freely inside the MFI pores, contrary to 2,2,4trimethylpentane, in accordance with its smaller kinetic diameter (0.60 and 0.62 nm, respectively40).

10490


Figure 4. Fresh catalyst methylcyclohexane conversion obtained on two BIPOMs and one MFI zeolite as a function of the site time at 748 K and 7 kPa partial pressure. Experimental: ×, BIPOM1; +, BIPOM3; ∆, CBV8014. The solid lines represent trendlines obtained by fitting the data series to a linear (BIPOMs) or a logarithmic (MFI) curve.

Figure 4 represents the conversion of methylcyclohexane achieved on the two BIPOMs as a function of the site time. For comparison, the conversion obtained on the commercial MFI CBV8014 with a Si/Albulk ratio of 40 is added. A clear difference in the activity of the individual sites is observed for both BIPOMs. On BIPOM1, methylcyclohexane conversion ranges from 2 to 5 mol %, while on BIPOM3, it varies between 5 and 12 mol % under similar operating conditions. BIPOM3 displays a methylcyclohexane cracking activity comparable to that of the commercial MFI CBV8014 with a similar Si/Al ratio. At 748 K, 7 kPa partial pressure, and site time 10 mol H+ s mol-1, the site time yields obtained in methylcyclohexane cracking on BIPOM1, BIPOM3, and CBV8014 are 2.2 × 10-3, 1.2 × 10-2, and 1.1 × 10-2 s-1, respectively. The lower activity of BIPOM1 compared to BIPOM3 and commercial MFI can be explained by its different structural properties. As mentioned above, BIPOM1 does not exhibit the long-range order of a zeolite material. The small size of the zeolitic building blocks this material is composed of may explain the absence of the typical acidity characteristic of an MFI zeolite. Presumably, the oxide bonds are relaxed resembling those in an amorphous material. Besides, the length of a micropore in BIPOM1 of a few nanometers is hardly longer than that of the reacting hydrocarbon molecules. BIPOM3, on the contrary, displays the XRD pattern of the MFI zeolite and has more pronounced zeolite properties. From Table 3, it was concluded above that methylcyclohexane does not suffer from mass transfer limitations inside the pores of FAU or MFI. Because both BIPOMs are composed of MFItype nanoslabs interconnected via supermicropores of larger dimension than the pores of FAU, it can be assumed that methylcyclohexane does not suffer from mass transfer limitations inside the BIPOMs either. This implies that the lower activity of BIPOM1 compared to BIPOM3 is not caused by mass transfer limitations. Product Distribution. As can be expected based on the reaction mechanism, catalytic cracking of methylcyclohexane produces a rather complex product distribution. More than 100 hydrocarbons have been identified in the reactor effluent. Figure 5 represents typical product distributions obtained on FAU, at low (20 mol %) and high (70 mol %) conversion. Methylcyclohexane cracking leads to C1-C7 alkanes, C2-C8 alkenes, C5-C8 cyclics, and C6-C10 aromatics. With increasing conversion, the total amount of alkanes and aromatics continuously increases at the expense of alkenes and cyclics. Over the whole conversion range, C3, C4, and C7 hydrocarbons are the dominant species; on the faujasites, isobutane, propylene, propane, dimethylcyclopentanes, and toluene are the most abundant reaction products. Isomerization of methylcyclohexane leads to 1,2- and 1,3dimethylcyclopentanes, while ring contraction produces ethyl-

cyclopentane. Very small amounts of trimethylcyclopentanes, isopropylcyclopentane, and dimethylcyclohexanes are also observed. These species must result from alkylation reactions. Toluene is formed from methylcyclohexane via successive hydride transfer and deprotonation reactions via methylcyclohexene and methylcyclohexadiene.18,21,24 Because the latter is not observed, its transformation into toluene must occur very fast. Benzene and xylenes are formed via disproportionation of two toluene molecules.21 The xylenes/benzene molar ratio is substantially higher than 1, suggesting that other routes toward xylenes must exist such as alkylation and cyclization of previously cracked products21 or disproportionation of methylcyclohexane.24 Small amounts of trimethylbenzenes are also present. Exocyclic protolytic scission produces methane, ethane, ethylene, cyclopentene, methylcyclopentane, cyclohexane, and cyclohexene. Endocyclic protolytic scission of methylcyclohexane leads to n-heptyl via ring opening. Desorption of these carbenium ions via hydride transfer yields n-heptane, while desorption via deprotonation produces n-heptene. Both are detected in small amounts at low conversion, pointing to a relatively high reactivity of n-heptane and n-heptene. Cracking of n-heptyl via β-scission results in propylene and linear butane/ butenes. Isomerization of this heptyl ion prior to cracking can produce branched C4 species. Isobutane/isobutene and propane/ propylene can also result from endocyclic protolytic scission of dimethylcyclopentanes, followed by β-scission. The relatively fast decrease in the selectivity toward dimethylcyclopentanes combined with the large quantities of isobutane, propylene, and propane imply that cracking of methylcyclohexane isomers contributes to a great extent of the product distribution obtained on FAU. Non-negligible amounts of branched C5 and C6 species (mainly isopentane) probably result from alkylation reactions, followed by β-scission. The contribution of alkylation reactions to the product distribution is in agreement with the observation of highly reactive 2,3,4-trimethylpentene at low conversion. Typical product distributions obtained on MFI at low (15 mol %) and high (55 mol %) conversion are depicted in Figure 6. C1-C7 alkanes, C2-C8 alkenes, C5-C7 cyclics, and C6-C10 aromatics were observed in the reactor effluent. As on FAU, the total amount of alkanes and aromatics continuously increases, while alkenes and cyclics are consumed. On MFI, C2, C3, and C4 are the major hydrocarbon fractions: ethylene, propane, propylene, and isobutene are the main reaction products of methylcyclohexane over the whole conversion range. Contrary to FAU, almost no cyclics were detected when cracking methylcyclohexane on MFI. Only at conversions below 10 mol %, small amounts of cyclopentene, methylcyclopentane, and cyclohexene are observed. This points to the occurrence of shape selectivity when cracking methylcyclohexane on MFI: either alkylcyclopentyl isomers are not formed (transition state shape selectivity), or they cannot desorb from the surface (transition state shape selectivity) or their diffusion out of the pores is hindered (product shape selectivity), which makes them subject to further cracking.21 However, distinguishing between different types of shape selectivity based on the experimental results is rather complicated, and several types may coincide. The (very) low contribution of methylcyclohexane isomers to the product distribution of methylcyclohexane cracking on MFI is also observed by other researchers.20,21,23 To investigate the effect of shape selectivity on the cracking behavior of MFI, a detailed product distribution observed on FAU (CBV720, Si/Albulk ) 15) and on MFI (CBV5524G, Si/ Albulk ) 25) obtained at the same reaction conditions (7 kPa partial pressure, 748 K, and 45 mol % methylcyclohexane


10491

Figure 5. Product distribution per carbon number of methylcyclohexane cracking on fresh FAU at 748 K and 7 kPa partial pressure at low (Y62) and high (CBV500) conversion. Experimental: 9, alkanes; [, alkenes; b, cyclics; 2, aromatics.

Figure 6. Product distribution per carbon number of methylcyclohexane cracking on fresh MFI at 748 K and 7 kPa partial pressure at low (CBV8014) and high (CBV3020) conversion. Experimental: 0, alkanes; ], alkenes; O, cyclics; 4, aromatics. Table 4. Product Selectivities (>1 mol %) Obtained on FAU (Si/Albulk ) 15) and MFI (Si/Albulk ) 25) at 748 K, 7 kPa, and 45 mol % Methylcyclohexane Conversiona selectivity (mol %) CN

hydrocarbon

1 2

methane ethane ethylene propane propylene n-butane n-butenes isobutane isobutene n-pentane isopentane isopentenes 2-methylpentane 3-methylpentane methylcyclopentane benzene 1,3-dimethylcyclopentanes 1,2-dimethylcyclopentanes ethylcyclopentane toluene ethylbenzene p- and m-xylene o-xylene 1,3,5-trimethylbenzene 1,2,4-trimethylbenzene

3 4

5 6

7

8

total total total total

alkanes alkenes cycloalkanes aromatics

FAU

MFI

1

5 2 32 44 35 7 6 8 8 1 1 2

6 18 13 5 2 33 1 1 14 2 2 5 1 8 3 3 12

5

7 2 1 3

14 1 9 3 1 2

76 23 18 27

69 83 1 36

a Site time yields on FAU and MFI are 1.9 × 10-2 and 1.2 × 10-2 s-1, respectively.

conversion) is given in Table 4. Product selectivities toward propane, propylene, and isobutene are substantially higher on MFI (44, 35, and 8 mol %, respectively, on MFI; 18, 13, and 1 mol %, respectively, on FAU), while on FAU, isobutane, isopentane, and all cycloalkanes are formed in considerably higher quantities (33, 14, and 18 mol %, respectively, on FAU;

8, 1, and 1 mol %, respectively, on MFI). For aromatics, only small differences are found between FAU and MFI, except for benzene (1 mol % on FAU; 5 mol % on MFI). Typical protolytic scission products such as methane, ethane, and ethylene are produced in markedly higher quantities on MFI than on FAU (approximately a 5-fold increase in mole percent), indicating that this reaction pathway is clearly more important on MFI than on FAU. The predominance of protolytic scission in MFI was also noticed in alkane cracking17,54 and in methylcyclohexane hydrocracking in the presence of hydrogen.55 This effect can be ascribed to the occurrence of transition state shape selectivity due to steric hindrance inside the pore channels of MFI, thereby restricting the bimolecular hydride transfer reaction. The suppression of this reaction in MFI can also be noticed when the alkane/alkene ratios obtained on FAU (3.30) and on MFI (0.83) are compared. As stated above, the very low amount of cycloalkanes in the product distribution of MFI compared to FAU (1 and 18 mol %, respectively) can be caused by three different shape selectivity effects or by a combination thereof. The suppression of hydride transfer reactions inside MFI certainly contributes to the low amount of cycloalkanes in the gas phase because two hydride transfer steps are required to convert methylcyclohexane into alkylcyclopentanes: one to convert methylcyclohexane into methylcyclohexyl and one to convert the isomerized alkylcyclopentyl into alkylcyclopentane. Hydrocracking of methylcyclohexane on Pt-ZSM-556 does produce high amounts of ethylcyclopentane and dimethylcyclopentanes over the whole conversion range, indicating that the formation of the alkylcyclopentyl isomers is surely not prevented. However, Calemma et al.56 observed that the isomer distribution obtained on Pt-ZSM-5 was different from that obtained on the large pore zeolite Pt-MOR. The authors suggested that product shape selectivity is responsible for the low quantities of 1,1- and 1,2-dimethylcyclopentanes on MFI. Hydrocracking of methylcyclohexane on a wide variety of platinum-containing zeolites57 showed that large pore zeolites, such as USY and MOR, do not impede the generation of equilibrium quantities of all dimethylcyclopentane isomers,

10492


Table 5. Product Selectivities (>1 mol %) Obtained on FAU (Si/Albulk ) 2.6), MFI (Si/Albulk ) 40), BIPOM1 (Si/Albulk ) 50), and BIPOM3 (Si/Albulk ) 50) at 748 K, 7 kPa, and 5 mol % Methylcyclohexane Conversiona selectivity (mol %) CN

hydrocarbon

FAU

MFI

BIPOM1

BIPOM3

1 2 3

methane ethylene propane propylene n-butane n-butenes isobutane isobutene 1,3-butadiene n-pentenes isopentane isopentenes cyclopentene methylcyclopentane benzene n-heptane 1,3-dimethylcyclopentanes 1,2-dimethylcyclopentanes ethylcyclopentane 1-methylcyclohexene 4-methylcyclohexene toluene 2,3,4-trimethylpentene p- and m-xylene o-xylene 1,2,4-trimethylbenzene

1 4 9 28 3 5 21 6

5 20 7 74 2 15 2 20 1 1

2 6 7 31 4 7 12 8

5 13 7 63 2 13 4 17 1 1 1 5 2 1 4 6 1

total total total total total

50 48 32 4 12

4

5

6 7

8

alkanes alkenes cycloalkanes cycloalkenes aromatics

9 2 4 1 4 19 6 4 2 2 5 3 3 1 2

5 2 5 4

4 2 7 4 2 1 21 140 8 17

1 6 6 1 2 2 6 8 4 2 4 2 9 6 3 1 2 38 70 17 7 20

3 2 6 5 3 1 1 26 122 3 6 16

Site time yields on FAU, MFI, BIPOM1, and BIPOM3 are 2.6 × 10 , 1.0 × 10-2, 2.1 × 10-3, and 1.7 × 10-2 s-1, respectively. a

-3

while medium pore zeolites, such as ZSM-5, ZSM-22, and ZSM-23, do hinder the formation of bulky dimethylcyclopentanes because of product shape selectivity. McVicker et al.57 propose to use the trans-1,2-/trans-1,3-dimethylcyclopentane ratio as a measure for in-pore constraint. Because no dimethylcyclopentanes are observed in the product distribution on MFI, one can assume that, under the conditions used in this study, product shape selectivity plays only a minor role in this work, if at all. To conclude, the very low amounts of cycloalkanes are likely caused by transition state shape selectivity suppressing hydride transfer. Table 5 shows the detailed product distribution obtained on FAU (Y62, Si/Albulk ) 2.6), MFI (CBV8014, Si/Albulk ) 40), BIPOM1 (Si/Albulk ) 50), and BIPOM3 (Si/Albulk ) 50) at 748 K, 7 kPa, and 5 mol % methylcyclohexane conversion. The large selectivity differences observed between FAU and MFI at 45 mol % conversion (Table 4) for ethylene, propylene, isobutane, isobutene, isopentane, and cyclics are also present at low conversion. Nevertheless, the propane selectivities are almost equal on FAU and MFI at 5 mol % conversion. Comparison of the product distributions obtained on both BIPOMs with those on FAU and MFI at equal reaction conditions allows one to identify whether the BIPOMs behave as a large or medium pore zeolite, or intermediate. The product selectivities found on BIPOM1 for methylcyclohexane cracking at 748 K, 7 kPa, and 5 mol % conversion are similar to those on FAU. The formation of relatively large amounts of cyclics and isopentane is typical for FAU. Small selectivity differences between BIPOM1 and FAU are found for isobutane, dim-

ethylcyclopentanes, isopentenes, and toluene, but these can be caused by a somewhat higher conversion on FAU (7 mol % instead of 5 mol %). Thus, it is concluded that the selectivity behavior of BIPOM1 in methylcyclohexane cracking is similar to that in a large pore zeolite. This is consistent with what is observed in 2,2,4-trimethylpentane cracking17 and in hydroisomerization and cracking of n-decane35,36 and confirms that the active sites of BIPOM1 are located mainly in the supermicropore network.17 The product distribution obtained on BIPOM3 at 748 K, 7 kPa, and 5 mol % methylcyclohexane conversion rather resembles that on MFI but shows also some features of that on FAU. High selectivities toward propylene, n-butenes, and isobutene correspond to MFI-type behavior, while the presence of cycloalkanes and isopentane in low amounts indicates FAU-type behavior. Moreover, the ethylene selectivity on BIPOM3 lies in between the selectivities observed on FAU and MFI (13 mol % on BIPOM3, 4 mol % on FAU, and 20 mol % on MFI). Therefore, it is concluded that the catalytic behavior of BIPOM3 displayed in methylcyclohexane cracking possesses features of both medium and large pore zeolites, although it resembles more the former. This mixed FAU/MFI behavior was also observed in 2,2,4trimethylpentane cracking,17 although in this study, it was observed that both pore networks contribute rather evenly to the observed selectivity behavior. This seems to indicate that the hindered diffusion of 2,2,4-trimethylpentane inside the ultramicropores has favored the relative contribution of the active sites in the supermicropores. On the basis of the present results, it can be stated that the active sites of BIPOM3 are present in both micropore networks but in a larger part in the ultramicropores. The differences in the selectivity behavior and active site location of both BIPOMs are in agreement with the different micropore volumes in both zeotype materials (0.51 cm3 g-1 supermicropores in BIPOM1 against 0.05 cm3 g-1 supermicropores and 0.10 cm3 g-1 mesopores up to 10 nm in BIPOM3) originating from the different synthesis procedures. Influence of the Acid Properties and Pore Topology on Selectivity. Representing the product selectivities as a function of methylcyclohexane conversion for all zeolites allows one to examine the combined effect of the acid properties and pore topology. In Figure 7, ethylene, propane, propylene, isobutane, isobutene, and isopentane selectivities on all catalysts are plotted as a function of conversion at 748 K and 7 kPa. For each framework type, it is observed that all experimental data follow the same trendline, indicating that the relationship between the product selectivities and conversion is unique and independent of the acid properties of the zeolite. For clarity, these trendlines have been added in Figure 7. This was observed for all reaction products, suggesting that within one framework type, the acid properties of the zeolite do not influence the product selectivities obtained in methylcyclohexane cracking. The absence of selectivity differences within one zeolite framework type has also been observed in catalytic cracking of alkanes,17,58,59 hydrocracking of alkanes,60 and liquid phase alkylation of benzene with 1-octene.61 However, the trendlines obtained for various framework types are different, indicating that the pore topology of the zeolite does change the dependence of the obtained product selectivities on conversion. This can be attributed to shape selectivity. From Figure 7, it can be seen that the selectivity behavior of the BIPOMs is very different. Although there is no overlap between the conversion range obtained on FAU and on BIPOM1 (see Table 2), the data obtained on BIPOM1 seem to follow the trendlines observed for the faujasites. For BIPOM3, propane,


10493

Figure 7. Product selectivities as a function of methylcyclohexane conversion on five fresh FAUs, three fresh MFIs, and two fresh BIPOM zeolites at 748 K and 7 kPa partial pressure. Experimental. FAU: [, Y62; 9, LZ-Y20; 2, CBV500; b, CBV720; 1, CBV760. MFI: b, CBV3020E; 0, CBV5524G; 4, CBV8014. BIPOM: ×, BIPOM1; +, BIPOM3. The two solid lines represent trendlines obtained by fitting all FAU and all MFI data to a second-order polynomial curve.

propylene, and isobutene selectivities follow the trendlines of MFI, while the selectivities toward ethylene and isobutane are situated in between those of FAU and those of MFI. Isopentane selectivity is also slightly higher on BIPOM3 than on MFI. The selectivity profiles confirm that the catalytic performance of BIPOM1 is similar to FAU, while BIPOM3 shows mixed FAU/ MFI behavior in methylcyclohexane cracking, as discussed above. Conclusions Methylcyclohexane was cracked over a series of five commercial faujasites, three commercial MFI zeolites, and two newly developed BIPOMs to study the influence of their acid properties and their framework topology on activity and selectivity. At equal experimental conditions, the site time yields obtained on FAU and on MFI are in the same range, indicating that mass transfer of methylcyclohexane is not hindered inside the medium pore zeolite. The site time yields achieved on BIPOM3 are comparable to those of commercial MFI with similar Al content, while the acid sites of BIPOM1 are considerably less active. This can be rationalized by their different structural properties. BIPOM1 does not present long-range order characteristic of zeolites, while BIPOM3 does. The main reaction products of methylcyclohexane cracking on FAU are C3, C4, and C7 hydrocarbons: propylene, propane, isobutane, dimethylcyclopentanes, and toluene are the most

important contributors to the product distribution. Isomerization of methylcyclohexane into various alkylcyclopentanes, followed by ring opening and subsequent cracking, is the main reaction pathway on faujasites. On MFI, C2, C3, and C4 species are the most abundant: ethylene, propane, propylene, and isobutene are produced in the largest quantities. The suppression of bimolecular hydride transfer reactions (transition state shape selectivity) due to steric hindrance inside the pores of MFI is responsible for the increase in typical protolytic scission products and for the (very) low contribution of alkylcyclopentane isomers to the product distribution. Protolytic scission, followed by cracking, is predominant in MFI. The product selectivities found on BIPOM1 are similar to those on FAU, indicating that the active sites are located mainly in the supermicropores. BIPOM3 displays mixed FAU/MFI-type catalytic behavior, although it resembles more the medium pore zeolite, suggesting that the active sites are located in both micropore networks with a larger contribution of the ultramicropores. This is in agreement with their different micropore volume. Within a given framework type, the relationship between the product selectivities and conversion obtained in methylcyclohexane cracking is unique and independent of the acid properties of the zeolite. This is valid for FAU as well as for MFI. Changing the framework type does change the variation of the product selectivity as a function of conversion because of shape selectivity. Therefore, it can be stated that, within a given zeolite framework type, the cracking activity is controlled by the acid

10494


properties, while the selectivity is governed by the framework topology in methylcyclohexane cracking. Acknowledgment The Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen) is gratefully acknowledged for their financial support to this “BIPOM” project (SBO 030202). The Belgian government is acknowledged by the authors for supporting an IAP-PAI network. J.A.M. and G.B.M. acknowledge the Flemish government for longterm structural funding (Methusalem). Nomenclature List of Symbols and AbbreViations Ai ) GC surface area of species i CFi ) GC calibration factor for species i CN ) carbon number Ct ) total molar concentration of active sites, mol kgcat-1 Fi ) molar flow rate of species i, mol s-1 MWi ) molecular mass of species i, kg mol-1 NH+ ) number of acid sites, mol SBET ) Brunauer-Emmett-Teller surface area, m2 g-1 Si ) selectivity toward species i, mol % pi0 ) partial pressure of species i, Pa T ) temperature, K Vmicro ) total micropore volume, cm3 g-1 W ) catalyst mass, kgcat X ) conversion, mol % Superscript 0 ) initial Subscripts DME ) dimethyl ether mch ) methylcyclohexane

Literature Cited (1) Busca, G. Acid catalysts in industrial hydrocarbon chemistry. Chem. ReV. 2007, 107, 5366. (2) http://www.iza-structure.org/databases/. (3) Sadeghbeigi, R. Fluid Catalytic Cracking Handbook; Gulf Publishing Company: Houston, TX, 1995. (4) Marcilly, C. Present status and future trends in catalysis for refining and petrochemicals. J. Catal. 2003, 216, 47. (5) Wilson, J. W. Fluid Catalytic Cracking Technology and Operation; PennWell Publishing Co.: Tulsa, OK, 1997. (6) Bollas, G. M.; Vasalos, I. A.; Lappas, A. A.; Iatridis, D. K.; Tsioni, G. K. Bulk molecular characterization approach for the simulation of FCC feedstocks. Ind. Eng. Chem. Res. 2004, 43, 3270. (7) Kim, H. N.; Verstraete, J. J.; Virk, P. S.; Fafet, A. NMR enhances mass-spec FCC feedstock characterization. Oil Gas J. 1998, 96, 85. (8) Buchanan, J. S. The chemistry of olefins production by ZSM-5 addition to catalytic cracking units. Catal. Today 2000, 55, 207. (9) Sto¨cker, M. Gas phase catalysis by zeolites. Microporous Mesoporous Mater. 2005, 82, 257. (10) Corma, A. From microporous to mesoporous molecular sieve materials and their use in catalysis. Chem. ReV. 1997, 97, 2373. (11) Corma, A.; Dıáz-Cabanãs, M. J.; Martıńez-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. (12) Triantafyllidis, K. S.; Lappas, A. A.; Vasalos, I. A.; Liu, Y.; Wang, H.; Pinnavaia, T. J. Gas-oil cracking activity of hydrothermally stable aluminosilicate mesostructures (MSU-S) assembled from zeolite seeds: Effect of the type of framework structure and porosity. Catal. Today 2006, 112, 33. (13) Park, D. H.; Kim, S. S.; Wang, H.; Pinnavaia, T. J.; Papapetrou, M. C.; Lappas, A. A.; Triantafyllidis, K. S. Selective petroleum refining

over a zeolite catalyst with small intracrystal mesopores. Angew. Chem., Int. Ed. 2009, 48, 7645. (14) Kirschhock, C. E. A.; Kremer, S. P. B.; Vermant, J.; Van Tendeloo, G.; Jacobs, P. A.; Martens, J. A. Design and synthesis of hierarchical materials from ordered zeolitic building units. Chem.sEur. J. 2005, 11, 4306. (15) Kremer, S. P. B.; Kirschhock, C. E. A.; Tielen, M.; Collignon, F.; Grobet, P. J.; Jacobs, P. A.; Martens, J. A. Silicalite-1 zeogrid: a new silica molecular sieve with super- and ultra-micropores. AdV. Funct. Mater. 2002, 12, 286. (16) Rouquerol, F.; Rouquerol, J.; Sing, K. Adsorption by powders and porous solids; Academic Press: San Diego, 1999. (17) Van Borm, R.; Reyniers, M.-F.; Martens, J. A.; Marin, G. B. Catalytic cracking of 2,2,4-trimethylpentane on FAU, MFI and bimodal porous materials: influence of acid properties and pore topology. Accepted for publication in Ind. Eng. Chem. Res., doi: 10.1021/ie901708. (18) Corma, A.; Mocholi, F.; Orchilles, V.; Koermer, G. S.; Madon, R. J. Methylcyclohexane and methylcyclohexene cracking over zeolite Y catalysts. Appl. Catal. 1991, 67, 307. (19) de la Puente, G.; Sedran, U. Conversion of methylcyclopentane on rare earth exchanged Y zeolite FCC catalysts. Appl. Catal., A 1996, 144, 147. (20) Scofield, C. F.; Benazzi, E.; Cauffriez, H.; Marcilly, C. Methylcyclohexane conversion to light olefins. Braz. J. Chem. Eng. 1998, 15, 218. (21) Cerqueira, H. S.; Mihindou-Koumba, P. C.; Magnoux, P.; Guisnet, M. Methylcyclohexane transformation over HFAU, HBEA, and HMFI zeolites: I. Reaction scheme and mechanisms. Ind. Eng. Chem. Res. 2001, 40, 1032. (22) Caeiro, G.; Magnoux, P.; Lopes, J. M.; Ramoaˆ Ribeiro, F. Deactivating effect of quinoline during methylcyclohexane transformation over H-USY zeolite. Appl. Catal., A 2005, 292, 189. (23) Caeiro, G.; Magnoux, P.; Ayrault, P.; Lopes, J. M.; Ramoaˆ Ribeiro, F. Deactivating effect of coke and basic nitrogen compounds during the methylcyclohexane transformation over H-MFI zeolite. Chem. Eng. J. 2006, 120, 43. (24) Al-Sabawi, M.; de Lasa, H. Kinetic modeling of catalytic conversion of methylcyclohexane over USY zeolites: adsorption and reaction phenomena. AIChE J. 2009, 55, 1538. (25) Al-Sabawi, M.; de Lasa, H. Modeling thermal and catalytic conversion of decalin under industrial FCC operating conditions. Chem. Eng. Sci. 2010, 65, 626. (26) Remy, M. J.; Stanica, D.; Poncelet, G.; Feijen, E. J. P.; Grobet, P. J.; Martens, J. A.; Jacobs, P. A. Dealuminated H-Y zeolites: relation between physicochemical properties and catalytic activity in heptane and decane isomerization. J. Phys. Chem. 1996, 100, 12440. (27) Collignon, F.; Mariani, M.; Moreno, S.; Remy, M.; Poncelet, G. Gas phase synthesis of MTBE from methanol and isobutene over dealuminated zeolites. J. Catal. 1997, 166, 53. (28) Morin, S.; Ayrault, P.; Gnep, N. S.; Guisnet, M. Influence of the framework composition of commercial HFAU zeolites on their activity and selectivity in m-xylene transformation. Appl. Catal., A 1998, 166, 281. (29) Bezman, R. D. Chemical stability of hydrothermally dealuminated Y-type zeolites: a catalyst manufacturer and user’s perspective. Stud. Surf. Sci. Catal. 1991, 68, 305. (30) Boreáve, A.; Auroux, A.; Guimon, C. Nature and strength of acid sites in HY zeolites: a multitechnical approach. Microporous Mater. 1997, 11, 275. (31) Imbert, F. E.; Gnep, N. S.; Ayrault, P.; Guisnet, M. Effects of commercial HFAU structural parameters over m-cresol transformation. Appl. Catal., A 2001, 215, 225. (32) Collignon, F.; Poncelet, G. Comparative vapor phase synthesis of ETBE from ethanol and isobutene over different acid zeolites. J. Catal. 2001, 202, 68. (33) Reyniers, M.-F.; Tang, Y.; Marin, G. B. Influence of coke formation on the conversion of hydrocarbons. II. i-Butene on HY-zeolites. Appl. Catal., A 2000, 202, 65. (34) Niwa, M.; Katada, N.; Sawa, M.; Murakami, Y. Temperatureprogrammed desorption of ammonia with readsorption based on the derived theoretical equation. J. Phys. Chem. 1995, 99, 8812. (35) Aerts, A.; Van Isacker, A.; Huybrechts, W.; Kremer, S. P. B.; Kirschhock, C. E. A.; Collignon, F.; Houthoofd, K.; Denayer, J. F. M.; Baron, G. V.; Marin, G. B.; Jacobs, P. A.; Martens, J. A. Decane hydroconversion on bifunctional zeogrid and nano-zeolite assembled from aluminosilicate nanoslabs of MFI framework type. Appl. Catal., A 2004, 257, 7. (36) Aerts, A.; Huybrechts, W.; Kremer, S. P. B.; Kirschhock, C. E. A.; Theunissen, E.; Van Isacker, A.; Denayer, J. F. M.; Baron, G. V.; Thybaut, J. W.; Marin, G. B.; Jacobs, P. A.; Martens, J. A. n-Alkane hydroconversion

Ind. Eng. Chem. Res., Vol. 49, No. 21, 2010 on zeogrid and colloidal ZSM-5 assembled from aluminosilicate nanoslabs of MFI framework type. Chem. Commun. 2003, 1888. (37) Patent WO 2008/095264. (38) Beirnaert, H. C.; Vermeulen, R.; Froment, G. F. A recycle electrobalance reactor for the study of catalyst deactivation by coke formation. Stud. Surf. Sci. Catal. 1994, 88, 97. (39) Berger, R. J.; Stitt, E. H.; Marin, G. B.; Kapteijn, F.; Moulijn, J. A. Chemical reaction kinetics in practice. CATTECH 2001, 5, 30. (40) Funke, H. H.; Argo, A. M.; Falconer, J. L.; Noble, R. D. Separations of cyclic, branched, and linear hydrocarbon mixtures through silicalite membranes. Ind. Eng. Chem. Res. 1997, 36, 137. (41) Degnan, T. F., Jr. The implications of the fundamentals of shape selectivity for the development of catalysts for the petroleum and petrochemical industry. J. Catal. 2003, 216, 32. (42) Rosenbach, N., Jr.; dos Santos, A. P. A.; Franco, M.; Mota, C. J. A. The tert-butyl cation on zeolite Y: A theoretical and experimental study. Chem. Phys. Lett. 2010, 485, 124. (43) Boronat, M.; Corma, A. Are carbenium and carbonium ions reaction intermediates in zeolite-catalyzed reactions. Appl. Catal., A 2008, 336, 2. (44) Corma, A.; Orchille´s, A. V. Current views on the mechanism of catalytic cracking. Microporous Mesoporous Mater. 2000, 35-36, 21. (45) Rigby, A. M.; Kramer, G. J.; van Santen, R. A. Mechanisms of hydrocarbon conversion in zeolites: a quantum mechanical study. J. Catal. 1997, 170, 1. (46) Tuma, C.; Sauer, J. Protonated isobutene in zeolites: tert-butyl cation or alkoxide. Angew. Chem., Int. Ed. 2005, 44, 4769. (47) Haw, J. F. Zeolite acid strength and reaction mechanisms in catalysis. Phys. Chem. Chem. Phys. 2002, 4, 5431. (48) Kazansky, V. B. Adsorbed carbocations as transition states in heterogeneous acid catalyzed transformations of hydrocarbons. Catal. Today 1999, 51, 419. (49) Quintana-Solo´rzano, R.; Thybaut, J. W.; Marin, G. B. Catalytic cracking and coking of (cyclo)alkane/1-octene mixtures on an equilibrium catalyst. Appl. Catal., A 2006, 314, 184. (50) Marques, J. P.; Gener, I.; Lopes, J. M.; Ramoaˆ Ribeiro, F.; Guisnet, M. Methylcyclohexane transformation over dealuminated HBEA samples: mechanisms and active sites. Appl. Catal., A 2006, 301, 96. (51) Raichle, A.; Traa, Y.; Fuder, F.; Rupp, M.; Weitkamp, J. HaagDessau catalysts for ring opening of cycloalkanes. Angew. Chem., Int. Ed. 2001, 40, 1243.

10495

(52) Matias, P.; Lopes, J. M.; Laforge, S.; Magnoux, P.; Russo, P. A.; Ribeiro Carrott, M. M. L.; Guisnet, M.; Ramoaˆ Ribeiro, F. Methylcyclohexane transformation over HMCM22 zeolite: mechanism and location of the reactions. J. Catal. 2008, 259, 190. (53) Kotrel, S.; Kno¨zinger, H.; Gates, B. C. The Haag-Dessau mechanism of protolytic cracking of alkanes. Microporous Mesoporous Mater. 2000, 35-36, 11. (54) Kotrel, S.; Rosynek, M. P.; Lunsford, J. H. Intrinsic catalytic cracking activity of hexane over H-ZSM-5, H-β and H-Y zeolites. J. Phys. Chem. B 1999, 103, 818. (55) Castanõ, P.; Gayubo, A. G.; Pawelec, B.; Fierro, J. L. G.; Arandes, J. M. Kinetic modelling of methylcyclohexane ring-opening over a HZSM-5 zeolite catalyst. Chem. Eng. J. 2008, 140, 287. (56) Calemma, V.; Carati, A.; Flego, C.; Giardino, R.; Gagliardi, F.; Millini, R.; Bellussi, G. Ring opening of methylcyclohexane over platinumloaded zeolites. ChemSusChem 2008, 1, 548. (57) McVicker, G. B.; Feeley, O. W.; Ziemiak, J. J.; Vaughan, D. E. W.; Strohmaier, K. C.; Kliewer, W. R.; Leta, D. P. Methylcyclohexane ringcontraction: a sensitive solid acidity and shape selectivity probe reaction. J. Phys. Chem. B 2005, 109, 2222. (58) Yaluris, G.; Rekoske, J. E.; Aparicio, L. M.; Madon, R. J.; Dumesic, J. A. Isobutane cracking over Y-zeolites I. Development of a kinetic model. J. Catal. 1995, 153, 54. (59) Narbeshuber, T. F.; Brait, A.; Seshan, K.; Lercher, J. A. The influence of extraframework aluminum on H-FAU catalyzed cracking of light alkanes. Appl. Catal., A 1996, 146, 119. (60) Thybaut, J. W.; Marin, G. B.; Baron, G. V.; Jacobs, P. A.; Martens, J. A. Alkene protonation enthalpy determination from fundamental kinetic modeling of alkane hydroconversion on Pt/H-(US)Y-zeolite. J. Catal. 2001, 202, 324. (61) Craciun, I.; Reyniers, M.-F.; Marin, G. B. Effects of acid proprerties of Y zeolites on the liquid-phase alkylation of benzene with 1-octene: a reaction path analysis. J. Mol. Catal. A: Chem. 2007, 277, 1.

ReceiVed for reView February 26, 2010 ReVised manuscript receiVed April 22, 2010 Accepted April 23, 2010 IE100429U

Catalytic Cracking of Methylcyclohexane on FAU, MFI, and Bimodal

Recommend Documents