Alkylation of Benzene with Methane over ZnZSM-5 Zeolites Studied

Feb 6, 2013 - Alkylation of benzene with methane was studied under oxidization condition over ZnZSM-5 zeolites by using in situ solid-state NMR ...
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Alkylation of Benzene with Methane over ZnZSM‑5 Zeolites Studied with Solid-State NMR Spectroscopy Xiumei Wang, Jun Xu,* Guodong Qi, Bojie Li, Chao Wang, and Feng Deng* State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Center for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China S Supporting Information *

ABSTRACT: Alkylation of benzene with methane was studied under oxidization condition over ZnZSM-5 zeolites by using in situ solid-state NMR spectroscopy and GC-MS analysis. The experimental results indicate that the alkylation reaction occurs with selective formation of toluene at temperatures of 523−623 K using O2 or N2O as the oxidant. Using 13 C isotope labeled reactants, the conversions of methane and benzene were independently monitored, and their respective role in the reaction was determined. It was found by NMR spectroscopy that methane was first activated into methoxy species and zinc methyl intermediates. As an electrophilic agent, the methyl group of methoxy species could directly attack phenyl ring to produce toluene via electrophilic substitution reaction, while the zinc methyl species was not directly involved in the alkylation reaction. However, the similar nature of zinc methyl species (Zn−CH3) to organozinc compounds allowed the facile oxidization of zinc methyl species (Zn−CH3) into methoxy species. As confirmed by GC-MS experiments, methane exclusively provided the methyl group of toluene product while benzene afforded the phenyl ring. Experimental results also indicated that neither methane nor benzene alone could generate toluene.

1. INTRODUCTION Being as important chemical intermediates, alkylaromatic compounds such as toluene and polymethylbenzene have been broadly used in industry for the production of fine chemicals. Currently, alkylaromatic compounds are industrially produced by alkylation of benzene with simple alcohols or alkenes.1−5 It would be more attractive if the abundant and low-cost light alkanes can be used as the alkylation reagent in place of alcohols and alkenes. The pioneer work on the catalytic synthesis of alkylaromatics from alkanes and benzene in the Friedel−Crafts systems was reported by Schmerling and Vesely6 using cupric chloride and aluminum chloride catalysts. The investigation was then extended to liquid superacidic media,7 and it was demonstrated that anhydrous fluoroantimonic acid (HF-SbF5) could catalyze the alkylation of benzene with C1−C5 alkanes to produce alkylbenzene. Although these catalytic systems are highly efficient for the alkylation process, intensive efforts have been made on the development of environmentally benign catalysts to overcome the environmental and corrosion drawbacks of those catalysts containing halide and liquid acid. In this context, acidic zeolites and their modified derivatives provide a promising alternative. Various metal (such as Pt, Ga, and Zn) modified zeolites (H-mordenite, H-Y, MCM-22, and HZSM-5) have been utilized in the alkylation of benzene with propane8−13 and ethane14−17 for preparation of propylbenzene and ethylbenzene. Among the light alkanes, methane is the most abundant resource available for utilization. However, chemical activation © 2013 American Chemical Society

of methane for alkylation is more challenging than other light alkanes due to its strongest C−H bond energy (about 104 kcal/ mol). Although conversion of methane with coreactants such as alkenes,18 alcohol,19 and CO20 has been achieved on solid catalysts, only a few studies concerning direct alkylation of benzene with methane have been reported.21−23 Moreover, there is still no consensus on the formation of alkylaromatics and to somewhat controversial. Long and co-workers21 reported that benzene could react with methane to produce toluene at 400 °C and under a high pressure (5.5 MPa) over Cu/beta and H-beta zeolite. By using isotopic tracer method, they confirmed that the 13C labeled methyl group of toluene was originated from the starting methane reactant. This was in good accordance with their previous report on methylation of naphthalene with methane over metal substituted aluminophosphate molecular sieves MAPO-5 (M = Pb, Cu, Ni, and Si), which showed that methane provided the methyl group of methylated naphthalene product.22 On the contrary, Lunsford et al.23 presented different viewpoint on the alkylation of benzene with methane. They claimed that methane reactant did not incorporate into the “methylated” aromatic products over various zeolites and that all of the observed hydrocarbon products were derived exclusively Received: November 3, 2012 Revised: February 3, 2013 Published: February 6, 2013 4018

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2.2. In Situ Solid-State NMR Experiments. 13CH4 (13C, 99%, Cambridge Isotope Laboratories, Inc.), 13C6H6 (13C, 99%, Cambridge Isotope Laboratories, Inc.), and O2 (99.99%) or N2O (99.99%) were introduced onto the activated ZnZSM-5 catalyst in a glass ampule on a vacuum line. The glass ampule was immersed in liquid N2 during the adsorption of reactants and then sealed off from the vacuum line. The reaction was performed in the sealed ampule under elevated temperatures for a specific reaction period, quenched by liquid N2, and then the ampule was transferred into a 7.5 mm rotor for NMR measurements. All solid-state NMR spectroscopy experiments were carried out at 9.4 T on a Varian Infinityplus-400 spectrometer, equipped with a Chemagnetic triple-resonance 7.5 mm probe, with resonance frequencies of 400.13 and 100.6 MHz for 1 H and 13C, respectively. Single-pulse 13C MAS experiments with 1H decoupling were performed by using a π/2 pulse width of 4.8 μs and a repetition time of 10 s. 1H MAS experiments were carried out with a π/2 pulse width of 5.3 μs and a repetition time of 4 s. The magic angle spinning rate was set to 3−5 kHz. For the 1H−13C CP/MAS NMR experiments, the Hartmann−Hahn condition was achieved using hexamethylbenzene (HMB), with a contact time of 2.0 ms and a repetition time of 2.0 s. The 1H and 13C chemical shifts were referenced to tetramethylsilane (TMS) and HMB (a second reference to TMS), respectively. 2.3. GC-MS Analysis. The catalyst with adsorbed products were dissolved in 15 wt % HF solution and then extracted with CH2Cl2. The bottom layer containing the organic phase of extracted solution was separated and analyzed on Shimadzu GC-MS QP 2010plus gas chromatograph with a Rxi-1 ms column (30 m length, 0.25 mm i.d., 0.25 μm film).

from benzene reactant. As such, the debate on the role of methane in the alkylation still remains. Since the incorporation of methane into aromatics is the key point for taking advantage of methane as reactant to be utilized, the activation of methane plays decisive role in determining the fate of methane in the reaction. In order to enhance reactivity of methane, gaseous oxidant (e.g., O2) has been employed to reduce the thermodynamic limit for methane activation.24−26 Stepanov et al. demonstrated that addition of molecular oxygen facilitated activation of methane in the coconversion of methane and propane over Ga/beta zeolite.27 Moreover, for the reaction of methane and benzene, other researchers proposed that the molecular oxygen had a remarkable enhancement on the formation of methylated aromatic products over various zeolites.28−31 Catalysts that contains metal ions exhibit enhanced catalytic performance in a wide range of catalytic reactions. Among them, Zn modified zeolites have been intensively studied in the conversion of light alkanes.19,32−35 However, investigation of alkylation of benzene with methane over this kind of catalysts is limited. Luzgin et al.36 found that benzene was methylated into methylbenzenes by methane via a surface methoxy (−OCH3) intermediate which could be generated over a Zn modified beta zeolite only when the reaction temperature was raised up to 523 K. In our previous work,37 we developed a new Zn modified ZSM-5 zeolite (denoted as ZnZSM-5) on which methane could be activated to simultaneously generate both surface methoxy (−OCH3) and zinc methyl (Zn−CH3) intermediates at room temperature (298 K). Experimental and theoretical calculation results demonstrated that the distinct active Zn sites were responsible for the high reactivity of the ZnZSM-5 catalyst toward methane activation.37 Therefore, it is desirable to have a detailed study on the alkylation of benzene with methane over such a catalyst, especially on the role of different intermediates (surface methoxy and zinc methyl species) in the reaction. In this work, the reaction of methane with benzene on the ZnZSM-5 catalyst in the presence of different oxidants (O2 or N2O) is explored by using in situ 13C solid-state NMR spectroscopy and GC-MS analysis. The experimental results show that methylation of benzene with methane occurs with selective formation of toluene under mild condition (523−623 K). The experimental data also reveal the mechanism of alkylation reaction: methane is transformed into the methyl group of toluene product via a methoxy species intermediate through two different pathways, while the phenyl ring of toluene is exclusively provided by benzene.

3. RESULTS AND DISCUSSION 3.1. Reaction of 13CH4 and 13C Unlabeled Benzene. Figure 1 shows in situ 13C CP/MAS NMR spectra obtained

2. EXPERIMENTS 2.1. Materials Preparation. The ZnZSM-5 catalyst was prepared by reaction of metallic Zn vapor with HZSM-5 zeolite according to previous procedure.20 In brief, on a vacuum line, HZSM-5 zeolite (Si/Al = 21, Nankai University) was dehydrated at a temperature of 673 K with a pressure below 10−3 Pa over a period of 12 h, and Zn powder (99.999%, Sinopharm Chemical Reagent Co, Ltd.) was degassed at a pressure below 10−3 Pa at room temperature. Then the dehydrated HZSM-5 and the degassed Zn powder were mixed (with a molar ratio of Zn/Al > 1) and transferred into a CAVERN device38 in a dry nitrogen atmosphere in a glovebox. The CAVERN device was then connected to the vacuum line, and the mixture was heated at a temperature of 773 K and a pressure of 10−2 Pa for 2 h. The excess of metallic Zn and the released hydrogen were removed by evacuation at 773 K for another 30 min. The Zn content was ∼3.8% as determined by inductively coupled plasma analysis.

Figure 1. 13C CP/MAS NMR spectra of products formed from coadsorption of 13CH4, C6H6, and O2 on ZnZSM-5 catalyst heated for 1 h at (a) 298 K, (b) 523 K, and (c) 623 K. Asterisks denote spinning sidebands.

after reaction of 13C labeled methane and unlabeled benzene in the presence of O2 over the ZnZSM-5 zeolite at 298−623 K. At 298 K, besides a low field signal at 132 ppm due to unlabeled benzene, three signals at 57, −7, and −20 ppm are observed. The signal at −7 ppm can be assigned to unreacted methane.39 The appearance of signal at −20 ppm due to zinc methyl 4019

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and benzene to phenol.46−49 Moreover, the utilization of N2O as an oxidant can reduce its environmental impact because it is largely emitted by industrial production of HNO3, being a potent greenhouse gas and stratospheric ozone destruction agent. Therefore, N2O is also used as oxidant in the alkylation reaction. When molecular oxygen is replaced by N2O in the system of 13C labeled methane and unlabeled benzene (Figure 2a),

species (Zn−CH3) evidences activation of methane on the catalyst. It has been demonstrated that heterolytic dissociation of C−H bond of methane over Zn modified zeolites leads to formation of zinc methyl species (Zn−CH3).20,37,39−41 The intense signal at 57 ppm is ascribed to surface methoxy species,20,27,36,37,41 formed upon adsorption of methane on Zn and Ga modified H-ZSM-5 and H-beta zeolites under different conditions. Our previous work demonstrated that the appearance of this signal at room temperature corresponds to activation of methane via homolytic cleavage of C−H bond on ZnOZn cluster over the ZnZSM-5 zeolite.37 The methoxy species are normally considered as active intermediates in various catalytic reactions such as methanol conversion.42 We also found that methanederived methoxy species over the ZnZSM-5 zeolite have a similar nature with the methoxy species derived from methanol.37 Thus, a further conversion of methoxy species into oxygenates or hydrocarbons could be expected. It is noteworthy that at 298 K no signal of toluene (such as a signal at ca. 20 ppm due to methyl group) is visible, indicating that the alkylation reaction does not occur at this temperature. After heating the sample at 523 K for 1 h (Figure 1b), two new major signals appear at 173 and 20 ppm, accompanied by the disappearance of the −20 ppm signal. The signal at 173 ppm corresponds to formation of formate species, as a result of the oxidation of methoxy species or zinc methyl species (Zn−CH3).43 The intense signal at 20 ppm can be attributed to the methyl group attached to phenyl ring.8 Although the detailed molecular structure of the methylbenzene can not be determined now, the appearance of this signal indicates that alkylation of benzene with methane has already occurred at 523 K. Other two signals at 65 and 6 ppm are observed as minor species that can be assigned to dimethyl ether (DME) and ethane, respectively. They are derived from the transformations of methoxy species which are typical reactions in the course of methanol conversion on acidic zeolites.44 Two factors may account for the disappearance of signal at −20 ppm. One is that the zinc methyl species (Zn−CH3) can be reversely protonated by Brønsted acid sites of zeolite to form methane.43 This is evidenced by the increase of methane signal at −7 ppm. Additionally, the oxidation condition can promote transformation of zinc methyl species (Zn−CH3) into methoxy species and formate species due to its analogy nature to that of organozinc compound.45 Further increasing of the reaction temperature to 623 K remarkably enhances the alkylation reaction to form methylated aromatics, reflected by the fact that the methyl group signal at 20 ppm is predominant in the spectrum (Figure 1c). Meanwhile, the methoxy species (57 ppm) is completely consumed, suggesting that it may be the precursor for alkylation of benzene, similar to the role of methoxy species formed on the Zn modified beta zeolite.36 It should be noted that the 132 ppm signal due to benzene ring remains almost unchanged, implying that no 13C labeled carbon from starting methane is incorporated into the phenyl ring. Otherwise, the corresponding signal should be largely enhanced due to the involvement of 13C labeled carbons. The relatively lower temperature alkylation of benzene with methane suggests the high activity of ZnZSM-5 zeolite. Moreover, the promotion effect of the oxidization condition on the reaction is evidenced by the higher methane conversion at 623 K (ca. 17%, estimated by 13C single-pulse MAS NMR experiment) in comparison with the system without any oxidant in which less than 1% methane conversion and a trace of methylated benzene are obtained (Figure S1). As an oxygen donor, N2O has been widely used for selective oxidation of hydrocarbons, particularly methane to methanol

Figure 2. 13C CP/MAS NMR spectra of products formed from coadsorption of 13CH4, C6H6, and N2O on ZnZSM-5 catalyst heated for 1 h at (a) 298 K, (b) 523 K, and (c) 623 K. Asterisks denote spinning sidebands.

the appearance of methoxy species (57 ppm) and zinc methyl species (Zn−CH3) (−20 ppm) at 298 K evidence the activation of methane, similar to that where O2 being the oxidant. With increasing the reaction temperature to 523 K (Figure 2b), a minor signal at 20 ppm due to the methyl group of methylated benzene is observable. Further increasing the temperature to 623 K results in a remarkable increase of the signal (at 20 ppm) of methylated benzene (Figure 2c) and a complete consumption of methoxy species (57 ppm). The results indicate that N2O can play a similar role as that of O2 in the activation of methane and the subsequent alkylation of benzene. However, N2O is less efficient than O2 for the alkylation reaction as reflected by the much lower concentration of methylated benzene detectable at 523 K. It is noteworthy that some zinc methyl species (Zn−CH3) (−20 ppm) still remain at 623 K in the presence of N2O, while it is readily oxidized into either methoxy species or formate species in the presence of O2 even at 523 K. This is likely due to the relatively weaker redox property of N2O, which leads to only partial oxidization of zinc methyl species (Zn−CH3) into methoxy species. As a result, deep oxidization of either methoxy species or zinc methyl species (Zn−CH3) is unfavorable in the reaction, accounting for the lack of formate species. 3.2. Reaction of 13C6H6 and 13C Unlabeled Methane. The aforementioned results have indicated that methane can be incorporated into methylated benzene by forming the methyl group. In order to have a deep insight into the conversion of benzene in the alkylation reaction, 13C labeled benzene is used; thus, the carbon atoms of benzene can be traced, and the transformation of benzene is followed. Figure 3a,b shows in situ 13C CP/MAS NMR spectra obtained from reaction of unlabeled methane and 13C labeled benzene in the presence of O2 at 523 and 623 K. The intense signal at 132 ppm is due to the carbons of phenyl ring. As known from above results, the alkylation reaction should occur with the formation of methylated benzene at the same temperatures. However, the absence of methyl 4020

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3.3. Reaction of 13C6H6 or 13CH4. It has been shown that benzene and methane can proceed alkylation to form toulene. A question still remains: could toluene be produced by methane or benzene alone? As suggested by previous reports, aromatization of methane to form alkylaromticas is a typical reacion for methane conversion on metal modified zeolites,51 and decomposition of benzene over some zeolites such as H-beta can lead to toulene without additional alkylated reagents.23 Therefore, further experiments are needed to address this issue. Figure 6 shows the 13C NMR spectra obtained from reactions of either 13 C labeled methane or 13C labeled benzene in oxygen atmosphere. In the absence of methane, only one signal at 132 ppm due to benzene is observed even at a high temperature of 623 K (Figure 6a,b). GC analysis of the product extract confirms that no methylated benzene such as toulene is formed (not shown). This indicates that benzene keeps intact and does not proceed any decomposition or transformation. In contrast, toluene has been formed when 13CH4 is coadded under the same recation conditions (see Figure 3c). With respect to reation of 13CH4 at 523 K, the initial activaion leads to formation of methoxy species (57 ppm) and further formate species (173 ppm) and dimethyl ether (65 ppm) (Figure 6c). However, no signal is observable due to methylated benzene such as toluene, which has typical chemical shifts at ca. 130 and 20 ppm for phenyl ring and methyl group, respectively. In comparison, toluene has been formed under the identical condition when benzene is coadded (see Figure 1b). GC analysis of the product extract also indicates that no methylated benzene such as toluene is formed. At 623 K, a new signal appears at 185 ppm, which falls in the chemical shift range of carbonyl groups. This signal can be ascribed to acetic acid formed by the oxidization of acetaldehyde intermediate that is produced by the interaction of zinc methyl species (Zn−CH3) and formate species.41 The coexisting signal at 20 ppm is accordingly assigned to the methyl group of acetic acid. Thus, aromatization of methane does not occur and the alkylaromatics are not formed in this case. Taking these results together, we conclude that neither methane nor benzene is able to produce alkylaromatics such as toluene alone. 3.4. Reaction Mechanism. On the basis of the above experimental results, we can conclude that benzene is alkylated by methane to form toluene on the ZnZSM-5 catalyst above 523 K. The reaction pathway is proposed, which is shown in Scheme 1. Prior to formation of toluene, methane activation produces zinc methyl (−20 ppm) and methoxy species (57 ppm), which can act as intermediates for further conversion. At room temperature, methane is activated via two kinds of C−H bond cleavage mechanisms, homolytic and heterolytic pathway, leading to the formation of methoxy species and zinc methyl species (Zn− CH3), respectively.37 The zinc methyl species (Zn-CH3) possesses similar chemical property to that of organozinc compounds in organometallic chemistry,45 reflected by its high reactivity with protons of zeolite to form methane and with O2 to form formate species and methoxy species, though the zinc methyl species (Zn−CH3) alone did not lead to any further reaction even being heated at 773 K.39 For the alkylation of aromatics, electrophilic substitution process normally occurs for generating alkyl groups attached to phenyl ring when there is no attached group with high electronegativity such as halide element. Thus, electrophilic reagent is required to interact with unsubstituted phenyl ring to provide the alkyl groups. However, for the Zn−CH3 species, it cannot be directly involved in the methylation reaction to form toluene because of the partial negatively charged nature of the methyl group bound to the positively charged Zn ions.

Figure 3. 13C CP/MAS NMR spectra of products formed from coadsorption of methane and benzene on ZnZSM-5 catalyst heated for 1 h. (a, b) CH4, 13C6H6, and O2 at 523 and 623 K. (c) 13CH4, 13C6H6, and O2 at 623 K. Asterisks denote spinning sidebands.

groups indicates that the methyl group of methylated benzene should be originated from unlabeled methane rather than 13C labeled benzene. This is confirmed by the reaction with both 13 C labeled methane and 13C labeled benzene under identical conditions, in which the methyl group signal at 20 ppm definitely comes from 13C labeled methane (Figure 3c), in agreement with the reaction result obtained from 13C labeled methane and unlabeled benzene (see Figure 1c). It should be noted that the benzene signal at 132 ppm exhibits no obvious change in the NMR spectra, though methylated benzene has been formed. Since alkylation of benzene with alcohol or alkene reagents usually produces polyalkylbenzenes,1,50 further characterization of the alkylation product is performed by GC-MS analysis. In the CH2Cl2 extract (Figure 4), toluene is solely found, indicating

Figure 4. GC chromatogram from CH2Cl2 extract of ZnZSM-5 sample after reaction of 13CH4, 13C6H6, and O2 for 1 h at 623 K. Asterisks denote impurity in the solvent.

the high selectivity of alkylation of benzene with methane on the catalyst. Moreover, mass spectra analysis of toulene obtained from reactions with alternative 13C labeled reactants provides detailed information on the carbon atoms distribution (Figure 5). In comparsion with that obtained from both natural abundance reatants, the molecular weight of toluene product is increased by 1 mass unit when 13CH4 replaces 12CH4 (Figure 5b) and by 6 mass units when only 13C labeled benzene is used (Figure 5c). This further confirms the aforementioned NMR results that methane provides methyl group and benzene affords phenyl ring to form toulene. 4021

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Figure 5. Mass spectra of toluene formed from reaction of alternative 13C isotope labeled methane and benzene at 623 K for 1 h on ZnZSM-5 zeolites in oxidation atmosphere: (a) C7H8 formed from CH4, C6H6, and O2; (b) C7H8 formed from 13CH4, C6H6, and O2; (c) C7H8 formed from CH4, 13C6H6, and O2.

of benzene to produce toluene can be realized by the interaction of methoxy species with benzene ring. Indeed, it has been proposed on the basis of IR and NMR spectroscopy that the methoxy species derived from methanol acts as precursor for alkylation of benzene or toluene.5,53 Moreover, it should be noted that the zinc methyl species (Zn−CH3) can be readily oxidized into methoxy species under oxidization condition, which would be indirectly involved in the methylation of benzene via the electrophilic substitution process. In analogy to the methylation of benzene with methanol in a stepwise pathway,5,53−55 the first step of methylation of benzene is the activation of methane to form methoxy intermediates, and then the methoxy intermediates consequently interacts with benzene to form toluene via the electrophilic substituted reaction.

4. CONCLUSION Alkylation of benzene with methane on the ZnZSM-5 catalyst has been explored by in situ solid-state NMR spectroscopy in a temperature range of 298−623 K. Toluene is selectively produced above 523 K under oxidization condition using O2 or N2O as oxidant. Methane is activated into zinc methyl species (Zn−CH3) and methoxy species at 298 K before the alkylation reaction occurs. The zinc methyl species (Zn−CH3) can be further converted into formate species, methane and methoxy species under elevated temperature. However, the zinc methyl species (Zn−CH3) cannot directly interact with benzene because its methyl group bears negative charge. On the contrary, the positively charged methyl group of the methoxy species allows it to interact with benzene via electrophilic substitution process, through which methane provides the methyl group of toluene product. The zinc methyl species (Zn−CH3) is indirectly involved in the methylation of benzene as it can be oxidized into methoxy species at high temperatures. Our experimental results also demonstrate that toluene cannot be produced by benzene alone. In addition, although the absence of benzene has no effect on the methane activation to form zinc methyl species (Zn− CH3) and methoxy species, further conversion of these species does not produce any aromatics, which excludes the aromatization reaction of methane. Therefore, the alkylation reaction necessitates both benzene and methane, in which methane provides the methyl group while benzene affords phenyl ring of the toluene product.

Figure 6. 13C CP/MAS NMR spectra of products formed from adsorption of benzene or methane on ZnZSM-5 catalyst heated for 1 h. (a, b) 13C6H6 and O2 at 523 and 623 K. (c, d) 13CH4 and O2 at 523 and 623 K. Asterisks denote spinning sidebands.

Scheme 1. Proposed Reaction Pathway for the Formation of Toluene from Methane and Benzene on ZnZSM-5 Catalyst in Oxidization Atmosphere (S Denotes Zeolite Support)

Since the simplest carbenium ion has not been identified in heterogeneous catalytic system up to now, methoxy species has been widely considered as “stabilized carbenium ion” and active intermediates in various acid-catalyzed reactions. As an electrophilic reagent, the methyl group of methoxy species can readily react with various nucleophilic reagents, such as NH3, CH3CH2I, CH3CN, CO, etc., to generate corresponding products on acidic zeolites.52 Therefore, here the methylation

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ASSOCIATED CONTENT

S Supporting Information *

Additional information about the methane conversion in the alkylation reaction of benzene with methane without oxidant 4022

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(26) Yamanaka, I.; Soma, M.; Otsuka, K. J. Chem. Soc., Chem. Commun. 1995, 2235−2236. (27) Luzgin, M. V.; Gabrienko, A. A.; Rogov, V. A.; Toktarev, A. V.; Parmon, V. N.; Stepanov, A. G. J. Phys. Chem. C 2010, 114, 21555− 21561. (28) Adebajo, M.; Long, M. A.; Howe, R. F. Res. Chem. Intermed. 2000, 26, 185−191. (29) Adebajo, M. O.; Howe, R. F.; Long, M. A. Catal. Today 2000, 63, 471−478. (30) Adebajo, M. O.; Long, M. A.; Frost, R. L. Catal. Commun. 2004, 5, 125−130. (31) Adebajo, M. O.; Frost, R. L. Energy Fuels 2005, 19, 783−790. (32) Pierella, L. B.; Eimer, G. A.; Anunziata, O. A. Stud. Surf. Sci. Catal. 1998, 119, 235−240. (33) Anunziata, O. A.; Eimer, G. A.; Pierella, L. B. Catal. Lett. 1999, 58, 235−239. (34) Lubango, L. M.; Scurrell, M. S. Appl. Catal. A: Gen. 2002, 235, 265−272. (35) Gabrienko, A. A.; Arzumanov, S. S.; Freude, D.; Stepanov, A. G. J. Phys. Chem. C 2010, 114, 12681−12688. (36) Luzgin, M. V.; Rogov, V. A.; Arzumanov, S. S.; Toktarev, A. V.; Stepanov, A. G.; Parmon, V. N. Catal. Today 2009, 144, 265−272. (37) Xu, J.; Zheng, A. M.; Wang, X. M.; Qi, G. D.; Su, J. H.; Du, J. F.; Gan, Z. H.; Wu, J. F.; Wang, W.; Deng, F. Chem. Sci. 2012, 3, 2932− 2940. (38) Munson, E. J.; Murray, D. K.; Haw, J. F. J. Catal. 1993, 141, 733−736. (39) Kolyagin, Y. G.; Ivanova, I. I.; Pirogov, Y. A. Solid State Nucl. Magn. Reson. 2009, 35, 104−112. (40) Kolyagin, Y. G.; Ivanova, I. I.; Ordomsky, V. V.; Gedeon, A.; Pirogov, Y. A. J. Phys. Chem. C 2008, 112, 20065−20069. (41) Stepanov, A. G.; Luzgin, M. V.; Rogov, V. A.; Arzumanov, S. S.; Toktarev, A. V.; Parmon, V. N. Angew. Chem., Int. Ed. 2008, 47, 4559− 4562. (42) Jiang, Y. J.; Hunger, M.; Wang, W. J. Am. Chem. Soc. 2006, 128, 11679−11692. (43) Wu, J. F.; Wang, W. D.; Xu, J.; Deng, F.; Wang, W. Chem.Eur. J. 2010, 16, 14016−14025. (44) Blasco, T.; Boronat, M.; Concepcion, P.; Corma, A.; Law, D.; Vidal-Moya, J. A. Angew. Chem., Int. Ed. 2007, 46, 3938−3941. (45) Inoue, S. J. Organomet. Chem. 1972, 39, 11−16. (46) Panov, G. I.; Uriarte, A. K.; Rodkin, M. A.; Sobolev, V. I. Catal. Today 1998, 41, 365−385. (47) Leanza, R.; Rossetti, I.; Mazzola, I.; Forni, L. Appl. Catal. A: Gen. 2001, 205, 93−99. (48) Starokon, E. V.; Parfenov, M. V.; Pirutko, L. V.; Abornev, S. I.; Panov, G. I. J. Phys. Chem. C 2011, 115, 2155−2161. (49) Yoshizawa, K.; Shiota, Y.; Yumura, T.; Yamabe, T. J. Phys. Chem. B 2000, 104, 734−740. (50) Saepurahman; Visur, M.; Olsbye, U.; Bjorgen, M.; Svelle, S. Top. Catal. 2011, 54, 1293−1301. (51) Aboul-Gheit, A. K.; Awadallah, A. E.; Abdel-Hamid, S. M.; Aboul-Enein, A. A.; El-Desouki, D. S. Petrol. Sci. Technol. 2012, 30, 893−903. (52) Wang, W.; Hunger, M. Acc. Chem. Res. 2008, 41, 895−904. (53) Ivanova, I. I.; Corma, A. J. Phys. Chem. B 1997, 101, 547−551. (54) Wang, W.; Buchholz, A.; Seiler, M.; Hunger, M. J. Am. Chem. Soc. 2003, 125, 15260−15267. (55) Forester, T. R.; Howe, R. F. J. Am. Chem. Soc. 1987, 109, 5076− 5082.

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Corresponding Author

*Tel +86-27-87198820; Fax +86-27-87199291; e-mail dengf@ wipm.ac.cn (F.D.), [email protected] (J.X.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Natural Science Foundation of China (20933009, 21221064, 21210005 and 21173254) and Wuhan Science and Technology Bureau (“Chen Guang” project for young scientists) for financial support (201271031383).

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REFERENCES

(1) Bellussi, G.; Pazzuconi, G.; Perego, C.; Girotti, G.; Terzoni, G. J. Catal. 1995, 157, 227−234. (2) Chandawar, K. H.; Kulkarni, S. B.; Ratnasamy, P. Appl. Catal. 1982, 4, 287−295. (3) Corma, A.; Martinez-Soria, V.; Schnoeveld, E. J. Catal. 2000, 192, 163−173. (4) Vijayaraghavan, V. R.; Raj, K. J. A. J. Mol. Catal. A: Chem. 2004, 207, 41−50. (5) Rakoczy, J.; Romotowski, T. Zeolites 1993, 13, 256−260. (6) Schmerli, L.; Vesely, J. A. J. Org. Chem. 1973, 38, 312−315. (7) Olah, G. A.; Schilling, P.; Staral, J. S.; Halpern, Y.; Olah, J. A. J. Am. Chem. Soc. 1975, 97, 6807−6810. (8) Ivanova, I. I.; Blom, N.; Derouane, E. G. J. Mol. Catal. A: Chem. 1996, 109, 157−168. (9) Smirnov, A. V.; Mazin, E. V.; Yuschenko, V. V.; Knyazeva, E. E.; Nesterenko, S. N.; Ivanova, I. I.; Galperin, L.; Jensen, R.; Bradley, S. J. Catal. 2000, 194, 266−277. (10) Abasov, S. I.; Babayeva, F. A.; Zarbaliyev, R. R.; Abbasova, G. G.; Tagiyev, D. B.; Rustamov, M. I. Appl. Catal. A: Gen. 2003, 251, 267− 274. (11) Todorova, S.; Su, B. L. J. Mol. Catal. A: Chem. 2003, 201, 223− 235. (12) Bigey, C.; Su, B. L. J. Mol. Catal. A: Chem. 2004, 209, 179−187. (13) Huang, X. Q.; Sun, X.; Zhu, S. K.; Liu, Z. M. React. Kinet. Catal. Lett. 2007, 91, 385−390. (14) Kato, S.; Nakagawa, K.; Ikenaga, N.; Suzuki, T. Chem. Lett. 1999, 28, 207−208. (15) Kato, S.; Nakagawa, K.; Ikenaga, N.; Suzuki, T. Catal. Lett. 2001, 73, 175−180. (16) Lukyanov, D. B.; Vazhnova, T. J. Mol. Catal. A: Chem. 2008, 279, 128−132. (17) Ordomskiy, V. V.; Rodionova, L. I.; Ivanova, I. I.; Luck, F. ChemCatChem 2012, 4, 681−686. (18) Choudhary, V. R.; Kinage, A. K.; Choudhary, T. V. Science 1997, 275, 1286−1288. (19) Choudhary, V. R.; Mondal, K. C.; Mulla, S. A. R. Angew. Chem., Int. Ed. 2005, 44, 4381−4385. (20) Wang, X. M.; Qi, G. D.; Xu, J.; Li, B. J.; Wang, C.; Deng, F. Angew. Chem., Int. Ed. 2012, 51, 3850−3853. (21) He, S. J. X.; Long, M. A.; Wilson, M. A.; Gorbaty, M. L.; Maa, P. S. Energy Fuels 1995, 9, 616−619. (22) He, S. J. X.; Long, M. A.; Attalla, M. I.; Wilson, M. A. Energy Fuels 1992, 6, 498−502. (23) Kennedy, E. M.; Lonyi, F.; Ballinger, T. H.; Rosynek, M. P.; Lunsford, J. H. Energy Fuels 1994, 8, 846−850. (24) Tabata, K.; Teng, Y.; Takemoto, T.; Suzuki, E.; Banares, M. A.; Pena, M. A.; Fierro, J. L. G. Catal. Rev.Sci. Eng. 2002, 44, 1−58. (25) Tabata, K.; Teng, Y.; Yamaguchi, Y.; Sakurai, H.; Suzuki, E. J. Phys. Chem. A 2000, 104, 2648−2654. 4023

dx.doi.org/10.1021/jp310872a | J. Phys. Chem. C 2013, 117, 4018−4023