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Activity of Oxalic Acid Treated ZnO/CuO/HZSM-5 Catalyst for the Transformation of Methanol to Gasoline Range Hydrocarbons H. A. Zaidi† and K. K. Pant*,‡ UniVersity School of Chemical Technology, Guru Gobind Singh Indraprastha UniVersity, Kashmere Gate, Delhi, India, and Department of Chemical Engineering, Indian Institute of Technology, Hauz Khas, Delhi 110016, India
The present study describes the stability of oxalic acid treated ZnO/CuO/HZSM-5 catalyst for the conversion of methanol to gasoline range hydrocarbons. A 0.5 wt % ZnO/7 wt % CuO/HZSM-5 catalyst was prepared by the wet impregnation method followed by dealumination using oxalic acid. Fresh and used catalysts were characterized by X-ray diffraction, scanning electron microscopy, surface area analysis, pore size analysis, thermogravimetric analysis, NH3 temperature programmed desorption, and X-ray photoelectron spectroscopy. All the kinetic experiments were carried out in an isothermal fixed bed reactor at 673 K. The major liquid reaction products were cyclopentene, n-hexane, 1-octene, cycloheptane, 2,5-dimethylhexane, n-nonane, cyclohexane, ethylbenzene, xylene, toluene, isopropylbenzene, trimethylbenzene, and tetramethylbenzene. The effect of run time was also studied to investigate the effect of oxalic acid treatment on catalyst stability. The oxalic acid treated catalyst was more resistant to deactivation compared to the untreated 0.5 wt %/ZnO 7 wt % CuO/HZSM-5 catalyst. 1. Introduction There has been an increasing global demand for petroleum feed stocks, fuels, and light hydrocarbons. Methanol is a good candidate because it can be used as a transportation fuel and obtained from renewable sources of energy. Methanol can be produced from synthesis gas as well as from steam reforming of natural gas, from gasification of coal, or from biomass. Efforts are being made to develop suitable catalysts for the transformation of methanol to gasoline with improved conversion, improved product yields, and lower coke deposition. A limited number of publications are available on catalytic conversion of methanol to gasoline range hydrocarbons.1-5 ZSM-5 catalysts can be used for MTG because of their high surface areas, acidic natures, and well-defined structures. The high surface area associated with zeolites allows a high degree of dispersion of active metals over the zeolites making maximum use of the metal deposited. During methanol conversion light olefin yield increases with space-time and reaches a maximum, indicating the intermediate characteristic of the light olefins formed. An important feature of the methanol to hydrocarbon reaction on ZSM-5 is the contact time that results in a change in the hydrocarbon product distribution.5-7 One of the major problems that needs to be overcome is the rapid deactivation of the catalyst. A moderate amount of ZnO addition increases the stability of active CuO species by retaining the formation of CuO/ZnO alloy over HZSM-5 catalyst.8 The presence of ZnO over HZ(7) catalyst reduces the rate of deactivation and stabilizes the catalyst activity in some reactions.9,10 Methanol conversion and hydrocarbon yields increase with the attainment of an optimal temperature of 673 K over HZSM-5 catalyst. Ga2O3-impregnated HZSM-5 catalyst remarkably increases the selectivity to aromatics at the expense of C2-C4 alkenes without affecting the overall conversion.11 Influence of the synthesis conditions of HZSM-5 on the selectivity toward light olefins * To whom correspondence should be addressed. Tel.: +91 11 26596172. Fax: +91 11 26581120. E-mail:
[email protected]. † University School of Chemical Technology. ‡ Indian Institute of Technology.
and aromatics has been reported by several investigators.12,13 Several modifications of ZSM-5 were suggested in order to improve the selectivity toward light olefins in the methanol to olefin conversion process with respect to impregnation of metal oxide. Ga2O3/HZSM-5 and Ga2O3/WO3 were used for the conversion of methanol to hydrocarbons.14 Modified silicate zeolites were used by impregnation with metal nitrates of Ag, Ca, Cd, Cu, Ga, La, and Sr to study the effect of the activity and selectivity of the catalyst to lower alkenes. Incorporation of La and Ag improved light alkene selectivity of the catalyst by 18% and 14%, respectively.13 It has been reported that dealumination leads to a catalyst more resistant to deactivation14 and also by lowering the aluminum content at the outer shell improves the catalyst properties and provides sites that are highly selective to gasoline. The present work aims at development of a suitable catalyst for the methanol conversion to gasoline range hydrocarbons and studies the rate of deactivation over modified catalysts at optimal operating conditions to reduce the rate of deactivation. ZnO/ CuO/HZSM-5 catalysts were prepared by the wet impregnation technique for the conversion of methanol to gasoline. In order to improve the dispersion of CuO, the impregnated catalysts were treated with ZnO. The loading of ZnO onto CuO/HZSM-5 was kept between 0 and 0.5 wt %. Another batch of the catalyst was prepared by treating ZnO/CuO/HZSM-5 pellets with oxalic acid. 2. Experimental Section 2.1. Catalyst Preparation. The mild dealumination of the catalyst was done by stirring 10 g of 0.5 wt % ZnO/7 wt % CuO/HZSM-5 catalyst (HZ(Zn/Cu)) in 300 mL of 1 M oxalic acid at 353 K for 2 min. The preparation details of HZ(Zn/Cu) have been discussed elsewhere.14 The dealuminated samples thus obtained were washed thoroughly with deionized water and finally dried overnight at 383 K. A high concentration of oxalic acid was not used for the study as it significantly reduces the acidic sites of the catalyst, which is highly undesired. The treated catalyst was washed thoroughly with deionized water and finally dried overnight at 393 K in an oven.
10.1021/ie071339y CCC: $40.75 © 2008 American Chemical Society Published on Web 03/28/2008
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2.2. Catalyst Characterization. The catalysts were characterized by X-ray diffraction (XRD), their surface areas, pore size analysis, their final metal content, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and temperature-programmed desorption (TPD). The surface areas and pore volumes of the catalysts were determined by using an ASAP 2010 (Micromeritics, USA) by adsorption with nitrogen (99.99% purity) at 77 K, employing the static volumetric technique. Prior to the analysis the catalyst samples were degassed for 6 h at 383 K under vacuum. With each incremental pressure increase, the number of gas molecules adsorbed on the surface increases. Analysis of the adsorption isotherm was done with the help of software (ASAP 2010) to get information about the pore size distribution and the surface area of the catalyst. X-ray diffraction patterns of all the catalysts were taken in order to characterize the phases present and also the crystallinity of the catalyst. The diffraction patterns were measured by the X-ray diffraction method using a Bruker D-8 Advance X-ray diffractometer with monochromatic Cu KR radiation and scanning 2θ from 0° to 40°. The wavelength of adsorption was kept at 1.54 Å. To determine the actual amount of CuO and ZnO doped over HZSM-5 and the Si/Al ratio, the catalyst samples were digested with nitric acid at 353 K for 2 h under reflux. The final metal content of the catalyst was determined using a metal trace analyzer (Metrohm 757 VA Computrace, Switzerland). To obtain surface textural details of the support, scanning electron microscopy (SEM) of fresh and used samples was performed. The morphologies and structures of the catalysts were studied using a Cambridge 360 scanning electron microscope (SEM). TGA was used to analyze weight loss during heat treatment and to estimate the amount of coke deposited on the catalyst surface after reaction. Thermogravimetric profiles were recorded on a TG/DTA 32 system (Sieko instruments, Japan). The TGA was performed with a heating rate of 10 K/min to attain a final temperature of 1023 K. The catalyst samples were crushed to fine powder and then transferred to a microbalance placed inside the temperature programmable furnace. The temperature of the furnace was raised from 303 to 1023 K and air was passed at a controlled rate of 30 mL/min. The variation in mass of the catalyst was determined with the increase in temperature. Temperature-programmed reduction (TPR-H2) was performed in automatic equipment (Chemisorb 2720, pulse chemisorption, Micromeritics) with a thermal conductivity detector. Fresh catalyst (50 mg) was submitted to heat treatment (10 K/min up to 770 K in a gas flow (30 mL/min) of H2-Ar (10:90). Temperature-programmed desorption (TPD) of NH3 was used to measure the changes in catalyst acidity. XPS was also used to determine the carbonaceous species deposited on the catalyst during reaction and to study the nature of bonding. Surface analysis of the coked catalyst was done using a Perkin-Elmer 1257 at a base pressure of 5 × 10-8 Torr with a dual anode, Al KR 1253.6 eV of X-ray source, and a hemispherical analyzer capable of 25 mV resolution. The energy positions of the peaks and their intensities were measured. The energy positions were used to discriminate the various chemical states of the element. 2.3. Fixed Bed Reactor Studies. The catalysts were compared for their performance for methanol conversion by conducting experiments in a fixed bed reactor under identical conditions. The details of the experimental procedure are given elsewhere.14 The experimental conditions were as follows: T
Table 1. Physical Properties of the Catalysts metal content (wt %) catalyst HZ(7) HZ(0) HZ(Zn/Cu) HZ(Ox)
SBET (m2/g)
pore radius (BJH)a
pore volume (cm3/g)
CuO ZnO fresh cokedb fresh cokedb fresh cokedb 7.0 0 7.0 6.9
0 0 0.5 0.5
254.6 289.8 241.6 241.6
212.2 279.2 200.2 230.4
30.00 35.92 40.25 40.25
28.94 33.42 35.45 38.4
0.34 0.39 0.33 0.33
0.30 0.35 0.31 0.32
a Cumulative pore radius of between 8.5 and 1500 Å radius. b Run time 12 h.
) 673 K, P ) 1 atm, W/FA0 ) 0.129 g of catalyst‚h/g of methanol fed, and run time ) 0-18 h. During an experimental run, the total condensed liquid and gases were analyzed to determine the composition of noncondensable gases and liquid at regular intervals. The noncondensable gases contained mainly C1-C5 hydrocarbons; CO and CO2 were trapped in sampling valves and analyzed by gas chromatography. The condensed hydrocarbon products were analyzed on a capillary column. The noncondensable gases were analyzed by gas chromatography using two columns: Poropak Q and Carbosphere. The analysis was done in two gas chromatographs (Model No. 5765, Nucon, India) provided with a flame ionization detector (FID) and a thermal conductivity detector (TCD). During the methanol conversion a number of liquid products were obtained. All the liquid hydrocarbon products were analyzed by a flame ionization detector using a capillary column (Petrocol DH column) on a 5765 chromatograph (Aimil-Nucon, India). 3. Results and Discussion The first part of the study includes the comparison of different catalysts with respect to their surface properties, methanol conversion, product yields, and coke deposition. 3.1. Characterization of Catalysts. The surface areas and pore volumes of the catalysts are shown in Table 1. The surface area of the CuO catalyst decreased from 290 m2/g on HZ(0) to 241.6 m2/g on HZ(Ox), and the total pore volume of the catalysts also reduced accordingly from 0.39 to 0.33 cm3/g with increasing metal content. The reduction in pore volume and surface area of the catalyst could be due to the diffusion of metal solution in the pores of zeolite catalysts. The volume of N2 adsorbed decreases with increasing copper/zinc oxide content due to partial coverage of the surface with copper/zinc oxide.9,15,16 Incorporation of 0.5 wt % ZnO onto CuO-doped HZSM-5 further reduced the surface area and pore volume of the catalyst. There is no change in surface area and pore volume after treating the catalyst with oxalic acid [HZ(Ox)], as shown in Table 1. Figure 1 shows the XRD patterns of CuO/ZnO and oxalic acid treated zeolite catalysts, and compared with the starting HZ(0) catalyst, they have similar XRD patterns. The X-ray diffraction patterns for copper oxide doped catalyst samples indicated that there was no new phase formation during heat treatment and CuO doping. The structure of zeolite remained intact after the different treatment procedures.14 No peak related to copper oxide species was found for these catalysts. This confirms that copper oxide in microporous HZSM-5 can be molecularly dispersed. However, the peak intensities differ depending upon CuO/ZnO contents, with the highest intensity observed for the starting zeolite HZ(0). The decrease in intensity was attributed to the higher absorption coefficient of CuO/ZnO. The decrease in pore radius compared with parent matrix is indicative of copper presence in the pores of the lattice.
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Figure 1. XRD Patterns of different catalysts.
However, the increase in intensity in the case of oxalic acid treated CuO/ZnO doped HZSM-5 catalyst was compared to that in the case of HZ(Zn/Cu) due to mild leaching of metal oxides. The necessary crystallinity required for better catalytic activity was obtained by the combined effect of CuO/ZnO on HZSM5. These results suggest that molecularly/atomically dispersed copper ion or very small copper oxide/zinc oxide clusters of size below the detection capacity of XRD should be present on the ZSM-5 matrix.17 The crystal morphology, formation of micropores, and surface properties were observed by scanning electron microscopy (SEM). The SEM photographs of various calcined catalysts indicated that there is no significant change in the morphology of the surface structure after doping of CuO/ZnO and oxalic acid treatment over HZSM-5. The shape of HZSM-5 particles seems to be spherical. Typical SEM photographs of fresh HZ(0), HZ(Zn/Cu), and HZ(Ox) catalysts are given in Figure 2. The TPR study of the catalyst was done in order to investigate the effect of ZnO addition to CuO/HZSM-5 catalyst. Addition of ZnO significantly lowered the reduction temperature of the catalyst compared to CuO/HZSM-5, as shown in Figure 3. The existence of dehydration components, which make CuO/ZnO dispersion increase, and the “synergetic effect” of CuO/ZnO with HZSM-5, which makes CuO/ZnO become more active and reduce more easily, can increase the activity of the catalyst. TPR profiles are characterized by single peaks centered at 505 and 532 K, respectively. A sharp reduction peak was obtained (505 K) with ZnO added to CuO/HZSM-5 catalyst, lower than that found for CuO/HZSM-5 (532 K), indicating better dispersion in this catalyst.18,19 The amount of H2 was consumed during the initial reduction of CuO to Cu0. The reduction temperature of CuO-doped HZSM-5 catalyst was higher than that of CuO/ ZnO-doped HZSM-5 catalyst. A separate study carried out over ZnO revealed that the ZnO peak appears at a much higher temperature (>750 K). The peak observed at 778 K is attributed to reduction of ZnO. 3.2. Effect of Oxalic Acid Treatment on the Conversion and Hydrocarbon Yield. Although 7 wt % CuO doped catalyst HZ(7) resulted in a significantly higher conversion and hydrocarbons product yield, its rate of catalyst deactivation was also significant. In order to reduce the deactivation of HZ(7) catalyst,
Figure 2. SEM photographs of (a) HZ(Zn/Cu) and (b) HZ(Ox) catalysts.
the catalyst was impregnated with different amounts of ZnO.15 A moderate amount of ZnO addition increased the stability of active CuO species by formation of CuO/ZnO alloy.20 Incorporation of ZnO reduced the rate of deactivation and stabilized the catalyst activity in some reactions.9,10 Several researchers have correlated the acidic properties and performance of the catalysts for methanol dehydration.1-11 Weak or intermediate strength of acidic sites has been responsible for the selective formation of DME, and strong acidic sites convert further the originally formed DME to hydrocarbons. To reduce
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Figure 4. Methanol conversion versus time in a fixed bed reactor [T ) 673 K, P ) 1 atm, W/FA0 (g of catalyst‚h/g of methanol fed) ) 0.129].
Figure 3. TPR profiles of HZ(7) and HZ(Ox) catalysts. Table 2. Product Distributions for the Conversion of Methanol over Different Catalysts [T ) 673 K, W/FA0 (g of catalyst‚h/g of methanol fed) ) 0.129, P ) 1 atm] compound
HZ(Zn/Cu)
HZ(Ox)
HZ(7)
HZ(0)
conversion (%) yield (wt %) CH4 C2 C3 C4 C5 C5+ C6H6 C7H8 C8H10 C9H12 C10H14 CH3OCH3 hydrocarbons (wt % feed) water (wt % feed) othersb (wt % feed)
95.0
94.0
97.0
38.0
0.69 1.23 1.72 1.24 0.84 7.36 0.13 1.91 9.58 10.38 3.52 2.20 40.80 37.0 17.20
0.15 0.52 0.69 0.60 0.68 11.50 0.33 2.87 10.47 10.76 0.44 1.04 40.05 37.20 16.98
0.33 0.96 0.85 0.61 0.55 9.08 0.10 3.34 12.20 12.98 0.43 0.73 42.16 37.2 17.64
1.0 1.35 3.47 1.89 2.12 1.0 0.27 0.72 1.10 1.10 tra 1.16 15.18 19.38 3.42
a
Figure 5. Hydrocarbon yield versus time in a fixed bed reactor [T ) 673 K, P ) 1 atm, W/FA0 (g of catalyst‚h/g of methanol fed) ) 0.129].
tr ) trace. b Others include CO and CO2.
the acidity, mild treatment of CuO/ZnO-impregnated catalyst with oxalic acid was done that leads to more resistance to deactivation. The activity of hydrocarbon processing catalysts was studied with time on stream to study the deactivation of various weight percent CuO- and ZnO-doped HZSM-5 catalysts. A comparison of products obtained with different catalysts studied is given in Table 2. From this table it was concluded that higher hydrocarbon yield and methanol conversion were obtained with HZ(7) catalyst. HZ(7) catalyst initially gave a higher conversion compared to HZ(0), HZ(Zn/Cu), and HZ(Ox) catalysts. Figures 4 and 5 show the methanol conversion and the hydrocarbon yield using HZ(7), HZ(0), HZ(Zn/Cu), and HZ(Ox) catalysts at a given temperature (673 K) and pressure (1 atm). The conversion of methanol and yield of hydrocarbons decreased with increase in time on stream due to deposition of coke. Incorporation of 0.5 wt % ZnO on the HZ(7) catalyst significantly reduced the deactivation rate, thereby facilitating methanol conversion and hydrocarbon yield. Treating this catalyst with oxalic acid further reduced deactivation during methanol conversion. The deactivation of HZ(7) and HZ(Zn/Cu) catalyst was higher compared to oxalic acid treated HZ(Ox) catalyst, while there was a marginal change in Si/Al ratio after treatment with oxalic acid. It can be seen from Figure 4 that initial conversion of HZ(0), HZ(7), HZ(Zn/Cu), and HZ(Ox) was 38%, 97%, 95%, and 94%, respectively, and after the 18 h run the methanol conversion decreased to 21.2%, 66.4%, 72.1%, and 79.5%, respectively, for these four catalysts. Figure 5 shows
Figure 6. NH3-TPD profiles for HZ(Zn/Cu) and HZ(Ox) catalysts.
the yield of hydrocarbons with respect to time. The increase in time of stream also results the decrease in the yield of hydrocarbons. Similarly, the initial hydrocarbon yields of HZ(0), HZ(7), HZ(Zn/Cu), and HZ(Ox) were 15.2, 42.2, 40.8, and 40.1 wt %, respectively, and after the 18 h run the hydrocarbon yield decreased to 8.1, 21.3, 26.6, and 30.1 wt %, respectively, for these four catalysts. HZ(Ox) shows a relatively lower decrease in the yield of hydrocarbon with run time compared to HZ(7) and HZ(Zn/Cu) catalysts. Thus the catalytic activity of oxalic acid treated catalyst was higher for methanol conversion due to its slow deactivation compared to other catalysts. Relatively low coke formation was observed over the surface of oxalic acid treated HZSM-5 catalyst. The experimental results indicated that the deactivation resistance of the catalyst may be improved by oxalic acid treatment where the external surface sites were
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Figure 7. SEM images of (a) coked HZSM-5 after 12 h run, (b) coked HZ(Ox) after 12 h run, and (c) coked HZ(7) after 12 h run.
eliminated during dealumination. It has been reported that a catalyst associated with externally dealuminated HZ(Zn/Cu) does not alter by starting deactivation as one associated with unmodified HZ(Zn/Cu).21 Since the dealumination is mainly concerned with the external sites, it can also be concluded that the formation of heavier products that need free space are no longer favored. Therefore, the stability against coking could be improved, resulting in apparent improvement of the overall activity under particular circumstances. TPD profiles shown in Figure 6 revealed that dehydration components of HZSM-5 catalyst have acidic sites with two kinds of acidic sites: weak acidic sites corresponding to low temperature desorption sites and strong acidic sites corresponding to high temperature desorption sites. As can be seen from NH3-TPD profiles in Figure 6, the acidic strength of the catalyst slightly decreased after treatment with oxalic acid. The NH3-TPD profiles showed the decrease in acidic content of oxalic acid treated HZ(Ox) as compared to 0.5 wt % ZnO/7 wt % CuO/HZSM-5 catalyst.
sample
coke content (wt %)
HZ(0) HZ(7) HZ(Zn/Cu) HZ(Ox)
2.1 5.0 3.6 2.7
The experimental results presented above show that the deactivation resistance of HZ(7) catalysts in the methanol transformation reaction could be considerably improved by adding ZnO and by giving an oxalic acid treatment. A metal trace analyzer was used to determine the final amounts of ZnO and CuO loaded on HZSM-5 and the Si/Al ratio. On treatment with oxalic acid over HZ(Zn/Cu), there was a slight decrease in the weight percent CuO; however, no significant difference in ZnO content was observed (Table 1). Mild leaching was observed during the treatment of oxalic acid, probably due to dissolution of extraframework zeolite. A mild decrease in aluminum content was observed with an increase in the Si/Al ratio from 45 to 47. In order to investigate the coking characteristics of the catalyst, SEM, thermogravimetric analysis, and X-ray photoelectron spectroscopic studies of spent catalyst were done. SEM photographs were made to study the morphology of coke deposition over the catalyst. Figure 7 shows SEM images of coked HZ(0), HZ(Ox), and HZ(7) after the run time of 12 h. It was observed that HZ(7) catalyst has a higher amount of coke deposited over the surface compared to HZ(0) and HZ(Ox) catalysts. The thermogravimetric profiles of the coked catalysts during various temperature-programmed treatments were also recorded. TGA analysis was used to determine the coke content using air as carrier gas. The typical plots of thermogravimetric analysis for different coked catalyst curves were obtained at a heating rate of 5 °C/min. The weight losses of the coked HZ(7), HZ(0), HZ(Zn/Cu), and HZ(Ox) catalysts were measured while heating the samples at a specific rate. The weight percent coke formed on different catalysts is given in Table 3. The coke contents on HZ(7), HZ(0), HZ(Zn/Cu), and HZ(Ox) for a 12 h run were 5.0, 2.1, 3.6, and 2.7 wt %, respectively. The coking activities were directly related to the availability of acidic sites, pore size, and nature of the channel network. XPS was also used to characterize the carbonaceous materials deposited over the HZ(Ox) catalyst, and this analysis was used to determine the chemical composition, the presence of impurities, and the nature of chemical bonds. However, the decomposition of the carbon C 1s during X-ray photoelectron spectra (XPS) is complicated when choosing all the parameters (intensity, line shape, binding energy) which indicate the species present, binding energies, and intensities for the HZ(Ox) catalyst exposed to different temperatures. Two carbon species were formed on the catalyst surface, with the peaks corresponding to a graphite carbon (C-C with binding energy of 284.9 eV) and oxidized carbon species (CO3 with binding energy of 289.5 eV). Methoxy and formate were also found on the surface of the deactivated catalyst as shown in C 1s spectra, which confirm the formation of intermediates to explain the reaction mechanism. It can be seen from Figure 8 that at higher temperature the peaks of carbon spectra become sharp and more intense due to an increased amount of carbon deposition on the catalyst surface.21-24 Carbon deposited on the surface of a catalyst covers the active sites; therefore, sites available for methanol adsorption during methanol to gasoline range hydrocarbons
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Figure 8. XPS C 1s spectra of postreaction HZ(Ox) catalyst exposed to different reaction temperatures.
reaction reduce, hence the methanol conversion and hydrocarbon yield decrease. 4. Conclusion HZ(Ox) was studied in experiments for the transformation of methanol to gasoline range hydrocarbons. Addition of 0.5 wt % ZnO to 7 wt % CuO/HZSM-5 and treatment with oxalic acid lead to a catalyst more resistant to deactivation. It was observed that addition of ZnO results in a smaller crystallite size, indicating higher dispersion of catalyst, and treatment with oxalic acid marginally dealuminated the catalyst. Catalyst performance was improved due to the elimination of external surface sites via selective dealumination by oxalic acid, which results in an easier access of methanol to the internal surface sites. Higher surface area and pore volume of HZSM-5 catalyst helped in redispersing the ZnO and CuO species. The major liquid reaction products were cyclopentene, n-hexane, 1-octene, cycloheptane, 2,5-dimethylhexane, n-nonane, cyclohexane, ethylbenzene, xylene, toluene, isopropylbenzene, trimethylbenzene, and tetramethylbenzene, whereas the major gaseous products were ethylene, propylene, pentane, and dimethyl ether. The acidtreated ZnO/CuO-doped HZSM-5 catalyst exhibited high activity, selectivity, and stability for the conversion of methanol to gasoline range hydrocarbons. Nomenclature DME ) dimethyl ether MTG ) methanol to gasoline HZ(7) ) 7 wt % CuO/HZSM-5 HZ(0) ) HZSM-5 HZ(Zn/Cu) ) 0.5 wt % ZnO/7 wt % CuO/HZSM-5 HZ(Ox) ) 0.5 wt % ZnO/6.89 wt % CuO/HZSM-5 (oxalic acid treated) Literature Cited (1) Alyea, E. C.; Bhat, R. N. Methanol Conversion to Hydrocarbons over WO3/HZSM-5 Catalysts prepared by Metal Oxide Vapor Synthesis. Zeolites 1995, 15, 318.
(2) Choudhary, V. R.; Kinage, A. K. Methanol-to-Aromatics Conversion over H-gallosilicate (MFI): Influence of Si/Ga ratio, degree of H+ exchange, Pretreatment Conditions, and Poisoning of Strong Acid Sites. Zeolites 1995, 15, 732. (3) Calleja, G.; de Lucas, A.; van Grieken, R. Co/HZSM-5 Catalyst for Syngas Conversion: influence of Process Variables. Fuel 1995, 74, 445. (4) Chang, C. D.; Chu, C. T.; Socha, R. F. Methanol Conversion to Olefins over ZSM-5. J. Catal. 1984, 86, 289. (5) Abdillahi, M. M.; El-Nafaty, U. A.; Al-Jarallah, A. M. Barium Modification of High Silica Zeolite for Methanol Conversion to Light Alkenes. Appl. Catal., A 1992, 91, 1. (6) Dewaele, O.; Geers, V. L.; Froment, G. F.; Marin, G. B. The Conversion of Methanol to Olefins: A Transient Kinetic Study. Chem. Eng. Sci. 1999, 54, 4385. (7) Marchi, A. J.; Froment, G. F. Catalytic Conversion of Methanol into Light Alkenes on Mordenite like Zeolite. Appl. Catal., A 1993, 94, 91. (8) Xi, J.; Wang, Z.; Lu, G. Improvement of Cu/Zn based Catalysts by Nickel additive in Methanol Decomposition. Microporous Mesoporous Mater. 2002, 225, 77. (9) Velu, S.; Wang, L.; Okazaki, M.; Suzuki, K.; Tomura, S. Characterization of MCM-41 Mesoporous Molecular Sieves Containing Copper and Zinc and their Catalytic performance in the Selective Oxidation of Alcohols to Aldehydes. Microporous Mesoporous Mater. 2002, 54, 113. (10) Anand, R.; Jyothi, T. M.; Rao, B. S. A Comparative Study on Catalyst Activity of ZnO Modified Zeolites in the synthesis of alkylpyrazines. Appl. Catal., A: Gen. 2001, 208, 203. (11) Freeman, D.; Wells, R. P. K.; Hutchings, G. J. Conversion of Methanol to Hydrocarbons over Ga2O3/WO3 Catalysts. J. Catal. 2002, 205, 358. (12) Bjørgen, M.; Kolboe, S. The Conversion of Methanol to Hydrocarbons over Deluminated zeolite H-beta. Micoporous Mesoporous Mater. 2002, 225, 285. (13) Al-Jarallah, A. M.; El-Nafaty, U. A.; Abdillahi, M. M. Effect of Metal Impregnation on the Activity, Selectivity and Deactivation of a High Silica MFI Zeolites when Converting Methanol to Light Alkenes. Appl. Catal., A 1997, 154, 117. (14) Zaidi, H. A.; Pant, K. K. Catalytic conversion of Methanol to Gasoline Range Hydrocarbons. Catal. Today 2004, 96, 155. (15) Zaidi, H. A.; Pant, K. K. Catalytic Activity of Copper Oxide impregnated HZSM-5 in Methanol Conversion of Liquid Hydrocarbons. Can. J. Chem. Eng. 2005, 83, 970. (16) Can˜zares, P.; Dorado, A. D. F.; Dura´n, A.; Asencio, I. Characterization of Ni and Pd Supported on H-Mordenite Catalysts: Influence of the Metal Loading Method. Appl. Catal., A 1998, 169, 137. (17) Gervasini, A.; Picciau, C.; Auroux, A. Characterization of Copper exchanged ZSM-5 and ETS-10 Catalysts with Low and High Degrees of Exchange. Microporous Mesoporous Mater. 2000, 35, 457. (18) Matter, P. H.; Braden, D. J.; Ozkan, U. S. Steam reforming of methanol to H2 over nonreduced Zr-containing CuO/ZnO catalyst. J. Catal. 2004, 223, 340. (19) Fierro, G.; Jacano, M.; Lo Inversi, M.; Porta, P.; Cioci, F.; Lavecchia, R. Appl. Catal., A. 1996, 137, 327. (20) Xi, J.; Wang, Z.; Lu, G. Improvement of Cu/Zn based Catalysts by Nickel additive in Methanol Decomposition. Microporous Mesoporous Mater. 2002, 225, 77. (21) Sarrioglan, A.; E-Sentalar, A.; Savasci, O. T.; Taarit, Y. B. The effect of dealumination on the apparent and the actual rates of aromatization of methane over MFI-supported molybdenum catalysts. J. Catal. 2004, 226, 210. (22) Nanse´, G.; Papirer, E.; Fioux, P.; Moguet, F.; Tressaud, A. Fluorination of Carbons Black: An X-Ray photoelectron spectroscopy study: I. A literature review of Fluorinated Carbons, XPS Investigations of some Fluorinated Carbons. XPS investigation of some reference compounds. Carbon 1997, 35, 175. (23) Burg, P.; Fydrych, P.; Cagniant, D.; Nanse, G.; Bimer, J.; Jankowska, A. The Characterization of Nitrogen-Enriched Activated Carbons by IR, XPS and LSER Methods. Carbon 2002, 40, 1521. (24) Szwarckopf, H. E. XPS photo Emission in Carbonaceous Material: A “defect” Peak beside the Graphitic Asymmetric Peak. Carbon 2004, 42, 1713.
ReceiVed for reView October 4, 2007 ReVised manuscript receiVed December 21, 2007 Accepted January 31, 2008 IE071339Y
