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Energy & Fuels 2008, 22, 1812–1823
Disproportionation of Light Paraffins Roland Schmidt,* M. Bruce Welch, Richard L. Anderson, Maziar Sardashti, and Bruce B. Randolph ConocoPhillips, BartlesVille Technology Center, BartlesVille, Oklahoma 74004 ReceiVed October 24, 2007. ReVised Manuscript ReceiVed February 5, 2008
Various acidic catalysts were synthesized or obtained commercially to examine their activity for the catalytic disproportionation of saturated hydrocarbons under mild, energy-conserving conditions. The goal was to upgrade lower-value light hydrocarbon streams, especially isopentane, to higher-value refinery products in a simple process. The desired products can then be used for upgrading petroleum products into cleaner burning, more environmentally friendly fuels. These efforts were conducted in anticipation of more stringent future regulations, especially on Reid vapor pressure (RVP) and renewable fuels standards in U.S. fuels, which will significantly impact the flexibility that refiners have to blend gasoline. Significant quantities of light hydrocarbons, such as pentanes, may be forced out of the blending pool, causing current alternate markets for these streams to become oversupplied. Lost opportunity costs associated with the growing volume of orphaned streams, such as pentanes, pose a significant threat to a refiner’s viability. Five different catalyst systems from zeolites to acidic ionic liquids were tested. All showed potential in converting light ends to value-added heavier products. Catalysts showed a typical trade off between high pentane conversion and selectivity to gasoline range products. A critical parameter for high conversion rates was space or contact time (liquid hour space velocity, LHSV) in order to allow for the unreactive paraffinic hydrocarbons to activate and react. Spent catalyst regeneration was also addressed in order to recover at least a portion of lost activity.
1. Introduction A significant portion of fuels-related research in the past 5–10 years has been directed at converting high RVP light naphtha streams1 unsuitable as a substantial gasoline blendstock to higher molecular weight gasoline and diesel range compounds.2 The desire for such capabilities continues to grow with downward pressure on gasoline RVP to reduce fugitive emissions into the atmosphere and off set the increasing use of high RVP ethanol. Although RVP waivers can reduce this problem, should such waivers be discontinued, the pressure for removal of high RVP components will increase. A measure of compounds vapor pressure at 38 °C, Reid vapor pressure has been targeted by the Environmental Protection Agency (EPA) as a means of regulating VOC emissions by transportation fuels and ultimately control the formation of ground level ozone.3 In the past decades, the EPA imposed regulations controlling hydrocarbon emissions from fuel sources2 in order to reduce ground ozone levels. Ozone, a major atmospheric pollutant in urban environments, generation is attributed to volatile organic compounds (VOC’s) emitted from fuels. Fuel with a lower volatility achieves emissions reductions in ozone precursors by reducing the evaporation rate of the fuel.4 C5 hydrocarbons are among the * To whom correspondence should be addressed. Phone: (918) 661-3506. Fax: (918) 662-1097. E-mail:
[email protected]. (1) Meyer, E. Chemistry of Hazardous Materials, 3rd ed.; Prentice Hall: Upper Saddle River, NJ, 1998; p 458. (2) Gary, J. E.; Handwerk, G. E. In Petroleum Refining, 4th ed.; Marcel Dekker: New York, 2001. (3) Standard Test Method for Vapor Pressure of Petroleum Products (Reid Method); Designation D 323–99a; American Society for Testing and Materials: West Conshohocken, PA, June 1999. (4) Indiana Air Facts; Office of Air Management Fact Sheet FCTMO5; Indiana Department of Environmental Management: Indianapolis, IN, Sept. 1998.
highest vapor pressure components remaining in gasoline today and have been reported to have a significant ozone formation potential.5,6 Butanes were earlier forced out of the gasoline pool during the summer season when ozone levels reached critical levels.7 Now, with increased interest in further lowering ozone atmospheric levels, increasing quantities of C5’s must be removed to further lower RVP in summer months as mandated by the Clean Air Act.8,9 Exacerbating the RVP problem is the increase in ethanol blending. Blending ethanol requires a lower RVP base stock to achieve overall final fuel RVP specifications. Even C6-range hydrocarbon removal might be necessary if summer RVP values are further lowered by the EPA. C6-range in addition to C5-range hydrocarbons would then become problem streams for refiners. Just as with C4and C5 streams, these would have to be converted to higher value streams for inclusion back into the gasoline or distillate pools. Several upgrading pathways can be considered depending on the specific compound. C4-olefins are used as alkylation feedstock. Saturated hydrocarbons present a greater challenge.8 The unreactive nature of paraffins normally demands high energy input and expensive noble-metal catalysts to convert them to more valuable products. Several C5 upgrading pathways can be considered depending on the specific compound.9 These (5) Simpson, D. J. Atmosph. Chem. 1995, 20, 163–177, No. 2. (6) Dunker, A. M.; Morris, R. E.; Pollack, A. K.; Schleyer, C. H.; Yarwood, G. EnViron. Sci. Technol. 1996, 30 (3), 787–801. (7) Guide on Federal and State Summer RVP Standards for ConVentional Gasoline Only; report EPA420-B-03–002; U.S. Environmental Protection Agency: Washington, D.C., March 2003. (8) Sommer, J.; Jost, R. Pure Appl. Chem. 2000, 72, 2309–2318, No. 12. (9) Rossini, S. Catal. Today 2003, 77 (4), 467–484.
10.1021/ef7006326 CCC: $40.75 2008 American Chemical Society Published on Web 03/14/2008
Disproportionation of Light Paraffins
pathways include oligomerization of olefins,10,11 structural isomerization,12 cracking,13–15 and reforming,16,17 or using them as fuel in the refinery. Less considered pathways include, among others, disproportionation, which has not been studied extensively.18 Disproportionation, as considered here, refers to the conversion of saturated hydrocarbons to paraffins with higher and lower carbon content: e.g., pentanes to butanes and hexanes. Ultimately, the disproportionation of pentane to hexanes results in an increase in stream RVP so that these can be blended easily back to the gasoline pool, especially in the summer months, whereas butanes are a more valuable feedstock as alkylation feed. Unlike reforming where aromatics are generated, this process would not lead to a significant loss in volume, because paraffins exhibit a lower blending density than aromatics. Disproportionation of light paraffins is the process by which two equivalents of a certain type of monomer, e.g., isopentane (iC5) are converted into one equivalent of a shorter (butane isomer) and one of a larger hydrocarbon (hexane isomer). The proposed mechanism involves the activation of the monomer (iC5) forming a carbo-cation (iC5+). In an intermediate step, this carbo-cation dimerizes with a second monomer to form a C10-activated molecule which tries to stabilize itself by cracking into two products with different carbon numbers (C4’s and C6’s) (Figure 1). Sometimes, this mechanism is facilitated through the addition of small amounts of carbo-cation forming feed additives such as olefins.19 The challenge is to find an inexpensive catalyst that selectively and efficiently performs this two-step reaction. A similar reaction was described in the literature as alkaneor σ-bond metathesis20–24 or molecular averaging.25 In contrast to the acid-catalyzed reaction here investigated, the σ-bond metathesis reaction involves the transfer of a hydride from a supported organometallic catalyst,26 whereas the molecular (10) Maxwell, I. E.; Stork, W. H. J. Introduction to Zeolite Science and Practice, 2nd ed.; Studies in Surface Science and Catalysis; Elsevier: Amsterdam, 2001; Vol. 137, pp 747819. (11) Bercik, P. G.; Metzger, K. J.; Swift, H. E. Ind. Eng. Chem. Prod. Res. DeV. 1978, 17 (3), 214–19. (12) Sie, S. T. Ind. Eng. Chem. Res. 1992, 31 (8), 1881–1889. (13) Meyers, R. A. Handbook of Petroleum Refining Processes, 2nd ed.; Mc Graw Hill: Columbus, OH, 1996. (14) Wojciechowski, B. W. Catal. ReV.-Sci. Eng. 1998, 40 (3), 209– 328. (15) Cumming, K. A.; Wojciechowski, B. W. Catal. ReV.-Sci. Eng. 1996, 38 (1), 101–157. (16) Steinberg, K. H.; Hermann, K.; Becker, K.; Bremer, H.; Franke, W.; Klotzsche, H.; Krueger, W. Chem. Tech. 1977, 29 (5), 269–272. (17) Anunziata, O. A.; Pierella, L. B. Catal. Lett. 1993, 19 (2–3), 143– 151. (18) Randolph, B. B. U.S. Patent 6573416 B1, 2003. (19) Cheung, T.-K. Gates, B. C. Book of Abstracts, 214th ACS National Meeting, Las Vegas, Sept 7-11, 1997. American Chemical Socity: Washington, D.C., 1997; PETR-089. (20) Basset, J. M.; Copéret, C.; Lefort, L.; Maunders, B. M.; Maury, O.; Le Roux, E.; Saggio, G.; Soignier, S.; Soulivong, D.; Sunley, G. J.; Taoufik, M.; Thivolle-Cazat, J. J. Am. Chem. Soc. 2005, 127, 8604–8605. (21) Taoufika, M.; Le Rouxa, E.; Thivolle-Cazat, J.; Copéret, C.; Basset, J.-M.; Maunders, B.; Sunley, G. J. Top. Catal. 2006, 40 Nos. 1–4. (22) Copéret, C. O.; Maury, J.; Thivolle-Cazat, J.-M.; Basset, Angew. Chem., Int. Ed. 2001, 40, No. 12. (23) Levebvre, F.; Basset, J.-M. J. Mol. Catal. A: Chem. 1999, 146, 3–12. (24) Vidal, V.; Théolier, A.; Thivolle-Cazat, J.; Basset, J.-M. Science 1997, 276, 4. (25) Chen, C.-Y. U.S. Patent 6 566 568 B1, 2003. (26) Maury, O.; Lefort, L.; Vidal, V.; Thivolle-Cazat, J.; Basset, J.-M. Angew. Chem., Int. Ed. 1999, 38, No. 13/14. (27) Kuznetzov, P. N.; Anufriev, D. N.; Ione, K. G. React. Kinet. Catal. Lett. 1985, 28, 35–40, No. 1.
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Figure 1. Proposed disproportionation reaction mechanism for one isomer pair. Various recombination pathways must be considered because of the variety of isomers formed.
averaging commences via alkane dehydrogenation followed by conventional olefin metathesis.27
2. Results and Discussions Acid catalysts are suitable candidates28,29 for paraffinic disproportionation reactions. Therefore, catalysts with known acidic properties (i.e., zeolites) and other acids with less well characterized properties were chosen or synthesized and tested in fixed-bed down-flow operations. Other nonzeolitic acid catalyst systems included ionic liquids supported on silica, “ionic solids”, aluminum dichloride on silica, and sulfated zirconias. 2.1. Zeolites. Zeolites are microporous crystalline solids with well-defined structures.30–32 Generally, they contain silicon, aluminum, and oxygen in their framework and metal cations, water, and/or other molecules within their pores. In refineries, they are mainly used for petroleum cracking in fluidized catalytic cracking (FCC) operations because of their unique porous, catalytic, and acidic properties.33–35 Many refining relevant reactions are catalyzed by zeolite framework-bound Brønsted-protons which make the catalyst (28) Corma, A. Mater. Sci. 1997, 2, 63–75, No. 1. (29) Arata, K. AdV. Catal. 1990, 17, 165–211. (30) Minachev, K. M.; Usacheva, O. N. Neftekimiya 1994, 17–28. (31) Virta, R. L. Minerals Information; U.S. Geological Survey: Reston, VA, 199714. (32) Barrer, R. M. Hydrothermal Chemistry of Zeolites; Academic Press: New York, 1982. (33) Whyte, T. E., Jr.; Dalla Betta, R. A. Catal. ReV.-Sci. Eng. 1982, 4 (4), 567–598. (34) Rabo, J. A.; Gajda, G. J. Catal. ReV.-Sci. Eng. 1989–1990, 31 (4), 385–430. (35) Babitz, S. M.; Williams, B. A.; Miller, J. T.; Snurr, R. Q.; Haag, W. O.; Kung, H. H. Appl. Catal., A 1999, 179, 71–86. (36) Jacobs, P. A. Catal. ReV.-Sci. Eng. 1982, 24 (3), 415–440. (37) Davis, R. J. Res. Chem. Intermed. 2000, 26, 21–27, No. 1.
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Table 1. Typical Liquid Sample Obtained during the Course of 1 Day with ZSM-5/iC5 (H-MFI-90) at 450 °C, 500 psi, LHSV ) 2.7; Mass Balance 92% time on stream (h) total iC5 conversion (wt %) iC5 to disproportionation products (wt % iC5 feed) iC4/hexanes molar ratio iC5 to aromatics (% iC5 feed) other reaction products (wt %) gas C4other C5’s C6+ incl. aromatics
1
2
3
4
5
6
7
8
9
0.41 0.17 6.23 0.14 0.89 0.52 0.50 0.17
37.35 5.19 4.81 9.29 23.49 19.11 8.14 10.60
41.53 5.76 5.15 11.4 24.97 22.66 6.56 12.78
56.76 7.67 15.06 6.88 42.67 40.61 8.90 7.59
56.14 7.62 15.07 7.06 41.92 39.80 8.91 7.77
55.77 7.58 14.65 6.99 41.66 39.58 8.82 7.72
55.4 7.58 14.85 6.56 41.73 39.66 8.82 7.27
55.42 7.32 12.39 8.2 40.37 37.58 9.17 9.03
54.34 7.52 14.45 5.99 41.29 39.2 8.77 6.73
very acidic.36–41 This acidity is exploited in crude oil cracking, structural isomerization of hydrocarbons, and fuel synthesis.42 2.1.1. iC5 ConVersions and Product Distributions. In these experiments, commercially available Beta-150, Mordenite-90, and ZSM-5 zeolites43 were tested as catalysts for their ability to disproportionate light paraffins.44–48 In all experiments, isopentane (iC5) was used as model feed. Initial experiments showed that liquid state conditions help improve conversion significantly. The desired reaction was much slower when the feed was in the gaseous state. Similarly, liquid hourly space velocities (LHSV) greater than 6 resulted in a decline in iC5 conversion but had almost no effect on product distribution. Disproportionation occurred in a temperature range between 300 and 450 °C. The overall iC5 conversion increased with temperature. Cracking reactions and the formation of aromatics also occurred. These undesired side reactions became dominant above 450 °C. ZSM-5 demonstrated the best conversion of 55% at relatively low temperatures around 350 °C. Table 1 presents a typical iC5 conversion and product distribution using zeolites during the course of one day. All tested catalysts exhibited low initial conversions which steadily increased until an upper limit was reached. The maximum selectivity for paraffinic disproportionation products was only 22 wt % and obtained when using Beta-150 at 400 °C. The identified aromatics and cracking products which made up 60+ vol % of the product were low in benzene (150 °C). Sulfated zirconias also proved to selectively disproportionate iC5 at moderate temperatures (>200 °C) with moderate conversions. The synthesized sulfated zirconias appear to be stable over an extended period of time (days). After loss of activity, these compounds were regenerated by heating them in a stream of dry nitrogen. Because of their relatively low iC5 conversion and their rather tricky synthesis, it is doubtful if they hold a potential as a viable catalyst system for this type of reaction. Overall, zeolites and sulfated zirconias are less desirable for disproportionation of light paraffins and other catalysts should be considered for this type of reaction due to the energy intensive high temperatures necessary and the extent of side reactions. Ionic liquids and ionic solids performed well for disproportionation but have only limited potential for a commercial process due to the discussed problems. The most promising (111) World Fuels Today; Hart: Houston, TX, Nov. 19, 2001; p 1. (112) Kinugasa, Y.; Okada, M.; Tanaka, T.; Fujimoto, Y.; Takei, Y. Automot. Eng. Int. 2001, 109 (7), 117–120.
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results were obtained with aluminum chloride immobilized on silica due to the benign reaction conditions at which the disproportionation reaction occurs while product selectivity was maintained. Critical to a high conversion rate was again contact time due to the relative inertness of isopentane. The main reason for catalyst deactivation was found to be catalyst coking when reaction conditions were fairly severe, whereas on the other hand, catalyst poisoning from feed contaminants and leachingoff of active catalyst species was another. Drying the isopentane feed also helped to improve catalyst performance and longevity. However, the question of effective catalyst regeneration remains a subject for further investigations. Regeneration of AlCl2/SiO2 appears to be possible employing supercritical extraction with light paraffins such as iC4. Of interest also are some of the observed reactions when this catalyst was exposed to feed other than iC5. Our investigations showed that AlCl2/SiO2 has good activity as a solid acid alkylation catalyst, although more tests have to be conducted. Furthermore, the catalyst was able to crack higher C5+ chain paraffins such as n-heptane under mild conditions to C6, C5, and C4 isomers as also observed during our IL and IS experiments. Unfavorable isomerization of branched hydrocarbons in the feed and products to their straight-chain equivalents accompanies the disproportionation reaction in all tested catalytic systems. The extent of isomerization is equilibrium dependent and favored by low temperatures. Regenerability and catalyst lifetime remains a major issue, especially for AlCl3-based low-temperature catalysts. Zeolites and sulfated zirconia can be easily regenerated by simple coke burnoff or a high-temperature nitrogen flush. Although various methods for regeneration were tested for supported IL’s and IS’s as well as the supported AlCl2/SiO2 catalysts, no good solution has been found. Despite their performance, especially with respect to selectivity at benign conditions, the regeneration issue needs to be resolved. Despite the need for further investigation, the AlCl3-based catalysts may find applications. They exhibited the ability to mildly crack higher paraffins to more desirable products than the higher-temperature-operating zeolites or sulfated zirconia. Because of the mild reaction conditions, no light gas products were formed. Also, theses catalysts showed that they may be suitable alternatives for solid acid alkylation in order to one day replace conventional liquid acid alkylation processes. 4. Experimental Section 4.1. Experimental Set-up. Isopentane was purchased commercially from Fisher Scientific Co. delivered to the reactor using a 500 mL volume ISCO syringe pump. The feed was pumped through two 76.2 cm × 1.27 cm tubing guard beds. The first guard bed held a split bed of 3 Å mol sieve and 3 mm silica gel beads and the second guard bed held a split bed of 3 mm silica gel beads and 13X mol sieves. Flow through the beds was in the order of 3 Å sieves, silica gel, and 13X sieves. The beds were activated in nitrogen flow at 250 °C for 2 h. The tube reactors were 1.9 cm OD piping with a thermowell. They were operated in down flow mode. The reactor was packed top and bottom with glass beads held in place with glass wool. The catalyst bed in the middle of the reactor contained approximately 10–30 g of catalyst determined by the flow rate and desired output. Bed temperature was controlled by temperature controllers using the thermowell thermocouple. The temperature of the outer wall of the reactor was measured with a thermocouple. The outer wall temperature was fed to a temperature override controller to prevent temperature runaways. A back pressure regulator was set to the desired pressure. Pressure gradually increased until the set pressure was reached at which point product was observed in the discharge line.
Disproportionation of Light Paraffins Product sampling was complicated due to gaseous cracking and disproportionation products in the sample. Therefore, the following procedure was followed: the product samples were collected in a vented dry ice cooled vessel. The volume of any escaping gases was monitored with a wet test meter. The product was transferred from the sampling vessel into a small dry ice cooled vial. A sample was taken with a dry-ice-cooled syringe. For zeolite regeneration, a nitrogen diluted air stream delivered using Brooks gas flow controllers. The obtained gas stream contained 4–6% oxygen. The coke burnoff was conducted for at least 1 h at 550 °C followed by a cooling in nitrogen. 4.2. Syntheses. 4.2.1. Zeolites. All zeolites were commercial grade. Mordenite 90 zeolite (S.C. T-4559), BEA-150 zeolite (S.C. BEA 150 Al-bound) and ZSM-5 zeolite (H-MFI-90) were obtained from Südchemie. The zeolites were activated and regenerated at 550 °C in a stream of 4% oxygen in nitrogen. The catalysts were stored in dry plant nitrogen to avoid any moisture contamination after the activation step and prior to use. 4.2.2. Ionic LiquidssIonic Liquids on Silica. Synthesis of IL’s. (a) N-butyl-N-methylimidazolium tetracholroaluminate:113,114 200 mL of N-methylimidazolium chloride was added to 500 mL of n-butylchloride via a dropping funnel. The mixture was stirred overnight and then refluxed. To ensure complete reaction the mixture was heated for a total of 7 h. Excess educts were distilledoff in vacuo. The product was stored at -20 °C for crystallization which occurred after 2 days. The solid was washed with cold ethylacetonate and dried in vacuo because recrystalization from ethylacetonate/acetonitrile (1:1) failed to result in a solid. To 125 g of N-butyl-N-methylimidazolium chloride was added 175 g of AlCl3 in small portions at 0 °C. The fast and exothermic reaction resulted in a green liquid. The liquid was filtered under nitrogen through glass-wool and stored in a nitrogen-filled glovebox. Yield: 302.1 g; approximate density: 1.189 g/mL. (b) Alkylammonium aluminumtetrachloride ([HxN(CH3)4-x]+Cl-: The following synthesis is a typical preparation of an alkylammonium aluminumtetrachloride. To 14.4 g (150 mmol) of trimethylammonium chloride was added 39.9 g (300 mmol) of AlCl3 under nitrogen. An exothermic reaction resulted in a clear to light yellowish liquid, which appeared within a few minutes after the two components were mixed. (c) IL on silica: In an incipient wetness type addition, the IL’s were separately contacted with their support material consisting of 20–40 mesh sized Davison silica (Davicat SI 1102 silica previously calcined at 200 °C) until the silica was saturated with the IL. Typically, the absorption rate of IL/SiO2 was about 2/1 to 3/1 (ca. 20–30 g IL/10 g SiO2) or until excess IL was observed. 4.2.3. “Ionic Solids” (IS). The following synthesis is a typical preparation of an ionic solid: 160 mL of a 20 wt % solution of poly(diallyldimethylammonium chloride) in water is added to 50 g of 20–40 mesh sized silica (Davicat SI 1102 silica). Excess liquid phase of the resulting mixture was decanted-off and the remaining solid was washed three times with deionized water. The resulting solid was dried overnight at 100 °C and subsequently stored in a nitrogen-filled glovebox. A nitrogen analysis showed a polymer/ SiO2 ratio of 1/9. In a glovebox, 5.32 g (40 mmol) AlCl3 were finely ground and added to 30 g of IS (approximately 19.7 mmol N content). To the resulting mixture was added 200 mL of dry toluene. The suspension was refluxed for 6 h during which a color change from white to red was observed. Toluene was decanted-off and the red solids were transferred into an extraction-thimble from which excess AlCl3 was removed by toluene extraction during the course of 4 h using a Soxhlet extraction apparatus. The resulting solid was dried in vacuo at ambient temperatures and stored in a glovebox. (113) Pilarski, B. Liebigs Ann. Chem. 1983, 1078, 1080. (114) Sundberg, R. J.; Mente, D. C.; Yilmaz, I.; Gupta, G. J. Heterocycl. Chem. 1977, 14, 1279–1281.
Energy & Fuels, Vol. 22, No. 3, 2008 1823 4.2.4. AlCl2/SiO2. (a) In a glovebox, 20 g of AlCl3 were finely ground and added to 15 g of silica (Davicat SI 1102 silica; calcined at 200 °C). To the resulting mixture was 200 mL of dry toluene. The suspension was refluxed for 3 h, during which a color change from light-red to dark-red was observed. Excess AlCl3 was decanted along with toluene after which the solids were washed three times with hexane. The solids were transferred into an extraction-thimble from which excess AlCl3 was removed with CH2Cl2 Soxhletextraction during the course of 4 h. The resulting solid was dried in vacuo at room temperature and stored in a glovebox. XRD and XRF data confirmed an Al/Cl ratio in the final product of approximately 1:2. (b) In a glovebox, ethylaluminum chloride (EtAlCl2) (1 M in hexane) was added in 3 portions of 25 mL each to 35 g of silica (Davison silica G57; calcined at 200 and 600 °C respectively) (incipient wetness preparation). Five minute time intervals were allotted to the mixture to cool back to RT before another EtAlCl2/ Hexane portion was added. Excess solvent was evaporated in vacuo. 4.2.5. Sulfated Zirconias. The following synthesis is a typical preparation for a series of sulfated zirconias. (a) Zirconias: 10 g fresh zirconylnitrate hydrate (ZrO(NO3)2 · H2O) (fresh) was dissolved in 100 mL of deionized water. The solution was added to 43 g of 20–40 mesh sized calcined (200 °C) silica (Davicat SI 1102 silica). The solids were dried in vacuo and calcined according to the following program: 10 °C/min to 575 °C; 5 °C/min to 595 °C; 1 °C/min to 600 °C/4 h. Alternatively, 20–40 mesh Al2O3 (Alcoa DD443 alumina) was used as support material. (b) One-hundred-fifty grams of fresh ZrO(NO3)2H2O was dissolved in 1000 mL of deionized water. Two-hundred-forty-four grams of Al(NO3)3 · 9H2O dissolved in 200 mL was added to the solution. The combined mixture was stirred for 10 min, after which 250 mL of 28 wt % NH4OH solution was added, resulting in the precipitation of white solids. The solids were filtered and washed with water until the washing solution was neutral. The solids were dried overnight and subsequently crushed and calcined according to the following program: 10 °C/min to 575 °C; 5 °C/min to 595 °C; 1 °C/min to 600 °C/4 h. (c) Sulfation: To 20 g of solid material was added 100 mL of a 1 M H2SO4 solution. The resulting slurry was dried and calcined according to the following program: 100 °C/10 h; 10 °C/min to 540 °C/3 h. A typical sulfate concentration for this method was approximately between 10 and 12 wt %. (d) Twenty grams of solid material was placed on a cone shaped filter paper and 100 mL of a 1 M H2SO4 solution were filtered through the solids. The acid solution was collected and filtered through the solids again. The resulting solids were dried and calcined according to the following program: 100 °C/10 h; 10 °C/min to 540 °C/3 h. A typical sulfate concentration for this method was approximately 3 wt %. (e) Activation: Prior to use the sulfated zirconias were heated to 450 °C in a dry nitrogen stream and hold at that temperature for 1 h. The catalyst then was cooled to RT in dry nitrogen. 4.3. NMR Analysis. Spectra were obtained on a Varian INOVA 400 NMR spectrometer, operating at 399.8 MHz for 1H, and 104.2 MHz for 27Al. The samples were run in a 5 mm screw cap NMR tube with a sealed capillary containing DMSO-d6 as a lock solvent. The peak from DMSO at 2.49 ppm was used as a chemical shift reference for 1H , and AlCl3 · 6H2O (0 ppm) in D2O was used as an external chemical shift reference for 27Al NMR, Table 8. Acknowledgment. The authors thank Edward L. Sughrue and Dan Fraenkel for their help and discussions working on this project. In addition, we thank Jon M. Nelson and Deborah E. Langley for their help in conducting the catalyst evaluation experiments. EF7006326
