Process of preparing catalyst; platinum-tin on zinc aluminate-calcium aluminate-zeolite catalyst for selective light alkane dehydrogenation

Abstract

Disclosed are supported platinum-tin (Pt—Sn) based catalysts and methods of their use in selective light alkane dehydrogenation to corresponding alkenes and preparation. The supported catalysts contain a support of blended zeolite, in particular SAPO-34, zinc aluminate compound, and calcium aluminate, impregnated with Pt and Sn metal and a promoter that includes an alkali metal or compound thereof, an alkaline earth metal or compound thereof, or any combination thereof.

Claims

1. A supported platinum-tin (Pt—Sn) based catalyst comprising: a support comprising: a zeolite; a zinc aluminate compound; and a calcium aluminate compound; catalytically active metals comprising: Pt metal or a compound thereof; and Sn metal or a compound thereof; and a promoter comprising an alkali metal selected from the group consisting of sodium and lithium or compound thereof, an alkaline earth metal or compound thereof, or any combination thereof; wherein the alkaline earth metal is not calcium; wherein the promoter further comprises a member selected from the group consisting of scandium, hafnium, mercury and lead; wherein if the promoter comprises hafnium, the promoter also comprises from 0.01 to 10 wt. % of the Pt metal or a compound thereof, based on the total weight of the catalyst.

2. The supported platinum-tin (Pt—Sn) based catalyst of claim 1, comprising from 25 to 95 wt. % of the zinc aluminate, based on the total weight of the support.

3. The supported platinum-tin (Pt—Sn) based catalyst of claim 1, wherein the promoter comprises lithium (Li).

4. The supported platinum-tin (Pt—Sn) based catalyst of claim 3, wherein the promoter comprises sodium (Na).

5. The supported platinum-tin (Pt—Sn) based catalyst of claim 1, wherein the promoter comprises mercury.

6. A process for preparing the supported platinum-tin (Pt—Sn) based catalyst of claim 1, the process comprising the steps of: (a) dry blending a zeolite, zinc aluminate, and calcium aluminate to form a support mixture; (b) adding an acid to the support mixture to form a support mixture paste; (c) calcining the support mixture paste to form a blended support material; (d) impregnating the blended support material with an aqueous promoter precursor solution comprising an alkali metal selected from the group consisting of sodium and lithium or a compound thereof, an alkaline earth metal, scandium, hafnium, mercury, lead or a compound thereof; (e) calcining the impregnated blended support material to form a calcined promoter/support material; (f) impregnating the calcined promoter/support material with Pt and Sn to form a Pt/Sn/impregnated promoter/support material; (g) calcining the Pt/Sn/impregnated promoter/support material to form the Pt—Sn based catalyst.

7. A supported platinum-tin (Pt—Sn) based catalyst comprising: a support comprising: a zeolite; a zinc aluminate compound; and a calcium aluminate compound; catalytically active metals comprising: Pt metal or a compound thereof; and Sn metal or a compound thereof; and a promoter consisting of lithium (Li), rubidium (Rb), cesium (Cs) and beryllium (Be).

8. A supported platinum-tin (Pt—Sn) based catalyst comprising: a support comprising a blend of: a zeolite; a zinc aluminate compound; and a calcium aluminate compound; catalytically active metals comprising: Pt metal or a compound thereof; and Sn metal or a compound thereof; and a promoter comprising an alkali metal or compound thereof, an alkaline earth metal or compound thereof, or any combination thereof; wherein the alkaline earth metal is not calcium; wherein the support comprises from 5 to 75 wt. % of the zeolite, based on the total weight of the support; and wherein the zeolite comprises a member selected from the group consisting of one or more of SAPO-34, SAPO-11, SAPO-35, ZSM-5, MCM-41 and SBA-15; and wherein the promoter further comprises at least one member selected from the group consisting of vanadium, rhenium, silver and gold.

9. The supported platinum-tin (Pt—Sn) based catalyst of claim 8, wherein the promoter comprises sodium and rhenium.

10. The supported platinum-tin (Pt—Sn) based catalyst of claim 8, wherein the promoter comprises barium and rhenium.

11. The supported platinum-tin (Pt—Sn) based catalyst of claim 1, wherein the zeolite comprises ZSM-5 and MCM-41.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 depicts a system for producing olefins from alkanes via a direct dehydrogenation process.

DETAILED DESCRIPTION OF THE INVENTION

(3) The catalysts of the present invention offer a solution to the problems associated with currently available supported dehydrogenation catalysts. The solution is premised on forming metal-based dehydrogenation catalysts supported by a blend of a zeolite and zinc aluminate and optionally calcium aluminate. The catalytically active metal can be platinum (Pt) or tin (Sn), both Pt and Sn. The resulting catalysts of the present invention can offer non-limiting advantages ranging from increased conversion of alkanes, increased selectivity towards olefins, lower catalyst deactivation rates, and/or robust hydrothermal stability.

(4) These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with reference to the Figures.

(5) A. Supported Catalysts

(6) 1. Support Material

(7) Embodiments herein describe the supported platinum and/or tin (Pt—Sn) based catalysts and methods of making and using the supported catalysts for the production of olefins. The support material of the catalysts of the present invention can include a zeolite, a zinc aluminate compound, and optionally a calcium aluminate compound. In preferred embodiments, the calcium aluminate is present in the support material.

(8) Zeolites are microporous (i.e., <2 nm), aluminosilicate minerals commonly used as commercial adsorbents and catalysts (e.g., ion-exchange beds and gas separation technologies). Many unique zeolite frameworks have been identified and over 40 naturally occurring zeolite frameworks are known. In one aspect, the supported catalysts of the present invention can include from 5 to 75 wt. % of zeolite and all values and ranges there between (e.g., 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, or 74 wt. %), based on the total weight of the support. The zeolite can include one or more of a SAPO zeolite, ZSM-5, MCM-41, SBA-15, etc.

(9) SAPO (i.e., silico-alumino-phosphate) zeolites have an open microporous structure with regularly sized channels, pores or “cages.” These materials are sometimes referred to as “molecular sieves” in that they have the ability to sort molecules or ions based primarily on the size of the molecules or ions. SAPO materials are both microporous and crystalline and have a three-dimensional crystal framework of PO.sub.4.sup.+, AlO.sub.4.sup.−, and SiO.sub.4 tetrahedra. Non-limiting examples of SAPO materials that can be used to make the support material of the present invention include SAPO-11, SAPO-17, SAPO-18, SAPO-34, SAPO-35, SAPO-42, and SAPO-44. The relationship between the SAPO numbers and their structures is mentioned, for example, in Encyclopedia of Inorganic Chemistry, Vol. 8, 4369 (1994). For instance, the IUPAC codes corresponding to SAPO-17, 18, 34, 35, 42, and 44 are ERI, AEI, CHA, LEV, LTA, and CHA, respectively. A preferred SAPO zeolite is SAPO-34. SAPO-34 has the same framework structure of chabazite zeolite. SAPO-34 and processes of making SAPO-34 are disclosed in U.S. Pat. No. 4,440,871, which is incorporated by reference.

(10) ZSM-5 (i.e., Zeolite Socony Mobil-5) is an aluminosilicate zeolite belonging to the pentasil family. The pentasil structures are linked together by oxygen bridges to form pentasil chains. A pentasil unit consists of eight five-membered rings where the vertices can include Al or Si and an O atom.

(11) MCM-41 (i.e., Mobil Composition of Matter No. 41) and SBA-15 are mesoporous (i.e., 2 to 50 nm) materials with a hierarchical structure from a family of silicate and alumosilicate solids with ordered arrangement of cylindrical mesopores that form a one-dimensional pore system. Both materials are characterized by an independently adjustable pore diameter, a sharp pore distribution, a large surface, and a large pore volume. The pores are larger than with zeolites and the pore distribution can easily be adjusted between diameters of typically 2 nm to 6.5 nm for MCM-41 and greater than 5 nm for SBA-15.

(12) Zinc aluminates including zinc dialuminum oxide composites [e.g., aluminum-doped zinc oxide (AZO), ZnAl.sub.2O.sub.4 spinel (gahnite), etc.] are a preferred material used in the catalyst support of the present invention due to their high chemical and thermal stability as well as high mechanical resistance and low surface acidity. The supported catalysts of the present invention can include from 25 to 95 wt. % of zinc aluminate compound and all values and ranges there between (e.g., 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, or 94 wt. %), based on the total weight of the support.

(13) Calcium aluminates include a range of minerals typically obtained by heating calcium oxide and aluminum oxide together at high temperatures. The calcium aluminate compound that can be used in the present invention can be any of those that form stable phase aggregates including aluminous calcium cements. Exemplary compounds include tricalcium aluminate (3CaO.Al.sub.2O.sub.3, C3A), dodecacalcium hepta-aluminate (12CaO.7Al.sub.2O.sub.3, C12A7, mayenite), Monocalcium aluminate, CaO.Al.sub.2O.sub.3(CA), monocalcium dialuminate (CaO. 2Al.sub.2O.sub.3, CA2), monocalcium hexa-aluminate (CaO.6Al.sub.2O.sub.3, CA6), dicalcium aluminate (2CaO.Al.sub.2O.sub.3, C2A), pentacalcium trialuminate (5CaO.3Al.sub.2O.sub.3, C5A3), tetracalcium trialuminate (4CaO.3Al.sub.2O.sub.3, C.sub.4A3), dicalcium silicate (Ca.sub.2SiO.sub.4, belite), Ca.sub.2Al[AlSiO.sub.7] (gehlenite), pleocrite, etc., or mixtures thereof. In particular aspect, the calcium aluminate compound is used as a binder in the blended support material. The supported catalyst can include from 0 to 20 wt. %, preferably 1 to 20 wt. %, of calcium aluminate compound and all values and ranges there between (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 wt. %), based on the total weight of the support, with 12 wt. % being preferred.

(14) 2. Catalytic Material and Promoter Material

(15) The catalytic material used to prepare the supported catalysts of the present invention include a Pt metal or a compound thereof and/or a Sn metal or a compound thereof. In certain instances, the catalysts of the present invention can be loaded with both Pt metal and with Sn metal (i.e., Pt—Sn supported catalyst). The active metal(s) included in the supported catalyst of the present invention can include from 0.01 to 10 wt. % and all values and ranges there between (e.g., 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9. 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, or 9.9 wt. %), preferably 0.1 to 3 wt. % of the Pt metal based on the total weight of the catalyst. Exemplary Pt metals or compounds thereof include Pt particles or Pt containing alloys, with Pt particles being preferred. Exemplary Pt metals thereof include Pt particles of nano-sized (0.1-2 nm) and well dispersed. In another aspect, the tin component includes tin, a tin oxide, other tin containing compounds, or a combination thereof. In yet another aspect, the tin component comprises a tin oxide. The catalyst composition can include from about 0.1 wt. % to about 5 wt. %, for example, about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.6, 2.7, 2.8. 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5.0 wt. % tin; from about 0.5 wt. % to about 1.5 wt. %, for example, about 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, or 1.5 wt. %; or from about 0.7 wt. % to about 1.2 wt. %, for example, 0.7, 0.8, 0.9, 1, 1.1 or 1.2 wt. % tin. In another aspect, the catalyst composition includes about 0.9-1.0 wt. % tin.

(16) In other aspects of the invention, the supported catalysts can further include a metal compound as a promoter. Non-limiting examples of promoters include one or more of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), or barium (Ba), preferably K. In certain aspects, the promoter can further include scandium (Sc), yttrium (Y), lanthanum (La), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt, (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), copper (Cu), silver (Ag), gold (Au), cadmium (Cd), mercury (Hg), gallium (Ga), indium (In), thallium (Tl), silicon (Si), germanium (Ge), lead (Pb), or phosphorus (P). Preferably, the promoter compound includes an alkali metal or compound thereof, an alkaline earth metal or compound thereof, or any combination thereof including at least potassium (K). Promoters can be added to the catalyst using known techniques, for example, impregnation, ion exchange, chemical deposition or the like. An amount of promoter can depend inter alia on the desired activity of the catalyst. In some embodiments, the amount of promoter can range from 0.001 to 5 wt. % or 0.01 to 2 wt. % and all ranges there between (e.g., 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9 wt. %), based on the total weight of the catalyst. Exemplary promoter metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), and calcium (Ca). The promoters or corresponding stable derivatives thereof (e.g., halides, oxides, etc.) can be purchased from commercial manufactures such as Sigma-Aldrich®, USA.

(17) B. Methods of Making the Catalysts

(18) The catalysts of the present invention can be prepared by using the following non-limiting steps.

(19) Step 1 of the method can include dry blending a zeolite, zinc aluminate and optionally calcium aluminate to form a support mixture. The dry blending step can be performed by using suitable mixing equipment such as grinders, tumblers, stationary shells or troughs, Muller mixers (for example, batch type or continuous type), impact mixers, and any other generally known mixers. Once blended, the blend can be contacted with an acidic aqueous solution to form a support mixture paste. Non-limiting examples of acids can include an organic acid or an inorganic acid. Organic acids can include formic acid (HCO.sub.2H), acetic acid (AcOH), trifluoroacetic acid (TFAA), propionic acid, butyric acid, valeric acid, carproic acid, oxalic acid, lactic acid, malic acid, citric acid, benzoic acid, carbonic acid, uric acid, p-toluenesulfonic acid (PTSA), trifluoromethanesulfonic acid (TfOH) or combinations thereof, preferably acetic acid (AcOH). Inorganic acids can include hydrochloric acid (HCl), nitric acid (HNO.sub.3), phosphoric acid (H.sub.3PO.sub.4), sulfuric acid (H.sub.2SO.sub.4) or combinations thereof, preferably hydrochloric acid (HCl). The resulting acidified paste can then be dried at a temperature of 60° C. to 120° C. and calcined at a temperature of 350° C. to 600° C. and all values and ranges there between, to form a blended and calcined support material.

(20) Step 2 of the method can include impregnating the blended and calcined support material from step 1 with an aqueous promoter precursor solution comprising an alkali metal salt and/or an alkaline earth metal salt solubilized therein. The catalyst composition of the present invention can also include a base promoter and one or more additional promoters. In a non-limiting example, the alkali metal promoter can be potassium metal, a potassium oxide, other potassium containing compounds, or a combination thereof. In yet another aspect, the potassium component can include a potassium oxide. The catalyst composition can include from about 0.2 wt. % to about 1.0 wt. %, about 0.2 wt. % to about 0.8 wt. %, or from about 0.4 wt. % to about 0.8 wt. %, or about 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0 wt. % potassium based on the total catalyst compositions. In another aspect, the catalyst composition include about 0.5-0.6 wt. % potassium. In one aspect, a support material can be contacted with a potassium containing compound. In another aspect, a support material can be contacted with a water soluble potassium containing compound. In other aspects, the potassium containing compound can include a salt, such as, for example, a potassium chloride. The concentration of any solution and/or suspension of a potassium compound can vary depending upon the specific target composition. In one aspect, a 0.03 M aqueous solution of KCl can be contacted with a support material. In another aspect, other potassium containing compounds can be used and one of skill in the art could readily select an appropriate potassium containing compound. Potassium containing compounds, such as, for example, potassium chloride, are commercially available. The impregnated material can then be dried at a temperature to remove water, and then calcined in a flow of air at a temperature of 400° C. to 600° C., preferably 500° C. and all values and ranges there between to form a calcined support containing the promoter material.

(21) In one aspect, a tin component is added to the potassium promoted support. In one aspect, a support material can be contacted with a tin containing compound. In another aspect, a support material can be contacted with a water soluble tin containing compound. In other aspects, the tin containing compound can include a salt, such as, for example, a stannic chloride. In some embodiments, the tin compound and the promoter are impregnated into the support as one solution. The concentration of any solution and/or suspension of a tin compound can vary depending upon the specific target composition. In one aspect, a 0.15 M aqueous solution of SnCl.sub.4 can be contacted with a support material. In another aspect, other tin containing compounds can be used and one of skill in the art could readily select an appropriate tin containing compound. Tin containing compounds, such as, for example, stannic chloride, are commercially available. The impregnated material can then be dried at a temperature to remove water, and then calcined in a flow of air at a temperature of 400° C. to 600° C., preferably 500° C. and all values and ranges there between to form a support material containing the promoter material and Sn. In some embodiments, the tin component is not added in Step 2.

(22) Step 3 of the method can include further include impregnating the calcined promoter/support material with Pt and/or Sn to form a Pt/Sn/impregnated promoter/support material. This impregnation step can be performed by obtaining a platinum and/or tin precursor material (e.g., platinum salts and/or tin salts) that are solubilized in an aqueous solution. The calcined promoter/support material can then be contacted with the aqueous solution to impregnate Pt and/or Sn into the material. The impregnated material can then be dried at a temperature to remove water, and then calcined in a flow of air at a temperature of 400° C. to 600° C., preferably 500° C. and all values and ranges there between, to form a supported platinum (Pt), tin (Sn), or platinum-tin (Pt—Sn) based catalysts of the present invention.

(23) The morphology, structure, and quality of the supported catalysts of the present invention can be evaluated using techniques, such as, but not limited to, X-ray fluorescence ( )XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS).

(24) C. Olefin Production

(25) 1. Methods and Systems

(26) The supported catalysts of the present invention can be used to catalyze the conversion of alkanes to olefins. Conditions sufficient for olefin production (e.g., ethylene, propylene, and butylenes) include temperature, time, alkane concentration, space velocity, and pressure. The temperature range for olefin production may range from about 520° C. to 620° C., preferably ranging 580° C. to 600° C. A gas hourly space velocity (GHSV) of alkane higher than 0.1 h.sup.−1 can be used, preferably between 2 and 10 h.sup.−1, more preferably between 3 and 8 h.sup.−1. The conversion of alkane can carried out at a pressure from about −0.1 MPa to 0.3 MPa, preferably ranging from 0.05 MPa to 0.15 MPa, or at atmospheric pressure. The conditions for olefin production may be varied based on the type of the reactor.

(27) The reaction of the methods and system disclosed herein can occur in any type of reactor. Non-limiting examples of reactors include a fixed bed dehydrogenation reactor or a fluidized-bed dehydrogenation reactor. It is also envision the method and systems may also include the ability to regenerate used/deactivated catalyst in a continuous process such as in a fluidized bed reactor. The method and system can further include collecting or storing the produced olefin hydrocarbon product along with using the produced olefin hydrocarbon product to produce downstream petrochemical and/or polymer products.

(28) Referring to FIG. 1, a system 10 is illustrated, which can be used to convert alkanes to olefin hydrocarbon products with the supported catalysts of the present invention. The system 10 can include an alkane source 11, a reactor 12, and a collection device 13. The alkane source 11 can be configured to be in fluid communication with the reactor 12 via an inlet 17 on the reactor. As explained above, the alkane source can be configured such that it regulates the amount of alkane feed entering the reactor 12. The reactor 12 can include a reaction zone 18 having the supported catalysts 14 of the present invention. The amounts of the alkane feed 11 and the catalyst 14 used can be modified as desired to achieve a given amount of product produced by the system 10. The reactor 12 can include an outlet 15 for products produced in the reaction zone 18. The products produced can include olefins such as C.sub.2 to C.sub.8 olefins. In preferred instances, the products are C.sub.2 to C.sub.4 olefins (e.g., ethylene, propylene, and butylene). The collection device 13 can be in fluid communication with the reactor 12 via the outlet 15. Both the inlet 17 and the outlet 15 can be open and closed as desired. The collection device 13 can be configured to store, further process, or transfer desired reaction products (e.g., C.sub.2-C.sub.8 olefins) for other uses. By way of example only, FIG. 1 provides non-limiting uses of ethylene and propylene produced from the catalysts and processes of the present invention. Still further, the system 10 can also include a heating source 16. The heating source 16 can be configured to heat the reaction zone 18 to a temperature sufficient (e.g., 500 to 620° C.) to convert the alkanes in the alkane feed to olefin hydrocarbon products. A non-limiting example of a heating source 16 can be a temperature controlled furnace. Additionally, any unreacted alkane can be recycled and included in the alkane feed to further maximize the overall conversion of alkane to olefin products. Further, certain products or byproducts such as alkynes can be separated and used in other processes to produce commercially valuable chemicals (e.g., propylene). This increases the efficiency and commercial value of the alkane conversion process of the present invention.

(29) 2. Alkane Feed

(30) The alkane feed may include one or more alkanes. An alkane or parafin is an acyclic saturated hydrocarbon having the following structure: C.sub.nH.sub.(2n+2), where n is an integer, n ranges from 2 to 8, preferably 2 to 4. Mixtures of alkanes can include linear straight chain and/or branched chain saturated hydrocarbons. Linear alkanes can include ethane, propane, n-butane, n-pentane, n-hexane, n-heptane, and n-octane. Branched alkanes can include isobutane, isopentane, neopentane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, 2,2-dimethylbutane, 2-methylhexane (isoheptane), 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane, 2,2,3-trimethylbutane, 2-methylheptane, 3-methylheptane, 4-methylheptane, 3-ethylhexane, 2,2-dimethylhexane, 2,3-dimethylhexane, 2,4-dimethylhexane, 2,5-dimethylhexane, 3,3-dimethylhexane, 3,4-dimethylhexane, 3-ethyl-2-methylpentane, 3-ethyl-3-methylpentane, 2,2,3-trimethylpentane, 2,2,4-trimethylpentane, 2,3,3-trimethylpentane, 2,3,4-trimethylpentane, 2,2,3,3-tetramethylbutane, and stereoisomers thereof, or mixtures thereof. The feed may include about 10, 15, 20, 40, 50 mole % or more of an alkane. The alkane feed may also contain nitrogen, helium, aromatic hydrocarbons, and so on as inert compounds. Preferably the alkane feed is relatively pure, containing less than 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 wt. % of impurities and/or inert compounds.

(31) Alkanes for use in the present invention can be isolated from natural gas and crude oil by fractional distillation, such as a petroleum refining process or prepared by a Fischer-Tropsch process. Alternatively, alkanes are commercially available from a wide range of sources (e.g., Praxair, Danbury, Conn.; Sigma-Aldrich Co. LLC, St. Louis, Mo.; BOC Sciences USA, Shirley, N.Y.).

(32) 3. Catalyst Activity/Selectivity

(33) Catalytic activity as measured by alkane conversion can be expressed as the % moles of the alkane converted with respect to the moles of alkane fed. In particular aspects, the selectivity to the corresponding olefin is at least 88 to 98%, preferably at least 91 to 94%, and/or wherein the conversion of alkane is at least 32 to 42%.

(34) As an example, propane (C.sub.3H.sub.8) is used here to define conversion and maximum selectivity of products by the following equations (I) and (II):

(35) $\begin{array}{cc}\%C_3{H}_8\mathrm{Conversion}=\frac{\left(C_3{H}_8\right)°-\left(C_3{H}_8\right)}{\left(C_3{H}_8\right)°}\times 100,& \left(I\right)\end{array}$
where, (C.sub.3H.sub.8)° and (C.sub.3H.sub.8) are moles of propane in the feed and reaction product, respectively.
Maximum selectivity is defined as mole % and are defined for propene, 1-butene, 2-butene and so on as follows:

(36) $\begin{array}{cc}\%\mathrm{Propene}\mathrm{Selectivity}=\frac{2\left(C_3{H}_6\right)}{\left(C_3{H}_8\right)°-\left(C_3{H}_8\right)}\times 100,& \left(\mathrm{II}\right)\end{array}$
where the numerator is the carbon adjusted mole of propene and the denominator is the moles of carbon converted.

EXAMPLES

(37) The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters, which can be changed or modified to yield essentially the same results. The materials used in the following examples are described in Table 1, and were used as-described unless specifically stated otherwise.

(38) TABLE-US-00001 TABLE 1 Material % Content SAPO-34 60 zinc aluminate 28 calcium aluminate 12 K 0.5 Pt 0.5 Sn 1

Example 1

Preparation of a Supported Pt—Sn Catalyst

(39) SAPO-34 (60 wt. %), zinc aluminate (28 wt. %), and calcium aluminate (12 wt. %) were mixed and dry blended to a well grinded form and then converted into a paste by diluted organic (e.g., acetic acid) and/or inorganic acid (e.g., HCl) and then calcined. The calcined support material was then impregnated with potassium (0.5 wt. %) dissolved in aqueous solution and then calcined. The calcined promoter/support material was then further impregnated with Pt (0.5 wt. %) and Sn (1 wt. %), dried, and then calcined to afford the final supported Pt—Sn catalyst.

Example 2

Dehydrogenation of Propane to Propylene Process

(40) The catalyst was tested in the dehydrogenation of propane to propylene reaction in an iso-thermal fixed bed reactor at a WHSV of 5.5 h.sup.−1 and 590° C. Table 1 lists the conversion and selectivity at 1 and 5 hours time on stream.

(41) TABLE-US-00002 TABLE 1 TOS = 1 hr TOS = 5 hr Conversion Selectivity Conversion Selectivity 36 94.5 32 96