Process for oligomerisation of olefins

Abstract

A process for the dimerization and trimerization of a branched olefin, wherein said branched olefin has from 3 to 10 carbon atoms, wherein the process comprises contacting a feedstream comprising the branched olefin with a tungsten single atom catalyst composition under dimerization / trimerization conditions.

Description

[0001] PROCESS FOR OLIGOMERISATION OF OLEFINS

[0002] Field of the invention

[0003] The present invention relates to a process for the dimerization and trimerization of branched olefins.

[0004] Background of the invention

[0005] Liquid branched olefins (e. g. C8-C12) are valuable products within the broad domains of the petrochemical industries, fine chemicals, reformulated gasoline and fuel additives. Therefore, the conversion of branched olefins such as isobutene into branched liquid hydrocarbons is of vital importance. Isobutene is an undervalued light hydrocarbon with the chemical formula (CH3) 2C=CH2 used as a liquefied petroleum gas (LPG). The catalytic conversion of isobutene into high molecular weight branched olefins has gained great attention for the production of aviation gasoline and fuel-boosting additives with high octane values. The renewed interest to convert isobutene into high octane gasoline additives has enriched the global fuel additive market striving to meet needs and regulations for efficient fuels. Moreover, the oligomerization of isobutene holds great potential for its separation from isobutene-rich streams and 04 mixtures such as in fluid catalytic cracker ( FCC) units within petroleum refineries and petrochemical industries.

[0006] The oligomerization of isobutene is an exothermic and complex process involving a sequence of parallel and consecutive reactions. As a consequence, various high molecular weight oligomer products including isobutene dimers (Cs), trimers (C12), tetramers (Cis) or even higher oligomers (e. g. C20+) can be formed. Conversion of isobutene into dimers (di-isobutylene, DIBs ) is advantageous and yields branched Cs olefins, mainly 2, 4, 4-trimethyl-2-pentene andSP3273

[0007] 2, 4, 4-trimethyl-l-pentene. The branched Cs olefin products are highly desirable since they fall into the gasoline fraction, have a high octane number, and can replace aromatics in reformulated fuel blends. In addition, their hydrogenation can produce 2, 4, 4-trimethylpentane (isooctane) which is a high octane and clean fuel component with low aromatic and sulfur content. Trimers of isobutene (triisobutylene, TIBs, C12 olefins ) formed in the process may be less preferred oligomer products for gasoline or diesel pools due to their low volatility. However, the trimers are desirable as precursor materials for the preparation of heavy alkylates and neo-acid compounds via hydrogenation or carboxylation of TIBs. The trimers are also important for plastic production and synthesis of premium solvents, specialty chemicals, or chemical intermediates such as dodecyl benzene, lubricants, solidifying agents, and gas oil additives.

[0008] Isobutene oligomerisation has been reported in the literature using a wide range of catalysts including cationic resins, resins modified with phosphotungstic acid, zeolitic catalyst systems, aluminosilicates, tungstosilicic acid impregnated on SiOs, HaPCh / activated carbon, ionic liquids, copper sulfide, sulphated TiOs, sulphated ZnO / ZrC>2, various Ni-based catalysts, FexZnY / SiO2, FeCls / zeolite, WOx / ZrC>2 and WOx / SiC>2. Even though several catalysts have been developed for the catalytic conversion of isobutene, there are some drawbacks regarding their production, utilization and commercialisation. The efficient conversion of isobutene into branched Cs and C12 liquid olefins with high selectivity while avoiding higher molecular weight hydrocarbons has not always been easy to achieve with currently available catalysts. Further, the activity, selectivity, stability and product quality of these catalysts has not always beenSP3273

[0009] optimal. It would therefore be desirable to develop new catalysts for the selective dimerization and trimerization of branched olefins, in particular for the selective dimerization and trimerization of isobutene. Such catalysts should ideally be efficient, stable, regenerable and inexpensive solid inorganic catalysts for converting branched olefins, such as isobutene, selectively into branched liquid olefins (e. g. Cs and C12 olefins ) while minimizing the formation of higher molecular weight oligomers (b Cie olefins ).

[0010] Summary of the invention

[0011] According to a first aspect of the present invention there is provided a process for the dimerization and trimerization of a branched olefin, wherein said branched olefin has from 3 to 10 carbon atoms, wherein the process comprises contacting a feedstream comprising the branched olefin with a tungsten single atom catalyst composition under dimerization and trimerization process conditions.

[0012] The use of a tungsten single atom catalyst has been found to be particularly advantageous for the efficient dimerization and trimerization of branched olefins, in particular isobutene, preferably at ambient temperatures, at high selectivity, while avoiding the production of higher molecular weight hydrocarbons.

[0013] Brief Description of the Drawings

[0014] Figure 1 shows PXRD (powder X-ray diffraction) patterns of the SIRAL-5, 5% SDA ( silica-doped alumina) support, and different SDA-supported tungsten single atom catalysts prepared in the Examples (loaded with 1. 6%, 3.7% and 6% tungsten) by using sacrificial Zn-BTC MOF, sodium tungstate (VI ) dihydrate and SDA via controlled pyrolysis at

[0015] 1000 °C / 2h / Argon, and subsequent annealing at 7000C / 5h / air.SP3273

[0016] Figure 2 shows TEM (transmission electron microscopy) images of the 5% SDA support prepared in the Examples from SIRAL-5 by calcination at 700 °C for 5 hours under static air.

[0017] Figure 3 shows ( (a) - (c) ) HRTEM images and ( (d) - (f ) ) HAADF-STEM images of the SDA-supported 3. 7% tungsten single atom catalyst prepared in the Examples by using sacrificial Zn-BTC MOF, sodium tungstate (VI ) dihydrate and SDA via controlled pyrolysis at 1000 °C / 2h / Ar, and subsequent annealing at 700 °C / 5h / air.

[0018] Figure 4 shows TEM images of the ( (a ) - (c) ) SDA-supported 1. 6%, and ( (d) - (f ) ) SDA-supported 6% tungsten single atom catalysts prepared in the Examples by using sacrificial Zn-BTC MOF, sodium tungstate (VI ) dihydrate and SDA via controlled pyrolysis at 1000 °C / 2h / Ar, and subsequent annealing at 700 °C / 5h / air.

[0019] Figure 5 shows (a) Dark-field, and (b) bright-field STEM ( Scanning transmission electron microscopy) images of the SDA-supported 3.7% tungsten single atom catalyst prepared in the Examples by using sacrificial Zn-BTC MOF, sodium tungstate (VI ) dihydrate and SDA via controlled pyrolysis at 1000 °C / 2h / Ar, and subsequent annealing at 700 °C / 5h / air.

[0020] Figure 6 shows EDS (Energy-dispersive spectroscopy) images of the SDA-supported 3.7% tungsten single atom catalyst prepared in the Examples using sacrificial Zn-BTC MOF, sodium tungstate (VI ) dihydrate and SDA via controlled pyrolysis at 1000 ° C / 2h / Ar, and subsequent annealing at

[0021] 700 °C / 5h / air.

[0022] Figure 7 shows (a) Nitrogen (N2) adsorption / desorption isothermal plots and BJH (Barrett- Joyner-Halenda) adsorption dV / dD pore size distribution plots of 5% SDA and the SDA-supported 3.7% tungsten single atom catalyst which was prepared in the Examples using sacrificial Zn-BTC MOF, sodiumSP3273

[0023] tungstate (VI ) dihydrate and SDA via controlled pyrolysis at 1000 °C / 2h / Ar, and subsequent annealing at 700 °C / 5h / air.

[0024] Figure 8 shows H2-TPR (temperature-programmed reduction in hydrogen) profiles of 5% SDA and the SDA-supported 3. 7% tungsten single atom catalyst which was prepared in the Examples using sacrificial Zn-BTC MOF, sodium tungstate (VI ) dihydrate and SDA via the controlled pyrolysis at

[0025] 1000 °C / 2h / Ar, and subsequent annealing at 700 °C / 5h / air.

[0026] Figure 9 shows High-resolution XPS (X-ray photoelectron spectroscopy) spectra of (a) Al 2p, (b) 0 Is, and ( c) Si 2p elements of the 5% SDA and SDA-supported 3. 7% tungsten single atom catalyst prepared in the Examples, and (d) W 4f element of the SDA-supported 3.7% tungsten single atom catalyst prepared in the Examples using sacrificial Zn-BTC MOF template, sodium tungstate (VI ) dihydrate and SDA and controlled pyrolysis / annealing processes.

[0027] Figure 10 shows a plot (based on GC analysis ) of % average isobutene conversion over the SDA-supported tungsten single atom catalysts produced in the Examples as a function of tungsten loading after 6 hours at 150 °C and 250 °C under fixed GHSV and WHSV of 2, 000 h-1and 12, 000 cm3g-1h-1, respectively.

[0028] Figure 11 shows plots (based on GC analysis ) of selectivity to (a, b) C8 and (c, d) C12 olefin products vs time for isobutene conversion over the SDA-supported 1. 6%, 3.7% and 6% tungsten single atom catalysts prepared in the Examples for up to 6h on stream at 150 °C (a, c) and 250 °C (b, d) under fixed GHSV and WHSV.

[0029] Figure 12 shows structures and chemical shifts of C8 and C12 olefin products for (a) 2, 4, 4-trimethyl 1-penetene, (b) 2, 4, 4-trimethyl 2-penetene, (c) 2, 2, 4, 6, 6-pentamethyl 3-heptene, and (d) 2, 2, 6, 6-tetramethyl, 4-methylene heptaneobtained from isobutene conversion over SAD-supported tungsten single atom catalysts produced in the Examples.

[0030] Figure 13 shows the PXRD pattern of the Zn-BTC MOF prepared using Zn (NOs). 6H2O and NaaBTC in a water / alcohol mixed solvent at room temperature.

[0031] Figure 14 shows a plot of isobutene conversion as a function of time over the SDA-supported 1. 6% and 6% tungsten single atom catalysts prepared in the Examples, at a reaction temperature of 150 °C and 250 °C under fixed GHSV ( 3, 000 h-1 ) and WHSV ( 12, 000 cm3g-1h-1) for 6h on stream.

[0032] Figure 15 shows a plot of isobutene conversion as a function of time over SDA-supported 3. 7% tungsten single atom catalyst prepared in the Examples, at an isobutene conversion reaction temperature of 150 °C and 250 °C under fixed GHSV ( 3, 000 h-1 ) and WHSV ( 12, 000 cm3g-1h-1) for 6h on stream.

[0033] Figure 16 shows a plot of product volume obtained for isobutene conversion as a function of tungsten loading after 6h at 150 °C under fixed GHSV and WHSV.

[0034] Figure 17 shows gas chromatograms of liquid products showing retention times and relative peak ratios of C8 and C12 olefins formed under 6h of isobutene conversion over the SDA-supported 3.7% tungsten single atom catalyst prepared in the Examples, at an isobutene conversion reaction temperature of 150 °C and 250 °C under fixed GHSV and WHSV of 3, 000 h-1and 12, 000 cm3g-1h-1, respectively.

[0035] Figure 18 shows plots of selectivity ( relative proportions, % ) obtained from GC analysis for the four C8 and C12 olefin products produced during isobutene conversion over SDA-supported 3.7% tungsten single atom catalyst, at an isobutene conversion reaction temperature of 150 °C and 250 °C for 6h under fixed GHSV and WHSV of 3, 000 h-1and 12, 000 cm3g_1h-1, respectively.SP3273

[0036] Figure 19 shows (a) XRD patterns of fresh and spent, and (b-d) high-resolution XPS spectra of (b) Al 2p, ( c) 0 Is, and (d) W 4f element of the spent SDA-supported 3.7% tungsten single atom catalyst prepared in the Examples.

[0037] Figure 20 shows the1H-13C HMBC spectra of the liquid reaction products obtained after 6 hours of isobutene conversion over the SDA-supported 1. 6% tungsten single atom catalyst prepared in the Examples, at an isobutene conversion reaction temperature of (a) 150 °C and (b) 250 °C.

[0038] Figure 21 shows the H-C HSQC spectra of the liquid reaction products obtained after 6 hours of isobutene conversion over the SDA-supported 1. 6% tungsten single atom catalyst prepared in the Examples, at an isobutene conversion reaction temperature of (a) 150 °C and (b) 250 °C.

[0039] Figure 22 shows the1H-13C HMBC spectra of the liquid reaction products obtained after 6 hours of isobutene conversion over the SDA-supported 3.7% tungsten single atom catalyst prepared in the Examples, at an isobutene conversion reaction temperature of (a) 150 °C and (b) 250 °C.

[0040] Figure 23 shows the H-C HSQC spectra of the liquid reaction products obtained after 6 hours of isobutene conversion over the SDA-supported 3.7% tungsten single atom catalyst prepared in the Examples, at an isobutene conversion reaction temperature of (a) 150 °C and (b) 250 °C.

[0041] Figure 24 shows the3H-13C HMBC spectra of the liquid reaction products obtained after 6 hours of isobutene conversion over the SDA-supported 6% tungsten single atom catalyst prepared in the Examples, at an isobutene conversion reaction temperature of (a) 150 °C and (b) 250 °C.

[0042] Figure 25 shows the H-C HSQC spectra of the liquid reaction products obtained after 6 hours of isobutene conversion over the SDA-supported 6% tungsten single atomSP3273

[0043] catalyst prepared in the Examples, at an isobutene conversion reaction temperature of (a) 150 °C and (b) 250 °C.

[0044] Figure 26 is a schematic illustrating the sacrificial MOF-conf inement / pyrolysis-oxidation strategy for the synthesis of tungsten single atom catalysts in the form of Wl-03 moieties bonded to a silicon-doped alumina support Detailed Description of the Invention

[0045] The catalyst used in the process of the present invention is a tungsten single atom catalyst composition.

[0046] In a preferred embodiment, the tungsten single atom catalyst composition used herein is a heterogeneous solid tungsten (W) single atom catalyst (SAC) supported on alumina, preferably silica-doped alumina (SDA). The hitherto known applications of tungsten-based SACs are focused on electrocatalytic water oxidation, hydrogen evolution, oxygen reactions, singlet-oxygen generation, nitrogen reduction, contaminants photooxidations and CO2 reduction reactions, but tungsten-based SACs have not been reported for the catalytic conversion of olefins such as isobutene into branched liquid hydrocarbons.

[0047] A preferred catalyst composition for use in the present invention has the formula WxOySizAlnwherein W is single atom tungsten, 0 is oxygen, Si is silicon, Al is aluminium, x is in the range from 0.5 to 10 wt%, z is in the range from 0 to 20 wt%, y+n is in the range from 70 to 99.5 wt%, and wherein the single atom tungsten has an average particle size from 0.2 to 2 nm.

[0048] The tungsten single atom catalyst used in the present invention possesses ultrasmall tungsten features. The single atom tungsten has an average particle size in the range from 0.2 to 2 nm. In a particular preferred embodiment, the single atom tungsten has an average particle size in the range from 1 nm to 2 nm. The particle size of the singleSP3273

[0049] atom tungsten can be measured by any suitable method known to those skilled in the art, for example by Transmission Electron Microscopy (TEM).

[0050] The amount of tungsten in the catalyst composition was found to have a particular effect on the selective dimerization and trimerization of isobutene. The amount of tungsten in the catalyst composition (x in the formula above) found to provide best results is in the range from 0.5 to 10 wt%, preferably in the range from 1 wt% to 6 wt%, more preferably in the range from 1.5 wt% to 4 wt% and even more preferably in the range from 1. 6 wt% to 3.7 wt%, and especially from 2 wt% to 3.7 wt%, based on the total weight of the catalyst composition.

[0051] In a particularly preferred embodiment, the catalyst composition demonstrating highest catalytic activity for the selective dimerization and trimerization of isobutene comprises 3.7 wt% tungsten.

[0052] Preferably, the tungsten in the catalyst composition is in the state from W3+to W6+, e. g. W2+, W4+or W6+. In a preferred embodiment, the tungsten is in the state of W6+. In a particularly preferred embodiment, the tungsten is in the form of WO3 moieties, having a monoclinic WO3 phase structure.

[0053] In the catalyst composition used in the process of the present invention, the tungsten species is preferably uniformly dispersed and evenly distributed on the surface of the alumina or silica-alumina support. In a preferred embodiment, the tungsten is in the form of WO3 moieties, where the WO3 moieties are anchored to the alumina or silica-alumina support. The SDA is preferably present as elongated particles having a particle size of from 20 to 30 nm. While not wishing to be limited by theory, it is believed that the ultrafine nature of the tungsten supported catalyst speciesSP3273

[0054] and the fact that the tungsten is atomically dispersed contributes to the excellent catalytic activity in the dimerization and trimerization of branched olefins.

[0055] The amount of silicon in the catalyst composition used herein ( z in the formula above) is in the range from 0 wt% to 20 wt%, preferably from 4 wt% to 15 wt%, more preferably from 4 wt% to 6 wt%, by weight of the total catalyst composition.

[0056] The total amount of aluminium and oxygen in the catalyst composition (y + n) is in the range from 70 to 99.5 wt%, preferably from 77 to 99. 5 wt%, more preferably from 84 to 95 wt%, by weight of the total catalyst composition.

[0057] Preferably, the aluminium and oxygen is in the form of an alumina support. In a preferred embodiment, the aluminium, oxygen and silicon are in the form of a silicon-doped alumina support (also referred to herein as SDA).

[0058] Process for preparation of tungsten single atom catalysts Published methods for the production of tungsten-based SACs are quite limited and focus on their preparation in solution, via DFT-guided synthesis, or MOF-based pyrolysis methods using a few MOFs such as MAF-6 or ZIF-8.

[0059] A preferred tungsten based single atom catalyst for use in the process of the present invention is synthesized using a facile route based on the high-temperature pyrolysis of sacrificial metal-organic framework, preferably a zinc metalorganic framework ( Zn-MOF). While not wishing to be limited by theory, a Zn-based MOF is a good candidate for the process of preparing the tungsten single atom catalyst because the boiling point of Zn ( 907 °C) is among the lowest of the transition metals. The melting point of the metal in the metal organic framework is also important as it has to be less than the melting point of tungsten so that the metal can be distilled off. Zinc is an ideal metal for the metal organic framework because the melting point of zinc is lessSP3273

[0060] than 1000 °C and therefore the zinc can be distilled off but not the tungsten. Owing to the crystalline and highly ordered porous structures, MOFs are ideal precursors and host materials for the production of well-defined heterogeneous single-atom catalysts (SACs ). The size, dispersion, porosity, surface, and interface properties can be controlled based on the properties of the sacrificial MOF and the synthesis parameters.

[0061] A preferred class of metal organic framework compounds are metal-trimesate compounds. Metal-trimesate compounds are a class of open MOFs with an extended structure of linked metal centres connected by trigonal planar trimesate ligands and are considered as good candidates for the process of preparing the single-atom catalysts described herein.

[0062] Preferably, the process for preparing the catalyst composition comprises the steps of:

[0063] ( i) providing an alumina, or silica-doped alumina;

[0064] ( ii ) providing a zinc-based metal organic framework;

[0065] ( iii) providing an alkali metal or alkaline earth metal tungstate (VI ) compound;

[0066] ( iv) mixing the alumina or silica-doped alumina, the zinc-based metal organic framework and the alkali metal or alkaline earth metal tungstate (VI ) dihydrate compound and pyrolyzing the resulting mixture at a temperature in the range from 800 °C to 1200 °C to produce a tungsten-based single atom catalyst; and

[0067] (v) annealing the tungsten-based single atom catalyst produced in step ( iii ) in air.

[0068] Steps (i ) - ( iv) are preferably carried out in an inert atmosphere, for example nitrogen or argon.

[0069] Figure 26 shows a schematic of a preferred embodiment of the process for preparing the catalyst composition used in the process of the present invention.SP3273

[0070] A preferred zinc metal-organic framework for use herein is Zn-BTC. Zn-BTC is an isostructural (homogeneous ) MOF with the general formula ( Zna (BTC) 2. 12H2) ), where BTC = 1, 3, 5-benzene-tricarboxylate. Zn-BTC is a highly porous MOF showing cage-like pores suitable for confining guest metals and minimizing their agglomeration during high-temperature treatments. The Zn-BTC can be prepared by reacting NaaBTC with Zn (NOa) 2. NaaBTC can be prepared by reacting NaOH with BTC.

[0071] A preferred alkali metal or alkaline earth metal tungstate (VI ) compound is sodium tungstate (VI ) dihydrate (H4Na2O6W. 2H2O).

[0072] The catalyst composition comprises an alumina-based support. Suitable supports for use herein include alumina and silica-doped alumina. In a preferred embodiment, the support is a silica-doped alumina (SDA). Silica-doped alumina can be prepared from hydrates of silica-alumina such as those commercially available from Sasol under the trade name SIRAL, and corresponding mesoporous oxides. In a preferred process, a silica-doped alumina is prepared via the calcination of silica-alumina hydrate at a temperature in the range from 800 °C to 1200 °C.

[0073] In a preferred embodiment herein, a tungsten single atom catalyst for use in the process of the present invention is prepared as follows: SDA is derived from a silica-alumina hydrate (e. g. from SIRAL-5 ex. Sasol) by calcination at 700 °C for 5 hours in static air and is used as a support. Then, the tungsten based single atom catalysts can be derived by sacrificing Zn-BTC via the high-temperature pyrolysis at 1000 °C in an inert atmosphere in the presence of a sodium tungstate (VI ) dihydrate compound and the support, followed by annealing in static air at 700 °C for 5 hours.SP3273

[0074] The morphological, structural and surface characteristics of the prepared catalyst can be studied using any suitable techniques, such as, for example, HRTEM and HAADF-STEM, EDS, PXRD, XPS, BET, H2-TRP, and NH3-TPD techniques.

[0075] Dimerization and trimerization of branched olefins According to the present invention there is provided a process for the dimerization and trimerization of a branched olefin, wherein said branched olefin has from 3 to 10 carbon atoms, wherein the process comprises contacting a feedstream comprising the branched olefin with a tungsten single atom catalyst composition under process conditions suitable for dimerization and trimerization of olefins.

[0076] The tungsten single atom catalyst composition for use herein preferably comprises an alumina support. In a preferred embodiment the tungsten single atom catalyst composition comprises a silica-doped alumina (SDA) support.

[0077] The catalyst composition described herein has been found to be particularly advantageous for the dimerization and trimerization of branched olefins, in particular isobutene, for the production of the relevant dimers and trimers (e. g. C8 branched olefins and C12 branched olefins).

[0078] The dimerization and trimerization of branched olefins can be carried out by contacting a feedstream comprising the branched olefin with the tungsten single atom catalyst under dimerization / trimerization conditions. Preferably, the feedstream comprises a mixture of branched olefins and unbranched olefins. In one embodiment, the feedstream comprises a mixture of branched olefins and ethylene. In a particularly preferred embodiment, the branched olefin is isobutene.

[0079] Preferably, the dimerization / trimerization process is carried out at a temperature in the range from 100 °C to 300 °C, preferably in the range from 150 °C to 300 °C, even moreSP3273

[0080] preferably from 200 °C to 300 °C. In one embodiment, the dimerization / trimerization process is carried out at a temperature in the range from 150 °C to 250 °C. In another embodiment, the dimerization / trimerization process is carried out at a temperature in the range 250 °C to 300 °C.

[0081] For the production of dimers, the process is preferably carried out at a temperature in the range from 200 °C to 300 °C. For the production of trimers, the process is preferably carried out at a temperature in the range from 100 °C to 200 °C.

[0082] Preferably, the dimerization / trimerization process is carried out at a pressure in the range from 0. 1 MPa to 2.5 MPa, preferably at ambient pressure ( lAt).

[0083] Preferably, the feedstream comprising the branched olefin has a gas hourly space velocity in the range from 600 to 15000 hour-1, more preferably in the range from 2000 to 6000 hour-1.

[0084] Preferably, the feedstream comprising the branched olefin has a weight hourly space velocity in the range from 2000 to 60000 cm3g-1h-1, more preferably in the range from 3000 to 15000 cm3g-1h-1.

[0085] Preferably, the dimerization / trimerization reaction is carried out in a continuous flow, fixed-bed catalytic reactor.

[0086] The invention is further illustrated by the following non-limiting Examples.

[0087] Examples

[0088] Example 1 - Preparation of tungsten single atom catalysts on silica-doped alumina supports (WSCS / SDA)

[0089] The following materials were used:

[0090] Zinc nitrate hexahydrate ( Zn (NOs). 6H2O, 98%, Sigma-Aldrich)SP3273

[0091] 1, 3, 5-benzene-tricarboxylic acid (H3BTC, 98% Acres Organic)

[0092] Ethanol ( 190 Proof )

[0093] Sodium hydroxide ( 97%, ACS reagent, Thermo Sci. Chem. ) 5% silica-alumina hydrate (SIRAL-5, Sasol)

[0094] Sodium tungstate (VI ) dihydrate (H4Na20eW. 2H2O, 99%, ACS reagent, Thermo Sci. Chem. ).

[0095] Synthesis of Sacrificial Zn-BTC MOE (Zinc-based metal-organic framework)

[0096] Zn-BTC MOE was prepared using zinc nitrate hexahydrate ( Zn (NOs). 6H2O, 98%, Sigma -Aldrich ) and 1, 3, 5-benzoic acid (H3BTC, 98%, Acres Organic) at room temperature according to the synthesis method set out in Nowacka, A., et al., Facile " Green" Aqueous Synthesis of Mono- and Bimetallic Trimesate Metal-Organic Frameworks. Crystal Growth & Design, 2019.

[0097] 19 ( 9): p. 4981-4989. An aqueous solution of NaOH (50 mL, 0. 6 M) was added to a solution of H3BTC (50 mL, 0.2 M) in ethanol under continuous stirring to form the corresponding NasBTC. To prepare the Zn-BTC MOE, 15 mmol of Zn (NO3) 2. 6H2O predissolved in 20 mL deionized water was added to the NasBTC solution under vigorous stirring. The reaction mixture was stirred at room temperature for 30 min, and the resultant white precipitate was separated by filtration and washed twice using a water / ethanol mixture. Then, the solid product was dried in an electric oven at 60 °C for 8 hours.

[0098] Synthesis of SPA-supported tungsten single atom catalysts First, the 5% silica-doped alumina ( SDA) support was prepared by calcination of SIRAL-5 at 700 °C for 5 hours. SIRAL-5 is a silica-alumina hydrate commercially available from Sasol. Then, the different WS C / SDA catalysts were prepared by a facile two-step process involving sacrificing Zn-BTC MOE via high-temperature pyrolysis in an inert atmosphere followed by annealing of the catalysts in airSP3273

[0099] ( Figure 26 ). In a typical synthesis, 1. 6 mmole Zn-BTC MOF (metal basis) and 30 mmoles of 5% SDA were dispersed in 30 ml of a water / ethanol mixed solvent by ultrasonication. Then, 0. 68 mmole of H4Na20eW was added to the mixture under vigorous stirring. The reaction mixture was heated in an oil bath at 110 °C under continuous vigorous stirring until the solvent was evaporated. The resultant precipitate was pyrolyzed in a tube furnace at 1000 °C under a continuous nitrogen (N2) flow for 2 hours. The obtained solid was finally activated by annealing in a muffle furnace at 700 °C for 5 hours. A fixed heating rate of 10 °C min-1was employed for both the pyrolysis and activation steps. The effect of tungsten (W) loading on the catalytic performance was evaluated by varying the tungsten content in the range of 0.34-1.36 mmoles. The experimental weight ratios of tungsten in the three different catalysts were determined using ICP (inductively coupled plasma mass spectrometry).

[0100] Characterization

[0101] The prepared catalysts were characterized using powder X-ray diffraction ( PXRD), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy ( STEM), electron diffraction spectroscopy (EDS ), BET surface area analysis, temperature-programmed reduction (H2-TPR), temperature programmed desorption using ammonia (NH3-TPD), and X-ray photoelectron spectroscopy (XPS ). XRD patterns were collected at room temperature using an X' Pert Philips materials research diffractometer equipped with a Cu emitter. HRTEM, STEM, and EDS images were acquired using JEM-F200 electron microscopes. BET surface area measurement was carried out using a Micromeritics 3Flex analyzer. H2-TPR and NH3-TPD measurements were conducted using a Micromeritics AutoChem II 2920 analyzer. XPS spectra were acquired using PHI VersaProbe III Scanning XPS Microprobe.SP3273

[0102] Conversion of isobutene into liquid hydrocarbons

[0103] The catalytic activity of the prepared catalyst compositions to convert isobutene into liquid hydrocarbons was studied using a continuous-flow fixed-bed tubular reactor. In all experiments, 250 mg of the catalysts was charged onto the middle of the reactor tube. Isobutene ( 99%, chemically pure grade, Linde, USA) was fed into the reactor in the gas phase and the flow rate was controlled using a Brooks mass flow controller to achieve a gas hourly space velocity (GHSV) of 3000 h-1. The isobutene conversion was studied under atmospheric pressure at two different reaction temperatures of 150 °C and 250 °C for 6 hours on stream. The outlet gas was passed through a cold trap set at -10 °C downstream of the reactor tube to condense any liquid products.

[0104] Gas Chromatography (GC) Analysis

[0105] The fraction converted from the initial isobutene was determined using an in-line industrial gas chromatograph (SRI 8610 C) equipped with a thermal conductivity (TCD) detector. Integral data of the isobutene peaks of chromatograms obtained for the inlet and outlet gas was used to express isobutene concentration. The catalytic activity was expressed as a function of isobutene converted and was calculated as % IB Conversion =

[0106]

[0107] — x 100. The condensate in the cold trap [IB]in

[0108] was collected and analyzed using an Agilent 6890 GC-MS system and products were identified using the NIST mass spectral database (library version 2 ). The product selectivity was calculated as the mole fraction of isobutene dimer (Cs=) and isobutene trimer (Ci2=) in the liquid olefins mixture.

[0109] Nuclear Magnetic Resonance (NMR) Spectroscopy Measurements NMR spectroscopy measurements were performed to determine the compositions of the liquid samples collected from the isobutene conversion reactions over different catalysts and temperatures. NMR data was collected using a Bruker NanoBaySP3273

[0110] Avance III HD 400 MHz NMR spectrometer. Samples were dissolved in deuterated chloroform and the following NMR spectra were collected for each sample: 1H ID, 1H-1H 2D COSY, 1H-13C 2D HSQC, and 1H-13C 2D HMBC. The data was processed using MestReNova software (version 14.2. 0-26256 ). For the ID NMR spectra, 32 k data points were collected and this was then zero-filled to a size of 64 k upon Fourier transform. The 1H spectral window covered the range from -4 ppm to +16 ppm. A line broadening of 0. 3 Hz was applied to the time-domain data before the Fourier transformation. The 2D NMR spectra were used to determine / conf irm structures and integrals of the signals in the ID spectrum were tabulated and analyzed. Integral data was normalized based on how many hydrogens generated each signal. The percent composition of each molecular component in a mixture was determined by the division of the integral-per-H in each molecule by the sum of all the integral-per-H values. The consistency of each molecular component' s integrals was evaluated and used to generate compositional uncertainties.

[0111] Powder X-ray Diffraction Properties

[0112] Powder X-ray diffraction ( PXRD) analysis was carried out to investigate the phase composition and purity of different samples including the fresh 5% silica-alumina hydrate (SIRAL-5 ), [the sacrificial Zn-BTC MOF prepared using Zn(NO3)2. 6H2O and NaaBTC in a water / alcohol mixed solvent at room temperature], the 5% silicon-doped alumina (SDA) support prepared from the SIRAL-5 by calcination at 700 °C for 5 h, and the WS C / SDA catalysts with different W loading of 2, 3. 7, and 6 wt. %. Figure 13 displays the PXRD patterns of the Zn-BTC MOF prepared at room temperature in a mixed water / alcohol solvent. The PXRD pattern of the sacrificial Zn-BTC MOF shows diffraction peaks at 8. 8°, 10. 1°, 13.5°, 16.5°, 17. 6°, 18. 6° 20.3°, 22. 1°, and 26. 1° characteristic to Zn-BTC crystal planes similar to those ofSP3273

[0113] the experimental and simulated ones reported in the literature. Figure 1 presents the PXRD patterns of the SIRAL-5, 5% SDA support, and different WSAC / SDA catalysts ( 1. 6%, 3. 7%, and 6% ) prepared using sacrificial Zn-BTC MOF by the controlled pyrolysis at 1000 °C under Ar for 2 h and subsequent annealing under air at 700 °C for 5 h. The SIRAL-5 exhibits a PXRD profile typical of the boehmite [AIO (OH) ] phase that is used as a precursor for alumina in the preparation of typical silica-alumina hydrate materials. The 5% SDA support synthesized by the calcination of SIRAL-5 at 700 °C for 5 h under air exhibits the cubic y-alumina phase as indicated by the characteristic peaks of Y-AI2O3 at 20 = 46.2° and 66. 9°. After loading WSAC with different ratios onto the SDA support, the two main PXRD peaks of the Y-AI2O3 remained unaffected, and only slight shifts to 20 = 46. 1° and 66. 8° in the cases of the 1. 6%, 3.7%, and 6% WSAC / SDA catalysts were observed. No new diffraction peaks corresponding to tungsten oxide species could be observed up to the highest loading of 6 wt. %. The domination of PXRD peaks of the γ-Al2O3and the absence of separate tungsten oxide phases in the PXRD patterns of the three WSAC / SDA catalysts indicate the uniform dispersion and even distribution of tungsten species on the surface of the SDA support. A similar conclusion has been reported in the literature for ultraf ine-supported catalysts. Nevertheless, the very small bands in the range of 20-250in the dif f ractogram of the 6% WSAC / SDA catalyst could reveal the presence of the WO3 phase, yet homogenously mixed with the support and evenly distributed on the surface Morphological Characteristics

[0114] The prepared samples were imaged with high-resolution TEM and STEM to investigate the morphological characteristics of the prepared 5% SDA support and different WSAC / SDA catalysts. Figure 2 shows the TEM images of the 5% SDA support prepared from fresh 5% SAR (SIRAL-5 ) by calcination at 700°C in air forSP3273

[0115] 5 h. The TEM images of the SDA ( Figure 2-a-c) are mostly characterized by elongated structures in a slightly wide range of particle lengths of around 20-30 nm. Figure 3 presents the high-resolution TEM and HAADF-STEM images of the 5% SDA upon incorporation of 3.7% WSAC catalyst using sacrificial Zn-BTC MOF and controlled pyrolysis at 1000°C for 2 h under Ar followed by annealing at 700°C for 5 h in air. The TEM and STEM images of the 3.7% WSAC / SDA catalyst show abundant bright spherical dots with an average particle size of >0. 2 nm which are isolatedly dispersed within the domains of the large elongated SDA particles. The bright dots represent the W atoms due to the higher atomic number of W (74 ), then the Al ( 13 ) or Si ( 14 ) of the support. This confirms the successful anchoring of W single atoms and their homogeneous distribution over the SDA support. On the other hand, the TEM images of the 1. 6% WSAC / SDA ( Figure 4 (a) - (c) ) and 6% WSAC / SDA ( Figure 4 (d) - (f ) ) catalysts show similar ultrasmall spherical particles present on the SDA matrix of elongated shape in agreement with the 3.7% WSAC / SDA sample, even though the 6% WSAC / SDA is also presenting some large aggregates ( Figure 4 (d) - (f ) ). The 3.7% WSAC / SDA sample which demonstrated the highest catalytic activity for isobutene conversion was chosen for the STEM and EDS imaging. Figure 5 presents the dark- and bright-field STEM images of the 3.7% WSAC / SDA catalyst which demonstrate the facile decoration of the surface of the SDA support with contrasting ultrasmall spherical particles. The EDS images displayed in Figure 6 show the elemental mapping of the W, Al, 0, and Si elements of the 3.7% WSAC / SDA powder catalyst. The EDS mapping reveals the homogenous dispersion of the active WOs species along with the SDA support as indicated by the homogenous distribution of W, Al, 0, and Si and the presence of W signature around alumina domains. The TEM, STEM, and EDS images ( Figures 3-6) confirm the controlled deposition ofSP3273

[0116] ultrasmall active tungsten oxide species on the 5% SDA via controlled pyrolysis and annealing processes using sacrificial Zn-BTC MOF.

[0117] Textural and Surface Properties

[0118] The textural and surface properties including surface area, pore volume, reducibility, and chemical oxidation state properties were studied for the SDA-supported 3.7% tungsten single atom catalyst which demonstrated the highest catalytic activity. About textural properties, Figure 7 compares the nitrogen (N2) adsorption / desorption isothermal plots and BJH adsorption dV / dD pore size distribution plots of SDA-supported 3.7% tungsten single atom catalyst to those of the 5% SDA support. The N2 adsorption / desorption isotherm of the SDA-supported 3. 7% tungsten single atom catalyst ( Figure 7a) exhibits an isotherm similar to the 5% SDA and typical of mesoporous materials. The SDA support exhibited a specific surface area (SSA) of 347 m2 / g similar to values reported in the literature for silicon-doped alumina. The loading of 3.7% of W onto the 5% SDA using sacrificial Zn-BTC MOF and consecutive processes of controlled pyrolysis and annealing resulted in approximately 18% increase of SSA from 347 m2 / g for SDA to 411 m2 / g for SDA-supported 3.7% tungsten single atom catalyst. On the other hand, the average pore width of the 5% SDA and SDA-supported 3.7% tungsten single atom catalyst is approximately 7.5 nm, with the SDA-supported 3.7% tungsten single atom catalyst presenting a relatively larger pore volume in the pore width range of 3-7.5 nm ( Figure 7 (b) ). Such a decrease in the range of pore width distribution infers that the ultrasmall tungsten particles could fill the pores of the mesoporous SDA matrix resulting in a narrower mesoporous distribution. The higher SSA and larger volume of the small pore width distribution (3-6 nm) for the SDA-supported 3.7%SP3273

[0119] tungsten single atom catalyst confirms the ultrafine nature of the active tungsten single atom catalyst species.

[0120] Further information on hydrogen consumption and reducibility for selected samples was obtained by H2-TPR. Figure 8 displays the H2-TPR profiles of 5% SDA and SDA-supported 3.7% tungsten single atom catalyst samples in the temperature range of 100-900 °C. For the SDA sample, no hydrogen consumption / reduction peaks were observed up to 900 °C due to the irreducibility and high stability of alumina support. The SDA-supported 3.7% tungsten single atom catalyst sample shows two prominent reduction peaks denoted a and p centered around 440 °C and 795 °C, respectively, which are ascribed to the reduction of SDA-supported tungsten single atom catalyst present as the WO3 phase. The IR-reduction peak at 440 °C could be attributed to the reduction of WO3 (W6+) to WOs-x (W5+and W6+), while the higher-temperature reduction peak at 795 °C could be assigned to the reduction of WOs-x (W5+and W6+) to WO2 (W4+). The H2-TPR results confirm that tungsten single atom catalyst species exist as WO3. It is worth noting that the initial reduction temperature for our 3. 7% W-SAC / SDA catalyst ( 440 °C) is lower by >180 °C compared to the H2- reduction temperature of bulk WO3 ( 627 °C). The decrease in the initial reduction temperature could be explained based on the ultrafine structure of the SDA-supported tungsten single atom catalyst and the availability of readily-reducible tungsten single atom catalyst species on the surface.

[0121] Next, the surface chemical states of the 5% SDA and 3.7% WSAC / SDA samples were analyzed by XPS. The high-resolution XPS scans of the Al 2p, 0 Is, and Si 2p elements of 5% SDA and 3.7% WS C / SDA samples, and the W 4f element of the 3.7% WSAC / SDA are illustrated in Figure 9. Both SDA and 3.7% W- SAC / SDA present a main Al 2p peak ( Figure 9 (a) ) centered around binding energy (BE) of ~ 74 eV indicating the 0-A1-0 bond. In light of theS P3273

[0122] information obtained f rom Figure 9 (b ), the XPS spectra of 0 I s of S DA and 3. 7 % W S C / S DA f itted by a Lorent zian Gaus s ian deconvolution display dual peaks for dif ferent lattice and adsorbed oxygen species. The main peaks at BE ~530. 6 eV elucidate the lattice oxygen involved in the metal-oxygen bond, while the shoulder peaks at a higher BE of ~ 532 eV are ascribed to adsorbed oxygen species such a s hydroxylated surface oxygen. As a comparison, S i 2p ( Figure 9 ( c ) ) of S DA and 3. 7 % W- S C / S DA show similar XPS prof iles with two peaks centered around 103. 1 eV ( 103. 3 eV) and 99. 2 eV ( 99. 1 eV) for SDA ( 3. 7 % W- SAC / S DA ) corresponding to fully oxidized silicon ( S i4+, Side ) and partially-oxidized silicon ( Si2+, SiO), respectively. For 3. 7 % W- SAC / S DA, a greater sub-stoichiometric to stoichiometric ( Si2+ / Si4+) peak ratio was observed. This can be understood based on favored oxygen defects or vacancie s at s ilicon sites a s a consequence of the incorporation of tungsten cations. As displayed in Figure 9 ( d), the deconvoluted XPS spectrum of W 4 f of 3. 7 % W SAC / SDA shows two maj or peaks at Binding Energy ( BE ) of 35. 3 eV (W 4 f? / 2 ) and 37. 4 eV (W 4 fs / 2 ) and a small additional peak at 41. 1 eV attributed to W 5ps / 2. The two maj or pea ks ( 35. 3 and 37. 4 eV) are a scribed to the W6+ions of WOc octahedra elucidating the exi stence of the monoclinic WOs phase structure. Following the H2-TPR result s ( Figure 8 ), the XPS studies further conf irm the existence of WSAC specie s in the oxide phase.

[0123] I sobutene Conversion

[0124] The activity of the prepared catalyst s for isobutene conversion was studied using a continuous-flow f ixed-bed catalytic reactor under atmospheric pres sure. The effects of temperature and tungsten ratio on the catalytic performance were investigated by employing two dif ferent reaction temperature s of 150 °C and 250 °C for 6 h on the stream and utilizing 1. 6%, 3. 7 %, and 6% WSAC / SDA catalyst s. Figure 10SP3273

[0125] compares the average isobutene conversion and liquid production as a function of catalyst loading at 150 °C and 250 °C for 6 h on stream under fixed GHSV and WHSV of 3, 000 h-1and 12, 000 cm3g-1h-1, respectively. The detailed plots of temporal isobutene conversion as a function of time over the different catalysts of 1. 6%, 3.7%, and 6% WSAC / SDA catalyst at 150 °C and 250 °C under fixed GHSV and WHSV for 6 h are displayed in Figures 14 and 15. For the 5% SDA support (containing 0wt% W loading), no catalytic conversion of isobutene or liquid product formation was observed at the two reaction temperatures used 150 °C and 250 °C, as can be seen in Figure 10. The low-and medium-loading catalysts of 1. 6% and 3.7% WS C / SDA showed similar catalytic performance at 150 °C with 21% conversion of isobutene on average for 6 h on stream. When the reaction temperature was increased to 250 °C, the catalytic performance of both the 1. 6% and 3.7% WSAC / SDA was enhanced with a halffold and a one-fold increase, respectively. The isobutene conversion was increased from 21% to 32% for the 1. 6% WSAC / SDA and from 21% to 41% in the case of 3.7% WSAC / SDA. On the other hand, the highest-loading catalyst ( SDA-supported 6% tungsten single atom catalyst) showed a significant difference, with an isobutene conversion of only 1% and 2% at 150 °C and 250 °C, respectively. The rate of liquid production at 150 °C was in the order of SDA-supported 3.7% tungsten single atom catalyst > SDA-supported 1. 6% tungsten single atom catalyst 1. 6% > SDA-supported 6% tungsten single atom catalyst. The volumes of the liquid products that were collected at 150 °C after 6 h on stream were 6 ml, 5 ml, and 0. 6 ml for the SDA-supported 3.7%, 1. 6% and 6% tungsten single atom catalyst catalysts, respectively, as shown in Figure 16. The results of isobutene conversion percentages and rate of liquid production ( Figures 10 and 14-15 ) imply the dependence of the catalytic performance of the supported WSAC catalysts on the textural and surfaceS P3273

[0126] characteristics of the catalysts. Among those, the most probable is the size and dispersion, known to be inf luential for heterogeneous gas- solid reactions, because the 6% showed larger density and some surface agglomerates as described in the above TEM results ( Figure s 3-4 ). The highest conversion of i sobutene ( ~ 41% ) and large st liquid production rate ( 1 ml min-3) were obtained using the SDA-supported 3. 7 % tungsten s ingle atom catalyst at the highest reaction temperature of 250 °C after 6 h ( Figure 10 and Figure 16 ). The further increase in the W loading to 6% resulted in the deterioration of the catalytic performance in terms of both catalytic conversion and capability to trimeri ze isobutene as dis cus sed earlier ( Figure 10 and Figure 16 ).

[0127] Figure 11 pre sents plots of selectivity to Cs ( dimer ) and C 12 ( trimer ) olefin products as a function of time and corresponding average selectivity for isobutene conversion over SDA-supported 1. 6%, 3. 7 %, and 6% tungsten single atom catalyst s at 150 °C and 250 °C under fixed GHSV ( 3, 000 h-1) and WHSV ( 12, 000 cm3g-1h-1) for 6 h on stream. See also Table 1 below which set out the average selectivity of Cs and C 12 products after 6h of isobutene convers ion over SDA-supported 1. 6%, 3. 7 % and 6% tungsten s ingle atom catalysts at 150 ° C and 250 ° C under fixed GHSV and WHSV.

[0128] Table 1 ( from GC analysis, _average product selectivity % of Cs and C12 products after 6h of isobutene convers ion over SDA-supported 1. 6%, 3. 7 % and 6% tungsten s ingle atom catalysts at 150 ° C and 250 ° C under fixed GHSV and WHSV)

[0129] Olefin: C8 ( % ) C12 ( % ) C8 ( % ) C12 ( % ) Temperature: 150 ° C 150 ° C 250 ° C 250 ° C

[0130] 1. 6% 61. 2 9494 38. 70506 92. 4617 7. 5383 3. 7 % 64. 03433 35. 96567 94. 37781 5. 62219 6% 93. 58452 6. 41548 95. 40031 4. 59969

[0131]

[0132] SP3273

[0133] Overall, the catalytic conversion of isobutene over different SDA-supported WS C catalysts led to the formation of selectively two main liquid products, namely dimers (Cs) and trimers (C12) at the two different reaction temperatures of 150 °C and 250 °C, as shown in Figure 11. No oligomers with high molecular weight (> Ci2) were detected at both reaction temperatures of 150 °C and 250 °C. The lowest-loading ( SDA-supported 1. 6% tungsten single atom catalyst) and mediumloading (SDA-supported 3. 7% tungsten single atom catalyst) catalysts showed similar olefin product distribution with a selectivity of >60% to dimers and >35% to trimers at 150 °C compared to the selectivity of >90% to dimers and >5% to trimers at 250 °C. At 150 °C, the SDA-supported 1. 6% tungsten single atom catalyst led to the formation of 61% and 39% of the Cs and C12 products, respectively. At the same temperature of 150 °C, the SDA-supported 3.7% tungsten single atom catalyst led to a slightly higher selectivity to dimers (Cs, 64% ) and a slightly lower selectivity to trimers (C12, 36% ). When the reaction temperature was increased to 250 °C, both the 1. 6% and 3.7% tungsten single atom catalysts favored the formation of dimer products demonstrating nearly a half-fold increase in C8 selectivity and a ~5-6-fold decrease in the C12 selectivity. The selectivity to Cs and C12 at 250 °C for the SDA-supported 1. 6% tungsten single atom catalyst (SDA-supported 3.7% tungsten single atom catalyst) was 92% ( 94% ) and 8% ( 6% ), respectively. Sample gas chromatograms of liquid products showing retention times and relative peak ratios of Cs and C12 olefins formed during isobutene conversion over SDA-supported 3.7% tungsten single atom catalyst at 150 °C and 250 °C are shown in Figure 17. On the other hand, the highest-loading catalyst (SDA-supported 6% tungsten single atom catalyst ), led mainly to the formation of dimers at both 150 °C and 250 °C. The selectivity to the Cs and C12 productswas 94% and 6% at 150 °C compared to 95% and 5% at 250 °C. At the relatively low temperature of 150 °C, the dimers produced in the gas-solid reaction could partly be retained on the catalyst surface, thus reacting with isobutene and giving rise to heavier olefins (trimers ). On the other hand, the increased temperature of 250 °C could favour the liberation of the produced dimers rather than retaining them on the catalyst surface, thus increasing selectivity to Cs products. The increase of the W loading from 1. 6% to 3. 7% did not alter the catalyst' s activity toward dimerization and trimerization of isobutene. However, a further increase of W loading to 6% resulted in a substantial shift of the product to dimers and a diminished activity toward trimer production as indicated by the low selectivity ( 6% ) to C12 at 150 °C where other two lower-loading catalysts ( 1. 6% and 3.7% ) demonstrated 6-fold higher production of Cs products. This could be partly due to the deteriorated reactivity of the catalyst toward high oligomerization. As discussed above, the conversion of isobutene over the different catalysts resulted in the formation of dimers and trimers with different selectivity based on temperature and W loading. For all cases, the dimerization and trimerization of isobutene were similar, where the same two isomeric dimers and the same two isomeric trimers were observed for all catalysts. The dimerization of isobutene over different catalysts involved the formation of the same two isomeric dimers, namely 2, 4, 4-trimethyl 1-pentene and 2, 4, 4-trimethyl 2-pentene. Likewise, the trimerization of isobutene involved two isomeric trimers, namely 2, 2, 6, 6-trimethyl-4-methylene heptane and 2, 2, 4, 6, 6-pentamethyl 3-heptene ( Figure 17 shows these compounds).

[0134] Figure 18 shows representative plots from GC and NMR analysis of relative proportions of the main isomers of both Cs and C12 olefin products produced during isobutene conversion over3. 7 % WS C at 150 °C and 250 °C for 6 h under f ixed GHSV and WHSV of 3, 000 h-1and 12, 000 cm3g-1h-1, re spectively. The maj ority of the dimers ( Cs ) and trimers ( C12 ) formed at both reaction temperatures of 150 ° C and 250 °C were the 2, 4, 4 -trimethyl 1 -pentene ( Cs ) and the 2, 2, 4, 6, 6-pentamethyl 3 heptene ( C12 ), re spectively. The relative proportions of the 2, 4, 4 -trimethyl 1-pentene ( Cs ) were 48. 3 % and 59. 2 % at 150 ° C and 250 °C, respectively, compared to 18. 8 % and 35. 1% in the case of minor dimer product ( 2, 4, 4 -trimethyl 2 -pentene ) at corresponding same reaction temperatures. The production of the two dimers was enhanced by different factors when the temperature was increased from 150°C to 250°C. The enhancement factor for the maj or and minor dimer product s upon increa sing the reaction temperature to 250 °C wa s 22 % and 100%, respectively. For the two trimers, the relative proportions of the maj or ( 2, 2, 4, 6, 6-pentamethyl 3 -heptene ) and minor ( 2, 2, 6, 6-trimethyl-4 -methylene heptane ) trimers were 20. 8 % and 14. 1% at 150 °C, compared to 3. 9% and 1. 8 % at 250 °C. The suppres s ion factors for the two trimers upon increasing the reaction temperature to 250 °C were similar with a decrea se of the maj or and minor trimers by factors of 81% and 87 %, respectively.

[0135] Structure Identification and Product Distribution f rom NMR Analysis

[0136] The3H NMR data of the six sample s obtained over the three dif ferent S DA-supported tungsten single atom catalysts compositions ( 1. 6%, 3. 7 %, and 6% ) at 150 °C and 250 °C are pre sented in Figures 22 -27. The structure s of the Cs and C12 products were determined using information contained in the NMR spectra. Initially, the HSQC cros s-peaks were used to pair3H signals of hydrogens with the13C signals of the carbons to which these hydrogens were directly attached. Next, COSY correlations were used to pair3H s ignals with one another -allowing the identification of which sets of3H signals were generated by the same mixture component. Finally, HMBC cross peaks were used to correlate the13C signals from nonprotonated carbon sites with3H signals from a particular component. Use of the intramolecular (through-bond) correlations found in the1H-13C 2D HSQC,1H-1H 2D COSY, and3H-13C 2D HMBC data sets therefore allowed all NMR signals to be grouped into component-specific subsets of the observed NMR signals.

[0137] Having identified which signals arose from each component found in a given mixture, the intensities (integrals ) of the various3H NMR signals were compared to determine how many hydrogens were responsible for the generation of each3H NMR signal. Plausible chemical structures were either confirmed or refuted based on3H and13C chemical shifts and also based on the3H signal intensities. In any case where the NMR data disagreed with a proposed structure, a new structure was formulated that was consistent with observed data. The HMBC spectrum was particularly useful at this stage, as through-bond, heteronuclear NMR correlations allowed the identification of13C signals from carbon sites two and three bonds removed from a given hydrogen. For1H' s bound to sp3-hybridized carbons, the HMBC spectrum contained cross peaks involving that3H signal and13C signals from carbon sites two and three bonds removed from the hydrogen, while for1H' s bound to sp2-hybridized carbons, the relative intensities of the HMBC cross peaks were used to differentiate between13C signals that were cis versus trans (the trans-three-bond couplings are larger than the cis three-bond couplings ).

[0138] The structures and chemical shifts of Cs and C12 olefin products obtained from isobutene conversion over SDA-supported WS C catalysts as determined by NMR included 2, 4, 4-trimethyl 1-pentene, 2, 4, 4-trimethyl 2-pentene, 2, 2, 4, 6, 6-pentamethyl 3-S P3273

[0139] heptene, and 2, 2, 6, 6-tetramethyl, 4 -methylene heptane and are shown in Figure 12.

[0140] Table 2 below sets out the selectivity as determined by NMR analysi s for the different Cs and C12 olefin products including 2, 4, 4 -trimethyl 1-pentene, 2, 4, 4 -trimethyl 2 -pentene, 2, 2, 4, 6, 6-pentamethyl 3 -heptene, and 2, 2, 6, 6-tetramethyl, 4 -methylene heptane obtained after 6 h of i sobutene convers ion over S DA-supported 1. 6%, 3. 7 %, and 6% tungsten s ingle atom catalysts at 150 °C and 250 °C under fixed GHSV and WHSV. At 150 °C, the 1. 6%, 3. 7 %, and 6% tungsten s ingle atom catalysts resulted in total Cs selectivities of 75%, 69%, and 89. 8 % compared to total C12 selectivities of 25 %, 31%, and 10. 2 %, respectively. When the temperature was increased to 250 °C, the 1. 6%, 3. 7 %, and 6% tungsten single atom catalysts resulted in total Cs selectivities of 84. 8 %, 98%, and 96. 5% compared to total C 12 selectivitie s of 15. 2 %, 2 %, and 3. 5 %, respectively.

[0141] Table 2 ( Selectivity to different C8 and C12 olef in products including 2, 4, 4 -Trimethyl 1-Penetene, 2, 4, 4 -Trimethyl 2 - Penetene, 2, 2, 4, 6, 6-Pentamethyl 3-Heptene, and 2, 2, 6, 6- Tetramethyl, 4 -Methylene Heptane obtained after 6 h of i sobutene conversion over SDA-supported 1. 6%, 3. 7 %, and 6% WS C catalysts at 150 °C and 250 °C under f ixed GHSV and WHSV) Temperature Olefin Product Selectivity ( % ) (°C ) 1. 6 % 3. 7 % 6 % 150 °C 2, 4, 4 -Trimethyl 1-Pentene 56. 6 48. 5 64. 3

[0142] 2, 4, 4 -Trimethyl 2 - Pentene 18. 4 20. 5 25. 5 2, 2, 4, 6, 6-Pentamethyl 3- 14. 7 18. 8 6. 3 Heptene

[0143] 2, 2, 6, 6-Tetramethyl, 4 - 10. 3 12. 2 3. 9 Methylene Heptane

[0144] 250 °C 2, 4, 4 -Trimethyl 1-Pentene 57. 5 66. 9 63. 9

[0145] 2, 4, 4 -Trimethyl 2 - Pentene 27. 3 31. 1 32. 6 2, 2, 4, 6, 6-Pentamethyl 3- 9. 3 1. 3 2. 3 Heptene

[0146] 2, 2, 6, 6-Tetramethyl, 4 - 5. 9 0. 7 0. 2

[0147]

[0148] Methylene HeptaneSP3273

[0149] Discussion

[0150] The results showed that a tungsten single atom catalyst can be produced via a route which involves a zinc MOF which is used as a sacrificial cage for tungsten single atom catalyst and silicon-doped alumina as support. The final prepared catalyst composition was found to contain W single atom sites in the form of W1-O3 moieties anchored on elongated-shaped SDA nanoparticulate support. The above experimental data shows that the tungsten single atom catalyst produced herein can be used as an effective catalyst for the selective formation of highly branched liquid hydrocarbons from isobutene oligomerization, in particular C8 and C12 branched olefins.

Claims

1. SP3273CLAIMS1. A process for the dimerization and trimerization of a branched olefin, wherein said branched olefin has from 3 to 10 carbon atoms, wherein the process comprises contacting a feedstream comprising the branched olefin with a tungsten single atom catalyst composition underdimerization / trimerization conditions.

2. A process according to Claim 1 wherein the feedstream comprises a mixture of branched olefins and unbranched olefins.

3. A process according to Claim 1 or 2 wherein the feedstream comprises a mixture of branched olefins and ethylene.

4. A process according to any of Claims 1 to 3 wherein the branched olefin is isobutene.

5. A process according to any of Claims 1 to 4 wherein the tungsten single atom catalyst composition comprises an alumina support.

6. A process according to any of Claims 1 to 5 wherein the tungsten single atom catalyst composition comprises a silica-doped alumina support.

7. A process according to any of Claims 1 to 6 wherein the tungsten-based single atom catalyst composition has the formula WxOySizAln wherein W is single atom tungsten, 0 is oxygen, Si is silicon, Al is aluminium, x is in the rangefrom 0.5 to 10 wt%, z is in the range from 4 to 6 wt%, y+n is in the range from 95 to 84 wt%, and wherein the single atom tungsten has a particle size from 0.2 to 2 nm.

8. A process according to any of Claims 1 to 7 wherein the dimerization / trimerization process is carried out at a temperature in the range from 100 °C from 300 °C, preferably in the range from 150 °C to 250 °C, even more preferably from 200 °C to 250 °C.

9. A process according to any of Claims 1 to 8 wherein the dimerization / trimerization process is carried out at a pressure in the range from 0. 1 to 2.5 MPa.

10. A process according to any of Claims 1 to 9 wherein the feedstream comprising the branched olefin has a gas hourly space velocity in the range from 600 to 15000 hour-1, more preferably in the range from 2000 to 6000 hour-1.

11. A process according to any of Claims 1 to 10 wherein the feedstream comprising the branched olefin has a weight hourly space velocity in the range from 2000 to 60000 cm3g-1h-1, more preferably in the range from 3000 to 15000 cm3g-1h-1.

12. A process according to any of Claims 1 to 11 wherein the process is carried out in a continuous flow, fixed-bed catalytic reactor.

Images