Photocatalytic dehydrogenation of light hydrocarbons using perovskites and synthesis of said perovskites

Abstract

Processes for photocatalytic dehydrogenation of light hydrocarbons using a metal oxide catalyst are disclosed. In preferred embodiments, the metal oxide catalyst is a substituted lanthanum manganese oxide perovskite (such as LnMn0.9Cu0.1O3). The light source used in the reaction has an intensity of at least 2 W cm-1. Processes for preparing copper substituted lanthanum manganese oxide perovskites for use as photocatalysts for dehydrogenation reactions are also disclosed.

Description

PHOTOCATALYTIC DEHYDROGENATION OF LIGHT HYDROCARBONS USING PEROVSKITES AND SYNTHESIS OF SAID PEROVSKITESTHEREFORField of the Invention

[0001] The invention relates to a method for the synthesis of unsaturated hydrocarbons and hydrogen by the photocatalytic non-oxidation conversion of light hydrocarbons. In this method, light hydrocarbons, which may be mixed with a diluent such as nitrogen (N2) or Argon (Ar), are introduced into a photocatalytic reactor, where the gas is exposed to a light source, which may be an LED light source was applied to produce unsaturated hydrocarbons and hydrogen. Catalysts may be selected to improve the photocatalytic performance, the conversion of the light hydrocarbons, and the selectivity of the photocatalytic conversion of the light hydrocarbons.Background of the Invention

[0002] Natural gas, consisting primarily of methane, along with ethane, propane, butane, and pentane, carbon dioxide, nitrogen, trace water and oxygen, is one of the most abundant fossil fuels currently available on the earth. In addition to its use as a fuel, natural gas is an important source of these light alkenes which can be processed to produce valuable chemicals including unsaturated hydrocarbons. The alkanes may be processed to undergo thermally powered catalytic dehydrogenation to alkenes and hydrogen, by carbon dioxide catalytic dry reforming to synthesis gas, carbon monoxide and hydrogen, or by with water vapour steam reforming to synthesis gas. However,these processes typically require extreme temperatures, which are usually achieved by burning fossil fuels, resulting in significant greenhouse gas emissions.

[0003] The direct conversion of methane under mild reaction conditions to produce carbon and hydrogen is a “holy grail” in chemistry, mainly because of the large energy (434 kJ mol-1) required to break the C-H bond.

[0004] Ethane (C2H6) has a high molar hydrogen content (75 mol %). Notably, ethane’s C-H bonds are easier to break than those of methane in commercial hydrogen synthesis, making ethane an ideal alternative hydrogen source. However, the reaction usually requires temperatures of several hundreds of degrees Celsius to overcome the high activation barrier of C-H bonds using traditional thermocatalysis methods.

[0005] The conventional method for ethylene production from light hydrocarbons, particular of methane and ethane, typically involves steam cracking. This process is widely used in the petrochemical industry due to its efficiency in breaking down larger hydrocarbon molecules into smaller ones, including ethylene, which is a crucial building block for various chemicals and plastics. In this process, the mixture of a hydrocarbon such as ethane, andsteam is fed into a cracking furnace, and then the furnace is rapidly heated to high temperatures, typically between 750°C and 950°C. Under high temperatures, the larger molecules (ethane) can break down (crack) into smaller molecules, primarily ethylene (C2H4) and hydrogen (H2). The ratio of steam to hydrocarbons is carefully controlled to prevent cooking and to optimize the reaction.

[0006] Oxidative dehydrogenation (ODH) with oxygen offers favorable thermodynamics and coking resistance, but ethylene selectivity may be hampered byover-oxidation of ethane to carbon monoxide and carbon dioxide. In contrast to oxidative dehydrogenation, non-oxidative dehydrogenation (EDH) can produce C2H4 and H2 in a single step, offering the highest carbon utilization potential among the conversion processes. Unfortunately, the process is still fossil-powered and energy- intensive, requiring temperatures between 550-700 °C due to the endotherm icity associated with the activation of the strong C-H bond in ethane (AH =412 kJ / mol).

[0007] Ethylene is widely used in the chemical industry, Its worldwide production (over 150 million tonnes in 2016) exceeds that of any other organic compound. Much of this production goes toward creating polythene, which is a widely used plastic containing polymer chains of ethylene units of various chain lengths. Production of polythenes emits greenhouse gases, including methane from feedstock production and carbon dioxide from any non-sustainable energy used.Summary of the Invention

[0008] The present invention provides a process for initiating catalytic reactions to utilize solar energy that can directly convert ethane or natural gas to ethylene and hydrogen. In contrast to thermochemically driven catalytic processes, which operate in the electronic ground state, a photochemically enabled catalytic process operates in the excited state and benefits from the chemical potential provided by photogenerated electron-hole pairs. In addition, electron-hole non-radiative relaxation processes can produce local heating through phonon confinement, introducing a photothermal advantage to the overall photochemical process. The alternative approach of the present invention is to use solar light or artificial lighting, which may be powered byrenewable energy, to drive the same reactions, producing a similar range of alkene, carbon monoxide and hydrogen products. Compared to traditional thermal strategies, using solar energy, or artificial light generated from renewable energy, to trigger natural gas dehydrogenation can break the thermodynamic limitation and access the reactions at milder conditions, as well as to mitigate greenhouse gas emissions. Owing to their various advantages, including low cost, environmental friendliness, good structural stability and tunable activity, the lanthanum manganese oxide-based perovskites of the present invention may be used to achieve efficient photocatalytic dehydrogenation of ethane and natural gas

[0009] In one embodiment of the invention, a series of Cu(ll) substituted lanthanum manganese oxides prepared (LaMm-xCuxOs ) by a hydrothermal method are used as catalysts in the photocatalytic reforming of an alkane, such as ethane, to an alkene. Substitution of Mn(IV) sites in LaMnOsby Cu(ll) creates more Mn(lll) sites forming oxygen vacancies and surface hydroxyl groups. This oxygen non-stoichiometry provides redox active Lewis acid Mn(IV) / Mn(lll) and Lewis base O(-ll), OH(-I) sites, resulting in the formation of surface frustrated Lewis pairs (SFLPs) which are used for the photocatalysis C-H activation of ethane.

[0010] These photocatalytic SFLP catalysts, including LaMm-xCuxOscan further improve the activity performance of ethane conversion to ethylene and hydrogen and provide a novel approach to the photocatalytic SFLP non-oxidative conversion of ethane.

[0011] In the catalyst’s preparation process, the hydrothermal method is applied which is the prerequisite to synthesis of the oxygen non-stoichiometry providing redox active Lewis acid Mn(IV) / Mn(lll) and Lewis base O(-ll), OH(-I) sites. The Lewis acid Mn(IV) / Mn(lll) and Lewis base O(-ll), OH(-I) sites are the prerequisites for the formation of SFLP. The catalysts prepared by the methods of the present invention may be used to drive the photocatalyitc reaction for the dehydrogenation of ethane or natural gas.Brief description of drawings

[0012] The following drawings only specific examples of the present disclosure and should not be considered as limiting its scope;, they may be used to understand the processes disclosed herein and the results of the experimental work discussed below.

[0013] FIG. 1 displays the powder X-ray diffraction (PXRD) patterns of LaMnOs and LaMno.9Cuo.1O3.

[0014] FIG. 2 displays X-ray photoelectron spectroscopy (XPS) spectra of (a) Mn 2p and O 1s for LaMnOsand LaMno.9Cuo.1O3 samples.

[0015] FIG. 3 displays Raman results of LaMnOsand LaMno.9Cuo.1O3.

[0016] FIG. 4 displays the Fourier Transform Infrared Spectroscopy (FT-IR) results of LaMnOs and LaMno.9Cuo.1O3.

[0017] FIG. 5 displays graphically the photocatalytic ethylene production activity by LaMnOs, LaMno.9Cuo.1O3 and Cu@ LaMnOs samples under atmospheric pressure in aHerrick cell reactor.

[0018] FIG. 6 displays graphically GC-MS analysis of (a) The total spectrum, (b)13CO2and (c)13C2H4 products after photocatalytic ethane dehydrogenation rection from13C2H6, (C) GC-MS analysis of13C2H6.

[0019] FIG. 7 displays graphically the effect of ethane concentration on LaMno.9Cuo.1O3 and photocatalytic performance.

[0020] FIG. 8 displays graphically is the photocatalytic performance of LaMnOs and LaMno.9Cuo.1O3 for ethane dehydrogenation under different light intensities and the corresponding surface temperatures as measured by an infrared (IR) camera.

[0021] FIG.9 displays graphically C2H4 production rates using LaMnOs and LaMno.9Cuo.1O3 under thermal conditions.

[0022] FIG. 10 displays the Arrhenius plots of LaMnOs and LaMno.9Cuo.1O3 photocatalytic and thermocatalytic ethane dehydrogenation reactions.

[0023] FIG. 11 shows the stability test results for each of the catalysts in catalyst regeneration experiments.

[0024] FIG. 12 displays the C2H6-TPRS results of C2H6, C2H4, CO, CO2, H2 acquired by adsorbing C2H6.

[0025] Fig. 13 displays X-ray diffraction patterns of spent LaMnOs and LaMno.9Cuo.1O3 after 10 test runs of the photocatalytic reactions in shown in FIG. 11 .

[0026] FIG. 14 provides in graphical form the XPS results of (a) Mn 2p and (b) O 1 s 2p for spent LaMnOsand LaMno.9Cuo.1O3 samples.

[0027] FIG. 15 displays the results of an in situ DRIFT spectroscopy study of the time evolution of the photocatalytic ethane dehydrogenation reaction over LaMnOs.

[0028] FIG. 16 displays the results of an in situ DRIFT spectroscopy study of the time evolution of the photocatalytic ethane dehydrogenation reaction over LaMno.9Cuo.1O3.

[0029] FIG. 17 provides the ex situ solid-state1H NMR spectra of LaMnOsand LaMno.9Cuo.1O3 after photo and thermal catalytic reaction with ethane.Detailed Description of the Invention

[0030] The present invention provides an improved method for the synthesis of unsaturated hydrocarbons and hydrogen by the dehydrogenation of light hydrocarbons, including natural gas and its component gases. The method includes the preparation and use of photocatalytic materials to provide photocatalytic reforming of the light hydrocarbons at lower temperatures and with lower power consumption than with conventional reforming methods.

[0031] Included in the process of the present inventions are methods for producing and using copper-substituted lanthanum manganese oxide-based catalysts to improve the rate of conversion of the light hydrocarbons.

[0032] The embodiments of the present invention also include a process for the dehydrogenation of one or more light hydrocarbons that comprises Introducing said light hydrocarbons into a reactor; and exposing said light hydrocarbons in said reactor to alight source having an intensity of at least about 2 W cm-1 ; with the dehydrogenation being carried out in the presence of a catalyst that is a metal oxide.

[0033] The dehydrogenation of said light hydrocarbons causes at least one such light hydrocarbon to dissociate into separable gaseous hydrogen and one or more alkene co-products.

[0034] In one embodiment of the present invention, a metal oxide is used as a catalyst in a process for the dehydrogenation of one or more light hydrocarbons, or a mixture of light hydrocarbons, such as natural gas. The process comprises Introducing said light hydrocarbons or mixture of light hydrocarbons into a reactor in which said metal oxide is present: , and closely contacting one or more of the light hydrocarbons with said metal oxide while exposing said metal oxide in said reactor to a light source having an intensity of at least about 2 W cm’1, and can range for about 2 W cm’1to about 10 cm’1.

[0035] In one embodiment of the present invention the metal oxide may be a stoichiometric (ABO3) or non-stoichiometric (ABOs-x) perovskite, or other stoichiometric or non-stoichiometric metal oxides, MOn. The metal oxides ABO3 or ABOs-x may be a redox active perovskite; or a version thereof doped by isomorphic substitution on the A and / or B sites of said perovskites, or modified with single metal atoms or dual-site single-atoms supported on said perovskites. The dopant in the redox active perovskites ABO3 or ABOs-x may be comprised of elements of the periodic table exemplified by isomorphic substitution of transition metals such as Cu, Fe, Ni, Co, In, Al, Sn on the B site.

[0036] In one embodiment of the present invention the metal oxide is a copper substituted lanthanum manganese oxide-based perovskite. In one embodiment of the present invention, the copper substituted lanthanum manganese oxide-based perovskite is a Cu(ll) substituted lanthanum manganese oxide represented by the formula LaMm-xCuxOs, where x can be from about 0.01 to about 0.5. In one embodiment of the present invention, the copper substituted lanthanum manganese oxide-based perovskite is LaMno.9Cuo.1O3.

[0037] In various embodiments of the present invention the light hydrocarbon may be a single light hydrocarbon or a mixture of light hydrocarbons selected from the group consisting of natural gas methane, ethane, propane, butane and methylcyclohexane.

[0038] In a preferred embodiment of the present invention the light hydrocarbon is ethane.

[0039] In another preferred embodiment of the present invention the light hydrocarbon is natural gas.

[0040] In another embodiment, the invention provides a process for the preparation of a copper substituted lanthanum manganese oxide-based perovskite for use as a catalyst in the dehydrogenation of one or more light hydrocarbons, comprising admixing stoichiometrically amounts of lanthanum nitrate, manganese t and copper nitrate to form a mixed salt solution, suspending the salts so obtained by adding a base to the solution, heating the suspension so obtained to about 180 °C for about 12 h before cooling the solution to room temperature, isolating the resulting copper substituted lanthanummanganese oxide-based perovskite precursor by centrifugation and washing and calcining the dried precursor.

[0041] An understanding of the embodiments of the present invention may bes be achieved by a review of the examples set out below, including the steps of: a. Preparing and characterizing the catalysts used; b. assessing the production of ethylene from ethane using the catalysts so prepared; c. confirming that the ethylene and hydrogen produced by the photocatalytic process of the present invention were formed from the ethane starting material; d. examining the effect of ethane concentration on rates and extent of conversion; e. assessing the effects of light intensity and temperature on rates and extent of conversion; f. assessing the stability and regeneration of the catalysts used; g. confirming the photochemical activity vs the photothermal activity involved in the process of the present invention; h. confirmed the applicability of the catalysts and processes of the present invention to the reforming of mixtures of light hydrocarbons, such as natural gas.Example 1 - Preparation of Catalysts

[0042] All chemicals used in the preparation of the catalysts were of analytical grade and used without further purification. Briefly, stoichiometrically amounts of lanthanum nitrate (La(NO3)3-6H2O), manganese nitrate (Mn(NO3)2-4H2O), and copper nitrate (CU(NO3)2 H2O) were dissolved and stirred for 30 mins in 25 mL of deionized water to form a mixed salt solution. Then, 1 mL KOH (10 M) was slowly added into the above solution under continuous stirring. After aging for 30 min, the obtained suspension was transferred into a 30 mL stainless-steel Teflon lined autoclave and heated to 180 °C for 12 h before being cooled to room temperature. The obtained products were collected following centrifugation and washing with deionized water several times and finally dried at 60 °C. The dried precursor was calcined at 250 °C for 2.5 h and then at 850 °C for 6 h in air.

[0043] A sample of Cu-loaded LaMnOs (referred to herein as Cu@LaMnO3) was prepared by mixing Cu(NO3)2 H2O and LaMnOs in stoichiometric ratios equivalent to the amount of copper in the LaMno.9Cuo.1O3 sample, and stirred in water for 12 hours in a glass beaker After drying the solution, the powders were collected and introduced into a tube furnace and heated to 160 °C for 2 h under air. This sample was used to confirm the importance of substitution of Cu in the lattice of the perovskite.

[0044] The transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of LaMnOs indicated that the LaMnOs consists of highly agglomerated and partially sintered nanoparticles with sizes in the range of 50-200 nm and the perovskite (110) planes with a spacing of 0.275 nm (FIG. 1 b).

[0045] Energy dispersive X-ray fluorescence (EDX) elemental mapping images of the prepared catalyst samples confirmed that there was a homogeneous distribution ofLa and Mn elements in the perovskite lattice.

[0046] Transmission electron microscopy (TEM) imaging of the catalyst samples was performed using a FEI TALOS-200X TEM operated at 300 kV accelerating voltage. The TEM and HRTEM results of LaMno.9Cuo.1O3, displayed a slight increase of the lattice spacing (0.280nm), demonstrating a slight expansion of perovskite lattice as expected with the substitution of larger Cu(ll) (0.073 nm) in a lattice of smaller Mn(lll) (0.064 nm) or Mn(IV) (0.060 nm) ions.

[0047] Powder X-ray diffraction (PXRD) studies on the catalyst samples were conducted on a Broker D2-Phaser X-ray diffractometer, using Cu Ka radiation at 30 kV. Powder X-ray diffraction (PXRD) patterns of LaMnOs and LaMno.9Cuo.1O3 catalysts, as shown in FIG. 1 , confirmed the rhombohedral perovskite crystalline phases of the prepared samples. A monotonic shift of diffraction peaks to smaller angles was observed as the Cu substituted, further confirming the successful preparation of Cu doped perovskite sample.

[0048] The Cu content of LaMno.9Cuo.1O3 sample was determined by inductively coupled plasma optical emission spectroscopy (ICP) on a Thermo Scientific iCAP Pro ICP-OES instrument. The results are set out in Table 1 , and show the closely matched stoichiometric loading of Cu during synthesis. The relative molar ratio of La to (Mn+Cu) was about 0.7:1. Brunauer-Emmett-Teller (BET) surface areas of LaMnOs and LaMno.9Cuo.1O3 were detected and recorded by an accelerated surface area andporosimetry analyzer (Micromeritics ASAP 2020, USA) with N2 adsorption analysis. The results are summarized in Table 2. The surface areas of 18.6 and 21.3 m2 / g over LaMnOsand LaMno.9Cuo.1O3 indicate an increased surface area of LaMno.9Cuo.1O3.Table 1Catalyst Detected Detected Cu / (Mn+Cu)La / (Mn+Cu) molar molar ratio ratioLaMnO30.687 N / ALaMrio.9Cuo.1O3 0.701 0.098Table 2BETSampleSBET (m2 / g) VP(cm3 / g) DP(nm)LaMnOs 18.6399 0.058001 124.466 A / 419.956 ALaMno.9Cuo.1O3 21.3151 0.071438 134.060 A / 368.482 A

[0049] To explore the physicochemical properties of LaMnOsand LaMno.9Cuo.1O3, X- ray photoelectron spectroscopy (XPS) study using a Perkin Elmer Phi 5500 ESCA spectrometer was applied to define the chemical state of elements, as shown in FIG.2. The Mn 2p spectrum can be deconvoluted into two peaks belonging to Mn(lll) andMn(IV), respectively. The slight shifts of Mn(lll) (641 .4 and 653.0 eV in LaMnOs; 641 .5 and 653.1 eV in LaMno.9Cuo.1O3) and Mn(IV) (643.1 and 654.4 eV in LaMnOs; 643.6 and 654.6 eV in LaMno.9Cuo.1O3) towards higher binding energy of LaMno.9Cuo.1O3 can be attributed to the higher electronegativity of Cu. In addition, the Mn(IV) / Mn(lll) intensity ratio decreases with Cu(ll) substitution.

[0050] Raman spectrums of each of the prepared catalysts were collected using a red laser (532 nm) in a Bruker Senterra Raman microscope at 1 mW. The results are shown in FIG. 3; the Raman mode at 657 cm-1in LaMno.9Cuo.1O3 related to the Jahn- Teller MnOe distortion also intensifies, which is consistent with the decreased Mn(IV) / Mn(lll) ratio seen in the XPS results.

[0051] To amplify, the O 1 s spectra of LaMnOsare shown in FIG.2b, which shows peaks at 533.5, 531.6 and 529.2 eV attributing to surface hydroxyl groups (OH), oxygen vacancies (Ov) and lattice oxygens (Oiatt), respectively. It was notable that the peak intensity at 533.3 and 531 .9 eV of LaMno.9Cuo.1O3 was stronger than that of LaMnOs, indicating more OH and Ov sites existed in LaMno.9Cuo.1O3.

[0052] Fourier-transform infrared spectroscopy (FT-IR) was used to further confirm the OH group; the results are shown in FIG. 4. From the results, the peak shown in 3606 cm-1 indicates that more OH was formed over LaMno.9Cuo.1O3.

[0053] The collected analytical results from this demonstrate that by controllingCu(ll) substitution in LaMnOs, it is possible to tune Mn(lll, IV) Lewis acid and O(-ll) and OH(-I) Lewis base sites within the perovskite lattice. This control allows for rational and systematic control over the physicochemical properties of the perovskite lattice. Theseresults also demonstrated that LaMno.9Cuo.1O3 shows higher Lewis acid and Lewis base properties, which provide the foundation for tuning the photo and redox activity of SFLPs for the dehydrogenation of ethane to ethylene.Example 2 - Production of ethylene by photocatalytic ethane dehydrogenation

[0054] The photocatalytic dehydrogenation of ethane over LaMnOs and LaMno.9Cuo.1O3 was investigated in a laboratory scale flow reactor. The reactor comprised a stainless steel reactor body with one or more quartz glass windows disposed on its circumference, and valves controlling the inflow and outflow of gas to and from the reactor body. The quartz glass windows in the reactor allowed light from LED light, simulating solar light, to irradiate the surface of the LaMnOs and LaMno.9Cuo.1O3 within the reactor and to promote the photocatalytic ethane dehydrogenation reaction. Four combined LED lights (UV, blue, green and red) were used as the light source for the reaction. Manually varying the power to the LED lights yielded varying light intensities. An OMEGA temperature controller was attached to a heating cartridge inserted into a copper block along with a thermocouple inserted into the catalyst bed for measuring and controlling the catalyst temperature. The reactant gas, composed of 9.1 vol% C2H6 and 90.9% balancing Ar, was introduced into the reactor with a total flow rate of 2.2 mL-min-1, giving a WHSV value of 5.0 IT1by two mass flow controllers (Alicat MC-2SCCM-D / 5M). The irradiated sample surface area was 0.785 cm2. New samples were used for every test condition. The concentration of the ethylene in the effluent gas was periodically sampled and analyzed by thermal conductivity detector (TCD) using Ar as the carrier gas.

[0055] As shown in FIG.5, Cu(ll) substitution impacted the photocatalytic activity; the C2H4 production rates and selectivity is as follows: LaMno.9Cuo.1O3 (1106.5 |imol g’1h’1; 91.0%) > LaMnOs (227.5 |imol g’1h’1; 52.3%). The activity results show a 4.86 times increase of C2H4 production rates over LaMno.9Cuo.1O3 compared to LaMnOs. The Cu loaded LaMnOs (denoted Cu@LaMnOs) with the same copper loading relative to LaMno.9Cuo.1O3 was also explored as a control sample, to investigate the effect of introducing Cu into the catalyst lattice using a different preparation method on ethane dehydrogenation. In the result, Cu@LaMnOs showed higher C2H4 activity (324.6 nmol g-1h’1) than LaMnOs, however, the activity of Cu@LaMnOs remained notably less than that shown by LaMno.9Cuo.1O3, indicating the importance of isomorphic Cu(ll) substitution in the photocatalytic ethane dehydrogenation reaction.Example 3: Use of13C to confirm photocatalytic ethane dehydrogenation

[0056] The performance of photocatalytic ethane dehydrogenation to ethylene on LaMno.9Cuo.1O3 was excellent among the reported photocatalytic cases. An isotopelabeling test using13C2He as the feedstock was conducted, and the products were analyzed by gas chromatography-mass spectrometry (GC-MS). The testing was conducted in a batch reactor under atmospheric pressure with a total volume of 20 mL. A gas mixture composed of 0.2 seem13C2He and 2 seem Ar was introduced into the reactor with an irradiated sample surface area of 0.785 cm2. LEDs were used tosimulate white light intensity at 4.8 W cm’2. New samples were used for every test condition. As shown in FIG.6, the fragmentation pattern of13C2H4 and13CO2 confirmed that these products were derived from the13C2He.Example 4 - Effect of Ethane Concentration

[0057] The effect of the C2H6feed concentration (vol%) on photocatalytic ethane to ethylene conversion over LaMn0.9Cu0.1 O3 was determined in a Herrick Cell reactor operated with a total flow rate of 2.2 mL-min-1, by varying the C2H6 feed concentration from 9.1 to 33.3 vol% (balanced with Ar) while the weight hourly space velocity (WHSV) was kept constant at 5.0 IT1The results are shown in FIG. 7. The total gas flow was set to 2.2 seem by changing the ethane and Ar ratio. LED simulated white light intensity used was 4.8 W cm’2. New samples were used for every test condition.

[0058] It was evident that an increase in C2H6 feed concentration resulted in increased C2H4 production rate but subsequently lowered C2H6 conversion. Thus, an ethane concentration of 9.1 vol% was used in subsequent photocatalytic ethane conversion activity tests.Example 5 - Effect of Light Intensity and Temperature

[0059] To differentiate between photothermal and photochemical contributions to the dehydrogenation of ethane, the extent and rate of photocatalytic ethane conversion were measured under different light intensities. LED simulated white light intensities used were 2.7, 3.2, 3.6, 4.0, 4.5 and 4.8 W cm’2, respectively. The total gas flow was set to 2.2 seem (0.2 seem ethane: 2 seem Ar) with an irradiated sample surface area of 0.785 cm2. New samples were used for every test condition. An infrared camera was used to measure the temperature generated on the sample surface under reaction gas in a photoreactor with a CaF2 window.

[0060] Thermalcatalytic reactions were conducted at temperatures of 500, 550, 600, 650 and 700 °C using a flow reactor.

[0061] As shown in FIG. 8, C2H4 production rates over LaMnOs and LaMno.9Cuo.1O3 were enhanced with increasing light intensity. Surface temperatures of LaMnOs and LaMno.9Cuo.1O3 were determined by using an IR camera during variable light intensities, as shown in right axis of FIG. 8. It was found that the surface temperatures of LaMnOs and LaMno.9Cuo.1O3 were similar and increased linearly with the light intensity from 330 and 331 °C at 2.68 W-crrr2to 447 and 452 °C at 4.80 W-crrr2, respectively. From the results in FIG. 8, it can be seen that LaMnOsand LaMno.9Cuo.1O3 show similar surface temperatures, which revealed that Cu(ll) substitution had a minor effect on photothermal conversion capacity between LaMnOsand LaMno.9Cuo.1O3, with a photochemical contribution to the photocatalytic reaction.

[0062] Further confirmation of photochemical contributions during the photocatalytic ethane dehydrogenation reaction was obtained by measuring the photocatalytic ethane conversion activity under thermal conditions under dark, i.e. in the absence of LED illumination, but within a temperature range including the temperatures reached when LED lighting was used, as shown in FIG. 9. No C2H4 was produced below 452 °C, and a rapid increase in the C2H4 production rate only occurred above 600 °C for both LaMnOs and LaMno.9Cuo.1O3. Different enhancement of the ethylene production rates in thermocatalytic and photocatalytic reaction of LaMno.9Cuo.1O3 in comparison to LaMnOs confirmed the photochemical contributions to the dehydrogenation of ethane, in addition to any photothermal role played by the LED lighting.

[0063] The activation energies (Ea) under photo and thermal chemical reaction conditions were calculated using the Arrhenius equation, shown in FIG. 10. For LaMno.9Cuo.1O3 and LaMnC , Eavalues for conversion of ethane to ethylene were calculated to be 90.94 and 94.62 kJ-mol’1for photocatalysis and 169.57 and 171.54 kJ-mol’1for thermocatalysis, respectively. The drastically lower activation energies under light emphasizes the advantages of ethane photocatalytic dehydrogenation compared to the thermal process.Example 6 - Assessment of Catalyst Stability

[0064] The durability of the LaMnOs and LaMno.gCuo.i O3 catalysts across multiple photodehydrogenation and regeneration cycles was explored. Stablity tests were carried out for five cycles. After each dehydrogenation reaction, the spent catalyst was irradiated by the same LED lights used in the photocatalytic ethane conversion reaction in open air under LED simulated white light intensity of 4.8 W cm-2light irradiation for 20 mins to remove the surface residual.. The results are shown in , see FIG. 11 . It can be seen from the results that both catalysts gradually deactivated with time but that, most importantly, they can be regenerated by ambient air oxidation.Example 7 - Study of the Ethane Dehydrogenation Reaction Pathway

[0065] C2H6 temperature-programmed surface reaction (C2H6-TPSR) experiments were conducted to provide additional insights into the ethane dehydrogenation pathway under thermal conditions. The experiment was performed with the samples loading amount of 50 mg. The reaction temperature was first purged by He (30 mL-min’1) at 200 °C for 10 mins, The gas flow was then switched to 5% C2H6 in He (30 mL-min’1) and thetemperature increased to 700 °C from 200 °C at a rate of 10 °C-min’1, the outlet gas was detected by an on-line QMS (Broker, MATRIX-MG(HR)-OI ).

[0066] As shown in FIG. 12a, more CO and CO2 were observed for LaMnOsthan for LaMno.9Cuo.1O3. Unexpectedly, H2O and H2 emerged at 350 and 600 °C for LaMnOs, while LaMno.9Cuo.1O3 required a relatively higher temperature for H2O release (500 °C) and a lower temperature for H2 (570 °C), indicating easier production of H2 (C2H6 — C2H4 + H2) in the latter.Example 8 - Evaluation of Structural Changes in the Catalysts

[0067] To study the structure changes of the spent LaMnOs and LaMno.9Cuo.1O3 samples, PXRD tests were performed on spent samples. As can be seen from the results in FIG. 13, the spent LaMnOs and LaMno.9Cuo.1O3 do not show any present apparent structure changes, indicating the bulk perovskite structure was stable after photocatalytic enthane dehydrogenation reactions.Example 9 - Examination of Spent Catalysts

[0068] X-ray photoelectron spectroscopy (XPS) of spent catalyst samples was conducted using a Perkin Elmer Phi 5500 ESCA spectrometer. The XPS spectra of spent LaMnOs and LaMno.9Cuo.1O3 after photocatalysis are shown in FIG. 14, . The results in Figure 14 indicate a greater Oiatt decrease on LaMnOs. Furthermore, the Mn(IV) / Mn(lll) ratio increased significantly in LaMnOs but not in LaMno.9Cuo.1O3, due to the greater loss of Oiatt in LaMnOs. In conjunction with catalytic activity results (FIG.5), these results indicate that the numbers of Mn(lll) / Mn(IV) play an important role for the dyhydrogenation of ethane to ethylene.Example 10 - DRIFTS - evaluation of surface chemistry

[0069] In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to identify any changes in the surface chemistry of the catalysts occurring during photocatalytic ethane-to-ethylene. DRIFT spectra were collected on a Thermo Scientific iS50 series Fourier transform infrared (FT-IR) instrument equipped with a Harrick Praying Mantis™ DRIFT accessory. Each spectrum was recorded at 4 cm-1resolution, using an average of 32 scans. Powder samples were placed into the holder without packing or dilution. A background IR spectrum was taken following 2 h of purging under He at 300 °C. Then C2He / Ar (1 :3; 5 seem ethane and 15 seem, respectively) was flowed for 30 mins at 30 °C for an ethane adsorption test. An ethane dehydrogenation test, it was conducted under the white LED light with the intensity of 2.1 W-crrr2at 300 °C. FIG. 15 is the in-situ DRIFTS result of LaMnOs under light conditions, no observable signals except for ethane peaks were found.

[0070] Figure 16 displays the in-situ DRIFTS result of LaMno.9Cuo.1O3, and demonstrates a series of fingerprint signature peaks for LaMno.9Cuo.1O3, the intensities of which gradually increased with irradiation time,. The peak at 1845 cm-1showed a fingerprint diagnostic of a manganese hydride Mn-H surface species. The OH vibrations at 3730 and 3700 cm-1indicated the formation of Mn-OH and a protonated MnOH2 species. The peak at 1976 cm-1was attributed to the vibration of C=C bond indicative of ethylene formation. This was confirmed by the peak appearing at 2984 cm-1of C2H4. The above results indicate that C2H6 underwent a heterolytic dissociative pathway on Lewis acidic Mn (III, IV) and Lewis basic O(-ll), OH(-I) SFLPs.Example 11 - Confirmation of Photochemical activity

[0071] Solid state1H NMR testing was used to obtain supportive information about the photochemical role from the thermolytic (T) and photolytic (L) ethane dehydrogenation reaction. The 1 H solid state NMR spectra were obtained at a spinning rate of 11 kHz. The NMR Spectra were calibrated to reference adamantane with optimized parameters: pulse width (pwX90) = 3.5 microseconds, number of scans = 1 , delay time = 10 s. Samples for 1 H solid state NMR were treated by ethane under photo or thermal (600 °C) and then tested immediately. The results are shown in FIG. 17; L and T are samples exposed to ethane under photo and thermal (600 °C) reaction conditions. A new1H NMR peak with a chemical shift associated with Mn-H appeared at around -3.14 ppm relative to the adamantane reference after the thermal reaction was observed. Under light, the modified Lewis acidity makes the Mn-H bonds lengthened, as evident by a positive1H NMR chemical shift from -3.14 to -2.37 ppm. These1H NMR observations showed that the photochemical effect lengthened and weakened the Mn-H bond to promote C-H bond breaking. These results demonstrate the photochemical contribution of the catalysts during the photocatalytic ethane dehydrogenation reaction in addition to any photothermal contribution from the heat of light source.Example 12 - Photocatalytic Natural Gas Direct Dehydrogenation

[0072] The photocatalytic dehydrogenation of natural gas to ethylene and syngas was carried out in the same flow reactor used for photocatalytic ethane dehydrogenation, at ambient conditions. A Xenon lamp was applied for the light source and the light intensity set to 8.64 W-crrr2The natural gas flow rate was 2 seem. The corresponding WHSV value was 8.6 IT1. The reactants and products were detected bygas chromatography (GC-2014, Shimadzu) equipped with both thermal conductivity (TCD) and flame ionization detectors (FID).

[0073] LaMnOs and LaMno.9Cuo.1O3 catalysts were used for the natural gas dehydrogenation reaction. Fig.18 shows the photocatalytic natural gas direct dehydrogenation activities over LaMnOs and LaMno.9Cuo.1O3 . Specifically, the C2H4 production rate of LaMno.9Cuo.1O3 was 673 mol g’1h’1, which is higher than that of LaMnOs (402 pmol g’1Tr1). In addition, LaMno.9Cuo.1O3 exhibited improved photocatalytic activity for the syngas generation, including carbon monoxide (1228 pmol g’1h’1) and hydrogen (910 pmol g’1Tr1). Compared to pure LaMnOs, the perovskites LaMno.9Cuo.1O3 with partial copper substitution show enhanced activity for photocatalytic natural gas dehydrogenation.

[0074] The use of a hydrothermal method for the preparation of LaMnOs and LaMno.9Cuo.1O3 samples allows controlled copper subsitution into the LaMnOs. With this controlled Cu(ll) substitution, LaMno.9Cuo.1O3 exhibits enhanced Lewis acid-base properties and improved photocatalytic performance in ethane and natural gas dehydrogenation compared to LaMnOs.

[0075] While the embodiments of the present disclosure have been described in detail, it is to be understood that, unless otherwise specified, the present disclosure is not limited to particular materials, reaction materials, manufacturing processes, or the like, as such can vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. Itis also possible in the present disclosure that steps can be executed in different sequences where this is logically possible.

Claims

CLAIMS1 . A process for the dehydrogenation of one or more light hydrocarbons comprising: a. introducing said light hydrocarbons into a reactor; and b. exposing said light hydrocarbons in said reactor to a light source having an intensity of at least about 2 W cm-1 ; said dehydrogenation being carried out in the presence of a catalyst that is a metal oxide.

2. The process of claim 1 wherein the dehydrogenation of said light hydrocarbons causes at least one such light hydrocarbon to dissociate into separable gaseous hydrogen and one or more alkene co-products.

3. The use of a metal oxide as a catalyst in a process for the dehydrogenation of one or more light hydrocarbons comprising: a. introducing said light hydrocarbons into a reactor in which said metal oxide is present; b. closely contacting said one or more light hydrocarbons with said metal oxide; and c. exposing said metal oxide in said reactor to a light source having an intensity of at least about 2 W cm-1 ;4. The process of any one of claims 1 , 2 or 3 wherein the metal oxide is a stoichiometric, ABO3 or non-stoichiometric perovskite, ABOs-xand other stoichiometric or non-stoichiometric metal oxides, MOn.

5. The process of any one of claims 1 , 2 or 3 wherein the metal oxide is a copper substituted lanthanum manganese oxide-based perovskite.

6. The process of claim 4 wherein the metal oxides ABO3 or ABOs-x may be a redox active perovskite; or a version thereof doped by isomorphic substitution on the A and / or B sites of said perovskites, or modified with single metal atoms or dualsite single-atoms supported on said perovskites7. The process of any one of claims 1 , 2, 3 or 4 wherein the copper substituted lanthanum manganese oxide-based perovskite is a Cu(ll) substituted lanthanum manganese oxide represented by the formula LaMm-xCuxOs, where x can be from 0.01 to about 0.5.

8. The process of any one of claims 1 , 2, 3 or 4 wherein the copper substituted lanthanum manganese oxide-based perovskite is LaMno.9Cuo.1O3.

9. The process of any one of claims 1 to 7 in which the intensity of the light source is greater than about 2 W cm’1.

10. The process of any one of claims 1 to 7 in which the intensity of the light source is between about 2 W cm’1and 10 W cm’1.11 . The process of any one of claims 1 to 7 in which the light hydrocarbon is selected from the group consisting of natural gas methane, ethane, propane, butane and methylcyclohexane.

12. The process of any one of claims 1 to 7 in which the light hydrocarbon is ethane.

13. The process of any one of claims 1 to 7 in which the light hydrocarbon is natural gas.

14. The process of claim 6 in which the dopant in the redox active perovskites ABO3 or ABOs-x may be comprised of elements of the periodic table exemplified by isomorphic substitution of transition metals such as Cu, Fe, Ni, Co, In, Al, Sn on the B site.

15. A process for the preparation of a copper substituted lanthanum manganese oxide-based perovskite for use as a catalyst in the dehydrogenation of one or more light hydrocarbons, comprising admixing stoichiometrically amounts of lanthanum nitrate, manganese t and copper nitrate to form a mixed salt solution, suspending the salts so obtained by adding a base to the solution, heating the suspension so obtained to about 180 °C for about 12 h before cooling the solution to room temperature, isolating the resulting copper substituted lanthanum manganese oxide-based perovskite precursor by centrifugation and washing and calcining the dried precursor.

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