Patent Description:
The present invention relates to the developing of a sustainable and catalytic process for functionalised styrene monomers synthesis from benzene or functionalized benzene compounds to reduce the overall production cost and provide benefits to pertinent industries and society. Accordingly the present invention provides a sustainable catalytic process for production of functionalised styrene monomers. The method comprises coupling of the benzene or functionalized benzene with ethylene at temperature range from <NUM>-<NUM> and pressure range from <NUM> to <NUM> bar over heterogeneous catalysts.

Polymer industries utilize a great portion of non-renewable crude oil-based resources. The global polymer production is <NUM> metric tons with annual growth of <NUM>-<NUM> % (<NPL>). Most commonly used polymers such as polyethylene, polystyrene, polyvinylchloride, and poly-methyl methacrylate have dominated the plastic industries for many decades due to their low cost and high durability. The low biodegradability of such polymers and the dependency of (depleting) fossil reserves have intensified interest in green and sustainable resources for the chemical synthesis of polymers. Lignocellulosic biomass represents a promising resource that can be either use as polymer backbones or deconstructed into aromatic molecules and sugar-based platform chemicals (<NPL>).

Styrene is an industrially important commodity chemical, widely used to produce polystyrene plastic, polyesters, protective coatings, resins, rubbers and other copolymers (<NPL>). The chemical structure of styrene contains an active vinyl group that can be further functionalized for the production of versatile synthetic intermediates. The global production of styrene is <NUM> million tons per year with the market value of approximately $<NUM> billion.

Industrially styrene is produced by the oxidative dehydrogenation of ethylbenzene. Several mild oxidizing agents such as O<NUM>, CO<NUM>, N<NUM>O and SO<NUM> have been proposed for a low-temperature oxidative dehydrogenation of ethylbenzene (<NPL>). However, molecular oxygen always causes side reactions that reduce the overall styrene selectivity. Additionally, the over-oxidation of ethylbenzene produces COx which makes this reaction highly explosive and greatly lowers the atomic efficiency of such a feedstock. The SNOW (Snamprogetti/Dow) process is a nice alternative that is competitive; nonetheless, multiple steps and the utilization of ethane in large amounts make this process expensive (<NPL>).

The dehydrogenation of ethylbenzene to styrene by using CO<NUM> as a soft oxidant is an interesting alternative, which was adopted for the first time by Sugino in <NUM> (<NPL>). Apart from a notable positive impact on the global carbon balance, the utilization of CO<NUM> can offer several advantages such as the acceleration of reaction rate, acting as a diluent, enhancing the product selectivity and thermodynamic stability. The dehydrogenation of ethylbenzene with CO<NUM> cannot be performed in the current industrial process because of its contribution to catalyst deactivation. Good performances of high-surface ceria, Fe<NUM>O<NUM>/Al<NUM>O<NUM>, TiO<NUM>-ZrO<NUM>, MnO<NUM>-ZrO<NUM>, MCM-<NUM> and SBA-<NUM>-supported CeO<NUM>-ZrO<NUM> catalysts have been reported in the literature (<NPL>). However, the reaction temperature of dehydrogenation over these catalysts is still high (above <NUM>). Therefore, developing an efficient catalyst with a high activity at lower temperatures is still highly desirable. Another concern is that the ethylbenzene utilized in these processes is derived from petroleum. Non-renewable fossil sources such as coal, natural gas and petroleum meet nearly <NUM>% of the world's energy and <NUM>% of basic, commodity and specialty chemical demands. The diminishing reserves of these sources, rising atmospheric CO<NUM> levels, and socio-economic concerns require a reduction of our dependence on these sources.

An alternative method for the production of styrene is a direct and single-step oxidative coupling of biomass derived benzene and ethylene. Rhodium metal based complexes that catalyze ethylene hydrophenylation by benzene C-H activation followed by ethylene insertion into a metal-phenyl bond have been reported as alternatives to dehydrogenation of ethylbenzene (<NPL>). However, these prior art catalysts give rise to problems in relation with catalyst removal, side- and by-product removal and furthermore often cannot be reused at all.

<CIT> discloses a method for production of dimethylstyrenes by reacting xylenes, ethylene and oxygen in the presence of a lower aliphatic carboxylate of palladium.

Currently, the majority of (functionalised) styrene monomers in the industry is produced by the multiple-step catalytic dehydrogenation reaction from petroleum-derived ethylbenzene using large feeding streams over the iron oxide-based catalyst. However; these processes are extremely endothermic; they consume <NUM>-times the amount of energy as in the production of similar chemicals. In addition, low atom economy, short catalyst lifetimes and the net emission of greenhouse gases are other drawbacks, associated with this industrial process, while the production is based exclusively on a non-renewable fossil-based resource. Natural resources are being consumed in the industrial production of functionalised styrene monomers; from an environmental and economic standpoint, it is important to recoup them in as great extent as possible. The use of petroleum based raw products is a major drawback, which has to be overcome. It would be desirable to have a simple and practicable synthetic route to produce functionalised styrene monomer on an industrial scale starting from non-petroleum sources. The developed processes would be a major breakthrough, complementing the shift of the world economy from the eventually depleting petrochemical feedstock to biomass-based resources.

In this context it would be advantageous to be able to provide a process as outlined above based on the use of sustainable feedstocks such as benzene and ethylene for the production of styrene. Benzene is a widely available renewable resource that can be produced from lignin. Ethylene can also be produced by the dehydration of bio-ethanol. We have also invented an environmental friendly one step process for the production of functionalised styrene monomers from non-renewable aromatic oxygenate compounds.

The industrial route for functionalised styrene monomers requires harsh reaction conditions (high temperature and pressure) that produce a significant amount of by-products which may be difficult to remove and cause further purification and processing problems. In this context, it would be advantageous if one could provide an efficient synthetic process that can replace the current multiple-step and energy-intensive industrial process of the styrene production with relatively mild operating conditions in order to achieve high selectivity. In the context of the prior art methods disclosed above it would also be advantageous if one could provide a process that required the use of heterogeneous catalyst to overcome the problem of homogenous metal complex catalyst that is expensive, difficult to remove and furthermore often cannot be reused at all.

The present invention solves the problems outlined above and provides the process as defined in claim <NUM>, as well as the use of the catalyst as defined in claim <NUM>. Preferred embodiments of the process and the use of the catalyst are disclosed in claims <NUM> to <NUM> and <NUM> to <NUM> respectively, as well as in the following description.

The present invention is based on a judiciously designed heterogeneous catalyst for the oxidative coupling of benzene or functionalized benzene and ethyleneto produce functionalized styrene monomer. In most of the reported routes, homogeneous metal complexes have been utilized for the production of such monomers but these catalysts have disadvantages in relation to high production cost, separation, recyclability and disposal. Heterogeneous catalytic systems, on the other hand, offer distinct advantages in terms of cost reduction, high activity and selectivity easy separation and reusability. Another merit of heterogeneous catalysts is their stability to high temperature and pressure.

The present invention accordingly provides a process for the oxidative coupling of bio-based or fossil based feedstocks to functionalized styrene monomer with a heterogeneous catalytic system that offers high selectivity under relatively mild reaction conditions. The heterogeneous catalyst of the present invention is a catalyst which in particular enables production of styrene under relatively mild conditions and furthermore allows an easy separation of the used catalyst from the reaction mixture. In particular it has been shown that the catalysts of the present invention can be reused, in many instances even without any reactivation (for example by reductive treatments to remove any undesired oxidation of the transition metals, if contained in the catalysts or other conventional processes known to the skilled person to re-activate a spent catalyst).

Preferred catalysts according to the invention are listed in the following: graphene oxide (GO), sulfonated graphene oxide (SGO), reduced graphene oxide (rGO), multiwalled carbon nanotubes (CNT), graphitic carbon nitride(g-C<NUM>N<NUM>), sulfonated graphitic carbon nitride (S-g-C<NUM>N<NUM>), palladium doped reduced graphene oxide (Pd/rGO), palladium doped multiwalled carbon nanotubes (Pd/CNT), palladium doped graphitic carbon nitride(Pd/g-C<NUM>N<NUM>), boron-doped graphitic carbon nitride(B/g-C<NUM>N<NUM>, palladium doped sulfonated graphitic carbon nitride (Pd/S-g-C<NUM>N<NUM>), ceria doped sulfonated graphene oxide (Ce/SGO), ceria doped reduced graphene oxide (Ce/rGO), ceria doped multiwalled carbon nanotubes(Ce/CNT), ceria doped graphitic carbon nitride(Ce/g-C<NUM>N<NUM>), ceria doped sulfonated graphitic carbon nitride (Ce-S-g-C<NUM>N<NUM>), ruthenium doped reduced graphene oxide (Ru/rGO), ruthenium doped graphitic carbon nitride (Ru/g-C<NUM>N<NUM>), ruthenium doped multiwalled carbon nanotubes (Ru/CNT), ruthenium doped sulfonated graphitic carbon nitride(Ru/S-g-C<NUM>N<NUM>), platinum doped reduced graphene oxide (Pt/rGO), platinum doped graphitic carbon nitride (Pt/g-C<NUM>N<NUM>), platinum doped multiwalled carbon nanotubes (Pt/CNT) and platinum doped sulfonated graphitic carbon nitride (Pt/S-g-C<NUM>N<NUM>). Preferred catalysts are based on graphitic carbon nitride. Accordingly, preferred catalysts of and to be employed in the present invention comprise a graphitic carbon nitride. It is to be understood that preferred embodiments described for the catalyst as such of course also are applicable to the use of the catalyst in the process of the present invention.

Examples of suitable graphitic carbon nitride based catalysts are palladium doped graphitic carbon nitride, platinum doped graphitic carbon nitride and ruthenium doped graphitic carbon nitride.

The catalysts in accordance with the present invention preferably are graphitic carbon nitride and transition metals (Pd, Pt and Ru) supported on this material. The suitable amount of transition metal in the catalysts of the present invention is in the range of from <NUM> to <NUM> weight percent relative to the support. The BET specific surface area of the catalysts of the present invention is generally from <NUM> to <NUM><NUM> /g, preferably from <NUM> to <NUM><NUM> /g, in particular from <NUM> to <NUM><NUM> /g. The pore volume preferably is between <NUM> to <NUM><NUM> per gram, preferably between <NUM> to <NUM><NUM> per gram. In a preferred embodiment the BET surface is from <NUM> to <NUM><NUM>, preferably from <NUM> to <NUM><NUM>, in combination with a pore volume of between <NUM> to <NUM><NUM> per gram, preferably between <NUM> to <NUM><NUM> per gram. BET specific surface area and pore volume are determined according to the methods disclosed in <NPL>.

The catalysts disclosed herein, in particular the graphitic carbon nitride catalytic system disclosed herein has particularly shown efficient activity for oxidative coupling reaction. Without being bound to the following explanation, it may be that the superior and unexpected activity is based on the fact that the surface of graphitic carbon nitride is decorated with several oxygen functionalities, such as epoxy, hydroxyl, carbonyls, and nitride groups which induce beneficial oxidised defect sites and promotes the oxidative coupling of benzene or aromatic oxygenate compounds with ethylene to produce functionalized styrene monomers. In any case, the catalytic system disclosed here shows very high activity, selectivity, higher than other catalysts tested or reported in the literature for the oxidative coupling of benzene or functionalized benzene and ethylene to functionalized styrene monomers.

Accordingly the process in accordance with the present invention comprises the step of converting a starting material, selected among benzene or functionalized benzene and ethylene, preferably obtained from renewable (bio-based) or fossil based resources to functionalized styrene monomers in the presence of a catalyst selected from graphene oxide (GO), sulfonated graphene oxide (SGO), reduced graphene oxide (rGO), multiwalled carbon nanotubes (CNT), graphitic carbon nitride(g-C<NUM>N<NUM>), sulfonated graphitic carbon nitride (S-g-C<NUM>N<NUM>), palladium doped reduced graphene oxide (Pd/rGO), palladium doped multiwalled carbon nanotubes (Pd/CNT), palladium doped graphitic carbon nitride (Pd/g-C<NUM>N<NUM>), boron-doped graphitic carbon nitride(B/g-C<NUM>N<NUM>, palladium doped sulfonated graphitic carbon nitride (Pd/S-g-C<NUM>N<NUM>), ceria doped sulfonated graphene oxide (Ce/SGO), ceria doped reduced graphene oxide (Ce/rGO), ceria doped multiwalled carbon nanotubes (Ce/CNT), ceria doped graphitic carbon nitride(Ce/g-C<NUM>N<NUM>), ceria doped sulfonated graphitic carbon nitride (Ce-S-g-C<NUM>N<NUM>), ruthenium doped reduced graphene oxide (Ru/rGO), ruthenium doped graphitic carbon nitride (Ru/g-C<NUM>N<NUM>), ruthenium doped multiwalled carbon nanotubes (Ru/CNT), ruthenium doped sulfonated graphitic carbon nitride(Ru/S-g-C<NUM>N<NUM>), platinum doped reduced graphene oxide (Pt/rGO), platinum doped graphitic carbon nitride (Pt/g-C<NUM>N<NUM>), platinum doped multiwalled carbon nanotubes (Pt/CNT) and platinum doped sulfonated graphitic carbon nitride (Pt/S-g-C<NUM>N<NUM>).

The oxidative coupling reactions are carried out in presence of redox agent. Preferably, redox agent is selected from one of the following: copper (II) acetate, palladium (II) acetate, manganese (II) acetate, silver acetate and sodium acetate. In some embodiments during the oxidation coupling reaction over palladium doped graphitic carbon nitride catalyst, the palladium(III) of the catalyst is reduced, typically to a palladium(I) state. In order for the reaction to be catalytic with respect to palladium, it is necessary to oxidize the palladium(I) back to palladium (III), and so regenerate the catalyst. In some embodiment, this oxidation achieved using a copper(II) acetate or copper(II) redox agent. The term "copper(II) redox agent," as used herein, pertains to a chemical compound comprising at least one copper atom in the +<NUM> oxidation State. In one embodiment, the copper(II) redox agent has only one copper atom.

In one preferred embodiment, the reaction is carried out neat, without a solvent. In one embodiment, the reaction is more preferably carried out neat, without a solvent, with a stoichiometric excess of the benzene, which acts both as reactant and solvent (reaction medium).

It has been found that the concentration of benzene is at least <NUM> and not more than <NUM>, such as from <NUM> to <NUM>, preferably <NUM> to <NUM>, such as <NUM>, <NUM>, <NUM>, or <NUM>. The pressure of ethylene typically is in the range of from <NUM> to <NUM> bar, preferably from <NUM> to <NUM> bar and more preferably from <NUM> to <NUM> bar, and in particular <NUM> bar or less and <NUM> bar or more, such as <NUM> bar.

It has been found that the amount of catalyst in the reaction mixture (calculated for a batch reaction, suitable adaptations have to be made for continuous processes) is not less than <NUM> mass percent and not higher than <NUM> mass percent with respect to substrate (i.e. the above identified starting material), such as from <NUM> to <NUM> mass percent. The process disclosed here typically is carried out at a temperature from <NUM> to <NUM>, preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>, such as <NUM>.

The reaction time is not critical and may depend from the desired balance of conversion and efficiency as well as selectivity, but generally reaction times of form <NUM> to <NUM> are suitable, such as from <NUM> to <NUM>, from <NUM> to <NUM> and in embodiments from <NUM> to <NUM>.

The reaction may be carried out in any suitable reactors known to the skilled person, but stainless steel reactors (autoclave) are in particular suitable. However, other materials may also be suitable as reactor materials and it is of course also possible to provide the inner surface of such a reactor, completely or partially with a coating of a material inert towards the reaction, such as a polymer coating, a ceramic coating etc..

As said above, the benzene or functionalized benzene and ethylene is/are fossil-based or biomass-derived.

The functionalized benzene according to this invention is a benzene substituted on the phenyl-ring with <NUM> to <NUM> substituents selected from C<NUM>-<NUM>-alkyl.

In an embodiment the functionalized benzene is benzene substituted by <NUM> or <NUM> substituents selected from C<NUM>-<NUM>-alkyl.

It is to be understood, that the various process parameters, such as starting material concentration, catalyst amount, temperature, pressure and reaction time (residence time), while being disclosed individually, are considered in the context of the present invention in combination, such as a starting material concentration of from <NUM> to <NUM>, a catalyst amount of from <NUM> to <NUM> mass percent, a reaction temperature of from <NUM> to <NUM>, preferably from <NUM> to <NUM>, a pressure of from <NUM> to <NUM> bar, preferably from <NUM> to <NUM> bar and a reaction time of from <NUM> to <NUM>. However, all other combinations possible from the ranges and preferred embodiments are also comprised by and disclosed in this invention.

In essence, this leads to the invention best described by the following aspects and embodiments:
In a first aspect is provided a process for the production of, optionally functionalized, styrene monomers comprising the steps:.

In an embodiment the ethylene is added as a gas to the reactor already being fed with the benzene or functionalized benzene and the heterogeneous catalyst.

In another embodiment the phenyl-ring of the functionalized benzene is substituted by <NUM> or <NUM> substituents selected from C<NUM>-<NUM>-alkyl.

In another embodiment the phenyl-ring of the functionalized benzene is substituted by <NUM> or <NUM> CH<NUM>-groups.

In another embodiment the, optionally functionalized, styrene monomer is selected from styrene, <NUM>-vinylphenol, <NUM>-methoxy-<NUM>-vinylphenol, or <NUM>-methyl-<NUM>-vinylphenol.

In another embodiment no solvent is used in the reaction step (b) or added in step (a) in addition to the benzene or the functionalized benzene; preferably while the benzene acts both as reactant and solvent and/or is added in step (a) in stoichiometric excess in relation to the ethylene.

In another embodiment the pressure (of ethylene) in step (b) is between and including <NUM> bar and <NUM> bar; and/or.

In another embodiment a redox agent is added to the mixture of step (a) before step (b).

In another embodiment the heterogeneous catalyst is selected from palladium doped sulfonated graphitic carbon nitride (Pd/S-g-C<NUM>N<NUM>), palladium doped graphitic carbon nitride (Pd/g-C<NUM>N<NUM>), ruthenium doped graphitic carbon nitride (Ru/g-C<NUM>N<NUM>), ruthenium doped sulfonated graphitic carbon nitride(Ru/S-g-C<NUM>N<NUM>), platinum doped graphitic carbon nitride (Pt/g-C<NUM>N<NUM>), and platinum doped sulfonated graphitic carbon nitride (Pt/S-g-C<NUM>N<NUM>).

In another embodiment the heterogeneous catalyst is selected from palladium doped graphitic carbon nitride (Pd/g-C3N4) and platinum doped graphitic carbon nitride (Pt/g-C3N4).

In a second aspect is provided the use of a heterogeneous catalyst based on or comprising graphitic carbon nitride for the production of, optionally functionalized, styrene from benzene or functionalized benzene with ethylene; wherein the functionalized benzene is a benzene substituted on the phenyl-ring with <NUM> to <NUM> substituents selected from C<NUM>-<NUM>-alkyl.

In an embodiment the heterogeneous catalyst is a catalyst comprising at least one transition metal or noble metal supported on graphitic carbon nitride.

In another embodiment the heterogeneous catalyst is selected from palladium doped sulfonated graphitic carbon nitride (Pd/S-g-C<NUM>N<NUM>), palladium doped graphitic carbon nitride (Pd/g-C<NUM>N<NUM>), ruthenium doped graphitic carbon nitride (Ru/g-C<NUM>N<NUM>), ruthenium doped sulfonated graphitic carbon nitride(Ru/S-g-C<NUM>N<NUM>), platinum doped graphitic carbon nitride (Pt/g-C<NUM>N<NUM>), and platinum doped sulfonated graphitic carbon nitride (Pt/S-g-C<NUM>N<NUM>); preferably.

In another embodiment the heterogeneous catalyst comprises the least one transition metal or noble metal in an amount of <NUM> to <NUM> wt %; and/or wherein the catalyst has a BT surface area of from <NUM> to <NUM><NUM> and a pore volume of from <NUM> to <NUM><NUM>.

In another embodiment the production of, optionally functionalized, styrene from benzene or functionalized benzene with ethylene is done by the process according to the first aspect of the invention.

In the examples described herein the catalytic oxidative coupling of benzene or with ethylene to styrene monomer was performed using a stainless steel high pressure reactor under the standard operation conditions. The novel process of the present invention was carried out at a temperature greater than <NUM>, most preferably between <NUM> and <NUM>, especially between <NUM> and <NUM>. The reactions were carried out under pressure. Preferably, the processes are carried out at pressures of at least <NUM> bar of ethylene, more preferably at least <NUM> bar, in some embodiments at least <NUM> bar, in some embodiments pressure is in the range of <NUM> bar to <NUM> bar. In general, the reaction should be conducted under conditions where the residence time of the feedstock solution over the catalyst is appropriate to generate the desired products. Preferably, the reaction time is in the range of between <NUM> and <NUM> minutes, typically <NUM>-<NUM> minutes, more preferably <NUM>-<NUM> minutes, most preferably <NUM>-<NUM> minutes.

Benzene, ethylene, copper (II) acetate, urea, palladium nitrate, ammonium hydroxide, palladium (II) acetate, manganese (II) acetate, silver acetate, sodium acetate, graphite powder, hydrochloric acid (<NUM>%), ethanol, ether, phosphoric acid, hydrogen peroxide (<NUM>%), and sulfuric acid, palladium nitrate, platinum nitrate and ruthenium chloride were purchased from Sigma-Aldrich.

Grephitic carbon nitride (g-C<NUM>N<NUM>) catalyst was synthesized by heating <NUM> of urea in air at a ramp rate of <NUM> min-<NUM> to a given temperature (<NUM>), keeping that temperature for <NUM>, then cooling without temperature control. Palladium doped Grephitic carbon nitride (Pd/g-C<NUM>N<NUM>) catalyst was synthesized by incipient-wetness impregnation method. In a typical procedure, <NUM> of g-C<NUM>N<NUM> support was added to <NUM> aqueous solution of Pd(NO<NUM>)<NUM>. The pH of the solution was adjusted to <NUM> by adding <NUM> NH<NUM>OH under vigorous stirring. The mixture was then stirred for <NUM> at <NUM>. After cooling to room temperature, the solid was recovered by filtration and washed with distilled water. The mixture was then placed in a vacuum oven and allowed to dry overnight at <NUM>. The dried material was then transferred to a Schwartz-type drying tube and reduced in a H<NUM> flow at <NUM> for <NUM>. The Pd/g-C<NUM>N<NUM> catalyst was subsequently cooled to RT under flowing N<NUM>.

Powder X-ray diffraction (XRD) studies were conducted using the PANalytical X'Pert Pro instrument. Scanning from <NUM> to <NUM>° was carried out using the CuKα radiation source with the wavelength of <NUM>. Nitrogen physisorption analyses were carried out by degassing the catalysts under N2 flow for <NUM> at <NUM>. The degassed samples were analyzed in the Micromeritics ASAP <NUM> multi-point surface area and porosity analyzer (<FIG>).

Temperature programmed desorption (TPD) was performed using the Micromeritics <NUM> Autochem II Chemisorption Analyzer (<FIG>). The catalysts were pre-treated at <NUM> under the stream of helium for <NUM>. The temperature was consequently decreased to <NUM>. % CO<NUM> in He was passed over the catalysts at the flow rate of <NUM> min-<NUM> for <NUM>. The excess gas was removed by purging with helium for <NUM>. The temperature was after that gradually raised to <NUM> by ramping at <NUM> min-<NUM> under the flow of helium, wherein the desorption data of NH<NUM>, is recorded. The structure and morphology of the prepared catalysts was studied using transmission emission scanning electron microscope (TEM) (Carl Zeiss, Supra 35VP), equipped with energy-dispersive X-ray spectroscopy (EDX) hardware (Oxford Instruments, INCA <NUM>) (<FIG>).

The Fourier-transform infrared (FT-IR) spectra of the samples were recorded on Spectrum Two FT-IR spectrometer (PerkinElmer, Waltham, USA) at the wavenumbers ranging from <NUM>-<NUM> to <NUM>-<NUM>(<FIG>).

X-ray photoelectron spectroscopy (XPS) analyses were carried out by the PHI XPS spectrometer (Physical Electronics). Sample was deposited on adhesive carbon tape and introduced into ultra-high vacuum spectrometer. The vacuum during XPS analyses was in the range of <NUM>-<NUM> mbar, as a high surface sensitivity is a general characteristic of the XPS methods. Sample surfaces were excited by the X-ray radiation from the monochromatic Al source at the photon energy of <NUM> × <NUM>-<NUM> J (<NUM> eV). High-energy resolution spectra were acquired with the energy analyser, operating at the resolution of about <NUM> × <NUM>-<NUM> J (<NUM> eV) and the pass energy of <NUM> × <NUM>-<NUM> J (<NUM> eV). During data processing, surface spectra were aligned by setting the C <NUM> peak at <NUM> × <NUM>-<NUM> J (<NUM> eV), the latter being characteristic for C-C bonds. The accuracy of binding energies was about ±<NUM> × <NUM>-<NUM> J (±<NUM> eV). XPS spectra were analysed by the MultiPak software, version <NUM> (<FIG>).

Oxidative coupling reaction can be performed in a high pressure batch reactor (e.g. <NUM>, Amar Equipment Pvt. ) equipped with a thermocouple, pressure gauge, rupture disk, and gas release valve.

In a typical experiment, <NUM> of Cu(OAc)<NUM> was dissolved in <NUM> of benzene. The solution was loaded into the autoclave reactor with catalyst (<NUM>) and sealed. The reactor was pressurized with N<NUM> to <NUM> bar and vented three times to remove any residual oxygen atmosphere. Finally the reactor was pressurized to <NUM> bars with ethylene, stirred (<NUM> rpm) and continued heating at <NUM>. The internal pressure reached <NUM> bar in heating up time of <NUM> minutes. The recorded reaction time started when the temperature reached the desired set-point. Once the reaction was completed the reactor was cool to room temperature (<NUM>). The liquid phase was analysed by GC (FID) and GC-MS at the end of the reaction. The results are summarized in table <NUM>. The conversion (Conv. ) refers to the percentage of ethylene that has been converted to anything, as a result of this process. The selectivity of styrene is the mole percentage of styrene retrieved in the product composition.

The same procedure and conditions as in Example <NUM> is applied to a variety of catalysts. The results are given in Table <NUM>.

Claim 1:
A process for the production of, optionally functionalized, styrene monomers comprising the steps:
(a) feeding benzene or functionalized benzene and ethylene, as well as a heterogeneous catalyst into a reactor forming a mixture of benzene or functionalized benzene and ethylene (the starting material), and
(b) heating said mixture and applying pressure to obtain crude styrene;
wherein the step (b) is carried out at a temperature ranging from and including <NUM> to <NUM>; and at a pressure (of ethylene) of between and including <NUM> bar and <NUM> bar;
wherein the heterogeneous catalyst is selected from graphene oxide (GO), sulfonated graphene oxide (SGO), reduced graphene oxide (rGO), multiwalled carbon nanotubes (CNT), graphitic carbon nitride(g-C<NUM>N<NUM>), sulfonated graphitic carbon nitride (S-g-C<NUM>N<NUM>), palladium doped reduced graphene oxide (Pd/rGO), palladium doped multiwalled carbon nanotubes (Pd/CNT), palladium doped graphitic carbon nitride (Pd/g-C<NUM>N<NUM>), boron-doped graphitic carbon nitride(B/g-C<NUM>N<NUM>, palladium doped sulfonated graphitic carbon nitride (Pd/S-g-C<NUM>N<NUM>), ceria doped sulfonated graphene oxide (Ce/SGO), ceria doped reduced graphene oxide (Ce/rGO), ceria doped multiwalled carbon nanotubes (Ce/CNT), ceria doped graphitic carbon nitride(Ce/g-C<NUM>N<NUM>), ceria doped sulfonated graphitic carbon nitride (Ce-S-g-C<NUM>N<NUM>), ruthenium doped reduced graphene oxide (Ru/rGO), ruthenium doped graphitic carbon nitride (Ru/g-C<NUM>N<NUM>), ruthenium doped multiwalled carbon nanotubes (Ru/CNT), ruthenium doped sulfonated graphitic carbon nitride(Ru/S-g-C<NUM>N<NUM>), platinum doped reduced graphene oxide (Pt/rGO), platinum doped graphitic carbon nitride (Pt/g-C<NUM>N<NUM>), platinum doped multiwalled carbon nanotubes (Pt/CNT) and platinum doped sulfonated graphitic carbon nitride (Pt/S-g-C<NUM>N<NUM>); and
wherein the functionalized benzene is a benzene substituted on the phenyl-ring with <NUM> to <NUM> substituents selected from C<NUM>-<NUM>-alkyl.