Ce-BASED CATALYST COMPOSITION FOR CO2 ACTIVATION FOR DI-ETHYL CARBONATE SYNTHESIS WITH 2-PICOLINAMIDE CO-GENERATION

Abstract

The invention relates to a Ce based catalysts, Ce-Zn mixed metal oxides (CZO) and Ce-Sm- Ru mixed metal oxides (CSRO), process for their preparation and their catalytic application in the synthesis of DEC from CO2 and ethanol at milder reaction conditions in the presence of 2- cyanopyridine.

Description

[0001] PT / 2025 / 16573

[0002] Ce-BASED CATALYST COMPOSITION FOR CO2ACTIVATION FOR DI-ETHYL CARBONATE SYNTHESIS WITH 2-PICOLINAMIDE CO-GENERATION

[0003] FIELD OF THE INVENTION

[0004] The present disclosure generally relates to Ce-based catalyst composition for CO2activation for di-ethyl carbonate (DEC) synthesis with 2-picolinamide co-generation. More particularly, the invention relates to a Ce based catalysts, Ce-Zn mixed metal oxides (CZO) and Ce-Sm-Ru mixed metal oxides (CSRO), process for their preparation and their catalytic application in the synthesis of DEC from CO2and ethanol at milder reaction conditions in the presence of 2-cyanopyridine.

[0005] BACKGROUND OF THE INVENTION

[0006] Diethyl carbonate (DEC) is a valuable compound for its versatile applications. The organic compound is applicable in various industries, such as pharmaceuticals, agro-chemicals, and as a solvent. Its synthesis from ethanol and CO2has gained significant attention due to the environmental and economic advantages associated with utilizing renewable resources and reducing greenhouse gas emissions. Wang, Y. et al. shows that the catalytic process for DEC synthesis offers a sustainable and efficient route to this valuable compound (Industrial & Engineering Chemistry Research, 58(27), 11693-11702, 2019). Li, Y et al. reports that the catalytic conversion of ethanol and CO2into DEC involves the activation of C-H and C-0 bonds through the use of suitable catalysts, leading to the formation of a valuable product with a reduced environmental footprint (Catalysts, 10(5), 521, 2020).

[0007] Various catalysts have been investigated for this process, including metal oxides, zeolites, and heterogeneous catalysts, each offering distinct advantages in terms of activity, selectivity, and stability. The development of efficient catalytic systems is crucial for optimizing the DEC synthesis process, ensuring high yields and minimizing by-products. Ganesh G. Giram et al. (New J. Chem., 2018, 42, 17546, DOI: 10.1039 / c8nj04090g') reported direct synthesis of diethyl carbonate (DEC) by carboxylation of ethanol with CO2by using commercial CeO2and Ceria (CeO2) with metal incorporation (Ce0.9M0.1O2-δ, where M = Zr, Al, Cu, Ni, and Zn). It reported 46.9% EtOH conversion and 45 % DEC selectivity. Masayoshi Honda et al. (Journal of Catalysis Volume 318, October 2014, Pages 95-107) reported commercial CeO2for the synthesis of organic carbonates. It reported combination system of CeO2- PT / 2025 / 16573

[0008] catalyzed carboxylation and 2-cyanopyridine hydration (CeO2+ 2-cyanopyridine system) for the direct synthesis of organic carbonates from CO2and alcohols. However, the catalyst system suffers with high reaction time and higher catalyst wt% loading. Keiichi Tomishige et.al (ChemSusChem 2023, 16, e202300768 (1 of 14), doi.org / 10.1002 / cssc.202300768) also studied dehydrating agents for the particular DEC synthesis. It reported comparative study between 2-furonitrile and 2-cyanopyridine as dehydrates in direct synthesis of dialkyl carbonates from CO2and alcohols over Cerium Oxide catalyst. However, DEC synthesis via CO2and ethanol becomes a more challenging reaction due to its low reactivity, high tendency of side reactions in the presence of dehydrating agent and catalyst durability issues. CO2 is thermodynamically stable molecule and thus high amount of energy is required to activate CO2.

[0009] The reported processes have several drawbacks including requiring high pressure conditions which makes the over all process expensive. The use of a homogeneous catalyst in such a process is necessary, so as to recover the catalyst from the reaction mass which is a challenging task as separation and recycling of catalyst adds more cost and complexity to the process. There are some reports with heterogeneous catalyst as well but with less activity and selectivity towards DEC and sometimes require high reaction time and temperature. Overall the conventional processes suffer from drawbacks such as excess catalyst wt. (%) loading, excess loading of dehydrating agent, addional inclusion of acetonitrile, which may further lead to separation issue and can increase total process cost. Therefore, there is a need in the art to develop an efficient, cost effective and scalable catalyst system and process for the preparation of di -ethyl carbonate (DEC).

[0010] OBJECTIVES OF THE INVENTION

[0011] An objective of the present invention is provide for a direct synthesis of diethyl carbonate (DEC).

[0012] Another object of the present invention is to develop a catalytic process for CO2utilization towards the synthesis of diethyl carbonate (DEC).

[0013] Another objective of the present invention is to provide for a Ce based catalyst for catalysing the direct synthesis of diethyl carbonate (DEC) by CO2 activation and co-generation of piconilamide. PT / 2025 / 16573

[0014] One more objective of the present invention is to provide a process for the preparation of Ce-based catalyst composition of formula (I).

[0015] Another objective of the present invention is to provide a process for the preparation of di-ethyl carbonate (DEC) with 2-picolinamide co-generation from CO2by using Ce-based catalyst composition of formula (I).

[0016] SUMMARY OF THE INVENTION

[0017] Accordingly, in order to accomplish an objective, the present invention provides a Ce-based catalyst composition of formula (I) for CO2activation for di-ethyl carbonate.

[0018] In an embodiment, the present invention provides a mixed metal oxide catalyst of formula (I) comprising:

[0019] AX(0.01-99) BY(0.01-99) CZ(0.0-25)

[0020] Formula (I)

[0021] wherein:

[0022] A is a catalyst support selected from an oxide of metal of a transition element or inner transition element selected from Ce, La, Sm, Pr, Gd, W and Ir;

[0023] X being the weight percentage of catalyst support varies from 0.01-99%;

[0024] B is a promoter selected from the oxides of divalent / trivalent transition metal or inner transition elements or mixture of their oxides; Y being the weight percentage of promoters varies from 0.01-99%;

[0025] C is a co-promoter selected from an oxide of transition element selected from Ru, Rh and Pd; and Z being the weight percentage of co-promoters varies from 0-25%, wherein the catalyst of formula lis a mixed phase catalyst comprising a combination of amorphous and crystalline phase.

[0026] In another embodiment, the Ce-based catalyst composition is selected from Ce-Zn mixed metal oxides (CZO) and Ce-Sm-Ru mixed metal oxides (CSRO). PT / 2025 / 16573

[0027] In yet another embodiment, the mixed metal oxide catalyst of the present invention is CeZnO with basic / acidic site ratio being 3.5 or CeSmRuO with basic / acidic site ratio being 1.

[0028] In an aspect, the present inevtion relates to a process of preparing a Ce-Zn oxide catalyst composition comprising the steps of:

[0029] a. preparing cerium nitrate solution A by adding ceria nitrate in a solvent and a zinc chloride solution B by adding zinc chloride in a solvent;

[0030] b. adding solution B as obtained drop wise into the solution A with continuous stirring;

[0031] c. adding NaOH solution into the reaction mixture of step b) and sonicating the resultant mixture;

[0032] d. digesting the obtained reaction mass obtained in step c);

[0033] e. filtering followed by washing with ethanolic solution, drying and calcining the obtained solid to obtain CZO catalyst.

[0034] In another aspect the present invention relates to a Ce-Sm-Ru oxide catalyst composition comprising the steps of:

[0035] a) preparing cerium nitrate solution A by adding ceria nitrate in a solvent and preparing solution B by adding samarium nitrate precursor solution in a ruthenium chloride solution;

[0036] b) adding solution B obtained drop wise into the solution A with continuous stirring and sonicating the resultant mixture;

[0037] c) digesting the obtained reaction mass at step b);

[0038] d) drying the slurry mass obtained at step c);

[0039] e) calcining the obtained solid cake as obtained in step d) to obtain CSRO catalyst.

[0040] In another aspect the present invention provides a process for the preparation of di-ethyl carbonate (DEC) and 2-picolinamide through CO2 activation by a mixed metal oxide catalyst of Formual I PT / 2025 / 16573

[0041] Ax (0.01-99) BY (0.01-99) Cz (0.0-25)

[0042] Formula (I)

[0043] with 2-picolinamide co-generation, wherein the process comprises the steps of:

[0044] a) charging ethanol and 2-cyanopyridine in a batch reactor and adding the catalyst in it;

[0045] b) purging the reaction mass obtained at step a) with CO2till saturation;

[0046] c) heating the reaction mass obtained at step b) and maintaining at a temperature in the range of 110-150°C.

[0047] In an embodiment, the Ce oxide support acts as a reaction initiator which adsorbs and dissociates water molecule and forming Ce-hydroxyl complex and a Ce-nitrile complex that further initiates the reaction. Sm / Zn and Ru oxides act as a promoter and co-promoter for the reaction as they provide acidic and basic sites for the reactant adsorption.

[0048] BRIEF DESCRIPTION OF DRAWING

[0049] Figure 1 represents N2 -adsorption-desorption isotherm: Figurela shows N2 -adsorptiondesorption isotherm for CSRO and figure lb shows N2 -adsorption-desorption isotherm for CSRO & CZO.

[0050] Figure 2 illustrates XRD spectrum for CSRO fresh and spent catalyst.

[0051] Figure 3 represents FE-SEM images: Figure 3a: FE-SEM images for CSRO-fresh catalyst and Figure 3b: FE-SEM images for CSRO-spent catalyst.

[0052] Figure 4 represents SEM-EDAX profile: 4a) SEM-EDAX profile of CSRO-Fresh catalyst; 4b) SEM-EDAX profile of CSRO-Spent catalyst.

[0053] Figure 5 represents SEM-elemental analysis of CSRO-Fresh catalyst.

[0054] Figure 6 represents XRD spectrum for CZO fresh and spent catalyst.

[0055] Figure 7 represents FESEM images: 7a) FE-SEM images for CZO-fresh catalyst; 7b) FE-SEM images for CZO-spent catalyst. PT / 2025 / 16573

[0056] Figure 8 represents SEM-EDAX profile: 8a) SEM-EDAX profile of CZO-Fresh catalyst; 8b) SEM-EDAX profile of CZO-spent catalyst.

[0057] Figure 9 represents SEM-elemental analysis of CZO-Fresh catalyst.

[0058] Figure 10.a represents CZO phase identification data, 10.b. representative phase idenfication for ceria oxide phase formation in CZO catalyst.

[0059] Figure 11.a represents CSRO phase identification data,11.b-c representative phase idenfication for ceria oxide and samarium oxide phase formations in CSRO catalyst, respectivly.

[0060] Figure 12 represents 12a) HR-TEM analysis of CSRO-single phase (up) and CSRO-mixed phases (down); 12b) HR-TEM analysis of CZO with single and mixed phases; 12c) (left) XPS analysis of CSRO and 12d) (right) XPS analysis of CZO catalyst.

[0061] Figure 13 represents EtOH: CO2 variation a) EtOH: CO2 variation by using CZO catalyst for EtOH conversion, DEC selectivity and yield; b) EtOH: CO2 variation by using CZO catalyst for 2-cp conversion, 2-PA selectivity, and yield.

[0062] Figure 14 represents catalyst loading (wt.%) variation with CZO catalyst; a) Catalyst (wt. %) loading variation by using CZO catalyst for EtOH conversion, DEC selectivity and yield; b) Catalyst (wt. %) loading variation by using CZO catalyst for 2-cp conversion, 2-PA selectivity and yield; c) Catalyst (wt. %) loading variation by using CZO catalyst for EtOH conversion, Acetone and MeOH selectivity.

[0063] Figure 15 represents CO2: EtOH variation: a) CO2: EtOH variation by using CZO catalyst for EtOH conversion, DEC selectivity and yield; b) CO2: EtOH variation by using CZO catalyst for 2-cp conversion, 2-PA selectivity, and yield; c) CO2: EtOH variation by using CZO catalyst for EtOH conversion, acetone, and ethyl methyl carbonate (EMC) selectivity and their yield respectively; d) Summarized effect of CZE (mol ratio) onto EtOH conversion and DEC selectivity.

[0064] Figure 16 represents a) Ru effect study by using catalyst with Ru (CSRO) and without Ru (CSO) comparative study for EtOH conversion, DEC selectivity and yield; b) Ru effect study PT / 2025 / 16573

[0065] by using catalyst with Ru (CSRO) and without Ru (CSO) comparative study for 2-Cp conversion and 2-PA selectivity; c) Ru effect study by using catalyst with Ru (CSRO) and without Ru (CSO) comparative study for acetone and MeOH selectivity.

[0066] Figure 17 represents Screening of dehydrating agents.

[0067] Figure 18 represents Schematic figure of batch reactor used comprising 1=CO2 feed, 2= Heating element, 3= Stirrer blade, 4= Vent, 5= Pressure gauge (PG)

[0068] DETAILED DESCRIPTION OF THE INVENTION

[0069] For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are delineated here. These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0070] ‘Catalyst support’ refers to any of the oxide components of a mixed metal oxide catalyst which are required to disperse the active components to increase their surface area, enhance the catalyst's stability by preventing active sites from agglomerating, and provide enhanced chemical interaction.

[0071] ‘Promoter’ refers to chemical species added in small amounts to a main catalyst to improve its performance, which may itself not have significant catalytic activity. Promoters increase a catalyst's efficiency by physically and chemically altering it to increase surface area, prevent deactivation, or create more active sites for the reaction to occur. They can also modify the catalyst's structure to create more surface area, which provides more locations for reactions to take place.

[0072] ‘Co-promoters’ refer to additional elements, added to a base mixed oxide to enhance its catalytic activity and stability. They work by creating more active sites, increasing the mobility of lattice oxygen, improving catalyst reducibility, and fine-tuning the electronic properties of the catalyst PT / 2025 / 16573

[0073] ‘Mixed-phase metal oxide catalysts’ refer to heterogeneous catalysts that combine two or more different oxide phases, having properties at their interface resulting in enhanced catalytic performance, such as higher activity and stability, compared to using a single oxide phase.

[0074] The present invention relates to a mixed metal oxide catalyst composition of formula (I) for diethyl carbonate synthesis. In an embodiment, the present invention provides a mixed metal oxide catalyst composition of formula (I), represented as:

[0075] AX (0.01-99)BY(0.01-99)CZ(0.00-25)

[0076] Formula (I)

[0077] wherein:

[0078] A is a catalyst support selected from an oxide of metal of a transition element or inner transition element selected from Ce, La, Sm, Pr, Gd, W and Ir;

[0079] X being the weight percentage of catalyst support varies from 0.01-99%;

[0080] B is a promoter selected from the oxides of divalent / trivalent transition metal or inner transition elements or mixture of their oxides; Y being the weight percentage of promoters varies from 0.01-99%;

[0081] C is a co-promoter selected from an oxide of transition element selected from Ru, Rh and Pd; and Z being the weight percentage of co-promoters varies from 0-25%, wherein the catalyst of formula lis a mixed phase catalyst comprising a combination of amorphous and crystalline phase.

[0082] In an embodiment, the mixed metal oxide catalyst of formula I comprises promoter B selected from an oxide of an element selected from Zn, La, Sm, Gd, Pr, Nd or a mixture of oxides thereof. Specifically the mixed metal oxide catalyst composition is selected from Ce-Zn mixed metal oxides (CZO) and Ce-Sm-Ru mixed metal oxides (CSRO).

[0083] In another embodiment the CSRO catalyst has a ratio of 0.972 for amorphous (49.28%) to crystalline (50.72 %) phase. In another embodiment the CZO catalyst, the ratio of 0.9845 for amorphous (49.61%) to crystalline (50.39%) phase. PT / 2025 / 16573

[0084] In yet another embodiment, in Ce-based catalyst composition, the oxide weight percentage of Ce is in the range of 50-98%, the weight percentage of Zn / Sm is in the range of 1-20% and the weight percentage of Ru is in the range of 0.1-10%.

[0085] In an embodiment, the BET surface area of the CZO catalyst is in the range of 120-125 m² / g and BET surface area of CSRO is in the range of 128-133 m² / g. The catalysts of the present invention such as CSRO and CZO are porous in nature, resulting in more surface site for reaction. In an embodiment, the pore size of the CSRO catalyst is in the range of 0.7-1.0 nm and pore size of CZO catalyst is in the range of 0.3 -0.5 nm. The total pore volume of CSRO catalyst is in the range of 0.3-0.5 cc / g and pore volume of CZO catalyst is in the range of 0.1- 0.3 cc / g.

[0086] In an embodiment, the crystal size of CSRO catalyst is in the range of 8-10 nm and crsytal size of CZO catalyst is in the range of 7-10 nm.

[0087] In another embodiment, the CSRO and CZO are mixed metal oxides of Formual I comprising a combination of amorphous and crystalline phase. The mixed metal oxides of Formula I form mixed phases of amorphous and crystalline of the catalyst, where amorphous phase of the the oxide catalyst supports for better interaction of reactants on catalytic surface / sites.

[0088] In an embodiment, the mixed metal oxide catalysts of the present invention CSRO and CZO are amphoteric in nature as it has an acidity of 0.43 and a basicity of 0.41 mmol / respectively. This amphoteric nature of catalyst enables the high conversion of ethyl alcohol and (EtOH) and diethyl carbonate (DEC) selectivity.

[0089] The basic / acidic site ratio on a mixed oxide catalyst is adjusted by controlling the proportion of its constituent oxides and their synthesis method. A higher ratio of basic oxides to acidic oxides results in a more basic catalyst, and vice versa. A mixed oxide of can be tuned to have different ratios, which in turn influences its performance in a specific reaction. The overall ratio of basic to acidic components is reflective of the catalyst's surface properties. The process of preparing the mixed oxide may also alter the surface area and the strength of the active sites. The metal oxide catalysts of the present invention CSRO and CZO have an appropriate basic / acidic ratio (B / A), where the B / A ratio for CSRO and CZO are near 1 and 3.5, respectively. The B / A ratio is the key parameter for DEC synthesis. The catalyst is tuned for its basic / acidic site ratio in such a way that it can activate highly stable CO2 molecule at the same time it will help to increase DEC selectivity by restricting side reactions. PT / 2025 / 16573

[0090] In an embodiment, XPS (X-ray Photoelectron Spectroscopy) analysis of CSRO and CZO catalyst shows that these catalyst have Ce3+, Ce4+, Sm3+, Ru3+,Ru4+and Zn2+oxidation states, which evidences the oxygen vacancies on each metal, which further could be the key parameter for DEC synthesis by activating substrate molecules.

[0091] In another aspect, the present invention provides a process for the preparation of Ce-based catalyst composition, wherein Ce-Zn mixed metal oxides (CZO) catalyst composition is prepared by co-precipitation method. The process comprises the steps of:

[0092] a) preparing cerium nitrate solution A by adding ceria nitrate in a solvent and a zinc chloride solution B by adding zinc chloride in a solvent;

[0093] b) adding solution B as obtained drop wise into the solution A with continuous stirring;

[0094] c) adding NaOH solution into the reaction mixture of step b) and sonicating the resultant mixture;

[0095] d) digesting the obtained reaction mass obtained in step c);

[0096] e) filtering followed by washing with ethanolic solution, drying and calcining the obtained solid to obtain CZO catalyst.

[0097] In an embodiment, the process comprises adding solution B obtained in step b) drop wise into the solution A obtained in step a) under stirring at a temperature in the range of 55-60 °C; adding 7.5 M NaOH solution into the reaction mixture of step b); sonicating the resultant mixture obtained at step c) further for 3-4 hr under sonication frequency of 30-35Hz; digesting the obtained reaction mass at step d) further at a temperature in the range of 80-100 °C for a time period in the range of 2-4 hr; filtering, washing with ethanolic solution (25.% v / v) till pH 7 drying the obtained solid at a temperature in the range of 120-130 °C for a time period in the range of 4-6 hr; and calcining the obtained solid further at a temperature in the range of 600-700 °C for a time period in the range of 5-6 hr with the ramp rate of 50°C ramp rate to obtain CZO catalyst.

[0098] The solvent is selected from water, methanol, ethanol, and mixtures therefrom. PT / 2025 / 16573

[0099] In another aspect, the present invention provides a process for the preparation of Ce-based catalyst composition, wherein Ce-Sm-Ru mixed metal oxides (CSRO) is prepared by wet impregnation method. The process comprises the steps of:

[0100] a) preparing cerium nitrate solution A by adding ceria nitrate in a solvent and preparing solution B by adding samarium nitrate precursor solution in a ruthenium chloride solution;

[0101] b) adding solution B obtained drop wise into the solution A with continuous stirring and sonicating the resultant mixture;

[0102] c) digesting the obtained reaction mass at step b);

[0103] d) drying the slurry mass obtained at step c);

[0104] e) calcining the obtained solid cake as obtained in step d) to obtain CSRO catalyst.

[0105] In an embodiment, the process of adding solution B obtained at step b) drop wise into the solution A is done via the wet impregnation process under stirring at a temperature in the range of 55-60 °C; sonicating the resultant mixture obtained at step b) further for 3-4 hr under sonication frequency of 30-35Hz; digesting the obtained reaction mass at step c) further at a temperature in the range of 80-100 °C for a time period in the range of 2-4 hr; drying the obtained slurry mass at step d) at a temperature in the range of 120-130 °C for a time period in the range of 4-6 hr to obtain dry cake; and calcining the obtained solid further at a temperature in the range of 600-700 °C for a time period in the range of 5-6 hr with the ramp rate of 10°C ramp rate to obtain CSRO catalyst.

[0106] The solvent is selected from water, methanol, ethanol, and mixtures therefrom.

[0107] In an aspect, the present invention provides a process for the preparation of di-ethyl carbonate (DEC) and 2-picolinamide through CO2 activation by a mixed metal oxide catalyst of Formual I

[0108] AX(0.01-99) BY(0.01-99) CZ(0.0-25)

[0109] Formula (I)

[0110] wherein: PT / 2025 / 16573

[0111] A is a catalyst support selected from an oxide of metal of a transition element or inner transition element selected from Ce, La, Sm, Pr, Gd, W and Ir;

[0112] X being the weight percentage of catalyst support varies from 0.01-99%;

[0113] B is a promoter selected from the oxides of divalent / trivalent transition metal or inner transition elements or mixture of their oxides;

[0114] Y being the weight percentage of promoters varies from 0.01-99%;

[0115] C is a co-promoter selected from an oxide of transition element selected from Ru, Rh and Pd; and

[0116] Z being the weight percentage of co-promoters varies from 0-25%,

[0117] wherein the catalyst of formula I is a mixed phase catalyst comprising a combination of amorphous and crystalline phase;

[0118] the process comprising the steps of:

[0119] a) charging ethanol and 2-cyanopyridine in a batch reactor and adding the catalyst of Formula (I) in it;

[0120] b) purging the reaction mass obtained at step a) with CO2till saturation;

[0121] c) heating the reaction mass obtained at step b) and maintaining at a temperature in the range of 110-150°C for a time period in the range of 0.5-6 hr; and

[0122] d) diluting the reaction mass obtained at step c) with a solvent to obtain diethyl carbonate.

[0123] The obtained product in the process then analyzed via GC-MS and GC for qualitative and quantitative results.

[0124] In an embodiment of the process of preparing, catalyst is selected from CZO and CSRO. In another embodiment, mole ratio of ethanol to 2-cyanopyridine is in the range of 1:0.25-l: 1. In yet another embodiment, catalyst loading is done in the range of 2.5-20 wt%

[0125] In yet another embodiment, mole ratio of carbon dioxide and ethanol is in the range of 0.5-1.51:1-2:3. PT / 2025 / 16573

[0126] Preferably in an embodiment the catalyst is mixed metal oxide of CeZnO having a DEC yield of around 38% with 51% ethanol (EtOH) conversion at 120°C, for 3hr of reaction time. The ethanol to CO2 (mol) and EtOH-2-cyanopyridine (mol) is 2:1 ratio by loading 10wt.% (EtOH) of catalyst.

[0127] Preferably, in another embodiment the catalyst is mixed metal oxide of Ce-Sm-Ru oxide having a DEC yield of around 40% with 54.8% EtOH conversion at 140°C, for 3hr of reaction time. The ethanol to CO2 (mol) and EtOH-2 -cyanopyridine (mol) were 2:1 ratio by loading 10wt.% (EtOH) of catalyst.

[0128] In another embodiment, the reaction equilibrium is enhanced by trapping water (generated) with 2-cyanopyridine, forming 2-picolinamide (2 -PA).

[0129] In another embodiment, the reaction temperature at step c) is controlled by a KLB controller.

[0130] In another embodiment, the solvent at step c) is selected from polar solvent selected from methanol, propanol, acetonitrile, dimethyl sulfoxide, dimethyl formamide, dichloromethane.

[0131] Ce oxide support acts as a reaction initiator which adsorbs and dissociates water molecule and forms Ce-hydroxyl complex and at the same time forms a Ce-nitrile complex that further initiates the reaction. Sm / Zn and Ru oxides act as a promoter and co-promoter for the reaction as they provide acidic and basic sites for the reactant adsorption.

[0132] EXAMPLES

[0133] Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

[0134] Example 1: Synthesis procedure Ce-Zn (CZO) catalyst:

[0135] The catalyst was synthesised by co-preci pi tati on method where ‘Ce nitrate’ precursor solution was prepared by adding 32.6 gm ceria nitrate in 50 ml water (solution A), whereas Zn chloride precursor solution was prepared by adding 0.416 gm Zn chloride in 25 ml water (solution B).

[0136] Solution B was added drop wise under stirring in solution A which was heated up to 60°C and then precipitates were formed by adding 7.5 M NaOH solution. The resultant mixture was PT / 2025 / 16573

[0137] further sonicated for 4 hr. under sonication frequency of 30-35Hz. The sonicated reaction mass was further kept under digestion for 2-4 hrs at 80-100’C. After digestion the resultant slurry mass was filtered to get a solid powder in the form of cake on filter paper. The cake obtained was further washed using ethanolic solution (approx. 25 v / v %) to remove excess NaOH and 5 adjust the neutral pH. This washed cake was further dried at 120°C for 4-6 hrs and then calcined at 600°C with the ramp rate of 50°C ramp rate and holding time of 5 hrs. After calcination, the catalyst was collected and used for reactions, denoted as CZO.

[0138] Example 2: Synthesis procedure Ce. Sm. Ru (CSRO) catalyst:

[0139] The catalyst was synthesised by wet impregnation method where£Ce nitrate’ precursor solution 10 was prepared by adding 22.71 gm ceria nitrate in 100 ml water (solution A), whereas Sm nitrate precursor solution was prepared by adding 2.43 gm Sm nitrate as promoter in Ru chloride solution (0.083 gm RuCh) as co-promoter in 10 ml water (solution B). Solution B was added drop wise under stirring in solution A which was heated up to 60°C and then a homogenous liquid phase in dark brown color were formed. The resultant mixture was further sonicated for 15 4 hr. under sonication frequency of 30-35 Hz. The sonicated reaction mass was further kept under digestion for 2-4 hrs at 80-100°C. After digestion the resultant slurry mass was dried in oven at 120°C for 4-6 hrs (till get dried), which resulted in a dried cake formation, which further was calcined at 600°C with the ramp rate of 10“C ramp rate and holding time of 5-6 hrs. After calcination the catalyst was collected and used for reactions, denoted as CSRO.

[0140] 20 Physicochemical characterizations of the CSRO and CZO catalyst:

[0141] BET analysis depicts that CSRO and CZO are porous in nature, resulting more surface site for reaction (Table-1). BET adsorption isotherms (fig la-lb) for both catalyst is type IV with relative pressure p / p° ≈ 0.150 and 0.225 respectively, can be attributed to mono and multi both layer adsorption which signifies that there are larger number of pores on the catalyst surface.

[0142] 25 Table.l Physicochemical characterization data of CSRO and CZO catalyst.

[0143] Catalyst BET-SA Average Total Crystal Unit cell D- Total Total Sr.

[0144] (m2 / g) pore size pore size parameters spacing acidity basicity no.

[0145] (nm) volume (nm) (nm) (nm) (mmol / g) (mmol / g)

[0146] (cc / g)

[0147]

[0148] PT / 2025 / 16573

[0149] 123.46 8.68 0.431 9.11 0.538 0.311 0.43 0.41 SRO

[0150] 130.53 4.25 0.203 8.59 0.537 0.310 0.12 0.42 ZO

[0151]

[0152] In an embodiment, CO2 / NH3-TPD analysis of CSRO and CZO catalyst showed that these catalyst have an appropriate basic / acidic site ratio, where B / A site ratio for CSRO and CZO are near 1 and 3.5 respectively. (Table-1), which is observed to play a key role in efficient EtOH conversion and DEC selectivity. Thus the appropriate B / A ratio is a key parameter for DEC synthesis.

[0153] Figure la and lb (wherein up direction of arrows show adsorption while down direction of arrows show desorption), represents the N₂ adsorption-desorption isotherms of CSRO and CZO catalyst respectively at -196°C and the pore size distribution (PSD) according the Barrett- Joyner-Halenda (BJH) method for the both catalyst samples. According to IUPAC, it classifies that, the shapes of the adsorption isotherms for samples are type IV for CSRO and CZO catalyst. The hysteresis loop H2 type for CSRO and CZO catalyst are observed. This shows that CSRO and CZO catalyst is associated with capillary condensation as they are meso porous. It is observed that the initial part of the isotherm where the relative pressure p / p° ≈ 0.150 and 0.225 of CSRO and CZO respectively, can be attributed to mono and multi both layer adsorption which signifies that there are large number of pores on the catalyst surface. Thus the isotherm shape directly confirms that both catalysts are mesoporous (with pores ranging from 2 to 50 nm) and undergo capillary condensation within their pore structures. Specific surface area (S- BET), total pore volume and average pore size for CSRO and CZO are mentioned in Table-1.

[0154] XRD analysis of CSRO and CZO depicts formation of mixed phases of amorphous and crystalline nature of catalyst, where amorphous phase of catalyst could be observed to provide support for better interaction of reactants on catalytic surface / sites (Table-1, figure 2 and figure 6 respectively). The present invention discloses the oxide phase formation for Ce. Sm. Ru oxide (CSRO) [Figure 11 a-c] and Ce -Zn oxide (CZO) [FigurelOa-b] as mixed metal oxide (MMO) catalyst and the formation of pure CeO? oxide phase which represents the multiphase formation on catalyst surface. Figure.10. a. and figure 11. a. are representative of mixed phase of formed oxides of each metal present in catalyst whereas figure lO.b and 1 l.b is individual representation for formation of Ceria oxide in both catalyst respectively. Figure.11,c. is representing the presence of samarium oxide formation in CSRO catalyst, which PT / 2025 / 16573

[0155] represents the multi-phase formation and alone metal oxide formation on catalyst surface. The formation of the crystallographic structure for both catalyst is cubic, having Fm-3m space group.

[0156] Elemental mapping results shows even distribution of metal species on catalyst surface, which shows the homogenous formation of mixed metal oxide surface of the catalyst, (figure 5 for CSRO catalyst and figure 9 for CZO catalyst). FE-SEM result indicate the irregular morphology of CSRO-fresh and deposition of reaction materials (RM) on spent catalyst (figure 3a-3b) FE-SEM analysis of CZO-fresh catalyst results indicate the rod and sheet type of morphologies which got changed in spent sample due to deposition of RM (figure 7a-7b). This clearly signifies the ability of the mixed metal oxide catalyst to free up active sites after hydration of 2-cyanopyridine for further activation of carbon dioxide for obtaining DEC. SEM-EDAX analysis of for fresh and spent of CSRO and CZO catalyst showed the absence of any other impurities in the catalyst compositions (figure 4a-4b, table-2 and figure 8a-8b, table-3, respectively). This establishes that the catalysts are the purest form of catalyst surface formation.

[0157] Table.2. SEM-EDAX analysis of CSRO-Fresh & CSRO-Spent catalyst

[0158] Sr.

[0159] Catalyst ID Element wt. % Element At %

[0160] no.

[0161] Ce Sm Ru O Ce Sm Ru O 1. CSRO-Fresh 58.57 18.31 1.34 21.78 21.83 6.36 0.69 71.11

[0162] 2. CSRO Spent 70.13 15.37 0.06 14.44 33.24 6.79 0.06 59.94

[0163]

[0164] Table.3. SEM-EDAX analysis of CZO-Fresh & CZO-Spent catalyst

[0165] Sr. no. Catalyst ID Element wt. % Element At %

[0166] Ce Zn O Ce Zn O 3. CZO-Fresh 73.24 1.45 25.31 24.58 1.04 74.38 4. CZO Spent 78.76 1.16 20.08 30.63 0.96 68.40

[0167]

[0168] PT / 2025 / 16573

[0169] The HR-TEM screening data supports the XRD phase identification studies by demonstrating the development of CeO₂, Sm₂O₃, and RuO₂ as single and mixed metal oxides in the CSRO (figure 12a) catalyst and in the CZO catalyst (figure 12b). The d-spacing (nm) values are observed to be 0.28, 0.375 for single phase and 0.379, 0.298, and 0.32 for multi-phase forms of (Ce. Sm. Ru) oxides and 0.298 for single phase, 0.291 and 0.198 for mixed metal phase formation in the case of CZO oxides. These illustrate the formation of homogenous solid solution. One cause for the shift in the d-spacing values for both catalysts is the metal-in-cooperation of the co-promoter and promoter in the host (support) ion lattices. The XPS analysis of CSRO (figure 12c) and CZO (figure 12d) catalysts revealed the presence and formation of Ce3+, Ce4+, Ru+, Ru+, Sm+, and Zn+respectively.

[0170] Example 3: General process for the synthesis of di-ethyl carbonate (DEC)

[0171] EtOH 6.3 ml (2.0 mol) and 2-cyanopyridine 5.5 gm(l mol) was charged in a sealed 50 ml batch reactor. 10 wt% catalyst was added in it. CO2 (1.0 mol) was purged to fill the reactor. CO2 was adsorbed onto the catalyst. Once saturated, the reaction temperature was set at 120°C, when CZO catalyst was used and at 140°C, when CSRO catalyst was used. Reaction equilibrium was enhanced by trapping water (generated) with 2-cyanopyridine, forming 2-picolinamide (2 -PA).

[0172] Reaction was maintained at above set temperature for 3 hr. The reaction temperature was controlled by a KLB controller. The final reaction mass was diluted in ACN as solvent and analysed via GC-MS (Gas Chromatography-Mass Spectrometry) and GC (Gas Chromatography) for qualitative and quantitative results.

[0173] Catalytic screening for DEC sythesis:

[0174] Among all screened catalysts, CSRO and CZO showed the best catalytic performance at 140°C and at 120°C respectively for DEC synthesis. The CSRO and CZO catalyst showed DEC yield of 39.84 % and 37.7% respectively which is the best among all the screened catalysts. Table 4 below shows the summarised results of comparative analysis of catalyst screening:

[0175] Table.4 Result table for catalyst screening for DEC synthesis from CO2 and EtOH.

[0176] GC-analysis report

[0177] Sr. Reaction EtOH DEC DEC 2- Acetone Catalyst* 2-PASel. MeOH No. temp. conv. Sei. Yield cyanopyri sei.

[0178] (%) Sei. (%) (°C) (%) (%) (%) dine (%)

[0179]

[0180] PT / 2025 / 16573

[0181] conv.

[0182] (%)

[0183] CeO2*

[0184] 1. 140 23.31 35.21 8.21 44.7 32.9 0 0 (reported)

[0185] CSRO

[0186] 2. 140 54.8 72.7 39.84 90.2 23.8 0.94 0 (inventive)

[0187] 3. CLR* 140 20.75 88.46 18.35 34.13 44.2 1.12 0.0

[0188] CZO

[0189] 4. 120 51 73.8 37.7 90.3 27.3 1.6 0 (inventive)

[0190]

[0191] Reaction conditions: - Reaction time 3hr, EtOH: CO2 (E: C) (mol ratio) -2:1, EtOH-2-Cyanopyridine (mol ratio) -2:1, catalyst 10 wt. (%) loading w.r.t. EtOH wt. (gm) loaded.

[0192] Note-50 mL batch reactor (Parr, SS) was used for this entire screening studies.

[0193] *References:

[0194] 1- Wang, Y., Zhang, X., Su, Y., etal. (2019). Catalytic Synthesis of Diethyl Carbonate from Ethanol and CO2 over La-Doped CeO2 Catalyst. Industrial & Engineering Chemistry Research, 58(27), 11693-11702.

[0195] 3-Li, T., & Xu, J. (2017). Recent advances in the synthesis of glycerol carbonate from glycerol. Green Chemistry, 19(22), 5352-5376. doi: 10.1039 / c7gc01997f

[0196] As shown in the experimental data in Table 4 above, the DEC synthesis process in the presence of CSRO catalyst at 140°C showed better DEC selectivity. It is also observed that inventive example (2) with CSRO catalyst, sees a combination of significant DEC yield as well as high cyanopyridine conversion indicating significant removal of water form in the reaction which in turn results in the formation of 2-piconilamide favouring more DEC yield. The experimental results shows that optimum temperature for CZO catalyst is 120°C. The yield of DEC was observed 37.7% thereby seeing a combination of significant DEC yield as well as high cyanopyridine conversion even at a lower temperature of 120°C indicating significant removal of water form the reaction which in turn results in the formation of 2-piconilamide favouring more DEC yield. PT / 2025 / 16573

[0197] It can be further observed from Table 4 that at a reaction time of 3 hrs, maximum DEC yield (37.7%) and 2-PA yield (24.65%) are obtained using CZO catalyst. It may be concluded that if the reaction time is further increased, it reduces the product selectivity drastically.

[0198] The experimental results are as shown in figur 13a and figure 13b The data shows that the optimum ethanol (EtOH): carbon dioxide (CO2) ratio for the DEC synthesis reaction is 2. DEC as well as 2-Picolinamide selectivity goes on reducing as the mole ratio of EtOH: CO2 was increased. This may be due to the EtOH cracking and other side reactions kinetically more dominant in presence of excess EtOH. The side products formed due to such reactions limit the formation of water and so 2-PA yield also reduced at higher EtOH ratios.

[0199] The experimental results are shown in figure 14a-14c for catalyst loading (wt %) variation with CZO catalyst. Figure 14a represents catalyst (wt. %) loading variation by using CZO catalyst for EtOH conversion, DEC selectivity and yield. Figure 14b represents catalyst (wt. %) loading variation by using CZO catalyst for 2 -cyanopyridine conversion, 2-PA selectivity and yield. Figure 14c represents catalyst (wt. %) loading variation by using CZO catalyst for EtOH conversion, Acetone and MeOH selectivity.

[0200] The experimental results shown in figure 15a and 15b, evidence that the optimum CO2: EtOH ratio for this reaction is 0.5. DEC yield of 37.63% is observed at this reaction condition. DEC as well as 2-PA selectivity was reduced as the mole ratio of CO2: EtOH was increased. This data shows that the optimum ratio required for this reaction is matching with stoichiometry. 2 mol EtOH per 1 mol of CO2 is the optimum condition where highest DEC yield is noted. The side products formed due to such reactions conditions where ratios are different than stoichiometric requirements promotes the side reaction and thus limits the formation of water. Thus the 2-PA yield was also reduced at higher CO2 ratios. Similar results can be seen in figure 15c and 15d.

[0201] The above plots indicated that higher CO2 pressure promoted the side reaction thus resulting in low yield of DEC.

[0202] The comparative screening results of with and w / o Ru, clearly shows that Ru helps to improve the DEC and 2-PA yield and plays a crucial role as co-promoter for the reactions. It is also evident that Ru helps to activate CO2 and thus promote DEC synthesis reaction. The results show that more DEC formation means more H2O formation and hence subsequent 2-PA yield also improved in the reactions where Ru is used as promoter. In short, CSRO catalyst has Ru's PT / 2025 / 16573

[0203] Lewis acidic site which activates 2 -cyanopyridine and CO2, enhancing reaction reactivity conversion towards 2-PA and DEC synthesis respectively when compared to catalysts w / o Ru (CSO) (figure 16a and 16b).

[0204] Different dehydrating agents screening was studied for the targeted molecule synthesis and the results are as shown above (figure 17). The experimental findings reveals that the 2-cyanopyridine is the best dehydrating agent as it also act as co-promoter and activate CO2 by forming a five membered ring intermediate to form DEC and 2-PA selectively at optimum reaction conditions.

[0205] ADVANTAGES OF THE INVENTION

[0206] • An eco-environmental friendly and novel Ce based catalyst composition is exemplified [Ce-Zn mixed metal oxides (CZO) and Ce-Sm-Ru mixed metal oxides (CSRO)] which reports good catalytic activities ensuring higher DEC yield at milder reaction temperature.

[0207] • An efficient water trap (2-cyanopyridine) is also demonstrated using the catalyst of the present invention which helps to remove formed water during reaction and thus pushes the reaction equilibrium towards product side resulting in high conversion.

[0208] • The synthesized catalysts have been successfully tested for CO2 activation for DEC synthesis. The same catalyst has a tendency to activate hydration reaction using 2- cyanopyridine as dehydrating agent by converting 90.3% and 90.2% 2-Cp during the in- situ synthesis reaction respectively.

[0209] • Heterogeneous catalyst composition of the present invention can be easily separated from reaction mass and is reproducible.

[0210] • The synthesized catalysts as per the present invention are heterogeneous, green, amphoteric, working at milder reaction condition(s), and cheap and can also be scaled-up at industrial interest.

Claims

PT / 2025 / 16573WE CLAIM:

1. A mixed metal oxide catalyst of formula (I) comprising:AX(0.01-99) BY(0.01-99) CZ(0.0-25)Formula (I)wherein:A is a catalyst support selected from an oxide of metal of a transition element or inner transition element selected from Ce, La, Sm, Pr, Gd, W and Ir;X being the weight percentage of catalyst support varies from 0.01-99%;B is a promoter selected from the oxides of divalent / trivalent transition metal or inner transition elements or mixture of their oxides;Y being the weight percentage of promoters varies from 0.01-99%;C is a co-promoter selected from an oxide of transition element selected from Ru, Rh and Pd; andZ being the weight percentage of co-promoters varies from 0-25%,wherein the catalyst of formula l is a mixed phase catalyst comprising a combination of amorphous and crystalline phase.

2. The mixed metal oxide catalyst of formula I as claimed in claim 1 wherein the promoter B is an oxide of an element selected from Zn, La, Sm, Gd, Pr, Nd or a mixture of oxides thereof.

3. The mixed metal oxide catalyst as claimed in claim 1 wherein the mixed metal oxide catalyst is CeZnO with basic / acidic site ratio is 3.5.

4. The mixed metal oxide catalyst as claimed in claim 1 wherein the mixed metal oxide catalyst is CeSmRuO with basic / acidic site ratio is 1.

5. A process of preparing a Ce-Zn oxide catalyst composition as claimed in claim 3 comprising the steps of:PT / 2025 / 16573a) preparing cerium nitrate solution A by adding ceria nitrate in a solvent and a zinc chloride solution B by adding zinc chloride in a solvent;b) adding solution B as obtained drop wise into the solution A with continuous stirring;c) adding NaOH solution into the reaction mixture of step b) and sonicating the resultant mixture;d) digesting the obtained reaction mass obtained in step c);e) filtering followed by washing with ethanolic solution, drying and calcining the obtained solid to obtain CZO catalyst.

6. A process of preparing a Ce-Sm-Ru oxide catalyst composition as claimed in claim 4 comprising the steps of:a) preparing cerium nitrate solution A by adding ceria nitrate in a solvent and preparing solution B by adding samarium nitrate precursor solution in a ruthenium chloride solution;b) adding solution B obtained drop wise into the solution A with continuous stirring and sonicating the resultant mixture;c) digesting the obtained reaction mass at step b);d) drying the slurry mass obtained at step c);e) calcining the obtained solid cake as obtained in step d) to obtain CSRO catalyst.

7. A process for the co-production of diethyl carbonate (DEC) and 2-picolinamide using mixed metal oxide catalyst of Formula IAX(0.01-99) BY(0.01-99) CZ(0.0-25)Formula (I)wherein:A is a catalyst support selected from an oxide of metal of a transition element or inner transition element selected from Ce, La, Sm, Pr, Gd, W and Ir;PT / 2025 / 16573X being the weight percentage of catalyst support varies from 0.01-99%;B is a promoter selected from the oxides of divalent / trivalent transition metal or inner transition elements or mixture of their oxides;Y being the weight percentage of promoters varies from 0.01-99%;C is a co-promoter selected from an oxide of transition element selected from Ru, Rh and Pd; andZ being the weight percentage of co-promoters varies from 0-25%,wherein the catalyst of formula I is a mixed phase catalyst comprising a combination of amorphous and crystalline phase;the process comprising the steps of:a) charging ethanol and 2-cyanopyridine in a batch reactor and adding the mixed metal oxide catalyst of Formula I;b) purging the reaction mass obtained at step a) with CO2till saturation;c) heating the reaction mass obtained at step b) and maintaining at a temperature in the range of 110-150°C for a time period in the range of 0.5-6 hr; andd) diluting the reaction mass obtained at step c) with a solvent.

8. The process as claimed in claim 7 wherein the temperature is mainteained at 120°C when the catalyst is a Ce-Zn oxide catalyst.

9. The process as claimed in claim 7 wherein the temperature is maintained at 140°C when the catalyst is a Ce-Sm-Ru oxide catalyst.

Images