Electrocatalytic conversion of disaccharide into value-added chemicals and concurrent green hydrogen production

Abstract

The present invention relates to a palladium-metal (Pd-M) alloy-based electrocatalyst system for the concurrent electrochemical oxidation of biomass-derived components and green hydrogen generation. More specifically, the invention enables the selective oxidation of disaccharides such as lactose, maltose, sucrose, and other C12 molecules into oxygenated organic compounds, with formate being the predominant product under optimized conditions. The electrocatalyst operates efficiently in alkaline media at low applied potentials and moderate current densities (10–40 mA / cm²), facilitating high conversion rates and selectivity. The process is compatible with both batch and continuous flow electrolyzer setups and demonstrates long-term operational stability, making it suitable for scalable and sustainable energy and biomass valorization applications.

Description

[0001] ELECTROCATALYTIC CONVERSION OF DISACCHARIDE INTO VALUE- ADDED CHEMICALS AND CONCURRENT GREEN HYDROGEN PRODUCTION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to alloy electrocatalysts for the conversion of disaccharide into value added products and concurrent green hydrogen production in a sustainable manner. More particularly, the present invention relates to Pd-M based electrocatalyst (M = Cu, Re, Co, Ag) for the selective production of formate (a C-l hydrocarbon) by electrochemical oxidation of disaccharide at the lowest potential. The invention also relates to a process of preparing the Pd-M catalyst.

[0004] BACKGROUND OF THE INVENTION

[0005] All technological advancements and communications in the modem world depend heavily on energy. Due to the increasing use of energy in all facets of our daily lives, there is exponential growth in the demand for energy consumption today. It is critical to recognize and establish the necessity of sustainable and renewable energy sources in this setting. Among the renewable energy resources, green hydrogen has attracted extensive attention due to its numerous benefits. It includes an eco-friendly clean energy source with a bountiful supply and has been thought to be one of the most promising energies to replace the currently used fossil energy sources, due to its 3-times higher energy per unit mass compared to petrol / diesel and pollution-free advantages.

[0006] At present, 95% of H2 is produced by steam reforming of methane / naphtha and coal gasification process. Since it is neither sustainable nor eco-friendly, electrocatalytic water splitting to hydrogen evolution reaction (HER) at the cathode is now receiving huge attention and is largely considered a viable technology for the production of hydrogen. However, an anodic oxygen evolution reaction (OER), which is counterpart to HER, requires a high overpotential and proceeds at a slow rate, which significantly increases the energy required for the overall water splitting process, and is an important factor for the high-running cost of electrolyzers; this limits its large-scale industrial applications. The practical energy consumption in electrolyzers is 1.5 to 2.2 times more than the theoretical energy consumption, with the actual efficiency between 48 and 70 % in current commercial electrolyzers. Additionally, in comparison to H2, the O2 generated at the anode is a low-value product. In the recent decade, electrolytic hydrogen generation by substituting anodic OER with oxidation of biomass -derived components has gained immense interest. Many biomass -derived organic molecules can get oxidized to value-added products, and by fine-tuning the intrinsic activity of the catalyst one can generate a particular product with high selectivity.

[0007] Further, in the thermal catalytic process, the overoxidation of products to carbon dioxide is a major issue, which is also called the run-away reaction. Electrocatalysis is a powerful yet underutilized method for biomass upgradation to the desired value-added products. In other words, instead of water oxidation to oxygen, biomass components get oxidized on the anode, and water splitting to hydrogen occurs on the cathode; indeed this makes the hydrogen produced as the carbon-negative hydrogen, which is indeed very attractive commercially. Therefore, electrooxidation of organic compounds particularly, Lactose electrooxidation reaction (LacOR) and Maltose electrooxidation reaction (MalOR) can be coupled with HER to accelerate hydrogen production at low over-potential in an alkaline electrolyzer.

[0008] Furfural and 5 -hydroxymethyl furfural (HMF), which are organic feeds used in conventional organic electrolyzers, are expensive but highly valuable platforms or value- added chemicals used in several organic transformations. Hence it is prudent to employ molecules that are considered as difficult to handle, waste components and available in plenty at negligible cost.

[0009] It is to be mentioned that cellulose is a polymer of thousands of D-glucose units, which is the most abundant biomass component. Hemicellulose is a heterogeneous polymer composed of different sugars, such as xylose, arabinose, and galactose, which is the next- highest abundant biomass component. Generally, cellulose and hemicellulose are composed of thousands of units of C6 and / or C5 sugars, and hence they are considered as buildingblock structures / molecules.

[0010] Dimer of two C6 sugars leads to several disaccharides, such as maltose, lactose. Lactose occurs due to a combination of galactose and glucose subunits and is present in milk. Similarly, maltose is a combination of two glucose sub-units joined together, and found in sweet potato, honey etc. It is to be underscored that biomass catalysis starts after the disintegration (or depolymerization) of woody and non-woody biomass into glucose-level components by one of the treatments, such as high-temperature pyrolysis, acid / base- treatment, and enzyme treatment.

[0011] The extent of conversion of the biomass component is the most important descriptor to evaluate counterpart hydrogen formation in biomass oxidation reactions and related processes. More oxidation products will occur as conversion increases, concurrently accelerating hydrogen creation at the cathode. However, due to the decreased conversion at low overpotential, the amount of hydrogen produced in biomass oxidation reactions and other related activities was rather small.

[0012] To maximize hydrogen generation and simultaneously reduce costs, a rational catalyst design should take into account the highest and potentially 100% conversion (of biomass components, such as lactose / maltose) at low potential with high current density (100 mA / cm2and higher). In other words, relative to the potential necessary for OER (occur at high potential and high current density), LacOR / MalOR-related processes should occur at a significantly lower potential to completely avoid OER, while operating at high current density. This would be possible by achieving higher intrinsic activity, than any other catalysts reported.

[0013] The article titled " Combined anodic and cathodic hydrogen production from aldehyde oxidation and hydrogen evolution reaction” by Wang T et al., and published in Nature Catalysis volume 5, pages66-73 (2022) reports the coupling of low-potential anodic oxidation of biomass -derived aldehydes (such as HMF and furfural) with the hydrogen evolution reaction (HER) at the cathode. However, the catalyst gets deactivated around 0.4 V due to oxidation of metallic Cu to Ci O, and also it does not not address more complex biomass molecules such as disaccharides and does not venture the critical aspect of catalyst design. Further, the use of Cu foam and specific aldehydes may limit industrial scalability due to feedstock cost and catalyst durability.

[0014] The article entitled “High entropy alloy electrocatalytic electrode towards alkaline glycerol valorization coupling with acidic hydrogen production” by Linfeng Fan et al., and published in “Journal of American Chemical Society 2022, 144, 7224-7235” reports the development of CoNiCuMnMo alloy material for glycol oxidation and concurrent hydrogen production in electrolytic cell in asymmetric and symmetric electrolyte-electrlyzer setup. This system delivered a current density of 10 mA / cm2at 1.25 V and 0.55 V vs RHE with symmetric and asymmetric setup with high Faradic efficiency (FE) for formate. Nonetheless, it needs to be highlighted that acidic condition (0.5 M H2SO4) was used for hydrogen production and therefore very difficult to scale up for industrial applications.

[0015] Yet another article titled “Efficient electrochemical production of glucaric acid and H2 via glucose electrolysis” by Wu-Jun Liu et al., and published in the journal “Nature Communication 2020, 11, 265” demonstrate the development of nickel iron nitride catalyst for glucose oxidation and concurrent hydrogen production. A minimum potential of 1.39 V (vs. RHE) was required to achieve a current density of 100 mA / cm2, which is significantly higher potential to be useful for practical applications. This is the only prior art available for glucose as the biomass component utilized in an electrolysis setup for concurrent hydrogen generation.

[0016] Another article entitled “Electrocatalytic oxidation of readily available disaccharides in alkaline medium at gold electrode” by P. Parpot et al., and published in the journal “Electrochimica Acta 55 (2010) 3157-3163” illustrated the electrooxidation of trehalose, maltose, isomaltulose and cellobiose using gold electrode. Parpot et al. studied the maltose electrooxidation in 0.1 M NaOH medium, and the selectivity observed for the maltobionic acid, which is the major product, is only 27%. Furthermore, the conversion is only 50% even after 8 h of electrolysis, which makes it less attractive.

[0017] There remains a significant challenge in the oxidation of biomass-derived compounds within electrolysis systems at low potentials that may be coupled with Hydrogen production to make the process more sustainable. The present invention addresses this need, by offering an inventive integration of hydrogen production and biomass utilization at low potential and at high current density.

[0018] OBJECTS OF THE INVENTION

[0019] It is an object of the present invention to provide an alloy electrocatalyst for the electrochemical production of hydrogen coupled with oxidation of biomass component(s) into value-added products. Another object of the present invention is to provide a process of preparation of said electrocatalysts for the conversion of biomass components into value-added products and carbon negative green H2 gas.

[0020] Yet another object of the present invention is to provide alloy electrocatalysts for the electrooxidation of biomass component(s) in alkaline solution at very low applied potential to generate value-added chemicals at the anode and hydrogen at the cathode.

[0021] Yet another object of the present invention is to provide a process of production of value- added product(s) by reacting biomass component(s) with said electrocatalysts.

[0022] Yet another object of the present invention is to achieve high intrinsic activity with 100 % or near 100 % conversion of biomass component(s) into value added products at high current density (more than 100 mA / cm2) at low applied potential less than 0.5+0.1 V (vs. RHE).

[0023] Yet another object of the present invention is to provide a process of production of value- added chemicals from lactose and / or maltose electrooxidation with electrocatalysts.

[0024] Yet another object of the present invention is to provide a process of production of value- added chemicals by achieving 100 % or near 100 % conversion of lactose / maltose with high current density (more than 100 mA / cm2) at a low applied potential of less than 0.5+0.1 V (vs. RHE).

[0025] Yet another object of the present invention is to provide a process of production of value- added chemicals coupled with hydrogen production concurrently from the water reduction on the noble metal cathode material with long-term performance.

[0026] SUMMARY OF THE INVENTION

[0027] The present invention provides palladium-Metal (Pd-M) alloy electrocatalysts for the electrooxidation of biomass component(s) to obtain value-added chemicals at the anode coupled with hydrogen production at the cathode.

[0028] In an aspect, the present invention provides an alloy electrocatalyst for electrochemical oxidation of biomass component(s) into value-added products and green hydrogen production, wherein the electrocatalyst is an alloy of palladium-metal (Pd-M) deposited onto support, wherein metal is selected from Copper (Cu), Silver (Ag), Rhenium (Re) and Cobalt (Co). The atomic ratio of Pd:M in palladium-metal alloys can be in the range of 4: 1- 1:4. preferably 1: 1. The support used in the electrocatalyst is selected from Ni foam, Cu foam, titanium foil and carbon cloth.

[0029] In another aspect, the present invention provides a process for preparation of palladiummetal (Pd-M) alloy electrocatalyst form by a solvothermal method, the process comprising the steps of: a) preparing the aqueous mixture comprising palladium and metal precursors in water and diluting it followed by ultrasonication for 30 minutes; b) adding the reducing agent instantly to the aqueous mixture of step a) at a temperature in the range of 75 to 85 °C; c) stirring the mixture of step b) for the time period in the range of 1 to 1.5 hrs at the same temperature range to obtain the Pd-M alloy; d) optionally, washing and purifying the Pd-M alloy forms of step c) with Millipore water to obtain pure Pd-M nanoparticle form followed by drying the product in an oven for 5 h at 70°C; and e) coating the Pd-M alloy of step c) or d) onto the support to afford the alloy electrocatalyst.

[0030] In another aspect, the atomic ratio of Pd:M in palladium-metal alloys is in the range of 4: 1- 1:4, preferably 3 : 1 - 1 : 3 , more preferably 1: 1.

[0031] In yet another embodiment, the present invention relates to a process for electrocatalytic biomass oxidation with concurrent hydrogen production comprising the steps of: i) providing a palladium-metal (Pd-M) alloy on a support as anode; ii) preparing an electrochemical setup comprising said anode along with a Pt / C cathode, and a reference electrode; iii) introducing an alkaline solution of biomass component(s) into the electrochemical cell; iv) applying a current density in the range of 10-40 mA / cm2for a suitable amount of time to obtain a value added product at the anode and concurrent hydrogen production at the cathode. In an embodiment, the concentration of biomass component(s) alkaline solution in step (iii) can be 0.05 to 1.5 M and the alkaline is selected from potassium hydroxide or sodium hydroxide.

[0032] In an embodiment, the biomass component(s) are derived from waste / biomass material comprising disaccharides, polysaccharides, such as maltose, lactose and cellulose.

[0033] In an embodiment, the time taken for the electrooxidation of biomass components to obtain value added products coupled with hydrogen production in the electrochemical set up is in the range of 30 min to 4 hours. The time taken is preferably 2 hours.

[0034] In an embodiment, the value added products obtained include all types of simple, branched or cylic C1-C3 acids or lactone acids.

[0035] In another embodiment, the electrochemical setup further comprises a graphite rod or Pt / C electrode as cathode material, and a saturated calomel electrode (SCE) as reference electrode.

[0036] In another embodiment, the metal precursor is selected from acetate, halide, nitrate, sulphate salts of metals.

[0037] In another embodiment, the reducing agent is selected from hydrazine hydrate, or sodium borohydride (NaBPE).

[0038] In a specific aspect, the present invention provides an electrocatalyst obtained by a simple slurry coat method on nickel foam for value-added chemicals production from LacOR, and MalOR at the anode and hydrogen generation at the cathode.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1. XRD pattern of PdM alloys (M=Co, Re, Ag). It may be noted that in addition to Pd- features, Pd-Ag only shows Ag-features also.

[0041] FIG. 2. XRD pattern of various ratios of PdCu alloy with pure Pd and Cu nanoparticles. The FWHM for the Pd (111) plane is 0.57 for the pure Pd, 1.54 for the Pd-Cu (3: 1) alloy, 1.59 for the Pd-Cu (1: 1) alloy and 1.97 for the Pd-Cu (1:3) alloy. Notably, the FWHM values are increasing with increasing the percentage of Cu. FIG. 3. HRTEM images of PdCu alloy at (a) 50 nm (b) 5 nm (c) PdCu alloy d spacing.

[0042] FIG. 4. (a) Linear sweep voltammetry (LSV) results of various Pd-Cu alloy and bimetal electrocatalysts for (a) Lactose electrooxidation (LacOR) and (b) Maltose electrooxidation (MalOR).

[0043] FIG. 5. Linear sweep voltammetry results of various Pd:Cu ratios of Pd-Cu alloys for (a) LacOR, and (b) MalOR.

[0044] FIG. 6. Linear sweep voltammetry results of various PdM (M= Cu, Co, Ag, Re) alloys for (a) LacOR and (b) MalOR.

[0045] FIG. 7. Chronopotentiometry measurement with PdCu (3: 1) alloy electrocatalyst as a function of applied current density in 1 M KOH and (a) 0.05 M lactose, and (b) 0.05 M maltose .

[0046] FIG. 8. Formate production as a function of applied current density with PdCu (3: 1) alloy electrocatalyst for (a) LacOR, and (b) MalOR.

[0047] FIG. 9a and 9b.1H NMR spectral data of lactose oxidation product and maltose oxidation product respectively at 30 mA / cm2constant current.

[0048] FIG. 10. Percent selectivity and conversion plot of (a) LacOR, (b) MalOR.

[0049] FIG. 11 . Linear sweep voltammetry of C12 molecules in 2 electrode alkaline electrolyzer with Pd-Cu(3: l) alloy as a anode and Pt / C as a cathode, (a) LSV for LacOR (b) LSV for MalOR

[0050] FIG. 12 . Sustainable operation of Lactose and Maltose electrooxidation process at 100 mA / cm2for 100 h. Active electrode area is 4 cm2in the electrolyzer setup.

[0051] DETAILED DESCRIPTION OF THE INVENTION

[0052] It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the invention. The detailed description will be provided herein below with reference to the attached drawing. The term biomass component(s) used herein refers to any organic matter including wood, plants, agricultural waste, and organic matter from human and animal sources.

[0053] The term “disaccharides” used herein describes the class of sugar molecules that contains two basic units (monomers) from which all carbohydrates are made. Examples of disaccharides comprise lactose, maltose, sucrose etc. Disaccharides are made by combining two monosaccharide units which can be either two same monomer units (such as maltose) or different (such as lactose).

[0054] The term “polysaccharides” refers to long chain or complex carbohydrates such as starch, cellulose, chitin and glycogen.

[0055] The present invention provides a palladium-Metal (Pd-M) alloy electrocatalysts for the electro-oxidation of biomass component(s) to obtain value-added chemicals at the anode and hydrogen production at the cathode.

[0056] In a primary aspect, the present invention provides an alloy electrocatalyst for the electrochemical oxidation of biomass component(s) into value-added products and green hydrogen production at low potential.

[0057] In an embodiment, the electrocatalyst comprises an alloy of palladium (Pd) and a metal (M) deposited onto a support. The incorporation of a metal into the palladium is critical for tuning the electronic structure, modifying surface adsorption properties, and enhancing catalytic activity and selectivity. Alloying Pd with transition or noble metals can reduce the onset potential for oxidation reactions, improve stability under alkaline conditions, and influence the reaction pathway toward desired products. The choice of M is based on its ability to synergistically interact with Pd and contribute to improved performance metrics such as current density, selectivity, and durability. In an embodiment, the metal (M) is selected from Copper (Cu), Silver (Ag), Rhenium (Re) and Cobalt (Co).

[0058] In another aspect, the atomic ratio of Pd:M in palladium-metal alloys in the electrocatalyst is in the range of 4: 1-1:4, preferably in the range of 3: 1-1:3. In an embodiment, more preferably, the atomic ratio of Pd:M in palladium-metal alloy of the electrocatalyst is 1: 1.

[0059] The support plays a vital role in facilitating electron transport, providing mechanical stability, and offering a high surface area for catalyst dispersion. The support used in the electrocatalyst is selected from Ni foam, Cu foam, titanium foil and carbon cloth. Preferably, the support is Ni foam. Nickel foam is preferred due to its three-dimensional porous structure, excellent electrical conductivity, and chemical compatibility with alkaline electrolytes.

[0060] In an embodiment, an electrocatalyst is in the form of an electrode, specifically, in the form of an anode.

[0061] In another aspect, the present invention provides a process of preparation of said Pd-M alloy electrocatalyst by a solvothermal method, the process comprising steps of: a) preparing the aqueous mixture comprising palladium and metal precursors in water and diluting it followed by ultrasonication for 30 minutes; b) adding the reducing agent instantly to the aqueous mixture of step a) at a temperature in the range of 75 to 85 °C; c) stirring the mixture of step b) for the time period in the range of 1 to 1.5 hrs at the same temperature range to obtain the Pd-M alloy; d) optionally, washing and purifying the Pd-M alloy of step c) with Millipore water to obtain pure Pd-M nanoparticle alloy followed by drying the product in an oven for 5-8 h at 60- 70°C; and e) coating the Pd-M alloy of step c) or d) onto the support to afford the alloy electrocatalyst.

[0062] In an embodiment, the palladium precursor is selected from KiPdCU, HiPdCU, Pd(acac)2, palladium(II) acetate (Pd(acetate)2) and sodium tetrachloropalladate (Na2PdC14). The precursor complex is generally selected based on their solubility, reactivity, and compatibility with aqueous synthesis.

[0063] The metal precursor employed in the electrocatalyst of the invention is selected from acetate, halide, nitrate, sulphate salts of metals selected form Copper, Silver, Rhenium and Cobalt. Representative examples include but not limited to Silver nitrate (AgNCh), Cobalt chloride hexahydrate (COCI2.6H2O) and Rhenium nitrate prepared from Rhenium metal powder, respectively. In particularly useful aspect, the metal is Copper and its precursor is copper sulphate pentahydrate (CuSCC.SfCO) due to its solubility and consistent reactivity.

[0064] In the preferred aspect of an embodiment, the amount of palladium reagent is in the range of 400 to 450 mg; the amount of metal precursor is in the range of 300 to 375 mg; the amount of reducing agent in the step b) is in the range of 400 to 1000 DL. Weight percentage (wt%) of palladium (Pd) ranges from 36 to 84%, and concurrently, Cu wt % varies from 16 to 64%. In another aspect, the atomic ratio of Pd:M in palladium-metal alloys is in the range of 4: 1- 1:4, preferably 3 : 1 - 1 : 3 , more preferably 1: 1.

[0065] In an embodiment, the reducing agent of step b) is hydrazine hydrate, Sodium borohydride (NaBH4).

[0066] In an embodiment, the present invention relates to a process of preparation of said electrocatalyst in the form of the electrode. The electrocatalyst in the form of electrode is obtained either by slurry coat method or by drop-casting method.

[0067] The slurry coat process of preparation of said electrocatalyst in the form of the electrode comprises the steps of:

[0068] - preparing a catalyst ink composed of 85% of the Pd-M (M = Cu, Re, Co, Ag) active catalyst, 10% of carbon black and 5% of Polyvinylidene fluoride (PVDF);

[0069] - making a slurry using N-Methylpyrrolidone (NMP) as the solvent;

[0070] - coating the slurry obtained at step ii over the (1*1 cm2) support substrate and drying in a vacuum oven for 12 h at a temperature in the range of 60-70 °C to afford electrocatalyst in the form of electrode.

[0071] The drop-casting process of preparation of said electrocatalyst in the form of the electrode comprises the steps of:

[0072] - preparing a catalyst ink by uniformly dispersing Pd-M alloy in ethanol for the anode and Pt / C in a water and isopropanol (iPA) mixture for the cathode;

[0073] - drop-casting the ink obtained at step I onto the support, which is placed on a hot plate maintained at a temperature in the range of 55 to 60 °C, resulting in the formation of the electrocatalyst in the form of an electrode.

[0074] In another embodiment, the support to the Pd-M electriocatalyst is Ni foam.

[0075] In a specific embodiment, electrocatalyst of the present invention is obtained by a simple slurry coat method on nickel foam for value-added chemicals production from LacOR (lactose oxidation), and MalOR (maltose oxidation) at the anode and hydrogen generation at the cathode. In yet another aspect, the present invention relates to a process for electrocatalytic oxidation of biomass with concurrent hydrogen production, comprising the steps of: i) providing a palladium-metal (Pd-M) alloy on a support as claimed in claim 1 as anode; ii) preparing an electrochemical setup comprising said anode along with a Pt / C cathode, and a reference electrode; iii) introducing a solution of biomass component(s) into the electrochemical cell; iv) applying a current density in the range of 10-40 mA / cm2to obtain a value added product at the anode and concurrent hydrogen production at the cathode.

[0076] In an embodiment, the reaction between biomass component(s) solution and said electrocatalyst under electrochemical setup is carried out for a time in the range of 30 minutes to 4 hrs, wherein electrocatalyst is in the form of the electrode comprises Pd-M alloy deposited onto support; and wherein the electrochemical setup comprises a applied current density in range of 10-40 mA / cm2and the process simultaneously produces hydrogen. The time taken for the reaction is preferably 2 hours.

[0077] In an embodiment, the voltage applied for oxidation of biomass component(s) is in the range of 0.0 to 2 V vs RHE or 0.0 to 2.2 V vs RHE.

[0078] In another embodiment, the electrochemical setup further comprises a graphite rod or Pt / C electrode as cathode material, and a saturated calomel electrode (SCE) or Ag / AgCl or Hg / HgO as reference electrode.

[0079] In another embodiment, the biomass component(s) solution is prepared by mixing and dissolving biomass component(s) in potassium hydroxide or sodium hydroxide solution. The concentration of KOH solution is in the range of 0.5 to 1.5 M. Preferably, the concentration of KOH solution is 1 M.

[0080] In another embodiment, the biomass component(s) is / are selected from disaccharides, or a mixture thereof. Preferably, the biomass component(s) is / are selected from a group comprisng waste / biomass material comprising disaccharides, polysaccharides, such as maltose, lactose and cellulose. In another embodiment, the amount or concentration of biomass component(s) is in the range of 0.05 to 1.5 M. Preferably, the concentration of biomass component(s) is 0.05 M. In an embodiment, the value-added products include all types of simple, branched or cylic C1-C3 acids or lactone acids, alcohols, or a mixture thereof. Specifically, the value-added products are formic acid, lactic acid, glycolic acid, acetic acid, methanol, or a mixture thereof. Preferably the value-added product is formate. The value added products by way of acid and alcohol products are obtained in the form of their potassium salts such as potassium formate, potassium acetate, potassium methanoate, etc. On neutralization with a mineral acid, potassium salts change to the corresponding acid or alcohol or the protonated compound.

[0081] In another embodiment, the oxidation process of biomass component(s) provides selectively a single value-added product i.e., one value-added product in one go reaction as the major product. Preferbaly the value-added product is formate. In another embodiment, said process may be carried out in batch mode within 4 hrs as well as continuous mode for several days / weeks to obtain value-added products and H2.

[0082] Fabrication of working electrode

[0083] Pd-Cu Alloy anode. For the fabrication of the working electrode, Pd-Cu alloy, or any anode material, the slurry coat method can be used. In an embodiment, 85% of the active catalyst along with 10% of carbon black and 5% of PVDF was made a slurry using NMP as the solvent. It was then coated over the (1*1 cm2) Ni foam substrate and dried in a vacuum oven for 12 h at a temperature 60-70°C. For the electrolyzer also, the Pd-Cu alloy electrode was prepared using the same method over the (2*2 cm2) Ni foam substrate.

[0084] Pt / C cathode: Using a drop casting approach, a 20% Pt / C standard catalyst was employed as the cathode part for the HER reaction.

[0085] Geometrical area of the substrate for the electrocatalytic reaction

[0086] In an embodiment a 1*3 cm2Ni foam substrate area was employed for the 1 cm2area electrode. For the non-conducting side, PTFE tape was used to cover the whole area except for the active 1 cm2anode region. A low-resistance copper wire was used for holding this Ni foam substrate. 3 M HC1 was used for ten minutes under sonication to clean the Ni substrate. This was followed by several rinses with deionized water and a final wash with ethanol. It was then vacuum-dried for 12 hours at 60-70°C. Optimization of catalyst amount

[0087] In an embodiment, on a pre-cleaned Ni foam substrate, a known amount (2-4 mg Pd-Cu) of Pd-Cu alloy was coated using the slurry coat method and dried for 12 hours. With an aqueous solution of 1 M KOH containing lactose / maltose serving as the reference electrode and a graphite rod (or Pt / C) serving as the counter electrode, the activity of the catalysts were investigated in a three-electrode electrochemical setup.

[0088] Electrocatalytic reaction condition for Lactose / Maltose oxidation to value-added products

[0089] A three-electrode system within one container was used for lactose oxidation reaction, with Pd-Cu alloy coated over Ni foam functioning as the working electrode and saturated calomel electrode (SCE) and graphite rod (or Pt / C) functioning as the reference and counter electrodes, respectively. The reaction was carried out in 7-8 ml of solution (I M KOH + 0.05 M Lactose / 0.05 M Maltose). The reactions were conducted at an applied current density of 10-40 mA / cm2.

[0090] 'H NMR Charecterization and Identification of Value added products

[0091] After the reaction, the liquid product was collected and examined by proton nuclear magnetic resonance (XH NMR) (AV-NEO 400 & 500, Bruker BioSpin AG; Magnet system 400-500 MHz), available at CSIR-NCL, Pune, India. Formic acid was the major product of lactose / maltose oxidation and the same was observed and confirmed. A minute amount of lactic acid, glycolic acid, acetic acid, and methanol was also observed. The product formation was further confirmed by comparing the experimental data to standard sample data of pure components.

[0092] EXAMPLES

[0093] Following examples are by way of illustration therefore should not be constructed to limited the scope of the invention.

[0094] Example -1: Preparation of Pd-Metal (M) Alloy

[0095] The solution phase method was adopted for the synthesis of Pd-Cu Alloy. In a 100 mL capacity 3 -neck round-bottom flask (RBF), 5 mL of 0.25M FGPdCE solution and 5 mL of 0.25 M CUSO4.5H2O were added and diluted the whole solution to 50 mL. The flask was sonicated for 30 minutes to ensure that a homogeneous mixture was formed and then heated to 75-85 °C under constant stirring. 0.01 mol of hydrazine hydrate was added in one go or instantly and stirred the mixture constantly for 1 hr under the same temperature. After 1 h, the Pd-Cu alloy solution obtained was cooled to 25-35° C and collected in centrifuge bottles. Washing or cleaning of the alloy was carried out by centrifuging the solution with Millipore water at 10000 rpm 5 times. The final precipitate was dried in the oven at 60-70 °C and then used for the catalytic reaction.

[0096] Pd-Co Alloy

[0097] The synthesis of palladium cobalt alloy followed the same procedure as that of Example 1 except for the use of cobalt chloride hexahydrate as the cobalt metal precursor.

[0098] Pd-Re Alloy

[0099] Rhenium metal powder was used for the synthesis of palladium rhenium alloy and it was dissolved in the required amount of nitric acid to convert Re to rhenium nitrate. Other steps were the same as that of Example 1 for Pd-Re alloy synthesis.

[0100] Pd-Ag Alloy

[0101] The palladium silver alloy was synthesized using silver nitrate as the metal precursor. The remaining procedure was the same as that of Example 1.

[0102] Synthetic process of Pd-Cu alloy nanoparticles

[0103] The synthesis of Pd-Cu alloy nanoparticles was achieved using the solution phase method. In a 25 mL, 3-neck round-bottom flask (RBF), containing 8 mL of water, variable amounts of PVP (25-150 mg), ascorbic acid (40-100 mg), and KC1 (100-300 mg) were dissolved. The flask underwent 10 minutes of sonication to ensure complete dissolution of the components, followed by heating to 75-85 °C under continuous stirring in an inert atmosphere. A solution containing PdCh and KC1 in a 1:2 mole ratio (20-100 mg), was dissolved in 2-6 mL of water, and CUCI2.2H2O, in 2-6 mL water was then added to the above solution. The temperature was maintained at 75-85 °C for 5-10 minutes, followed by three hours of constant stirring at the same temperature. After 3 hours, the resulting Pd-Cu bimetal nanoparticle alloy solution was cooled to 25-35° C and transferred to centrifuge bottles. The nanoparticles were washed by centrifuging the solution with excess acetone once, and then with an ethanol: hexane mixture (in a 1:5 ratio) five times at 10000 rpm. Finally, the precipitate containing the Pd-Cu bimetal nanoparticles alloy was dried in an oven at 60 °C and subsequently utilized for catalytic reactions. FIG. 1 represents the XRD pattern of various Pd-M (1: 1) alloys (M=Co, Re, Ag). It may be noted that in addition to Pd-features, Ag-features are also observed for Pd-Ag.

[0104] Example-2: Characterization of Pd-Cu Alloy [X-ray Diffraction (XRD) studies]

[0105] The XRD patterns of various ratios of Pd-Cu alloy with pure Pd and Cu nanoparticles are indicated in FIG. 2. For the face-centered cubic (fee) phase of pure Pd nanoparticles, the diffraction peaks at 40.15°, 46.62°, 68.10°, and 82.22° are assigned for diffraction from the crystallographic facets of (111), (200), (220), and (311) respectively. The XRD peaks for Pd-Cu (3: 1) alloy appear at 40.24°, 46.89°, 68.21°, and 82.63°, which clearly showed that the diffraction peaks from (111), (200), (220), and (311) planes, and for the synthesized Pd- Cu alloy, shift towards higher 29 values due to the incorporation of Cu atoms was observed. Similarly, for Pd-Cu(l : l) alloy also diffraction peaks appeared at a higher 29 angle, due to the larger amount of incorporation of Cu atoms into the Pd fee lattice. For Pd-Cu(l: 1) alloy peaks are observed at 40.99°, 47.54°, 70.23°, and 84.87°. In the XRD pattern of PdCu(l:3) alloy, apart from above mentioned Pd-features, Cu nanoparticle peaks are also observed due to the large amount of Cu. The peaks at 35.10° and 61.03° correspond to the (111) and (113) planes of monoclinic CuO, respectively. The diffraction peaks corresponding to the (111) and (200) planes of fee Pd nanoparticles are also observed.

[0106] Example-3: HRTEM imaging

[0107] Fig. 3 shows the HRTEM images of as prepared PdCu alloy. It shows the agglomerated spherical morphology as in FIG. 3a of the Pd-Cu alloy and an HRTEM image of the alloy is shown in FIG. 3b. The PdCu alloy d-spacing is found to be -0.224 nm in FIG. 3c which corresponds to the (111) facet of the alloy.

[0108] Example-4: Electrocatalytic oxidation of Biomass [Pd-Cu Alloy Vs Bimetal electrocatalyst]

[0109] FIG. 4a shows the Linear sweep voltammetry (LSV) results of various Pd-based electrocatalysts with different geometric current densities for LacOR. In the absence of lactose, the Pd-Cu (1: 1) alloy anode drives the OER (from water splitting) and exhibits a significantly high potential of 1.75 V vs RHE (with an overpotential of 0.5 V) at a current density of 50 mA / cm2. In the presence of lactose, the onset of LacOR decreases significantly to the low potential. Importantly, Pd-Cu alloy shows the highest current density even at the low applied range. The catalytic current density of 100 mA / cm2is observed at a low applied potential of 0.87 V vs RHE. In contrast, Pd-Cu (1: 1) alloy combination exhibits lower LacOR current density. Moreover, Pd-Cu alloy shows the lowest onset potential of 0.12 V vs RHE, and Pd-Cu alloy exhibits an onset of 1.3 V vs RHE. It is also to be emphasized that OER occurs at comparable potential for both alloy and bimetal forms of Pd-Cu (1: 1), while addition of lactose in LacOR exhibits a large difference in activity. FIG. 4b shows the Linear sweep voltammetry (LSV) results of various Pd-based electrocatalysts with different geometric current densities for MalOR. In the absence of maltose, the Pd-Cu alloy anode drives the OER (from water splitting) and exhibits a significantly high potential of 1.75 V vs RHE at a current density of 50 mA / cm2. In the presence of maltose, the onset of MalOR decreases significantly to the low potential for Pd-Cu alloy catalyst anode evaluated. Importantly, Pd-Cu alloy shows the highest current density even at the low applied potential range. The catalytic current density of 100 mA / cm2is observed at a low applied potential of 0.91 V vs RHE. In contrast, Pd-Cu alloy form exhibits lower LacOR current density. Moreover, Pd-Cu alloy shows the lowest onset potential of 0.09 V vs RHE. In contrast, PdCu bimetal exhibits an onset of 1.3 V vs RHE. In a similar way to LacOR, addition of maltose in MalOR exhibits a large difference in activity, compared to OER with both forms of PdCu. Notably, The Pd-Cu alloy is distinctive from the PdCu bimetal in its structure. There is near atomic mixing of Pd and Cu in the alloy electrocatalyst of the present invention whereas bimetal Pd-Cu has significant segregation of individual metals within the bimetal catalyst.

[0110] Example-5: Electrocatalytic oxidation of Biomass with varying ratios of Pd-Cu Alloy

[0111] FIG. 5a represents the Linear sweep voltammetry (LSV) results of various ratios of Pd-Cu alloys (1:3 to 3: 1) for LacOR. The Onset potential of all PdCu alloys is significantly low compared to pure Pd and Cu. Among the Pd-Cu alloys, Pd-Cu (3:1) showed the lowest onset potential of 0.07 ± 0.01 V vs RHE, and this is the lowest potential being reported to the best of the inventor”s knowledge. PdCu (3: 1) exhibited the catalytic current density of 50, 100 and 250 mA / cm2at low applied potentials of 0.1, 0.67 and 1.29 V vs RHE, respectively. Indeed this performance is significantly superior than that of PdCu(l: l) for LacOR (Fig. 7a). In contrast, pure Pd and Cu, exhibit an onset potential at 1.3 V vs RHE. The LSV results of various ratios of Pd-Cu alloys for MalOR are represented in FIG. 5b. All the Pd-Cu alloys show an onset potential below 0.2 V vs RHE. In contrast, pure Pd and Cu, exhibit an onset potential at 1.3 V vs RHE. Among the Pd-Cu alloys, Pd-Cu (3: 1) and Pd-Cu (1: 1) show the lowest onset potential of 0.09 ± 0.01 V vs RHE. PdCu(3: 1) exhibited the catalytic current density of 50 mA / cm2and 100 mA / cm2at low applied potentials of 0.2 V and 0.4 V vs RHE, respectively. Pd-Cu(3: l) exhibits a characteristic difference in LSV pattern for LacOR and MalOR.

[0112] Example-6: Electrocatalytic oxidation of Biomass with various Pd-M alloys

[0113] The Linear sweep voltammetry (LSV) results of various combination of Pd-M (3: 1) for M= Cu, Co and Pd-M (1: 1) for M= Ag, Re alloys for LacOR is represented in FIG. 6a. Among the as-prepared alloys, PdAg and PdCu alloys showed a comparable onset potential of 0.06 ± 0.01 V vs RHE towards LacOR. While PdCu alloys showed a current density of 50 mA / cm2and 100 mA / cm2at low applied potentials of 0.18 V and 0.6 V vs RHE, respectively, PdAg required marginally higher voltage for the same current density. The PdCo and PdRe exhibit a high onset potential of 0.9 V vs RHE. FIG. 6b represents the LSV results of various ratios of Pd-M (3: 1) for M= Cu, Co and Pd-M (1:1) for M= Ag, Re alloys for MalOR. Among the as-prepared alloys, Pd-Cu alloy shows the lowest onset potential of 0.1 V vs RHE towards MalOR. Pd-Cu exhibits the catalytic current density of 50 mA / cm2and 100 mA / cm2at low applied potentials of 0.2 V and 0.4 V vs RHE, respectively, Pd-Ag requirs marginally higher voltage for the same current density. All the other Pd-M alloys show a catalytic current density of 100 mA / cm2at a high applied potential of 1.5 ± 0.1 V vs RHE. It is also to be noted that Pd-Ag shows entirely different LSV for LacOR and MalOR. Another interesting aspect is an exponential increase in current density from 1.4 V and above for Pd-Re, and shows significantly higher current densities (300 mA / cm2) than PdCu at comparable voltage. It is possible to exploit the high potential regime for faster kinetics by optimizing the reaction parameters, especially by optimizing the concentration of disaccharide and flow rate, while carefully avoiding / minimizing OER with Pd-Re.

[0114] Example-7: Electrocatalytic oxidation of Biomass with Pd-Cu alloy (3:1) with varying current density

[0115] The LacOR activity on Pd-Cu (3: 1) alloy is evaluated by chronopotentiometry measurement as a function of applied current density in 1 M KOH and 0.05 M lactose (FIG. 7a). All the chronopotentiometry measurements are carried out for 4 h. For all the current densities, formic acid is observed as the major product along with glycolic acid, lactic acid, acetic acid, and methanol as the minor products. Notably, no appreciable change in the potential is observed for the current densities of 10 , 20 , and 40 mA / cm2. For 20 mA / cm2, the potential increases after 3 h from 0.77 V to 1.37 V vs RHE. A potential of 0.4 ± 0.1, 0.55+ 0.1, and 1.34 + 0.04 V vs RHE is observed for the current densities 10, 20, and 40 mA / cm2respectively. Apart from that carbonate peak in the13C NMR spectrum is observed at the highest applied current density of 40 mA / cm2. The MalOR activity on PdCu (3: 1) alloy is evaluated by chronopotentiometry measurement as a function of applied current density in 1 M KOH and 0.05 M maltose (FIG. 7b). The current density ranges from 10 to 40 mA / cm2with the Pd-Cu (3: 1) alloy catalyst. All the chronopotentiometry measurements are carried out for 4 h. Formic acid is observed as the major product at all the current densities, along with glycolic acid, lactic acid, and acetic acid, as the minor products. Notably, no appreciable change in the potential is observed for 10 mA / cm2and 20 mA / cm2, current densities. For 10 mA / cm2, the potential observed is 0.53 + 0.15 V vs RHE and that of 20 mA / cm2is 0.65 + 0.07 V vs RHE. Apart from that carbonate peak in the13C NMR spectrum is observed at the highest applied current density of 40 mA / cm2.

[0116] The product analysis of LacOR is carried out after each chronopotentiometry experiment and the results are shown in FIG. 8a. Among the alloys, Pd-Cu (3: 1) alloy shows higher formic acid production. At the lowest current density of 10 mA / cm2, the formic acid product is about 0.0290 M. When the applied current density is 20 and 30 mA / cm2, it is observed that the formic acid production increases around 0.0813 and 0.247 M, respectively. It is interesting to note that at 30 mA / cm2, there is a drastic increase in formic acid production and it is the highest formic acid concentration obtained by LacOR. Another important observation is at 40 mA / cm2current density, the formic acid concentration decreases slightly, due to overoxidation to CO2. The product analysis of MalOR is carried out after each chronopotentiometry experiment and the results are shown in FIG. 8b. For MalOR also, the highest formic acid production is observed by Pd-Cu (3: 1) alloy. At the lowest current density of 10 mA / cm2, the formic acid product is about 0.0428 M. When the applied current density is 20 and 30 mA / cm2, it is observed that the formic acid production increases to 0.095 and 0.197 M, respectively. At 40 mA / cm2current density, the formic acid production is significantly increased to 0.223 M. The1H NMR spectra in FIG. 9a and 9b illustrate the different products obtained from the oxidation of lactose and maltose, respectively.

[0117] Under different constant current densities, namely, 10, 20, 30 and 40 mA / cm2for 4 hours, following chronopotentiometry experiments, product analysis are conducted, and the outcomes are depicted in FIG. 10 for lactose oxidation (LacOR) and maltose oxidation (MalOR). Even at the lowest current density of 10 mA / cm2, LacOR exhibits approximately 35% selectivity for glyceric acid and about 22% selectivity for formic acid as seen in FIG. 10a. At a higher current density of 40 mA / cm2, the selectivity for formic acid peaks at around 75%, accompanied by a 95% conversion rate. In the case of MalOR as in FIG. 10b , at 10 mA / cm2constant current density, the selectivity for glyceric acid and formic acid is found to be 30 and 42%, respectively. At 40 mA / cm2, the selectivity for formic acid reaches -81% with an 85% conversion rate. As shown in Figs. 11 and 12, some amount of unreacted disaccharide and some of the unidentified minor products, make the accurate carbon balance calculation difficult. Nonetheless, a back calculation from the products identifies and the initial concentration of disaccharide, it is safe to state that more than 75-80 % disaccharide is converted into value added products.

[0118] Example-8: Electrocatalytic oxidation of Lactose and Maltose with Pd-Cu alloy (3:l)||Pt / C

[0119] The two-electrode electrolyzer study is used to evaluate the activity of Pd-Cu(3: l) alloy catalyst towards LacOR and MalOR with concurrent HER performance. A sustainion membrane functions as a separator is employed between the two compartments of the electrolyzer. In both cases, Pt / C serves as the cathode, and Pd-Cu (3: 1) remains the anode (or working electrode). FIG. Ila represents the LSV curve for LacOR in the electrolyzer. It requires a potential of 0.35 V and 1.79 V to achieve 50 mA / cm2, with and without lactose respectively. The system exhibits the catalytic current density of 100 mA / cm2at a low applied potential of 0.84 V towards LacOR. The LSV curve for MalOR in the two-electrode system is shown in FIG. 11b. The PdCu (3: 1) alloy shows the catalytic current density of 50 mA / cm2and 100 mA / cm2, at an applied voltage of 0.39 V and 0.96 V, respectively. However, in both cases, no significant OER (oxygen evolution reaction) current is observed at 1.5 V when the experiment is carried out without lactose / maltose. Example-9: Stability of the Pd-Cu alloy catalyst in the alkaline electrolyzer for Lactose and Maltose Oxidation Reactions

[0120] A chronopotentiometry experiment for 100 h is carried out at 400 mA current density for 4 cm2area electrode to evaluate the stability of the Pd-Cu alloy catalyst in the alkaline electrolyzer for LacOR and MalOR. For LacOR as seen in FIG. 12a, the system operates at an average potential of -2.25V throughout the 100 h reaction and it concurrently produces hydrogen at a rate of 160-170 mL / h. For MalOR, the average potential of the two electrode system is -2.2V and the catalyst is stable throughout the 100 h operation as shown in the FIG. 12b. The electrolyzer continuously produces hydrogen over 100 h at a rate of 160-170 mL / h.

[0121] ADVANTAGES OF THE INVENTION

[0122] • The present work not only the first to successfully employ C 12 molecules for anodic oxidation, but also sets a new benchmark in the area of research and technology of biomass component oxidation at the lowest voltage.

[0123] • The present invention provides a Pd-M alloy based electrocatalyst for electrochemical oxidation of biomass -derived components into value-added products and grran hydrogen productionin sustainable manner

[0124] • The present invention also provides a easy mehod for the production of said Pd-M based electrocatalysts

[0125] • The present invention also provides a electrochemical oxidation process of biomass- derived components by using Pd-M electrocatalyst in alkaline solution at very low applied potential to generate value-added chemicals at the anode and hydrogen at the cathode

[0126] • The process for the production of value-added products as provided by the present invention is energy saving (lesser mA requirement), shows higher scalability, and easy to obtain oxidized products by breaking complex molecule containing 12 or more carbons.

[0127] • The process of the present inveniont to produce value-added products provides clean and green H2 production, no CO2 production.

[0128] • The pocess of production of value-added products shows complete conversion of reactants into products or mixture of products i.e., conversion rate of 100%, selectivity and yield upto 90%, etc.

Claims

WE CLAIM1. An alloy electrocatalyst for electrocatalytic oxidation of biomass with concurrent hydrogen generation, comprising: a palladium-metal (Pd-M) alloy on a support; wherein the metal (M) is selected from the group consisting of copper (Cu), silver (Ag), Rhenium (Re) and cobalt (Co), wherein the atomic ratio of palladium to metal in the Pd-M alloy is in the range of 4: 1 to 1:4.

2. The electrocatalyst as claimed in claim 1 wherein the atomic ratio of palladium to metal in the Pd-M alloy is 1: 1.

3. The electrocatalyst as claimed in claim 1, wherein the support is selected from a group comprising nickel foam, copper foam, titanium foil, and carbon cloth.

4. A process for preparation of the alloy electrocatalyst as claimed in claim 1, comprising the steps of: a) preparing an aqueous mixture comprising palladium and a metal precursor in water followed by ultrasonication; b) adding a reducing agent instantly to the aqueous mixture of step a) at a temperature in the range of 75 to 85 °C; c) stirring the mixture of step b) at the same temperature range to obtain Pd-M alloy; d) optionally, washing and purifying the Pd-M alloy of step c) with water to obtain pure Pd-M nanoparticle alloy followed by drying the product in an oven; e) coating the Pd-M alloy of step c) or d) onto the support to afford the alloy electrocatalyst; wherein the atomic ratio of palladium to metal in the Pd-M alloy is in the range of 4: 1 to 1:4.

5. A process for electrocatalytic oxidation of biomass with concurrent hydrogen production, comprising the steps of:i) providing an alloy electrocatalyst as claimed in claim 1 as anode; ii) preparing an electrochemical setup comprising said anode of step (i) along with a Pt / C cathode, and a reference electrode; iii) introducing an alkaline solution of biomass component(s) into the electrochemical setup of step (ii); iv) applying a current density in the range of 10-40 mA / cm2to obtain a value added product at the anode and concurrent hydrogen production at the cathode.

6. The process as claimed in claim 5, wherein the biomass component(s) are derived from waste / biomass material comprising disaccharides or polysaccharides.

7. The process as claimed in claim 6, wherein the disaccharides or polysaccharides are selected from the group consisting of maltose, lactoIse, cellulose or a combination thereof.

8. The process as claimed in claim 5, wherein the concentration of the biomass component(s) alkaline solution is in the range of 0.05 M to 1.5 M and the alkaline is selected from potassium hydroxide or sodium hydroxide.

9. The process as claimed in claim 5, wherein voltage applied is in the range of 0.0 V to 2.2 V vs RHE and the value added products are selected from the group consisting of simple, branched or cylic C1-C3 acids or lactone acids.

10. The process as claimed in claim 4, wherein the the metal precursor is selected from acetate, halide, nitrate, sulphate salts of metals and the reducing agent is selected from hydrazine hydrate, or sodium borohydride (NaBH4).

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