DESC:PLURIMETALLIC MESOPOROUS CATALYST FOR MULTI FUEL REFORMING AND METHOD OF PRODUCING THEREOF

CROSS-REFRENCE
The application claims priority from provisional application no. 201921024747.

TECHNICAL FIELD
The present disclosure relates to catalysts for reforming fuels into hydrogen and more particularly relates to a plurimetallic mesoporous catalyst for multi-fuel reforming and method of producing the same, by doping at least one of the elements selected from alkali, Transition metals, Lanthanoids or nonmetals on a porous oxide support.

BACKGROUND
Environmentally clean energy source hydrogen finds its place in power generation. Hydrogen based fuel cells as a solution offers transition to a low carbon economy. Fuel cells as an alternative power source has great potential to solve future energy demands. With reduction in cost, a surge in hydrogen-based fuel cells manufacturing has been observed. However, availability of hydrogen distribution infrastructure remains the biggest barrier. Hence, the current scenario mandates development of competitive technologies for production of low-cost hydrogen. One such technology is catalytic reforming of fossil fuels (methanol, gasoline, diesel, natural gas) to produce hydrogen. Amongst the various reforming technologies, it will not be wrong in considering autothermal / oxidative reforming technologies as the most feasible technology, due to its high thermal efficiency and lower system complexity.
Extensive research for development of active and stable catalysts for reforming individual fuels have been reported but there are no findings on single and stable catalyst for reforming multiple fuels. One of the prior arts proposes a proprietary Pd/ZnO catalyst for methanol, diesel and gasoline steam reforming but it was reported to deactivate due to low sulfur tolerance, leading to sintering and high carbon deposition.
Yet another prior art proposes a Rh-Ce-La/?-Al2O3, a catalyst tested for diesel, gasoline and methanol. The catalyst however showed higher selectivity for methanol decomposition instead of reforming, thereby decreasing hydrogen yields for methanol.
It was observed that none of the prior arts show a stable performance for all the fuels. Thus, there is a need for a stable multi fuel catalyst for reforming fuels into hydrogen.

OBJECT OF THE INVENTION
It is the primary object of the present disclosure to provide a method for producing a stable, mesoporous, multifuel reforming plurimetallic catalyst resistant to coke formation.

Another object of the present disclosure is to provide a porous alkali/Lanthanoid or non-metal doped support for metallic impregnation.

Another object of the present disclosure is to show that addition of alkali/Lanthanoid or nonmetal during support preparation is more beneficial than adding alkali/Lanthanoid or nonmetal after support preparation and impregnating thereafter with transition metals.

Another object of the present disclosure is to impregnate transition metals onto the support.

Yet another object of the present disclosure is to provide stable reforming regions for each fuel using the catalyst prepared.

Yet another object of the present disclosure is to provide stable catalyst performance for each fuel for long operation times.

Yet another object of the present disclosure is to develop a catalyst with low coking tendency, which if high leads to catalyst deactivation.

SUMMARY
This summary is provided to introduce a selection of concepts in a simplified format that are further described in the detailed description of the invention. This summary is not intended to identify key or essential inventive concepts of the claimed subject matter, nor is it intended for determining the scope of the claimed subject matter.
The present disclosure focuses on a stable, mesoporous, multifuel reforming plurimetallic catalyst and a method of producing the same. The catalyst is composed of a mesoporous support embedded with at least one metal ion. The porous support is further doped with at least one of the elements selected from the group of alkali, lanthanoids, transition metals or non-metals. The present invention further relates to a method of preparation of mesoporous support embedded with metal ions wherein the method comprises the steps of dissolving the precursors of metal ions along with said support to form a mixture, followed by stirring the mixture at elevated temperature for a pre-defined time, the mixture is then dried for a predefined time, dried mixture is subsequently reduced by H2/N2 and the resultant reduced mixture is flushed with Nitrogen to remove the traces of hydrogen, the catalysts are then labeled and characterized using sophisticated characterizing techniques like X-Ray Diffraction (XRD), Nitrogen physisorption and Transmission Electron Microscopy.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
The detailed description is described with reference to the accompanying figures and tables.
Figure 1 illustrates reaction setup for reforming reaction.
Figure 2a, illustrates catalyst activity results for various catalysts for oxidative reforming of diesel, operating conditions: SCR: 4, OCR:0.2, T: 700 °C and GHSV: 5000 ml/ (hSTP.gcat)
Figure 2b, illustrates H2 production rates for various catalysts for oxidative reforming of diesel, operating conditions: SCR: 4, OCR:0.2, T: 700 °C and GHSV: 5000 ml/ (hSTP.gcat)
Figure 3, illustrates TGA results for the various catalysts for oxidative reforming of diesel, operating conditions: SCR: 4, OCR:0.2, T: 700 °C and GHSV: 5000 ml/ (hSTP.gcat)
Figure 4a, illustrates catalyst activity results for various catalysts for oxidative reforming of gasoline, operating conditions: SCR: 4, OCR:0.2, T: 700 °C and GHSV: 5000 ml/ (hSTP.gcat)
Figure 4b, illustrates H2 production rates for various catalysts for oxidative reforming of diesel, operating conditions: SCR: 4, OCR:0.2, T: 700 °C and GHSV: 5000 ml/ (hSTP.gcat)
Figure 5, illustrates TGA results for the various catalysts for oxidative reforming of gasoline, operating conditions: SCR: 4, OCR:0.2, T: 700 °C and GHSV: 5000 ml/ (hSTP.gcat)
Figure 6a, illustrates conversion rate for oxidative reforming of diesel for various K loadings (SCR: 4; OCR:0.2; T: 700 °C and GHSV: 5000 (scc/h.gcat)).
Figure 6b, illustrates H2 Production rate for oxidative reforming of diesel for various K loadings (SCR: 4; OCR:0.2; T: 700 °C and GHSV: 5000 (scc/h.gcat)).
Figure 6c, illustrates TGA results (DTG curves) for oxidative reforming of diesel for various K loadings (SCR: 4; OCR:0.2; T: 700 °C and GHSV: 5000 (scc/h.gcat)).
Figure 6d, illustrates TGA results (C evolution) for oxidative reforming of diesel for various K loadings (SCR: 4; OCR:0.2; T: 700 °C and GHSV: 5000 (scc/h.gcat)).
Figure 7a, illustrates XRD of fresh v/s spent catalysts (tested on Diesel) Ni-Pt/Al2O3 (i) – Laponite (ii) ?-Al2O3 (iii) Ni (111) (iv) Ni (200) (v) Ni (220) (vi) Pt (111) (vii) Pt (200) (viii) Pt (311)
Figure 7b, illustrates XRD of fresh v/s spent catalysts (tested on Diesel) Ni-Pt/K2-Al2O3 C) Ni-Pt/K5-Al2O3 D) Ni-Pt/K8-Al2O3; (i) – Laponite (ii) ?-Al2O3 (iii) Ni (111) (iv) Ni (200) (v) Ni (220) (vi) Pt (111) (vii) Pt (200) (viii) Pt (311)
Figure 7c illustrates XRD of fresh v/s spent catalysts (tested on Diesel) Ni-Pt/K5-Al2O3 D) Ni-Pt/K8-Al2O3; (i) – Laponite (ii) ?-Al2O3 (iii) Ni (111) (iv) Ni (200) (v) Ni (220) (vi) Pt (111) (vii) Pt (200) (viii) Pt (311)
Figure 7d illustrates XRD of fresh v/s spent catalysts (tested on Diesel) Ni-Pt/K8-Al2O3; (i) – Laponite (ii) ?-Al2O3 (iii) Ni (111) (iv) Ni (200) (v) Ni (220) (vi) Pt (111) (vii) Pt (200) (viii) Pt (311)
Figure 8 illustrates Stability test for Ni-Pt/K10-Al-PILC for gasoline, diesel and methanol, ¦ – Conversion v/s time, ? – H2 production rate v/s time (gasoline- SCR 6, OCR 0.3, T 780 °C, GHSV 6100 (ml/hSTP.gcat); diesel- SCR 4, OCR 0.2, T 780 °C, GHSV 6100 (ml/hSTP.gcat); Methanol- SMR 1.25, OMR 0.1, T 420 °C, GHSV 6350 (ml/hSTP.gcat))
Figure 9 (a-p) illustrates TEM, PSD, HRTEM and SAED images of Ni-Pt/K5-Al2O3 (fresh) and spent catalyst after 5 days of reaction for each fuel. Ni-Pt/K5-Al2O3 (fresh) = a) TEM image, b) PSD, c) HRTEM and d) SAED. Ni-Pt/K5-Al2O3 (Diesel Spent) = e) TEM image, f) PSD, g) HRTEM and h) SAED. Ni-Pt/K5-Al2O3 (Gasoline Spent) = i) TEM image, j) PSD, k) HRTEM and l) SAED. Ni-Pt/K5-Al2O3 (Methanol Spent) m) TEM image, n) PSD, o) HRTEM and p) SAED.
Figure 10 illustrates TPD-CO2 profiles for the promoted and unpromoted catalysts
Figure 11 illustrates Effect of K doping on reformate gas composition during oxidative reforming of diesel. (SCR= 4; OCR=0.2; T= 700 °C and GHSV= 5000 ml/ (hSTP.gcat)
Table 1 illustrates Ni (111) crystal size estimation using Scherrer Equation for the reduced and spent catalysts
Table 2(a), 2(b) and 2(c) illustrates comparison of other catalysts reported in literature with our work for oxidative reforming of methanol, diesel and gasoline.
Table 3 illustrates CO2-desorption results for promoted and unpromoted catalysts
It should be appreciated by those skilled in the art that any diagrams herein represent conceptual views of illustrative systems embodying the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.
Unless otherwise defined, 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 invention belongs. The system, methods, and examples provided herein are illustrative only and are not intended to be limiting. Embodiments of the present invention will be described below in detail.
The present invention discloses, a novel plurimetallic catalyst for multifuel reforming and a method of preparation thereof. The disclosure further relates to a mesoporous support and a method of preparation thereof, wherein the support is doped with at least one of the elements selected from an alkali, a non-metal or a lanthanoid. The support is further impregnated with one or more transition metals.
One of the embodiments of the present invention discloses a method to prepare a mesoporous mixed oxide support embedded with transition metal ions. The mesoporous support is doped with at least one element selected from an alkali, a non-metal, or a lanthanoid group to stabilize the catalyst and make said catalyst resistant to coke formation. An aspect of the present invention discloses a method for preparation of the mesoporous support. The method comprises of mixing a precursors of at least one of the elements selected from an alkali, a non-metal, or a lanthanoid along with a precursor of aluminum (solution of aluminium hydroxychloride or any other salt of aluminum) in an aqueous media while being constantly stirred at elevated temperature, to form a mixture. The mixture is then stored in an airtight vessel at a temperature in the range of 60°C to 120°C for a duration in the range of 50 to 150 hours, to obtain a solution B. In another vessel, clay is added to another aqueous media and stirred till it becomes a clear solution, to this clear solution a surfactant is added while being constantly stirred to obtain a Solution A. Solution B is then added dropwise to solution A under continuous stirring, after complete addition of solution B to solution A, a resultant solution is obtained, which is further stirred vigorously. Pursuant to vigorous stirring the contents are transferred to an airtight vessel and aged at a temperature in the range of 60°C to 200 °C for a duration ranging from 40 to 100 hours, which is then centrifuged to obtain a precipitate, the precipitate is then washed with distilled water. The precipitate is further dried overnight at elevated temperature and calcined to obtain powdered form of the support.
In another exemplary embodiment of the present invention, the support is doped with at least one of the elements selected from an alkali, a non-metal or a lanthanoid; wherein the alkali is Potassium, the non-metal is Phosphorous and the Lanthanoid is either Cerium or Gadolinium. The precursor of Potassium is selected from at least one of Potassium Chloride, Potassium Nitrate, or any other salt of Potassium; the precursor of Cerium is selected from at least one of Cerium Chloride, Cerium Nitrate, or any other salt of Cerium; precursor for Gadolinium is selected from at least one of Gadolinium Nitrate, or any other salt of Gadolinium and precursor of Phosphorous is selected from at least one of Phosphorous Trichloride, Ammonium Dihydrogen Phosphate, or any other salt of Phosphorous. Further, a linear nonionic surfactant Tergitol 15-s-9, is added in the preparation of support, wherein the concentration of the surfactant is in the range of 1-3 g per g of calcined support. The support is further impregnated with metal ions selected from the group of transition metals like Nickel, Platinum, Rhodium, and Rhenium. The precursor of Nickel is selected from at least one of Nickel Nitrate Hexahydrate (Ni (NO3)2.6H2O), Nickel Chloride, Nickel Sulfate, or any other salt of Nickel. The precursor of Platinum is selected from at least one of Chloroplatinic acid solution (H2PtCl6.6H2O), Platinum Tetrachloride (PtCl4), Platinum Chloride (PtCl2), or any other salt of Platinum. The precursor of Rhodium is selected from at least one of Rhodium Nitrate (Rh (NO3)2.6H2O), Rhodium Chloride (RhCl3), or any other salt of Rhodium and the precursor for Rhenium is selected from ammonium perrhenate (NH4ReO4), or any other salt of rhenium. The above-mentioned precursors are exemplary embodiments of the present invention and should not be construed to limit the scope of the present invention.
Yet another embodiment of the present invention discloses a method to synthesize a metallic catalyst. The method comprises mixing precursors of the transition metal ions in an aqueous media along with the powdered support prepared in the previously disclosed method to form a slurry. The slurry is stirred at elevated temperature for a predefined time followed by overnight drying. The dried material is reduced using H2/N2 and it is further flushed with N2 at elevated temperature to remove traces of hydrogen.
Another exemplary embodiment of the present invention discloses a method to synthesize metallic catalyst. The method comprises dissolving a precursor of at least one transition metal selected from Nickel, Platinum, Rhodium, or Rhenium in aqueous medium (e.g. Deionized water) along with a support to form a mixture. The mixture is then stirred at a temperature ranging between 50°C to 80 °C to obtain a homogenous solution. The homogenous solution is then dried to remove aqueous medium followed by reducing the dried mixture with H2/N2 at a temperature in the range of 500? to 600?, followed by flushing with N2 at a temperature in the range of 500°C-600°C, to obtain the support impregnated with metal particles.
Another embodiment of the present invention discloses a method for preparation of the mesoporous support. The method of preparation of support comprises mixing a precursor selected from at least one of Potassium, Phosphorous, Cerium, or Gadolinium, along with a precursor of Aluminium in an aqueous media (e.g. Distilled water) to form a mixture, while being constantly stirred at a temperature ranging between 80 °C to 200 °C. The mixture is aged in an airtight Teflon® coated stainless steel vessel at a temperature in the range of 60? to 120? for a duration ranging between 50 to 150 hours to obtain a solution B. Further, Lithium Magnesium Sodium Silicate (0.3-1.3 gm / gram of calcined support) is added in another aqueous medium to form a homogenous suspension followed by addition of a linear non ionic surfactant Tergitol (1-3 gm/gram of final calcined support ) to form a homogenous mixture solution A. Solution B is then added to solution A dropwise while being constantly stirred to form a final homogenous solution, this final homogenous solution is aged in the Teflon® coated stainless steel airtight vessel for a duration ranging between 40 to 100 hours at temperature ranging between 60°C to 200 °C to obtain a clear white suspension. The white suspension is then washed with aqueous media to remove free Cl- ions and dried to remove aqueous media. The dried material is then calcined at a temperature in the range of 450°C to 550 °C for a duration ranging between 12 to 25 hours to obtain the support in powdered form.
The starting material lithium magnesium sodium silicate has a cation exchange capacity of 55 meq per 100 g of clay, BET surface area of 370 m2/g with the following chemical composition (SiO2: 59.5%, MgO: 27.5%, Li2O: 0.8%, Na2O: 2.8%). The commercial solution of aluminium hydroxychloride is used as the pillaring agent. The commercial solution contains polyoxycations of aluminium hydrate with an Al2O3 content of 23±1 wt%, a OH/Al ratio of 2.5 and pH between 2.8 to 4.
In the above referred process potassium loadings were varied between 2, 5 and 8 wt%. The supports were labelled as Al2O3- (no potassium), K2-Al2O3 (2 wt% Potassium), K5-Al2O3 (5 wt% potassium) and K8-Al2O3 (8 wt% potassium). Similarly, other supports were prepared wherein potassium precursor was replaced with Cerium (Ce) and Phosphorus (P) precursors. They were named as Ce2-Al2O3, and P2-Al2O3. Yet another embodiment of the present invention discloses a method for preparation of metallic catalyst. The method comprises, dissolving Nickel nitrate hexahydrate and chloroplatinic acid solution in deionized water along with the support prepared in above sections. The final concentration of Nickel and Platinum in the catalyst are adjusted in the range of 7.5 to 12.5% and 0.05 to 1.2% (w/w), respectively. The mixture is then stirred at a temperature ranging between 50°C to 80 °C to obtain a homogenous solution followed by drying (overnight) in an oven. The dried material is reduced using 10% H2/N2 at a temperature in the range of 500°C-600°C for 4-6 h followed by flushing with N2 at 500°C-600°C for 1 h to remove any traces of hydrogen before being used for reforming reactions. The catalysts thus obtained are labelled as Ni-Pt/Al2O3, Ni-Pt/K2-Al2O3, Ni-Pt/K5-Al2O3 and Ni-Pt/K8-Al2O3.
In another embodiment of the present invention, catalysts are prepared on potassium-based support (K2-Al2O3) and Pt is replaced with Rh/Re in the same ratio as Pt. These catalysts are named as Ni-Rh/K2-Al2O3 and Ni-Re/K2-Al2O3.
In another embodiment of the present invention, catalysts are also prepared by first preparing the non-potassium support. This is followed by addition of potassium nitrate / cerium nitrate / gadolinium nitrate / ammonium dihydrogen phosphate to the mixture containing nickel nitrate hexahydrate, chloroplatinic acid solution and distilled water such that the final concentration of metals are 2 wt% for Ce, K, Gd, and P and 10 and 1 % for Ni and Pt, respectively. The mixture is stirred for 5 h at 60 °C followed by drying at 100 °C (overnight) in an oven. The dried material is reduced using 10% H2/N2 at 550 °C for 5 h followed by flushing with N2 at 550 °C for 1 h to remove any traces of hydrogen before being used for reforming reactions. The catalysts are labelled as Ni-Pt-K2/Al2O3, Ni-Pt-Ce2/Al2O3, Ni-Pt-Gd2/Al2O3 and Ni-Pt-P2/Al2O3

Catalyst Characterization Techniques
X-Ray Diffraction (XRD): Powder X-Ray Diffraction of the catalysts using Rigaku Miniflex powder diffractometer with mono-chromatized Cu K-a (? = 0.154 nm) at 40KV and 15 mA.
TPR/TPD/Pulse: The analysis was performed using Thermo Scientific TPDRO 1100. For CO pulse chemisorption, the quartz reactor was loaded with 0.1 g of catalyst and was then reduced using 5% H2/Ar at 550 °C for 5 h. The sample was flushed with Ar for 1 h and cooled down to room temperature under Ar flow. CO Pulse was then injected with 0.34 ml of 10 % CO / He during each injection. TCD detector was used to quantify adsorbed CO from which the TOF’s were estimated. For TPR (Temperature programmed reduction) studies, 0.1 g of sample was placed in the quartz tube and the temperature was ramped at 10 °C/min under 10 ml/min (10% H2/Ar) flow from 30 °C to 900 °C. Oxygen – Temperature programmed desorption (O2-TPD) of spent samples was conducted by loading 0.1 g of spent sample in the quartz tube and the temperature was ramped at 10 °C/min under 10 ml/min (10% O2/He) flow from 30 °C to 900 °C. CO2-TPD was done after pulsing with CO2 (procedure similar to CO-pulse) wherein after flushing with Ar, the temperature was ramped from 30 °C to 900 °C at 10 °C/min under Ar flow. The gas used was 99.99% pure CO2.
Nitrogen physisorption: The catalyst specific surface area, pore diameter and pore volume were measured by liquid nitrogen in a Micromeritics 3flex instrument. Characterizing the surface area using the Brunauer-Emmett-Teller (BET) method while the pore diameter, pore size distribution and pore volume were measured using the Barrett-Joyner-Halenda (BJH)adsorption-desorption isotherm curve.
Transmission Electron Microscopy (TEM): TEM specimens were prepared using a solvent method. A small amount of catalyst powder (less than 10 mg) was dissolved in 5 ml of solvent(iso-propanol). The mixture was sonicated for 20 mins followed by loading onto holey carbon coated copper grid. The grid is dried under IR lamp for 10 minutes before analysis to ensure complete drying of sample. fresh and spent catalysts is analyzed using FEI Tecnai G2 T20. Ni, Pt, Al, K, Si and Mg is mapped using EDX-STEM methodology. HRTEM and SAED patterns of fresh and spent samples were also obtained.
Thermo-gravimetric analysis (TGA): TGA analysis was done using a Shimadzu DTG-60H wherein placing 10 mg of the sample onto the crucible followed by heating the sample to 900°C at a ramp rate of 50 °C/min under air at 100 ml/min.
Other techniques used for characterization:
X-ray Photoelectron Spectroscopy (XPS)
Inductively Coupled Plasma – Atomic emission Spectroscopy (ICP-AES)
X-Ray Fluorescence (XRF)

The catalysts thus prepared were tested using commercial diesel in a bench scale reactor setup consisting of an Inconel based 25 mm OD and 500 mm length tube (M/S Amar Equipments Private Limited, India). Overall setup is represented in Figure 1. Prior to reforming, 0.4 g of catalyst was loaded in the reactor and held in center by means of quartz wool. For catalyst testing, diesel flow was kept at 0.1 ml/min and the reforming conditions were, steam to carbon ratio (SCR, (mol/mol)): 4, oxygen to carbon ratio (OCR, (mol/mol)): 0.2, reforming temperature (T, °C): 700 and GHSV 5000 (scc/h.gcat).
Reforming Conditions optimization – Based on catalyst activity results, the reforming conditions for the best catalyst were optimized, by checking effect of each parameter on catalyst performance. Once a stable operating region was achieved, the fuel was changed, and the process was repeated. The starting reforming conditions were obtained based on initial screening experiments which are not reported in this work.
Catalyst Performance Evaluation - For the reforming experiments, the catalyst was firstly reduced followed by flushing under N2 flow for 1 h at 550 °C followed by ramping up furnace and vaporizer temperatures to set values. Once steady temperatures were achieved, fuel and water flows (using calibrated HPLC pumps) were started. After 10 minutes of operation, oxygen flow was started by means of calibrated metering valve (M/S Swagelok). The reformate thus produced then passes through a gas-liquid separator wherein unconverted liquid fuel and water condense. Non-condensed gases are then passed through a 50 ml pre-calibrated bubble flow meter (for measuring volumetric flow rate) before being collected in a sample bag and injected into a Shimadzu gas chromatograph GC-2014 equipped with a molecular sieve 5 Å column (60/80 mesh, 1/8 inch in diameter, 6 feet in length) using a thermal conductivity detector and a flame ionization detector. The condensed liquid samples for diesel and gasoline were two phase (aqueous and organic) and they were analyzed using a 7820A GC (M/S Agilent) equipped with a 7650A Autosampler and VF-5HT column. The condensed liquid samples for methanol (homogenous) were analyzed using the capillary column installed in GC-2014. The system takes 40 minutes to reach steady state and thereafter liquid and gas samples were collected every 30 minutes. Steady state performance of the catalyst is reported.
Conversion was calculated using the following formula (Equation 1),
Conversion= (?(mol of Carbon)?_(in,liquid)-?(mol of Carbon)?_(out,liquid))/?(mol of Carbon)?_(in,liquid) Equation 1
For estimating the moles of carbon in diesel, 8 prominent compounds present in commercial diesel (C10H22, C12H26, C14H30, C16H34, C18H38, C20H42, C22H46, C24H50) were calibrated using diesel standards from M/S Agilent in 7820A GC and the difference in the amount of carbon in diesel fed and the liquid sample obtained post gas-liquid separator was used to estimate conversion as per Equation 1. Similarly, for gasoline, 6 prominent compounds present in commercial gasoline (Benzene, Toluene, o-xylene, p-xylene, pseudocumene and 1,3,5-trimethyl benzene) were calibrated and used for carbon conversion analysis. The gas flow rates measured from bubble flow meter along with the composition of carbon containing compounds obtained from GC was used for carbon measurement in gas phase. Apparent mass of gas was estimated using ideal gas law (atmospheric pressure). Carbon collected on catalyst was estimated using TGA. Taking the carbon from the analyzed liquid samples in GC completed carbon balance. The carbon balance over all the runs were within ± 5% of experimental error. The gas phase mol fractions were all reported in terms of N2 free basis. The product gas yields (H2, CO and CO2) were estimated from the gas flows obtained by the bubble flow meter measurements and the mol % values obtained from GC analysis. Gas Yields were estimated based on the following formulae:
H_2 Yield= (?(mol of H?_2))/?(mol of C)?_fed Equation 2
CO Yield= (mol of CO)/?(mol of C)?_fed Equation 3
?CO?_2 Yield= ?mol of CO?_2/?(mol of C)?_fed Equation 4
Catalyst performance was reported in terms of Carbon conversion and H2 production rate (mmol H2/kgcat. s).
For stability test, the catalyst was first reduced using H2/N2 gas mixture. Thereafter, the reforming temperature was achieved after flushing for 1 h under N2 flow. Once, the vaporizer and the reformer were at the desired temperatures, fuel and water flows were started and continued for 10 minutes. On achieving steady temperature profiles, oxygen flow was started. Gas and liquid samples were collected every 60 minutes after steady state was achieved (40 minutes). After a pre-set interval of operation, the reactants flow (first oxygen, followed by fuel and water) were shut off but the N2 flow was kept on and the temperatures were maintained. This condition was known as “hot standby condition”. No samples were collected during this condition. After keeping the setup in hot standby condition overnight, next morning, the condition is changed from hot standby condition to reaction condition. This operation was repeated for a total of 5 days. The average reaction condition run time per day was 500 minutes while hot standby condition time was 940 minutes. The test was repeated for every fuel in a similar manner.
Results and Discussion
All the catalysts thus prepared were first checked for their activity for hydrogen production from diesel reforming. Figure 2a and 2b reports the activity results and hydrogen production results for the catalysts thus prepared. Clearly, without addition of coke mitigating promoters (potassium, cerium, etc), the catalyst deactivates rapidly. It can be seen that the catalysts prepared wherein the metal ions are added during support preparation give higher activity as well as higher H2 production rates compared to the catalysts wherein the metal ions are added along with Nickel and Platinum. Above result can be explained on the basis that addition of potassium, cerium, phosphorous or gadolinium along with nickel and platinum in co-impregnated mode leads to blocking of active sites thereby reduction in surface area and hence inferior activity for hydrogen production. Amongst the metal ions added during support preparation, potassium gave the highest activity and selectivity for hydrogen. The inferior activity of other catalysts can be deemed to be due to higher carbon formation leading to reduction in catalyst activity. In order to check for carbon formation, TGA results are plotted in figure 3. It can be seen from figure 3 that, the Ni-Pt/K2-Al2O3 combination gives superior activity as well as the least carbon formation amongst the catalysts tested. This catalyst was then tested on gasoline in order to check the performance for a different fuel. Figures 4a and 4b report the activity and H2 production rates for Ni-Pt/K2-Al2O3, Ni-Rh/K2-Al2O3 and Ni-Re/K2-Al2O3 catalysts. Ni-Rh and Ni-Re show higher activity for limited time on stream and then show a rapid decrease in catalytic activity as well as H2 production rates. Although, the activity of Ni-Pt combination is lower than Ni-Re and Ni-Rh catalysts initially, it is found to be more stable than the other two catalysts. The carbon formation rates are also found to be the lowest for Ni-Pt/K2-AL2O3 catalyst. Hence, Ni-Pt/K2-Al2O3 is studied in further detail as the catalyst of choice for multi fuel reforming as seen in figure 5.
The effects of K loading on oxidative reforming of diesel are plotted in Figure 6. Figure 6a shows that the catalyst without K loading deactivated after 275 min, while giving low H2 yield (Figure 6b). The conversion and H2 yield both increased with K loading up to 5 wt% and reduced thereafter with further increase in K loading. TGA analysis of the spent catalysts revealed highest carbon formation for the catalyst without K loading and lowest for K5-Al2O3at <1 wt%, which is 88% lower than the former (Figure 6c). The DTG plots exhibit carbon peaks ranging between 500 to540°C, with the K5-Al2O3 showing a peak at the highest temperature of 536°C (Figure 6d). The peaks at the lower temperatures correspond to release of moisture. The results indicate the formation of graphitic carbon on the catalyst surface. Comparison of XRD micrographs of fresh and spent catalysts showed that the highest sintering (increase in Ni crystallite size after reaction) was observed for the catalyst without K loading. All the K loaded catalysts were relatively more stable but the K5-Al2O3 catalyst showed negligible impact on Ni crystal size (Table 1 and Figure 7). Figure 7 shows that the XRD peaks for K2-Al2O3 and K5-Al2O3 catalyst remain unchanged after the reaction. It is therefore evident that 5 wt% potassium loading is optimum for minimising coke deposition and Ni sintering.
The catalyst was then used to derive optimum reforming conditions
for each fuel i.e. diesel, methanol and gasoline. The optimum conditions derived were SCR: 4, OCR: 0.2, T: 780 °C, GHSV: 6100 ml/(hSTP.gcat) for diesel, SCR: 6, OCR: 0.3, T: 780 °C, GHSV: 6100 ml/(hSTP.gcat) for gasoline and SMR: 1.25, OMR: 0.1, T: 420 °C and GHSV: 6350 ml/(hSTP.gcat) for methanol. A stability test was then conducted based on the optimized parameters to check for the stability of the catalyst for all the fuels. Figure 8 shows the results of the stability test for all the three fuels. Conversion for gasoline remained constant (~98 %) for the entire test duration. However, H2 production rate dropped from 380 mmol H2/kgcat. s on the 1st day to 263 mmol H2/kgcat. s on the 3rd day and remained steady thereafter. Though the fresh catalyst showed highest selectivity towards H2 formation, the selectivity shifted slightly towards CH4 (not reported) after the first day of operation which explains the drop in H2 yields. In case of diesel, there was a gradual drop in conversion (98% to 85%). The rate of H2 production also gradually decreased from ~350 mmol H2/kgcat. s on the 1st day, to ~310 mmol H2/kgcat. s on the2nd day and later stabilized at ~217 mmol H2/kgcat. s for the remaining duration. The apparent drop in conversion could be due to initial poisoning of the catalyst sites either by the sulphur present in the fuel or due to carbon formation. However, we cannot conclusively state as there were no intermediate samples collected for analysis. Since the catalyst did not show any drop in conversion as reported in Figure 8, it can be considered as being stable. Methanol conversions remained steady at 98% and H2 production rates at 243 mmol H2/kgcat. s for the test duration after initial variations.
Morphology of the fresh and spent Ni-Pt/K5-Al2O3catalyst (after 5 days) were analysed via TEM and are reported in Figure 9. Metal and particle size distribution for the fresh (Figure 9a and 9b) and spent catalysts (Figures 9e and 9f for diesel; 9i and 9j for gasoline; 9m and 9n for methanol) looked similar. The nanoparticles retain their shape without signs of significant particle size increase. A HRTEM image of the fresh catalyst is shown in Figure 9c. The lattice spacing corresponding to Ni nanoparticles was calculated at 0.203 nm consistent with the d-value plane (111) of cubic Ni phase. Adjacent to the Ni lattice, Pt nanoparticles with lattice spacing measured at 0.226 nm consistent with the d-value plane (111) of Pt cubic phase were observed. Such interfaces forming adjacent to each other enhance the catalytic properties. The Selected Area Electron Diffraction (SAED) pattern in Figure 9d confirms the crystalline nature of Ni (111) and Pt (111) phases consistent with the HRTEM observations and XRD results. Similar conclusions regarding the presence of Ni (111) and Pt (111) phases in the spent catalysts can be made from the HRTEM and SAED patterns in Figures 9g and 9h, 9k and 9l, and 9o and 9p for diesel, gasoline and methanol, respectively. This clearly shows that the spent catalyst retained the original morphology of the fresh catalyst after 42 h of time on stream.
The current results were compared with literature values reported in Table 1, which clearly shows that the newly developed catalyst is better than the previously reported catalysts – both in terms of catalytic performance and in terms of reforming multiple fuels. Except for Rh1/Ce10-Al2O3 and our work, none of the other catalysts reported in Table 2 were tested against all the fuels.
Pillared clays exhibit both Lewis and Brönsted acid sites. Tuning the ratio of the Lewis to Brönsted sites has been reported for controlling catalytic reactions. K-doped supports are expected to have higher basicity than pillared alumina as illustrated in Supplementary Figure 10 through CO2-TPD experiments. Interestingly, two peaks were observed for all the four catalysts – the peak at the lower temperature is attributed to weak basic centers while the peak at the higher temperature is attributed to strong basic sites. The strong active sites shift to higher temperatures with increasing potassium loading. The amount of CO2 desorbed (Table 3) increases with increase in potassium loading confirming the observed increase in basicity. Increase in basicity helps in facilitating CO2 adsorption which mitigates CO disproportionation via reverse Boudouard reaction leading to lower carbon deposition. This explains the lower carbon deposits observed with increase in potassium loading till 5 wt%. The apparent increase in C deposits beyond 5 wt% K loading can be explained on the basis of increase in Ni crystallite size which promotes carbon deposition –
Oxidative reforming of diesel proceeds through a series of complex reactions wherein firstly partial oxidation causes breakdown of higher hydrocarbons along with the formation of CO, CO2, H2 and H2O which then get adsorbed on the porous catalyst surface. The acid-base characteristics of the catalyst and the reforming conditions determine the product selectivity. The results clearly suggest that the method of potassium addition plays an important role with an optimum loading of 5 wt%. The doped K also interacts with the impregnated Ni nanoparticles, leading to higher stability and prevents sintering at the reaction conditions. K doping also reduces acidic centers on the support, which lowers the coke forming tendency. To illustrate the role of acid-base centers, gas phase composition of the reformate is plotted in Figure 11. An increase in H2 concentration was observed as the K loading increased up to 5 wt%. Over un-doped alumina support, methanation and C forming reactions reduce the H2 selectivity and deactivate the catalyst rapidly. Poor metal support interaction over alumina support leads to sintering of Ni nanoparticles, deactivating the catalyst further. K-doping promotes water gas shift and methane reforming reactions, and hinders the reverse Boudouard reaction. However, 5 wt% K doping is the optimum, since higher loading does limited intercalation, causes Ni nanoparticles to grow in size due to strong metal-support interaction and blocks the pores – this increases the mass transfer resistance and lowers the catalytic activity. Moreover, literature suggests that K doping on Ni catalysts helps in improving the coking resistance but retards the reforming activity which is not observed in our results. This is attributed to the synthesis process in which potassium is added to modify alumina during intercalation – this resulted in a mixed metal oxide framework that enhanced the porosity and moderated the acid sites. However, an increase in blockage of sites due to larger size of K is observed with increase in K loading beyond 5 wt%. Also, an increase in Ni particle size is observed which is attributed to Ni diffusing in the support leading to agglomeration of closely bound Ni particles thus suggesting an optimum of 5 wt% of potassium.
The present invention establishes that impregnation of Ni-Pt on potassium modified alumina support results in high H2 selectivity and remarkable stability in the oxidative reforming of multiple hydrocarbons over a 42 h test period. The proprietary preparation method has been demonstrated to be the reason for obtaining high reforming activity and high coking resistance. The catalyst (Ni-Pt/K5-Al2O3) exhibits superior performance compared to catalysts reported in the literature. The optimum potassium loading of 5 wt% plays a key role in tuning the acid-base properties of the support leading to enhancement of the water gas shift and methane reforming reactions, and suppression of the reverse Boudouard reaction – this finally results in the high H2 productivity observed. These findings coupled with the simple synthesis method, commercial availability of support precursors and possibilities to extend the catalyst applications to other available fossil fuels for reforming purposes makes this catalyst a lucrative option for multi-fuel reforming applications to produce H2.
Although the present disclosure has been described in the context of certain aspects and embodiments, it will be understood by those skilled in the art that the present disclosure extends beyond the specific embodiments to alternative embodiments and/or uses of the disclosure and obvious implementations.
,CLAIMS:We Claim:
1. A plurimetallic catalyst for reforming fuels, the catalyst comprises:
a mesoporous mixed oxide support embedded with at least one transition metal ion, wherein the support is further doped with at least one element selected from Potassium, Phosphorous, Cerium or Gadolinium to stabilize the catalyst and make the catalyst resistant to coke formation.

2. The catalyst as claimed in claim 1, wherein the transition metal ions are selected from at least one of Nickel, Platinum, Rhodium, or Rhenium.

3. The catalyst as claimed in claim 2, wherein the precursor of Nickel is selected from at least one of Nickel Nitrate Hexahydrate, Nickel Chloride, Nickel Sulfate, or any other salt of Nickel.

4. The catalyst as claimed in claim 2, wherein the precursor of Platinum is selected from at least one of Chloroplatinic acid, Platinum Tetrachloride, Platinum Chloride, or any other salt of Platinum.

5. The catalyst as claimed in claim 2, wherein the precursor of Rhodium is selected from at least one of Rhodium nitrate, Rhodium Chloride, or any other salt of Rhodium.

6. The catalyst as claimed in claim 2, wherein the precursor of Rhenium is selected from at least one of Ammonium Perrhenate, or any other salt of Rhenium.

7. The catalyst as claimed in claim 1, wherein the support is further composed of Alumina, or a combination of Alumina.

8. The catalyst as claimed in claim 1, wherein the precursor for Potassium is selected from at least one of Potassium Chloride, Potassium Nitrate, or any other salt of Potassium.

9. The catalyst as claimed in claim 1, wherein the precursor of Phosphorous is selected from at least one of Phosphorous Trichloride, Phosphorous Pentachloride, or any other salt of Phosphorous.

10. The catalyst as claimed in claim 1 wherein the precursor of Cerium is selected from at least one of Cerium Chloride, Cerium Nitrate, or any other salt of Cerium.

11. The catalyst as claimed in claim 1, wherein the precursor for Gadolinium is selected from at least one of Gadolinium Nitrate, or any other salt of Gadolinium.

12. A method for synthesizing plurimetallic catalyst, the method comprising:
dissolving a precursor of at least one transition metal selected from Nickel, Platinum, Rhodium, or Rhenium in an aqueous medium along with a support to form a mixture;
stirring the mixture at a temperature ranging between 50°C to 80 °C to obtain a homogenous solution; and
drying the homogenous solution to remove aqueous medium followed by reducing the dried mixture with H2/N2 at a temperature in the range of 500? to 600?, followed by flushing with N2 at a temperature in the range of 500°C-600°C, to obtain the support impregnated with metal particles.

13. The method as claimed in claim 12, wherein the support is prepared using the method comprising:
mixing a precursor selected from at least one of Potassium, Phosphorous, Cerium, or Gadolinium, along with a precursor of Aluminium in an aqueous media to form a mixture, while being constantly stirred at temperature ranging between 80°C to 200°C;
storing the mixture in an airtight vessel at a temperature in the range of 60? to 120? for a duration ranging between 50 to 150 hours to obtain a solution B;
adding Lithium Magnesium Sodium Silicate in another aqueous medium to form a homogenous suspension followed by addition of a linear non ionic surfactant to form a homogenous mixture solution A;
adding solution B to solution A dropwise while being constantly stirred to form a final homogenous solution;
aging the final homogenous solution in an airtight vessel for a duration ranging between 40 to 100 hours at temperature ranging between 60°C to 200 °C to obtain a clear white suspension;
washing the white suspension with aqueous media to remove free Cl- ions;
drying the washed suspension to remove aqueous media; and
calcining the dried material at a temperature in the range of 450°C to 550 °C for a duration ranging between 12 to 25 hours to obtain the support in powdered form.
14. The method as claimed in claim 13, wherein the airtight vessel is a stainless-steel Teflon® coated vessel.

15. The method as claimed in claim 13, wherein the precursor of Aluminium is selected from at least one of Aluminium Hydroxychloride, or any other salt of Aluminium.

16. The method as claimed in claim 13, wherein the linear nonionic surfactant is Tergitol.

17. The method as claimed in claim 16, wherein the concentration of Tergitol is in the range of 1-3 gm/gram of final calcined support.

18. The method as claimed in claim 13, wherein the concentration of Lithium Magnesium Sodium Silicate is in the range of 0.3-1.3 gm/gram of calcined support.

19. The method as claimed in claim 13, wherein the concentration of Potassium, Phosphorous, Cerium, or Gadolinium is in the range of 2-8 wt%.