CA2733865C - Catalytic hydrogel - Google Patents

Abstract

Abstract A hydrogel is provided to retain a liquid phase catalyst in a contained state, suitable for low temperature, orientation independent reforming of hydrocarbon fuels. A hydrogel is composed of a network of hydrophilic polymer chains dispersed in a water based medium. The hydrophilic chains can take the form of a super absorbent polymer such as sodium polyacrylate, and the liquid phase is an aqueous hydrocarbon solution. The active reforming species is contained in the hydrogel, and takes the form of a ruthenium complex suitable for the active and selective generation of hydrogen at low temperature. The catalytic hydrogel can be used in multiple reforming cycles without regeneration. The catalytic hydrogel allows product reforming gases and/or vapors to escape while retaining liquid species within the polymer matrix, thus allowing fully orientation independent operation. The free movement of liquid species within the polymer matrix further acts to ensure an even composition of the hydrocarbon solution throughout the catalytic hydrogel. The resulting product gas stream is suitable for use in PEM fuel cell systems

Description

, CATALYTIC HYDROGEL
Field of the invention The invention relates to materials used in the catalytic production of hydrogen via hydrocarbon reforming. In particular, this invention relates to a catalytic hydrogel, in which a hydrophilic polymer matrix supports an aqueous hydrocarbon solution and a catalytically active ruthenium complex. The invention is best suited for low temperature, orientation independent reforming of formic acid.
Background of the invention Hydrogen gas, H2, is a versatile energy carrier that can be used in energy conversion devices such as fuel cells and combustion engines. The primary challenges in the widespread adoption of H2 as an energy carrier lie in the low volumetric energy density of a gaseous fuel, especially in portable applications where high power density is required. The ideal solution is to utilize an energy dense liquid hydrocarbon fuel, and generate hydrogen on-demand in a fuel processor via chemical reforming. Small chain alcohol and carboxylic acids have been widely exploited for this purpose, though formic acid in particular has many desirable properties, being liquid at nominal temperature and pressure, non-toxic, inflammable, and derivable in a carbon-neutral process. One major drawback with traditional hydrocarbon reforming, however, is the high temperature (i.e.
>
200 C) environment required in attaining significant hydrogen production rates, which is problematic for safety and also inefficient, consuming a significant portion of the energy produced. Catalysts for high temperature reforming are conventionally supported or stored in a solid phase in solid support such as Zeolite or Carbon, as the catalyst coating methods and processing (sintering) typically require high temperatures unsuitable for polymers.
In addressing the limitations of high temperature reforming (>200 deg. C), a number of recent publications have dealt with low temperature (i.e. < 150 C) reforming of formic acid utilizing a class of ruthenium complexes in aqueous ir 1, , , solution. These homogeneous catalysts have several advantages for use in fuel cell applications in particular, such as very high selectivity to H2, with ppm levels of carbon monoxide (CO); rapid start-up time due to low temperature operation;

and the ability to use a wide range of formic acid concentrations (15 ¨ 98%
w/w) as feedstock.
For reformed H2 use in hydrogen fuel cells, it is important to have a hydrogen gas production process producing high purity hydrogen on demand at acceptable pressures, as carbon monoxide is poisonous to the catalyst in most fuel cells. For the case of formic acid decomposition has two paths, dehydrogenation producing H2 and CO2, or decarbonylation producing CO and H20, as shown in the equations 1, 2 below.
HCOOH-4 H2 + CO2 Eq.1 Dehydrogenation HCOOH4C0 + H20 Eq.2 Decarbonylation Effective reforming of formic acid for fuel cells, then benefits from highly selective dehydrogenation for increased H2 yield and low levels of CO
poisonous to most proton exchange membrane (PEM) cells. This high selectivity has not been shown using solid state catalyst with low temperature reforming of formic acid.
New developments in liquid phase catalysis have demonstrated the desired selective dehydrogenation. A novel process for high selectivity and low temperature formic acid decomposition has been recently published and patent pending(US publication No: US2010/0068131] using a Ruthenium catalyst in aqueous phase. This novel process achieves rapid low temperature decomposition at rates up to 50X faster by the addition of sodium formate to >

95% conversion within 4 hours. Further recycling the catalyst led to 200X
faster conversion within 1 hour.

2 ir 1, This aqueous catalyst formulation ('8131 patent) has many advantages for reforming formic acid through selective dehydrogenation efficiently to produce high pressure hydrogen product for use in portable fuel cells with acceptable trace amounts of CO poison, specifically active long life and producing a positive pressure of hydrogen and primarily all gas product, as reviewed in the references.
In spite of this, liquid phase catalysts still suffer several drawbacks that render them unsuitable for portable applications: the most serious of which are an inherent sensitivity to orientation, and difficulty maintaining an aqueous reservoir near the normal boiling point of water. Hence, there is a need to provide a novel method of containing an aqueous catalyst that enables continuous hydrogen production at a high rate, and in any orientation. The major difficulty with this class of aqueous catalyst arises from the fact that liquid water is an integral part of the reaction mechanism, and must be retained in the catalyst.

Firstly, this puts the practical operating temperature limit well below 100 C. at atmospheric pressure, greatly restricting the potential hydrogen generation rate.
Specifically, we have found in tests using 100% liquid catalyst that pressurization of 100PSI or more was required due to partial water vaporization from higher temperatures required for adequate reaction rates, such pressure is unsuitable for consumer or portable use. In addition to this, water balance considerations may limit the upper concentration of the fuel, thus reducing the effective energy density. Finally, a conventional liquid-filled vessel is inherently sensitive to the orientation in which it is placed; that is, a preferred orientation may meet a specified design hydrogen output, while an off-axis orientation may produce hydrogen sporadically or not at all. This is due to gravity separation in gas-liquid systems, whereby natural gravitational forces induce spatial non-uniformity in gas-liquid systems. For example, the '8131 patent teaches a reactor vessel impermeable to water and air and able to withstand acidic reaction conditions and recommends glassware as discussed. In portable applications, where device size, energy density, and orientation sensitivity are the key performance metrics,

3 ir 1, these challenges can be very difficult or impossible to overcome. In view of this, a passive method of liquid phase catalyst management is needed to increase technical viability for portable applications. There is a need for designs and materials to support and contain the catalyst adequately while maintaining conditions for high reaction rates in any orientation.
There is a further need for a liquid catalyst support that enables the generated hydrogen gas to easily permeate through the support when the support is in any orientation. In addition to absorbing and retaining water based catalyst a material support is needed that can handle the chemical and physical requirements of reforming, including high absorption per unit weight of material, reliable under repeated cycles, substantially inert to the reaction process and formic acid, and meets standards for safe consumer use including recycling.
There are other low temperature formic acid processes in the early stages of development. These additional liquid catalyst low temperature formulations and methods are typically again demonstrated in a lab environment with a beaker type reactor holding the liquid catalyst and fuel and with the liquid catalyst at the bottom due to gravity and the resulting hydrogen gas bubbling up and being trapped and processed, and have not met the needs described herein.
Some variations on solid state catalyst show conversion at low temperature below 100 deg. C, however are estimated to have limited utility as they require extra salt/ionic liquids and resulting solid byproducts and lower reaction rate per unit volume and are orientation dependent

4 Existing solutions to contain aqueous catalyst include primarily supported aqueous phase catalyst (SAPC). SAPC patents teach solid support, which is inadequate to meet the needs as described earlier.
In reviewing use of highly absorbing materials with fuel cell applications, use of hydrogels in fuel cells has been limited and for unrelated applications. Specifically for formic acid reforming in fuel cells, hydrogels have been limited in use as;
a) hydraulic barrier [US patent publication no. US 200810274393, US
patent publication no. US 200810248343, US patent publication no.
U520090035644]
b) as a temporary material phase in manufacturing membranes potentially used in fuel cells [US patent no. 4664194]
c) forming solid catalyst as a hydrogel layer on nanomaterial structure [US patent publication no. US 200110000889, US patent no. 6531704], d) holding a liquid electrolyte between anode and cathode in microfluidic fuel cells [US patent publication no. US 201010196800].
As a class of hydrogels, the use of super absorbent polymers (SAP) more generally within fuel cells and associated reforming shows unrelated uses.
US patent publication no. US 200810057381 references using a SAP to hold electrolyte and formic acid fuel, however the catalyst is solid. US patent no.

6781249 references using SAP ancillary to a fuel cell system for water storage and disposal, but no mention of using liquid catalyst. US patent publication no.
US
2009/0071334 more generally references use of SAP in collection of water in steam reforming, however this is more general not related to liquid catalyst or formic acid fuel cells.
Date Recue/Date Received 2020-12-18 Summary of the Invention A catalytic hydrogel is provided for the purpose of low temperature, orientation independent hydrocarbon reforming. The catalytic hydrogel consists of a network of hydrophilic polymer chains dispersed in an aqueous hydrocarbon solution, preferably a formic acid solution; the catalytically active species is preferably a ruthenium complex.
An embodiment of an absorbent polymer for stably retaining liquid catalyst in a hydrogel state for use in fuel reforming, is provided having, an absorbent polymer formable as a catalytic hydrogel, such that when contacted with a liquid phase catalyst, the polymer forms a hydrogel that absorbs liquid phase catalyst in a proportion greater than the polymer weight and retains the liquid catalyst within the hydrogel state independent of orientation. An additional detailed embodiment of a system is further provided, including the addition of a liquid phase catalyst absorbed and retained in the absorbent polymer forming a catalytic hydrogel.
A preferred embodiment involves the soluble ruthenium complex being mixed with the aqueous formic acid solution, allowing free movement of the complex throughout the catalytic hydrogel. Most significantly, catalyst structures as described above allow product gases and/or vapors to escape while retaining liquid species within the polymer matrix. In other words, the catalytic hydrogel is not subject to, or dependent on, gravity separation of gas and liquid phases, and can easily be adapted for orientation independent operation in portable fuel processors.
An additional benefit of using the catalytic hydrogel compared to an aqueous solution can be ascribed to the ability of the hydrophilic polymer chains to retain water: it has been experimentally observed that a proper water balance can be maintained even at the normal boiling point of water. The relaxed temperature restrictions allow higher operating temperatures than were previously possible, resulting in higher catalyst output and a corresponding decrease in both size and weight.
Further benefits of the catalytic hydrogel are absorbance of incoming fuel to react homogenously with the catalyst and remaining stable during reforming reaction and extended use and storage.

Brief Description of the Drawings FIGURE 1 is a schematic illustration of a super absorbent polymer, showing hydrophilic polymer backbone and light cross linking allowing swelling when hydrated.
FIGURE 2 is an image of SAP crystalline dry pellets prior to interaction with liquid catalyst solution.
FIGURE 3 is an image of SAP crystalline pellets following absorption of a liquid catalyst solution to form a catalytic hydrogel.
FIGURE 4 is a perspective view of a layer formed of the catalytic hydrogel illustrating use in a reformer reaction converting formic acid fuel to hydrogen and CO2 gases, while retaining excess water.
FIGURE 5 is a graph showing extended low temperature hydrogen production from reforming formic acid using a catalytic hydrogel.

Detailed Description A new class of aqueous catalysts has recently been described for low temperature hydrogen production from hydrocarbon fuels, including formic acid.

These aqueous organo-metallic complexes display unusually high activity towards formic acid decomposition. High purity hydrogen is produced via high selectivity towards the dehydrogenation pathway ( 1 ), with little or no CO
production through dehydration ( 2 ).
liC0011 CO2.q- ( 1 ) FICOOff CO + 1120 ( 2 ) This quality makes the new catalyst formulations eminently suitable for use in fuel cell applications, where CO content of the fuel gas can cause rapid deactivation. Specifically ruthenium formulations have achieved good yields of H2 > 95% conversion from formic acid at fast rates suitable for use in real-time power applications. This catalyst composition results in the conversion of a dehydrogenatable pre-cursor in an aqueous solution at high conversion rates of near pure H2 for an extended period of time (and following very extended storage periods) , suitable for portable device use and commercial operations.
Use of the catalyst in liquid state in a vessel is orientation dependent so doesn't meet the needs described. Attempts to use such a liquid catalyst with a solid state support (Zeolite) were found unsatisfactory, as the liquid catalyst was not properly contained (attracted and retained) such that when formic acid fuel was added, to approach adequate reaction rates and H2 production rates, the reaction temperature had to be higher than the vaporization temperature of the retained water, causing heated water vapor to expand and exhaust out of the system at high pressure. The Zeolite or typical solid support then is found unacceptable for use in compact portable reformers and fuel cell packs, as safety standards would not be met or cost feasibility and portability with this constraint.

1, Hence, to meet the needs described, a novel absorbing material is provided that contains liquid catalyst and enables low temperature reforming of formic acid to be practically and commercially realized. Such absorbing material maintains reaction rates under various orientations, stable in use, maintains water balance and finally has suitable material properties for reliable repeated use over long use cycles common in portable electronic power systems.
The present invention makes use of super absorbent polymers (SAPs), that, when mixed with aqueous catalyst solutions and/or an active ruthenium complex, form a stable hydrogel state. Specifically, we have discovered an effective liquid catalyst support material that holds aqueous Ru catalyst in a hydrogel state and is super absorbing, has temperature stability, holds the liquid at standard pressure during reaction, and enables high rates of hydrogen production when reforming formic acid. The catalyst support enables orientation independence of reforming reactions for generating hydrogen for PEM fuel cell systems.
The present invention is described using terms of definitions below:
"Catalysis," as the term used herein, is the acceleration of any physical or chemical or biological reaction by a small quantity of a substance-herein referred to as "catalyst"-the amount and nature of which remain essentially unchanged during the reaction. For teachings contained herein, a raw material is considered catalyzed by a substance into a product if the substance is a catalyst for one or more intermediate steps of associated physical or chemical or biological reaction.
"Chemical transformation," as the term used herein, is the rearrangement, change, addition, or removal of chemical bonds in any substance or substances such as but not limiting to compounds, chemicals, materials, fuels, pollutants, biomaterials, biochemicals, and biologically active species. The terms also includes bonds that some in the art prefer to not call as chemical bonds such as but not limiting to Van der Weals bonds and hydrogen bonds.

ir "Activity" of a catalyst, as the term used herein, is a measure of the rate of conversion of the starting material by the catalyst.
"Selectivity" of a catalyst, as the term used herein, is a measure of the relative rate of formation of each product from two or more competing reactions. Often, selectivity of a specific product is of interest, though multiple products may interest some applications.
"Stability" of a catalyst, as the term used herein, is a measure of the catalyst's ability to retain useful life, activity and selectivity above predetermined levels in presence of factors that can cause chemical, thermal, or mechanical degradation or decomposition. Illustrative, but not limiting, factors include coking, poisoning, oxidation, reduction, thermal run away, expansion-contraction, flow, handling, and charging of catalyst.
"Porous" as used herein means a structure with sufficient interstitial space to allow transport of reactant and product materials within the structure to expose the reactant materials to the constituent compositions contained within the porous structure.
"Hydrogel" as used herein means a colloid gel in which water is the continuous phase. The gel remains swelled without leaking solvent/solution, unlike fiber based absorbers. Equivalent terms to hydrogel include sponge, fibrous filaments, soft polymer or co-polymer or gel.
For H2 use in hydrogen fuel cells, it is important to have a hydrogen gas production process producing high purity hydrogen on demand at acceptable pressures, as carbon monoxide is poisonous to the catalyst in most fuel cells.

Formic acid decomposition has two paths, dehydrogenation producing H2 and 002, or decarbonylation producing CO and H20, as shown in the equations 1, 2 previously. Effective reforming of formic acid for fuel cells, then benefits from highly selective dehydrogenation for increased H2 yield and low levels of CO
poisonous to most PEM cells.

ir A novel process for high selectivity and low temperature formic acid decomposition has been recently published and patent pending (US
publication No: US201010068131) using a Ruthenium catalyst in aqueous phase. This reaction achieves fast selective formic acid decomposition by homogenous catalysis, with very low levels of carbon monoxide poison.
This method of producing hydrogen gas and carbon dioxide in a chemical reaction from formic acid uses a catalyst in aqueous solution in the presence of added formate salt where the catalyst has the form;
M(L) n (I) Eq. 3 in which, M is a metal selected from Ru, Rh, Ir, Pt, Pd, and Os, preferably Ru;
n is in the range of 1-4; L is a carbine, or a ligand comprising at least one phosphorus atom, said phosphorus atom being bound by a complex bond to said metal, the phosphorus ligand further comprising at least an aromatic group and a hydrophilic group, wherein, if n> 1, each L may be different from another L; and wherein the complex of formula (I) optionally comprises other ligands and is provided in the form of a salt or is neutral.
A brief description of the reaction of the preferred formulations of the '8131 patent are included as useful for illustrating how the novel catalytic hydrogel meets the required needs, by rapid production of hydrogen gas (up to 90 liter H2/minute) with high purity and little to no carbon monoxide. The amount of hydrogen gas produced can be controlled and varied by fuel quality, temperature and pH, and also produced continuously with the addition of fuel to replace the consumed HCOOH. The preferred catalyst metal is Ruthenium [Ru].
The preferred complexes of the liquid catalysts are water soluble phosphine TPPTS [meta-trisulfonated triphenyl-phosphine], and include active species;

Date Recue/Date Received 2021-10-07 [Ru(H20)6]2+ , [Ru(H20)6]3+ and RuC13.xH20.
Specifically a Ruthenium complex selected from the group of RuCI3xH20/TPPTS, [Ru(H20)6][tosy112/TPPTS and [Ru(H20)6][tosylpiTPPTS is preferred. These catalyst complexes are stable at the pH the reaction is conducted at, and at the reaction temperatures, and have been shown to have no loss in activity over 12 cycles, 1 year storage. Exposure to air did not deactivate the catalyst. These results are ideal for portable commercial use.
The reaction rate and conversion efficiency are influenced by pH level of the incoming formic acid fuel ¨ this is controlled by adding a formate to the catalyst complex. The preferred formulation has optimum ratio of HCOOH:HCOONa in terms of reaction rate and conversion efficiency is identified to be around 9:1, providing pH in the range of 2.6-3.1.
The reaction rate also directly correlates with temperature, over a wide range. Conversion higher than 90% is achieved at 70deg C and higher, i.e.
considered in a low temperature range for Hydrocarbon reforming. The reaction is endothermic enabling novel low temperature reforming. Ru complex formulations are preferred for adequate reaction rates at low temperature range, to retain the water in liquid phase, to meet safety standards and to reduce design complexity and cost required to filter the water vapor out of the product gas.
The preferred operating range of the novel catalytic hydrogel is then 70-100 deg.
C. In some embodiments it may be acceptable to use reaction temperatures lower or higher than this preferred range.
Realizing benefits of such aqueous catalyst for low temperature hydrocarbon reforming has to overcome challenges of containing liquid phase catalyst. As outlined earlier these challenges include, reaction rate sensitive to orientation, maintaining an optimum homogenous phase for extended production, selectively permeable to product H2 gas, inert under operating temperature range and acidity.

A hydrogel material is discovered that provides an unusual and unexpected solution to the needs of the fuel reforming process and chemistry, in particular for suitably containing both the liquid catalyst and formic acid fuel, both passively in storage and actively in use. Hydrogels absorb many times their body weight in water. A class of hydrogels is "superabsorbent polymers [SAP's]. A
super absorbent polymer as defined herein is a lightly cross-linked, partially neutralized, hydrophilic three dimensional polymer network which can increase in weight up to several hundred times on absorption of aqueous solutions. Various combinations of grafting different co-monomers such as acrylic acid, acrylamide, and PVA, have been used. SAPs may also be formed of sodium polyacrylate, polyacrylamide copolymer, ethylene maleic anhydride copolymer, cross-linked carboxymethylcellulose, polyvinyl alcohol copolymers, cross-linked polyethylene oxide, or starch grafted copolymer of polyacrylonitrile. For consumer products, the most suitable choice is found to be poly(acrylic acids), providing the best performance to cost.
Illustrated in FIG. 1 is a super absorbent polymer formed of poly (acrylic acids), showing a hydrophilic polymer backbone and light cross linking allowing swelling when hydrated. The poly (acrylic acids) structure contains ionizable carboxylic acid groups, -COOH, on each repeating unit, making the polymer backbone hydrophilic. The structure of the polyacrylate is [-CH2-CH(000X)An, where X is one or more Alkali metals such as Na. The alkali terminated polymer is soluble. The backbone is cross-linked with hydrophilic crossliners to enable expansion without dissolution. When water is absorbed, hydration and formation of hydrogen bonds creates solvent-polymer interactions.
An SAP particle 2 is shown in FIG.1, with a hydrophilic backbone 8 and light cross linking between the chains as represented by crosslink region 6 and others (not numbered). In a dry state, Positive counter ions are balanced with the negative carboxylic groups. Hydrated counter ions move more freely within the particle 2 as part of bigger network (not shown), which increases the osmotic pressure within the polymer, however they are still weakly bound along the polymer backbone and do not exit the polymer to surrounding solution (not shown). This resultant difference in osmotic pressure pulls more water molecules inside the polymer and enables relatively uniform diffusion. The charged groups repel as shown in repulsion region 4 which expands the polymer and adds to swelling capacity. The absorbing capacity of the SAP is greatest with water and decreases with ionic solutions, such as electrolytes. For example, when absorbing an aqueous catalyst solution based on Ruthenium, absorption may drop on the order of 5 times dry weight. Various polymerization techniques have been used for synthesizing SAP's such as inverse suspension polymerization, solution polymerization, suspension polymerization, bulk polymerization, foamed polymerization and graft polymerization.
It is desired to achieve a continuous absorption of aqueous catalyst and fuel within the hydrogel and various modifications can be made to tailor a specific SAP material. For example, techniques to introduce structural porosity by use of foaming agents, surfactants or grafting comb like chains with improved molecular mobility. Reducing the smallest dimension of the SAP particles within the hydrogel can achieve rapid kinetics, for example by suspended polymerization techniques.
FIG.2 shows an image of a hydrogel 10 using a SAP formed of sodium polacrylate crystals in a dry state before addition of liquid catalyst.
Individual polycrystalline pellets 12 are shown for illustration, however the hydrogel 10 can be formed by known techniques to a wide range of forms including as a thin sheet, powder, segments of thin sheets, weave, mesh, laminate, pellets, sponge or non-uniform layers. For applications in reformers for fuel cells, a laminate or thin sheet is preferred, as shown in FIG. 4.
FIG. 3 shows a catalytic hydrogel 14, following contact and absorption of an aqueous ruthenium-based catalyst (not numbered), formed as individual pellets 12. The SAP has expanded approximately 10 times by weight compared ir 1, to the dry volume weight, and shows the dark color of the Ruthenium based solution. The degree of absorption varies with solution concentration and typically for the preferred ruthenium based solution is greater than 5 times dry weight.
We further observed that the aqueous solution is retained independent of orientation of the SAP material as is shown by various pellet surfaces at different orientations and the lack of observed excess solution underlying the catalytic hydrogel 14, i.e. the solution is fully absorbed by each pellet and not flowing out with gravity.
This orientation independence is further confirmed during reforming operation where the rate of hydrogen production is shown to be independent of orientation of the material. The catalytic hydrogel 14 holds the catalyst for long periods in any orientation and allow repeated uses, with minimal reduction in reactivity. Therefore the catalytic hydrogel 14 is suitable to safely and efficiently store reformer catalyst which can be used in any orientation, enabling use with formic acid fuel to power consumer mobile products.
The catalytic hydrogel further contains the aqueous catalyst in a "gel-like"
state ("hydrogel state") between solid and liquid, which is advantageous to allowing extended high reaction rates. There are several novel benefits of the catalytic hydrogel. Firstly, this catalytic hydrogel retains aqueous solution regardless of orientation. Secondly, it is stable under high temperatures and does not suffer hot spots or breakdown under reforming reaction. Thirdly, in comparison to rigid solid supports, the catalytic hydrogel is flexible and absorbs a high capacity of fuel relative to its weight, for rapid ongoing production of.
hydrogen. Fourthly, the material is commercially produced in high volumes with reliable consistency.
The use of the catalytic hydrogel in reforming formic acid fuel is shown in FIG. 4. Catalytic hydrogel layer 26 is placed for receiving an incoming formic acid fuel formulation which reacts with the catalyst as per Eq. 2 in a dehydrogenation process, producing a positive pressure of H2 and CO2 gases which exit the 1, catalytic hydrogel layer 26. The hydrophilicity and osmotic properties of the resulting catalytic hydrogel 26 allow the hydrogel to retain both water solutions and fuel.
The catalytic hydrogel is found to hold the Ru based solution in a suitable partial "liquid-solid" state. The Ru based catalyst solution and fuel are retained independent of gravitational direction, suitable for mobile use, while not substantially restricting the further absorbance of new incoming fuel throughout the catalytic hydrogel. The catalytic hydrogel is an unusual and fortunate discovery due to common support materials being limited by not retaining aqueous solution and being orientation dependent. Hence, the catalytic hydrogel represents an ideal novel catalytic material suitable for mobile reforming, orientation independence, and multiple cycles.
Measurement data of a low temperature formic acid reforming process using catalytic hydrogel is shown in FIG.5, with hydrogen production as a function of time over 500 hours of operation. Assuming typical mobile power use of 3 hours of H2 generation a day, this test range is equivalent to 160 days of mobile device power requirements. Reaction temperature is shown (lower line) and is maintained between approximately 90-100 deg. C,. This test is done using the catalytic hydrogel described and shown in FIG. 3, specifically aqueous Ruthenium based solution absorbed in polyacrylate SAP hydrogel. The catalytic hydrogel is formed using discrete pellets of polyacrylate stored in a glass bottle container in which formic acid fuel is introduced (-15% aqueous). The glass bottle container (not shown) is heated using a conventional electrical heater (not shown), and production of hydrogen gas is shown in mVmin. The catalytic hydrogel test demonstrates conversion of > 95%, as measured by remaining unused formic acid fuel found to be less than 5% by weight indirectly, and the hydrogel remains substantially unchanged over this period. A suitable ongoing water balance is shown to be maintained even around the normal boiling point of water. This relaxed temperature restriction allows higher operating temperatures than were previously possible, resulting in higher catalyst output and a corresponding decrease in both size and weight. .As the catalytic hydrogel in this test is not a continuous single-part, but discrete pellets in liquid fuel, and heating is not fully distributed, the resulting experimental variance is larger than can be achieved. Consistent uniform gas production in this prototype test is improvable with better heating integration, process optimization, and using continuous hydrogel material with uniform fuel distribution, however this test is suitable to demonstrate operation.
Another benefit and novelty of using the catalytic hydrogel in formic acid reforming is there are only trace elements of CO produced. Further benefits of the catalytic hydrogel are absorbance of incoming fuel to react homogenously with the catalyst and remaining stable during reforming reaction and extended use and storage.
Alternate formulations for aqueous catalysts are known that can produce hydrogen from formic acid at low temperature and are included herein as operable to form a catalytic hydrogel. Such liquid phase catalysts have similar requirements for a supporting material, and can be substituted equivalently.
One of these is a soluble Ruthenium phosphine complex, RuCl2 (triphenylphosphane)2. This formulation has performance 93% conversion at ambient pressure and 25-40 deg., C. Another formulation results in 100%
conversion at ambient pressure and temperature with a soluble Rhodium complex; Rh" (Cpl(bP0(H20)SO4CP*=Pentamethyl-cycloPentadienyl. This formulation similarly uses pH control to optimize the reaction rate by diluting the reactant formic acid with HCOONa. Either of these alternate formulations above, and any other aqueous catalyst formulations for homogenous liquid phase reactions can be substituted equivalently for the formulation described in detail.

While the embodiments are described for use with the aqueous Ruthenium based catalytic hydrogel with formic acid fuel, they may be also be used in a wider range of liquid catalysts for reforming hydrocarbons in general.
The embodiments described herein have solved these various unmet needs in an efficient, effective and integrated manner Alternatives to using polyacrylate SAP in the catalytic hydrogel, may include combinations of other polymers or co-polymers for tuning material properties. Additionally hybrid blends of other materials with a super absorbent polymer may be used. The catalytic hydrogel can be used with liquid catalysts for other hydrocarbon fuels, such as catalysts to reform methanol and the like.
The advantage of using the catalytic hydrogel described in the embodiments is that a liquid catalyst is held in an ideal contained state for high efficiency fuel conversion, with extended stable use to produce high rates of hydrogen gas. While particular elements, embodiments and applications for the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.

Claims (13)

What is claimed is:

1. A catalytic hydrogel for use in producing hydrogen via dehydrogenation of formic acid, the catalytic hydrogel comprising:
a superabsorbent polymer in an aqueous solution; and a catalyst soluble in the aqueous solution, wherein the superabsorbent polymer absorbs the aqueous solution in a proportion greater than the polymer weight of the superabsorbent polymer and retains the catalyst within the hydrogel state independent of orientation of a vessel holding the catalytic hydrogel, wherein the catalyst has the form:
M(L)n where M is Ru, Rh, lr, Pt, Pd or Os, n is 1-4, and L is meta-trisulfonated triphenyl-phosphine (TPPTS), wherein the phosphorus atom is bound to the metal by a complex bond, and wherein the catalyst is in the form of a salt or is neutral.

2. The catalytic hydrogel of claim 1, wherein M is Ru.

3. The catalytic hydrogel of claim 1, wherein the catalyst is RuCl3.xH20/TPPTS, [Ru(H20)6][tosyl]2/TPPTS or [Ru(H20)6][tosyl]3/TPPTS.

4. A catalytic hydrogel for use in producing hydrogen via dehydrogenation of formic acid, the catalytic hydrogel comprising:
a superabsorbent polymer in an aqueous solution; and a catalyst in the aqueous solution, wherein the superabsorbent polymer absorbs the aqueous solution in a proportion greater than the polymer weight of the superabsorbent polymer and retains the catalyst within the hydrogel state independent of orientation of a vessel holding the catalytic Date Recue/Date Received 2021-10-07 hydrogen, wherein the catalyst is RuCl2(triphenylphosphane)2 or Rh(Cp*)(bpy)(H20)(s0.4) where Cp* is pentamethyl-cyclopentadienyl and bpy is 2,2'-bipyridine, and wherein the catalyst is in the form of a salt or is neutral.

5. The catalytic hydrogel of any one of claims 1 to 4, wherein the superabsorbent polymer absorbs the aqueous solution in a proportion greater than 5 times the polymer weight.

6. The catalytic hydrogel of any one of claims 1 to 5, wherein the superabsorbent polymer comprises polyacrylate of chemical structure [-CH2-CH(COOX)-], wherein X is one or more alkali metals.

7. The catalytic hydrogel of claim 6, wherein X is Na.

8. The catalytic hydrogel of any one of claims 1 to 5, wherein the superabsorbent polymer comprises sodium polyacrylate, a polyacrylamide copolymer, an ethylene maleic anhydride copolymer, cross-linked carboxymethylcellulose, a polyvinyl alcohol copolymer, cross-linked polyethylene oxide, or a starch grafted copolymer of polyacrylonitrile.

9. The catalytic hydrogel of any one of claims 1 to 8, wherein the superabsorbent polymer is formed as a sheet, a powder, segments of sheets, a weave, a mesh, a laminate, pellets, a sponge or a non-uniform layer.

10. The catalytic hydrogel of any one of claims 1 to 9, wherein the aqueous solution further comprises formic acid.

11. A method of producing hydrogen via dehydrogenation of formic acid, the method comprising:
adding an aqueous formic acid solution to a catalytic hydrogel as defined in any one of claims 1 to 9; and heating to produce hydrogen.

12. The method of claim 11, wherein the heating step is done at 70-100 C.

13. The method of claim 11 or 12, wherein a pH of the aqueous formic acid solution is 2.6-3.1.

Date Recue/Date Received 2021-10-07