Hydrogen Purification Catalysts - HeraPur ^®

Catalysts used to remove oxygen from hydrogen gas are typically precious metal-based catalysts. These De-Oxo catalysts contain finely distributed active materials such as platinum, palladium, or their alloys on dedicated refractory metal oxides, enabling efficient catalytic hydrogen purification by converting oxygen with hydrogen into water. 

These materials are selected because they provide a high activity at low temperatures, along with strong durability and stability under industrial operating conditions. The choice of active metal can also be adjusted based on precious metal prices to optimize capital expenses. 

As a gas purification catalyst for oxygen removal, these materials are available as pellets, spheres, extrudates, or coated structures. The selection depends on application-specific requirements such as pressure drop, mechanical stability, and resistance to system vibrations. 

This way, De-Oxo catalysts are easily integrated into combined deoxygenation and drying systems. 

The selection of suitable hydrogen dryer catalysts follows a defined process. The customer specifies operating conditions such as impurity levels, flow rate, temperature, pressure, and purification targets. Based on these inputs, precious metal experts propose optimized catalyst options and bed designs to ensure an efficient and reliable performance.

A De-Oxo dryer package for electrolyzers is a hydrogen purification system that removes oxygen and moisture from hydrogen gas. 

Its core is a catalytic reactor with a hydrogen dryer catalyst, where oxygen is converted with hydrogen into water, followed by a drying stage to remove the formed moisture. 

Together, these units form an integrated hydrogen De-Oxo-drying system. 

The package includes piping, valves, and an enclosure, as well as instrumentation for temperature, pressure, and flow measurement. Oxygen monitoring and safety interlocks ensure reliable gas purification and safe operation. 

De-Oxo dryer packages can be directly integrated into the hydrogen gas production process or supplied as skid-mounted units. 

The full component can include PSA or membrane systems, redundant dryers, bypass lines, and temperature conditioning. 

Safety features comprise continuous monitoring, automatic shutdown, and pressure relief devices. The final design depends on purification targets, efficiency requirements, and customer-specific integration needs, including control and software interfaces.

Catalytic hydrogen purification using a hydrogen purification catalyst can reduce oxygen concentrations in hydrogen gas to 1 ppm or even the ppb range, depending on the operating conditions and the required purification target.

As a gas purification catalyst for oxygen removal from hydrogen, precious metal-based De-Oxo catalysts achieve high conversion efficiency at low ambient or even below-ambient temperatures. 

Due to the high catalytic activity, only compact catalyst beds are required. This allows reliable hydrogen purification at high space velocities while keeping the hydrogen purification system compact and efficient. 

The achievable purity depends on the hydrogen purification system‘s operating conditions, and the required target specifications. With an appropriately designed hydrogen purification catalyst, oxygen concentrations of 10 ppm, 5 ppm, or 1 ppm are readily achieved. Optimized catalyst bed designs can reduce residual oxygen even to the ppb range. 

When combined with the appropriate downstream refinement steps, catalytic hydrogen purification therefore enables hydrogen purification to purity 5.0 and supports compliance with ISO 14687 hydrogen purity requirements, including Grade D hydrogen for fuel cell applications.

The selection of a hydrogen deoxygenation catalyst depends on the required hydrogen purification target and the operating conditions of the hydrogen purification system. Key criteria include the oxygen concentration to be removed, the overall composition of the hydrogen feed such as the presence of moisture, further impurities, or potential catalyst poisons. 

Application-specific requirements such as allowable pressure drop, available installation space, operating pressure, operating temperature, and the desired catalyst lifetime also influence the selection. In addition, current precious metal prices can affect the choice of platinum-, palladium-, or alloy-based catalyst formulations to optimize the overall investment. 

Based on these parameters, the most suitable catalyst for hydrogen deoxygenation and catalyst bed design can be selected to achieve reliable and efficient catalytic hydrogen purification. 

Heraeus will support its customers by selecting a highly effective catalyst type and designing an efficient system for a specific purification task.

Hydrogen dryers with a De-Oxo catalyst are a key component in a hydrogen purification system post electrolysis. It combines catalytic oxygen removal with the removal of the resulting water and other process-based impurities to produce high-purity hydrogen gas. 

The hydrogen dryer determines the final hydrogen quality and enables compliance with product purity specifications for fuel cell hydrogen, electronics-grade hydrogen, and high-purity industrial hydrogen. It protects downstream equipment, supports safe high-pressure storage, and acts as the final polishing step before hydrogen is transported or used. 

Integrated hydrogen dryer / catalytic oxygen removal systems combine deoxygenation and drying as a compact solution for efficient hydrogen purification in modern electrolyzer applications.

Catalytic hydrogen purification is typically carried out in a fixed-bed reactor using a hydrogen purification catalyst. Reliable operation is generally achieved at temperatures of at least 10 K above the dew point to prevent water condensation in the catalyst bed, although operation at room temperature or below is feasible depending on the process conditions. 

Typical space velocities range from 5,000 to 20,000 /h. Higher values above 20,000 /h can also be achieved, depending on the hydrogen feed composition, oxygen concentration, and required purification target. 

HeraPur® precious metal catalysts are supplied as plug-and-play materials, allowing straightforward integration into hydrogen purification systems while delivering efficient low-temperature catalytic hydrogen purification.

The lifetime of a hydrogen purification catalyst depends primarily on the hydrogen feed quality, impurity levels, operating temperature, and overall operating conditions. Contaminants that act as catalyst poisons can reduce catalyst activity over time, while optimized process conditions help maximize catalyst performance and lifetime. 

For catalytic hydrogen purification, a time on stream (TOS) of 5–10 years is common in many industrial applications and HeraPur® have demonstrated to even exceed this. 

At the end of their service life, precious metal-based hydrogen purification catalysts retain significant material value. Heraeus offers precious metal recycling, allowing valuable platinum group metals to be recovered and reused, reducing the total cost of ownership.

Hydrogen purification after steam methane reforming is required to remove carbon monoxide from the reformer gas before downstream use. Carbon monoxide can poison and deactivate catalysts in subsequent process steps, reducing performance and shortening equipment lifetime. 

For PEM fuel cells, carbon monoxide concentrations typically need to be below 10 ppm to prevent significant poisoning of the platinum anode. Effective CO cleanup for hydrogen for fuel cells and final CO polishing of hydrogen for fuel cell use are therefore essential to meet the stringent hydrogen purity requirements of ISO 14687, including fuel cell-grade hydrogen. 

Carbon monoxide removal also supports safe hydrogen storage and distribution while enabling customer-specific hydrogen quality requirements for industrial applications.

Hydrogen purification after steam methane reforming typically combines several catalytic process steps. First, the water-gas shift (WGS) reaction increases the hydrogen yield by reacting CO with steam to form carbon dioxide and additional hydrogen. WGS typically reduces the CO concentration to below 1 vol.-%. 

The remaining CO is then removed in a downstream polishing step. A CO methanation catalyst selectively reacts CO with hydrogen to form methane, while a preferential oxidation (PROX) catalyst preferentially oxidizes CO in the presence of excess hydrogen. 

Depending on the required hydrogen purity, either technology can serve as the final polishing step and reduce residual CO concentrations to below 10 ppm.

Several catalyst technologies are used for CO removal in hydrogen purification, depending on the process step and the required hydrogen quality.

• Water-gas shift (WGS) catalysts are applied as the primary CO reduction stage after reforming, increasing the hydrogen yield while reducing the CO concentration.
• For downstream hydrogen polishing, methanation or selective CO methanation catalysts remove residual CO by converting it into methane.
• Alternatively, preferential oxidation (PROX) catalysts selectively oxidize CO, typically after a gas separation stage.

The choice of hydrogen purification catalyst depends on the process configuration, operating conditions, and the required CO concentration in the final hydrogen product.

Water-gas shift (WGS) catalysts increase the hydrogen yield in reformate syngas by reacting CO with steam to form carbon dioxide and additional hydrogen. As the primary CO reduction step after reforming, WGS hydrogen purification increases hydrogen production while reducing the CO concentration before downstream gas purification.

High reaction rates are achieved at elevated temperatures, whereas lower temperatures favor higher hydrogen yields due to the reaction equilibrium. For this reason, WGS is often carried out in multiple stages.

A high- or medium-temperature shift (HTS/MTS) catalyst first provides rapid CO conversion. This is followed by a low-temperature shift (LTS) catalyst, which converts residual CO and further increases the hydrogen yield by taking advantage of the more favorable equilibrium at lower temperatures.

Although WGS significantly reduces the CO concentration, it typically leaves less than 1 vol.-% CO, making a downstream polishing step necessary. HeraPur® MTS catalysts operate at 250–375 °C and can reduce process complexity by minimizing the need for multiple shift reactors and intercooling. HeraPur® LTS catalysts operate at 140–250 °C, making them well suited for compact and decentralized hydrogen production systems.

Preferential oxidation (PROX) is a downstream polishing process used in hydrogen purification to remove residual CO after the water-gas shift (WGS) reaction. A preferential oxidation catalyst selectively reacts CO with oxygen in the presence of excess hydrogen, reducing the CO concentration to typically below 10 ppm.

The PROX process requires a controlled oxygen supply and dosing. Stoichiometrically, the PROX reaction converts CO into carbon dioxide, while water may also form as a by-product. A small amount of hydrogen is consumed through an unwanted but not fully avoidable side reaction, so the catalyst must provide high oxygen selectivity.

HeraPur® PROX catalysts provide good oxygen selectivity and very low reverse water-gas shift activity, even at elevated temperatures. This enables efficient and reliable hydrogen purification with limited hydrogen losses.

The choice between a CO methanation catalyst for hydrogen purification and a preferential oxidation (PROX) catalyst depends on the process configuration, operating conditions, hydrogen purity target, and overall system design.