Autocar Professional, in collaboration with ECMA, recently organised a webinar on 'Innovative Metallic Substrate Solutions for Stringent Emission Norms'. Narayan Prakash, General Manager – Head of Technical Project Management at Emitec Technologies India, made a data-backed case for metallic substrates playing a greater role as automakers prepare for Bharat Stage 7 and TREM V norms.

Cold-start and low-load conditions remain the primary technical challenge across L-category vehicles, trucks and tractors, while cost impact — especially in the agricultural sector — is an equally pressing concern. Enhancing engine efficiency reduces exhaust temperatures, straining existing aftertreatment systems, and OEMs want solutions that minimise system redesigns. Emitec's compact catalyst architectures address both packaging constraints in hybrid applications and cost pressures through innovative substrate designs and over two decades of optimised production. Below are excerpts from the responses provided by Prakash during the Q&A session: 

How is metallic substrate fundamentally different from ceramic, and what makes it particularly relevant as emission norms tighten?

A metallic substrate reduces the exhaust system's overall back pressure by lowering the pressure drops across it. The foil design is engineered to maintain a turbulent flow of exhaust gases throughout the length of the substrate — what we call Turbulence Generating Structures. Metallic substrates also offer the advantage of cross-flow between channels, aiding better engagement of exhaust gases with the catalyst and resulting in higher efficiency. By integrating sensors into the substrate and offering different sizes and shapes, exhaust layouts with metallic substrates can be made more compact and cost-efficient.

What are the headline advantages over ceramic, and is there a downside?

Metallic substrates offer high GSA (Geometric Surface Area), greater mechanical durability, lower backpressure, better light-off performance during cold start, and a wide portfolio of cell designs. At the same CPSI (Cells Per Square Inch), a metallic substrate has a superior GSA compared to ceramic. The downside is that this superior performance comes at a higher price per litre. Very often, though, system cost optimisation can more than compensate for that price- per-litre gap.

Cold-start emissions keep coming up as the hardest problem to solve. Why, and how do metallic substrates help?

During cold start, exhaust temperatures are very low, and it takes considerable time for the catalyst to reach light-off temperature — the minimum temperature at which the catalyst begins converting harmful gases effectively. Thermal management strategies used today have limitations and carry a significant fuel economy penalty. Metallic substrate technologies such as LS-Design, CS-Design and BM can achieve light-off temperatures faster due to lower heat capacity, helping to control cold emissions. All the technologies introduced by Emitec over the past four decades have significantly contributed to cold-start performance. The flexibility in substrate shapes, sizes and canning with BM design also allows catalysts to be made more compact, placing them closer to the engine and helping achieve the required exhaust temperatures faster.

Can metallic substrates reduce hydrocarbons more effectively than ceramic?

Yes, with Emitec's latest technologies — CS foil and Belt Mantle. In a comparison test on a 1.2- litre engine run over the WLTC, the CS-Design Metalit achieved a 24% reduction in THC (Total Hydrocarbons) and a 52% reduction in CO compared to a series-production ceramic substrate, while meeting the NOx limit.

Ceramic is thermally insulating. Metallic is conductive. Does that conductivity create problems?

It matters very much, but as an advantage. The higher conductivity of metallic foil helps limit the negative effects of local overheating, which is a typical phenomenon in CNG applications. It also limits localised accelerated washcoat ageing — the washcoat being the thin catalytic layer applied to the substrate surface — which leads to overall PGM reduction potential and hence system cost reduction.

Is ceramic or metallic more cost-effective?

The two cannot be compared at the component level. With the latest substrate technologies from Emitec, system cost can be optimised through the right catalyst sizing and PGM loading. A metallic substrate with CS foil technology achieves better emission results with 11% lower volume and 20% less PGM loading compared to ceramic, and the coating process itself remains the same, though there is the additional possibility of reducing PGM quantity using turbulence- generating structures.

The cost difference is offset through lower substrate volume, reduced PGM loading, compact exhaust system designs, higher durability and lower warranty costs. There are many examples from European applications where migration to metallic has happened purely based on system cost advantage. Emitec has delivered almost half a billion substrates to date across applications that are very cost-sensitive. We supply not only to Audi, BMW and Ferrari, but also to VW, Skoda, Stellantis and other projects at the lower price end.

Where is metallic substrate currently used in India, and why has it not become as widespread as ceramic in BS6?

Metallic substrate is used on BS6 vehicles across 2W, 3W and SCV applications. Emitec's metallic substrates are the market-leading solution for 2W in India. Our German plants cater mainly to 4W and NRMM (Non-Road Mobile Machinery) applications worldwide. For CNG commercial vehicles, metallic substrate is a preferred choice since it can offer flexible designs to handle higher operating temperatures and the thermal peaks that come from a misfire event. With future emission and CAFÉ (Corporate Average Fuel Economy) norms, metallic substrate is expected to play a greater role.

What are the catalytic conversion strategies for HEVs and PHEVs, where packaging is already a constraint?

These applications present significant challenges regarding packaging space. Innovative packaging architectures drawn from Emitec's experience in EU and USA projects offer compact TWC (Three-Way Catalyst — converts CO, HC and NOx simultaneously), DOC (Diesel Oxidation Catalyst), LNT (Lean NOx Trap) and SCR (Selective Catalytic Reduction) solutions that integrate into existing engine compartments without affecting overall dimensions. This is achieved through small sizes starting with 33mm diameter and 40mm length, flexible shapes such as oval and ring-cat, sensor catalyst integration that reduces packaging space, and the feasibility of packaging on mufflers, which is not possible with traditional ceramic substrates due to higher temperatures.

With electrification rising, how do you see the role of advanced catalyst systems evolving over the next decade?

The BEV market globally has not progressed the way it was expected to. The primary hurdles are the purchase price, which is not in line with the principle of affordable mobility, and the lack of recharging infrastructure. Both are very relevant globally, but especially in India. The actual trend indicates that the PHEV and Range Extender share is likely to grow. Production numbers of high-voltage hybrids — HEV, PHEV and Range Extenders — will continue to grow and will hold a significant share of all powertrains for a long time to come. In our opinion, there is still a long way to go for the ICE powertrain in India. With advanced catalyst systems, ICE engines are expected to be cleaner — they could even clean the surrounding atmosphere in mega-city environments. 

BS7 and TREM V are described as the toughest emission norms India has seen. Where do you see the biggest challenges?

The biggest challenge is controlling emissions in cold conditions to achieve better HC and CO margins. The NOx and PM trade-off throughout the emission cycle could also become a critical criterion. On commercial vehicles like trucks, quick heat-up is required for early SCR dosing — a 50% NOx reduction is expected under Euro 7 HD (Heavy Duty) legislation. Real driving conditions could become more challenging for meeting the Conformity Factor — the ratio of real-world emissions to lab test results, used to ensure vehicles perform on the road as they do in testing — in urban driving, where cold-condition emissions are significantly higher. System cost and Total Cost of Ownership also need to be addressed alongside the technical challenges.

For TREM V specifically, we must wait for the final notification of emission norms, but we believe achieving compliance in the transient test cycle — the NRTC (Non-Road Transient Cycle, the standard test procedure for off-road equipment emissions) — could be critical. Packaging the exhaust system without affecting driver visibility will be another real challenge.

Can catalytic converters contribute to reducing CO2 as well?

Since metallic substrates have lower back pressure, they offer fuel consumption advantages through which lower CO2 emissions can be achieved. Beyond the tailpipe, the reduction of atmospheric CO2 is a primary topic globally. Work is being done on DAC (Direct Air Capture — a process that extracts CO2 directly from the atmosphere), where CO2 is adsorbed on specifically designed metallic substrates with maximum surface area and minimum backpressure. The output of that process is carbon, which serves as a precursor for synthetic fuel production.