MHI Marine Machinery & Equipment and Mitsubishi Shipbuilding Secure Approval in Principle for Methane Oxidation Catalyst System

On April 22, 2026, Mitsubishi Heavy Industries Marine Machinery & Equipment Co., Ltd. (MHI-MME) and Mitsubishi Shipbuilding Co., Ltd. Announced they have received Approval in Principle (AiP) from Nippon Kaiji Kyokai (ClassNK) for the basic design of a methane oxidation catalyst system intended for marine LNG-fueled engines. The certification confirms the system’s feasibility from regulatory and safety perspectives, marking a significant step toward reducing greenhouse gas emissions from shipping.

Understanding the Methane Oxidation Catalyst System

The methane oxidation catalyst system is designed to address methane slip — unburned methane present in the exhaust gas of marine engines fueled by liquefied natural gas (LNG). Methane is a potent greenhouse gas with a high global warming potential, and controlling its release is critical for improving the environmental performance of LNG-powered vessels. The system oxidizes methane slip in the exhaust stream, thereby reducing overall greenhouse gas emissions from ships.

According to the approval documentation, initial performance measurements during verification testing on an actual ship confirmed a methane oxidation rate of more than 90% for the exhaust gas treatment system alone.

Collaborative Development and Technical Expertise

The system was developed through a joint effort combining the specialized capabilities of three companies within the MHI Group and its partners:

• MHI-MME contributed its core expertise in catalyst design and manufacturing technology.
• Mitsubishi Shipbuilding provided shipboard installation technology and integration know-how.
• Daihatsu Infinearth Mfg. Co., Ltd. Supplied engine optimization technology to ensure compatibility with marine LNG engines.

This collaboration leverages each partner’s strengths to create a solution that is both technically viable and practical for deployment on existing and future LNG-fueled vessels.

Significance of the Approval in Principle

An Approval in Principle (AiP) from a recognized classification society like ClassNK indicates that a design concept has been reviewed and found to comply with relevant statutory and regulatory requirements at the basic design stage. Although not a full certification, the AiP validates the system’s safety, environmental performance, and technical feasibility, enabling further development toward sea trials and eventual commercial deployment.

The AiP was presented during a ceremony held at Sea Japan 2026, an international maritime exhibition taking place at Tokyo Big Sight in Koto-ku, Tokyo, underscoring the industry’s growing focus on sustainable marine technologies.

Industry Context and Environmental Impact

As the maritime sector seeks to decarbonize, LNG has emerged as a transitional fuel due to its lower carbon dioxide emissions compared to conventional marine fuels. However, methane slip during combustion remains a challenge that could undermine the climate benefits of LNG use. Technologies that mitigate methane slip, such as the oxidation catalyst system approved by ClassNK, are therefore essential to ensuring that LNG serves as a genuine stepping stone toward zero-emission shipping.

By enabling over 90% oxidation of methane in exhaust gases, the system directly supports global efforts to reduce greenhouse gas emissions from ships, which is increasingly mandated by international regulations and regional policies aimed at curbing air pollution and climate impact from maritime transport.

Future Outlook

With the AiP secured, MHI-MME and Mitsubishi Shipbuilding can now advance the methane oxidation catalyst system toward further validation, including prototype testing and integration trials on operational vessels. Successful progression beyond the AiP stage could lead to broader adoption across the LNG-fueled shipping fleet, contributing to cleaner oceans and improved air quality in port communities.

This development reflects the maritime industry’s ongoing investment in innovative emissions control technologies and highlights the importance of cross-sector collaboration in achieving sustainable shipping goals.