Background
The applicant, a Dutch organization, filed a patent application on March 4, 2019, claiming priority to a European Patent Office application filed March 5, 2018, for a method of electrochemically reducing carbon dioxide in an electrochemical cell. The claimed method involves introducing a CO₂-rich absorbent into the cathode compartment of an electrochemical cell, applying sufficient electrical potential to reduce the CO₂ to target products, and extracting the products on-site. The cathode compartment contains a cathode liquid with at least one of an acid, base, or their salts, and the anode is separated from the cathode by multiple separators.
The Japan Patent Office initially issued a rejection notice on February 21, 2023, identifying a Chinese patent (CN 102240497) as prior art and citing sodium carbonate solution or alkanolamine solution as the relevant “absorbent” element in the cited reference. The applicant responded with arguments and amendments, but received a final rejection on September 28, 2023. The applicant then appealed the rejection on February 9, 2024, presenting further amendments (Appeal No. 2024-2395).
On March 28, 2025, the Patent Office issued an appeal decision rejecting the application. However, the appeal decision changed its prior identification of the “absorbent” element—instead identifying it as a “formic acid and sodium formate mixture solution” rather than the sodium carbonate or alkanolamine solutions mentioned in the rejection notice. The applicant challenged this appeal decision in court.
The Court’s Holding
The Intellectual Property High Court held that the Patent Office’s appeal decision must be reversed due to a procedural violation of the Patent Law. The court found that the sodium carbonate solution or alkanolamine solution cited in the rejection notice and the formic acid/sodium formate mixture solution identified in the appeal decision are entirely different materials used in completely different processes within the cited reference. In the cited prior art, the sodium carbonate and alkanolamine solutions are used to absorb CO₂ from exhaust gas, while the formic acid mixture is used in a separate electrochemical reduction process. These materials are not substitutes or equivalent elements.
The court concluded that identifying a different substance as the “absorbent” in the appeal decision constitutes a “rejection ground differing from the grounds stated in the rejection notice” under Patent Law Article 159(2). Because this new ground was not disclosed to the applicant during the appeal proceedings, the applicant was denied the opportunity to submit written arguments and amendments in response. The court noted that formic acid/sodium formate mixture is not described as a CO₂ absorbent in standard literature on CO₂ recovery, and there is no evidence it is commonly known in the field, so it was reasonable for the applicant not to anticipate this argument.
Key Takeaways
- Patent offices must provide applicants with fair notice of the specific rejection grounds and must not switch to materially different grounds in appeals without disclosure.
- When prior art elements are used in different processes and contexts, they cannot be treated as equivalent without clear notice to the applicant.
- Applicants have a statutory right under Patent Law Articles 159(2) and 50 to receive notice of rejection grounds and an opportunity to respond before an appeal decision is issued.
- Procedural violations in patent examination proceedings warrant reversal of the substantive decision, even if the prior art may otherwise be valid.
Why It Matters
This decision reinforces fundamental principles of procedural fairness in patent examination systems. Even where prior art may appear to defeat a patent application on the merits, the Patent Office cannot rely on novel or unexpected interpretations of that prior art without notifying the applicant and allowing response. The ruling protects applicants from unfair “ambush” rejections where the Patent Office shifts its theory during appeal. For practitioners prosecuting patent applications in Japan, the decision underscores the importance of the record made during examination—if the rejection notice relies on particular prior art elements or technical interpretations, applicants should anticipate that these specific grounds will govern the appeal proceeding.
The decision also reflects judicial concern about the technical characterization of functional elements. The court’s analysis suggests that calling something by a functional label (e.g., “absorbent”) does not automatically expand to cover all substances that might capture or absorb a chemical in any context. The specific technical role and context of a prior art element matter for claim construction and novelty analysis.