Ecovyst Inc.

Evaluation of Disclosure Controls and Procedures

Our management, with the participation of our Chief Executive Officer and Chief Financial Officer, evaluated the effectiveness of our disclosure controls and procedures as of September 30, 2026, the end of the period covered by this Quarterly Report on Form 10-Q.

The term “disclosure controls and procedures,” as defined in Rules 13a-15(e) and 15d-15(e) under the Securities Exchange Act of 1934, as amended (“Exchange Act”), means controls and other procedures of a company that are designed to ensure that information required to be disclosed by a company in the reports that it files or submits under the Exchange Act is recorded, processed, summarized and reported within the time periods specified in the SEC’s rules and forms. Disclosure controls and procedures include, without limitation, controls and procedures designed to ensure that information required to be disclosed by a company in the reports that it files or submits under the Exchange Act is accumulated and communicated to the company’s management, including its principal executive and principal financial officers, as appropriate to allow timely decisions regarding required disclosure. Management recognizes that any controls and procedures, no matter how well designed and operated, can provide only reasonable assurance of achieving their objectives and management necessarily applies its judgment in evaluating the cost-benefit relationship of possible controls and procedures. Based on that evaluation, our Chief Executive Officer and Chief Financial Officer concluded that, as of such date, our disclosure controls and procedures were effective at a reasonable assurance level.

Management’s assessment of disclosure controls and procedures excluded consideration of Calabrian’s internal control over financial reporting. Calabrian was acquired during the second quarter of 2026, and the exclusion is consistent with guidance provided by the staff of the Securities and Exchange Commission that an assessment of a recently acquired business may be omitted from management’s report on internal control over financial reporting for up to one year from the date of acquisition, subject to specified conditions. Calabrian’s total assets represent 16% of our consolidated total assets as of September 30, 2026 and its net sales represent 9% and 4% of our consolidated sales for the three and nine months ended September 30, 2026, respectively.

Changes in Internal Control Over Financial Reporting

As a result of the Calabrian Acquisition, we are in the process of evaluating Calabrian’s internal controls to determine the extent to which modifications to Calabrian’s internal controls would be appropriate. As we continue to integrate the acquired operations of Calabrian, we have extended our oversight and monitoring processes that support our internal control over financial reporting, as well as our disclosure controls and procedures, to Calabrian. During the quarter ended September 30, 2026, there were no other changes in our internal control over financial reporting that materially affected, or which are reasonably likely to materially affect, our internal control over financial reporting.