Interconversion between Lewis and Brønsted-Lowry acid sites on vanadia-based catalysts

Area of Science:

• Catalysis
• Surface Chemistry
• Materials Science

Background:

• Lewis acid sites (LAS) and Brønsted-Lowry acid sites (BAS) are crucial for catalytic reactions.
• These acid sites are particularly important in the selective catalytic reduction (SCR) of nitrogen oxides (NOx) using ammonia.
• Understanding the interplay of these sites is key to optimizing catalyst performance.

Purpose of the Study:

• To investigate how operational conditions affect the relationship between LAS and BAS on vanadia-based catalysts.
• To explore the role of water in modifying BAS under SCR conditions.
• To provide insights into how the ratio of LAS to BAS influences catalytic reactivity.

Main Methods:

• Utilized transient experimentation to enhance the sensitivity and differentiate individual LAS signals.
• Analyzed vanadia-based materials under conditions relevant to selective catalytic reduction (SCR).
• Investigated the impact of temperature, gas feed composition, and catalyst formulation on acid site behavior.

Main Results:

• Demonstrated that temperature, gas feed, and catalyst composition significantly alter the interplay between LAS and BAS.
• Showed that individual LAS signals can be resolved using sensitive transient techniques, unlike steady-state spectra.
• Confirmed that water can increase BAS by converting existing LAS and by generating new acid sites.

Conclusions:

• The study elucidates the dynamic relationship between LAS and BAS on vanadia catalysts under SCR conditions.
• Findings highlight the significant role of water in modulating BAS, impacting catalyst reactivity.
• The research provides a foundation for understanding how the LAS/BAS ratio governs catalytic activity in SCR and other transformations.