Views: 0 Author: QT Publish Time: 2025-08-15 Origin: QT
In refinery operations and heavy-duty industries, controlling nitrogen oxides (NOx) through Selective Catalytic Reduction (SCR) has become standard practice. Yet one challenge consistently emerges across field reports: how to maintain stable SCR performance at high operating temperatures.
Many refinery units—particularly those handling residual fuels or operating under variable load—see exhaust temperatures exceeding 650–750 °C. This creates a harsh environment where traditional SCR catalysts suffer from deactivation, leading to efficiency loss and costly downtime.
Below, we explore the most common high-temperature NOx control challenges, supported by academic research and industrial case studies.
High water vapor concentrations combined with extreme heat lead to dealumination of zeolite structures. This reduces Brønsted acidity and collapses active micropores, directly lowering NOx conversion.
Beale et al., Journal of Catalysis (2015) demonstrated that conventional ZSM-5-based catalysts lost significant activity after prolonged exposure above 700 °C.
In contrast, CHA-type zeolites such as SSZ-13 retained structural integrity even after 16 hours at 800 °C, making them a promising solution for refinery conditions.
At elevated temperatures, active Cu or Fe species in the catalyst can migrate and aggregate. This reduces the number of available redox sites for the NH₃-SCR reaction.
Kwok et al., Applied Catalysis B (2016) reported that copper aggregation was a key cause of performance loss in ZSM-5 above 700 °C.
Stabilizing these active sites within narrower CHA channels, as in SSZ-13, has been shown to slow this sintering process.
Above 700 °C, undesired side reactions can occur:
Oxidation of NH₃ to N₂O (a potent greenhouse gas).
Formation of ammonium bisulfate when SO₂ is present, which further blocks catalyst pores.
These not only reduce NOx conversion efficiency but also create secondary environmental compliance issues.
Thermal cycling in refinery SCR units causes expansion and contraction of the catalyst bed. Over time, this leads to micro-cracking and structural attrition, which accelerates deactivation.
Routine inspection and correct loading procedures are critical to extending lifetime under such harsh conditions.
While operational controls remain the frontline defense, material innovation is redefining what is possible for high-temperature SCR.
CHA-type zeolite frameworks, particularly SSZ-13, exhibit:
Superior hydrothermal stability under 800 °C conditions.
Stronger resistance to SO₂ and hydrocarbon poisoning.
Consistent NOx reduction performance across wide temperature windows.
This makes SSZ-13 an increasingly preferred option for refinery operators aiming to balance durability with environmental compliance.
Beale, A. M., et al. "Ex situ and in situ studies of Cu-SSZ-13 for selective catalytic reduction of NOx." Journal of Catalysis, 319 (2015): 161–172.
Kwok, T., et al. "Hydrothermal aging of Cu-ZSM-5 and Cu-SSZ-13 NH₃-SCR catalysts." Applied Catalysis B: Environmental, 198 (2016): 341–351.
IEA Clean Coal Centre. SCR Catalyst Management in Refinery Applications, 2019.
Q1: Why do refinery SCR units face more severe high-temperature challenges than automotive SCR systems?
Because refinery exhaust streams often have higher sulfur content, more variable load cycles, and longer high-temperature exposure compared to automotive diesel exhaust.
Q2: Can hydrothermal deactivation be reversed?
No. Once dealumination occurs, the zeolite framework is permanently altered. The best solution is to prevent it through material selection and operational controls.
Q3: Does SSZ-13 completely solve high-temperature deactivation?
Not entirely. It significantly slows the degradation process but still requires good upstream gas treatment and proper ammonia injection management.
Q4: What is the expected lifetime of an SSZ-13-based catalyst in refinery SCR?
Case studies suggest 4–6 years, compared to 2–4 years for conventional ZSM-5, though results vary by flue gas composition and maintenance practices.
