Increased use of natural gas as a fuel in efficient, lean-burning engines could offer environmental advantages, but this necessitates a catalytic oxidation of methane escaping from the engine. The challenge for the catalytic oxidation of CH₄ is that the catalyst must operate in the exhaust, which contains H₂O (5–15 vol %) and SO₂ (∼1 ppm), and both components cause a severe inhibition of the catalyst. Here, we report that a 2 wt % Rh/ZSM-5 catalyst offers great promise by showing that high methane conversion can be reached at practically achievable conditions and high space velocities also in the presence of H₂O and SO₂. Rh-based catalysts, which are in the form of Rh₂O₃ under reaction conditions, become superior to the state-of-the-art Pd-based catalysts in an atmosphere with both H₂O and SO₂. Although both H₂O and SO₂ inhibit Pd and Rh catalysts, water is found to have a destabilizing effect on rhodium sulfate that enables a partial decomposition of the sulfate below 400 °C. We propose that this partly alleviates the sulfur poisoning of Rh catalysts; wherefore, the combined inhibition from H₂O + SO₂ is weaker for Rh than that for Pd.

中文翻译：

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高耐受H ₂ O和SO _2的铑基甲烷氧化催化剂

在高效的稀薄燃烧发动机中增加使用天然气作为燃料可能会带来环境优势，但这需要对从发动机逸出的甲烷进行催化氧化。CH ₄催化氧化的挑战在于催化剂必须在废气中运行，该废气中含有H ₂ O（5–15 vol％）和SO ₂（〜1 ppm），并且这两种成分都会严重抑制催化剂。在这里，我们报道了2 wt％的Rh / ZSM-5催化剂，通过显示在H ₂ O和SO ₂存在下，在实际可达到的条件下和高空速下都可以实现高甲烷转化率，提供了广阔的前景。以Rh ₂ O形式存在的Rh基催化剂₃在反应条件下，在同时具有H ₂ O和SO ₂的气氛中变得优于现有的Pd基催化剂。尽管H ₂ O和SO _2均抑制Pd和Rh催化剂，但发现水对硫酸铑具有去稳定作用，在低于400°C的温度下硫酸盐可以部分分解。我们建议这部分缓解了Rh催化剂的硫中毒现象。因此，Rh对H ₂ O + SO ₂的综合抑制作用要弱于Pd。